Research@Dept2015 · Research@Dept 2015 Poster Abstract Book ‐ Updated version 2 ‐ 23/4/2015...

Research@Dept2015

Monday April 27th, 2015, 8h45 – 18h00 Thermotechnisch Instituut, Heverlee

Poster Abstract Book updated version 2 – April 23rd, 2015

Department of Physics and Astronomy Research@Dept 2015 Poster Abstract Book ‐ Updated version 2 ‐ 23/4/2015

2/32

Programme

08h45 – 09h00 Welcome

09h00 – 10h30 Interdepartmental realities & dreams

Welcome & Vision

Joseph Indekeu, Department Chair of Physics and Astronomy

Listening matters

Monika Rychtarikova, Laboratory for Soft Matter and Biophysics

Fabrication and characterisation at the nanoscale

Jean‐Pierre Locquet, Laboratory of Solid State Physics and Magnetism

The Physics of DNA

Enrico Carlon, Institute for Theoretical Physics

AEROSOL: Astrochemistry of old stars: direct probing of unique chemical laboratories

Leen Decin, Institute of Astronomy

BREATHE: The new IvS‐CmPA initiative

Conny Aerts, Institute of Astronomy

To “Steer” or not to “Steer” Steven De Feyter, Department Chair of Chemistry

10h30 – 11h00 Coffee break

11h00 – 12h30 Science Communication & Outreach

Why a scientist should (not) stay away from science communication

Geert Vanpaemel, Faculty of Economics and Business

Pump up your visibility

Conny Aerts, Institute of Astronomy

The intellectual duty of a scientist to be more than an expert

Bart Pattyn, Institute of Philosophy

12h30 – 14h00 Lunch break

14h00 – 15h30 Global Concerns

Set‐up of climate models

Olivier Giot, Royal Meteorological Institute of Belgium, Brussels

Social Media and Science ‐ a wedding made in Heaven... or in Hell?”

Erik Duval, Department of Computer Science

15h30 ‐17h30 Poster session

16h00 – 18h00 Concluding remarks and reception


3/32

Poster Abstracts

Table of Contents

1. Astronomy & Astrophysics ............................................................. 51.1. X. Fang, Multidimensional modelling of Coronal Rain ................................................... 51.2. R. Huygen, The PLATO mission: PLAnetary Transits and Oscillations of stars ............... 51.3. A.J. van Marle, On the influence of interstellar magnetic fields on the shape of circumstellar bubbles ............................................................................................................ 61.4. J. Menu, The transition disk around TW Hydrae ............................................................ 61.5. D. Millas, Simulations of Jet‐Environment Interactions ................................................. 71.6. E. Moravveji, Mixing in Massive Stars ............................................................................ 71.7. G. Raskin, METIS, the Mid‐IR instrument for the E‐ELT ................................................. 71.8. G. Raskin, The Mercator Telescope: relevance, status and future ................................ 81.9. S. Regibo, ESA's Galactic Cencus .................................................................................... 81.10. P. Royer, Infrared Astrophysics: Science with Herschel‐PACS ..................................... 91.11. P. Royer, Herschel Space Observatory: The PACS instrument at KU Leuven ............... 91.12. A. Sans, Detecting the Milky Way's Building Blocks ..................................................... 91.13. V. Schmid, A mixture of tidally‐excited and kappa‐driven p‐ and g‐modes in the Kepler eccentric binary KIC10080943 ................................................................................... 91.14. B. Vandenbussche, The James Webb Space Telescope ............................................. 10

2. Biophysics .................................................................................... 112.1. Y. de Coene, Investigation of molecular mechanisms involved in optogenetic activation of neurons .......................................................................................................... 112.2. B. Gysbrechts, Light propagation in the brain at visible and NIR wavelengths ........... 112.3. B. Lannoo, Generation of oscillating gene regulatory network modules .................... 122.4. N. Kolomiiets, CuGeTe barriers and hydrogen induced dipoles at Pt/high‐k oxide interfaces from internal photoemission experiments ........................................................ 122.5. D. Pelegrín‐García, Human echolocation: active auditory perception of the environment ........................................................................................................................ 132.6. C. Spaas, Functionalizing layer thickness influences gold nanoparticle radiosensitization ................................................................................................................ 132.7. A. Ungureanu, The influence of amyloid β oligomers on the mechanical properties of the neuronal membrane: an AFM study ............................................................................. 142.8. K. de Wijs, Fluorescence Activated Cell Sorter Based on On‐chip Micro Vapor Bubble Jet Flow ............................................................................................................................... 14

3. Condensed Matter Physics ........................................................... 153.1. S. Boeckx, Back focal plane imaging of directional plasmonic nanoantennas ............. 153.2. B. van den Broek, First‐principles transport through Sn nanoribbons ......................... 163.3. F. Cerbu, Spectroscopy of gap states in amorphous and crystallized HfO2 ................ 163.4. S.K. Dhayalan, Structural understanding of Epitaxial Si:P layers ................................. 163.5. J.‐Y. Ge, Bound vortex dipoles generated at pinning centers by Meissner current .... 173.6. S.P. Gurunarayanan, All Plasmonic Logic Devices ........................................................ 173.7. S. Iacovo, Multi‐frequency electron spin resonance study of inherent Si dangling bond defects at the thermal (211)Si/SiO2 interface .................................................................... 18


4/32

3.8. T. Ivanova, DBA‐based molecules on Au(111): From single molecules to quantum dot molecular networks ............................................................................................................ 183.9. J. K. Jochum, Study of phonon mediated phenomena using synchrotron light .......... 193.10. A. Kasina, Stable glass properties of glycerol revealed by simultaneous dielectric and a.c calorimetric measurements .......................................................................................... 193.11. S. Kerman, On‐chip Optical Trapping by Focusing Grating Outcouplers ................... 203.12. K. Levrie, Electrochemically in‐situ synthesized DNA probe arrays ........................... 203.13. Y. Li, Tuning the structure and magnetic properties in cobalt doped silicon clusters 213.14. Z. Li, Manipulation of Cl Vacancies and atoms in Ultrathin NaCl Insulating Films by an STM Tip ................................................................................................................................ 213.15. H. Liu, Manipulating the asymmetry of magnetization reversal in epitaxial CoO/Co films ..................................................................................................................................... 223.16. O. Madia, Charge transition level of GePb1 centers at interfaces of SiO2/SiGe/SiO2 heterostructures investigated by PAS ................................................................................. 233.17. Md. Mahmud‐Ul‐Hasan, Single Molecule Fluorescence Spectroscopy on a Chip ..... 233.18. M. Menghini, Metal‐insulator transition and low temperature resistive switching of VO2 microbridges ................................................................................................................ 243.19. F. Piero, Tolerance of Pt clusters to CO poisoning induced by Sn, Ag, Mo and Nb doping ................................................................................................................................. 243.20. K. Schouteden, Scanning tunneling microscopy: Ultra‐high vacuum and low temperatures ...................................................................................................................... 253.21. M. V. Shestakov, White light generation and non‐linear optical properties of Ag nanoclusters and nanoparticles dispersed in glass host ..................................................... 253.22. S. Thayumanasundaram, Towards better batteries ................................................... 263.23. N. Verellen , Optical nanoantennas – controlling light at the nanoscale .................. 27

4. Nuclear Physics & Nuclear Solid State Physics .............................. 274.1. M. Bisht, Electric field polarity dependent modification of the metal/ferroelectric oxide interface chemistry ................................................................................................... 274.2. C. Granados, In Gas Laser Ionization and Spectroscopy of neutron deficient Actinium isotopes ............................................................................................................................... 284.3. E. Menéndez, Planar GMR in laterally modulated Co/(Co‐CoO) microscale patterns . 294.4. F. Renzi, Study 7He with 6He(9Be,8Be) reaction ......................................................... 294.5. K. van Stiphout, The reaction of ultrathin Ni films with Ge ......................................... 30

5. Theoretical Physics ....................................................................... 305.1. M. Laleman, Probing DNA‐protein interactions ‐ combining theory and experiment. 305.2. C‐Y Lin, Holographic surface superconductivity/superfluidity ..................................... 315.3. K. Moors, An improved model for surface roughness in metal nanowires ................. 315.4. W. Xintian, Critical phenomena of a single defect ....................................................... 31

6. Physics Education ......................................................................... 326.1. L. Bollen, Investigating students’ use of the divergence and curl in electrodynamics 326.2. P. Coppens, Students and signals ................................................................................. 32


5/32

1. Astronomy & Astrophysics

1.1. X. Fang, Multidimensional modelling of Coronal Rain Xia Fang, Rony Keppens, Chun Xia, Tom Van Doorsselaere CmPA, Mathematics Department, KU Leuven, Belgium We present multidimensional, magnetohydrodynamic simulations of coronal rain appearance with grid‐adaptive computations covering a long ($>6$ hour) timespan in which shows that rain showers can occur in limit cycles for the first time in 2.5D setups. The simulations show how thermal instability can induce a spectacular display of in situ forming blob‐like condensations which then start their intimate ballet on top of initially linear force‐free magnetic arcades. We quantify how in‐situ forming blob‐like condensations grow along and across field lines, and point out the correlation between condensation rates and the cross‐sectional size of loop systems where catastrophic cooling takes place. We discuss dynamical, multi‐dimensional aspects of the rebound shocks generated by the siphon inflows and quantify the thermodynamics of a prominence‐corona‐transition‐region like structure surrounding the blobs. Our virtual coronal rain displays the deformation of blobs into V‐shaped features, interactions of blobs due to mostly pressure‐mediated levitations, and gives the views of blobs that evaporate in situ or are siphoned over the apex of the background arcade. We find plenty of shear flows generated with relative velocity difference around 80 km s$^{‐1}$ in our simulations. These shear flows are siphon flows set up by multiple blob dynamics and they in turn affect the deformation of the falling blobs. In particular, we show how shear flows can break apart blobs into smaller fragments, within minutes.

1.2. R. Huygen, The PLATO mission: PLAnetary Transits and Oscillations of stars C. Aerts, J. De Ridder, S. Regibo, P. Royer, B. Vandenbussche, R. Huygen Instituut voor Sterrenkunde, KU Leuven, Belgium PLATO has recently been selected as the ESA M3 mission as part of ESA's Cosmic Vision 2015‐2025 programme. The main goal of the mission is to hunt for and characterise exoplanets around their host star. PLATO will monitor nearby stars and find tiny, regular dips in their brightness when a planet temporarily blocks a small fraction of the light from the star. PLATO’s 34 small‐aperture telescopes are expected to identify and characterise thousands of exoplanetary systems and determine accurately the radius, mass, and age of both the exoplanet and the host star using asteroseismology. In addition to the detection and characterisation of planetary systems, PLATO will provide a unique database of variable phenomena with high precision for which a full complementary science project is set up and led by the Institute of Astronomy in Leuven.


