Master Nanoscience and Nanotechnology - KU Leuven · Master Nanoscience and Nanotechnology...

Master Nanoscience and Nanotechnology

Thesis titles proposals April 2011

Titles: Page number: 1) ....... Solid-state lithium ion batteries for micro-storage 6

2) ....... Diamond thin films for micro-devices 7

3) ....... Nano-structured Co-Sn/Ni-Sn Multilayered Coatings 9

4) ....... Design of flip-chip packages for mm-wave ICs - Ontwerp van flip-chip verpakking voor mm-golf geintegreerde schakelingen 11

5) ....... Development of mm-wave circuits in nanometer-CMOS Technologies - Ontwerp van mm-golf schakelingen in nanometer CMOS 13

6) ....... Analysis of a Schistocerca gregaria small RNA database 14

7) ....... Nanostructuring Graphene: a new approach for sensors? 15

8) ....... In situ nanowire formation on a surface 16

9) ....... Molecular Nanovalves 17

10) ..... Nanopatterning using the bottom-up approach: addressing the 5 nm to 15 nm regime by combining physisorption and chemisorption 18

11) ..... Two-dimensional nanoporous materials: reactivity in confined space 19

12) ..... Raman spectroscopy of self-assembled structures with nanometer resolution: beating the diffraction limit 20

13) ..... Nanoscale chirality 21

14) ..... Measuring and Modeling of complex patterns of synaptic plasticitiy obtained by Multielectrode-Array (MEA) recording in brain slices 22

15) ..... Living computers on the basis of biological responses 24

16) ..... Mobility and performance extraction in sub-22nm node FiNFET 25

17) ..... Positive/Negative Bias Temperature Instabilities on ultrathin EOT (sub-1nm) planar/finfet Logic devices. 26

18) ..... Radiation-induced soft error in nanoscale combinational and sequential logics 27

19) ..... ESD evaluation and optimization for sub-22nm Bulk FinFet CMOS process 28

20) ..... The world’s smallest accelerometer 29

21) ..... Image sensor readout circuits implemented in IMEC 3D-stacked technology 30

22) ..... Spray coating for MEMS applications 31

23) ..... Integration of carbon nanotubes in microsystems 32

24) ..... Synthesis and post processing of Graphene 33

25) ..... Characterization of backside illuminated hybrid CMOS Active Pixel Sensor Arrays 34

26) ..... Modeling backside illuminating CMOS imagers using TCAD software 35

27) ..... Microfluidic mixing for lab-on-a-chip applications 37

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28) ..... Biocompatible packaging and metallization for miniaturized implantable biomedical systems 38

29) ..... Luminescent lanthanide-doped fluoride nanoparticles 39

30) ..... Porous Organic Materials for Gas Storage and Separation 40

31) ..... Investigation and optimization of the electrical switching properties of Resistance RAM memory cells (RRAM) 41

32) ..... Atomistic Phase-Field-Crystal Simulations of the Zener Drag Effect of Nanoparticles on Grain Boundaries 43

33) ..... Design of the transistor selector element in a 1T1R-cell based embedded RRAM Memory 45

34) ..... Digital lab-on-a-chip technology for functionalization of nanomaterials in femtoliter droplet arrays 46

35) ..... Integrating optics in digital lab-on-a-chip technology 48

36) ..... 3D Lithographic fabrication technology for cylindrical neural stimulator electrodes. 49

37) ..... Probing the structural quality of semiconductor/heterostructures using electron spin resonance 50

38) ..... Internal electron photo-emission in nano-layers and nano-structures 51

39) ..... First-principles modeling of high-mobility semiconductors/insulator interface 52

40) ..... Embedded semiconductor nanoparticles and nanowires characterized by electron spin resonance 53

41) ..... Digital microfluidics for cell membrane permeability measurements 54

42) ..... Innovative Vis/NIR spectroscopic measurements in combination with light propagation models to determine the size of the scattering particles. 55

43) ..... Optimization of the optical characterization of food products 56

44) ..... Nano-structures: Second Harmonic Generation 57

45) ..... Modeling and design of nanostructures: nantennas of the second generation 59

46) ..... Stress field induced lifetime degradation of minority carriers in thin silicon for solar cell applications 61

47) ..... Simulation of Advanced Solar Cells 62

48) ..... Intelligent epitaxial silicon foils for thin film solar cells and modules 63

49) ..... Photonic nanostructures for efficiency enhancement of ultrathin solar cells 64

50) ..... Thin-film photovoltaic solar cells: optimization and electrical characterization of polycrystalline silicon material 65

51) ..... Metallic nanoparticles for the efficiency enhancement of thin solar cells 66

52) ..... Polysilicon emitter contacts on bulk crystalline silicon solar cells 67

53) ..... Nanostructured carbon supercapacitors 68

54) ..... GaN high voltage devices – investigation of self-heating limitations to device scaling 69

55) ..... Scope of the study: LED aging 70

56) ..... Characterization of very high permittivity dielectrics for DRAM applications 72

57) ..... Superlattices: defining the boundaries of the ultimate CMOS scaling 73

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58) ..... Process simulations to improve the link between electrical data of processed tunnel field-effect transistors and simulated predictions 74

59) ..... Effect of confinement and position of dopants on the ionized impurity scattering limited mobility in a few-dopant double gate FET or all-around gate cylindrical nanowire FET 75

60) ..... Electronic structure and electrostatics of a square cross section gate all-around junctionless pinch-off nanowire FET 76

61) ..... Remote Coulomb, surface roughness and ionized impurity scattering in novel nanowire all-around gate FET devices 77

62) ..... Graphene plasmonics 78

63) ..... Sub band decomposition method for modeling nanodevices 79

64) ..... Tunneling in two dimensions 80

65) ..... Tunneling in semiconductor heterostructures 81

66) ..... Studying quantum transport in nano-MOSFETs using spectral functions 82

67) ..... A semi-analytical model for leakage currents in MOS capacitors 83

68) ..... Design and analysis of on-chip reliability and characterization circuitry 84

69) ..... Identification and modelling of gene networks in bone tissue engineering. 85

70) ..... Characterization of solute diffusive transport using fluorescent solute analogs 86

71) ..... A network-based modeling approach to quantify diffusive transport in a hydrogel carrier 88

72) ..... The role of cell mechanics in cartilage engineering 89

73) ..... in situ polymerization of electroactive polymers 90

74) ..... Feasibility of millimeter-waves for thermoacoustic imaging 91

75) ..... Capacitive micromachined ultrasound transducers for imaging, telecom and power transmission applications 92

76) ..... Phononics, MEMS/NEMS acoustic devices and circuits 93

77) ..... Nano logics – NEMS relays 94

78) ..... SASER - sonic laser 95

79) ..... MEMS-based microloudspeaker 96

80) ..... investigation of nanostructures as piezoelectrochemical transducers 97

81) ..... Synthesis of semiconducting nanoparticles from ionic liquid 98

82) ..... Development of Mini-Wireless Sensor for Avian Egg-Shell Temperature Monitoring 99

83) ..... Nano-structuring of metal-oxide electrodes for solar cells application 100

84) ..... Visualization of vortices 101

85) ..... Exchange bias by ion implantation in low-dimensional structures 102

86) ..... Manipulating superconductivity by implanting Fe atoms 103

87) ..... Nanostructure Formation with Ion Beam Sculpting 104

88) ..... Lattice site location of the electrical dopant Mg in GaN 105

89) ..... The role of Sn in the structural and electronic properties of GeSn 106

90) ..... Ferromagnet/ferroelectric heterostructures: towards synthetic multiferroic materials 107

91) ..... Optimization of a high-field magnet for pulsed operation 108

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92) ..... Design of a new magnetic deflection system for atomic clusters 109

93) ..... Electrical and electromechanical properties of ZnO nanowires 110

94) ..... Influence of adsorbates on the electrical properties of few-layer graphene 111

95) ..... Probing the magneto-electrical properties with scanning probes 112

96) ..... Electrical properties of metalized peptide nanotubes 113

97) ..... Laser spectroscopy and mass spectrometry of doped clusters 114

98) ..... Clusters for Catalysis 115

99) ..... Magnetron sputter source for cluster production and deposition 116

100) ... Zero-energy SIMS 117

101) ... Unraveling the quantum mechanical properties of nanoparticles with scanning tunneling microscopy 118

102) ... Interactions of semiconductor nanowires with cells 119

103) ... Characterization of Functionalized Magnetic Nanoparticles for Medical Diagnostics and Treatments. 120

104) ... Rare-earth doped nanoscale glass-ceramics for light frequency down-conversion. 121

105) ... Superconductivity in diamond films: doping effects induced by chemical substitution and electric gate field 122

106) ... Near field optical microscopy beyond the classical diffraction limit 123

107) ... Superconducting weak links 124

108) ... Visualization of Vortex – Antivortex dynamics in Superconductor / Ferromagnet hetero-structures 125

109) ... Oxides with a high dielectric constant on high mobility semi-conductors Ge and InGaAs126

110) ... Electric Field induced Metal - Insulator – Transition for NVM applications 128

111) ... Magneto-electric oxide heterostructures for novel devices 130

112) ... Oxide semiconductors with high mobility and low band-gap for photovoltaic applications132

113) ... Fabrication of Lithium coin cells using Ionic liquids and Olivine 134

114) ... Optical and electrical properties of amorphous and crystalline group IV materials 136

115) ... In-situ atomic layer / molecular beam deposition and characterization of oxide high mobility semiconductor interfaces. 138

116) ... Nanoparticles for Electron Emission Cancer Tumor Treatment 140

117) ... Theoretical study of strongly correlated electron systems 142

118) ... Particles in Nanodrops: Improving Medical Diagnostics 144

119) ... Digital lab-on-a-chip as an innovative platform for stem cell research 146

120) ... Automated optical DNA mapping using a digital lab-on-a-chip 148

121) ... Modified building blocks for ultra-sensitive aptamers 150

122) ... Nanostructuring of fiber optic surface towards improved biosensing 152

123) ... Multiplexed single nanoparticle based bioassay in fiber optic nanowells. 154

124) ... Surface nanopatterning for femtoliter droplet generation 156

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125) ... Luminescent patterning of nanostructured materials 158

126) ... Study of colloidal phase transitions of nanoparticles by direct visualization with super resolution optical microscopy 159

127) ... Smart labels for bio-imaging 160

128) ... Control and characterization of surface plasmons on nano-particle decorated metallic wires161

129) ... Quantum conductance of carbon and boron materials 162

130) ... Dynamical properties of anisotropic nanomagnets 163

131) ... Design of efficient single-molecule magnets 164

132) ... Molecular Archeology: Structural analysis of the of protein evolution applied on S. cereviseae MALS enzymes and their resurrected ancestors. 165

133) ... Growth of carbon nanotubes through a membrane 166

134) ... Measurement of mechanical properties of individual CNTs and CNT bundles. 167

135) ... Optical thin films for organic solar cells 168

136) ... Development of solution-based inorganic semiconductors for p-type thin film transistors169

137) ... Nanostructured anti-reflecting coatings for organic solar cells 170

138) ... Degradation mechanisms in organic solar cells 171

139) ... Transparent conductive electrode for organic devices 172

140) ... Nanometer-scale dynamics in DNA enzymatic restriction 173

141) ... Structure and mechanics of DNA supercoiling by nanoscale imaging 174

142) ... Nano-photonic imaging techniques for optical metamaterials 175

143) ... Formation of superporous frameworks 176

144) ... Lego Chemistry – reassembling building units from one structure into another 177

145) ... Unravelling and tuning crystal growth of nanosized metal-organic frameworks with second-harmonic scattering 178

146) ... Holey MOFs – constructing highways for molecules 179

147) ... Thesis title: Nanoscaled 3D Luminiscent Grids 180

148) ... Molecular domino: nanoscale positioning of transition metals during self-assembly of structured hierarchical composites 181

149) ... Zeotronics: organic nano-electronics build into zeolites 182

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Solid-state lithium ion batteries for micro-storage Description: Many of the ideas for local and small-form energy storage can come for the IC industry, where the downscaling of the transistor has driven tremendous research efforts into new materials and technologies. Recently solid-state Li-ion thin-film batteries have gained much interest as they allow miniaturization and integration of charge-based storage devices. To allow autonomous operation of microsystems for extended periods of time, high storage capacities are required, which a planar thin-film technology cannot deliver. To attain significant volumetric energy densities the effective surface area can be increased by micro- and eventually nano-structuring the surface. Many challenges associated with the high aspect ratio of the 3D structures have to be overcome. There are the obvious issues associated with the conformal coating which need to be solved in tandem with the need to produce virtually defect free layers over huge areas. Additionally, stress points can form at the tips and corners of the nanostructured 3D supports leading to increased local electric fields and leakage, or local overcharging of the battery. Structure optimization for resolving this issue becomes paramount for the viability of the 3D thin-film storage devices. In our group, processes are developed for fabrication of functional thin-film electrode materials, solid electrolytes and interface control. Thin film deposition techniques include chemical vapor deposition (CVD), atomic layer deposition (ALD) and electrochemical deposition (ECD). The materials are characterized by electrochemical and physical methods. Selected materials are incorporated in battery (half-) cells for further testing. As many different aspects of the battery are of interest (thin-film deposition, electrochemistry, solid-state ionics, transport ...), the generic topic will be more specified towards the background of the student; i.e. being chemistry, material science, electrical engineering or (applied) physics. Promoter: Philippe Vereecken; Stefan De Gendt, Marc Heyns Faculty/research group: Bio-engineering/COK; Natural Sciences/Chemistry; Engineering Science/MTM

Daily supervision: Cedric Huyghebaert, Geoffrey Pourtois, Philippe Vereecken

Graduating option: Bio-engineering, Natural Sciences, Engineering Science Type of work (experimental, theoretical, simulations): experimental and/or simulations

Number of students: 2

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Diamond thin films for micro-devices Description: Problem statement: Friction, wear, and adhesion currently limit the well-established Si manufacturing technology at micro- to nano scale. Nanocrystalline diamond thin films can solve actual reliability problems in micro-device applications. Synthetic diamond is attractive due to the unique combination of material properties such as extremely high hardness and Young’s modulus, high chemical inertness, and very high thermal conductivity. The recent progress on the development of diamond-based micro-systems has already resulted in the fabrication of prototype miniature resonators as shown in Fig. 1, and the formation of arrays of nano-diamond 3-D microstructures as shown in Fig. 2. However, the micro-device fabrication technology of nano-diamond materials is still in its infancy and the scientific understanding and technological control of the early stages of nano-diamond film formation and conformality on complex shaped 3-D microstructures is limited. Also, the mechanical properties and friction and wear behaviour of nano-diamond thin films still have to be investigated at micro- to nano-scale to ascertain their potential in future micro-devices. Aims: - To investigate synthesis methods for the architecture of 3-D, microstructures of nano-diamond thin films. - To study the adhesion and tribological behaviour of flat and microstructured nano-diamond thin films from the meso-scale down to the micro- and nano-scales. - To evaluate the functional properties of nano-diamond thin films in prototype micro-device structures. Activities: - Characterization of nano-diamond thin films by surface analysis techniques (SEM-FIB, TEM, micro-Raman, AFM). - Determination of mechanical properties like nano-hardness and elastic modulus as well as tribological aspects like friction and wear under fretting and sliding conditions at different length scales. - In-depth evaluation of the functional properties of micro-structured nano-diamond thin films in order to explore the potential use of these microstructures in micro-device applications. This will be done in cooperation with IMEC. Frame of the project: This thesis is part of a Marie Curie project called NANODIA funded by the EU and directed to the development of nano-diamond building blocks for micro-device applications. Other information: International ERASMUS exchange with the Radboud University Nijmegen (The Netherlands) is possible to get familiar with the synthesis of diamond films. Contact person: [email protected], office MTM room 01.35

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Figure 1: Nano-resonator fabricated from a 30-nm thick nano-diamond layer. (Naval Research Laboratory and Cornell University, USA) Figure 2: Array of 3-D micro-scale pyramids etched in a nano-diamond thin film. (Advanced Diamond Technologies, USA) Promoter: Prof. Jean-Pierre Celis Faculty/research group: MTM, Surface and Interface Engineered Materials

Daily supervision: Dr. Ivan Buijnsters

Graduating option: Engineering, Bio-engineering, Science Type of work (experimental, theoretical, simulations): Experimental


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Nano-structured Co-Sn/Ni-Sn Multilayered Coatings Description:

Nanostructured materials and coatings have been the subject of significant scientific research and industrial development efforts over the past decades due to their superior physical and mechanical characteristics over conventional crystalline materials (Fig 1). However, the increasing demand for novel materials allowing to fulfill new industrial and technological applications especially in the aeronautical field (Fig 2), has led to the search for nano-structured multilayered coated materials. Their microstructure and mechanical properties, as well as the effect that a layering may have on them, attract the attention of many researchers and engineers around the world. In addition, the knowledge on the elastic modulus, hardness and wear performance are considered vital for a better understanding of the performance in terms of load carrying capacity and of possible future applications.

The main objectives of this thesis are:

(1) to deposit by electrolysis on metallic substrates and to characterize Ni-Sn/Co-Sn nanostructured multilayered coatings (Fig 3),

(2) to investigate the limit in lowest thickness reachable for each type of sublayer deposited by electrodepostion,

(3) to study the effect of a layering of tin containing multilayers on the self-lubricating properties of such coatings.

Figure 2: Aeronautical applications involving a lot of bearings exposed to

b d i t f ti l

Figure 1: Effect of grain size on the hardness of materials

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Promoter: Prof. Dr. Ir. Jean-Pierre Celis Faculty/research group: MTM / Surface Engineering and Tribology

Daily supervision: Dr. E.P. Georgiou

Graduating option: Engineering, Science Type of work (experimental, theoretical, simulations): experimental


2μm Figure 3: SEM view of a cross‐section of a nanostructured Ni‐Sn/Co‐Sn multilayer

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Design of flip-chip packages for mm-wave ICs - Ontwerp van flip-chip verpakking voor mm-golf geintegreerde schakelingen

Description

Standard CMOS technology is entering the mm-wave frequency range. Indeed, the fT and fMAX of an nMOS transistor in 45nm CMOS goes towards 120GHz and 200GHz. This allows the design of mm-wave integrated circuits for data-communication, imaging, security and other extremely high-frequency applications. But one of the biggest challenges is to package and measure these ICs that operate at 100-200GHz. Indeed, such measurements are typically done with (expensive) IC-probes, but this is only feasible in a lab-environment and not useful for a commercial product. Therefore, this thesis will investigate the feasibility of integrating the antenna in the IC package, and using flip-chip instead of bond-wires. Flip-chip uses extremely short metal studs as interconnection between the IC and the package substrate (typically PCB), on which the antenna is integrated. One possible approach is to create a transmissionline made from these metal studs. This should allow a wideband interconnection usefull up to 300GHz so that the designed ICs can be measured ‘wireless’. The goal is to develop a mm-wave IC package or interface solution in general, and demonstrate this with a co-design between the package and

a mm-wave integrated circuit.

Figure: flip-chip packaging approach

Promoter: Prof. P. Reynaert (K.U.Leuven ESAT-MICAS)

W. De Raedt (Imec)

Daily supervisor: Noel Deferm (91.12)

Maarten Strackx

Number of students: 1 of 2

Number of students: 1 of 2

Language: Dutch or English

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Workload: 20% literature study 20% system study 40% design 20% text and presentation

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Development of mm-wave circuits in nanometer-CMOS Technologies - Ontwerp van mm-golf schakelingen in nanometer CMOS

Description

Nanometer CMOS technologies (45nm, 32nm ...) require a uniform metal density over the entire chip area. To achieve this uniform density, empty spaces (i.e. where no metal is drawn by the designer) are filled with small metal tiles (see picture below). These small tiles, also called ‘dummies’, have a huge influence on the behavior and performance of passive structures like inductors, transformers and transmission lines. This influence becomes more pronounced at higher frequencies and poses a fundamental problem for CMOS IC design at high frequencies in nano-meter technologies.

The objective of this Thesis is to develop new passive components that either take this metal tiling into account or even better, that are insensitive to metal tiling. These results will then be used in the design of an actual circuit to demonstrate the effectiveness of the proposed solutions.

Close-up of a chip showing the small metal tiles between the metal interconnections. Promoter: Prof. P. Reynaert

Daily Supervisors: Noel Deferm (91.12) Shailesh Kulkarni

Number of Students: 1 or 2

Language: Dutch or English

Workload: 10% theoretical 30% simulations 40% design 20% text and presentation

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Analysis of a Schistocerca gregaria small RNA database Description: The desert locust (Schistocerca gregaria) is a feared pest insect. Swarms consisting of billions of individuals are able to seriously damage the crop production in large parts of the world, corresponding to ±20% of the planet’s surface. Remarkably, these animals also occur in a solitary-living, harmless state. Because of extreme phenotypic plasticity, desert locusts can indeed develop in two completely different phenotypes, which are referred to as the solitarious and gregarious (swarming) phase. The molecular mechanisms underlying desert locust phase polyphenism are only beginning to be unraveled and research has hitherto mainly been approached from the ‘classic’ view of protein(-encoding gene)s. A large portion of eukaryotic genomes is however transcribed into non-coding RNA (ncRNA). Some classes of small ncRNAs, such as microRNAs (miRNA), small interfering RNAs (siRNA) and Piwi-interacting RNAs (piRNA), have recently been acknowledged as an important regulatory level of gene expression, thereby controlling a range of biological processes. It can thus be assumed that small RNAs may (indirectly) contribute to the pronounced distinction between the solitarious and gregarious desert locust phases. We plan to construct two small RNA libraries, derived from locusts in either the solitarious or gregarious condition. Deep sequencing of the libraries will result in at least 25 million reads per condition. The aim of this project will be to filter out sequence information corresponding to miRNA, siRNA and piRNA molecules, based on specific criteria for each. By using the relative number of reads per sequence we will identify those small RNAs that are differentially expressed in the solitarious and gregarious condition. Targets for these small RNAs will subsequently be searched and analyzed by making use of the available S. gregaria ‘expressed sequence tags’ database. The project will involve a lot of (Perl or other) programming. We will also make use of some freely available algorithms designed to search miRNA targets in EST or genome data. And finally, analysis of target sequences will mainly involve studying their ‘Gene Ontology’-based annotation.

Promoter: Prof. J. Vanden Broeck Faculty/research group: Faculty of Science (Department of Biology)

Daily supervision: Dr. Liesbeth Badisco

Graduating option: Natural Science Type of work (experimental, theoretical, simulations): a combination of these

Number of students: 1 or 2

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Nanostructuring Graphene: a new approach for sensors? Context: Highly oriented pyrolytic graphite (HOPG) is one of the best sources for high crystallinity graphene layers. Graphene, a popular material of recent times, is a single layer of graphite and a perfect 2D crystalline material with very high electron mobility and other interesting properties. Graphene has become an ideal object for both fundamental studies and electronic applications, including sensing. Objective: A first objective is to investigate using scanning tunneling microscopy or atomic force microscopy, the adsorption of (bio)molecules - organic molecules, proteins, and DNA - on these surfaces. A key question is to what extent the interaction strength and interaction mode of molecules on graphene differs from the adsorption of molecules on highly oriented pyrolytic graphite. A second objective is the exploration of molecule covered graphene sheets as active platforms for sensing. Work to be done: First, you will optimize the protocol for transferring graphene layers on silicon. Secondly, you will investigate the self-assembly of molecules on top of the graphene layers by state-of-the-art microscopy tools such as scanning probe microscopy. Finally, you will probe how the adsorption of molecular nanopatterns on graphene affects the electronic properties of graphene (sensing). Based on these insights, you will explore the proof-of-concept of using graphene layers covered with a molecular nanopattern as a template for the adsorption of analyte. Expected results: Established protocol for transferring and imaging (bio)molecules on graphene surfaces and the exploration of the sensing properties. Promoter: Prof. Steven De Feyter, Prof. S. De Gendt Faculty/research group: Science / Division of Molecular and Nano Materials

Daily supervision: Dr. Bing Li

Graduating option: Everyone welcome Type of work (experimental, theoretical, simulations): Experimental


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In situ nanowire formation on a surface Context: Metal and semiconductor nanorods are the potential building blocks for self-assembled nanoscale electronic circuits and energy-conversion devices. The spatial assembly of such nanorods is not only necessary for making functional devices but also presents an opportunity to explore novel collective properties. One strategy in arranging nanoblocks into ordered arrays is the template-directed synthesis in which guest molecules are deposited or react according to the spatial registry of host patterns and lattices. Objective: The objective is to prepare a chemical template on a surface, and use this chemical template to direct the in-situ formation of nanowires, e.g. gold nanorods. The goal is in this way to control the dimensions of these nanowires, their orientation, and properties.

Work to be done: First, you will investigate the self-assembly properties of the molecular templates on gold and other surface. Among different techniques, you'll use atomic force and scanning tunneling microscopy. Subsequently, you will target the in-situ formation of especially gold nanorods. You will investigate with local spectroscopy tools the electronic properties of these nanorods and evaluate their optical properties by optical spectroscopy tools. Expected results: First demonstration of a molecular template directed nanoparticle - nanorod formation on a surface. Promoter: Prof. Steven De Feyter Faculty/research group: Science / Division of Molecular and Nano Materials

Daily supervision: Dr. Kunal S. Mali, Dr. Bing Li



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Molecular Nanovalves Context: A relatively new but very exciting development in self-assembly is the formation of molecular nanopatterns on surface with a spatial periodicity between 1 and 10 nm. Especially, the formation of 2D nanoporous patterns is 'hot'. There are compounds which intrinsically contain a cavity such as macrocycles. However, nanoporous structures can also be formed by intrinsically non-porous molecules. These nanopores can host guest species. However, so far it is not possible to fill or empty the pores on demand. Recently, we have designed in collaboration with a Japanese group a system which in principle should allow us to do so. Objective: The objective is to self-assemble on a surface a 2D array of molecular valves which can be addressed by light.

Work to be done: By means of high-resolution scanning tunneling microscopy techniques, you will investigate the self-assembly of the functional nanoporous matrix and its ability to trap guest molecules. Subsequently, you will probe the response of the system to light and evaluate the efficiency of these molecular nanovalves, which have a diameter of less than 10 nm. Expected results: First demonstration of molecular nanovalves on a surface. A strong background in chemistry in not required. Promoter: Prof. Steven De Feyter Faculty/research group: Science / Division of Molecular and Nano Materials

Daily supervision: Dr. Oleksandr Ivasenko, Dr. Matthew Blunt



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Nanopatterning using the bottom-up approach: addressing the 5 nm to 15 nm regime by combining physisorption and chemisorption Context: Patterning surfaces with a periodicity between 5 and 15 nm is not obvious. On the one hand, state-of-the-art lithography techniques could be used via a top-down approach. On the other hand, self-assembly methods are promising to achieve such patterns with a high fidelity via a bottom-up approach. Self-assembled monolayers of alkylthiols on gold are a textbook example of chemisorbed systems. Typically, they are spontaneously formed by exposing a gold surface to a solution containing the alkylthiols As a result, they form a homogeneous monolayer on gold. How to pattern them? Using soft-lithography, it is possible to pattern 'patches' of these self-assembled monolayers. The spatial resolution is limited to about 50 nm though. Can one do better? Objective: The objective is to pattern patches of self-assembled monolayers with a periodicity between 5 and 15 nm on gold. The approach you will follow is the use of nanoporous physisorbed monolayers as templates for the self-assembly of the chemisorbed systems. Basically, the alkylthiols should 'fill' the nanopores.

Work to be done: First, you will investigate the self-assembly properties of the molecular templates on gold. Among different techniques, you'll use atomic force and scanning tunneling microscopy. Subsequently, you will target the self-assembly of the alkyl thiols in the nanopores. You will investigate the stability of these patches after removal of the template layer and their functionality. Expected results: Superior patterning method for alkyl thiols on gold. Promoter: Prof. Steven De Feyter Faculty/research group: Science / Division of Molecular and Nano Materials

Daily supervision: Dr. Bing Li, Drs. Tanya Balandina



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Two-dimensional nanoporous materials: reactivity in confined space Context: A relatively new but very exciting development in self-assembly is the formation of molecular nanopatterns on surface with a spatial periodicity between 1 and 10 nm. Especially, the formation of 2D nanoporous patterns is 'hot'. There are compounds which intrinsically contain a cavity such as macrocycles. Upon twodimensional (2D) self-assembly, a regular lattice of these macrocycles (and therefore also the cavities) can be formed, which subsequently can be addressed by guest particles. However, such porous structures can also be formed by intrinsically non-porous molecules. These porous networks are typically sustained via hydrogen bonds, metal-ligand coordination or even van der Waals interactions. Recently, our group has developed, in collaboration with a research team in Japan (Osaka University), a molecular system which forms 2D porous matrices which are in many aspects superior to those described in literature.

Objective: These two-dimensional nanoporous materials are ideal to host (reactive) molecular species. It is the objective to capture guest molecules in these nanoporous sites and to carry out chemical reactions in the nanovessels. Work to be done: By means of high-resolution scanning tunneling microscopy techniques, the self-assembly of the nanoporous matrix and its ability to trap reactive species will be investigated. Then, the in-situ reactivity of the trapped species will be probed by scanning probe and other techniques. Expected results: First demonstration of reactivity in molecular nanoporous systems on a surface. A strong background in chemistry in not required. Promoter: Prof. Steven De Feyter Faculty/research group: Science / Division of Molecular and Nano Materials

Daily supervision: Dr. Olekandr Ivasenko

Graduating option: Everyone welcome Type of work (experimental, theoretical, simulations): Experimental + simulation


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Raman spectroscopy of self-assembled structures with nanometer resolution: beating the diffraction limit Context: A relatively new but very exciting development in self-assembly is the formation of molecular nanopatterns on surface with a spatial periodicity between 1 and 10 nm. Especially, the formation of 2D nanoporous patterns is 'hot'. Scanning tunneling microscopy is an ideal tool to probe their self-assembly. Unfortunately, this technique barely provides information on the chemical nature of the species adsorbed. Objective: The objective is the development and implementation of a new technique, called Tip Enhanced Raman Scattering (TERS) to probe the composition of thin films (monolayers) with nanometer-scale resolution on surfaces. This is basically the only approach to spectrally characterize monolayer composition at the nanoscale. In TERS a STM or AFM is coupled with Raman spectroscopy. The electromagnetic field confined at the very end of the tip (in few nm region) induces Raman scattering. The principle is based on surface-enhanced Raman scattering (SERS) which is known to enhance the Raman scattering cross section by a factor of 1015 to 1016, resulting in a similar sensitivity as fluorescence. Therefore, a single-molecule sensitivity can be reached with this technique.

Work to be done: First, you will inplement Tip Enhanced Raman Scattering. In a second stage, you'll investigate its sensitivity and spatial resolution, by using "standard" samples, and apply the technique to probe with nanometer scale precision the functionality of self-assembled monolayers. Expected results: Accomplishing the setup of Tip Enhanced Raman Scattering. First results on sensitivity and spatial resolution on functional molecular nanopatterns physisorbed on atomically flat gold. A strong chemistry background is not required. Promoter: Prof. Steven De Feyter, Prof. Johan Hofkens Faculty/research group: Science / Division of Molecular and Nano Materials

Daily supervision: Dr. Hiroshi Uji-I, Dr. Matthew Blunt

Graduating option: Everyone welcome Type of work (experimental, theoretical, simulations): Experimental + simulation


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Nanoscale chirality Context: Chiral chemical systems with nanometer scale features - the effects of chirality on structuring at the nanoscale, how chirality is recognized and transferred at the molecular and supramolecular levels, how chirality is expressed in terms of chemical interactions and physical properties - are of vital significance to society as a whole because of the socio-economic areas where chiral products are the merchandise. Pharmaceutical science depends largely on chiral recognition, it is important for catalysis for the fine chemicals industry, and in liquid crystal displays. A major concern is the separation of enantiomers in a mixture. How to separate molecules which are identical, except for the fact that they are mirror images? Objective: The objective is to probe how chiral molecules self-assemble on surfaces (the enantiomers and racemic mixtures) and how the separation of enantiomers on a surface can be promoted and controlled. A further objective is the use of chiral monolayers to direct the enantiospecific crystallization of other molecules in solution.