6/32

The PLATO mission will be launched in 2024 by a Soyuz launcher from Kourou. The nominal mission will last for about 6 years.

1.3. A.J. van Marle, On the influence of interstellar magnetic fields on the shape of circumstellar bubbles A.J. van Marle1 and N.L.J. Cox2 and L. Decin2 and Z. Meliani3 1Centre for mathematical Plasma‐Astrophysics, KU Leuven, Belgium; 2Institute of Astronomy, KU Leuven, Belgium; 3Observatoire de Paris, France; The extended circumstellar envelopes of evolved low‐mass stars display a large variety of morphologies. Understanding the various mechanisms that give rise to these extended structures is important to trace their mass‐loss history. We aim to examine the role of the interstellar magnetic field in shaping the extended morphologies of slow, dusty winds of asymptotic giant branch (AGB) and red supergiant (RSG) stars. Using the MPI‐AMRVAC magneto‐hydrodynamics code we simulate the interactions between stellar winds, the interstellar gas, and the interstellar magnetic field. This allows us to pinpoint the origin of so‐called eye shaped circumstellar envelopes of three carbon‐rich AGB stars. It also provides us with an explanation for the lack of hydrodynamical instabilities in the bow shock of the stellar wind of the RSG alpha‐Orionis.

1.4. J. Menu, The transition disk around TW Hydrae J. Menu1, R. van Boekel2, Th. Henning2, M. Benisty3, C. Chandler4, H. Linz2, and C. Waelkens1 1Instituut voor Sterrenkunde, KU Leuven, Belgium; 2Max Planck Institute for Astronomy, Heidelberg, Germany; 3Institut de Planetologie et de l'Astrophysique de Grenoble, France; 4National Radio Astronomy Observatory, Socorro, USA For over a decade, the structure of the inner "hole" in the transition disk of TW Hydrae has been a subject of strong debate. Observations at different wavelengths have been modeled largely on an individual basis, and by consequence the inferred size scales are not necessarily agreeing. The disagreement at different wavelengths can simply be an indication for inconsistency, but may as well point to radial changes in dust properties, e.g., caused by dust growth or the disk interaction with a sub‐stellar companion. To probe the innermost region of the protoplanetary disk, observations at the highest possible spatial resolution are required. We present new near‐ and mid‐infrared (VLTI/PIONIER and VLTI/MIDI) and millimeter (EVLA) interferometric data of TW Hya. On the basis of the new and archival data, we investigate the shortcomings of existing models, both on the inner‐disk and the outer‐disk scales. Using a genetic fitting algorithm, a detailed radiative‐transfer model is determined that reproduces the multi‐wavelength data set. The modeling work shows that: 1)


7/32

the inner disk structure agrees with surface‐density profiles following from hydrodynamical simulations for disks with a companion; 2) the (sub‐)mm data agrees with a centrally concentrated large grain population. Considering the latter observation, we indicate that the inferred surface densities agree with results from dust‐growth simulations in protoplanetary disks. A current "best model" is proposed.

1.5. D. Millas, Simulations of Jet‐Environment Interactions D. Millas1,2 and N. Vlahakis2 1Departement Wiskunde, KU Leuven, Belgium; 2Faculty of Physics, National and Kapodistrian University of Athens, Greece Jet ‐ environment interactions can produce interesting astrophysical phenomena and may explain features in jets such as the HST‐1 in M87. We simulate numerically the interaction between a relativistic, magnetized, axisymmetric jet with a selection of different environments, assuming that the poloidal component of the magnetic field is negligible at large distances from the source. Two different simulations are shown: the jet interacts with either a static atmosphere (first case) or with accreting material (second case). These interactions are explored by performing magnetohydrodynamic simulations of both the jet and the static atmosphere/Bondi accretion and may provide information about changes in the jet structure. We also examine if conditions which permit rarefaction to appear are created during the interactions and calculate the efficiency of the acceleration to compare with previous works. The simulations are performed using the PLUTO code, v.4.0 created by A. Mignone et al.

1.6. E. Moravveji, Mixing in Massive Stars E. Moravveji, C. Aerts Instituut voor Sterrenkunde, KU Leuven, Belgium Using the NASA Kepler satellite, KIC 10526294 was recently discovered by Papics et al. (2014) as a very slowly rotating and slowly pulsating late B‐type star. Its 19 consecutive dipole gravity modes constitute a series with almost constant period spacing. We carefully model the observed pulsation spectrum of this star, and constrain its internal structure. This star is pretty young (~ 63 million years old), and is 3.25 more massive than our Sun. We find that the size of the turbulent overshooting layer on top of its convective core is roughly equal to the Earth diameter.

1.7. G. Raskin, METIS, the Mid‐IR instrument for the E‐ELT G. Raskin, B. Vandenbussche, W. Pessemier, L. Decin, S. Regibo and C. Waelkens Instituut voor sterrenkunde , KU Leuven, Belgium ESO, the European Southern Observatory, has started the construction of the E‐ELT, the European Extremely Large Telescope with a 39‐metre main mirror. It will be the largest optical/infrared telescope in the world. The E‐ELT will tackle some of the highest priorities in ground‐based astronomy, like e.g. the study of Earth‐like planets


8/32

around other stars in the "habitable zones" where life can possibly exist. The Institute of Astronomy (IvS) of the KU Leuven is heavily involved in the construction of METIS, a thermal‐infrared imager and spectrograph, and one of the three first‐generation scientific instruments of the E‐ELT. Within the METIS consortium, the IvS is responsible for the control electronics and software, and for the calibration of the instrument, and it takes part in the definition of the METIS science case.

1.8. G. Raskin, The Mercator Telescope: relevance, status and future G. Raskin1 and F. Merges2 and J. Morren3 and J. Pérez Padilla2 and W. Pessemier1 and S. Prins2 and H. Van Winckel1 and Christoffel Waelkens1 1Instituut voor Sterrenkunde, KU Leuven, Belgium; 2Mercator telescope, La Palma, Spain; 3Departement Natuurkunde en Sterrenkunde, KU Leuven, Belgium In todays era of ever growing telescope apertures, a specific niche remains for meter‐class telescopes, provided they are equipped with efficient and dedicated instruments. In case these telescopes have permanent and long‐term availability, they turn out extremely useful for intensive monitoring campaigns over a large range of time‐scales, and this at only a fraction of the cost of a large facility. Moreover, for the observations of variable astrophysical phenomena, the sampling frequency and the campaign duration are in many cases much more relevant than the collecting power of the telescope. Flexible scheduling and time allocation allow small telescopes to rapidly seize new opportunities or provide immediate follow‐up observations to complement data from large ground‐based or space‐borne facilities. For obvious reasons, both long‐term availability and flexibility are very difficult to attain from large telescopes. The Mercator telescope, a 1.2‐m telescope installed at the Roque de Los Muchachos Observatory on La Palma (Canary Islands, Spain), successfully targets this niche of intensive monitoring and flexible scheduling. Mercator allows stellar astrophysicists to embark on intensive monitoring campaigns that cover an extremely broad range of time scales, extending from a few nights up to several years. It provides our astronomers with a wealth of high‐quality time series of high‐resolution spectra and of simultaneous three‐color precision photometry. The Mercator telescope is funded by the Flemish Community of Belgium and operated by the Institute of Astronomy of the University of Leuven (KU Leuven, Belgium).

1.9. S. Regibo, ESA's Galactic Cencus Regibo S., De Ridder J., Debosscher J., and the Instituut voor Sterrenkunde, KU Leuven Instituut voor Sterrenkunde, KU Leuven The main objective of the Gaia mission is to make a detailed study of our Milky Way, hence finding clues to its content, structure, dynamics, and formation history. A full‐sky survey will be performed during five years, at an unprecedented accuracy. This poster illustrates the range of scientific disciplines to which Gaia will contribute.


9/32

1.10. P. Royer, Infrared Astrophysics: Science with Herschel‐PACS P. Royer and B. Vandenbussche and R. Huygen and W. De Meester and K. Exter and S. Regibo and C. Waelkens Instituut voor Sterrenkunde, KU Leuven, Belgium The far infrared wavelength range is our only possible access to the energy released in dust‐obscured distant galaxies and star forming regions, and to observe spectroscopic diagnostics of those objects. This poster illustrates some achievements of the PACS instrument during the 2009‐2013 Herschel mission.

1.11. P. Royer, Herschel Space Observatory: The PACS instrument at KU Leuven P. Royer, B. Vandenbussche, R. Huygen, W. De Meester, K. Exter, S. Regibo, C. Jean, J. Blommaert, M.A.T. Groenewegen, C. Waelkens Instituut voor Sterrenkunde, KU Leuven The far infrared wavelength range is our only possible access to the energy released in dust‐obscured distant galaxies and star forming regions, and to observe spectroscopic diagnostics of those objects. This poster illustrates the involvement of the Institute of Astrophysics of the KU Leuven in the development, the calibration and the operations of the PACS instrument onboard the Hershel Space Telescope.

1.12. A. Sans, Detecting the Milky Way's Building Blocks Sara Alejandra Sans Fuentes, Joris De Ridder Instituut voor Sterrenkunde, KU Leuven, Belgium The Λ‐CMD model proposes that large galaxies, like the Milky Way, are the cumulative result of interactions, accretions and mergers over large time scales. Such events leave chemical and kinematic imprints within the host galaxy as incoming material is accreted. The relaxation time for most of the large accreted structures exceeds the galactic age, making them identifiable within either the 3D spatial domain and/or the 6D phase‐space; thereby leaving directly observable clues to the formation and evolution of the host galaxy within the stellar halo. In the case of the Milky Way, the stellar halo holds some of the best preserved fossils of our galaxy's formation in over‐densities such as the Sagittarius stream, Magellanic stream, and the Virgo over‐density etc. However their low surface density and broad spatial distribution have made detection by eye tedious and in some cases troublesome. While automated detection methods do exist, GAIA's upcoming unprecedented astrometry, photometry and spectroscopy provides an enormous data‐set which requires an algorithm with good time complexity and a comprehensive visualization of N‐dimensional space. We present the use of OPTICS, a density based clustering algorithm which satisfies both conditions, to detect structure and sub‐structure within the Milky Way stellar halo.

1.13. V. Schmid, A mixture of tidally‐excited and kappa‐driven p‐ and g‐modes in the Kepler eccentric binary KIC10080943 V. Schmid et al. Instituut voor Sterrenkunde, KU Leuven, Belgium


10/32

We present the analysis of four years of Kepler data and ground‐based spectroscopy of the pulsating double‐lined binary KIC10080943. The radial velocities reveal two early F‐type stars, with a mass ratio close to unity, in a 15.3364‐day orbit. This information and the photometric reflection signal provide crucial constraints for the modelling of the target’s seismic properties, which besides independent pulsations also contains tidal effects. In the highly structured pulsation spectrum, we identify six series of g‐modes equally spaced in period that bear signatures of the conditions near the cores of the two stars. Furthermore, we detect rotational splittings in both the g‐modes and p‐modes, allowing us to trace the rotation throughout the stellar interior and prove that both stars are pulsating as gamma Dor/delta Sct hybrids. We use these stringent observational constraints to evaluate stellar models and theoretically predicted tidal interactions among binary stars.

1.14. B. Vandenbussche, The James Webb Space Telescope B. Vandenbussche, L. Decin, W. De Meester, R. Huygen, P. Royer, C. Waelkens Instituut voor Sterrenkunde, KU Leuven, Belgium The James Webb Space Telescope (also called JWST) is a large, infrared‐optimized space telescope planned to be the successor of the Hubble Space Telescope. JWST is a partner project between NASA, ESA and the Canadian Space agency. The launch is planned in 2018. JWST will have a large mirror of 6.5 meters in diameter, and a sunshield the size of a tennis court. These won't fit into the Ariane 5 launcher so the mirror and the sunshade will be launched folded up, and will be unfolded in orbit. The telescope will carry four scientific instruments: the Near‐Infrared Camera NIRCam, the Near‐Infrared Spectrograph NIRSpec built by ESA and NIRISS build by the Canadian Space Agency, and the Mid‐infrared Camera and Spectrograph MIRI, built by a UK‐lead consortium of European and US research institutes, including KU Leuven. The MIRI instrument will operate between wavelengths of 5 to 27 microns, providing broad and narrow‐band imaging, a coronagraph and low resolution slit spectroscopy (R~100) using a 1024x1024 pixels (Si:As) array. The pixels scale will be 0.1". The integral field spectrograph will provide simultaneous spectral and spatial data on a field of view of 3.6" by 3.6" to about 7.6." by 7.6" with increasing wavelength. The wavelength range it will operate in is 5‐27 micron with a spectral resolution of about 3000. The MIRI instrument team at the institute of Astronomy at KU Leuven develops Ground support software, participates in ground tests at Rutherford Appleton Laboratories (UK), NASA's Goddard Space Center (MD), works on the MIRI calibration, MIRI operations strategy, MIRI pipeline software algorithms and detector characterisation. Thanks to the involvement in the MIRI instrument development, our institute has


11/32

prime access to JWST and prepares observing programmes on Exoplanet atmosphere spectroscopy, the origin of planetary systems / protoplanetary disks, Protostars and outflows and Evolved Stars in nearby galaxies.

2. Biophysics

2.1. Y. de Coene, Investigation of molecular mechanisms involved in optogenetic activation of neurons Y. de Coene1, C. Bartic1, K. Clays1, V. Baekelandt2 1Faculty of Physics, KuLeuven; 2Faculty of medicine, KuLeuven Understanding the pathophysiology of many complex neural disorders (like Alzheimer’s, Parkinson’s, depression, obsessive compulsive disorder, etc.) requires the ability to selectively interfere and record the neural activity underlying the brain processes. ‘Optogenetics’ describes a variety of techniques for specifically controlling the neural activity with light (Fiala et al. 2010). Optical control has several advantages in comparison to classical electrical or pharmacological control. By genetic targeting, control can be achieved in a cell type‐specific manner. In contrast, electrical stimulation and drug compounds can interfere with all cell types. In the case of electrical stimulation because of the unselective nature of electricity (e.g. it chooses the path of least resistance). Non‐specific effects are a major concern of pharmaceuticals. This project will focus on molecular and in vitro cellular investigation of linear and nonlinear optical properties of opsins relevant for the cellular activation and also for their use as voltage sensitive probes. Also, very little is known about the spatial localization of opsins expressed in mammalian neurons. The concrete goals of this project are to quantify the molecular nonlinear optical parameters of several opsins (hyperpolarizability(β), two‐photon absorption (TPA) cross section) and to investigate the membrane localization and activation of opsins expressed in cells under two‐photon illumination. The data obtained would allow further deploying the potential of optogenetics by building efficient in vivo stimulation strategies (relevant for all neuromodulation applications) as well as in combining neuromodulation with optical readout (relevant for all basic research in neurophysiology).

2.2. B. Gysbrechts, Light propagation in the brain at visible and NIR wavelengths B. Gysbrechts1, L. Wang1, N. Nguyen Do Trong2, Z. Navratilova3, H. Cabral3, F. Battaglia3, W. Saeys2, C. Bartic1 1Soft Matter and Biophysics, KU Leuven, Belgium; 2MeBIOS, KU Leuven, Belgium; 3Donders Institute, Radboud University, The Netherlands Optical stimulation of the brain gained a lot of attention in neuroscience due to its superior cell‐type specificity. In the design of illumination strategies it is essential to predict how light propagates in a specific tissue. This requires knowledge of the


12/32

optical properties of that tissue. We present the estimated absorption and reduced scattering in rodent brain tissue using non‐destructive contact spatially resolved spectroscopy. The obtained absorption and scattering in the cortex, hippocampus and striatum are similar, but significantly lower than in the thalamus, leading to a less deep but broader light penetration profile in the thalamus. Next, the light distribution was investigated for different stimulation protocols relevant for fiber‐optic based optogenetic experiments using Monte Carlo simulation. The temperature increase of the tissue during irradiation was calculated for relevant stimulation protocols in order to evaluate the potential of thermally induced side effects.

2.3. B. Lannoo, Generation of oscillating gene regulatory network modules B. Lannoo , M. van Dorp , Q. Thommen , B. Pfeuty , M. Lefranc , E. Carlon 1Instituut voor Theoretische Fysica, KU Leuven, Belgium; 2Laboratoire de Physique des Lasers, Atomes et Molécules, Lille1, France As a first step towards understanding the complex behavior of Gene regulatory networks (GRN), a lot of effort has been devoted in studying the dynamics of smaller modules in the past decades. Here we focus on modules in which a target protein oscillates in time. Oscillatory behavior is found in many processes in the cell. For instance the circadian rhythms are driven by genetic modules, but there are also oscillations which are sub circadian like those in NF‐kB, p53, Wnt … For the production of these modules we used an improved version of the evolutionary algorithm proposed by François and Hakim. The most crucial part of this algorithm is the design of a score function used to define which elements are considered the fittest. Here we show this score function, the simplest modules capable of showing oscillatory behavior and the characteristics of the heterodimer autorepression loop module, which shows some interesting characteristics not yet discussed in the literature.

2.4. N. Kolomiiets, CuGeTe barriers and hydrogen induced dipoles at Pt/high‐k oxide interfaces from internal photoemission experiments N. Kolomiiets1 , V. Afanasiev1, L. Goux2, W. Devulder3, K. Opsomer2, M. Houssa1, A.Stesmans1 1Department of Physics and Astronomy, KU Leuven, Belgium; 2Imec, Belgium; 3University of Gent, Belgium Interface barriers determine major electron transport properties and built‐in voltage in memory cells. Thanks to its thermal stability and high vacuum work function, platinum (Pt) is widely used for prototyping metal‐oxide‐semiconductor (MOS) devices. Using the spectroscopy of internal photoemission of electrons, we evaluated the barrier heights Φe between the conduction band of various dielectrics and the Fermi level of Pt or CuGeTe alloys , and the possible impact of: a) alloy composition, b) thermal budget, c) interface dipoles, d) annealing in hydrogen.


13/32

2.5. D. Pelegrín‐García, Human echolocation: active auditory perception of the environment D. Pelegrín‐García, M. Rychtarikova and C. Glorieux Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Belgium In the absence of vision, audition takes a predominant role for sensing the environment. By making use of self‐generated sounds, like tongue clicks or finger snaps, trained blind (or even sighted) people are able to recognize echoes from distant surfaces and are thus able to identify obstacles, walls, room size and cornersâ€”similarly to the echolocation ability of bats and other animal species but with a lower accuracy. This knowledge enables them to orient themselves more easily than non‐echolocating blind people in unknown environments. In our project, we have developed an auditory virtual reality system, which allows a flexible control of the sound reflections in response to self‐generated oral sounds. In this way, we have been able to measure the sensitivity of human echolocation (i.e. the smallest detectable objects) by untrained sighted people. We have also validated the system in dynamic conditions, such as finding the incidence direction of reflected sounds through echolocation.

2.6. C. Spaas, Functionalizing layer thickness influences gold nanoparticle radiosensitization C. Spaas1, R. Dok2, O. Deschaume1, L. Wouters1, V.S. Rangasamy1, S. Thayumanasundaram1, B. De Roo1, J.W. Seo3, C. Bartic1, P. Hoet4, F. Van den Heuvel2, S. Nuyts2, J.P. Locquet1, C. Van Haesendonck1 1Department of Physics and Astronomy, KU Leuven, Belgium; 2Department of Oncology, KU Leuven, Belgium; 3Department of Materials Engineering, KU Leuven, Belgium; 4Department of Public Health and Primary Care, KU Leuven, Belgium With as main prospective the localized eradication of malignant cells, the radiosensitization of gold nanoparticles (GNPs) is most effective in close proximity to the cellular DNA. However, the functionalizing polymers or antibodies, necessary for the internalization to the nucleus, attenuate the irradiation dose enhancement caused by the GNPs. By evaluation of the relaxation pattern of supercoiled DNA (scDNA), in suspension with functionalized GNPs, the influence of the nanoparticle capping layer thickness on the radiosensitizing effect of GNPs is demonstrated. Therefore, different sizes of organic coatings, build up with PEG polymers of MW 1 to 20 kDa are applied on GNPs with diameters of 5 to 30 nm. After controlled irradiations of the suspensions, the molecular damage of the DNA, assessed with gel electrophoresis, displays a mainly circular and linear configuration. Consecutive image analysis and quantification concludes that on average 63% of the radiosensitizing efficiency is lost when the radial dimensions of the functionalizing layer are increased from 4.1 to 15.3 nm. An experimental supplement is thereby provided for biophysical simulations and demonstrates the influence of an important parameter in the development of nanomaterials for targeted therapies in cancer radiotherapy.