Work to be done: First, you will investigate the self-assembly of chiral molecules using scanning probe microscopy tools, the pure components, as well as their mixtures. In addition, you will probe the interaction of these template layers with other molecules, in order to find out if separation is possible. Finally (if time allows), you will use these molecular layers as templates for the directed crystallization of molecules in solution. Expected results: New method for chiral separation on surfaces. Promoter: Prof. Steven De Feyter Faculty/research group: Science / Division of Molecular and Nano Materials

Daily supervision: Drs. Elke Ghijsens, Drs. Inge De Cat

Graduating option: Everyone welcome Type of work (experimental, theoretical, simulations): Experimental + modelling


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Measuring and Modeling of complex patterns of synaptic plasticitiy obtained by Multielectrode-Array (MEA) recording in brain slices Description: Uncovering model equations that underlie complex dynamic biological systems directly from observations, is an open, challenging problem in many life science disciplines. In the proposed research, we aim at developing a model-based methodology for gaining insight in electrical “read-outs” of memory storage that are obtained by recording with multielectrode arrays on brain slices in vitro. We will employ two complementary cellular mechanisms of memory storage: (i) long-term potentiation (LTP), an activity-dependent, long-lasting increase in synaptic strength, and ii) long-term depression (LTD), a persistent decrease in synaptic efficacy. As outlined above, LTP and LTD are extensively studied for understanding how the mechanisms of learning and memory work. They are the most established models of learning and memory at the cellular level. LTP- and LTD-like processes have a multiple function in memory storage in regulating the storage capacity, the signal-to-noise ratio and the amount/content of information that will be consolidated. A recent study supports the idea that the brain may use an LTP-like process to store new information while using an LTD-like process for clearing space by removing old memories. Conceptually, the model-based methodology will consist of different interacting steps, transforming the observed time series data of the considered biological responses into mechanistic insight in the coupled biological system. First, candidate input-output model structures of the biological system are estimated, based on the measured input-output time series data by using system identification techniques. Second, each estimated candidate model structure is mathematically decomposed into all its possible configurations (submodels with their interactions). In a following step, formal mathematical criteria together with existing a priori knowledge and directed experiments are used to select the most likely configuration describing the biological system and to identify the biological processes in each element of the selected configuration. The methodology will be developed as an iterative procedure, resulting in a reverse engineering loop. The data will be obtained from the recording of extracellular field potentials in brain slices of rodents (mice and rats) with multi-electrode arrays (MEAs). The latter allow the recording with multiple electrodes and a high spatial resolution. This kind of experiment is suitable to approach and model processes that determine the capacity of information processing which depends critically on the bandwidth with which information arriving from receptors, sensory organs and other brain areas is conveyed. Thus, the question is, how much information can be conveyed and processed in a particular brain structure in parallel with a sufficient signal-to-noise ratio without being disturbed by processes in neighboring fibers / synapses / neurons. This is usually designated as input-specificity and heterosynaptic interaction. These experiments will be conducted in the Laboratory of Biological Psychology (Faculty of Human Sciences) and will also employ new advanced MEAs developed in collaboration with IMEC (Leuven). Objectives:

(i) Development of a model-based methodology for uncovering the physiological mechanisms underlying coupled biological systems directly from time series data (“reverse engineering”) at the cellular level.

(ii) Computational model describing the spread and interaction of different types of synaptic plasticity (LTP, LTD) in a brain slice after their induction. This is expected to allow conclusions about the bandwith of information processing in the brain.

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Promoter: Jean-Marie Aerts Faculty/research group: Faculty of Bioscience Engineering/ Division Measure, Model & Manage Bioresponses (M3-BIORES)

Daily supervision: ir. Tim Tambuyzer

Graduating option: Type of work (experimental, theoretical, simulations): experimental, simulations


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Living computers on the basis of biological responses Description: The development in sensors, hardware and software creates more and more opportunities for the engineering (monitoring and/or control) of biological processes. Today, technology allows already that people wear their personal body area network that monitors their health, sport performances, stress levels, etc. Part of the energy that is needed to power these networks can already be harvested from the body of the individual. The next challenge is to extract also calculation power from the organism itself (i.e. living computer). It has already been demosntrated that DNA can be used to perform mathematical calculations, but in general every biological response can be regarded as the result of a mathematical processing. In this thesis, it is aimed at working out a first proof-of-principle of a living computer on the basis of a unicellular organism. More specifically, the objective is to develop a test installation that allows quantifying automatically the response of the Photosystem II of unicellular algae (Chlamydomonas reinhardtii) to variations in light intensity as a first step towards the development of a living computer on the basis of algae. The thesis will be carried out in collaboration with Prof. Koenraad Muylaert (K.U.Leuven, Campus Kortrijk). Promoter: Jean-Marie Aerts Faculty/research group: Faculty of Bioscience Engineering/ Division Measure, Model & Manage Bioresponses (M3-BIORES)

Daily supervision: Ali Youssef

Graduating option: Type of work (experimental, theoretical, simulations): experimental, simulations


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Mobility and performance extraction in sub-22nm node FiNFET Description: State of the art sub-22nm CMOS node devices are currently evaluated at IMEC. Mobility is one of the key parameters to benchmark Si- and non-Si based materials (Ge, III-V,...). Due to the high leakage in sub-1nm EOT oxides the assessment of inversion charge with conventional split-CV measurements is not feasible. In this thesis alternative extraction techniques based on high speed measurements are used for correct mobility extraction. These techniques are also used as a metrology tools to assess additional key parameters for series resistance, parasitic overlap contribution and effective gate length measurements. This thesis is experimental and will give a hands-on experience to the candidate on several state-of the art technologies and electrical characterization tools. The ideal candidate should have a good understanding of both high speed electrical measurements and the technology issues associated with advanced transistor technologies. Promoter: G.Groeseneken Faculty/research group: Faculty of Engineering/ESAT/imec/DRE

Daily supervision: Luigi Pantisano

Graduating option: Engineering Type of work (experimental, theoretical, simulations): experimental


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Positive/Negative Bias Temperature Instabilities on ultrathin EOT (sub-1nm) planar/finfet Logic devices. Description: The continuous device scaling down allows the integration of a large number of transistors on a chip and increases the speed. One of the physical parameter reducing with the scaling is the equivalent oxide thickness (EOT). However in thin dielectrics, BTI is known as a sever reliability issue limiting the scaling down. In thick high-k stacks with an EOT higher than 1nm, the dielectric consists a (~1nm) SiO2 interfacial between high-k material and Si substrate. Therefore, the methodology and the models built-up with SiO2 dielectric are still applicable. In sub-1nm EOT high-k stacks, the interfacial layer is intermixed with the high-k and the first studies showed different degradation mechanisms compared to the thick EOT staks. In this study, both P/NBTI degradation mechanisms in very thin EOT regime will be investigated by exploring defects in the gate oxide. Also, the impact of the process conditions including replacement gate with high-k last, and different high-k stacks will be studied in order to optimize BTI reliability for thin EOT logic devices. For the applicant, a good knowledge of semiconductor physics is required. During the project, the student will have the opportunity to participate and interact with the researchers of the Logic/DRAM program. Promoter: Guido Groeseneken Faculty/research group: Faculty Engineering/ESAT/imec/DRE

Daily supervision: Moonju Cho

Graduating option: Engineering or Natural Sciences Type of work (experimental, theoretical, simulations): experimental+theoretical


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Radiation-induced soft error in nanoscale combinational and sequential logics Description: Technology scaling has driven the computer industry for several decades now. Scaling has not only resulted in cheaper and more powerful microprocessors, it has also resulted in microprocessors that contain many millions of devices with ever-decreasing node charges. Because of this trend, radiation-induced failure rate has recently become a substantial Achille’s heel for the reliability of even Earth-based advanced CMOS technologies. Both high-energy neutrons induced by cosmic radiation and alpha particles emitted by chip and package materials are capable of producing soft errors. In some IC technologies also the interaction of low-energy neutrons with boron atoms is a significant source of soft errors. At the chip level, the contribution to the soft error rate (SER) from sequential logic, i.e., latches and flip-flops (FFs), is growing. The SER per FF has increased due to feature size reduction and supply voltage downscaling. At the same time, it is more and more common to protect (embedded) memories with error-correction-coding circuitry, thus reducing their SER. As a consequence, the relative SER contribution from sequential logic is increasing. Combinatorial logic currently has a minor impact on the chip SER, particularly at moderate operational frequencies, but its contribution to chip SER is also growing with technology scaling. On top of that, the random variations in process parameters have emerged as a major design challenge in circuit design in the nanometer regime. This thesis work involves the understanding and simulation of radiation behavior of basic sequential and combinational logic circuits in advanced CMOS technologies. Both process variation and timing vulnerability factors need to be evaluated under radiation conditions. Based on these results, a radiation hard strategy can be defined. Promoter: Guido Groeseneken Faculty/research group: Faculty of Engineering

Daily supervision: Alessio Griffoni

Graduating option: Engineering Type of work (experimental, theoretical, simulations): Theoretical and simulations


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ESD evaluation and optimization for sub-22nm Bulk FinFet CMOS process Description: CMOS technology is continuously evolving to ensure that the scaling remains on track according to Moore’s law. This scaling involves continuous thinning of the gate oxide, even down to a few nanometers, making the oxide more and more susceptible for ElectroStatic Discharge (ESD) stress. Traditional ESD protection would not be useful anymore as the sum of all voltage drops along the ESD path could easily exceed the breakdown voltage of the gate oxide of the core circuit. The situation for the sub-22 nm node is even worse, as any overshoot due to slow turn-on of the ESD protection device needs to be carefully monitored, in order not to damage the core circuit. On top of that, the traditional planar CMOS transistor architecture is moving to a more complex 3D FinFet architecture that can be realized on SOI or bulk silicon wafers. This thesis work involves characterization and understanding of the ESD behavior of basic ESD protection structures in IMEC finFET and planar CMOS processes. Both the quasi-static and transient device response under ESD stress conditions needs to be evaluated. Based on these results together with ESD TCAD simulations to understand the physical dynamics inside the devices, an ESD protection strategy can be defined. Various test circuits are available to assess the ESD behavior of stand-alone devices as well as devices placed in ESD protection circuits. Promoter: Guido Groeseneken Faculty/research group: Faculty of Engineering/ESAT/imec

Daily supervision: Steven Thijs

Graduating option: engineering Type of work (experimental, theoretical, simulations): All


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The world’s smallest accelerometer Description: Since the 90’s MEMS accelerometers have been used for automotive applications (e.g. crash sensor for airbags). Recently accelerometers are also finding rapidly their way into consumer products (e.g. Nintendo Wii game controllers, Apple iPhone and iPod..). Consumer applications require low cost, compact and low-power sensors. These requirements can be met by making the sensor small and preferably monolithically integrated with its driving electronics. Indeed, cost calculations by MEMS companies predict that the cost of a monolithically integrated sensor becomes lower than that of a hybrid sensor once the die area goes below 1 mm2. Imec has developed a very interesting and flexible poly-SiGe MEMS (Micro ElectroMechanical Systems) platform that can be used to process sensors and actuators above their CMOS readout and driving electronics. This pure CMOS integration results in much smaller packages with fewer interconnections than current hybrid systems, which combine MEMS and electronics on separate chips. With this platform imec already realized an integrated gyroscope, an 11 MPixel micro-mirror array and an array of probes for data storage. The purpose of this master thesis is to design, model and simulate “the smallest possible” micro/nano-accelerometer, which could be used in consumer applications such as a cell phone. In order to make a very small accelerometer, it will be necessary to look beyond the standard capacitive actuation and detection schemes. Possible alternative detection principles that can be used are piezoresistive sensing, the use of a tunneling tip or a field effect transistor with suspended gate. The technology should however still fit in imec’s poly-SiGe above-IC MEMS process to allow for a very compact integrated accelerometer. The goals of this research are: 1. To look into novel detection mechanisms, which are in line with standard processing techniques and which would lead to smaller-sized accelerometers and compare these mechanisms with capacitive detection. 2. To investigate and to describe the effect scaling has on the achievable signal/noise ratio and on the sensitivity of the accelerometer. 3. To come up, through dedicated Finite Element Modelling, with the most compact (smallest) design possible, in function of the specifications. 4. To come up with a conceptual fabrication process flow for the chosen detection principle and design. This research will be done in close collaboration with a PhD student working on the design and fabrication of nano-accelerometers.

Promoter: Guido Groeseneken (ESAT/imec), Ann Witvrouw (MTM/imec) Faculty/research group: Engineering Faculty/ groups: ESAT/MTM/imec

Daily supervision: Ashesh Ray Chaudhuri

Graduating option: Engineering Type of work (experimental, theoretical, simulations): theoretical, simulations


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Image sensor readout circuits implemented in IMEC 3D-stacked technology Description: A smart pixel level readout circuitry (tier1) will be designed in IMEC 130nm technology and will be stacked vertically to a detector layer and a third layer containing A-D converters (tier2). The student(s) involved in this thesis project will design and layout tier 1. Focus of the design will be low noise and low power operation and will use smart analog circuitry to increase the readout speed and the dynamic range of the sensor. The student(s) will learn the full design process from idea to chip implementation. Knowledge of main analog circuits together with basics of digital design are required.

3D-stacked image sensor concept. Promoter: Prof. Georges Gielen

Faculty/research group: Engineering / ESAT-MICAS

Daily supervision: Adi Xhakoni

Graduating option: Engineering

Type of work: 20% literature study, 40% transistor level simulation, 20% layout , 20% thesis writing


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Spray coating for MEMS applications Description: Spray coating plays an important role in today's MEMS fabrications due to its excellent conformal coating capability over severe topography, providing opportunities to realize 3D micropatterns. In this master thesis, spray coating recipes will be developed for various MEMS applications by thoroughly studying the influences of solvent vapor pressure, dispense rate, nozzle pressure, ultrasonic power, dispense arm velocity profile, etc. Widely used micromachining photoresists such as S1818, SU8, SPR200, AZ-series...will be sprayed on different substrates and geometries. Rigid substrates like trenched and bumped silicon and glass wafers will be used, as well as flexible foils and polymer structures. A demonstrator of the developed spray coating process is expected, such as a 3D antenna patterned on a hemisphere structure. If the hemisphere is fabricated using functional materials capable of expanding and shrinking upon activation, the proposed antenna will possess reconfigurable capabilities.

EVG101 spray coater. Concept of 3D antenna.

Promoter: Prof. Robert Puers

Faculty/research group: Engineering / ESAT-MICAS

Daily supervision: Tiannan Guan, Felix Godts

Graduating option: Engineering

Type of work: 10% literature study, 10% simulation, 70% fabrication, 10% characterization


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Integration of carbon nanotubes in microsystems Description: Since Iijima discovered carbon nanotubes in 1991, many researchers have investigated these intriguing molecules showing exceptional mechanical (extremely high Young’s Modulus), electrical (ballistic conductor with very high current capacity) and thermal properties (higher conductivity than diamond). These promising attributes have inspired technologists to integrate CNTs inside electrical integrated circuits and electromechanical systems (MEMS). Though single tube transistors and sensors and sensors based on carbon nanotube composites have been shown, current processes lack reproducibility and large scale integration. This thesis aims to improve microelectromechanical systems based on in situ grown carbon nanotube forest composites or multi-walled carbon nanotube composites currently developed at our research group. In these microsystems carbon nanotube composites based on polymers such as polydimethylsiloxane (PDMS), SU-8 and parylene act as piezoresistive sensors replacing the conventional metal or polysilicon strain gauges enabling a route towards fully polymeric sensors. This thesis will cover the complete cycle from design and simulation to fabrication and testing of a CNT based microsystem. The thesis involves the following tasks: - A concise literature study to get yourself acquainted with the subject and previous work (10%); - Design of a novel or improved sensor based on carbon nanotubes including the required simulation and layout tasks (20%); - Microfabrication in MICAS cleanroom (40 %); - Electromechanical characterization (10 %); - Text and defense (20%).

Promoter: Robert Puers ([email protected]), Michaël De Volder ([email protected]) Faculty/research group: ESAT-MICAS

Daily supervision: Grim Keulemans ([email protected])

Graduating option: Engineering Type of work (experimental, theoretical, simulations): Experimental


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Synthesis and post processing of Graphene Graphene, an atomically-thin sheet of carbon atoms arranged in a sp2 honeycomb lattice, has been successfully isolated for the first time only in 2004. The peculiar electronic properties of graphene arise mainly from the configuration of its energy band structure, which, combined with the intrinsically low occurrence of defects and the stiffness of its lattice, allows for the featuring of intriguing 2-D physical phenomena. Graphene has been proposed as a candidate for CMOS and post-CMOS electronics; however, in order to make electronic applications of graphene realistic, one has to necessarily tune its electronic properties, so that, for example, a bandgap is introduced. Another aspect of the current graphene research entails the finding of a synthesis technique alternative to micromechanical exfoliation for graphene production, in order to achieve graphene deposited over large areas, available for CMOS-compatible device fabrication.

The objective of this internship is to develop processes to synthesize graphene by means of Chemical Vapor Deposition techniques, or by annealing of SiC-based film stacks. The candidate will also learn how to manipulate graphene in order to transfer it to alternate supports, and will be involved in the design, fabrication, and characterization of graphene devices. Part of the work will entail the manipulation of graphene produced by mechanical exfoliation, for benchmarking purposes. The challenges involved are:

(1) fine tuning of process parameters to control the number of graphene layers grown;

(2) investigation of the influence of the substrate texture/crystallinity on the properties and quality of synthesized graphene;

(3) study of the interfacial reactions between the substrate and graphene;

(4) post-processing of as-grown graphene (e.g., transfer, modification, device design).

The work will start from earlier findings within the graphene team. Contact persons : Dr.Mirco Cantoro ([email protected]).

Promoter: M. Heyns/S. De Gendt Faculty/research group: FIW/MTM/, FW/Chemie, imec/NCAIS/NAME

Daily supervision: Mirco Cantoro

Graduating option: Engineering/Science Type of work (experimental, theoretical, simulations): experimental


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Characterization of backside illuminated hybrid CMOS Active Pixel Sensor Arrays Description: For the past few years, complementary metal oxide semiconductor (CMOS) image sensors have gradually taken the place of charged coupled device’s (CCD) technology in many applications. In one of those, being space exploration, these imagers should exhibit near-perfect behavior in terms of high quantum efficiency, low crosstalk and high radiation tolerance. For several years imec’s Imager team has been active in that domain: backside-thinned monolithic and fully-hybrid CMOS active pixel sensors (APS) possessing excellent imaging properties have been successfully designed, fabricated and tested. Currently, an improved version of CMOS APS is under fabrication and will be available shortly. Their performance is expected to be superior to the previous one, since various limitations and problematic areas are taken under consideration during design and processing. To evaluate this enhancement some of the key parameters of detectors arrays should be defined and quantified. Understanding the basic nature of the detector array, investigation of the performance limits and the calibration procedures and subsequent opto-electrical characterization on wafer or on packaged level are the main tasks involved in this Master Thesis. Various semiconductor physical mechanisms will be studied during the measurement of key parameters like inter-pixel electrical crosstalk, conversion gain, quantum efficiency, intrinsic device and off-chip noise, non-linearities, thermal dark signal, transient time phenomena etc. This Master topic will focus on the application of characterization procedures on CMOS APS. The work is mostly experimental and the goal is that the student comes to an improvement of the quantitative sensitivity evaluation of the 2D Sensor Arrays. Modifications to the measurement setup and procedures will be implemented and/or proposed. For further information or for application please contact: Kiki Minoglou ([email protected]), Koen De Munck ([email protected]) Promoter: Prof. Chris Van Hoof Faculty/research group: Engineering / ESAT-imec

Daily supervision: Kiki Minoglou, Koen De Munck

Graduating option: Type of work (experimental, theoretical, simulations): 60% experimental, 40% theoretical Number of students: 1

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Modeling backside illuminating CMOS imagers using TCAD software

Topic description: Context

Since the past few years, the technology of complementary metal oxide semiconductor (CMOS) image sensor has taken the place of charged coupled device’s (CCD) technology in many applications. One of those being the space investigation, the developed imagers should exhibit very high quality properties in terms of high quantum efficiency, low crosstalk and high radiation tolerance.

The Imager team in IMEC has been involved for the past years in that domain: backside-thinned monolithic and fully-hybrid CMOS active pixel sensors (APS) possessing excellent imaging properties have been successfully designed, fabricated and tested. In order to design and manufacture fully-hybrid CMOS APS possessing excellent imaging properties, different Technology Computer-Aided Design (TCAD) software tools were used. Those powerful tools are able to solve numerically complex physical equations and predict the performance of the device. Also critical microelectroning processing steps can be identified and optimized. Understanding the behavior of our current backside-thinned CMOS imagers and any further improvement requires different simulation models to be studied and developed.

Figure: 2D array of five backside illuminated pixels (top) and simulated results of electrostatic potential and srh recombination (bottom)

Description of the work

The goal of this Master Thesis is to study physical mechanisms of the photodiodes, get familiar with the TCAD tool software, implement the physical models and the actual device design into the simulator and confirm the accuracy of the developed model by comparing simulations to measurements. Simulations can be done with existing software packages, Process and Device simulators of the Sentaurus Synopsis

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TCAD software. The student will start from existing CMOS imager models and will focus on specific improvements and modifications. The student will interact a lot with the Imager team at IMEC.

For this master thesis, the student is expected to have a strong interest and/or background in semiconductor physics. IMEC will provide training to UNIX/LINUX and to the device modeling techniques. Previous experience with the tools is not required. However, knowledge of TCAD software and/or physics of optoelectronic devices is an advantage.

Duration Minimum 5-6 months.

Degree: Master in Microelectronics and/or Master in Engineering

Student majoring in: Electrical engineering, physics

Responsible scientist(s): For further information or for application please contact Kiki Minoglou

([email protected])

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Microfluidic mixing for lab-on-a-chip applications Description: Microfluidics is an emerging technology that is changing the future of instrument design. Most popular applications are inkjet printheads, DNA chips, lab-on-a-chip technology, micro-propulsion, and micro-thermal technologies. At imec, microfluidics are investigated for various applications in the biomedical domain. Microfluidics deals with the behavior, precise control and manipulation of fluids that are geometrically constrained to channels and fluidic components in the micrometer scale. It is a multidisciplinary field intersecting engineering, physics, chemistry, micro-technology and biotechnology. Microfluidic mixing is important in a variety of microscale chemical and biological systems. Mixing fluids in larger (macro-scale) devices is not that difficult. In micro-scale devices on the opposite, the low flow rates coupled with the small channel dimensions in these devices make effective mixing a challenging task. Furthermore, the mixing of particulate suspensions (i.e., a liquid which contains small -nanometer scale- particles) in these microscale devices has received less attention in the literature. Appropriate methodologies for predicting the mixing of particulate suspensions is essential in order to enable the fabrication of future complex microfluidic systems. Various prototype microfluidic mixers have been fabricated at IMEC. The student’s task will be to experimentally characterize the mixing of both single-phase liquid streams (i.e., liquids which do not contain particles) and particulate liquid streams in these prototype mixers. The student will also conduct computational fluidic dynamics simulations to better under the mixing in these devices. Based on the experimental and computational results, new, higher performance mixers can be proposed. The project tasks will include a review of the literature on microfluidic mixing, conducting experiments, and conducting numerical simulations. The precise breakdown of the workload will be dependent on the student’s own interests and capabilities as well as IMEC’s current research needs, but it is anticipated the student’s time will be allocated accordingly: 10% literature review, 60% experiments, and 30% numerical simulations. Promoter: Chris van Hoof Faculty/research group: ESAT-INSYS

Daily supervision: Ben Jones and Paolo Fiorini

Graduating option: master of nanoscience & nanotechnology Type of work (experimental, theoretical, simulations): 10% literature review, 60% experiments, and 30% numerical simulations


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Biocompatible packaging and metallization for miniaturized implantable biomedical systems Description: For implantable electronic devices, a biocompatible packaging process is under development at imec, combining biocompatibility with extreme miniaturization, taking cost aspects into account. In a first phase, encapsulation of chips is essential, to realize a bi-directional diffusion barrier around each die preventing body fluids to leach into the package causing corrosion, and preventing IC materials such as Cu to diffuse into the body, causing various adverse effects. Realizing a hermetic chip sealing is not straightforward. For cost effectiveness, all corresponding fabrication is performed as post-processing at wafer level in a standard clean room (CR). Adjusted fabrication techniques are explored, such as wafer level based die rounding in order to ensure very good step coverage of the diffusion barriers. In order to ensure CR compatibility of the final process, known materials used for chip passivation layers and conductive barriers such as Ti, TiN, Ta, TaN are investigated with respect to biocompatibility, diffusion properties and corrosion prevention. Various tests are performed: cell cultures using various primary cells, TXRF analysis of extracts, corrosion tests at 37C and at elevated temperatures. In a second phase, all chips of the final device should be electrically connected, applying a biocompatible metallization scheme using eg. gold or platinum. Finally, all system components, such as electronics, passives, a battery,... need to be interconnected during device assembly. A biocompatible embedding using PDMS will provide sufficient mechanical support to the components, while the body reaction upon implantation will be limited due to the biomimetic nature of PDMS (flex, soft material cfr. tissue). The project tasks will include a literature study on biocompatible packaging and biomaterials, conducting experiments (fabrication, testing, characterization), and conducting calculations/simulations to explain the experimental results. The precise breakdown of the workload will be dependent on the student’s own interests and capabilities as well as IMEC’s current research needs, but it is anticipated the student’s time will be allocated accordingly: 10% literature review, 70% experiments, and 20% calculations/simulations. Promoter: Chris Van Hoof Faculty/research group: ESAT-INSYS

Daily supervision: Karen Qian. Maaike Op de Beeck

Graduating option: master of nanoscience & nanotechnology Type of work (experimental, theoretical, simulations): 10% literature review, 70% experiments, and 20% calculations/simulations


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Luminescent lanthanide-doped fluoride nanoparticles Description: The light emitted by trivalent lanthanide ions can be distinguished from the luminescence of organic molecules or most transition-metal complexes by its highly monochromatic nature. The spectroscopically active 4f electrons of the lanthanide ions are not involved in any binding molecular orbital, and they are protected from the environment by the fully occupied 5s and 5p orbitals. This results in the typical narrow emission lines in lanthanide luminescence spectra. Examples of luminescent lanthanide ions are europium(III) (red color), terbium(III) (green color), samarium(III) (orange-red color), and the near-infrared emitting lanthanide ions ytterbium(III), neodymium(III), and erbium(III). Lanthanide compounds have been successfully used as phosphors in numerous applications such as OLEDs (organic light-emitting diodes), fluorescent lamps, lasers, and luminescent probes in biology. Fluoride host crystals such as LiYF4, KY3F10, NaYF4, and LaF3 are ideal matrices for luminescent lanthanide ions, because of their low phonon energies. These low phonon energies reduce the desactivation of the excited of the lanthanide ion via radiationless processes, so that the luminescence properties are enhanced. Unfortunataly, large single crystals of fluoride crystals are difficult to grow and to process. Nanosized fluoride crystals can provide a solution. Not only, they can be prepared via wet chemical routes at very moderate temperatures, but they can be dispersed in aqueous solutions or in organic solvents. This project is about the exploration of new synthetic routes for the preparation of fluoride nanoparticles, doped with trivalent lanthanide ions. The target is to obtain nanoparticles with a spherical shape and with a high monodispersity. The student will prepare the nanoparticles and will determine their size and size distribution by different experimental methods like dynamic light scattering and transmission electron microscopy (TEM). The luminescence of the particles will be investigated by steady-state and time-resolved luminescence spectroscopy. This type of nanoparticles can find applications in medical diagnostics as bimodal contrast agents (MRI and luminescence), after decoration of the surface of the nanoparticles with MRI contrast agents, such as Gd-DTPA or Gd-DOTA. Promoter: Prof. Dr. Koen Binnemans + Prof. Dr. Tatjana Parac-Vogt Faculty/research group: Deparment of Chemistry, Molecular Design and Synthesis

Daily supervision: Sophie Carron

Graduating option: Natural Sciences Type of work (experimental, theoretical, simulations): experimental


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Porous Organic Materials for Gas Storage and Separation

The threat of global environmental pollution caused by the emission of greenhouse gases has inspired the scientific community to find an economically and technologically viable way towards novel materials for sequestration and gas storage. In this context the search for highly porous materials showing unique properties such as gas storage, selective gas recognition and separation has emerged as a forefront issue of present-day research. A variety of porous materials such as silica gels, activated carbons, zeolites and metal organic frameworks (MOFs) have been investigated in this regard, but only low to moderate selectivity was achieved so far. Therefore, there is a continuing demand for new solution processable porous materials towards advances in cost effective and environmentally benign gas separation.

In this project, we propose a novel class of potentially porous materials from within the calixarene family, known as “homodithiacalix[n]arenes”, which allow fine-tuning at the molecular level by systematic variation of the functional groups, that could enable to control pore size and surface area. We envision that by exploiting this, selective gas separation could be achieved by preferential adsorption of certain components of a gas mixture over others in nanopores of particular size.

The practical work will constitute of (1) synthesis of potentially porous calixarenes, (2) crystal growth and structure determination, (3) further characterisation of materials using various techniques (including thermogravimetric analysis, differential scanning calorimetry, gravimetric and volumetric sorption analysis, and X-ray powder diffraction). Emphasis can be put on the synthetic part or gas sorption part (running isotherms for a variety of gases - CO2, CH4, O2, H2, etc. under different conditions – temperature, pressure and their further detailed studies) depending on the student’s preferences.