14/32

2.7. A. Ungureanu, The influence of amyloid β oligomers on the mechanical properties of the neuronal membrane: an AFM study A. Ungureanu1,2, I. Benilova2,3, C. Van Haesendonck1, C. Bartic1,2 1Laboratory of Solid State Physics and Magnetism, KU Leuven, Celestijnenlaan 200D, B‐3001, Leuven, Belgium; 2Imec, Kapeldreef 75, B‐3001 Leuven, Belgium; 3VIB Center for the Biology of Diseases, ON 4Campus Gasthuisberg, Herestraat 49, B‐3001, Leuven, Belgium, Alzheimer ‘s Disease (AD) is correlated with toxic effects induced by particular conformations of small amyloid β (Aβ) peptides produced in the cell membrane [1]. A wide range of evidence shows that Aβ in oligomeric forms are inducing neurotoxic effects such as the disruption of Ca2+ homeostasis, activation of free radicals production, asymmetric carpeting of cellular membrane, tau protein phosphorilation [2].The affinity and insertion of Aβ oligomers into the neurons membrane seems to be dictated by the membrane properties that are changing during aging [3,4]. To determine the importance of the age factor in AD we employed fluorescence microscopy and AFM in studying the Aβ interaction with young and senescent cultured hippocampal neurons. AFM is a powerful and versatile technique allowing the mechanical characterization of attached living cells in their physiological condition (optimal media, temperature and pH) [4]. Our results show that the aged hippocampal neurons, the most susceptible to the Aβ toxicity, and show more pronounced changes in their membrane/actin cortex and cytoskeleton elasticity when exposed to the toxic oligomeric species. References: [1] Membrane incorporation, channel formation, and disruption of calcium homeostasis by Alzheimer’s β–Amyloid protein [2] Membrane and surface interaction of Alzeheimer’s Aβ peptide‐insights into the mechanism of cytotoxicity, Thomas L. Williams and Louise C. Serpell, The FEBS Journal, 2011. [3]Differing modes of interaction between monomeric Aβ1‐40 peptides and model lipid membranes: an AFM study, khizar Sheikh et al., Chemostry and Physiscs of Lipides, 2012. [4] Lipid change in the aged brain: Effect of synaptic function and neuronal survival, Maria Dolores Ledesma, Mauricio G. Martin, Carlos G. Dotti, Progress in Lipid Research, 2012. [5] Cellular Biomechanics Investigated by Atomic Force Microscopy, B. a Smith, McGill University, Montréal, 2004

2.8. K. de Wijs, Fluorescence Activated Cell Sorter Based on On‐chip Micro Vapor Bubble Jet Flow K. de Wijs1, C. Liu2, A. Dusa3, D. Vercruysse4, B. Majeed5, L. Lagae6 1imec, Leuven, Belgium; 2Departement Natuurkunde en Sterrenkunde, KU Leuven, Belgium The instrument size, cost and trained operator requirements have prevented FACS from being truly amenable to portable applications and limited its use to core laboratories. We believe the main bottleneck preventing FACS evolution is the lack


15/32

of a technical solution for fast, accurate and generic single cell sorting in a disposable chip. Here we report a rapid microfluidic cell sorter platform (µFACS) based on on‐chip vapor bubble jet flow. In the µFACS chip (42 x 18 mm2) cells were sorted by a thermal jet flow, whose principle is similar to thermal inkjet printers. Cells were hydrodynamic focused into a channel and fluorescently detected. Two jet flow generators were placed downstream the detection spot, one on each side of the channel. Every jet flow generator consisted of 288 micro thermal hotspots placed in a chamber, where micro vapor bubbles were created by joule heating. The dedicated heater design led to rapid (< 10 µs) thermal vapor formation at specific nucleation spots. The ensemble creation of vapor bubbles created a sudden pressure wave pulse in the jet flow generation chamber, and fired a jet flow into the main channel. Synchronized to the fluorescent cell detection, the jet flow deflected the passing cell into one of the outlets. As such, cells were sorted in the completely closed µFACS chip in the absence of aerosols or any mechanical moving part. Cell sorting was achieved at a flow speed of 0.8 m/s with a 30 µs wide sort pulse. The recorded jet flow life time of 100 µs allows up to 10,000 sorting events per second. To visually track the transient cell sorting behavior, stroboscopic illumination of the chip was used at distinct intervals when a cell was sorted. With 5 % flow speed variation limited by the fluidic system, a sorting accuracy of 93 % was achieved with 99% purity. A cell viability assay with PI & Annexin V labelling of monocytes indicated a 75 % viability for the sorted cells, compared to 80 % viability for the unsorted control cells.

3. Condensed Matter Physics

3.1. S. Boeckx, Back focal plane imaging of directional plasmonic nanoantennas S. Boeckx1 and D. Vercruysse2,1 and P. Van Dorpe2,1 and V. Moshchalkov1 and N. Verellen1 1Instituut voor Sterrenkunde, KU Leuven, Belgium; 2imec, Leuven, Belgium Plasmonic nanoantennas are small metallic nanoparticles that support collective oscillations of the conduction electrons in the particle, called surface plasmons. These oscillations occur at optical frequencies and as such these particles can be considered as antennas for light. We study the scattering patterns of these antennas using a technique called back focal plane imaging. Here, the Fourier plane of an objective lens is imaged rather than its image plane. By properly designing the antenna geometry the scattering pattern can be changed and shaped to a desired distribution. In particular, we are studying unidirectional antennas that scatter light in one preferred direction perpendicular to the incident light. Moreover, we show that the design of a double split‐ring resonator can switch these directions by tuning the wavelength. This type of antenna forms the basis for a directional color router that can be used for bio‐sensing or on‐chip communication applications.


16/32

3.2. B. van den Broek, First‐principles transport through Sn nanoribbons B. van den Broek1, M. Houssa1, G. Pourtois2, V.V. Afanas'ev1, A. Stesmans1 1KULeuven, Physics & Astronomy, Belgium; 2imec, Multiscale Modeling group, Belgium

3.3. F. Cerbu, Spectroscopy of gap states in amorphous and crystallized HfO2 F. Cerbu1, V. Afanasev1, J. Lisoni2, A. Stesmans1, M. Houssa1 1Department of Physics and Astronomy, Semiconductor Physics Section, KU Leuven, Belgium; 2IMEC, Leuven, Belgium; Energy distribution and density of defect energy levels inside the bandgap of insulating HfO2 were evaluated using photoionization/photodepopulation experiments. The studied samples were prepared by atomic layer deposition of 19 nm HfO2 or Hf0,8Al0,2OX films on top of 7.5 nm thick SiO2 layer thermally grown on (100)Si surface. By observing the illumination ‐induced oxide charge variations in the non charged state and the electron‐injected samples we were able to evaluate the density of donor and acceptor states, respectively. The energy levels of trapped electrons are found in the wide energy range below conduction band bottom in the 5.6‐eV wide HfO2 bandgap. Upon crystallization to cubic phase by annealing at 1000 0C, a band of deep electron traps emerges at (3 eV≤ Et ≤4 eV). In the amorphous Hf0,8Al0,2OX layers more shallow trap distributions are found at (1.8 eV≤ Et ≤3 eV).

3.4. S.K. Dhayalan, Structural understanding of Epitaxial Si:P layers Sathish Kumar Dhayalan1,2, Jonatan Slotte3, Eddy Simoen2,4, Geoffrey Pourtois2, Roger Loo2, Andriy Hikavyy2, Erik Rosseel2, Yosuke Shimura1,2, Wilfried Vandervorst1,2 1Dept of Physics, Instituut voor Kern en Stralingsfysica, K.U.Leuven, Celestijnenlaan 200D, 3001 Heverlee (Belgium);2Imec, Kapeldreef 75, 3001, Leuven (Belgium); 3Dept of Applied Physics, Aalto University School of Science, Finland; 4Dept of Solid State Sciences, University of Gent, Belgium The microelectronics industry is currently in the 14nm node where FinFET based devices have been started to be used. Introduction of Source ‐Drain stressors to FinFETs is a promising approach to continue scaling of FinFETs. Usually SiGe:B S/D stressors are preferred for p‐type FinFETs and Si:P or Si:C:P S/D stressors are preferred for n‐type FinFETs. In recent studies, Si:P S/D stressors have received much attention. P has a reduced covalent radius than silicon and hence doping Si with > 1% of P leads to a reduced lattice constant in the resulting material. Sandwiching a Si fin between such a layer would exert tensile strain upon the Si fin and aids in improving the mobility of electrons. The benefit of improed mobility as well as better conductivity are expected from Si:P layers. However in the as epitaxially grown Si:P not all P atoms are active. Annealing leads to activation with slight reduction in strain. We try to understand the reason for inactive P using DFT simulations. Preliminary results indicate that P‐V complexes might be present which might be responsible for the deactivated dopants.


17/32

3.5. J.‐Y. Ge, Bound vortex dipoles generated at pinning centers by Meissner current Jun‐Yi Ge1, Joffre Gutierrez1, Vladimir N. Gladilin1,2, Jozef T. Devreese2, Victor V. Moshchalkov1 1Institute for Nanoscale Physics and Chemistry (INPAC), Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, B‐3001 Leuven, Belgium; 2Theory of Quantum and Complex Systems (TQC), Department of Physics, Universiteit Antwerpen, Universiteitsplein 1, B‐2610 Antwerpen, Belgium One of the phenomena that make superconductors unique materials is the Meissner‐Ochsenfeld effect. This effect results in a state in which an applied magnetic field is expelled from the bulk of the material because of the circulation near its surface of resistance‐free currents, also known as Meissner currents. Notwithstanding the intense research on the Meissner state, local fields due to the interaction of Meissner currents with pinning centres have not received much attention. Here we report that the Meissner currents, when flowing through an area containing a pinning centre, generate in its vicinity two opposite sense current half‐loops producing a bound vortex‐antivortex pair, which eventually may transform into a fully developed vortex‐antivortex pair ultimately separated in space. The generation of such vortex dipoles by Meissner currents is not restricted to superconductors; similar topological excitations may be present in other systems with Meissner‐like phases.

3.6. S.P. Gurunarayanan, All Plasmonic Logic Devices S.Gurunarayanan1,2 and N.Verellen1,3 and I.Radu1 and B.Soree1 and J.Van de Vondel3 and A.Stesmans3 and P.Dorpe1,3 and M.Heyns1,2 1imec,Belgium; 2Department of Materials Engg., KULeuven; 3Department of Physics and Astronomy, KULeuven Plasmons are collective excitations of an electron gas and are typically investigated in metals. Plasmons are being considered as a means of transmitting information in computer chips since they can support high frequencies (into the 100 THz range) and can propagate very fast. Also, plasmons are interesting for possible applications in logic devices based on interference. In spite of the fast advance in plasmonics, there are still important missing blocks before logic circuits with plasmons become feasible. For example, at the material level, the trade‐off between group velocity and wavelength needs further investigation. At the device level, electrical injection of plasmons needs to be demonstrated and at the detection side, work to improve plasmon detection using semiconducting photodetectors is needed. The main goal of this PhD is to study and demonstrate plasmonic circuits and their interaction with optical waveguides. The first phase of the work focusses on the electrical excitation/injection of plasmons. Electro‐migrated tunnel gaps were shown to emit light on application of potential between the electrodes in controlled environments like in STM. Electrons tunnel inelastically leading to the generation of gap plasmons which then couple out into the far‐field as photons. Preliminary FDTD simulations of tunnel gaps in ambient conditions show that gap plasmons can indeed be excited, which are very sensitive to the gap dimensions, the design of the


18/32

electrodes and finally to the applied potential. These localized gap plasmons can then couple to the propagating modes of the electrodes which act as plasmonic waveguides. Design optimization and experimental demonstration of the idea will conclude the first phase of the PhD. The second phase of the PhD will then focus on manipulating the injected plasmons for building very compact yet scalable logic devices. Such devices are expected to pave way for future high speed transmission technology.

3.7. S. Iacovo, Multi‐frequency electron spin resonance study of inherent Si dangling bond defects at the thermal (211)Si/SiO2 interface S.Iacovo2 and A. Stesmans1 1 Laboratory for Semiconductor Physics & LESEC, KU Leuven (Belgium) 2 Laboratory for Semiconductor Physics, KU Leuven (Belgium) Multifrequency low temperature electron spin resonance (ESR) studies were carried out to atomically assess inherent point defects at the thermal ‘higher index’ (211)Si/SiO2 interface. This reveals, as dominant imperfections, Pb‐type centers (generic entity Si3≡Si•, the dot represen ng an unpaired sp3‐like hybrid) occurring in densities of ~1 × 1013 cm‐2 for oxidation temperatures ~400 °C. On the basis of the pertinent ESR characteristics, the inherent basic defect is typified as the Pb0(211) variant, resembling closely the Pb0 center in standard (100)Si/SiO2. At the higher index (211)Si/SiO2 interface, this defect pertains to defected Si atoms located at (111)‐oriented terraces. Q‐band ESR saturation spectroscopy reveal a 29Si hyperfine (hf) doublet associated with the central Pb0(211) Zeeman signal, with hf parameters closest to those of the similar hf structure of the Pb0(100) defect in thermal (100)Si/SiO2, adducing support to the Pb0(211) typification. Combination of angular and frequency (n) dependent studies show the Pb0(211) peak‐to‐peak line width DBpp to be composed of a residual width (n®0) of 2.2 ± 0.1 G, to which dipolar broadening contributed an essential part, and a substantial inhomogeneous

broadening component due to g distribution, predominantly in g, induced by non‐uniform interface strain –also similar to the Pb0(100) properties.

3.8. T. Ivanova, DBA‐based molecules on Au(111): From single molecules to quantum dot molecular networks K. Schouteden1, Ts. Ivanova1, Z. Li1, V. Iancu1,2, K. Tahara3, Y. Tobe3, J. Adisoejoso4, S. De Feyter4, C. Van Haesendonck1 and E. Janssens1 1Laboratory of Solid State Physics and Magnetism, KU Leuven, 3001 Leuven, Belgium; 2Extreme Light Infrastructure‐Nuclear Physics/ Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering , Bucharest‐Magurele, RO‐077125, Romania; 3Graduate School of Engineering Science, Division of Frontier Materials Science, Osaka University, Toyonaka, Osaka 560‐8531, Japan; 4Molecular Imaging and Photonics, KU Leuven, 3001 Leuven, Belgium. Self‐assembled two‐dimensional (2D) molecular networks have an excellent potential as templates for memory, sensor and spintronic applications. In this study we demonstrate the effective confinement of surface electrons in the pores of molecular networks formed by dehydrobenzo[12]annulene (DBA) molecules with


19/32

butoxy groups (DBA‐OC4) on Au(111). Investigation of the network formation starting from single molecules reveals a strong interaction of the molecules with the substrate, which is at the origin of the observed confinement. Our findings open perspectives for use of DBA‐derivatives for obtaining highly ordered quantum dot arrays.

3.9. J. K. Jochum, Study of phonon mediated phenomena using synchrotron light K. Houben1, J. K. Jochum1, S. Couet2, T. Peissker1, R. Lieten1, M. Bisht2, M. Trekels2, D. Pérez2, B. Opperdoes1,2, D. G. Merkel3, A. Chumakov3, R. Rüffer3, M. Y. Hu4, J. Y. Zhao4, E. E. Alp4, A. Vantomme2, K. Temst2, M. J. Van Bael1 1Laboratory of Solid‐State Physics and Magnetism, KU Leuven, Belgium; 2Institute for Nuclear and Radiation Physics, KU Leuven; 3European Synchrotron Radiation Facility, France; 4Advanced Photon Source, Argonne National Laboratory, USA The behaviour of phonons influences many material properties, such as thermal and mechanical attributes. Furthermore, phonons have been identified to play an essential role in conventional superconductivity. When reducing the system’s dimensions to the nanoscale, the phonon behaviour will deviate from the corresponding bulk phonon behaviour due to restriction of phonon propagation caused by e.g. grain boundaries. Due to the close relationship between critical temperature (TC) and phonon density of states (PDOS) it is imminent that the phonon confinement influences TC. Several different nanostructures have been characterized and their phonon behaviour has been investigated by nuclear resonant inelastic x‐ray scattering at the European Synchrotron Radiation Facility (ESRF) and the Advanced Photon Source. Softening of the high‐energy phonon modes, which resulted in an increase in TC of up to 11% has been observed. Not only the superconducting behaviour in Sn is phonon‐mediated, also the structural phase transition from the α‐Sn to the β‐Sn phase is driven by phonons. The semiconducting α‐Sn phase transforms into the metallic β‐Sn phase above a temperature of 286 K, driven by a change in vibrational entropy (Svib)[1]. α‐Sn thin films can however be stabilized at room temperature by choosing an appropriate substrate [2]. The Sn phase transition has been studied during an in situ experiment at the ESRF. Measuring the PDOS at different stages during transition provides a deeper insight into the mechanisms involved in the phase transition. Furthermore, thermodynamic properties, such as Svib, can be extracted from the experimentally obtained PDOS. The transition has been studied for different thicknesses, and an increase in the transition temperature with decreasing thickness has been observed. Equivalent to bulk, a strong increase in Svib during the transition from α‐ to β ‐Sn has been found. [1] P. Pavone et al. PRB 57 (1998) [2] B. Roldan Cuenya et al. PRB 64 (2001)

3.10. A. Kasina, Stable glass properties of glycerol revealed by simultaneous dielectric and a.c calorimetric measurements A. Kasina; M. Wübbenhorst


20/32

Departement Natuurkunde en Sterrenkunde, KU Leuven, Belgium Molecular dynamics and thermal signature of stable glycerol are investigated by means of in‐situ simultaneous broadband dielectric spectroscopy and ac‐calorimetric measurements. The glasses are produced by slow vapour deposition of organic molecules from the gas phase to a cooled target at a temperature well below the glass transition temperature. After deposition the dielectric and calorimetric signal are monitored during slow heating from the glassy state to complete liquid transformation and finally to desorption of the liquid film.

3.11. S. Kerman, On‐chip Optical Trapping by Focusing Grating Outcouplers S. Kerman , T. Claes, D. Vercruysse, Md. Mahmud‐Ul‐Hasan, P. Neutens, V. Mukund, X. Rottenberg, L. Lagae, P. Van Dorpe 1imec; 2KU Leuven Department of Physics Dielectric particles like cells are attracted to where the light has the highest intensity. Manipulation of particles by exploiting those optical forces has been widely used for the detection of biological particles. This usually implies the use of bulky, expensive conventional optical building blocks, like microscopes. The recent advances in integrated photonics and lab‐on‐chip technology, however, has spurred interest to miniaturize optical trapping. We propose to trap anywhere in the channel by custom focusing of the light using tailored waveguide‐fed diffraction gratings. In addition, we propose to detect trapping events by collecting fluorescent light from the trapped object using other diffraction gratings and integrated waveguides, which will pave the way for a complete integration of trapping and detection of micro‐objects on Si chips.

3.12. K. Levrie, Electrochemically in‐situ synthesized DNA probe arrays K. Levrie1,3, Tim Stakenborg1; Pol Van Dorpe1,2; Liesbet Lagae1,2 and Chris Van Hoof1,3 1IMEC, Leuven, Belgium; 2Department of Physics and Astronomy, KU Leuven, Belgium; 3Department of Electrical Engineering (ESAT), KU Leuven, Belgium The human body consists of several trillion cells. Despite having virtually identical DNA, all cells ‐ even within a tissue ‐ can show a drastically different morphology or behavior. For instance, in solid tumors, large cell heterogeneity has been observed and a better understanding of this cell diversity holds the promise to revolutionize future cancer therapies. However, most current technologies are typically based on ensemble measurements impeding analyses at the single‐cell level. As an answer to this need, a disruptive methodology called spatial transcriptomics has recently been developed by Joakim Lundeberg and his group at the SciLifeLab in Stockholm. Here, using a DNA array, expressed nucleic acids are locally hybridized and linked to unique barcodes for positional identification during sequencing. As this approach will help to unravel the real diversity of cells within their natural microenvironment, this methodology will provide new insight in single‐cell dynamics as well as in the understanding of cellular processes and human life in general. As current DNA arrays are limited in various aspects including resolution, the aim of


21/32

the presented research is to develop a dedicated CMOS chip, including an active matrix coupled to electrochemically active electrodes, that allow in‐situ synthesis of a custom DNA sequence on each electrode. By taking advantage of state‐of‐the‐art lithographic processes, a dense DNA array with unprecedented, single‐cell resolution can be created.