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Investigation and optimization of the electrical switching properties of Resistance RAM memory cells (RRAM) Description: The Resistance RAM is a new class of memories emerging as serious candidate for future memory replacement, in particular for high-density memory application. Resistance RAM cells typically consist of insulating oxide layers sandwiched between two metal electrodes, and exhibiting resistive-switching properties, that is to say the application of an electrical current/voltage to the cell induces reversible changes of the cell resistance, which allows thus programming different memory states. For numerous resistive-switching metal/oxide/metal stacks, the switching to the low resistance state (LRS) is due to the formation of a conductive filament through the oxide while the return to the high resistance state (HRS) is due to partial rupture of this filament, the two operations being electrically induced. Depending on the materials used in the stack, the conductive filament is formed due to a sort of oxide breakdown leading to oxygen depletion along the breakdown path (Fig1a) or the conductive filament may be formed due to injection of the electrode metallic element into the oxide (Fig1b).

a b

Fig1. (a) Current-Voltage characteristics showing switching to different resistance states, and conductive filament formed by local oxygen depletion in the oxide (from “A. Sawa, Materials Today, 11, 2008”); (b) Current-voltage switching traces and schematic of filament formation due to electrochemical dissolution and growth of the electrode metal element (from “R. Waser et al., Adv. Mater., 21, 2009”) The purpose of the thesis is to study the resistive-switching properties of different types of Resistance RAM stacks, in order to (1) better understand the switching mechanism, and (2) identify optimum material stack characteristics improving the memory parameters of the cell. To this aim the study will mainly consist in electrical measurements using conventional Current-Voltage measurements, as well as pulse-programming testing for scaled devices. Specific measurements like temperature-dependent I-V or impedance measurements may also be required. The effects of different stack parameters will be addressed by varying the nature of electrodes and oxides, the thicknesses, the microstructures, applying special treatments or anneals... Promoter: Dirk Wouters Faculty/research group: Ingenieurswetenschappen (ESAT/INSYS – IMEC)

Daily supervision: Ludovic Goux

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Graduating option: nanotechnology Type of work (experimental, theoretical, simulations): experimental


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Atomistic Phase-Field-Crystal Simulations of the Zener Drag Effect of Nanoparticles on Grain Boundaries Description: An important technique to control grain boundary movement in thin films and nanocrystalline materials is by the addition of nanoparticles or -precipitates. They have the capacity to retard and even stop grain boundary movement and grain coarsening. This is called Zener drag. The effect of the particles on grain boundary movement has been studied extensively, experimentally and by means of mesoscale simulations. However, the pinning capacity of nanoparticles is largely determined by mechanisms on the atomistic scale, which are still poorly understood. It is for example not well understood whether the grain boundary envelops or goes through the particle or whether it splits up into 2 parts. There are also indications that the particle may change shape or rotate during passage of a grain boundary. These atomistic details have an important effect on the pinning capacity of the particles. In general, however, the resolution of in-situ observation techniques is too low to be conclusive on the atomistic mechanism.

Density field with high probability density marked by red and low probability of atomic occupancy by blue. Time is increasing from left to right. Particle rotation in a 2D system can be seen as an

interface is swept past the particle. The goal of this master thesis is to simulate the passage of a grain boundary by a particle on the atomistic scale using the Phase Field Crystal modeling technique. In the PFC technique, one starts from a free energy functional ( ( ))F n rΔ

r which is a function of the local atomic density

( )n rr

and reflects the crystal structure, lattice spacing and the elastic and plastic response of the atoms. The time evolution of the atomic arrangement is obtained from conservative dissipative dynamics,

( )( )

n r FMt n r

δδ

⎛ ⎞∂ Δ= ∇ ⋅ ∇⎜ ⎟∂ ⎝ ⎠

r

r .

The evolution equation above is solved numerically using a spectral algorithm programmed in C++. Existing 2D and 3D codes can be used to test the effect of parameter space of elastic moduli, lattice parameter of the particle and matrix, relative orientation and mismatch tilt of the two bulk grains and particle size. All of which could have an effect on the particle's interaction with the boundary. The atomistic interactions will be studied as a function of particle size and shape.

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This thesis does not require experience in programming. A strong interest in mathematical modeling and computer simulations is however needed. Please also contact [email protected] for further information before choosing this topic. Promoter: N. Moelans Faculty/research group: Faculty of Engineering, Dept. Metallurgy and Materials Science, Solidification and microstructure simulation group

Daily supervision: M. Greenwood (UBC, Canada), N. Moelans

Graduating option: Engineering Type of work (experimental, theoretical, simulations): Simulations


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Design of the transistor selector element in a 1T1R-cell based embedded RRAM Memory Description: Resistance-change based memories (Resistive-RAM or RRAM) are investigated as a new class of memories that offer improved scalability compared to the classical charge-based memories as DRAM and Flash. However, similar to DRAM, their functionality requires the incorporation of a selector device in each cell. Due to the current drive requirement through that selector, the final cell size scaling may become limited by the selector element rather than by the RRAM element itself. In this thesis, the design of a transistor selector device suitable for a scaled embedded RRAM application will be investigated. Both bulk and vertical transistor concepts will be compared, and the effect on the possible asymmetry for bipolar programming operation studied. As a starting point, existing device models of current technologies will be used, but the effects of further scaling on both device operation and also variability will be explored

Figure 1: Resistive-RAM array with in each cell a select Transistor combined with the Resistive element (1T1R cell). Promoter: Dirk Wouters Faculty/research group: Ingenieurswetenschappen ESAT/INSYS (IMEC)

Daily supervision: Dirk Wouters

Graduating option: Nanotechnology Type of work (experimental, theoretical, simulations): theory & simulations


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Digital lab-on-a-chip technology for functionalization of nanomaterials in femtoliter droplet arrays Description: Lab-on-a-chip technology offers revolutionary analysis platforms for numerous biological and chemical applications. On such a lab-on-a-chip, different laboratory processes are integrated and miniaturized on a microchip of maximum a few centimeters size. The goal of these miniaturized systems is to complete a wide variety of (bio)chemical analyses on a very automated way with maximum sensitivity. There are two ways to transport liquids (reagents) on a lab-on-a-chip: as a continuous flow or as a discrete amount of liquid. In your research, fluids are manipulated as individual liquid droplets with a volume in the nanoliter range. A key advantage of working with droplets is that the execution of all laboratory protocols such as pipetting, diluting and mixing is done on a micro- to nanometer scale. The droplets are manipulated on hydrophobic surfaces made from Teflon. Recent research efforts at the MeBioS biosensor lab have shown that local functionalization of the Teflon surface with hydrophilic micropatches allows femtoliter sized liquid samples to be generated with very high precision on the chip platform. This offers interesting applications for the functionalization of nanomaterials such as nanoparticles.

Figure: our EWOD lab-on-chip platform. More media can be found at: http://www.biosensors.be/biosensors-home/research-topics/micro-and-nanofluidics.aspx Your goal will be to evaluate the potential of digital lab-on-a-chip technology for the immobilization of nanoparticles in these femtoliter droplet chambers. First, different fabrication techniques will be introduced in order to create the hydrophilic micropatches. In first instance, these will consist of conventional photolithographic techniques at the cleanroom facilities of ESAT. In a further stage, Focused Ion Beam (FIB) technology will be used to introduce hydrophilic patches in the nanometer range on the chip platform. In a subsequent stage, you will learn how to locally deposit liquid samples and nanoparticles in these fabricated nanochambers. This will be achieved by immobilizing nanoparticles inside these hydrophilic patches and subsequently functionalizing them with biomolecules such as DNA or antibodies. Finally, you will use the functionalized lab-on-a-chip for detecting very low concentrations of DNA or proteins. Because of the very low volume that is present in the femtoliter chambers, very low detection limits can be achieved. This makes the digital lab-on-a-chip very promising for applications in different fields of biosensing technology.

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Promoter 1: Jeroen Lammertyn

Promoter 2: Robert Puers Faculty/research group: Bioscience engineering/MeBioS biosensors

Daily supervision 1: Daan Witters

Daily supervision 2: Frederik Ceyssens

Graduating option: Type of work (experimental, theoretical, simulations): Experimental


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Integrating optics in digital lab-on-a-chip technology Description: Lab-on-a-chip technology offers revolutionary analysis platforms for numerous biological and chemical applications. On such a lab-on-a-chip, different laboratory processes are integrated and miniaturized on a microchip of maximum a few square centimeters size. The goal of these miniaturized systems is to complete a wide variety of (bio)chemical analyses in a very automated way with maximum sensitivity at high speed. There are two ways to transport liquids (reagents) on a lab-on-a-chip: as a continuous flow or as a discrete amount of liquid. In this research, fluids are manipulated as individual liquid droplets with a volume in the nanoliter range. A key advantage of working with droplets is that the execution of all laboratory protocols such as pipetting, diluting and mixing is done on a micro- to nanometer scale. The droplets are manipulated on Teflon hydrophobic surfaces by electrowetting using electrodes underneath.

Figure: Left: our EWOD lab-on-chip platform . Right: integrated optical waveguides with optical fiber clamps, forming a splitter structure Up to now, optical readout of the nanoliter-size reaction in our platform is done with an external optical setup. For some applications, a more fully integrated solution would be superior. Therefore, in this thesis, fabrication procedure will be sought that allows to integrate optics (light sources, waveguides, detectors) with our existing lab-on-chip technology. This would allow more integrated readout based on fluorescence or absorbance. In a second phase, optical surfaces can be functionalized allowing surface plasmon resonance (SPR) based measurements. Promoter 1: Jeroen Lammertyn

Promoter 2: Robert Puers Faculty/research group: Bioscience engineering/MeBioS biosensors & ESAT-MICAS

Daily supervision 1: Daan Witters


Graduating option: Nano, biomedical Type of work (experimental, theoretical, simulations): Experimental


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3D Lithographic fabrication technology for cylindrical neural stimulator electrodes. Description:

Figure: Electrode of cochlear implant (left) and application in the cochlea. In several recent developments in medicine, implanted neural stimulator electrodes are used. This is the case in deep brain stimulation (Parkinson's disease, tremor, chronic pain), cochlear implants (profound deafness) etc. Up to now commercial electrodes used in humans are fabricated in a manual, labor intensive process based on molding and microwelding. Nevertheless, lithography would have very significant advantages in terms of available resolution and cost. However, the cylindrical shape of the electrodes rules out direct application of processes developed for MEMS or IC fabrication. In this thesis, you would have to chance to engineer a 3D lithography based fabrication process that can bring closer a more automated high resolution way of fabricating these electrodes. Promoter 1: Robert Puers

Faculty/research group: ESAT-MICAS


Graduating option: Nano, biomedical Type of work (experimental, theoretical, simulations): Experimental


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Probing the structural quality of semiconductor/heterostructures using electron spin resonance Description: describe context, objective, work to be done, expected results When dimensionally downward scaling solid structures from the macro over the microscopic down to the nano (quantum) size, the relative importance of surfaces and interfaces gradually increases, even towards taking an all dominant role: One atomic-size imperfection my imply life or dead for the envisioned functional (physical) property. The technique of magnetic resonance, applied to electrons (ESR), is the unique tool enabling, besides characterization, identification on true atomic scale of imperfections in fully non-destructive way through sensing the magnetic moment of unpaired electrons. Part of the work to be performed implies assisting in taking ESR spectra at low temperatures and simulation of observed spectra to infer the relevant parameters. Actual challenges imply the interfaces in Ge/GeO2/SiO2, Ge/Si/HfO2, and GaAs/oxide entities, where identification of crucial interface traps is envisioned. One more item of interest concerns a center in near-interfacial Si layers. Promoter: Prof. A. Stesmans Faculty/research group: Sciences/Department of Physics/Semiconductor Physics Section

Daily supervision: Prof. A. Stesmans, Dr. M. Jivanescu, Mr. Duc Nguyen

Graduating option: Master thesis Type of work (experimental, theoretical, simulations): experimental Number of students: 1

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Internal electron photo-emission in nano-layers and nano-structures Description: describe context, objective, work to be done, expected results The energy spectrum of electron states in nanometer-thin insulating layers and at their interfaces with, e.g., semiconductors (Si, Ge, AIIIBV, etc.) can be characterized into great detail using observations of optically-induced electron transitions across the interface (the internal photo-emission effect, as compared to the better known classical solid/vacuum photoelectric effect ingeniously described way back by A. Einstein). This method allows the most straightforward and unique determination of the fundamental energy parameters of a two-solids nanostructure, like band gap, height of energy barriers and band offsets at the interfaces. The spectroscopy of internal photoemission will be applied to the study of insulating materials currently tested for use in new novel micro-and nanoelectronic devices, this within a framework of international collaboration, including IMEC. Part of the experimental work will imply electrically contacting a basic heterostructure and measure photoemission currents through a computerized monitoring system. Among the targeted results, the student should acquire the skill of inferring interfacial band offsets at a newly conceived semiconductor/insulator heterostructure based on the understanding of the physical processes occurring during carrier emission. Promoter: Prof. V. V. Afanas’ev Faculty/research group: Sciences/Department of Physics/Semiconductor Physics Section

Daily supervision: Ms. M. WanChih Wang, Ms. Hsing-Yi Chou, Prof. V. V. Afanas’ev,


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First-principles modeling of high-mobility semiconductors/insulator interface Description: describe context, objective, work to be done, expected results A next step in boosting progress and performance of semiconductor devices implies, in replacement of the current Si, incorporation of semiconductors of higher intrinsic carrier mobility. When introduced at the nano scale, this will require new analysis and physics insight. Understanding the fundamental properties of such gate stacks is important in order to understand their behavior in devices. The work to be performed encompasses computation and modeling the structural and electronic properties of interfaces of high-mobility semiconductors (e.g., Ge, GaAs) with high-quality metal oxide insulators, based on density functional theory. A second point of interest includes 2 dimensional carbon (graphene) and Si layers with main focus, besides practical stability, on band structure and transport properties. As a propelling tool, the results will be correlated, when possible, to experimental results obtained through structural and electrical observations. This work will be performed in collaboration with IMEC. Promoter: Prof. M. Houssa Faculty/research group: Sciences/Department of Physics/Semiconductor Physics Section

Daily supervision: Prof. M. Houssa, Mr. E. Scalise


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Embedded semiconductor nanoparticles and nanowires characterized by electron spin resonance Description: describe context, objective, work to be done, expected results Part of the enhanced attention paid to solid state nanoparticles derives from the interest in the study of changing fundamental properties of solids when size is reduced down to the nanoscale. A separate class concerns semiconductor nanoparticles embedded in dielectrics, particularly studied for interesting properties, such as remarkable photoluminescence, and potential for (memory) electronic devices. In these phenomena, occurring point defects commonly play a crucial role, of fundamental impact, making their characterization, and much hoped for, ultimate identification, main targets. In the current work, electron spin resonance (ESR) is applied as a prime non-destructive technique to attain identification on atomic scale, simultaneously enabling probing of the immediate atomic and structural environment. Part of the work to be carried out implies assisting in taking ESR data at low temperatures and simulation of relevant parameters to infer relevant parameters. Interpretation on the basis of underlying theories will reveal specific particle properties. Of current interest are Si and Ge particles embedded in various dielectric matrices as well as Si nanowires embedded in SiO2, the research being carried within continuous international collaboration. This is done in conjunction with application of electrical studies to infer properties such as charge trapping and altering band structure properties. Promoter: Prof. A. Stesmans Faculty/research group: Sciences/Department of Physics/Semiconductor Physics Section

Daily supervision: Prof. A. Stesmans, Dr. M. Jivanescu


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Digital microfluidics for cell membrane permeability measurements Description: Aquaporins selectively conduct water molecules in and out of the cell, while preventing the passage of ions and other solutes. Also known as water channels, aquaporins are integral membrane pore proteins. The scientist that discovered aquaporins was awarded the Nobel Prize in Chemistry 2003. Aquaporines are implicated in drought stress resistance, and a better understanding of the presence of aquaporines and how they effect the water permeability of the plasmamembrane may guide the development of crops that may survive increased drought because of global warming. The objective of this thesis is to develop a digital microfluidics platform to measure water permeability of the membrane of individual plant protoplasts and relate this to its aquaporine content. Digital microfluidics refers to the transport of individual droplets on a chip, most commonly by the principle of ‘electrowetting-on-dielectric’ (EWOD). When an electric field is applied over electrodes, covered by a dielectric layer, the contact angle between the droplet and the dielectricum changes. With a digital lab-on-a-chip, droplets can be generated, transported, mixed and merged on a matrix of microelectrodes without the intervention of micropumps, microvalves, and microchannels as in the classical microelectromechanical systems. The membrane permeability of the protoplast will be determined by mixing droplets, containing different PEG-concentrations with the droplet (microreactor), containing the cell. The volumetric decrease or increase is monitored over time with microscopy and the membrane permeability is derived from this volumetric change. The presence of aquaporins will be determined quantitatively by labeling them on-chip with a fluorescent probe.

Promoter: Bart Nicolaï / Jeroen Lammertyn Faculty/research group: Bioscience Engineering / MeBioS

Daily supervision: Steven Vermeir

Graduating option: Bioscience Engineering / Science Type of work (experimental, theoretical, simulations): Experimental


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Innovative Vis/NIR spectroscopic measurements in combination with light propagation models to determine the size of the scattering particles. Description: Food products usually contain a certain amount of non-uniformities like cell walls, nuclei, membranes, mitochondria, particles or air pores (size 0.1 - 10 μm) which cause scattering of Vis/NIR light. These scattering phenomena seriously complicate the use of Vis/NIR spectroscopy to determine the composition of such products. Traditional Vis/NIR reflection or transmission measurements will only provide information on the light attenuation caused by both absorption and scattering. As a result, a change in the scattering properties might be misinterpreted as a change in the composition. Moreover, the properties (like size, shape, refractive index, …) of the scattering particles can also give more information about the microstructure of the food products. Therefore it is interesting to determine these properties and use this information together with light propagation models in order to correct for the light scattering. Calculation of the interaction between Vis/NIR radiation and spherical scatterers in a medium requires solution of the Mie scattering theory, taking into account the size, shape density and refractive indices of the particles. The obtained light propagation models can be inverted and combined with innovative multiple spectroscopic measurements acquired by a Double Integrating Sphere (DIS) setup or Spatially Resolved Spectroscopy (SRS), resulting in the absorption (composition) and scattering (information about the scattering particles) properties. In a first stage, this approach can be tested and optimized on model systems with liquid optical phantoms made up of polysytrene or lipid spheres (known size and concentration) emulsified in water. In later stages also combinations of two or more particle diameters (polydisperse) in different concentrations will be considered. Finally, the inverted model can be tested to predict the size of particles in food products (e.g. fat globules in milk). Laser light scattering will be used as the reference method for validation. Promoter: Prof. Wouter Saeys and Prof. Jeroen Lammertyn Faculty/research group: Faculty of Bioscience Engineering, Department Biosystems, MeBioS

Daily supervision: Ir. Ben Aernouts and Ir. Rodrigo Watté

Graduating option: Type of work (experimental, theoretical, simulations): Experimental and simulations


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Optimization of the optical characterization of food products Description: The food industry has evolved significantly the last few years as a result of the increasing demand of quality products. The consumer expects a high and uniform quality. In order to realize this issue, one needs fast, non-destructive measuring techniques. Food can be seen as a collection of biomaterials – composed of multiple components and phases – which are altered as a result of digestion. From this vision, one can adapt fatty or sugary food, to obtain a more healthy adaptation. There are however some restrictions due to the relationship between the microstructure of food, and its sensory taste. Modifying the chemical composition for health benefits often has a negative effect on the microstructure and therefore on the perceived taste. Fat reduced chocolate doesn’t melt as fast in one’s mouth, has a rougher feel and is therefore less appreciated. If one wants to alter food for health reasons, it is important to recognize the importance of measuring the microstructure. An important technique which allows to obtain this information is Vis/NIR spectroscopy. Advanced versions of this technique measure the spatially resolved reflectance profile. With the help of light propagation models, one can simulate the reflectance/transmittance of a sample with specific optical properties. In this thesis project, the student will make an evaluation of different light propagation models. Different methodologies exist, which vary in accuracy and computational speed. At first, the student will cooperate on the optimization of the computational speed of different light propagation models. Afterwards a comparative study of the different models will follow. A protocol will be developed to verify the validity of each technique. Promoter: Prof. Wouter Saeys & Prof. Herman Ramon Faculty/research group: MeBioS

Daily supervision: Ir. Rodrigo Watté

Graduating option: Type of work (experimental, theoretical, simulations): theoretical/simulations


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Nano-structures: Second Harmonic Generation In the last decade, nanostructures bridging the macroscopic world of bulk materials and the microscopic world of atoms and molecules attract thriving attention from electrical engineers and physicists. For example, by the virtue of the exotic behavior of metal at optical frequencies, several novel effects, such as the surface plasmon polariton (= the confinement of electromagnetic waves at optical frequencies on the interface between a dielectric and a metal), and metamaterials allowing cloaking (artificial materials with negative permittivity and permeability that allow to design structures that make things invisible), to name a few, are observed and studied. These studies need proper modeling tools. During the last few years the in-house developed solver MAGMAS, which was originally developed for the microwave frequency range, has been extended to the optical frequency regime. To our knowledge, MAGMAS is currently the only integral equation solver available that is able to handle this kind of structures. With the help of MAGMAS, our research group is able to predict accurately linear electromagnetic interactions in the optical frequency range for a rich range of topologies, which is a quite unique asset in this field. Moreover, since last year MAGMAS goes even one step further. It enters the region where no man has gone before: the computational study of Second Harmonic Generation (SHG). SHG can be considered as very important in Physics. One of the direct applications of SHG is for example the perfect imaging of the linear electromagnetic response at the fundamental frequency (see the Figs at the end of the proposal). This is of real crucial importance to the physics community in order to be able to study the vast range of inexplicable (up to now !) phenomena.

The goal of this thesis is to use the unique capabilities of MAGMAS to predict effects that stun the physics community. The steps are organized as following:

1. Become familiar with MAGMAS, the dedicated CAD tool developed at TELEMIC to analyze nanostructures;

2. Study the basic theory of Second Harmonic Generation (SHG) in the framework of classical physics;

3. Implement the available models into MAGMAS3D;

4. Justify the implementation by the results using other methods (FDTD, etc.) ;

5. Analyze specific structures proposed by the INPAC group from the physics department.

This is a master thesis with a strong “physics” flavour. The student is expected to be highly involved in the on-going research within the framework of the nanoscale projects currently running.

Promotor: Guy Vandenbosch ([email protected], room 02.17)

Daily advisor: Xuezhi Zheng (room 02.39)

Nature of the work: 20% literature study, 30% theory, 50 % design and testing

Students: 1 or 2

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Fig. (a) Simulation Results from MAGMAS; (b) SHG microscopy of G structure; (c) “Decoration” of the manufactured G Unit Cell (in white) after the illumination with strong bright light at 800 nm: observe the

“Christmas balls” growing out of the structure.

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Modeling and design of nanostructures: nantennas of the second generation

In recent years, there is a growing cooperation between the antenna research group of ESAT-TELEMIC and several other research groups of the K.U. Leuven in the field of nanostructures. The cooperation is stimulated by a spectacular progress both in fabrication technology and in computer modeling. The cooperation is both-ways and allows to merge experience gained in different fields.

For antenna applications, it is of interest to analyze wide varieties of new materials with very specific properties that can be manufactured using new available technologies, and to implement them in antenna design. The goal is to make use of the expertise of the antenna group in electromagnetic modeling in order to boost the efficiency in understanding the behavior of structures in the optical frequency range.

Concrete, this thesis looks at nanostructures, more specifically nano-antennas of the second generation. It will investigate the behavior of these nanostructures based on the correct material properties. It should be mentioned that due to the technological progress achieved and the extraordinary material properties at optical frequencies, nanantennas and nanostructures in general offer new possibilities in different areas: physics, electrical engineering, chemistry, and bio-engineering. The in-house modeling capabilities of TELEMIC will be used. The thesis consists of different steps.

- The first step is to get familiar with the dedicated CAD tools developed at TELEMIC to analyze nano-structures.

- The second step is to select several interesting topologies that are going to be investigated. Although the choice will be made later, the structures chosen will be aiming at realizing nano-antennas, and/or periodic metamaterials (cfr. antenna arrays) in the optical range. These structures are expected to contribute to a break-through in micro-electronics, by overcoming the boundaries coming nearer and nearer with traditional fabrication technologies.

- The third step is to make a thorough analysis of these structures, using the range of available software tools.

- The fourth step is the selection of a structure for fabrication. - The last step is the planning of the fabrication and measurement of a sample.

It is clear that this thesis follows the complete process of a typical design cycle, from original idea to realization and measurement, in a very challenging and fundamental research area.

Promotor: Guy Vandenbosch ([email protected]. be, room ESAT 02.17), Dominique

Schreurs ([email protected], room ESAT 02.16)

Daily advisor: Vladimir Volski (room 02.39)

Nature of the work: 20% literature study, 30% theory, 50 % design and testing

Students: 1 or 2

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Figure 1. Study of a nano-dipole and its current distribution.

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Stress field induced lifetime degradation of minority carriers in thin silicon for solar cell applications Description: In order to reduce the cost of silicon solar cells, one needs to make the base material and production processes cheaper and/or improve device architecture in such a way that the cells become more efficient in terms of energy conversion. In the Solar Explore team of imec, we can produce very thin foils of silicon by a lift-off method with a crack propagating in a controlled way about 50µm underneath the surface of a thicker slab of silicon. If this foil can be processed into a solar cell, a large cost reduction in terms of base material is already achieved in comparison to conventional silicon sawing. The goal of this thesis is to find out the full potential of these foils for solar cell application. We want to examine how the imperfections in these foils (structural, elemental, residual stress fields,...) affect their potential for conversion of photons into electron-hole pairs. In order to do so, we can opt for metallographic methods (defect etching of polished cross-sections) or opto-electronic measurements (microwave reflection photo conductance decay, quasi steady state photo conductance, deep-level transition spectroscopy, electron-spin resonance...). The main challenge of this thesis work consists of making the measurement procedure precise and thus sensitive, separating bulk-Si effects from surface effects and finally correlating results of different methods with one another. This will be done by studying and comparing defect-free samples, samples with ‘controlled’ amounts of defects and stress (e.g. by applying external loads) and finally lift-off samples with ‘uncontrolled’ amounts of defects. Promoter: Jef Poortmans Faculty/research group: ESAT/imec photovoltaic group

Daily supervision: Jan Vaes ([email protected])

Graduating option: Nanotechnology Type of work (experimental, theoretical, simulations): Experimental


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Simulation of Advanced Solar Cells Description: Solar Cells have become a very popular alternative energy source and its market will continue to grow enormously during the next decades worldwide. The competiveness of the different cell types depends very much on cost and performance. In the Si Solar Cell Explore Group of imec, several new state-of-the-art solar cell concepts are being investigated to improve the efficiency and reduce cost. The surface recombination effects require special attention in thin Si cells, and hence a detailed study of the nano structure and the impact of the charges in the passivation layer (and at its interface with Si) on the device behavior are of great scientific interest. The learning cycles for optimization of the efficiency of solar cells can be accelerated considerably by using the predictive capability of advanced numerical simulation tools. Moreover, better insight is obtained in the different design trade-offs and loss mechanisms through simulation. Therefore, device simulations are an attractive and complementary approach to improve our knowledge and understanding. At imec, extensive experience has been acquired with a powerful semiconductor device simulator Sentaurus, a commercial TCAD (technology computer-assisted design) software package from SYNOPSYS using Finite Element Method that solves numerically the semiconductor device equations in 1D, 2D or 3D, in particular for solar cell devices. The simulation of a solar cell consists of 2 parts: First, the light absorbed in the active silicon is calculated. Optical features of a solar cell to enhance the light trapping in the solar cell include front-side texture, anti-reflective coating, rear-side reflection layer, gratings and several others. Secondly, the electrical behavior of the solar cell is calculated from the Poisson, drift/diffusion and carrier continuity equations, applying all recombination loss mechanisms (Auger, Shockley-Read-Hall,...). The dark-IV curve and spectral response of a solar cell are calculated because they provide important insight in the device. Characterization and calibration data from specific process steps will be used as input in the simulator to create a realistic model. In a power loss analysis of the solar cell, the different electrical and optical losses are identified. We are looking for a motivated student with good computer skills (tcl, Matlab, python, ..) and a strong interest in device simulations, sound knowledge of semiconductor device physics and optics. Promoter: Jef Poortmans Faculty/research group: ESAT/imec photovoltaics group

Daily supervision: Koen Van Wichelen ([email protected])

Graduating option: Nanotechnology Type of work (experimental, theoretical, simulations): simulation


63


Intelligent epitaxial silicon foils for thin film solar cells and modules Description: Imec is aiming at reducing the thickness of the silicon wafers in crystalline silicon modules. Several concepts are now under investigation on how to release thin foils from a mono-crystalline mother substrate in order to produce those very thin wafers. In the frame of this thesis proposal, a concept where a foil is formed by means of epitaxy on a weak layer of porous silicon is explored. Foils created by epitaxy not only enable us to create high quality layers, but epitaxy also gives us the freedom to design the doping profile as desired. Those two main advantages offer the possibility to aim for very high efficiency solar cells. First experiments show that it is possible to detach the epitaxial layers (40um) from the mother substrate while bonded to a glass substrate just after epitaxial growth. However, this detachment procedure needs to be further developed: in the final concept, the detachment process will take place after processing the front side of the solar cell. In parallel, a solar cell process flow needs to be defined and tested step by step. Characterization of the foils after each critical step in the solar cell process is needed to get the process under control. In order to optimize this solar cell concept, imec is looking for 2 motivated and engaged people willing to work in a multicultural environment. The final goal is to help us realizing a high efficiency cell based on epitaxial silicon foils. Promoter: Jef Poortmans Faculty/research group: ESAT/imec photovoltaic group

Daily supervision: Kris Van Nieuwenhuysen ([email protected])

Graduating option: Master Nanotechnology Type of work (experimental, theoretical, simulations): Experimental


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Photonic nanostructures for efficiency enhancement of ultrathin solar cells

Description: One of the main levers to decrease the cost of silicon photovoltaic cells is to decrease the amount of silicon consumed. However, the thinner the material, the lower its light absorption, particularly at long wavelengths (near infrared), and therefore the lower the cell efficiency. The development of cheaper, thinner solar cells thus requires developing light scattering and light trapping techniques to compensate for these losses. Amongst all the techniques explored, this proposal focuses on nanopatterning: thanks to the progress of photonics, we are now able to pattern a material in such a way that its optical properties are strongly modified. We can yield increased reflection (and control its directionality) control transmission, and therefore absorption. These techniques have mostly been used so far for specific applications like lasers, and are only starting to be applied to solar cells; there is therefore a need for a simultaneous effort in design, simulation and fabrication. For the latter, nanoimprint lithography is a very promising method for it enables high-resolution with high-throughputs and low-cost. And, just like photonics, it is only starting to be used for solar cells. In this frame you will participate to the modelling and experimental fabrication of solar cells incorporating light-management features, and to their characterisation. You will learn various simulation tools, and try to integrate light-management effects in the overall simulation of a photovoltaic cell. In parallel, you will participate to the fabrication of thin (industrial) and ultrathin (long-term research) solar cells. You will in particular develop the nanoimprint lithography process and the following plasma-etch step in order to gain control on the patterns. Finally, you will perform optical characterisation of the yielded light trapping, and optical and electrical characterisation of the resulting solar cells. The balance between these three components will be up to your preferences and skills.