3.13. Y. Li, Tuning the structure and magnetic properties in cobalt doped silicon clusters Yejun Li1, Nguyen Minh Tam2, Pieterjan Claes1, Alex P. Woodham3, Jonathan T. Lyon3, Vu Thi Ngan2, Minh Tho Nguyen2, Peter Lievens1, Andrei Fielicke3, Ewald Janssens1 1 Laboratory of Solid State Physics and Magnetism, KULeuven; 2 Department of Chemistry, KU Leuven; 3 Institut fur Optik und Atomare Physik, Technische Universitait Berlin

The structural, electronic and magnetic properties of cobalt doped silicon clusters, Si_nCo^+ (n = 5âˆ’8) and Si_nCo_2^+ (n = 8âˆ’12), are inves gated by a combined experimental and theoretical techniques. Experimental spectra are obtained by IR‐MPD spectroscopy on the corresponding clusterÂ∙xenon complexes, and the theoretical results are calculated by DFT using the B3P86 functional. For the singly doped cluster, Si_nCo^+ (n = 5âˆ’8), it is found that they all have exohedral structures and in general, the Co dopant prefers to substitute a Si atom of bare Sin+1+ clusters. Different from the singly doped clusters, the additional Co dopant of the doubly doped clusters, Si_nCo_2^+ (n = 8âˆ’12), favors to adsorb to the singly doped counterpart. Due to the introduction of the additional Co dopant and the possibility of multiple spin states, exist multiple isomers exist for each size. From Si9Co2+ onward, one of the Co is completely encapsulated inside the silicon cages. According to natural population analysis on the experimentally assigned isomers, the Co dopants in the singly doped clusters possess magnetic moments about 1.8âˆ’2 Âµ_B. For doubly doped clusters, the outside Co dopants s ll have the same amount of magnetic moments. Most surprisingly, the Co dimers of Si9Co2+ and Si10Co2+ are either ferro‐ or antiferro‐ magnetic coupled and the magnetic moments of the encapsulated Co dopants are partially retained (0.8 Âµ_B and 0.45 Âµ_B, respectively), although they are completely quenched for larger sizes (n = 11, 12). The magnetic coupling of the Co dimers in these clusters is found to be closely related to the distance between them and above certain critical distance, it is significantly reduced. The partial density of states (DOS) are analyzed to explain this distance dependent behavior and it is the interplay between the hybridization the Co dopants and the Si cages, and the coupling between the Co‐Co dimers that determines the magnetic properties of these clusters.

3.14. Z. Li, Manipulation of Cl Vacancies and atoms in Ultrathin NaCl Insulating Films by an STM Tip Zhe Li1, Koen Schouteden1, Koen Lauwaet1, Ewald Janssens1, Chris Van Haesendonck1, Peter Lievens1, Hsin‐Yi Tiffany Chen2, Gianfranco Pacchioni2, and Jorge I. Cerdá3 1Laboratory of Solid‐State Physics and Magnetism, KU Leuven, Celestijnenlaan 200 d – box 2414, BE‐3001 Leuven, Belgium; 2Dipartimento di Scienza dei Materiali,


22/32

Università di Milano‐Bicocca, Via Cozzi 55, I‐20125 Milano, Italy; 3Instituto de Ciencia de Materiales, ICMM‐CSIC, Cantoblanco, 28049 Madrid, Spain. During the last 20 years, using scanning tunneling microscopy (STM) and atomic force microscopy, scientists have successfully achieved vertical and lateral repositioning of individual atoms on and in different types of surfaces. Such atom manipulation allows the bottom‐up assembly of novel nanostructures that can otherwise not be fabricated. While the possibility of lateral manipulation of atomic vacancies across a surface lattice using an atomic force microscope has been predicted theoretically [1], experimental realization of controlled vacancy repositioning has not been achieved thus far. Here we use STM at liquid helium temperature (4.5 K) to create individual Cl vacancies and subsequently to laterally manipulate them across the surface of ultrathin sodium chloride films. The Cl vacancies can be created in thin NaCl films by bringing the STM tip into contact with the NaCl surface [2], which results in a single Cl vacancy at the location of the tip approach and at the same time in a chemically functionalized STM tip. The functionalized tips achieve a neat atomic resolution imaging of the NaCl(100) islands and metallic clusters. The STM tip induced lateral manipulation of the created vacancies allows monitoring the interactions between two neighboring vacancies with different separations. Our findings are corroborated by density functional theory calculations and STM image simulations. The lateral manipulation of atomic vacancies opens up a new playground for the investigation of fundamental physical properties of vacancy nanostructures of any size and shape and their coupling with the supporting substrate, and of the interaction of various deposits with charged vacancies. [1] T. Trevethan, M. Watkins, L.N. Kantorovich, and A.L. Shluger, Controlled Manipulation of Atoms in Insulating Surfaces with the Virtual Atomic Force Microscope, Phys. Rev. Lett. 98, 028101 (2007).

3.15. H. Liu, Manipulating the asymmetry of magnetization reversal in epitaxial CoO/Co films Hao‐Liang Liu1 and Steven Brems3 and Yu‐Jia Zeng1 and Kristiaan Temst2 and Andre Vantomme2 and Chris Van Haesendonck1 1Laboratorium voor Vaste‐Stoysica en Magnetisme, KU Leuven, Celestijnenlaan 200 D, BE‐3001 Leuven, Belgium; 2Instituut voor Kern‐ en Stralingsfysica, KU Leuven, Celestijnenlaan 200 D, BE‐3001 Leuven, Belgium; 3Imec vzw, Kapeldreef 75, 3001 Leuven, Belgium We investigated the training eect and magnetization reversal in CoO/Co bilayer lms grown epitaxially on MgO (001) substrates. The asymmetry of the magnetization reversal, which appears due to the exchange bias after eld cooling, survives after training, in contrast to the case of polycrystalline bilayers. By applying hysteresis loops with the magnetic eld perpendicular to the cooling eld, we are able to modify the orientation of the average uncompensated magnetization of the antiferromagnetic CoO. Subsequently, the untrained state can be partially restored, and more importantly the magnetization reversal asymmetry can be inverted by starting the perpendicular loop with the appropriate eld polarity. Consequently, we


23/32

succeeded in manipulating the magnetization reversal asymmetry and even in achieving opposite reversal asymmetries in the same exchange bias system.

3.16. O. Madia, Charge transition level of GePb1 centers at interfaces of SiO2/SiGe/SiO2 heterostructures investigated by PAS O.Madia1, N.Segercrantz2, V.Afanas'ev1, A.Stesmans1, L.Souriau3, J.Slotte2, F.Tuomisto2 1Semiconductor Physics Laboratory, KULeuven; 2Department of Applied Physics, Aalto University, Finland; 3IMEC Re‐charging of interface defects may impair microelectronic device performances and therefore requires reliable evaluation. In this work we addressed the trapping properties of Ge dangling bond (DB) defects ‐GePb1 centers as typified by electron spin resonance spectrometry (ESR)‐ found at the interfaces between the condensation‐grown Si1‐xGex (0.28<x<0.93) alloys and insulating SiO2. The ESR observation, at the temperature of 4.3K, of singly‐occupied paramagnetic GePb1 centers is complemented by temperature‐dependent positron annihilation spectroscopy in the Doppler broadening mode, which enables observation of the neutral‐to‐negative defect transitions as the temperature increases from 50K to 300K. Through correlation of this re‐charging behavior with the temperature‐induced shift of the Fermi energy in the Si0.27Ge0.73 alloy, the energy level of the Ge DB acceptor state is inferred to be energetically distributed in the interval between 0.02 and 0.13 eV above the top of the semiconductor valence band. This result refines previous estimates from capacitance voltage measurements, which detect only the negatively charge fraction of the GePb1 centers, and independently provides the affirmation that the energy levels of Ge DBs lie inside the bandgap of the Si1‐xGex alloys.

3.17. Md. Mahmud‐Ul‐Hasan, Single Molecule Fluorescence Spectroscopy on a Chip Md. Mahmud‐Ul‐Hasan1,2 ,Pieter Neutens1,2 ,Tim Steylaert1,Tim Stakenborg1,Liesbet Lagae1,2 ,Pol Van Dorpe1,2 1Imec, Kapeldreef 75, 3001 Leuven, Belgium;2KU Leuven department of Physics, Celestijnenlaan 200D, 3001 Leuven, Belgium The aim of this work is to develop an integrated nano‐photonic platform for single molecule fluorescence spectroscopy. This is an ideal bio‐sensing platform and will also allow to analyze protein‐protein interaction of many single molecules in parallel. The technology is based on near‐field excitation and collection using nanophotonic waveguides and is able to target and sense a single molecule, even in the presence of a large background. The platform is based on SiN which, like silicon, provides the combination of high‐index‐contrast and compatibility with CMOS processing technology. That made it possible to use the electronics fabrication facilities to make photonic circuitry for visible wavelength applications, for example integrated fluorescence and Raman measurements. The most important aspect of this single molecule study is to confine the excitation


24/32

light to a very small volume. We use the evanescent tail of the waveguide mode to have vertical confinement and nano‐fabrication is used to obtain lateral confinement by processing small holes in the top cladding of the waveguides. So a very small number of fluorescent molecule can be isolated and excited by this technique. The emission is also collected on chip by placing the resonator in the near field of the dye. That ensures the enhancement of the emission by using the Purcell‐effect. The numerical calculations using the Finite Difference Time Domain (FDTD) simulation confirms the viability of this project.