Promoter: Jef Poortmans Faculty/research group: ESAT / imec photovoltaics

Daily supervision: Valerie Depauw and Ounsi El Daif ([email protected])

Graduating option: Type of work (experimental, theoretical, simulations): experimental and simulations


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Thin-film photovoltaic solar cells: optimization and electrical characterization of polycrystalline silicon material Description: The relatively new “thin-film polycrystalline-silicon (grain size of 0.1-100 µm) solar cell on foreign substrate” technology aims at low-cost devices with energy conversion efficiencies above 12 %. This technology combines the cost reduction potential of a thin-film technology with the material quality potential of a crystalline material. Direct deposition of silicon on a non-silicon substrate results in amorphous or small-grained material. To fulfill the demand of relatively large grains, different methods to (re)crystallize Si are investigated at IMEC, namely aluminum-induced crystallization (AIC), solid phase crystallization (SPC) and laser crystallization. The absorber layers of our solar cells are formed by a two step process of seed layer formation (with the technologies mentioned before) and epitaxial growth on top. Recently we showed that the efficiency of such solar cells is limited by electrically active intragrain defects present in the absorber layer. The electrical activity of these defects can be triggered by (metal) impurities. The task of this thesis will be two-fold: improve the polycrystalline silicon and study the obtained material with different electrical characterization methods. The improvement of the material will be done by tuning the seed layer crystallization process, whereby you will mainly study the AIC process. Improving the epitaxial growth is out of the scope of this thesis. For electrical characterization you will mainly use C-V, Hall, resistivity versus temperature, resistivity versus illumination and impedance spectroscopy measurements. The work in this thesis has a clear experimental character. Therefore we are looking for a motivated student with a hands-on mentality capable to do independent research. Moreover, to be able to interpret the characterization results, an interest in and knowledge of solid-state and semiconductor physics is a useful asset. Promoter: Prof. Jef Poortmans Faculty/research group: ESAT/imec photovoltaic group

Daily supervision: Dr. Dries Van Gestel ([email protected])

Graduating option: Nanotechnology

Type of work (experimental, theoretical, simulations): experimental

Number of students: 1 or 2: 1 student

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Metallic nanoparticles for the efficiency enhancement of thin solar cells Description: Context Metallic nanoparticles can have peculiar reflection and transmission properties, thanks to the plasmon effect. Plasmons are coupled light-matter modes that occur at a metal-dielectric interface. The use of these effects may be beneficial for Silicon solar cells based on very thin layers, as the latter have low absorption efficiency due to the low absorption coefficient of Silicon at high wavelengths. Silicon is at the basis of 90% of commercialised solar cells. However, its fabrication has an important energetic and economical cost. This is why research is presently looking for ways to have solar cell structures based on thinner Silicon layers. But in order to keep the light absorption high, it is necessary to implement advanced light scattering and trapping techniques inside the absorbing silicon layer. IMEC frame Forming nanoparticles at the rear of a solar cell may be an efficient way for the achievement of this aim. IMEC has a unique possibility to efficiently create such structures, as it combines knowledge on the fabrication and characterisation of metallic nanoparticles (thanks to a team devoted to plasmonic studies) and on fabrication of ultrathin solar cells thanks to the Thin Film Solar Cell team of IMEC. Internship description

The aim of a student working on this thesis topic is to participate to the numerical modelling and experimental fabrication of plasmon assisted solar cells, and to their characterisation. You will learn various optical and photoelectrical simulation tools, and how to integrate plasmonic effects in the overall simulation of a photovoltaic cell. You will in parallel, follow the fabrication process of solar cells. You will perform optical characterisation of the nanoparticles, and optical and electrical characterisation of the resulting solar cells. The

interpretations of the results will be done in close collaboration with both the plasmonic and thin film solar cells teams. Promoter: Jef Poortmans Faculty/research group: ESAT/imec photovoltaics

Daily supervision: Ounsi El Daif ([email protected])

Graduating option: Nanotechnology Type of work (experimental, theoretical, simulations): experimental and simulations Number of students: 1

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Polysilicon emitter contacts on bulk crystalline silicon solar cells Description: The master proposed will be realized in the framework of photovoltaics and, in particular, in the field of bulk crystalline silicon solar cells technology. Silicon solar cells are semiconductor devices (p-n junctions) which operate by converting sunlight directly into electricity. The research work proposed focuses on the optimization of the n-type emitter and, in particular, on the study of the potential that polysilicon emitter contacts may have to improve solar cell efficiency. It has been investigated and already reported in literature that the introduction of heavily doped polycrystalline silicon in the emitter contact of bipolar transistors improves current gain by a factor of 3-30 compared to the conventional bipolar transistor technology. This current gain is attributed to the decrease in surface recombination velocity at the mono/polysilicon interface and the decrease in the emitter dark saturation current. Therefore, it is expected that for the same reason the use of polysilicon on the front surface of a silicon solar cell may enhance the open circuit voltage and, as a result, the solar cell efficiency. In fact, presently photovoltaics community is doing very significant research to decrease the emitter dark saturation current by modifying the emitter design and improving passivation. The work during the master internship will consist of the design of the emitter polysilicon contact structures and comparing their performance with the standard emitter structures in crystalline silicon solar cells. The performance of the emitter will be measured in terms of emitter saturation current densities by QSSPC (quasi-steady-state photo-conductance), PL (photoluminescence)..., and the emitter design will be characterized by TEM (transmission electron microscopy), SIMS (secondary ion mass spectrometry), SRP (spreading resistance profiling)... In cooperation with the imec researcher responsible of this topic, the master student will work to design, realize and characterize the different emitter structures. The main goal of this research is to determine the feasibility and potential advantage of the polysilicon emitter contact over the standard design in the final solar cell efficiency. Promoter: Jef Poortmans

Faculty/research group: ESAT/imec photovoltaics group

Daily supervision: Maria Recaman Payo ([email protected])

Graduating option: Nanotechnology

Type of work (experimental, theoretical, simulations): 60% experimental, 40% theoretical


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Nanostructured carbon supercapacitors

Description: One of the main drivers of worldwide economic growth is the need for new energy resources. The scarcity of oil resources and the increasing difficulty in exploiting them combined with ever increasing energy needs is attracting renewed interest in other energy sources. Utilization of renewable sources of energy such as sunlight and wind power, which are inherently discontinuous, poses new challenges for energy transport and storage. Many of the ideas for energy storage can come for the IC industry, where the downscaling of the transistor has driven tremendous research efforts into new materials and technologies.

Drawing upon IMEC’s vast expertise on materials for transistor application combined with group expertise in nanomaterials, we are planning to design and build new solutions for on-chip energy storage. One approach to increase energy density in capacitors is to increase the effective surface area by nanostructuring the substrates holding the capacitor or having electrodes with very large area. Such large area high conductivity electrodes can be achived by using several forms of graphitic carbon.

Nanostructured graphitic carbon films have high surface area, high optical transparency, resistance to oxidation and high electrical conductivity. These properties make them interesting candidates not only for nanostructured electrode applications but also for a host of optical,and biological applications. These films are made up of a finite number (5– 20) of carbon planes. At the very limit of this is graphene a single hexagonal (sp2) bonded carbon sheet with phenomenal electronic properties. Interestingly, thin layered graphitic films can still retain some of these properties.

The main purpose of the project is to produce and characterize capacitors with carbon nanostuctured films as a bottom electrode. On these structures dielectrics and a top electrode will be deposited via atomic layer deposition.

The student’s main focus will involve the fabrication and electrical characterization of materials for these supercapacitors. You will contribute to the scientific understanding of these materials and help design novel structures for on-chip energy storage. You will learn and perform various physical characterisation tecniques as needed for the understanding of the materials produced.

Promoter: Marc Heyns

Faculty/research group: NCAIS/ imec or TFSCIGRP/imec

Daily supervision: Iuliana Radu and Daire Cott, Annelies Delabie

Graduating option: physics, material science, electrical engineering, nanoscience, chemistry Type of work (experimental, theoretical, simulations): experimental


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GaN high voltage devices – investigation of self-heating limitations to device scaling Description: GaN (Gallium Nitride) technology is expected to replace Si-devices in power and high voltage applications due to their inherently better voltage-handling capabilities resulting in reduced conduction & switching losses, size and overall cost. Such solutions allow to boost efficiency of general power supplies (like PCs and laptop adapters or data centers) and reduced their overall size/volume, and hence supporting society trends towards reduction of electricity consumption and CO2 production, as well as more user-friendly and sustainable mobility (miniature adapters and electrical vehicles). NXP Semiconductors is investigating devices build in GaN layers on Si substrates for high voltage applications, while SiC substrates are used for RF applications. As the GaN transistors become much smaller, the heat dissipation per unit area substantially increases and eventually becomes limiting factor of the device scaling. This is strongly dependent on application operations (efficiency, duty cycle, frequency of switching). SiC substrates with its much better heat conduction (and hence better heat sinking) are preferred for RF functionality. The purpose of this thesis work is to assess suitability of GaN high voltage transistor on Si substrates in view of heat dissipation and draw boundary conditions on on-resistance vs. self-heating limitations for device scaling. This work will involve both experimental characterization as well as numerical simulations using e.g. COMSOL software. The student will carry out specific characterization on existing NXP high voltage GaN transistor on both Si and SiC substrates using operating conditions similar to anticipated applications. The student work will be divided to the following blocks (1) Define device operation conditions in a typical power supply circuit, (2) Literature review of self-heating and heat-dissipation effects in GaN devices on different substrates, (3) Characterization (DC and pulsed) of NXP 600V GaN devices on Si- and SiC substrates and summary of self-heating observations vs. device bias conditions, (4) Results interpretations using COMSOL simulations. Within this thesis work, the student will gain basic insights into basics of power supply circuit operation, GaN transistor characteristics and in particular self-heating effects. The student will build capability of electrical characterization and learn how to use COMSOL simulation software. Promoter: G. Groeseneken, E. Hijzen (NXP) Faculty/research group: NXP Semiconductors, Central Research & Development

Daily supervision: J. Sonsky

Graduating option: Engineering, Science Type of work (experimental, theoretical, simulations): experimental & simulations Number of students: 1

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Research topic for student within Solid State Lighting Project

Scope of the study: LED aging

Introduction to the Solid State Lighting (SSL) project:

The general aim of the SSL project within NXP Research is to offer timely technology and system solutions, identify differentiators and create a broader SSL portfolio for NXP, in alignment with the strategy of the Business Units.

The Envisioned Application is "Smart LED drivers": adding smart, novel features to LED drivers for sensing and controlling luminance and wavelength.

We have identified a portfolio of key differentiators that we can offer to our smart solutions to LED flux and color management. Among those, one of the most important is the LED aging: the mechanism for LED aging, solutions that offer correction for the aging effects, implementation of these solutions into the final products, the Smart LED drivers.

In view of the growing interest of NXP into the SSL market, in particular in the drivers for LEDs, the SSL project will provide data, understanding and models of LED electronic behavior, aging and reliability, for a wide area of applications in Automotive, General Lighting and Displays (Backlighting for LCD panels) domains.

Short description of student’s project:

LED will be used as light source; LED aging mechanism is unclear at this moment. Understanding of LED aging mechanism is useful for product development (LED as well as LED driver).

Objectives:

‐ Gain basics knowledge of LED device ‐ Improvement test system for accelerated aging experiment (hardware and software)

o Current system handles 1 LED sample at a time, in the future we will move to smaller size LED and therefore it will be beneficial if the system is modified to handle more samples at a time.

o High Power LED aging setup ‐ Perform accelerated aging experiment on LEDs. ‐ Analysis and explanation of the obtained data with plausible theoretical arguments.

Time-line in weeks:

0 --> 2nd week: Literature study on LED

2nd --> 4th week: Get familiar with Lab equipments, software environment; understand accelerated aging methodology for LED.

4th --> 8th week: implement improvement on test system, stat measuring samples

8th -->10th week: round up the obtained results, substantiate the data with arguments

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10th --> 12th week: final report.

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Characterization of very high permittivity dielectrics for DRAM applications Description: Future dynamic random access memory (DRAM) nodes require metal-insulator-metal capacitors (MIMcaps) with equivalent oxide thicknesses (EOT) ≤ 0.5 nm and low leakage current densities (≤ 10-7 A/cm2). These technological specifications imply the introduction of high dielectric constant (K) materials in semiconductor fabrication lines. Alternative high-K materials with K>40 typically have to be identified and integrated in MIMcap devices. IMEC, together with several industrial partners, has been recently very active in this field working on identification and screening of new high K materials as well as on the integration of potential candidates in devices. For example, several materials like SrTiO3, TiO2, BaSrTiOx with several kinds of electrode (TiN, Ru, RuOx) are actively studied by physical and electrical characterization. The future trainee will be working in the framework of this project. His/her main interest will be turned towards electrical characterization of the candidates of choice. His/her work will also involve sample preparation and stack definition. We are looking for a highly motivated person who wants to apply his/her fundamental knowledge to applied research and development project. The candidate has also to be ready to present his/her work in internal meetings when necessary. Promoter: Guido Groeseneken Faculty/research group: Faculty of Engineering/ESAT/IMEC/ DRE

Daily supervision: Ben Kaczer and Tomida Kazuyuki

Graduating option: Engineering/Sciences Type of work (experimental, theoretical, simulations): experimental, theoretical


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Superlattices: defining the boundaries of the ultimate CMOS scaling Description: Graphite-like 2D nanolattices of dielectrics and semiconductors with enhanced anisotropic electronic properties are good candidates to pave the way to the ultimate scaling and performances of future nanoelectronic devices. Graphene, the most studied representative of the 2D graphitic materials, has overshadowed research on other potential quasi-2D nanolattices with totally unexplored physical properties. For instance, 3D materials, in which a strong anisotropy is introduced in the band structure could potentially lead to enhanced mobilities and display quasi-2D properties. Such structures could be induced in regular ultrathin Si and Ge, in which, the periodicity along the vertical growth direction is artificially broken by the insertion of monolayer-thick non-semiconducting layers. In such a case, the band structure and the density of states could be strongly modified reducing in-plane effective mass while inhibiting the transport perpendicular to the layers. This could reduce gate leakage and carrier scattering, thus maintaining high mobility at low equivalent oxide thickness. Unfortunately, little is known on the fundamental physical properties of these materials. To properly engineer them, one needs to obtain a deep insights into the very fundamental properties of matter (electronic gap, effective mass, scattering processes,...). In that respects, modeling techniques based on the combination of simplified one-dimensional quantum mechanical model for the charge carriers (effective mass approximation) with density functional theory, are tools of choice that can be used to predict their electronic and transport properties and hence provide the guidance needed to boost the mobility of the charge carriers in the material. The project consists in modeling the properties of such superlattices by using advanced solid state physics techniques. The simulations will provide both guidelines and fundamental understanding into the electronic and transport properties of the structures. IMEC will provide training to both UNIX/Linux and to the material modeling techniques. To be eligible, applicants must have a Master degree in either physics, chemistry or in electrical/material engineering. A strong motivation, a good knowledge of solid-state physics and UNIX/LINUX are a plus. Excellent writing and oral communication skills are desired. Promoter: Marc Heyns Faculty/research group: Faculty of engineering/MTM/imec/MSP

Daily supervision: G. Pourtois, B. Soree

Graduating option: engineering, sciences Type of work (experimental, theoretical, simulations): simulations, modeling


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Process simulations to improve the link between electrical data of processed tunnel field-effect transistors and simulated predictions Description: Straightforward downscaling of the basic components of the electronics industry according to Moore's law will reach its end within the next 10 years. To continue towards the nanoscale, complex technological barriers will have to be overcome, and eventually further downscaling will be prevented due to physical limitations associated with the small dimensions. This prospect stimulates research towards alternatives for the current CMOS nano-electronic devices. Promising candidates for integration in post-CMOS nano-electronic devices are semiconducting anowires. Nanowires allow the fabrication of heterostructures, without the typical high defect concentration at the interface between two materials with different lattice constant, which is a consequence of the capability of nanowires to tolerate material stress. The fabrication of heterostructures, which also includes the integration of III-V materials on silicon, offers many new perspectives for nano-electronic devices. In this master thesis, the student will investigate a nanowire-based tunnel field-effect transistor. Based on the input from the processing experts, the student will set up a process simulation mimicking as closely as possible the actual fabrication process. The resulting device configuration, in particular the resulting two-dimensional doping profile, will be inserted in the device simulator. The student will interpret the predicted characteristics of the device simulator and compare the results to the experimental data. The extracted information will be communicated back to the processing experts and a feedback loop to optimize the process flow will be established. For this master thesis, a good knowledge of semiconductor physics is required. Process and device simulations can be done with existing software packages. If needed, additonal measurements can be performed in imec’s electrical characterization labs. During this master thesis, the student will also learn about the tunnel field-effect transistor fabrication process as well as the additional electrical, optical and profilometric characterization techniques. Promoter: Guido Groeseneken Faculty/research group: Faculty of Engineering/ESAT/imec/MSP

Daily supervision: Anne Verhulst

Graduating option: engineering, sciences Type of work (experimental, theoretical, simulations): simulations


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Effect of confinement and position of dopants on the ionized impurity scattering limited mobility in a few-dopant double gate FET or all-around gate cylindrical nanowire FET Description: As nanowire dimensions are scaled down the number of dopants in the nanowire becomes small. Even for a relatively large doping density of 1019 cm-3 a cylindrical nanowire with radius 5 nm and channel length 10 nm will only contain about 7 dopants. As a result, the usual method of impurity averaging does not work and the discrete nature of dopants needs to be taken into consideration. In this thesis the student is expected to calculate the electrostatic potential of a single Coulomb charge in a nanowire surrounded by a dielectric and metal gate. The Coulomb field of a charge residing in a semiconducting nanowire or double gate structure is determined by the boundary conditions imposed on the electrostatic potential of this charge. In a semiconducting nanowire FET with surrounding dielectric and gate or a double gate FET structure with dielectric and metal gate, the electrostatic potential is determined by solving Poisson’s equation for a single charge with appropriate boundary conditions. For a double gate FET the presence of the planar dielectric and metal gates will also determine the electrostatic potential of the Coulomb charge. The obtained electrostatic potential is used to calculate the scattering rate for ionized impurity scattering using the Boltzmann equation in the relaxation time approximation together with Fermi’s golden rule. The student is expected to investigate the effect of confinement (wire radius, gate voltage) and of dopant position in the wire on the low-field mobility. The candidate should have a strong background/interest in solid-state physics, quantum mechanics and computational physics. Promoter: Guido Groeseneken Faculty/research group: Faculty of Engineering/ESAT/imec/MSP

Daily supervision: Bart Soree, Anh-Tuan Pham

Graduating option: engineering, sciences Type of work (experimental, theoretical, simulations): theoretical, modeling


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Electronic structure and electrostatics of a square cross section gate all-around junctionless pinch-off nanowire FET Description: A junctionless pinch-off nanowire FET is a novel device invented in imec which is uniformly doped throughout source, channel and drain. It has been shown that the junctionless transistor offers the promise of superior scaling to sub-22 nm dimensions compared to regular transistors. Originally, the junctionless nanowire transistor was designed to avoid detrimental surface interactions which have a negative impact on the transport properties of charge carriers inside the channel of the device such as surface roughness or remote phonon scattering. The uniform doping throughout source, channel and drain greatly simplifies the fabrication process due to the absence of doping junctions. The current-voltage characteristics of this novel device are very similar to a conventional inversion mode (MOSFET) device. The current in this device is carried by the majority carriers delivered by the dopants. In order to switch off the current, an all around gate must deplete the doped channel by applying a gate voltage (field effect). The student is expected to investigate a square cross sectional nanowire of macroscopic dimensions and obtain the pinch-off voltage as a function of the dimensions of the cross section and the doping density. For ultrathin nanowires where quantization due to confinement kicks in, a self-consistent Poisson-Schrodinger solver needs to be written to obtain the electronic structure (energy spectrum and electron density). Also in this case, one can obtain the pinch-off voltage as a function of wire dimensions and doping density. The candidate should have a strong background/interest in solid-state physics, quantum mechanics and computational physics. Promoter: Guido Groeseneken Faculty/research group: Faculty of Engineering/ESAT/imec/MSP


Graduating option: engineering, sciences Type of work (experimental, theoretical, simulations): modeling, theoretical


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Remote Coulomb, surface roughness and ionized impurity scattering in novel nanowire all-around gate FET devices Description: In nanowire MOS field-effect transistors (FETs) degradation of the low-field mobility due to interactions occuring at or near the interface between the substrate and the insulator are important in the strong inversion regime. In this strong inversion regime, the electrons are mainly residing near the interface which results in a stronger coupling of the electrons with interactions which are localized near or at the substrate-insulator interface. The working principle of the novel junctionless pinch-off transistor does not require a strong inversion regime, but is based on current carried by majority carriers flowing throughout the entire volume of the channel. As a result one expects a lower impact of the detrimental surface interactions. On the other hand, the junctionless pinch-off nanowire transistor requires doping, which in turn will depress the low-field mobility due to ionized impurity scattering. In order to calculate the low-field mobility one needs the scattering rates obtained from the Boltzmann transport equation in the relaxation time approximation in combination with Fermi’s golden rule together with the energy spectrum and group velocities obtained from a self-consistent Poisson-Schrodinger solver. The student is expected to derive the scattering rates for the scattering mechanisms mentioned above and tu numerically implement these into an existing Poisson-Schroedinger solver for a all-around gate nanowire FET. The student will compare the obtained results for such a device when operating in inversion mode (MOSFET) and operating as a junctionless transistor. The candidate should have a strong background/interest in solid-state physics, quantum mechanics and computational physics. Promoter: Guido Groeseneken Faculty/research group: Faculty of Engineering/ESAT/imec/MSP

Daily supervision: Dr. Bart Soree, Dr. Anh-Tuan Pham

Graduating option: engineering, sciences Type of work (experimental, theoretical, simulations): modeling, simulations


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Graphene plasmonics

Description: Plasmonics is a fast growing field in nano-electronics/optics/photonics because it allows efficient coupling of light with nanostructures. The possibility of capturing light with a wave length larger than the dimensions of the nanostructure through plasmonic excitations opens new avenues towards interesting new applications. Traditionally, noble metals such as silver or gold are used in plasmonic nanostructures. Recently, however, intriguing plasmonic behavior has been observed in graphene, a single atom thick graphite sheet, which has not been explored before in this field. In this thesis the student is expected to perform a literature study of this new and fast growing field with a focus on graphene plasmonics. The student is also expected to perform a few theoretical calculations relevant for graphene plasmonics. The candidate should have a strong background/interest in solid-state physics, quantum mechanics and computational physics. Promoter: Marc Heyns Faculty/research group: Faculty of Engineering/MTM/imec/MSP

Daily supervision: Bart Soree, Pol Vandorpe

Graduating option: engineering, sciences Type of work (experimental, theoretical, simulations): modeling, theoretical


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Sub band decomposition method for modeling nanodevices

Description: The modeling of ballistic quantum transport in nanodevices usually involves a self-consistent solution between the Schrödinger and the Poisson equations. This usually requires huge computer resources to obtain the current voltage characteristics. The sub band decomposition approach relies on the decomposition of the wave function on sub band eigen functions, which account for the confinement of the electrons in the whole structure. The method can be applied to study large 2D and 3D real systems with a drastic reduction of the numerical cost, since the dimension of the transport problem for the Schrödinger equation is now reduced in real space. The student is expected to get acquainted with the formalism and write code to numerically implement the formalism for either a nanowire, double gate or a graphene device. The candidate should have a strong background/interest in solid-state physics, quantum mechanics and computational physics. Promoter: Marc Heyns Faculty/research group: Faculty of Engineering/MTM/imec/MSP


Graduating option: engineering, sciences Type of work (experimental, theoretical, simulations): modeling


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Tunneling in two dimensions

Description: Tunneling is a quantum mechanical phenomenon where a particle travels through a region where classical mechanics prohibit its presence. The phenomenon has fascinated many since the first discoveries of quantum mechanics until today. Sometimes the products of tunneling are unwanted, for example: radiation from nuclear decay or leakage current in MOSFETs. But in other cases tunneling can be used to our advantage: the human scent relies on a tunneling process to distinguish smells. Zener and Esaki diodes rely on tunneling for their operation. Recently a tunnel transistor has been proposed with the promise of greatly improved performance compared to the existing MOSFETs. Although the basic tunneling principle is well established, almost all investigations have been done with respect to tunneling in a straight line that is, tunneling in one dimension. In a transistor with three terminals, the potential can have rapid changes in two- or three dimensions. For this reason the investigation of tunneling beyond the one-dimension is necessary. The student will investigate the tunneling process in two dimensions, try to gain understanding in the process and observe the deviations from the use of existing one-dimensional models. The candidate should have a strong background/interest in solid-state physics, quantum mechanics and computational physics. Promoter: Guido Groeseneken Faculty/research group: Faculty of Engineering/ESAT/imec/MSP

Daily supervision: Bart Soree, Wim Magnus, William Van Vandenberghe

Graduating option: engineering, science Type of work (experimental, theoretical, simulations): theoretical, modeling


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Tunneling in semiconductor heterostructures

Description: At very small operating voltages, the MOSFET can no longer be switched off and this could put an end to the progress that has been made in semiconductor device scaling. Fortunately, a new kind of tunnel transistor (TFET) has been proposed with the promise of being able to operate at much smaller operating voltages than the MOSFET. A drawback of these new tunnel transistors is their low on-current when they are fabricated from silicon which has a large bandgap. When smaller bandgap materials such as germanium or III-V semiconductors are used, the on-current greatly improves but silicon is the material of choice in the semiconductor industry. A natural solution is the use of a heterostructure: germanium/III-V and silicon in the same device. Starting from the Schrödinger equation, the student will investigate the tunneling in a one-dimensional heterostructure. The candidate should have a strong background/interest in solid-state physics, quantum mechanics and computational physics. Promoter: Guido Groeseneken Faculty/research group: Faculty of Engineering/ESAT/imec/MSP


Graduating option: engineering, science Type of work (experimental, theoretical, simulations): modeling, theoretical


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Studying quantum transport in nano-MOSFETs using spectral functions

Description: With continued device scaling, modern day transistors (MOSFETs) have dimensions in the order of a few nanometers making quantum effects play an important role. Studying these quantum effects encompasses the formidable task of finding all solutions to the Schrödinger equation on the entire device. The result is a set of wavefunctions with quantum numbers labeling each different wavefunction. From the wavefunctions and the energy spectrum, the quantum effects and the electronic transport in the device can be studied. Rather than directly using the wavefunctions with its quantum numbers. The student will study quantum effects in a MOSFET using so-called spectral functions. Using spectral functions has some advantages: it eliminates the need of keeping track of all the quantum numbers and facilitates the calculation of tunneling phenomena for example. The student will investigate methods to calculate the spectral functions and use them to obtain the current in a MOSFET. The candidate should have a strong background/interest in solid-state physics, quantum mechanics and computational physics. Promoter: Guido Groeseneken Faculty/research group: Faculty of Engineering/ESAT/imec/MSP


Graduating option: engineering, science Type of work (experimental, theoretical, simulations): modeling, theoretical


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A semi-analytical model for leakage currents in MOS capacitors

Description: Recently, a new model has been devised to predict the leakage current in a planar MOS capacitor. The model incorporates the competition between the local generation and recombination of electrons and holes in the inversion layer, and the tunneling of electrons penetrating through the oxide layer. Moreover, the new model is found to solve also the "current" paradox dealing with the absence of net electric currents carried by quasi-bound states. Presently, the model is implemented in a computer program that traces the time evolution of decaying charge packets, but there is also room for analytical exploration. The purpose of this thesis is to calculate semi-analytically the tunneling decay rate of the electrons residing in the inversion layer as a function of the oxide thickness and other relevant material parameters. In particular, the student will examine to which extent the time dependent decay can be considered exponential. Promoter: Guido Groeseneken Faculty/research group: Faculty of Engineering/ESAT/imec/MSP

Daily supervision: Wim Magnus, Bart Soree

Graduating option: engineering, science Type of work (experimental, theoretical, simulations): modelings


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Design and analysis of on-chip reliability and characterization circuitry Description: Each new CMOS technology option and process modification requires thorough characterization of many devices, which is both time and resource intensive. Furthermore, degradation of FET devices during operation also needs to be investigated. This is typically done at accelerated voltages and temperatures. To facilitate the characterization and reliability tests, circuits designed directly on chip can facilitate and speed up the measurements. For example, a circuit could stress many tested devices in parallel while monitoring their degradation, or poll the tested devices one by one in between stressing to measure the degraded parameters. Challenges include designing circuits that themselves can withstand the accelerated testing conditions and monitor/measure circuits that do not drift. The thesis will build on a previous work involving design of an on-chip array for parallel device stressing and testing. It will consist of an initial review of the project, evaluation of the on-chip array, and the design of new, improved test structures. The student should be proficient in SPICE, CAD layout, electrical measurements, and data analysis. Promoter: Guido Groeseneken Faculty/research group: Faculty of Engineering/ESAT/imec/DRE

Daily supervision: Ben Kaczer and Geert Van der Plas

Graduating option: Engineering Type of work (experimental, theoretical, simulations): experimental, simulations


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Identification and modelling of gene networks in bone tissue engineering. Description: The research division (http://www.kuleuven.be/prometheus) endeavours to develop biological bone substitutes that provide relief for patients suffering from non-union fractures or large bone defects due to bone cancer or trauma. A novel strategy to reach this goal is developmental engineering. This strategy turns to nature for guidance in developing bone forming processes by incorporating information from developmental biology. Bone formation can be either direct, through the process of intramembranous ossification, or indirect, through formation of a cartilage intermediate in a process termed endochondral ossification. During bone formation in the embryo numerous growth factors and other instructive signals cooperate to form bone in a robust fashion. Transferring of these signals and consequently the robustness of this embryonic process to an in vitro environment provides promising perspectives in the development of bone substitutes.

In order to provide more clarity on the host of regulatory mechanisms in bone formation a gene network will be drafted in the course of thesis. This network encompasses the crucial genetic players and their mutual interactions. Since little to no information is available on the kinetic parameters of these interactions, a qualitative approach by means of Boolean modelling is opted for. In the past BMGO has applied this approach in order to build up a gene network describing endochondral ossification. Other implementation forms of the model, in consultation with promoter and supervisor, are also possible. This thesis aims to specifically derive the gene network responsible for the regulation of the fate of mesenchymal stem cells, which are capable of forming many tissues, including bone and cartilage. External signals determine whether a mesenchymal stem cell will differentiate into a cartilage cell or a bone cell, initiating respectively intramembranous and endochondral ossification. By analysing the developed models it can be investigated which signals are determinative in this decision.

Promoter: Hans Van Oosterwyck, Lies Geris Faculty/research group: Division of Biomechanics and Engineering Design

Daily supervision: Johan Kerkhofs

Graduating option: Type of work (experimental, theoretical, simulations): simulations


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Characterization of solute diffusive transport using fluorescent solute analogs

Description:

Background:

Within a tissue or a cell-seeded hydrogel, concentration gradients can exist for any medium-soluble molecule that is consumed or produced by the cells. These molecules vary from basic nutrients (such as oxygen and glucose) to signaling factors (BMP, TGF-beta, FGF, …). Gradients result from the competition of mass transport (diffusion and convection) with consumption or production by the cells. Possible impacts of these gradients on the cell behavior vary from differences in cell phenotype to deteriorating viability patterns from center to surface of the hydrogel construct.

Accurate measurement and modeling of ongoing mass transport phenomena is therefore crucial in predicting the overall outcome of the construct. Since focus within this study is on characterization of solute transport through hydrogels (dense network of nano-size fibers), the main governing mass transport process will be diffusion.

Content:

The student applying for this thesis will look at the use of fluorescent solute analogs (e.g. 2-NBDG for glucose) to monitor and measure diffusive transport inside a hydrogel. To this end the student has to design and built an appropriate experimental setup that can be integrated within a fluorescent confocal imaging system. Furthermore he/she has to gain insight into the physics underlying the process by which fluorescence read-outs are obtained. In a final phase results obtained for fluorescent analogs are compared to diffusion data measured with an existing diffusion setup available within Prometheus (www.kuleuven.be/prometheus), the Division of Skeletal Tissue Engineering Leuven.

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Promoter: Hans Van Oosterwyck, Johan Hofkens, Maarten Roeffaers Faculty/research group: Division of Biomechanics and Engineering Design, Laboratory for Photochemistry and Spectroscopy

Daily supervision: Dennis Lambrechts

Graduating option:

Type of work (experimental, theoretical, simulations): experimental


88


A network-based modeling approach to quantify diffusive transport in a hydrogel carrier Description: Background: Within a tissue or a cell-seeded hydrogel, concentration gradients can exist for any medium-soluble molecule that is consumed or produced by the cells. These molecules vary from basic nutrients (such as oxygen and glucose) to signaling factors (BMP, TGF-beta, FGF, …). Gradients result from the competition of mass transport (diffusion and convection) with consumption or production by the cells. Possible impacts of these gradients on the cell behavior vary from differences in cell phenotype to deteriorating viability patterns from center to surface of the hydrogel construct. Accurate measurement and modeling of ongoing mass transport phenomena is therefore crucial in predicting the overall outcome of the construct. Since focus within this study is on characterization of solute transport through hydrogels (dense network of nano-size fibers), the main governing mass transport process will be diffusion.

Content: The approach presented here requires the student to develop a network model that describes the solute-fiber hydrodynamic interactions and hence captures the diffusion process in really realistic manner. Relevant input data for modeling the network geometry can be obtained through the use of fluorescently labeled fibers and is visualized using confocal imaging microscopy. Promoter: Hans Van Oosterwyck, Johan Hofkens, Maarten Roeffaers Faculty/research group: Division of Biomechanics and Engineering Design, Laboratory for Photochemistry and Spectroscopy

Daily supervision: Dennis Lambrechts

Graduating option:

Type of work (experimental, theoretical, simulations): simulations


89


The role of cell mechanics in cartilage engineering Description: Background: Damage to articular cartilage forms a major health problem and can be encountered as a result of rheumatoid arthritis, osteoarthritis or trauma. As cartilage tissue has only a limited capacity to repair, joint replacement is often the only solution in the case of large cartilage defects. Tissue engineering offers an alternative, by using the patient’s own (stem) cells and inducing them to form cartilaginous tissue. This can be done in vitro and involves among others the creation of small cellular aggregates that serve as functional units for cartilage engineering. One of the key factors in the successful induction of cartilage differentiation are intercellular mechanical forces, which in turn are determined by cell-to-cell adhesion and cell mechanical properties. Content: the role of cell mechanics on the induction of cartilage differentiation in cellular aggregates will be analysed. Depending on the interest of the student, the focus can be on experimental or computational techniques to quantify cell mechanical properties. For the experiments, the viscoelastic properties of individual cells and cellular aggregates at various stages of cartilage differentiation will be measured. To this end, the student will use and extend an existing setup (micropipette aspiration). The student will also quantify cell-to-cell adhesion in order to relate this to intercellular forces. For the computational techniques, a individual cell-based model, previously developed for the study of the growth of yeast colonies, will be extended to simulate cartilage growth and differentiation. The work is embedded in Prometheus, the Division of Skeletal Tissue Engineering at K.U.Leuven (www.kuleuven.be/prometheus). This among others guarantees a strong interaction with biologists and the availability of biological data that can be related to the mechanical data.

Promoter: Hans Van Oosterwyck, Herman Ramon Faculty/research group: Division of Biomechanics and Engineering Design (BMGO), Division Mechatronics, Biostatistics and Sensors (MeBioS),

Daily supervision: Bart Smeets, Dennis Lambrechts

Graduating option: Type of work (experimental, theoretical, simulations): experimental / simulations

Number of students: 1 / 2

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in situ polymerization of electroactive polymers Description: Recent research has shown the possibility to polymerise PEDOT, an electroactive polymer, in the tissue where it is needed as an electrode. This research topic is about extending the technique to form wires of conducting polymer within living tissue, as a precursor of the next generation of long-term implantable electrodes. Promoter: Chris Van Hoof Faculty/research group:

Daily supervision: Herc Neves

Graduating option: Type of work (experimental, theoretical, simulations): mostly experimental


91


Feasibility of millimeter-waves for thermoacoustic imaging Description: Medical science uses a wide range of scanning techniques for early diagnosis. These include acoustic (e.g. ultrasonography) and electromagnetic methods (e.g. X-ray). The aim of this thesis is to improve the imaging resolution and/or reduce the power level required to realize an image by use of a relative new approach called thermoacoustic imaging. Thermoacoustic imaging relies on the absorption of electromagnetic energy and the subsequent emission of an acoustic wave (sound). Several parts of the electromagnetic spectrum can be used for the electromagnetic heating including infrared, microwaves and radio frequencies. Microwave frequencies are suited due to the large contrast in the losses of biologic tissues at microwave frequencies. The imaging resolution at microwaves on the other hand is limited due to the relative large wavelength. Millimeter wave frequencies offer a potential improved imaging resolution. The objective of this thesis is therefore a feasibility study of millimeter waves as an excitation source for thermoacoustic imaging. A model is constructed to simulate the detection of a breast tumor. It consists of coupled electromagnetic, thermal and acoustic simulations. A simplified experiment will be constructed to detect an inhomogeneous particle in a homogeneous body-simulating fluid. Promoter: Prof. Chris Van Hoof Faculty/research group: EPT/NANO

Daily supervision: Steven Brebels, Xavier Rottenberg

Graduating option: Master in Science and/or Master in Engineering Type of work: 30% experimental, 10% theoretical, 60% simulations Number of students: 1 or 2

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Capacitive micromachined ultrasound transducers for imaging, telecom and power transmission applications Description: Microelectronics experiences since the early seventies a period of sustained run-away development. Researchers strive to keep up with and fulfill Moore's law by scaling transistors down thus cramming always more circuits, more computing power and more functions on a chip always smaller and faster. However, this More of Moore era is said to be coming to an end. The past decade has seen the start of a paradigm shift. Acknowledging the limitations of the scaling model for microelectronics, the emergence of novel technology drivers and appearance of new usage scenarios, e.g. low power, nomadism, health care and health monitoring, ..., researchers started exploring alternative technological paths. This defines the so-called More than Moore approach that departs from the one technology fits all approach and aims at developing a plurality of diverse ad-hoc technologies and according interfacing solutions. RF-MEMS is one of these technologies. High-frequency MEMS resonators are the basic building blocks for embedded ultrasound systems. With their high Q-factor, high-level of integrability, MEMS devices allow to define arrays of ultrasound sources and receivers on-wafer, with their CMOS drivers and readouts. Besides the obvious extension of the well-known concept of echography, such systems are promising alternative solutions for example to the problems of in-vivo power delivery to implanted devices. The objective of this work is to design and characterize MEMS-based ultrasonic sources and receivers. These devices will have to be optimized for example for power-delivery. Major attention will be laid on the isotropic power-scavenging ability of the receiver and increased directivity of the source obtained through appropriate arraying. Required simulations will be performed in COMSOL and/or ANSYS (with hands-on training). Promoter: Prof. Chris Van Hoof Faculty/research group: EPT/NANO

Daily supervision: Xavier Rottenberg, Harrie Tilmans


93


Phononics, MEMS/NEMS acoustic devices and circuits Description: Microelectronics experiences since the early seventies a period of sustained run-away development. Researchers strive to keep up with and fulfill Moore's law by scaling transistors down thus cramming always more circuits, more computing power and more functions on a chip always smaller and faster. However, this More of Moore era is said to be coming to an end. The past decade has seen the start of a paradigm shift. Acknowledging the limitations of the scaling model for microelectronics, the emergence of novel technology drivers and appearance of new usage scenarios, e.g. low power, nomadism, health care and health monitoring, ..., researchers started exploring alternative technological paths. This defines the so-called More than Moore approach that departs from the one technology fits all approach and aims at developing a plurality of diverse ad-hoc technologies and according interfacing solutions. RF-M/NEMS is one of these technologies. Guided wave acoustic devices, e.g., resonators, transmission lines, filters, …, are key building blocks for future telecommunication systems. Indeed, with their extremely high Q-factors and linearity, these devices promise making the natural trade-offs of system design obsolete. The objective of this work is to design and characterize multi-stage acoustic filters, delay lines, oscillators or acoustic black holes and cloaking structures. Using the technology available at imec, and especially the sub-micron gap feature of our SiGe-MEMS technology, the candidates will endeavor in the booming field of phononics while enjoying the opportunity of realizing transducers, drivers and sensors, with high electrostatic transduction efficiency. Required simulations will be performed in COMSOL, Coventorware, MEMS+ and/or ANSYS (with hands-on training). Promoter: Prof. Chris Van Hoof Faculty/research group: EPT/NANO

Daily supervision: Xavier Rottenberg, Steven Brebels


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Nano logics – NEMS relays Description: Conventional logic switching is done by CMOS-based transistors, but these suffer from energy-efficiency limitations imposed by the finite sub-threshold slope (large leakage current) in the CMOS transistors (especially for sub 90nm CMOS). Purpose of this thesis topic is to replace the MOS transistor-based logic gates by NEMS transistor-based logic gates thereby exploiting the low effective threshold voltage and zero leakage achievable with these “NEMS switching devices”. These NEMS-based logic gates are expected to approach the “ideal” logic gate behavior, which is characterized by two clearly distinct binary output levels (the “1” and the “0”), by a minimum (ideally “zero”) power consumption, by an abrupt transition between states at the output for a certain applied input signal level, and, by a negligible time delay between the input transition and the output transition. A typical implementation of a “NEMS transistor” is that of a “NEMS relay”. It is a nano-scale version of a conventional electromechanical relay. Realizing these “NEMS logic” devices in imec’s SiGe NEMS technology, under development at the moment, allows integration of the NEMS logic devices above standard CMOS logic circuits, thereby co-designing CMOS-to-NEMS. The candidate will study and investigate the various typical NEMS logic implementations. Next, (s)he will devise (novel) concepts for NEMS logic gates, along with a conceptual NEMS process flow (and choice of materials). The focus will be on the detailed design, model and simulation of the performance of these NEMS logic gates. Promoter: Prof. Chris Van Hoof Faculty/research group: EPT/NANO

Daily supervision: Harrie Tilmans, Xavier Rottenberg


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SASER - sonic laser Description: Saser devices, or sonic lasers, are a novel type of devices that can generate high intensity, high directivity, high frequency, high purity, high coherence sound waves. These waves can be used for sensing applications (material analysis, follow up of progression of chemical reaction, view through the surface of materials, ...) or actuation applications (material ablation/modification, localized polymerisation, heating, cooling, displacement, ...). The purpose of this work is to model and design sasers as generators for acoustic applications. The designed structure will then be validated and further optimized for applications in the field of acoustic manipulation of particles. In close collaboration with the processing team at imec, the candidate will have to first model and subsequently design and characterize sasers targeting THz frequencies. The candidate will have to devise a 2-saser or 3-saser setup for particle trapping at the surface or in the bulk of a fluid. Promoter: Prof. Chris Van Hoof Faculty/research group: EPT/NANO

Daily supervision: Xavier Rottenberg, Steven Brebels


96


MEMS-based microloudspeaker Description: A typical loudspeaker is an electromechanical transducer that converts electrical audio signals (20Hz to 20kHz) at its input into sound waves generated at its output due to changes in the air pressure in the vicinity of the loudspeaker. Conventional loudspeakers typically rely on the electro-dynamic (moving-coil) principle. “Microspeakers” are (miniaturized) loudspeakers fabricated using micromachining or MEMS technologies and offer small size and low weight. Compared to electrodynamic loudspeakers, electrostatic loudspeakers appear more amenable to miniaturization and to MEMS fabrication. Down scaling the size (of the speaker diaphragm) however has a degrading effect on the loudness of the speaker (becoming more severe for the lower frequencies). Conventional speakers are always of the “analog type”. A novel speaker concept is based on so-called Digital Sound Reconstruction (DSR). DSR is a process by which discrete acoustic pulses of energy created from an array of speakers (or ‘speaklets’) are summed to produce a time-varying sound (pressure) waveform. As such, the acoustic output (sound) is provided directly from a digitally-encoded signal. From first studies it appears that DSR based speakers suffer much less when downscaling the system and thus offer potential for ultra-slim, small loudspeakers. The candidate will study and investigate the various typical MEMS loudspeaker implementations (both of the analog and the digital type) and more in particular (s)he will explore the impact of down scaling (miniaturizing) and ultimate size limits of the speaker (application dependent). A (performance) comparison will be made of the different electromechanical transduction mechanisms. Next, (s)he will devise (novel) concepts for MEMS loudspeaker, analog as well as digital (thereby implementing the most effective transducer), along with a conceptual MEMS process flow (and choice of materials). The focus will be on the detailed design, model and simulation of the performance of these MEMS loudspeakers. Promoter: Prof. Chris Van Hoof Faculty/research group: EPT/NANO

Daily supervision: Harrie Tilmans, Xavier Rottenberg


97


investigation of nanostructures as piezoelectrochemical transducers Description: It has been reported in the literature that zinc oxide and barium titanate nanostructures exhibit exceptional ferroelectric and piezoelectric properties. Recent publications also report on their piezoelectrochemical effect. The purpose of this topic is to explore these effects in the context of biological transducers, in particular those for in vivo use. The work will involve the synthesis of these nanomaterials, their characterization and the implementation of test vehicles to verify their possibilities in autonomous sensing. Promoter: Chris Van Hoof Faculty/research group:

Daily supervision: Herc Neves

Graduating option: Type of work (experimental, theoretical, simulations): mostly experimental


98


Synthesis of semiconducting nanoparticles from ionic liquid Description: Various techniques exist for the synthesis of nanoparticles. One of these techniques is the electrodeposition of metals from non-aqueous solvents containing surfactants, also known as the Mülheim process. The advantages of this process are the control of the particle size, the monodisperse nature of the nanoparticles and the versatility of the method. Mono-disperse particles with a size between 1 nm and 20 nm have been made of most transition metals that can be electrodeposited like Cu, Ag, Co, Cu, Pt, Pd, Ru,…. We recently discovered that it is also possible to make nanoparticles in this way from ionic liquids. Ionic liquids are salts that are liquid at room temperature and their large electrochemical stability enables the deposition of metals that so far could not be deposited like Ge, Si and Al. This enables the synthesis of particles that have interesting quantum, optical and magnetic properties. In this work, we will make nanoparticles of Ge, Si and Al by electrodeposition from ionic liquids. The size distribution will be determined by TEM and dynamic light scattering. The influence of electrodeposition parameters on the size and size distribution will be evaluated. The effects of quantum confinement on the optical properties of the Ge and Si semiconductor nanoparticles will be investigated by absorption and luminescence spectroscopy. The spectroscopic properties will be measured in the Coordination Chemistry Group of the Department of Chemistry. Most of the work will be done in the state-of-the-art glove boxes of the ionic liquid lab of MTM. The student will receive training on the processing tools (glove box, electrodeposition, potentiostats) and characterization tools (DLS, SEM, TEM). After this training period, the student can work independently and focus on his/her investigation. Promoter: Jan Fransaer/Koen Binnemans Faculty/research group: SURF

Daily supervision: Evert Vanecht

Graduating option: Student majoring in nanotechnology, physics or material science. Type of work (experimental, theoretical, simulations): experimental Number of students: 1 or 2

99


Development of Mini-Wireless Sensor for Avian Egg-Shell Temperature Monitoring Description: During incubation process of avian eggs, temperature is a very important factor affecting embryo development, hatchability and posthatch performance. It can be assumed that embryo development and hatchability are more influenced by embryo temperature than by air temperature. However, measurement of embryo temperature requires destructive methods that influence embryo development and hatchability. Use of eggshell temperatures as a reflection of embryo temperature can solve this problem. The specific objective of this topic is to design a wireless and battery-less sensor that is small enough to be attached to the egg-shell and yet not to oppose the respiration of the embryo through the egg-shell. The proposed sensor will be equipped with a short range transmitter (e.g. 2-5 m) to transfer the data to a receiver in the control panel of the incubator. The proposed sensor should be robust and sustainable to be used for control proposes. Promoter: Daniel Berckmans Faculty/research group: Faculty of bioscience engineering

Daily supervision: Ali Youssef



100


Nano-structuring of metal-oxide electrodes for solar cells application Description: Nanostructured materials are of great importance because they can display novel characteristics which are not exhibited by the bulk material, characteristics which may be exploited for applications in areas such as high density recording, MRAM and spin transport devices, solar cells and vortex pinning sites in superconductors. A possible route to the fabrication of arrays of nanostructures is via the use of an ordered nano-template. Part of the work will be focus on the fabrication of thin (<1µm), ordered and disordered nanoporous anodic aluminium oxide (AAO) templates on a range of substrates for device fabrication, predominantly via electrodeposition. By controlling the template morphology it will allow to control the nanostructures arrays produced using the templates. Disorded porous templates are formed upon anodisation in an acidic solution, due to local field enhanced etching of the oxide produced by random surface roughness. The site of pore formation may be controlled by producing arrays of indentations on the surface of the aluminium film before anodisation using a focussed ion beam (FIB) or nanoindentation as alternative to usual two step anodisation procedure. The indentations lead to the necessary local field enhancement required to influence pore growth and allows to fabricate templates with controlled morphology. This allows the pore geometry and position to be controlled with nanometre precision. Highly ordered arrays of nanowires may be produced after prepatterning as described here. E.g. ordered arrays of nanorods can be produce by electrodepositing into highly ordered square and hexagonal AAO templates. Hybrid organic-inorganic solar cells hold great promise as scalable, low-cost photovoltaics. This research will focus on the nano-structuring of metal-oxide electrodes to increase the interfacial area for charge separation and improve charge transport within these devices. AAO and electrodeposition will be use to fabricate large-area arrays of metal-oxide nanowires/naotubes on transparent conducting substrates. Morphological control of the nanostructures produced by this method is paramount for optimizing interfacial interactions and improving cell efficiencies. In order to develop the hybrid device described above, it is necessary to produce free standing oxide nanowires/nanotubes arrays on transparent, conducting substrates. One route to the fabrication of such structures is by templated electrodeposition into AAO templates supported on transparent, conducting substrates (on an ITO on glass substrate). Promoter: Prof. Jean-Pierre Celis Faculty/research group: Surface Engineering and Tribology

Daily supervision: Dr. Natalia Tintaru

Graduating option: Engineering, Science Type of work (experimental, theoretical, simulations): experimental


101


Visualization of vortices Description:

A vortex is a quantum mechanical object, consisting of a rotating current and a localized magnetic field, which can be induced in a superconductor by applying a magnetic field. At the KULeuven, the visualization of the vortex lattice is done using both scanning Hall probe microscopy (SHPM) and scanning tunneling microscopy (STM) (e.g. Figure 1). The SHPM has been substantially improved during the last years to a world-class level. This has led to publications in top journals. The purpose of this thesis is to use the aformentioned techniques to study the dynamics of the vortex lattice. As a concrete example, we will investigate the so-called “vortex dam”. This system combines two

superconducting materials to construct a container for vortices, separated in two parts by an asymmetric membrane (See Figure 2). We can shake these particles by an external ac driving force and visualize their rectification dependent on different parameters: the number of particles, the strength of the ac drive, etc. This investigation has a broad relevance to other systems, such as biological cell, colloidal particle and electron rectifiers, to name a

few.. Promoter: Prof. V.V. Moshchalkov Faculty/research group: Nanoscale superconductivity and magnetism

Daily supervision: Dr. J. Van de Vondel

Graduating option: FW Type of work (experimental, theoretical, simulations): Experimental


Figure 1: Scanning Hallprobe microscopy imagesafter field cooling thesample down to 4.2 K.

Figure 2: Vortex container. Light blueindicates a weak pinning superconductor (e.g.MoGe) and the dark region is a secondsuperconductor, acting as a repulsive barrier.

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Exchange bias by ion implantation in low-dimensional structures Description: In the world of today advanced electronics like computers or mp3 players are everywhere and data storage on hard disks is indispensible. The read heads of these hard disks make use of the so-called giant magnetoresistance (GMR) effect to read out the stored data. For this purpose, one benefits of an effect called ‘exchange bias’ to pin (i.e.fix) the magnetization of a thin ferromagnetic layer in a certain direction. Exchange bias is an interaction occurring at the interface between a ferromagnetic and an antiferromagnetic material. It results in a pronounced modification of the magnetic properties of the ferromagnet, e.g., it is more difficult to reverse its magnetization. An interesting example of exchange bias is ferromagnetic Co, coupled to antiferromagnetic CoO. Recently, we developed a new way of inducing exchange bias in thin films, in particular by means of ion implantation. By implanting O in Co, it is possible to form antiferromagnetic cobalt oxides embedded in the Co thin film, which induces exchange bias. In this study, we will use this approach to induce exchange bias in low-dimensional ferromagnetic structures, like stripes and dots, prepared with lithographic techniques. In these structures we can then combine the unique properties of magnetism at the nanometer-scale with the exchange bias phenomenon. We will make these exotic structures in the Ion- and Molecular Beam Laboratory and we study their magnetic properties using magnetization and magnetotransport properties, as well as neutron scattering experiments (at the Helmholtz-Zentrum Berlin).

Promoter: Prof. Kristiaan Temst, Prof. André Vantomme Faculty/research group: Faculty of Science / Institute for Nuclear and Radiation Physics (nuclear solid state physics group)

Daily supervision: Drs. Joost Demeter, Dr. Enric Menendez Dalmau

Graduating option: Master of Physics / Master in Nanoscience and Nanotechnology Type of work (experimental, theoretical, simulations): Experimental


103


Manipulating superconductivity by implanting Fe atoms Description: Superconductivity and ferromagnetism are well known to be two antagonistic phenomena, which implies that they exclude each other. When an interface between a superconductor and a ferromagnet is created, a “proximity effect” appears which leads to a modification of the superconducting properties. This effect can be used to manipulate the superconducting properties by modifying the magnetic state of the ferromagnet. It is expected, however, that the ferromagnet is also influenced by the superconductor. So far, very little is known on how the ferromagnet behaves when the superconductor becomes superconducting since the strong diamagnetic response of the superconductor prevents the study of the ferromagnet using conventional methods. In this project, local-probe nuclear methods will be used to gain this unique insight into the ferromagnet. The system to be studied is a granular superconductor/ferromagnet hybrid created by implantation of Fe ions into a Nb thin film. This is a new class of hybrids which offers new possibilities in terms of superconductivity tuning. The project includes the development of optimal preparation parameters to create the hybrid and advanced characterization using laboratory-based (magnetization and magnetotransport, Mössbauer spectroscopy) and synchrotron source based methods (nuclear resonant scattering). Promoter: Prof. Margriet Van Bael, Prof. Kristiaan Temst, Prof. André Vantomme Faculty/research group: Faculty of Science / Laboratory for Solid-State Physics and Magnetism & Institute for Nuclear and Radiation Physics (nuclear solid state physics group)

Daily supervision: Drs. Maarten Trekels, Dr. Sebastien Couet



104


Nanostructure Formation with Ion Beam Sculpting Description: In the recent past we have witnessed an increasing interest in the techniques for manipulating and patterning matter on the nanoscopic scale. The limited throughput and natural physical limits of top-down techniques push the focus towards self-assembly approaches. Ion beam sculpting (IBS) is an excellent example. Generally, bombardment of surface with an ion beam induces surface roughening. This roughening can be random and uncorrelated, but upon proper bombardment conditions it is possible to create highly organized 1D or 2D periodic patterns with periodicities ranging from few nanometers up to several micrometers. Moreover, in contrast to some other self-assembly techniques, IBS is very well suited for large scale applications. We have pursued an extensive experimental study of the patterning behavior of the crystalline nickel surface upon bombardment with Ar ion beam. Further, we have developed a physical model for patterning of the metallic surfaces. In the near future, this project will involve several distinct topics. One part will be to study the physical properties of the prepared nickel nanostructures. In particular, the interaction of the surface morphology with the magnetic anisotropy and the magnetic domain structure. Further, we will study IBS of compound materials. The preferential sputtering and different diffusivities can lead to the segragation of the compounds. This can further heavily affects the surface morphology and leads to unexpected phenomena. So far there are only few results available, mainly concerning compound semiconductors. We will study other groups of materials, such as FePt, NiSi… The majority of the experimental equipment is located in the Ion and Molecular Beam Laboratory. The work would involve preparation of the samples with Molecular Beam Epitaxy, ion beam irradiation and sample characterization mainly with Scanning Probe Microscopy techniques and X-ray diffraction Promoter: Prof. Kristiaan Temst, Prof. Wilfried Vandervorst, Prof. André Vantomme Faculty/research group: Faculty of Science / Institute for Nuclear and Radiation Physics (nuclear solid state physics group)

Daily supervision: Drs. Tomas Skeren

Graduating option: Master of Physics / Master in Nanoscience and Nanotechnology Type of work (experimental, theoretical, simulations): Experimental Number of students: 2

105


Lattice site location of the electrical dopant Mg in GaN Description: For many applications in micro-electronics, the behaviour of impurity atoms (such as electrical, optical, ... dopants) in semiconductors such as Si, Ge, GaAs, GaN,... plays a very important role. A very crucial factor is the exact position occupied by the impurities in the single crystalline semiconductor lattice: the impurity can replace one of the semiconductor host atoms, or can be located in between these atoms. In this master thesis, the lattice location of magnesium (Mg) atoms will be studied in gallium nitride (GaN), since Mg is known to be a very important electrical dopant in GaN. The Mg will be introduced in the gaN lattice by means of ion implantation (this will be carried out in the Ion and Molecular Beam Laboratory in Leuven). In order to accurately determine the lattice location of Mg, we will make use of a very sensitive technique, called electron emission channelling. To use this technique, radioactive Mg ions will be implanted in GaN, and the emission of beta-electrons will be studied. The resulting emission patterns are characteristic for the occupied lattice sites, and enable us to accurately determine the position of Mg atoms in GaN (more information can be found on http://fys.kuleuven.be/iks/nvsf/exp_fac_emchan.php). The emission channelling experiments take place at the ISOLDE facility in CERN (Geneva, Switzerland), and the master student will be highly encouraged to participate. The data analysis will be performed in Leuven. Promoter: Prof. Kristiaan Temst, Prof. André Vantomme Faculty/research group: Faculty of Science / Institute for Nuclear and Radiation Physics (nuclear solid state physics group)

Daily supervision: Drs. Ligia Amorim, Dr. Stefan Decoster



106


The role of Sn in the structural and electronic properties of GeSn Description: In the last decades significant improvements in microelectronic devices have been achieved by scaling, i.e. reducing the physical dimensions of the device elements, by implementing new transistor designs or by altering the materials such as using high mobility semiconductors, e.g. germanium (Ge). The intrinsic charge carrier mobility of Ge can be further enhanced by straining the lattice, adding elements with a larger lattice constant, e.g. Sn. In addition, it is known that the band gap in group IV semiconductors is likewise strongly affected by the lattice parameter. Thus, it is expected that by varying the Sn content the band gap can be tuned yielding a crossover from indirect to direct band transitions. These properties render GeSn alloys very interesting novel group IV semiconductor materials. However, one of the main challenges is the low solubility of Sn in Ge (0.5 – 1%), which results in a strong tendency of Sn to precipitate at concentrations above this limit5. The potential of epitaxial growth techniques to produce Ge1-xSnx layers with a sufficiently high substitutional Sn content has been demonstrated recently. Yet, a detailed understanding of the physical and chemical processes that govern the film growth as well as the resulting electronic and physical material properties of these GeSn layers is still lacking. In the first instance we will study the surface morphology and atomic configuration of the Ge1-xSnx layers. These are crucial parameter in the sense that they yield information about the onset of Sn precipitation and atomic processes that govern the film growth. We will use scanning tunneling microscopy (STM) as this is a beneficial method to probe the surface morphology on different lateral length scales (scan size), ranging from 1 μm down to a few tens of angstrom (atomic scale) with high spatial resolution. To study the influence of Sn on the surface electronic structure we will use scanning tunneling spectroscopy (STS). With this method we can measure the conductivity versus the applied tip-sample voltage, which is directly related to the local surface density of states (LDOS) close to the Fermi level. Hence, we can reveal information on the band gap, the Fermi level position, the valance band edge and the conduction band edge of the Ge1-xSnx films. Promoter: Prof. Kristiaan Temst, Prof. André Vantomme Faculty/research group: Faculty of Science / Institute for Nuclear and Radiation Physics (nuclear solid state physics group)

Daily supervision: Drs. Claudia Fleischmann

Graduating option: Master of Physics / Master in Nanoscience and Nanotechnology

Type of work (experimental, theoretical, simulations): Experimental


107


Ferromagnet/ferroelectric heterostructures: towards synthetic multiferroic materials Description: In recent years, a new paradigm has emerged in the field of magnetism which aims at the control of the magnetic state of material by use of electric fields using magneto-electric effects. This control is in principle best achieved in bulk multiferroic material such as perovskite-type oxides (TbMnO3, LaBiMnO3, BiFeO3 ...). However, such materials combining ferro-electricity and ferromagnetism are rare and their structure and chemical properties prove to be difficult to control. Another promising approach is to use heterostructures composed of ferroelectric (FE) and ferromagnetic (FM) thin layers. In these systems, it is expected that the modification of the interfacial strain induced by an electric field applied to the FE material can lead to a modification of the magnetic properties of the FM. This area of research is still in an early stage of development, and many systems and realizations have still to be discovered. The current project is embedded in this framework and aims at a deeper understanding of the magneto-electric coupling in synthetic multiferroics, as they are called. During the thesis, a number of possible ferromagnetic-ferroelectric systems will be investigated. The particular approach that will be taken here is that alongside with conventional macroscopic magnetization measurements like MOKE or SQUID, microscopic methods like nuclear resonant scattering of synchrotron radiation will be employed to obtain layer specific, depth resolved information on the local magnetic state. This combination of macro and microscopic experimental methods will allow to highlights the properties of the interface, which is key component of this class of systems, where coupling occurs through the interface Promoter: Prof. MargrietJ. Van Bael, Prof. Kristiaan Temst, Prof. André Vantomme Faculty/research group: Faculty of Science / Laboratory for Solid-State Physics and Magnetism & Institute for Nuclear and Radiation Physics (nuclear solid state physics group)

Daily supervision: Dr. Sebastien Couet




108


Optimization of a high-field magnet for pulsed operation Description: In the Pulsed Fields Group at the Department of Physics and Astronomy, pulsed magnetic fields of about 70 T are generated in the bore of a cylindrical magnet submersed in liquid nitrogen and excited by a capacitor bank. During autumn 2011, the existing capacitor bank of in total 1 MJ will be replaced by a 2 MJ capacitor bank. In theory, this would enable to operate the magnets at a substantially higher field. However, severe thermal and mechanical restrictions hamper such straightforward up scaling. The present magnets have been designed and optimized for several decades until now [1,2,3]. To that purpose, calculation routines on the basis of (semi-)analytical formulae have been developed. Over the years, expertise has been gained on the magnet layout, winding techniques, reinforcement fibers (carbon, glass fiber) and impregnation technology. Until today, magnets are constructed, tested and used in the laboratory. The simulation of the magnet system requires the calculation of coupled electromagnetic, structural dynamic and thermal fields in time domain. Despite of the remarkably high accuracy of the existing semi-analytical techniques, it is expected that finite-element simulation offer a higher design flexibility, thereby possibly opening the way towards a higher fields and longer life times. A coupled finite element simulation has already been reported in [4]. This thesis proposal aims at the application 2D transient, electromagnetic, structural dynamic, thermal finite element field simulation to an axisymmetric model of the magnet (although mechanical deformation disturbs the cylindrical symmetry). An intermediate goal consists of achieving a sufficiently reliable simulation tool, e.g. comparable to the existing semi-analytical models. Finally, the model will be applied for parameter studies, i.e., for changing the existing design according to the new capacitor bank and the new design of the nitrogen vessel. [1] L. Li, F. Herlach, Deformation analysis of pulsed magnets with internal and external reinforcement, IEE

Science Meas. Technol. 6, 1995, 1035–1042. [2] F. Herlach, T. Peng, J. Vanacken, Experimental and theoretical analysis of the heat distribution in

pulsed magnets, IEEE Trans. Appl. Supercond. 16(2), 2006, 1689-1691. [3] F. Herlach, N. Miura (eds), High Magnetic Fields: Science and Technology, World Scientific Publishing,

ed. 1, vol. 1, Magnet technology and experimental techniques, 2008. [4] H. Witte, A. Gaganov, N. Kozlova, J. Freudenberger, H. Jones, Pulsed magnets - advances in coil

design using finite element analysis, IEEE Trans. Appl. Supercond. 16(2), 2006, 1680-1683. Promoter: Prof. Herbert De Gersem, Prof. Johan Vanacken, Prof. Em. Fritz Herlach Faculty/research group: Faculty of Science / Solid State Physics and Magnetism Section

Daily supervision: Prof. Herbert De Gersem

Graduating option: Master of Physics / Master in Nanoscience and Nanotechnology Type of work (experimental, theoretical, simulations): simulations Number of students: 1

Remark: The thesis work can be carried out everywhere and can be supervised accordingly. However, a regular presence (e.g. one day per week) in Kortrijk (www.kulak.be) is recommended. Travelling (train) and additional lodging costs (student home) will be refunded.