3.18. M. Menghini, Metal‐insulator transition and low temperature resistive switching of VO2 microbridges Mariela Menghini, Anton Brown, Pía Homm, Bart van Bilzen and Jean‐Pierre Locquet Functional Nanosystems Group, Dept. of Physics and Astronomy, KU Leuven, Leuven, Belgium

Metal‐insulator transition (MIT) in oxides has been a topic of long‐standing interest in condensed matter materials sciences. Among the different materials that show a MIT, particular attention is given to those that are promising for devices operable near room temperature wherein the phase transition can be triggered by small thermal, electrical, or optical perturbations. This is the case of vanadium oxide (VO2) with a MIT of about five orders of magnitude in resistance change at around 70 C in bulk crystals. These remarkable properties make VO2 a compelling candidate for field effect switches, optical devices, nonlinear circuit components, and solid‐state sensors. In this work we study the resistance switch in micrometer VO2 structures induced by an electric field. We have fabricated VO2 microbridges using a combination of molecular beam epitaxy growth, ex‐situ annealing, UV lithography and dry etching. Resistivity measurements are done as a function of temperature using a four‐point configuration. We have measured voltage‐current characteristics (VIs) at different temperatures across the MIT by sweeping up and down the voltage. We observe a sudden jump in the resistance of the device while continuously increasing the electric field. The observed resistance switch is always a change towards a more metallic state. The maximum resistance ratio obtained after the electric filed is switched off occurs around 70 C. We have also investigated the effects of voltage pulses on the resistive switching.

3.19. F. Piero, Tolerance of Pt clusters to CO poisoning induced by Sn, Ag, Mo and Nb doping Piero Ferrari, Vladimir Kaydashev, Ewald Janssens and Peter Lievens Laboratory of Solid State Physics and Magnetism, KU Leuven, Belgium "Pt nanoparticles have been widely studied the last decades due to their use as catalysts in proton exchange membrane fuel cells (PEMFCs). Unfortunately the cell performance is often limited by CO poisoning, which is the CO adsorption, present


25/32

either as a contaminant or as a side product of the catalytic reaction, on the Pt surface. It has been shown that the CO poisoning can be reduced by doping Pt with a proper element, such as Ru, Sn or Mo among others [1]. Although experimental evidence is conclusive a detailed explanation of this effect is still under debate. Two main mechanisms are proposed: a bifunctional mechanism in which Pt centers are released from CO via reactions with OH groups on neighboring dopant atoms, and a dopant induced modifica on of the electronic structure of Pt reducing the Ptâˆ’CO bond strength. Unfortunately, tests performed in real PEMFCs are not able to clearly distinguish between these effects. In this contribution we present a study of the CO adsorption on bare Ptn

+ and single doped MePtn‐1

+ (Me = Nb, Mo, Sn, Ag) clusters (13≤ n ≤23). The clusters are produced by laser vaporization and detected by time‐of‐flight mass spectrometry. The CO adsorption is investigated as function of the gas pressure using few‐collision cell. The well‐defined conditions of a gas phase experiment could exclude the presence of OH groups and allow to study the effect of modifications of the electronic structure. Opposite results were found depending on the selected dopant atom. The inclusion of a single Nb or Mo atom reduced by 70‐90% the adsorption probability of two CO atoms onto the cluster, while no effects were observed when Sn or Ag are used as dopants. [1] S.M.M. Ehteshami et al., Electrochim. Acta, 93 (2013) 334â€“345. This work is supported by the Research Foundation Flanders (FWO), by the KU Leuven Research Council (BOF and GOA 14/007) and by the COST Action MP0903 Nanoalloy. P. Ferrari acknowledge CONICyT for Becas Chile scholarship.

3.20. K. Schouteden, Scanning tunneling microscopy: Ultra‐high vacuum and low temperatures Koen Schouteden and Chris Van Haesendonck Departement Natuurkunde en Sterrenkunde, KU Leuven, Belgium A visual overview of 10 years of scanning tunneling microscopy and spectroscopy performed at low temperatures and under ultra‐high vacuum conditions: Atomic structure, Moiré effects, self‐assembly, nanomagnetism, quantum confinement, energy dispersion, charging, nanomanipulation, metalation, doping, ... of graphene surfaces, carbon nanotubes, preformed gas‐phase clusters, thin insulating films, cleaved semiconductors, molecular networks, nanoislands, ...

3.21. M. V. Shestakov, White light generation and non‐linear optical properties of Ag nanoclusters and nanoparticles dispersed in glass host Mikhail V. Shestakov1, Vladimir E. Kaydashev 1,2, Hong Hanh Mai 1,2, Ewald Janssens2, Maria Meledina3, Stuart Turner3, Peter Lievens2, Gustaaf Van Tendeloo3 and Victor V. Moshchalkov1 1INPAC‐Institute of Physics and Chemistry, KULeuven, B‐3001 Leuven, Belgium; 2Laboratory of Solid State Physics and Magnetism, KULeuven, B‐3001 Leuven, Belgium; 3EMAT, Department of Physics, University of Antwerp, 2020 Antwerp, Belgium


26/32

Ag‐ doped bulk oxyfluoride glasses have been prepared by conventional melt‐quenching method. The photoluminescence excitation and emission spectra of the as‐prepared glass cover wide range from 300 to 500 nm and from 400 to 900 nm, respectively, corresponding to the typical spectra of Ag nanoclusters with size less than 1.2 nm [1, 2]. The particular preparation conditions result in a glass with white light luminescence based solely on emission of Ag nanoclusters under excitation in UV [3]. Likewise, the white light generation may be achieved via co‐doping with Tm3+ ions emitting in the blue region [4]. The quantum yield of the prepared glasses was found to be up to 70% [1]. The as‐prepared glasses were heat‐treated at 350 oC (below glass transition temperature) preserving glassy state of the samples. Under heat‐treatment the Ag nanoclusters coalesce into the amorphous nanoparticles larger than 2 nm exhibiting a broad surface plasmon absorption band centered at 480 nm in the visible range. These amorphous Ag nanoparticles do not emit light due to the ascribing plasmonic properties. Open aperture z‐scan experiments were conducted using 480 nm nanosecond laser pulses. These experiments revealed that the Ag nanoclusters and nanoparticles exhibit non‐saturated and saturated non‐linear absorption with large non‐linear absorption indices, respectively [5]. The prepared glasses may be applied for white light generation under UV excitation, optical limiting and object’s contrast enhancement.

3.22. S. Thayumanasundaram, Towards better batteries T. Savitha1, R. Vijay Shankar1, J.W.Seo2, J.P. Locquet1 1Departement Natuurkunde en Sterrenkunde, KU Leuven, Belgium; 2Departement Metaalkunde en Toegepaste Materiaalkunde (MTM) KU Leuven, Belgium

Recently, Na‐ion batteries have been gaining much attention among various battery technologies due to the natural abundance and relatively low toxicity and cost of sodium resources. But Na‐ion batteries have lower energy density ‐ in the range of 300‐700 Wh/Kg ‐ than Li‐ion batteries. This can be improved by the development of new electrode and electrolyte materials as well as by improved battery design [1]. Among various cathode materials, NaMn1/3Ni1/3Co1/3O2 which belongs to the family of layered oxide compounds, is the most promising material due to its high specific capacity of the order of 120 mAhg‐1 in the voltage range 2.0‐3.75V. In this work, we have synthesized NaMn1/3Ni1/3Co1/3O2 by a modified sol‐gel technique using citric acid and ethylene glycol to enhance the polymerization reaction (Pechini method). The samples were characterized by various techniques such as TGA, XRD and charge‐discharge cycling to study its thermal, structural and electrochemical properties, respectively. Electrochemical studies of the cathode material were performed after assembling coin‐type half cells with Na metal as the anode and 1 M NaClO4 in EC/DMC as electrolyte. Charge‐discharge studies were done on a Maccor 4000 Battery Test Station with a current density corresponding to C/20 rate. XRD pattern confirms the formation of a stable and phase‐pure cathode material at 950 °C. Coupled TGA‐FTIR analysis was used to optimize the pyrolysis and calcination conditions of the sample to obtain phase pure products. FTIR spectra extracted at different temperatures indicate the sequential evolution of various functional groups such as carbonates and nitrates. SEM analysis shows spherical and platelet


27/32

morphologies of samples synthesized by sol‐gel method. The reversible electrochemical reaction of the electrode material studied by cyclic voltammetry and the results of galvanostatic charge/discharge studies are also discussed.

1 J. Xu, D. Hoe Lee and Y. Shirley Meng, Functional Materials Letters 6, 1330001 (2013).

3.23. N. Verellen , Optical nanoantennas – controlling light at the nanoscale N. Verellen1 and D. Denkova1 and D. Vercruysse2,1 and X. Zheng3 and G. Vandenbosch3 and P. Van Dorpe2,1 and V. Moshchalkov1 1Departement Natuurkunde en Sterrenkunde, KU Leuven, Belgium; 2imec, Leuven, Belgium; 3ESAT, KU Leuven, Belgium Optical nanoantennas are nanosized metallic antennas that convert electromagnetic waves at optical frequencies into localized fields, providing an effective route to couple photons in and out of nanoscale volumes. This unique ability makes these nanostructures excellent tools to study and manipulate light‐matter interaction at the nanoscale. Metallic nanorod‐shaped antennas can for instance be considered as an analogue to classical half‐wave dipole antennas. Our research, however, stretches far beyond the fundamental dipole mode. We investigate higher order modes, Fano resonance, and sub‐radiance in both single and coupled antennas, [1‐5] using techniques such as FTIR spectroscopy, confocal spectroscopy, scanning near‐field optical microscopy, [6‐7] and two‐photon absorption luminescence, [8] while using the newly acquired insights to design unidirectional optical antennas, [9‐10] and better optical bio‐sensors. [11] [1] N. Verellen et al., Nano Letters 9(4), 1663‐1667 (2009). [2] Y. Sonnefraud et al., ACS Nano 4(3), 1664‐1670 (2010). [3] N. Verellen et al., Optics Express 19(12), 11034‐11051 (2011). [4] J.‐H. Cho et al., Small 7(14), 1943‐1948 (2011). [5] N. Verellen et al., Nano Letters 14(5), 2322‐2329 (2014). [6] D. Denkova, et al., ACS Nano 7(4), 3168‐3176 (2013). [7] D. Denkova, et al., Small, 10(10) 1959‐1966 (2014). [8] N. Verellen et al., ACS Photonics 2(3), 410–416 (2015). [9] D. Vercruysse, et al., Nano Letters 13(8), 3843‐3849 (2013). [10] D. Vercruysse, et al., ACS Nano 8(8), 8232‐8241 (2014). [11] N. Verellen et al., Nano Letters 11(2), 391‐397 (2011).