109


Design of a new magnetic deflection system for atomic clusters Description: At the K.U. Leuven the current cluster setup will be extended with a Stern-Gerlach deflector. Stern and Gerlach developed in 1922 an experiment to deflect particles to illustrate basic principles of quantum mechanics. They were able to demonstrate that electrons and atoms have intrinsically quantum properties. The Stern-Gerlach experiment involves sending a beam of particles through an inhomogeneous magnetic field and observing their deflection (see figure 1) [1].

Figure 1: Typical set-up for the Stern-Gerlach experiment.

Figure 1: 3D electromagnetic simulation of a Rabi-type magnet.

In 1922, computer simulations were not an option. Therefore, the magnetic field system was kept simple so that the fields could be calculated analytically. Today, we have access to powerful computer simulation packages that make it possible to design more complicated magnets, using mathematical optimization algorithms. The particle accelerator group of the K.U. Leuven Kulak is specialized in electromagnetic calculations using 2D and 3D Finite Element Modeling tools. Figure 2 shows an example of a magnetostatic calculation with CST Studio Suite [2] of a Rabi-magnet. Together with the research team, your work will consist of studying and optimizing new designs for a magnetic deflection system using state-of-the-art 3D simulation tools. [1] Stern-Gerlach experiment. Information from Wikipedia. [2] Computer Simulation Technology: http://www.cst.de Promoter: Prof. Dr. Herbert De Gersem, Dr. Bert Masschaele Faculty/research group: Faculty of Science / Solid State Physics and Magnetism Section

Daily supervision: Dr. Bert Masschaele, Dr. Ewald Janssens


Type of work (experimental, theoretical, simulations): Simulations Number of students: 1

Remark: The thesis work can be carried out everywhere and can be supervised accordingly. However, a regular presence (e.g. one day per week) in Kortrijk (www.kulak.be) is recommended. Travelling (train) and additional lodging costs (student home) will be refunded.

110


Electrical and electromechanical properties of ZnO nanowires Description: Oxide based semiconductors and in particular ZnO based materials with wide band gap offer unique possibilities for applications in electronic devices due to their remarkable electronic, optical and optoelectronic characteristics. The application potential is further increased by considering ZnO nanowires, where the strongly reduced dimensions give rise to pronounced quantum confinement effects that allow a further tailoring of the functional properties. For your master thesis you will probe with nanometer resolution the electronic properties of individual ZnO wires using a combination of electrostatic force microscopy (EFM) and scanning gate microscopy (SGM). Such microscopy requires to first attach electrical contacts to individual ZnO nanowires using electron beam lithograph. The appropriate doping is introduced by ion implantation. With EFM you will then be able to measure the electrical potential distribution in a current-carrying nanowire. On the other hand, with the conductive EFM tip acting as a gate electrode, it is possible to induce a controllable local potential perturbation and to obtain an SGM image of the nanowire. The contacted ZnO wires are prepared in such a way that the central part of the wires is suspended above a hole in the oxidized silicon substrate, allowing to mechanically deform the nanowires. This way you will be able to probe the electromechanical response of a ZnO nanowire by measuring its electrical resistance while it is mechanically deformed with the oscillating sharp tip of the force microsope.

Promoter: Prof. Chris Van Haesendonck

Faculty/research group: Faculty of Science / Solid State Physics and Magnetism Section

Daily supervision: Dr. Yujia Zeng, Dr. Alexander Volodin



111


Influence of adsorbates on the electrical properties of few-layer graphene Description: Recently, it became possible to isolate individual atomic layers of carbon from a graphite crystal. These so-called graphene layers have unique two-dimensional electrical transport properties that are very sensitive to the attachment of atoms or molecules to the layers. This offers interesting possibilities for the use of graphene as gas sensor or as biosensor. You will prepare few-layer graphene flakes by mechanical exfoliation of graphite. To the flakes you will attach electrical contacts using electron beam lithography after deposition of the flakes on an oxidized silicon substrate. You will then investigate in detail how the two-dimensional electronic properties of the graphene are affected by the attachment of atoms or molecules. This investigation will make use of standard electrical transport measurements as well as of scanning probe microscopy based measurements of the local electrical properties. For the interpretation of the experiments you will rely on density functional theory (DFT) based simulations (collaboration with the theory group of Prof. François Peeters at the University of Antwerp). Promoter: Prof. Chris Van Haesendonck


Daily supervision: Dr. Alexander Volodin, Dr. Yujia Zeng




112


Probing the magneto-electrical properties with scanning probes Description: For your master thesis you will investigate thin films of complex oxides that reveal at the same time ferroelectric and ferromagnetic order. The coupling between both order parameters in these so-called magneto-electrical materials results in a multifunctional material, where the ferromagnetism can be affected by applying an electrical field and the ferroelectricity can be affected by applying a magnetic field. The samples that you will investigate are thin films of multifunctional metal oxide materials that are obtained by co-deposition of the metallic components in a reactive oxygen atmosphere. You will determine the coupling between ferromagnetism and ferroelectricity using magnetic force microscopy (MFM) and piezoelectric force microscopy (PFM) that can image with nanometer resolution the ferromagnetic domain structure and the ferroelectric domain structure, respectively. The available MFM and PFM measuring systems provide the unique possibility to do measurements down to liquid helium temperature while applying an electric and/or a magnetic field. Promoter: Prof. Chris Van Haesendonck, Dr. Alexander Volodin


Daily supervision: Danying Li, Dr. Yujia Zeng



113


Electrical properties of metalized peptide nanotubes Description: Self-assembly of biological molecules into complex and functional systems is omnipresent in nature. Intriguing nanostructures are not only waiting to be discovered, but are also being duplicated and modified for applications in nanoelectronics and as a template for nanostructured materials. Nanotubes formed from diphenylalanine, one of the simplest dipeptides capable of self-assembly into nanotubes, will be the subject of your master thesis. You will rely on atomic force microscopy (AFM) and transmission electron microscopy (TEM) (collaboration with Prof. Sara Bals of he University of Antwerp) to visualize the nanotube structure with high spatial resolution. You will use the peptide nanotubes as a template for the deposition of metallic nanoparticles that can then coalesce into continuous metallic nanowires. You will in particular investigate the possibility to metalize the inside of the nanotubes in order to prepare electrically conducting nanowires. After characterization of the metalized wires with AFM and TEM you will probe the electrical quality of the wires by measuring their electrical resistance down to liquid helium temperatures and in the presence of a magnetic field. On the longer term, the research in which you will be involved may pave the way for the affordable production of large quantities of well-defined nanostructures of inorganic materials that are not capable of self-assembly themselves and for the precise ordering and interconnection of these nanostructures. Promoter: Prof. Chris Van Haesendonck, Dr. Johan Snauwaert


Daily supervision: Katrien Herdewyn



Number of students:

114

Vibrational spectra of the Si13V+ cluster. The upper trace

shows the experimental IR spectrum. It is compared to the l l d ib i l f h l l i i


Laser spectroscopy and mass spectrometry of doped clusters

Description:

How does the composition of doped silicon clusters influence their geometry and electronic structure?

We produce beams of mixed clusters of a few up to several hundreds of atoms with a laser vaporization source, and study their properties with laser spectroscopy and mass spectrometry. With deep infrared spectroscopy we can identify vibrational transitions that are characteristic for the cluster geometry, while visible light (or near infrared) spectroscopy identifies the electronic transitions. The employed technique is so-called action spectroscopy where absorption of laser light results in dissociation, fragmentation and/or ionization. For this research we have several laser systems available providing nanosecond pulsed light with wavelengths tunable between 195 and 2000 nm. For the absorption of infrared light, through the vibrational degrees of freedom in a frequency range from 100 cm-1 up to 500 cm-1, we move to the free electron laser FELIX (Free Electron Laser for Infrared eXperiments) of the FOM Institute for Plasma Physics Rijnhuizen (Nieuwegein, Nederland).

Promoter: Prof. Peter Lievens, Dr. Ewald Janssens


Daily supervision: Pieterjan Claes, Hai Thuy Le,




115


Clusters for Catalysis Description: Catalytic technologies are at the core of more than 80 % of the processes in the chemical industry today. Improvement of their per-formance is expected to have a major impact in the near future in the crucial strategic issues of environment and renewable energy. Most of the catalysts nowadays consist of highly dispersed very small metallic (nano)particles supported on oxide supports. Two key parameters that are directly influencing their performance are the size of the metallic particles and the nature of the support. We have recently implemented a new physical method of producing very homogeneous model catalysts based on size-selected gas phase clusters. By studying their catalytic properties in collaboration with catalysis groups, we aim at understanding the role of the size and support on the catalytic activity with as ultimate goal the design of novel high performance catalysts. The goal of this thesis research is to produce series of size-selected Au, Pd, and Pt clusters using the laser vaporization cluster source (between few atoms and 4.0 nm) and deposit them onto different types of thin oxide layers. You will characterize these transparent materials by grazing incidence X-ray diffraction and by atomic force and scanning tunneling microscopies (AFM and STM). In a second stage their catalytic activity will be monitored by fluorescence microscopy detection techniques using reactive fluorescent probe molecules. Promoter: Prof. Peter Lievens Faculty/research group: Faculty of Science / Solid State Physics and Magnetism Section

Daily supervision: Dr. Didier Grandjean, Christian Romero




116


Magnetron sputter source for cluster production and deposition Description: Nanoparticles and clusters can be produced in many different chemical and physical ways. Advanced technologies have recently been developed to facilitate cluster deposition in order to study properties of clusters and cluster-assembled systems on surfaces. As physical properties (magnetic, optical, superconducting, etc.) of these nanometer sized particles are strongly size dependent, controlling the size of the produced clusters is of utmost importance. In this thesis you will optimize a new cluster source for cluster production and deposition, based on magnetron sputtering and gas aggregation. In this type of source, atoms are sputtered from the target material by an Ar plasma, while a stream of He gas carries the atoms into a liquid nitrogen cooled aggregation tube. The cluster growth takes place in this growth tube after which the formed clusters are expelled into high vacuum where they can land on a surface. This type of cluster source is able to generate an intense beam of clusters with sizes ranging from a few atoms to 10 nm. Your work will consist of exploring different ways to control and tune the size of the produced clusters. There are several ways to tune the cluster size, e.g., by varying the position of the sputter head in the growth tube or by controlling the flow of Ar and He gas. Mass selection of the cluster beam will be achieved by implementing a quadrupole mass selector. The size distribution of the produced clusters can be determined by time-of-flight mass spectrometry. You will also study in detail the size and shape of clusters of different materials after deposition on a substrate by scanning probe microscopy. Promoter: Dr. Ewald Janssens, Prof. Peter Lievens, Prof. Margriet Van Bael Faculty/research group: Faculty of Science / Solid State Physics and Magnetism Section

Daily supervision: Kelly Houben, Dr. Thomas Picot


Type of work (experimental, theoretical, simulations): Experimental Number of students: 1

117


Zero-energy SIMS Description: Due to the ongoing scaling of semiconductor structures (Moore’s law), the position of dopant atoms which determine the electrical properties of a device becomes more important. Until now, secondary ion mass spectrometry (SIMS) is used to determine these dopant profiles because of its high sensitivity. However, quantitative depth profiles with a high depth resolution (sub-nm) are becoming more and more challenging due to the ion-substrate interaction. Zero-energy SIMS aims at eliminating these drawbacks by replacing the ions by a combination of electrons and a reactive gas mixture, and by ionizing the emitted species by laser post-ionization. First results are very promising. In this thesis subject the technique will be optimized further, with emphasis to the fundamental etching and laser post-ionization mechanisms. (Research in collaboration with Imec.) Promoter: Prof. Peter Lievens, Prof. Wilfried Vandervorst Faculty/research group: Faculty of Science / Solid State Physics and Magnetism Section

Daily supervision: Nico Vanhove




0 5 10 15 20 25 30 35 40 45 50100

101

102

103

104

105Zero-energy SIMS:

10B 11B 47SiF

Conventional SIMS: 10B 11B 28Si

118


Unraveling the quantum mechanical properties of nanoparticles with scanning tunneling microscopy Description: Nanoparticles, providing the bridge between the atomic and the bulk level, attract a lot of attention in solid state physics. Their properties do not simply scale with their size and cannot be readily predicted. A profound knowledge of their behavior is of crucial importance for fundamental physics, but also, e.g., for the operation of future nanoelectronic circuits and data storage media. Controlled preparation of nanoparticles on a substrate allows probing their physical properties with high spatial and energy resolution by means of scanning tunneling microscopy (STM) and spectroscopy (STS). For this thesis project, you will create nanoparticles (clusters) in the gas phase by means of condensation of evaporated atoms, and deposit them on atomically flat substrates. The central goal of this research project is a systematic investigation of the size dependence of the electronic properties of these deposited clusters by STS. More precisely, you will study the properties of individual nanoclusters for which the interaction with the substrate is minimized. This can be achieved by depositing the nanoclusteres on metallic substrates that are covered with a thin NaCl layer that acts as a tunnel barrier and basically eliminates the interaction with the underlying substrate. Quantum-mechanical confinement phenomena and Coulomb charging effects are expected to play a dominant role because of the finite size of the nanoclusters, while also the particle shape will play a prominent role. Figure: Left: 80 x 80 nm2 STM image of deposited Co clusters on the herringbone reconstructed Au(111) surface. Right: 170 x 170 nm2 STM image of atomically flat NaCl islands located across atomic steps at the Au(111) surface.

Promoter: Dr. Ewald Janssens, Prof. Peter Lievens, Prof. Chris Van Haesendonck Faculty/research group: Faculty of Science / Solid State Physics and Magnetism Section

Daily supervision: Koen Lauwaet, Dr. Koen Schouteden




119


Interactions of semiconductor nanowires with cells Description: Semiconductor nanoparticles (NPs) have been used in biological applications primarily in the imaging field [1], where the interfaces created between NPs and cells were mainly passive (i.e. not used for direct stimulation or activation of cellular responses). However, semiconductor NPs and nanowires (NWs) display a unique range of optoelectronic properties which have motivated their use in photovoltaics, lasers, and light emitting diodes. Recently, it has been shown that stimulation of cellular electrical activity occurs under the influence of light if cells were impaled with glass electrodes coated with surface deposited PbSe NP films [2]. This is because electrogenic cells like neurons transmit electrical signals by adjusting their interior and exterior ion concentrations using membrane bound proteins, among which voltage-gated ion channels open/close under the influence of local voltage changes. Such voltage changes can be in principle produced by the dipole moment of an optically-excited nanocrystal. In this project we aim to further explore the light-induced cellular activation with semiconductor NWs. For this purpose, we will grow and investigate the optoelectronic properties of semiconductor nanostructures and their interaction with membranes containing voltage-sensitive ion channels (i.e. model membranes and living cells). The main objectives of the project are: (1) to deposit monodisperse Au particles on Si or other substrates for the growth of NWs; (2) to grow vertical semiconductor ZnO NWs by chemical vapor deposition (CVD) and evaluate their structure and optoelectronic properties as a function of their dimensions and growth conditions; (3) to culture cells on the grown NWs and investigate the NW/membrane interface, cytotoxicity and the possibility to obtain light-induced cellular stimulation Methods to be used in this work by the thesis student self: - CVD, UV-visible spectroscopy, photoluminescence, cell culturing, cell viability assaysMethods used in this work performed by others: - SEM/EDX/TEM/XRD, AFM, confocal microscopy References: [1] McDowell M. Et.al., Materials 2010, 3, 614-637; doi:10.3390/ma3010614 [2] Zhao Y. et.al., Angew. Chem. Int. Ed. 2009, 48, 2407 –2410 Promoter: Prof. Carmen Bartic, Prof. JW Seo, Prof. JP Locquet Faculty/research group: Department of Physics and Astronomy/MTM

Daily supervision:

Graduating option: Master in Nanotechnology (EN + NL) Type of work (experimental, theoretical, simulations): experimental


120


Characterization of Functionalized Magnetic Nanoparticles for Medical Diagnostics and Treatments. Description: This research aims to develop magnetic nanoparticles with physico-chemical properties tailored for in vivo diagnostic MR imaging and cell tracking following the exvivo labeling of cells. Desirable properties from such nanoparticles are stronger signal intensity using a smaller number of particles, better and more specific cellular uptake, the potential to be utilized for quantification and non-toxicity, improved specificity and stability in time. Such requirements can be met by tuning the magnetic composition, the physical size and geometry, the chemical and biofunctional coatings, polymeric/silica based core-shell thickness and/or lipidic coating techniques which are developed at IMEC (Dr. J. Trekker, Prof. L. Lagae –coordinator iMAGiNe project). Such nanoparticle development also requires co-development of analytical techniques to assess the properties of these novel materials.. To reach the above objectives, we need to develop diagnostic magnetic nanoparticle imaging/tracking methods to obtain high sensitivity and specificity. Whereas current MRI diagnostic imaging techniques are optimized to provide maximal tissue contrast, the same instruments can be tuned to be sensitive towards information enhanced by magnetic particles. Such imaging method can be used for sensitive stem cell tracking. The particular task of the thesis student consists out of the magnetic characterization of these nanoparticles. This will be done by VSM (vibrating sample magnetometer), SQUID (Superconducting Quantum Interference Device), Scanning Hal probe and Magnetic Force Microscope. The experiments will be coupled with/related to NMR measurements (at UZG –Prof. U. Himmelreich) and relaxivity measurements (UCL –Prof. R.N. Muller). This subject is multidisciplinary and will allow the student to get into contact with several other important disciplines Promoter: Prof. Victor Moshchalkov Faculty/research group: Faculty of Science / INPAC

Daily supervision: Dr. Thomas Nuytten, Dr. Johan Vanacken

Graduating option: Master of Physics / Master in Nanoscience and Nanotechnology Type of work (experimental, theoretical, simulations): Experimental Number of students:

121


Rare-earth doped nanoscale glass-ceramics for light frequency down-conversion. Description: Rare-earth ions, such as erbium (Er), ytterbium (Yb), europium (Eu), neodymium (Nd), are known for efficient luminescence and are commonly used in lasers, optical telecommunications amplifiers and phosphors. Recently, a new area of application for rare-earth doped materials has emerged: light-frequency down-conversion, i.e. conversion of light frequency from ultraviolet and violet part of the spectrum to the visible and near-infrared part of the spectrum. This effect is proposed for use in energy saving phosphorescent lamps, energy saving plasma displays and silicon solar cells. Recently we have found that rare-earth doped nanoscale glass-ceramics can be used for efficient light-frequency down-conversion with quantum yield approaching 200%. The advantage of our materials is a possibility of high doping level and low host phonon energy, which assure their prevailing performance over alternative materials. The particular task of the thesis student consists of the: a) Preparation of rare-earth doped glass-ceramics b) Optical spectroscopy characterization of the samples This subject is multidisciplinary and will allow the student to get into contact with other important scientific disciplines.

Promoter: Prof. Victor Moshchalkov Faculty/research group: Faculty of Science / INPAC

Daily supervision: Dr. Victor Tikhomirov, Drs Niels Verellen


122


Superconductivity in diamond films: doping effects induced by chemical substitution and electric gate field Description: Although diamond has always been adored as a jewel, it shows even more fascinating physical properties; it is the hardest material ever known, it has the highest thermal conductivity at room temperature and in its pure form it can withstand very high electrical fields. When charge carriers are introduced in diamond, e.g. by chemical doping with Boron (B), the C1-

xBx diamond:B can exhibit an insulator-to-metal transition (pMott ~2 1020 cm-3 ). Diamond with moderate boron doping (p~1017-1019 cm-3) becomes a p-type semiconductor, with boron acting as an acceptor. In this form, it is a promising material for electrical applications, such as high frequency and high power devices, because of its high breakdown field (>10MV/cm) and high carrier mobility. Heavily doped boron-diamond shows metallic conduction, and even more, C1-xBx becomes superconducting, with relatively high critical temperatures Tc. This project will concentrate on studying the superconducting properties of this heavily doped diamond. Promoter: Prof. Victor Moshchalkov Faculty/research group: Faculty of Science / INPAC

Daily supervision: Drs. Gufei Zhang, Dr. Johan Vanacken


123


Near field optical microscopy beyond the classical diffraction limit Description: A fundamental principle in diffraction-limited optical microscopy requires that the spatial resolution of an image is limited by the wavelength of the incident light and by the numerical apertures of the objective lens systems. The development of near-field scanning optical microscopy (NSOM) has been driven by the need for an imaging technique that retains the various contrast mechanisms afforded by optical microscopy methods while obtaining spatial resolution beyond the classical optical diffraction limit. In this project the student gets the opportunity to work with a brand new state-of-the-art SNOM system to locally probe and visualize the near field optical properties of various metallic nanostructures. These are widely investigated in new booming branches of physics – nanophotonics and plasmonics - because they can sustain pronounced electromagnetic resonances - known as surface plasmon modes (light waves that are trapped on the surface because of their interaction with the free electrons of the conductor). These surface plasmons provide a means for light localization below the diffraction limit, large electromagnetic field enhancements, as well as for enhanced scattering and absorption of photons. For the past few years, nanotechnology has provided us the tools to exploit this classical phenomenon for applications ranging from single-molecule sensing to nanoscale photonic waveguides and even complete on-chip optical circuits. Promoter: Prof. Victor V. Moshchalkov Faculty/research group: Faculty of Science / INPAC

Daily supervision: Drs Niels Verellen, Dr. Johan Vanacken


Type of work (experimental, theoretical, simulations): Experimental Number of students: 1

124


Superconducting weak links Description: When two superconducting reservoirs are weakly linked by a constriction for instance, the superconducting order parameter can tunnel from one reservoir to the other. As a result one can send a dissipationless current through the constriction which depends on the phase difference ∆φ in both reservoirs (DC Josephson effect). Above a certain current a voltage will develop across the constriction leading to a linear increasing phase difference ∆φ (AC Josephson effect). By use of nanolithography a superconducting bridge will locally be cut to create a constriction. The Josephson effect will be investigated as a function of the constriction width. Possibly a loop with two junctions will be created to make a SQUID magnetometer. Promoter: Dr. A. V. Silhanek, Prof. V.V. Moshchalkov Faculty/research group: Faculty of Science / Nanoscale Superconductivity and Magnetism

Daily supervision: Dr. W. Gillijns, Dr. A. V. Silhanek




125


Visualization of Vortex – Antivortex dynamics in Superconductor / Ferromagnet hetero-structures Description: Over the last decades, phenomena originating from the interplay of two mutually exclusive states of matter, superconductivity and ferromagnetism, combined in superconductor-ferromagnet hybrids, have attracted much attention in both experimental and theoretical studies. Considerable efforts, fuelled to a great extent by perspectives to improve the superconducting critical parameters, have been focused on vortex pinning in heterostructures, composed by planar superconductors and _sub_ micron ferromagnetic dots. In particular, a dot with sufficiently strong magnetization and/or large enough size can create vortices or pairs of vortices in the superconductor giving rise to a variety of nontrivial commensurability effects and novel stable vortex-antivortex (V-AV) configurations in superconducting films with regular arrays of magnetic dipole [1]. The objective of this master thesis is to investigate the vortex dynamics in superconductor-ferromagnet (S/F) hetero-structures with a single in-plane magnetic dipole in the regime where the magnetic dipole periodically generates V-AV pairs. We will visualize superconducting vortex patterns in such Superconductor/Ferromagnet hybrid by means of the Scanning Hall Probe microscopy technique, which will provide a rich overview of the vortex distribution in a wide range of fields and temperatures. In specific conditions, the use of an applied transport current will allow the study of vortex dynamics in these systems. -As first step, the student will learn how to prepare the samples. This is mainly divided in two steps: (i)Grow the S/F hetero-structures. For this, the student will be taught the use of vacuum systems as Molecular Beam Epitaxy, electron beam evaporation and sputtering systems. (ii)To be able to study the vortex dynamics in such systems the samples need to be patterned in narrow strips, through which an electrical current (strong enough to depin the V-AV pairs) will be sent. For this, the student will gain the skills in using optical and e-beam lithography systems. -The second step will be the visualization and study of vortex patterns and dynamics on these systems. For this a Low Temperature Scanning Hall Probe Microscope (LT-SHPM) which incorporates in-situ electrical transport measurements will be used. Promoter: Dr. J. Gutierrez, Prof. V.V. Moshchalkov Faculty/research group: Faculty of Science / Nanoscale Superconductivity and Magnetism

Daily supervision: Dr. J. Gutierrez




126


Oxides with a high dielectric constant on high mobility semi-conductors Ge and InGaAs Description: Dielectric oxides are critical elements in many electronic devices for logic applications such as metal-oxide-semiconductor field-effect-transistors (MOSFET) as well as in several memory devices (FLASH and DRAM). The requirements (band gap and dielectric constant) for the different applications (F=Flash, L=Logic, D=Dram) are illustrated in the adjacent Figure.

From a fundamental viewpoint, one of the key design challenges in this field, is to create dielectrics heterostructures with a very high dielectric constant while maintaining a very low leakage current. The appropriate materials currently do not exist! Artificial structures with novel electric dipole configurations will be designed, developed and tested during this project1.

From an experimental point of view, these oxides will be integrated with semiconductors such as Ge and InGaA in capacitor and transistor structures2. One of the major issues that prevents the use of Ge and InGaAs MOSFETs today, is the large amount of electrically active defects at the interface. By controlling the interface structure and chemistry as well as the interatomic stacking sequence using molecular beam epitaxy, novel surface passivation strategies will be developed on top of which a high K oxide will be grown (ε > 60).

This project can be executed both from a fundamental viewpoint or from a more experimental viewpoint. The activities will take place in the framework of a European collaboration with industrial partners such as IBM and ST.

1EM Vogel, Nature Nanotechnology, 2, 25 (2007); W. Andreoni et al, Appl. Phys. Lett., 96, 062901 (2010).

2YN Sun et al., IEEE Elec. Dev. Lett., 28, 473-475 (2007); C. Marchiori et al., J. Appl. Phys., 106, 114112 (2009).

Promoter: Prof JP Locquet, Prof JW Seo

Faculty/research group: Faculty of Science / Faculty of Engineering

Daily supervision: Dr Mariela Menghini, Drs Tomas Smets

Graduating option: Master in Physics / Master in Nanoscience and Nanotechnology Type of work (experimental, theoretical, simulations): Experimental / Simulations

127

Number of students: 1-2

128


Electric Field induced Metal - Insulator – Transition for NVM applications

Description: For non-volatile memory (NVM) applications, the goal is to change from flash technology towards more compact and scalable designs using alternative mechanisms. Phase change (PCM) and resistive switching memories (RRAM) are two popular approaches. While many “switching” mechanisms are proposed, we focus here on purely electronic phase transition between an insulating and a metallic state. The adjacent Figure shows the resistivity changes versus temperature for the Pr(Ca,Sr)MnO3 compound.

From a fundamental viewpoint, one of the key challenges is that the metal insulator transition (MIT) in correlated electron systems is still not fully understood (Mott vs Peierls transition). In addition, novel materials and/or heterostructures must be designed1 and tested whereby the gap opens far above room temperature, and far from “disturbing” structural phase transitions.

From an experimental point of view, MIT oxide thin films will be deposited using sol-gel and molecular beam epitaxy methods. The metal-insulator transition will be determined as function of applied electric fields and temperature. Finally they will be integrated into functional devices such as memory elements and varistors2.

This project can be performed both from a fundamental and from an experimental viewpoint. The activities take place in the framework of a collaboration with industrial partners.

1J Cao et al., Nature Nanotechnology 4, 732, (2009); M Tomczak et al., EuroPhysics Letters, 86, 37004 (2009).

2MJ Lee, Advanced Materials, 19, 3919 (2007); BJ Kim et al., IEEE Electron Device Letters 31, 14 (2010).

Promoter: Prof JW Seo, Prof JP Locquet Faculty/research group: Faculty of Science / Faculty of Engineering

QuickTime™ and a decompressor

are needed to see this picture.

129

Daily supervision: Dr Mariela Menghini, Drs Leander Dillemans

Graduating option: Master in Physics / Master in Nanoscience and Nanotechnology

Type of work (experimental, theoretical, simulations): Experimental / Simulations Number of students: 1-2

130


Magneto-electric oxide heterostructures for novel devices

Description:

In many applications of magnetic materials – as in hard disk storage – a large magnetic field is needed to reverse the magnetization. However the application of a large magnetic field required the integration of bulky electro-magnets, which is not easy to achieve. A remedy is offered by magneto-electric materials, where there is an intimate coupling between the magnetic spins and the electric dipoles. Hence the application of an electric field leads to a magnetization reversal. And vice versa, the application of a magnetic field leads to a ferroelectric dipole moment.

From a fundamental viewpoint, one of the key design challenges is that this magneto-electric coupling is rather weak leading to unpractically small effects. A strong magneto-electric material operating above room temperature does not exist today! Artificial structures with a strong coupling between the magnetic spins and electric dipoles -- such as the one illustrated in the adjacent figure -- must be designed, developed and tested1.

From an experimental point of view, magneto-electric oxide thin films will be deposited using sol-gel and molecular beam epitaxy methods. The magneto-electric coefficients will be determined as function of applied magnetic and electric fields, both as a function of frequency and temperature. Finally they will be integrated into functional devices such as tunnel junctions as well as electric field and magnetic field tunable microwave filters2.

This project can be performed both from a fundamental or an experimental viewpoint. The activities will take place in the framework of a collaboration with industrial partners.

1RJ Zeches et al., Science 326, 5955, 977 (2009); AJ Hatt et al., Physical Review B81, 054109 (2010).

2P Maksymovych et al., Science, 324, 5933, 1421 (2009); AS Tatarenko et al., J. Electroceramics 24, 5 (2010).



131

Promoter: Prof JP Locquet, Prof JW Seo


Daily supervision: Dr M Menghini, Dr S Thayumanasundaram Drs. L Dillemans


Type of work (experimental, theoretical, simulations): Experimental / Simulations Number of students: 1-2

132


Oxide semiconductors with high mobility and low band-gap for photovoltaic applications

Description: Semiconductor technology including solar cells combines two very different and incompatible materials, namely simple semiconductors and oxides. The former (Si, Ge, InGaAs) are essential for efficient carrier transport while the latter enable various functionalities (such as dielectric, ferroelectric, piezoelectric, ...). These material incompatibilities always lead to sub-optimal properties and devices. There exists however a large class of oxide semiconductors with a carrier mobility around 100 cm2/Vs much larger than amorphous Si. Some of these are currently used as transparent conducting oxides (TCO).

From a fundamental viewpoint, there are two key challenges, namely to design1 materials and heterostructures wherein first a higher carrier mobility is possible and second whereby the band-gap can be reduced to the range 0.7 - 2 eV. Oxide compounds that fulfill these goals currently do not exist! In particular the options related to suboxides have not been explored much.

From an experimental point of view, oxide semiconductors will be grown using sol-gel and molecular beam epitaxy. After growth they will be annealed at high temperature under different conditions. The electrical properties (resistivity, carrier mobility, band-gap) will be determined as a function of temperature. Finally an n and p-type oxide will be combined with oxide transparent conductors (TCO) into photovoltaic devices and structures2.

This project can be performed both from a fundamental and from an experimental viewpoint. The activities will take place in the framework of a collaboration with industrial partners.

1B. Falabretti et al., J Applied Physics 102, 123703 (2007); J Robertson, J Non-Crystalline Solids 354, 2791 (2008).

2H. Ohta et al., Advanced Functional Materials, 13, 139 (2003); K. Nomura et al., Science, 300 1269 (2003).

Promoter: Prof JP Locquet, Prof. JW Seo




133

Daily supervision: Drs Leander Dillemans, Drs Chenyi Su


Type of work (experimental, theoretical, simulations): Experimental / Simulations


134


Fabrication of Lithium coin cells using Ionic liquids and Olivine

Description:

Lithium-ion batteries are the systems of choice, offering high energy density, flexibility and longer lifespan than most other types of battery. The life time of a battery depends on the nature of the interfaces between the electrodes and electrolyte, whereas safety is a function of the stability of the electrode materials. Cathode materials based on lithium metal phosphates (LiMPO4, M= Co, Ni, Fe, Mn) (operation voltage ≥5 V) can offer safety, power and energy to satisfy the fast growing large platform applications.

The strongest assets of ionic liquids (ILs) such as stability at high anodic potentials, wide liquid range and high conductivity make them attractive as lithium battery electrolytes.

From a fundamental viewpoint, there are two challenges, i) creating materials (fluorophosphates see adjacent figure) that allow a better strain accommodation upon charging/discharging and low interfacial resistance ii) selection of suitable ILs to overcome its electrochemical stability problem at the cathode and to prevent cathodic decomposition into electrolytes.

From an experimental point of view, Li2MPO4F (M = Co, Ni) will be synthesized either by solid state reaction or sol-gel method and its thermal and structural properties will be investigated. Finally complete Lithium coin cells will be fabricated using optimized cathode and ILs.

1S. Nishimura et al., Nature Materials, 7, 707 (2008)

2H. Ohno et al., Journal of Power Sources 1174, 342 (2007)

Promoter: Prof JP Locquet, Prof JW Seo Faculty/research group: Faculty of Science / Faculty of Engineering

Daily supervision: Dr Savitha Tayumanasundaram, Dr Edina Couteau



135

Graduating option: Master in Physics / Master in Nanoscience and Nanotechnology Type of work (experimental, theoretical, simulations): Experimental / Simulations Number of students: 1-2

136


Optical and electrical properties of amorphous and crystalline group IV materials

Description: Silicon, germanium and tin belong to group IV of the periodic table. When these elements are ordered in a crystal, they become semiconducting and exhibit unique optical and electrical properties. The degree of structural ordering determines these properties. Silicon is the most widely used semiconductor material, especially in electronics and photo voltaics (PV). Alloying Si with Ge lowers the band gap and increases the carrier mobility. Even higher carrier mobilities and lower band gaps can be obtained by alloying Ge with Sn. Higher carrier mobilities are useful to increase the switching speed of electronic devices. Low band gap energies are useful to better match the solar spectrum in PV applications or for infrared photodetectors.

In this project SixGeySn1-x-y layers will be characterized. The optical and electrical properties in function of composition will be determined. The influence of order (amorphous, poly crystalline and single crystalline) on the optical and electrical properties will be investigated. The ordering and crystal quality will be measured by X-ray diffraction (XRD). Atomic force microscopy will be applied to get information on the surface morphology and roughness. Absorption spectroscopy will be used to determine the extinction coefficient and deduce the optical band gap energy. The carrier mobility and concentration will be investigated with Hall effect and capacitance-voltage measurements, respectively. SiGeSn layers, deposited by molecular beam epitaxy or plasma enhanced chemical vapor deposition, will be provided to the student.

The main goal of this thesis is to determine the optical and electrical properties of amorphous and crystalline semiconducting layers of group IV. Al2O3 substrates will be used as transparent substrate for absorption spectroscopy measurements. Si and Ge substrates will be used to obtain crystalline layers of high structural quality.

The activities of this master thesis include absorption spectroscopy, X-ray diffraction, atomic force microscopy, Hall effect and capacitance-voltage measurements to investigate the optical band gap, crystal quality, surface morphology, carrier mobility and carrier concentration, respectively.

Promoter: Prof JW Seo, Prof JP Locquet


Daily supervision: Dr Ruben Lieten

137


Type of work (experimental, theoretical, simulations): experimental , simulations


138


In-situ atomic layer / molecular beam deposition and characterization of oxide high mobility semiconductor interfaces.

Description:

To drive further the performance of MOS technology, there is an increased focus on replacing Si by semiconductors with a higher carrier mobility (e.g. Ge, GaAs, InGaAs or InP). The key stumbling block preventing high performance III-V MOS devices is the presence of a high density of defects at the interface between the semiconductor and the dielectric. While traditional deposition techniques such as atomic layer deposition (ALD) are widely used for the deposition of dielectrics, they are not well suited to control the interface properties. On the other hand, ultrahigh vacuum techniques such as those used in molecular beam epitaxy can provide a much better prepared and cleaner semiconductors surface state.

In this project we will combine the best properties of both deposition approaches with in-situ characterization. Using our ultrahigh vacuum systems, we will first prepare different dedicated semiconductor surface configurations (substrate termination, specific reconstructions, monolayer deposition, interface templates, etc). The properties of these surfaces will be verified with different in-situ analysis techniques. In a second step, these surfaces will be introduced into the ALD deposition system and the growth of the oxide ALD layers will be performed. As the oxide layers are build up, their properties will again be monitored in-situ.

The main goal of this thesis is to find that oxide interface configuration on high mobility semiconductors that leads to the lowest defect density. The starting substrates will be Ge, GaAs and InGaAs (for the semiconductors) and Al2O3 for the gate oxide. The activities of the student will include the substrate preparation with MBE as well as the growth of the oxide with ALD, besides using the different in-situ characterization methods.

These research activities are well aligned with our international industrial partners and the student will be able to exchange results and interact with them on a regular basis including visits.

Promoter: Prof JW Seo, Prof JP Locquet, Dr. Jean Fompeyrine (IBM Research)


Daily supervision: Dr Ruben Lieten, Drs Tomas Smets, Drs Chenyi Su


139

Type of work (experimental, theoretical, simulations): Number of students: 1 or 2

140




Nanoparticles for Electron Emission Cancer Tumor Treatment

Description: Many different chemical and physical routes are currently followed of the treatment of tumor cells. One such method is based on the natural emission of Auger electrons from radionuclides such as 123I, whereby one decay releases about 15 electrons with an average energy of 7.5 keV. This methods has several disadvantages and an alternative method is to use photo-excited electrons from K and L shells under x-ray radiation as illustrated in the adjacent Figure. These electrons will be emitted from a nanoparticle (NP).

From a fundamental viewpoint, one of the key challenges is to determine the optimal size, shape and material composition of the NP that will lead to the maximum amount of double DNA strand breaks for the lowest irradiation dose. For this, novel alloy core-shell nanoparticles will be designed1 -- as illustrated in the above Figure -- and their electron emission spectrum will be simulated numerically.

From an experimental point of view, alloy NP will be synthesized in a core-shell structure using different methods2. In the next step, the NP will be functionalized using antibodies that bind to cancer cells. Finally, the functionalized NP will be dispersed in cancer cel cultures, their uptake will be determined and the therapeutic effect of the x-ray irradiation on the tumor growth rate will be determined.

This project can be performed both from a fundamental as well as from a practical viewpoint. The activities will take place in the framework of a collaboration with industrial partners.

1F Van den Heuvel et al., Phys Med Biol, 55, 4509-4520 (2010)

2S Pal et al., J. Nanoscience and Nanotechnology 10, 775 (2010).

Promoter: Prof JP Locquet, Prof F Van den Heuvel, Prof S. Nuyts, Prof J Lammertyn, Prof JW Seo


Daily supervision: Dr Edina Couteau, Dr Karel Knez

141

Graduating option: Master in Physics / Master in Nanoscience and Nanotechnology Type of work (experimental, theoretical, simulations): Experimental / Simulations


142


Theoretical study of strongly correlated electron systems

Description: The theoretical description of interacting many-particle systems remains one of the grand challenges in condensed-matter physics. Solving the full many-particle Schrodinger equation is impossible, as the computational effort increases exponentially with system size. One solution is to treat the electron-electron interactions at a mean-field level, reducing the many-electron problem to a single-electron problem. Models based on this approximation, e.g. density functional theory (DFT), are very successful at explaining the properties of weakly correlated systems, but generally fail at describing properties due to strongly correlated electrons such as metal-insulator transitions, magnetoelectricity, high Tc superconductivity, colossal magnetoresistance, …Another approach is to simplify the full Hamiltonian to a model Hamiltonian. This simplified model can’t explain the detailed features of real materials, but still can give a good quantitative description. However, even for the simplest model, in which only the on-site Coulomb interaction is considered, the exact solution is only knows for the one dimensional model. Therefore, various approximations were developed to gain insights into the model. The dynamical mean-field theory (DMFT), is such an approximation which maps the lattice onto a quantum impurity model subject to a self-consistent condition.

The real breakthrough in describing strongly correlated electron systems came recently, with the combination of DFT and DMFT (DFT+DMFT). The strategy here is based on the observation that although DFT often leads to qualitatively wrong results for the strongly correlated materials, it can usually provide quite reliable parameters for these systems. These parameters can be in turn used to construct a many-body Hamiltonian which is specific for the particular material under study.

The main goal of this project is to study strongly correlated electron systems like those showing a metal-insulator transition (V2O3, VO2) or multiferroic behavior (BiFeO3, BiMnO3) in connection with the experimental work performed in the group. The activities of the student will include the further implementation of the impurity solver as well as the application to real materials. Extensive programming experience is a plus.

This project is performed in close collaboration with ETH Zurich and the student will be able to exchange results and interact with them on a regular basis including visits.

Promoter: Prof JP Locquet, Prof JW Seo Faculty/research group: Faculty of Science / Faculty of Engineering

Daily supervision: Drs Bart Ydens, Drs Peter Staar (ETH Zurich)


143

Type of work (experimental, theoretical, simulations): theoretical, simulations Number of students: 1 or 2

144


Particles in Nanodrops: Improving Medical Diagnostics

Description:

Drug tests, hormone tracing, virus detection, monitoring of biomarkers for cancer ... all these tests require a reliable and rapid analysis of blood or serum samples. In order to develop more sensitive methods of analysis, there is a trend towards miniaturization of the equipment (Yager et al. 2006, Nature; Weibel et al. 2007, Nature Reviews). The sample preparation and concentration of target molecules becomes increasingly important.

In this thesis, a proof of concept lab-on-a-chip biosensor will be developed, combining drop-based microfluidics and magnetic microparticles to achieve nanoliter scale sample analysis. The nano-drops are generated at high speed in microchannels – up to thousands of drops a second – resulting in a high throughput setup combined with an extremely low consumption of sample and reagents. Using magnetic microparticles with immobilized antibodies or DNA on the surface, the molecules of interest can be caught in of the blood or serum. With external magnets, the particles are separated and the amount of bound molecules can be determined using standard quantification techniques such as fluorescence.

The student will start with designing the chip configuration and can participate in de micro-fabrication of the lab-on-a-chip in PDMS polymer. The droplet size of the blood or serum and manipulation of the magnetic particles in the drops will need to be optimized, aided with CFD modeling of the microfluidic system. The microfluidic setup will be used in the biosensor assay: extract specific target molecules, such as allergens, hormone or DNA from blood or serum and determine the concentration with fluorescence microscopy.

Depending on his interests and experience, the student can direct this research towards experimental optimization, modeling or the (bio)-chemistry of the assay.

For more information visit www.biosensors.be

Promoter: Jeroen Lammertyn

Faculty/research group: Faculty of Bioscience Engineering, MeBioS Biosensors

145

Daily supervision: Bert Verbruggen (and Karel Knez)

Graduating option: Bioscience Engineering (Bionanotechnology) or Nanosciences

Type of work (experimental, theoretical, simulations): Experimental and simulations


146


Digital lab-on-a-chip as an innovative platform for stem cell research

Description:

Lab-on-a-chip technology offers revolutionary analysis platforms for numerous biological and chemical applications. On such a lab-on-a-chip, different laboratory processes are integrated and miniaturized on a microchip of maximum a few centimeters size. The goal of these miniaturized systems is to complete a wide variety of (bio)chemical analyses on a very automated way with maximum sensitivity.

There are two ways to transport liquids (reagents) on a lab-on-a-chip: as a continuous flow or as a discrete amount of liquid. In your research, fluids are manipulated as individual liquid droplets with a volume in the nanoliter range. A key advantage of working with droplets is that the execution of all laboratory protocols such as pipetting, diluting and mixing is done on a micro- to nanometer scale.

The lab-on-a-chip research domain is very promising and finds its applications in medical diagnostics, DNA synthesis, and genomics. For cell-based assays, digital lab-on-a-chip technology offers great potential for the miniaturization and parallelization of experiments, while offering a convenient way to integrate sample preparation and automated cell and reagent handling on-chip.

Your goal will be to investigate the potential of digital lab-on-a-chip technology for performing adherent cell-based assays on stem cells. Using microfabrication techniques, you will introduce micron-sized cell-adhesion sites on the digital microfluidic chip. Next, a viability study will be performed to confirm that immobilized stem cells remain viable on the chip platform. The cells will be manipulated in suspension and as adherent cells. Next, the culturing of stem cells on-chip will be evaluated. To demonstrate the applicability of the chip platform for performing automated cell-based assays, a transfection assay will be performed on-chip. Stem cells will be transfected with a plasmid encoding green fluorescent protein expression in cells.


Promoter: Jeroen Lammertyn Co-promoter: Robert Puers

Faculty/research group: Faculty of Bioscience Engineering, MeBioS Biosensors

147

Daily supervision: Daan Witters

Graduating option: Bioscience Engineering (Bionanotechnology) or Engineering Type of work (experimental, theoretical, simulations): Experimental Number of students: 1

148


Automated optical DNA mapping using a digital lab-on-a-chip

Description:

Lab-on-a-chip technology offers revolutionary analysis platforms for numerous biological and chemical applications. On such a lab-on-a-chip, different laboratory processes are integrated and miniaturized on a microchip of maximum a few centimeters size. These miniaturized systems are mainly used to complete (bio)chemical analyses in an automated high throughput fashion.

There are two ways to transport liquids (reagents) on a lab-on-a-chip: as a continuous flow or as a discrete amount of liquid (‘digital microfluidics’). In your research, fluids are manipulated as individual nanoliter droplets. The use of this system reflects the idea of a ‘true’ lab-on-chip integrating the different manual operations (pipetting, diluting, mixing, and reaction) at the microscale. The digital lab-on-a-chip (dLOC) analysis platform is very promising with respect to the implementation of bioassays, such as enzymatic assays, cell-based assays and proteomics.

In this thesis proposal, we aim to use this platform to execute DNA-combing and mapping studies in collaboration with the research group of prof. Hofkens. The DNA will be labeled with a fluorescent dye at specific sites along its length. It will then be deposited and stretched on a surface using a technique known as molecular combing. DNA combing (cfr. figure) will be achieved on the dLOC-platform by the introduction of small hydrophilic patches on the chip, using special micropatterning techniques. The DNA will then be visualized using advanced fluorescence microscopy techniques, such as dSTORM. The resulting image is a barcode of the DNA sequence that we call a DNA fluorocode.

This thesis will focus on (i) the optimization of this micropatterning technique (dimensions, biomaterials,…) for the DNA combing, on the digital lab-on-a-chip analysis platform, (ii) the study of specific DNA-hybridization, (iii) on-chip generation of DNA fluorocodes.The combination of both technologies (DNA fluorocodes and dLOC) will result in a very dedicated application, allowing the massively parallel DNA barcoding.


149

Promoter: Jeroen Lammertyn Co-promoter: Prof. Johan Hofkens Faculty/research group: Faculty of Bioscience Engineering, MeBioS Biosensors

Daily supervision: Steven Vermeir and Rob Neely

Graduating option: Bioscience Engineering (Bionanotechnology) or Nanosciences Type of work (experimental, theoretical, simulations): Experimental Number of students: 1

150


Modified building blocks for ultra-sensitive aptamers

Description: Aptamers are nucleic acid based macro molecules that can tightly bind to specific molecular targets. Like all nucleic acids, aptamers consist of linear sequences of nucleotides (A, U, T, C and G), typically with a length of 15-40 nucleotides. In solution, the chain of nucleotides forms intra molecular interactions that fold the molecule into a complex three-dimensional shape. The shape of the aptamer allows it to bind tightly to the surface of its target molecule. Because of the extraordinary structural diversity available in the sequence space, aptamers can potentially be developed against virtually any target molecule including proteins, enzymes and their active sites, virus particles but also toxins or even whole cells. This is achieved through systematic Evolution of Ligands by Exponential Enrichment (SELEX,

see inset).

With the recent emergence of novel technologies, the development and production of aptamers has become significantly more accessible. Therefore, aptamers can be instrumental in the development of new proteomics based bio-detection systems with applications in medical diagnostics and food safety, analogous to the highly-successful nucleic acid hybridization microarrays.

Recently, research has shown that the incorporation of modified nucleotides could lead to a significant increase in aptamer performance. One could envision that expansion of the set of naturally occurring nucleotides with new building blocks would allow for the development of aptamers with “protein like” properties without compromising the many advantages that aptamers hold over classic antibody technology.

To this end, synthetic or enzymatic methods need to be devised to efficiently incorporate these new building blocks in the aptamer sequence and additional insight is needed to better understand how different modifications will influence aptamer specificity and affinity. To achieve these goals, modern PCR and chromatographic technologies will be used in nanoparticle based immuno-assays and aptamer selections.


Promoter: Jeroen Lammertyn Faculty/research group: Faculty of Bioscience Engineering, MeBioS Biosensors

Daily supervision: Kris Janssen

151

Graduating option: Bioscience Engineering (Bionanotechnology) or Nanosciences Type of work (experimental, theoretical, simulations): Experimental


152


Nanostructuring of fiber optic surface towards improved biosensing

Description:

The Surface Plasmon Sensor, which uses visible light and a gold surface to excite a propagating electromagnetic wave which can be applied to quantify biomolecules, or even to follow up molecular reactions, is a very interesting biosensor. However this type of biosensor is fairly bulky and expensive and therefore not suited for small point of care biosensors. Recently we developed a fiber optic variant of this sensor, which is relatively cheap and compact. Controlled deposition of sensing structures on the sensing surface would allow a further improvement of the biosensor sensitivity.

In this thesis the gold surface will be nanostructured and different metal surfaces will be tested to improve the sensing surface towards higher biosensor sensitivity and stability. First, the existing gold adhesion on the fiber optic silica surface will be optimized. Afterwards, strategies will be explored to pattern/structure the sensing surface. Finally, functionalization of the surface will be optimized to use these surfaces in bioassays. The main application of this setup is DNA detection and discrimination of several bacterial strains.

The student will use molecular beam epitaxy technology to deposit the metal layers and to study the adhesion properties. Several factors will be crucial in this phase and the sputtering of the round fiber surface will be a real engineering challenge. Next the student will evaluate how and which nanostructures on the surface can be created. Finally the student will apply these structures on the biosensor and the most optimal biosensor configuration will be chosen for a thorough evaluation. The student has the option to focus his/her research efforts either on the patterning or biosensing.

This project is a collaboration between the physics and biosystems department. The opportunity of working in two departments will allow the student to learn a range of techniques and gain valuable insights in two different fields of science.


Promoter: Jeroen Lammertyn Co-promoter: Margriet Van Bael Faculty/research group: Faculty of Bioscience Engineering, MeBioS Biosensors Daily supervision: Karel Knez


153


154


Multiplexed single nanoparticle based bioassay in fiber optic nanowells. A promising tool to screen for protein biomarkers at subfemtomolar concentrations

Description:

The ability to detect single protein molecules in blood would enable the use of more sensitive diagnostic biomarkers. To detect low-abundance proteins in blood, a promising new tool has recently been described in Nature Biotechnology. In this thesis we will adapt this nanotechnology and go one step further.

Our assay will capture serum biomarkers on single nanoparticles decorated with specific antibodies and then label the immunocomplexes with an enzymatic reporter capable of generating a fluorescent product. After isolating the beads in 50-fl reaction chambers designed to hold only a single bead, we will use fluorescence imaging to detect single protein molecules. We expect this single-molecule enzyme-linked immunosorbent assay (digital ELISA) approach to detected as few as ~10–20 enzyme-labeled complexes in 100 μl of sample (~10−19 M), much lower than conventional ELISA.

The project involves three parts. First the student will have to learn how to make the nanowells and include the bioconjungated nanoparticles. Then, the digital ELISA test will be validated with a detection assay for hIgE, an important serum antibody involved in allergenic reactions. In a last phase some new innovation concerning the possibilities for multiplexing will be examined.

(Based on Rissin et al., Nature Biotechnology Volume: 28, Pages: 595–599, 2010)


155

Promoter: Jeroen Lammertyn Faculty/research group: Faculty of Bioscience Engineering, MeBioS Biosensors

Daily supervision: Kris Janssen and Jeroen Pollet



156


Surface nanopatterning for femtoliter droplet generation

Description:

Lab-on-a-chip technology offers revolutionary analysis platforms for numerous biological and chemical applications. On such a lab-on-a-chip, different laboratory processes are integrated and miniaturized on a microchip of maximum a few centimeters size. The goal of these miniaturized systems is to complete a wide variety of (bio)chemical analyses on a very automated way with maximum sensitivity.

A key advantage of working with droplets is that the execution of all laboratory protocols such as pipetting, diluting and mixing is done on a micro- to nanometer scale. Recent research efforts at the MeBioS biosensor lab have shown that local functionalization of the Teflon surface with hydrophilic micropatches allows femtoliter sized liquid samples to be generated with very high precision on the chip platform. This offers interesting applications for the functionalization of nanomaterials such as nanoparticles.

First, different fabrication techniques will be introduced in order to create the hydrophilic micropatches. In first instance, these will consist of conventional photolithographic techniques at the cleanroom facilities of ESAT. In a further stage, Focused Ion Beam (FIB) technology will be used to introduce hydrophilic patches in the nanometer range on the chip platform.

In a subsequent stage, you will learn how to locally deposit liquid samples and nanoparticles in these fabricated nanochambers. This will be achieved by immobilizing nanoparticles inside these hydrophilic patches and subsequently functionalizing them with biomolecules such as DNA or antibodies. Finally, you will use the functionalized lab-on-a-chip for detecting very low concentrations of DNA or proteins. This makes the digital lab-on-a-chip very promising for applications in different fields of biosensing technology.


Promoter: Jeroen Lammertyn Co-promoter: Robert Puers Faculty/research group: Faculty of Bioscience Engineering, MeBioS Biosensors

Daily supervision: Daan Witters and Frederik Ceyssens

157

Graduating option: Bioscience Engineering (Bionanotechnology) or Engineering Type of work (experimental, theoretical, simulations): Experimental


158


Luminescent patterning of nanostructured materials Description: In contrast to bulk silver metal, small subnano-sized silver clusters, consisting of only a few atoms, have pronounced luminescent properties. The main challenge for synthesizing such clusters is their stabilization, as they tend to aggregate into larger, inert particles. By incorporation of such clusters in the molecularly sized cages and channels of zeolite materials, this undesired aggregation can be efficiently avoided. Our research team recently succeeded in the creation of well-defined monodisperse reduced silver clusters in zeolites by a light-induced autoreduction of silver ion exchanged zeolites. Interestingly the formed clusters show peculiar bright fluorescence, with colors that vary as a function of cluster type. As the process is light-induced, diffraction-limited patterns of fluorescence can be ‘written’ inside a single silver-zeolite crystal (see figure).

In this project, the photoactivation process will be explored in more detail. More in particular, we would like to get grips on the complex kinetics of this process. Moreover, we will aim for pushing the spatial resolution beyond the diffraction limit. By using a state-of-the-art femtosecond-pulsed laser systems in a two-photon excitation approach, the non-linear nature of the photoexcitation process can be exploited for resolution enhancement. The possibility of creating nanopatterns inside individual zeolite crystals opens many perspectives for use as smart bio-labels, as microscopic safety labels or even as base materials for the creation of photonic crystals. Promoter: Johan Hofkens, Co-promotor: Johan Martens Faculty/research group: Laboratory of Photochemistry and Spectroscopy

Daily supervision: Gert De Cremer

Graduating option: Natural science and Bio-engineering



159


Study of colloidal phase transitions of nanoparticles by direct visualization with super resolution optical microscopy Context: One of the most promising developments in fluorescence microscopy is the invention of schemes that allow obtaining an improved, nanoscale, resolution in fluorescence microscopy. To date, two types of approaches have successfully established. The first one is based on zero-intensity-based read-out (STED), the second one on stochastic photoactivation and localization of single molecules (PALM/STORM). The PALM method is based on cycles of stochastic switching on, reading out and switching off of individual fluorophores. Within a cycle, the activated molecules should be well enough separated from each other (further apart than the distance resolved by the microscope). It is then possible to localize with high precision the centroid of the individual fluorescent signals for each cycle and construct a subdiffraction-limited image of the sample incorporating all the centroid positions of all the cycles. With these super resolution optical microscopy modes, objects as small as 30-50 nm can be imaged. The time scale of PALM/STORM and STED is sufficient to allow direct visualization of the dynamics of selected phase transitions of colloidal systems (30-50 nm fluorescent NPs). Objectives: The goal of this project is to use PALM microscopy and or STED microscopy for the real time, in situ study of phase transitions in colloidal systems. Work to be done: Until now mainly colloidal systems based on micrometer sized particles have been imaged by confocal fluorescence microscopy. We propose to expand colloidal science in the realm of nano by using superresolution microscopy. For this research task we will start with the investigation of the simplest possible experimental system of interacting particles: hard colloidal spheres (dye labeled nano-particles (NPs) that will be obtained via several collaborations). These NPs can then be modified by grafting them with polymer patches, which leads to directional and anisotropic interactions between the particles. The explicit goal of the project is to link the microstructure and dynamics of sub-micron particles with macroscopic properties, which also includes their investigation by established rheological methods (expertise of Prof Vermant) Expected results: One expected result is the first direct observation of phase transitions of nanometer sized colloidal particles. We also expect to establish the influence of different types of interactions (between the NPs) on colloidal dynamics. Promoter: Johan Hofkens, co Promoter Jan Vermant (CIT) Faculty/research group: Faculty of Science, Laboratory for Photochemistry and Spectroscopy

Daily supervision: Hiroshi Uji-i

Graduating option: Natural sciences, Engineering Type of work (experimental, theoretical, simulations): experimental Number of students: 2

160


Smart labels for bio-imaging Description: In contrast to bulk silver metal, small subnano-sized silver clusters, consisting of only a few atoms, have pronounced luminescent properties. Our research team recently succeeded in creating luminescent patterns of small silver clusters inside zeolitic host materials by laser-writing in silver ion exchanged zeolites. Upon illumination the silver ions undergo an autoreduction process yielding highly luminescent clusters. As the process is light-induced, diffraction-limited patterns of fluorescence can be ‘written’ inside a single silver-zeolite crystal (see figure).

This project will focus on one of the possible applications of this new approach: smart bio labels. We will attempt to functionalize the silver-exchanged nano-zeolites to make them compatible with typical biological buffers and to allow binding of the crystals to cells. Specific cells can then be labeled by writing a fluorescent code in the nano-zeolites attached to that cell. This particular cell can then be followed over extended periods of time and will remain recognizable by its code. Practically this project will consist of developing a coating procedure to seal the nano-zeolites from the buffer components and to add functional groups for cell binding. Moreover, we will aim for a real proof-of-concept of this principle on living cells. Promoter: Johan Hofkens, co promoter: Johan Martens Faculty/research group: Laboratory of Photochemistry and Spectroscopy

Daily supervision: Gert De Cremer, Charlotte David and Jeroen Vangindertael

Graduating option: Natural Sciences and Bio-engineering Type of work (experimental, theoretical, simulations): Experimental


161


Control and characterization of surface plasmons on nano-particle decorated metallic wires Context: Nano- and micrometer sized metal structures exhibit specific optical properties due to the resonant excitation of co-operative electron oscillation (surface plasmons polaritons: SPPs). The coupling of the incident light to electrons in metal allows the translation (i.e. guiding) of light energy via SPPs along nanometer to micrometer long wave-guiding structures. We recently observed the appearance of regular, high intensity spots along silver nano-wires as a response to wide field illumination. We tentatively attribute these spots to surface plasmon modes coupled to nanocrystals decorating the nano-wire. Indeed, the procedure to isolate silver nano-wires on a microscope cover slip comprises drop casting and spin coating of the solution used to synthesize the wires (polyol process). This solution also contains nano-crystals of silver of different size and shape. TEM images of the wires showing spots in wide field microscopy underpin this hypothesis as they show irregular features along the nano-wire. The topic of this master thesis is hence a full characterization of the above described observation. . Objectives: The topic of this master thesis is hence a full characterization of the above described nano-wires decorated with nanoparticles. Work to be done: To this end, we will measure a statistical sufficient number of wires and try to correlate the number of observed spots with the length of the wire, as well as the influence of different excitation wavelengths on the appearance of spots. Spectra of the observed spots will be recorded as well. These measurements will be complemented by TEM measurements. At the same time we will try to get control over the size and shape of the nano-crystals that eventually will decorate the mono-crystalline wires after depositing them as described above. The influence of size and shape of the nano-crystals on the spacing and intensity of the observed spots will be investigated. We will also address if it is possible to use the generated hot-spots for Raman measurements. Expected results: One expected result is finding a correlation between shape, size and composition of the nano-particles and the appearance of hot-spots along the nano-wire. We also expect to establish the possibility of measuring Raman scattering on remote excitation via Plasmon wave guiding. Promoter: Johan Hofkens, co Promoters Johan Martens, Hiroshi Uji-i Faculty/research group: Faculty of Science, Laboratory for Photochemistry and Spectroscopy

Daily supervision: Hiroshi Uji-i

Graduating option: Natural Sciences, Bio-engineering Type of work (experimental, theoretical, simulations): experimental Number of students: 2

162


Quantum conductance of carbon and boron materials Description: describe context, objective, work to be done, expected results Quantum conductance in organic nanostructures is a central domain of research in the field of nanomaterials. Besides a clear goal of miniaturization of electronic devices, the electronic conductance of nanomaterials, containing single or aggregates of several molecules allows to exploit new quantum phenomena, not accessible in bulk materials. The project specifically addresses the topic of electronic conductance through carbon and boron bucky balls (fullerene) sandwiched between two metallic electrodes. The main objective will be the study of the effect of vibronic dynamics of buckyballs on the electron conductance. Among the targeted results we expect to be able to demonstrate the possibility to achieve the adiabatic electron pumping regime of conductance via the strong Jahn-Teller effect on the buckyballs. The project is intended for students who wish to develop their research skills in theoretical material science. The work will include theoretical derivations and programming. An interesting link is: http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=4617132&isnumber=4616982 Promoter: Liviu Chibotaru and Arnout Ceulemans Faculty/research group: Faculty of Science/Dept Chemistry

Daily supervision: Erwin Lijnen

Graduating option: nanotechnology/Engineering and Nanoscience/Natural Sciences Type of work (experimental, theoretical, simulations): theoretical Number of students: 1

163


Dynamical properties of anisotropic nanomagnets Description: The dynamical properties of molecular magnets and magnetic nanoparticles involving metal ions in strong anisotropy limit (lanthanides, transition metal ions with unquenched orbital moments) are of primary interest from the point of view of fundamental research and for potential applications in the field of molecular spintronics and magnetic nanomaterials. Compared to the nanomagnets with weak magnetic anisotropy, the nanomagnets in the strong anisotropy regime exhibit new dynamical properties such as strong dependence of magnetic dynamics on the exchange interaction, several relaxation times and their non-monotonous behavior in applied field, toroidal magnetic moments and many others. The proposed project aims at a theoretical investigation of dynamics of magnetization in nanomagnets with strong magnetic anisotropy. To these end the quantum kinetic equations will be set up and solved for several representative examples. The results of this investigation will be applied for the explanation of novel dynamical properties of recently synthesized and experimentally studied nanomagnets. Promoter: Liviu Chibotaru Faculty/research group: Faculty of Science/Dept Chemistry

Daily supervision: Liviu Ungur, Erwin Lijnen

Graduating option: Nanotechnology/Engineering and Nanoscience/Natural Sciences Type of work (experimental, theoretical, simulations):theoretical, simulations Number of students: 1

164


Design of efficient single-molecule magnets

Description: Single-molecule magnets and single-chain magnets display the phenomenon of blocking of magnetization within one single molecule, thus playing the role of a ferromagnetic nanodomain. Given their nanometer (or even smaller) size , these nano-objects are widely viewed as the limit of miniaturization of magnetic storage devices and are therefore intensively investigated. In order to be efficient, the single-molecule and single-chain magnets should (i) possess a high barrier of reversal of magnetization, (ii) be addressable and (iii) be protected from the action of surrounding magnetic molecules. The proposed project aims at a theoretical investigation of blocking of magnetization in single-molecule magnets by combining ab initio quantum chemistry calculations with theoretical modeling. The main goal is to calculate the barrier of reversal of magnetization, to explain why some molecules possess this barrier and the other not and, finally, to predict the ways of enhancing the single-molecule magnet properties. A special attention will be devoted to molecules involving metal ions with strong spin-orbit coupling (lanthanides, actinides, 4d and 5d metals). Besides being strongly magnetic anisotropic (a necessary condition to obtain efficient blockage of magnetization), such molecules also display non-collinear magnetization, which allows designing of single-molecule magnets protected from the action of environmental magnetic field. Promoter: Liviu Chibotaru Faculty/research group: Faculty of Science/Dept Chemistry

Daily supervision: Liviu Ungur, Erwin Lijnen

Graduating option: Nanotechnology/Engineering and Nanoscience/Natural Sciences Type of work (experimental, theoretical, simulations):theoretical, simulations Number of students: 1

165


Molecular Archeology: Structural analysis of the of protein evolution applied on S. cereviseae MALS enzymes and their resurrected ancestors.

Abstract:

Evolution is driven by duplication and mutations of genes. There are different theory towards the driving forces of evolution, each attributing different origins and roles of such amino acid mutations. In this project we will structurally analyze the evolution S.cereviseae yeast MALS enzymes to analyze the influence of these mutations and validate the different evolutionary models. There are in total 7 different present day MALS proteins which evolved via different intermediates out of a single gene. These ancestor genes have been reconstructed and catalytic activity has been determined for each protein. During the evolution the enzymes have become specific for certain substrates.

In this project we will analyze these proteins on a structural level using crystallography and biomolecular modelling. The final goal is to develop better protein design tools.

This research will use experimental techniques (see below) and computational methods, as such interest in computational aspects is expected. This project is in collaboration with CMPG laboratory for Genetics and Genomics (prof. K. Verstrepen, K.U.Leuven and VIB)

Promotor: Prof. Marc De Maeyer

Co-promotor: Dr. Arnout Voet

Number of student: 1

Requirement: Biochemistry background Scientific software MOE Rosetta Laboratory techniques -protein purification -protein crystallization e-mail contact: [email protected]

166


Growth of carbon nanotubes through a membrane Description: Carbon nanotubes (CNTs) are molecular-scale tubes of graphitic carbon with outstanding properties. The diameter of a nanotube is in the order of a few nanometers while the length can reach up to several centimeters. They are among the stiffest and strongest fibers known, and have remarkable electronic properties and many other unique characteristics combined with light weight. For these reasons they have attracted huge academic and industrial interest. Nowadays high density, vertically aligned CNT “carpets” can be grown on a substrate. However, infinite length remains problematic because diffusion of reaction gases to catalyst particles becomes more and more difficult with the dense CNT carpet thickness, and the growth finally stops because of the obstruction of the gas flow. The aim of this master thesis is growing CNTs through a porous support material, which is one of the main objectives of our SBO-3 project “Light steel fibers / aCNTb’s” within the Nanoforce program funded by the Flemish Strategic Initiative Materials (SIM). CNTs will be grown by catalytic chemical vapour deposition using porous membranes loaded with catalyst particles on the pore walls. The main objectives of the project are: - Deposition of catalyst particles into the pore walls (dipp-coating, electrodeposition etc.) - New holder design for the CVD reactor: By considering the feeding gas flow through the pores, a new holder design needs to be made in order to ensure that sufficiently high amount of reaction gases flow through the pores. - Exploration of alternative porous support: also beside commercially available alumina membranes, innovative ideas of obtaining appropriate porous supports will be considered. - Study of the influence of the growth parameters, such as temperature, support, catalyst, reaction gases and gas flow Promoter: Prof. Maria Seo, Prof. Jean-Pierre Locquet Faculty/research group: MTM-SIEM, Physics-VSM

Daily supervision: Dr. Edina Couteau, Niels De Greef

Graduating option: engineering Type of work (experimental, theoretical, simulations): experimental


167


Measurement of mechanical properties of individual CNTs and CNT bundles. Description: Carbon nanotubes (CNTs) are molecular-scale tubes of graphitic carbon with outstanding properties. The diameter of a nanotube is in the order of a few nanometers while the length can reach up to several centimeters. They are among the stiffest and strongest fibers known, and have remarkable electronic properties and many other unique characteristics combined with light weight. For these reasons they have attracted huge academic and industrial interest. However, CNTs produced by the catalytic chemical vapor deposition (CVD) process exhibit substantially poorer mechanical properties than nanotubes grown by arc-discharge method. The reason is the incorporation of defects in the CNT structure, which is much more favoured at the temperatures typically used for catalytic CVD (700 – 1000°C) compared to 3000°C representative for arc-discharge processes. This master thesis aims at measuring the mechanical properties of individual CNTs as well as bundles of CNTs grown by CVD following different growth parameters (e.g. as temperature, catalyst, catalyst support, C-source, gas flows and gas mixture). For individual CNTs, the experiment will be carried out inside a transmission electron microscope (TEM) using an integrated atomic force probing holder. The measurement of CNTs bundles will be performed in a scanning electron microscope (SEM). Vertically aligned CNT carpets as well as CNTs grown on powders will be produced. After extraction and collection of CNTs and CNT bundles, they will be mechanically tested by optimizing and modifying the existing test set-ups. The ultimate goal is to study the role of relative slippage of individual CNTs within a bundle leading to a low shear modulus of CNTs. This master thesis project is linked to the SBO-3 project “Light steel fibers / aCNTb’s” within the Nanoforce program funded by the Flemish Strategic Initiative Materials (SIM) as well as to our KU Leuven GOA project “New model based concepts for nano-engineered polymer composites”. Promoter: Prof. Maria Seo, Prof. Jean-Pierre Locquet Faculty/research group: MTM-SIEM, Physics-VSM

Daily supervision: Dr. Edina Couteau, Niels De Greef

Graduating option: engineering Type of work (experimental, theoretical, simulations): experimental


168


Optical thin films for organic solar cells Description: In the organic photolvoltaics group of IMEC, we are work on solar cells containing thin organic layers. The unique properties of organic semiconductors enable light harvesting and electrical energy generation by thin layers with film thicknesses of about 50nm to 300nm. Due to the flexibility of organic chemistry highly absorptive, transparent or colored devices can be produced that are furthermore mechanically flexible and offer a potential low cost product. Within the framework of this project, the efficiency and optical properties of organic solar cells should be improved by the application of optical thin films. In general, optical thin films alter the transmission and reflection properties of surfaces by the application of structured layers with thicknesses in the order of the light wavelength. The candidate is going to start with the fabrication of antireflection coatings for increased light in-coupling. Later on more sophisticated systems containing conductive layers and dielectric mirrors will be produced and combined with organic solar cells of die=iff3erent composition. The unique properties and large variety of organic semiconductors enables a number of different applications. While for a standard solar cell a highly reflective broadband mirror is demanded, window applications might need a combination of transparency and spectrally selective high reflection. Fortunately, the design rules for optical thin films and the vast number of organic materials give a lot of freedom in the design according to the specifications. The work includes the design of layer systems, the fabrication in high vacuum systems and the optical analysis by different methods. Easily applicable optical simulation tools will improve the understanding of the investigated systems. Finally, the candidate will gain a deep insight into optical thin films in general and their implementation in organic solar cells in particular. Promoter: Prof. Paul Heremans Faculty/research group: IMEC Leuven, organic photovoltaics group

Daily supervision: Robert Gehlhaar

Graduating option: Type of work: 80% experimental, 20% simulations


169


Development of solution-based inorganic semiconductors for p-type thin film transistors Description: Organic p-type semiconductors achieving hole mobilities up to 1 cm2/(V.s) are nowadays well established in the development of low cost flexible electronic circuits such as radio-frequency identification tags (RFID-tags) and TFTs of display backplanes. Current research activities targeting CMOS applications involve, in addition to p-type organic semiconductors, n-type metal oxides. However, because of the much higher mobility of these last materials (up to 10-50 cm2/(V.s)) the circuit design requires to have much larger p-type organic TFTs than n-type metal oxide TFTs in order to achieve matching of the currents. For this reason material scientists are currently looking forward to the development of new p-type (inorganic) materials exhibiting high hole mobilities. Currently investigated p-type inorganic materials are typically metal oxides which have to be deposited by vacuum techniques such as sputtering or thermal evaporation. However, the instability of the involved metal-oxygen bonds limits the possible experimental conditions and influences the actual stoichiometry of the deposited layer. Since this might hamper future industrial applications, alternative processes – such as solution-based deposition methods- should be considered for the preparation of the p-type materials. In this work different solution-based processes will be evaluated for their suitability for the preparation of high mobility p-type inorganic semiconductors. The research is mostly experimentally oriented and involves laboratory work such as: preparation of different solutions from which the inorganic p-type semiconductor will be made, deposition of the material on top of substrates by various techniques (e.g. spin-coating), deposition of metallic source and drain contacts from high vacuum, and electrical characterization of the final TFT transistors. Cadidates for this topic must have practical experience in lab work involving chemicals (e.g. preparation of solutions, pH measurements etc.), be interested in performing electrical measurements, be familiar with data treatment, and speak sufficient well English for reporting (Dutch is an asset). Promoter: Prof. Paul Heremans Faculty/research group: IMEC Leuven, organic ad oxide transistor group

Daily supervision: Robert Muller and Maarten Rockelé

Graduating option: Type of work: 80% experimental, 20% interpretation


170


Nanostructured anti-reflecting coatings for organic solar cells Description: Organic solar cells offer the potential for low-cost, lightweight energy production, and efficiencies of organic-based solar cells have recently reached 8%. While significant effort has been focused on material and device architecture development, relatively little work has been made on improved light in-coupling strategies. Due to the index contrast between air and glass, reflection off this initial interface can be as much as 8%. As a consequence, less light enters the thin film device structure, and efficiency is reduced. In this topic, we propose to develop nanostructures that are able to effectively couple light into a thin film structure, and reduce reflection by at least a factor of two over the solar spectral region where organic solar cells are functional. Promoter: Prof. Paul Heremans Faculty/research group: IMEC Leuven, organic photovoltaics group

Daily supervision: Barry Rand



171


Degradation mechanisms in organic solar cells Description: Organic photovoltaic devices are one of the most promising applications of organic semiconductors. As organic semiconductors can be manufactured by low temperature processes, such as printing from solution based inks, these materials are compatible with flexible plastic substrates resulting in a lightweight, inexpensive and very practical product. Over the last years impressive progress has been achieved in organic photovoltaic device efficiency and promising roll-to-roll compatible deposition techniques have been also reported. This rapid technological development brings applications close-by, and consequently also the importance of device reliability. Cost evaluations suggest that a lifetime of 5-10 years is necessary with current power conversion efficiencies to achieve low prices. Nevertheless, currently only 1 year of outdoor lifetime was reported on polymer solar cells, other studies in accelerated conditions estimated the device lifetime to 2-3 years. Currently, polymer solar cells are comprised of a multilayer stack of a transparent anode, a polymeric interlayer, a photoactive bulk heterojunction composed of polymer and fullerene capped with an evaporated cathode. Reaction with oxygen and humidity as well as light induces degradation both in the volume and at the interfaces of these layers leading to multiple concurrent degradation mechanisms. Therefore discriminating between the parallel mechanisms is one of the biggest challenges in reliability research. The focus of this master thesis lies in the investigation of the degradation of charge transport and charge extraction in polymer based organic solar cells. Implementation of new device architectures, advanced electrical measurements will assist the distinction between the simultaneously occurring degradation mechanisms. Most of the work will be done in the state-of-the-art organic device processing lab of IMEC. The student will receive a broad training on full device processing (spin-coating, metal evaporation) and characterization tools. After a short training period it is expected that the student can work independently and focusing on his/her investigation.

Promoter: Prof. Paul Heremans Faculty/research group: IMEC Leuven, organic photovoltaics group

Daily supervision: Eszter Voroshazi



172


Transparent conductive electrode for organic devices Description: In order to make ITO free opto-electronic organic devices (LED’s and solar cells), there is need to produce as transparent as possible electrode with sufficient sheet conductivity. This can be realized maybe by using different oxides, combination of oxides with semitransparent metallic layers or combination of metallic grids with conductive polymers as PEDOT:PSS. This research focused on making those new types of electrodes and testing them in organic solar cells as a bench mark. Working in lab (practical work and applying a lot of experiments) is a must. Promoter: Prof. Paul Heremans Faculty/research group: IMEC Leuven, organic photovoltaics group

Daily supervision: Afshin Hadipour

Graduating option: Type of work: 70% experimental, 30% theory


173


Nanometer-scale dynamics in DNA enzymatic restriction

Context: Atomic force microscopy (AFM) is a relatively new microscopy technique that allows to resolve biomolecular structures with a resolution comparable to electron microscopy. However, in contrast to electron microscopy, AFM allows to image biomolecules in aqueous solution, which is a significant advantage. Indeed, the molecules maintain their hydrated (functional) state, and it is even possible to see dynamic interactions between individual molecules. Objectives: Here, we want to track the interactions of individual enzymes on DNA; this includes the target search (1D diffusion, hopping, intersegmental transfer) and the catalytic cycle (does the binding to the target site induce a bend or a loop in the DNA; (how) does the enzyme dissociate; ...). Except for these rather challenging time-resolved experiments, also other important questions in DNA restriction might be addressed: what is the multimerization state of the enzyme? What is the structural basis for the lower/ higher efficiency of supercoiled vs linear substrates?... Work to be done: AFM imaging of DNA and DNA-protein interactions (dried samples as well as time-resolved imaging in buffered aqueous solution), combined with standard biochemical techniques. Expected results: Proof-of-principle that AFM might be used to (qualitatively/quantitatively) characterize the important reaction steps in DNA enzymatic restriction Promoter: Prof. Steven De Feyter Faculty/research group: Science / Division of Molecular and Nano Materials

Daily supervision: Drs. Willem Vanderlinden



174


Structure and mechanics of DNA supercoiling by nanoscale imaging

Context: In the cell nucleus, many of the biomolecular machines generate torsional stress in the DNA while tracking the double helix. This might overwind or unwind the DNA, leading to positive or negative supercoiling respectively. Specialized enzymes, called topoisomerases, have evolved to release excess torsional stress, allowing vital processes such as transcription and replication to take place. Because this is especially important in actively dividing cells, topoisomerases are a preferred target for anticancer agents. It is however not clear how these enzymes recognize DNA supercoiling. Even worse, the structural features of DNA under different levels of torsional stress have not been elucidated. Objectives: Recent results in the lab have shown that it is possible to obtain quantitative information on DNA supercoiling at the single molecule level and with nanometer resolution, by using atomic force microscopy (AFM). The primary objective is to create and purify plasmid DNA molecules with well-defined torsional stress, which structure will than be quantitatively analyzed using AFM. Work to be done: Creating a wide range of topoisomers (chemically identical molecules but with different levels of supercoiling) and their separation by preparative (2D) gel electrophoresis. AFM on the purified samples. Quantitative analysis of the observed structures. Expected results: Fundamental insight in the mechanics and mechanochemistry of supercoiled DNA. An answer on how a small enzyme can recognize supercoiling. Promoter: Prof. Steven De Feyter Faculty/research group: Science / Division of Molecular and Nano Materials

Daily supervision: Drs. Willem Vanderlinden



175


Nano-photonic imaging techniques for optical metamaterials Description:

Throughout history, important advancements in material science have had a dramatic influence on humankind – from the Stone Age, that marked humanity’s first technological developments, to the Silicone Age, that brought modern electronics, computers, internet and the related social developments. In the past ten years, a new class of materials has emerged and it has quickly become the hottest topic in material science due to its counterintuitive optical behavior and revolutionary potential applications – metamaterials. Metamaterials are artificially engineered materials to possess unusual electromagnetic properties. Because they bring all the spectacular properties of metamaterials to the frequency range of the human eyes, optical metamaterials are particularly important when it comes to applications.

Optical metamaterials are mainly based on surface plasmon resonances – the property whereby, in metallic nanostructures, light can collectively excite surface electron waves. These electron waves have the same frequency as light, but much shorter wavelengths, which allow their manipulation at the nanoscale. In other words, with the help of plasmons, light can be captured, modified and even stored in nanostructures. This emerging nanotechnology could find applications in curing cancer, biochemical sensing, solar cells, optical computing, negative refractive index materials, and invisibility. The imaging of surface plasmons provides a direct way to map and understand the local electric fields that are responsible for the unusual electromagnetic properties of metamaterials; the imaging of surface plasmons, however, requires a bright master student to help us develop new imaging techniques. In the last few years, our team has discovered two new methods for visualizing plasmons in optical metamaterials – second harmonic generation microscopy and hotspot decoration mapping. We are looking for a student with strong interest in experimental work to help us in further developing the techniques and in performing experiments on plasmonic nanostructures. This is a great opportunity for a student looking to pursue a carrier in the booming fields of photonics and metamaterials. Part of the experiments will be performed in the Cell Imaging Core (CIC) at Gasthuisberg. Our team includes many foreign collaborators and, therefore, good level of English language is required. However, the most important qualifications for the student are his/hers enthusiasm for science and generally positive attitude to working within a team. Promoter: Prof. Victor V. Moshchalkov, Prof. Pieter Vanden Berghe Faculty/research group: Moshchalkov Methusalem Group

Daily supervision: Dr. Ventsislav K. Valev



176


Formation of superporous frameworks Zeolite molecular sieves are classic workhorses in adsorption, catalysis and sensing. Their ordered pore system with nanooporous channels, their robustnes and environmental tolerance make them unique functional materials. Although zeolite-based catalysts are used in almost half of all large-scale technological units, their main limitations arise from their restricted size of their channels of about 1 nm. Therefore, particular attention focusses on the development of new synthetic strategies for extra-large pore zeolites based on silicates and germanates. Current research showed that zeolites can be formed from nanostructured precursors which aggregate in a self-organization mechanism into the final microporous crystal structure. Combination of small and wide angle X-ray scattering (SAXS and WAXS), nuclear magnetic resonance (NMR), dynamic light scattering (DLS), scanning and transmission electron microscopy (SEM and TEM) are applied to understand the entire crystallization process – from molecular building block, to initial nuclei, to the final crystalline product. In case of the new germanosilicates some evidence indicates that germanate cubes play an important role to expand silica frameworks in a pillar-like fashion but direct proof still is missing. Further development and understanding of zeolite crystallization mechanisms can lead to achievements in both - zeolite preparation and new insight in their functions. The goal of this project is to improve insight into the molecular mechanisms of germanosilicate zeolite formation using SAXS, WAXS, DLS, SEM, TEM, NMR methods.

Promoter: Johan Martens/ Christine Kirschhock Faculty/research group: Center for Surfacechemistry and Catalysis

Daily supervision: Elke Verheyen

Graduating option: FBIW Type of work (experimental, theoretical, simulations): Experimental Number of students: 1

177


Lego Chemistry – reassembling building units from one structure into another Zeolites are intriguing silicate materials built from nanoscale structural units. Their ordered pore system with nanoporous channels, their robustnes and environmental tolerance make them unique functional materials. Consequently, almost half of all industry processes are based on zeolite catalysts. Of course, ideally, researchers should be able to create a new zeolite for a specific demand but a lot of more insight into the formation of zeolites is needed before these structures can be tailored for a specific need. Recently evidence emerged that zeolites form through oriented aggregation of nanoscale building units. This concept needs to be studied in more detail. A highly curious trans-formation of one zeolite structure into another can help. The Faujasite (FAU) and the Chabasite (CHA) structures are both built of hexagonal prisms in different linkings and FAU can be transformed into CHA by simply heating in KOH solution. Only FAU is able to form CHA - any other frameworksource fails to link the hexagonal prisms into CHA. The task ist to identify the path from one structure to the other by closely monitoring the nanoscopic building blocks and the evolution of the two crystalline phases during transformation. This study will be a great step towards identification of the building blocks and verify the concept of zeolite growth by the Lego-pathway. You will analyse the alumosilicate species in solution with liquid state NMR, IR and Raman spectroscopy, the solids with X-ray diffraction and solid state NMR. You also will learn the synthesis of nanoporous frameworks as you will prepare the samples you want to study by yourself. The whole project is embedded in an interdisciplinary team with as aim the mastering of nanostructured framework synthesis and material design.


Daily supervision: Elena Gobechiya

Graduating option: Type of work (experimental, theoretical, simulations): Experimental Number of students: 1

178


Unravelling and tuning crystal growth of nanosized metal-organic frameworks with second-harmonic scattering Metal-organic frameworks (MOFs) consist of metal ions that are bonded together by bridging organic groups, making the structure to extend infinitely in two or three dimensions and creating a uniformly structured nanoporous network. MOFs are a popular research topic because of their high promise for applications in materials science: they can be applied as catalysts, as conductive materials, as nanoporous light-weight magnets, as materials for spin-transition and as materials for gas storage and molecular separation.

In many applications, it is critical to have nano-sized MOFs of uniform size and shape, e.g. for thin sensor films, for controlled drug delivery, or as contrast agent for MRI imaging. This has lately led to much effort towards synthesizing such nano-sized MOFs, often by trial-and-error.

We have recently identified Second-Harmonic Scattering as a technique that can probe crystal growth of MOFs in real time. Uniquely the technique can give the size ánd crystallinity of the present structures simultaneously, and this starting from the very first bonds! Having this information will allow us to unveil the self-assembly process. Hence, it will allow defining synthesis strategies that lead to nano-sized MOFs of controlled size and shape.

Second-harmonic generation or frequency doubling occurs when a material is illuminated with very intense light such as laser light. A part of the laser light of frequency ω is then converted into light of exactly the double frequency 2ω. As SHG is very sensitive to the organization and symmetry of the system under investigation, it is an excellent probe for crystallization. The technique will provide size and crystallinity simultaneously starting from the first bonds between the metal ions and the organic ligands.

All the proposed research will be completely original and pioneering work. You will work in two research labs: the Centre for Surface Chemistry and Catalysis (COK) and the Laboratory for Molecular Electronics and Photonics (MEP). In the MEP group you will perform the real-time second-harmonic scattering during crystal growth. You will also use an SHG-microscope to evaluate the formed MOF-crystals. In the COK you will use an array of standard techniques to characterize the synthesized materials (X-ray diffraction, nitrogen sorption, Small-Angle X-ray Scattering, Dynamic Light Scattering, and Scanning Electron Microscopy).

Promoter: prof. Dirk E. De Vos (fac. of bio-engineering, Centre for Surface Chemistry and Catalysis), prof. T. Verbiest (fac. of Science, Laboratory for Molecular Electronics and Photonics).

Daily supervision: dr. Monique van der Veen


179


Holey MOFs – constructing highways for molecules Over the last decade, metal organic frameworks (MOFs), a new class of nanoporous materials, have attracted a great interest due to their fascinating properties and potential for sensing, catalysis, and adsorption. MOFs are synthesized from the reaction between organic and inorganic species to build up three-dimentional frameworks whose skeletons contain both organic and inorganic moieties only linked by strong coordinative bonding. In general, active sites confined in nanopores are often victims of their own success as they can impose severe mass-transfer constraints. To overcome this drawback, two basic strategies can be pursued: (1) shortening the diffusion lengths or (2) enhancing the effective diffusivity. Improved diffusion, can be accomplished by introducing mesopores into crystalline microporous materials, resulting in a new class of hierarchical porous materials, which provide highways for molecules entering the frame before reaching the active sites for sensing or catalysis. The aim of this project is to develop a method to induce mesoporosity in Cu3(BTC)2 encapsulated phosphotungstic acid (HPW) polyanions hybrid materials. Hierarchical mesoporous MOF will be synthesized by exploiting self-organisation concepts: Before the MOF framework components are added to the reaction volume a mesostructuring agent is used to provoke framework formation exclisively in the prestructured regions. Synthesis will occur at room temperature, solvothermal and hydrothermal conditions. The synthesized materials will be characterized by a scanning electron microcope (SEM), powder X-ray diffraction (XRD), small angle X-ray diffraction, N2 adsorption, and thermogravimetric analysis (TGA). During this project you will become familiar with a large number of synthetic and characterisation techniques and will be embedded in a large team working on the development of new high performance functional materials.


Daily supervision: Lik Hong Wee


180

z Master Nanoscience and Nanotechnology

Thesis title: Nanoscaled 3D Luminiscent Grids Description: Many future applications will depend on a reliable arrangement of luminiscent centers in a 3D grid, where each centre can be activated separately. Recently a new concept for achieving such an arrangement has been devloped. A crystalline metalorganic framework is assembled around individual Keggin type heteropolyanions. The Keggin ions in the composite are located on a cubic grid with a precise spacing of 1.9 nm. Depending on the water or solvent content the interaction of metalions in framework and functional guest can be switched. Up to now only the classic Keggin ions containing transitionmetals have been studied for this new class of materials. But Keggin ions are easily modified by exchanging these by luminiscent rare earth metal ions. The luminiscence of Keggin ion functionalised in this way is highly sensitive to the environment. The task which will be pursued in this thesis is to synthesise and to explore the optical and chemosensing properties of composites of metalorganic scaffold hosting luminsicent heteropolyanions. At first heteropolyanions will be functionalised following standard procedures. These then will be locked into the 3D array of the scaffold. The obtained materials will be thoroughly characterised by spectroscopic means and crystallographic structure analysis. The composites will also be evaluated for their response to the presence of solvent in the surounding. In an advanced state of the project the spatial resolution will be determined with which individual luminiscent centers can be activated. This project is embedded in two projects whereof one is studying the formation of metalorganic frameworks in detail whereas the other is questing for materials for a photocatalytic cell to directly convert sunlight into chemical energy. Promoter: Johan Martens/ Christine Kirschhock (FBIW), Tatjana Parac-Vogt (Department of Chemistry ) Faculty/research groups: “Centre for Surface Chemistry and Catalysis” and “Molecular Design and Synthesis”

Daily supervision: Sneha Bajpe and Gregory Absillis

Graduating option: FBIW Type of work : experimental Number of students: 1

181


Molecular domino: nanoscale positioning of transition metals during self-assembly of structured hierarchical composites Modern society depends on the availability of chemicals formed in a sustainable and energy conserving way. Transition metals as catalyst play a prominent role in this field. The design of highly selective materials, locking the active transition metal (TM) centers securely in a specific nanoscale environment is a sustainable route to accommodate environmental restrictions while increasing the energy efficiency of industrially important processes. Template directed positioning of TMs during self-assembly of hierarchical structures such as nanocapsules and their assembly in hierarchical structures is a highly promising strategy to exploit the full spectrum of transition metal functionality. Mastering the formation and properties of TM based assemblies enables their use as building blocks for increasingly structured, hierarchical materials. This ambitious goal requires detailed fundamental knowledge of the factors governing the assembly, stability and behaviour of TM colloid assemblies on nanoscale. This study will focus on decorated heteropolyacid colloid assemblies. Heteropolyacids can be used to arrange TM ions in specific spatial organisations. The functional nanoparticles then can be used as building blocks assembled by structural framework components in macroscopic hierarchical materials.

During this study you will become familar with probing interactions between molecular sized species leading up to their assembly into large structures. The understanding which will be gained in your project will be directly applied to generate new functional materials. You will be working in a multi-discplinary team, combining specialties in the field of transition metal chemistry, material characterisation and testing, and aiming at a detailed analysis of fundamental principles leading to functional materials and their applications. Promoter: Johan Martens / Christine Kirschhock Faculty/research group: Center for Surface Chemistry and Catalysis

Daily supervision: Eric Breynaert


182


Zeotronics: organic nano-electronics build into zeolites Electronics are manufactured on a continually smaller scale in order to be able to put as much as possible calculating capacity onto a single chip. The smallest possible entity is a molecule. That is why molecular materials, e.g. molecular nanowires, are intensively investigated. This research often faces the same problem: it is extremely hard to control the 3-D organization of these materials (instead of straight nanowires, usually a jumble of nanowires is obtained.

Zeolites can be the answer to this problem. The architecture of zeolite pores can control the organization of the molecular material in 3-D and this means that the electronic properties can be controlled on the molecular/nano level. That is the goal of this thesis: to assemble superior organic systems inside zeolites for electronic applications, more specifically opto-electronic applications. Opto-electronic materials manipulate light via an electric potential over the material and vice versa. They are necessary for the development of ultrafast light switches for telecommunication and the generation of THz waves for medical imaging and security screening.

In this thesis we focus on molecular systems in zeolites with a dipolar organization. This means that all dipolar molecules orient in the same direction, so a global dipole moment is maintained. This can happen spontaneously in zeolites, but we can also induce this process by applying electric fields. These dipolar molecular chains are very interesting because they can behave as diodes: electric current can only flow in one direction. And, very importantly, it is exactly from these systems that expect opto-electronic properties.

In this master thesis you will synthesize and characterize zeolite crystals of certain pore structures and crystal morphologies. From these crystals you will assemble well-thought out host/guest systems, as well with monomer chains as with in situ polymerized chains. Subsequently you will explore the opto-electronic properties of these systems.

You will use X-ray diffraction, Scanning Electron Microscopy, thermo-gravimetric analysis and polarized Infrared microscopy for the characterization of the crystals and the host/guest systems. To determine the opto-electronic properties you will use Second-Harmonic Generation Microscopy.

Promoter: prof. Dirk E. De Vos (fac. of bio-engineering, Centre for Surface Chemistry and Catalysis), prof. T. Verbiest (fac. of Science, Laboratory for Molecular Electronics and Photonics).

Daily supervision: dr. Monique van der Veen


Date post:	13-Jun-2020
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Master Nanoscience and Nanotechnology - KU Leuven · Master Nanoscience and Nanotechnology...

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