4. Nuclear Physics & Nuclear Solid State Physics

4.1. M. Bisht, Electric field polarity dependent modification of the metal/ferroelectric oxide interface chemistry M. Bisht1, S. Couet1, V.Lazenka1, H. Modarresi1, J.P. Locquet2, R. Rüffer3, M. J. Van Bael2, A. Vantomme1 and K. Temst1 1Instituut voor Kern‐ en Stralingsfysica, K.U.Leuven, Leuven, Belgium; 2Laboratorium voor Vaste‐Stoffysica en Magnetisme, K.U.Leuven, Leuven, Belgium; 3European Synchrotron Radiation Facility, Grenoble, France.


28/32

Multiferroic materials with magnetoelectric (ME) coupling are rare in nature and the coupling is rather weak, therefore we investigate an alternative approach by coupling the ferromagnetic and the ferroelectric phases via an interface in a multilayer structure. Our aim is to study in detail the magnetic spin structure at the interface. Based on the longitudinal magneto‐optic Kerr effect (MOKE), we observed the electric‐field modulation of the magnetic properties of Fe or Co50Fe50 films on barium titanate (BTO) and lithium niobate (LNO) substrates. A change in the coercive field (Hc) of the ferromagnetic layer was observed as a function of the electric field applied across the thickness of the piezoelectric substrate. These changes were irreversible which can possibly be due to electric field induced structural changes at the interface, causing the interfacial atoms to become non‐magnetic (magnetically dead layer). The ME coupling in such systems is via interface due to which a detailed understanding of the chemistry and the structure of the interface is necessary. Hence, we study the evolution of the metal/oxide interface of Fe/BTO and Fe/LNO system with the applied electric field using Mössbauer spectroscopy and Nuclear Resonant scattering of the synchrotron radiation on the samples with 1nm 57Fe probe layer at the interface. The use of two complementary characterization techniques (MOKE and NRS) is a beneficial combination for the investigation of the ME coupling since they provide both a macroscopic and microscopic probe of magnetism. We proposed a model for the electric field–induced oxidation of ferromagnetic/ferroelectric interface based on MOKE and NRS results. Mössbauer spectroscopy results confirmed the hypothesis and showed a systematic trend of evolution of the interface with the electric field depending on the direction of the field.

4.2. C. Granados, In Gas Laser Ionization and Spectroscopy of neutron deficient Actinium isotopes C. Granados, P. Creemers, R. Ferrer, L. Ghys, M. Huyse, Yu. Kudryavtsev, S. Sels, P. Van den Bergh, P. Van Duppen, S. Zadvornaya, Y. Martinez, Liam Gaffney, S. Raeder, C. Van Beren. KU Leuven , Instituut voor Kern‐ en Stralingsfysica, Celestijnenlaan 200D, B‐3001 Leuven, Belgium. The study of the nuclear structure of short‐lived isotopes far from the beta‐stability line is mainly motivated by the fact that their properties might highlight hidden aspects of the strong interaction. Measurements of the spin, charge radii, isotope shift and the nuclear moments of nuclei far from stability, can provide important information to test and improve our understanding of the nuclear structure. With the development of laser techniques like In Gas Laser Ionization and Spectroscopy (IGLIS), these nuclear properties can be determined through the measurement of the hyperfine structure of the electronic levels and of their shifts. Resonant ionization spectroscopy of (213,215,225)Ac was performed for the first time. (213,215)Ac were produced and investigated at LISOL setup while the 225Ac isotope was investigated in the hot‐cavity setup at TRIUMF. Magnetic moments for


29/32

(213,215,225)Ac are presented. Tentative assignment of the nuclear ground‐state spin for 225Ac is reported. For (213,215Ac) a tentative assignment from the analysis of the single‐particle behavior expected around the close shell N= 126, for the odd‐even nuclei, is presented. This tentative assignment is in concordance with previous radioactive‐decay studies.

4.3. E. Menéndez, Planar GMR in laterally modulated Co/(Co‐CoO) microscale patterns E. Menéndez1, H. Modarresi1, C. Petermann1, J. Nogues2,3, B. J. Kirby4, J. A. Borchers4, L. Lagae5,6, A. S. Mohd7, A. Koutsioumpas7, E. Babcock7, S. Mattauch7, H. Liu5, C. Van Haesendonck5, A. Vantomme1 and K. Temst1 1KU Leuven, Instituut voor Kern‐ en Stralingsfysica, Celestijnenlaan 200 D, 3001 Leuven, Belgium; 2ICN2‐Institut Catala de Nanociencia i Nanotecnologia, Campus UAB, 08193 Bellaterra (Barcelona), Spain; 3ICREA‐Institució Catalana de Recerca i Estudis Avancats, Barcelona, Spain; 4NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA; 5KU Leuven, Laboratorium voor Vaste‐Stoffysica en Magnetisme, Celestijnenlaan 200 D, 3001 Leuven, Belgium; 6IMEC, Kapeldreef 75, 3001 Leuven, Belgium; 7Jülich Centre for Neutron Science (JCNS), Forschungszentrum Jülich GmbH, Aussenstelle am FRM‐II c/o TU München, Lichtenbergstrasse 1, D‐85747 Garching b. München, Germany A laterally modulated pattern consisting of alternating Co and Co‐CoO microscale lines has been prepared by oxygen ion implantation into a pre‐lithographed Au‐sandwiched Co thin film. The lithography is used to obtain a shadow mask for ion implantation. At room temperature, magnetoresistance along the lines (i.e., current and applied magnetic field are parallel to the lines) reveals an overall GMR (giant magnetoresistance) behavior. Conversely, traces of AMR (anisotropic magnetoresistance) and GMR are distinguished at low temperature (i.e., 10 K) since the O‐implanted areas become exchange‐coupled. The occurrence of GMR is ascribed to the anti‐parallel alignment of the magnetization of adjacent lines and its magnitude to the large amount of in‐plane Co/Co‐CoO interfaces. The combination of ion implantation and lithography is demonstrated to be a suitable approach to prepare lateral multilayers.

4.4. F. Renzi, Study 7He with 6He(9Be,8Be) reaction F. Renzi Instituut voor Kern‐ en Stralingsfysica, KU Leuven, KU Leuven, Belgium Much interest has been devoted to the investigations of the 7He nucleus in recent years. This nucleus is unbound and the identification of excited states is particularly challenging and controversial. Indeed, despite a significant number of experiments, a detailed information about excited states is still lacking, in particular for the first excited 1/2‐ state. In this work the results of a further measurement are discussed. Using the 6He (9Be,8Be)7He transfer reaction, we took advantage of a very clear signature of the 8Be decay to select the reaction channel of our interest. After the identification of alphas from the decay 8Be ground state, 8Be momentum was calculated, then the


30/32

excitation energy spectrum of 7He was reconstructed with the missing mass method. Detailed Geant4 Monte‐Carlo simulations of the experimental setup have been carried out in order to accurately determine acceptance and efficiency. Moreover, the simulations have permitted the identification of the various reaction channels leading to 8Be ground state in the final state and, therefore, all background contributions in the excitation energy spectrum of 7He. The preliminary results of the analysis and the comparison with previous measurements will be presented.

4.5. K. van Stiphout, The reaction of ultrathin Ni films with Ge K. van Stiphout1, F. Geenen2, C. Detavernier2, K. Temst1, A. Vantomme1 1Instituut voor Kern‐ en stralingsfysica, KU Leuven, Belgium; 2Department of Solid State Sciences, Ghent University, Belgium Thin film growth by reactive diffusion has been studied extensively during the past decades. The formation of metal silicides and germanides by annealing a metal layer deposited onto Si or Ge is considered a model system for such thin film growth. Such reactions typically consist of a sequence of intermediate phases until thermodynamical equilibrium is achieved. Diffusion of atoms across the growing compound plays a crucial role in determining the reaction path. Our research focuses on the reaction of ultrathin Ni films (<10 nm) with Ge (100) substrates. The behavior of thin Ni films (10 ‐ 100 nm) with Ge during annealing is unusual for thin film reactions: two germanide phases grow simultaneously, limited by diffusion. When the dimensions of the metal films are reduced to a few nanometer however, diffusion plays a less significant role in the reaction, whereas interface energy, texture and nucleation of new phases become increasingly important for phase formation. Our experiments show that reducing the thickness of the metal layer does influence the reaction: the germanide phases appear sequentially when the thickness of Ni is smaller than 4 nm. Additionally, the final germanide forms only at higher temperatures for thinner films, a clear departure from diffusion‐limited reaction rates. Moreover, low‐energy interfaces of the germanide grains facilitate the breaking up of the continuous film into physically separated islands, which occurs at lower temperatures than for thicker films.

5. Theoretical Physics

5.1. M. Laleman, Probing DNA‐protein interactions ‐ combining theory and experiment. M. Laleman Instituut voor Theoretische Fysica, Departement Natuurkunde en Sterrenkunde, KU Leuven, Belgium


31/32

Probing the interactions between DNA and proteins has become more and more accessible due to advancements in experimental techniques. This allows to test microscopical theories of DNA and DNA‐protein interactions in the lab. Our research focuses on protein induced bending of DNA. We provide automated analysis of the AFM images and theoretical interpretation of the results.

5.2. C‐Y Lin, Holographic surface superconductivity/superfluidity C.‐Y. Lin1, Z. Deng1, D. Krym2, J. Estes3, and J. Indekeu1 1Institute for Theoretical Physics, KU Leuven, Celestijnenlaan 200D, B‐3001 Leuven, Belgium; 2New York City College of Technology & Center for Theoretical Physics, 300 Jay Street, Brooklyn, NY, 11228, USA; 3Blackett Laboratory, Imperial College, London, SW7 2AZ, United Kingdom

We develop a gravitational dual of surface superconductivity, strictly localized on the outer surface or a defect plane of a material. Our calculations reveal such phenomena with its critical temperature higher than the bulk value. A phase diagram is also constructed to relate the inhomogeneity of a material to various interfacial phenomenon such as surface superconductivity, Josephson junction, and partially bulk superconductivity.

5.3. K. Moors, An improved model for surface roughness in metal nanowires

K. Moors1,2, B. Soree2,3 and W. Magnus2,3 1Instituut voor Theoretische Fysica, KU Leuven, Belgium; 2Imec, Belgium; 3Departement Fysica, U Antwerpen, Belgium We present an improved model for surface roughness scattering in metal nanowires, based on Ando's surface roughness model. Ando's model is improved and adapted for metal nanowire simulations by taking into account the penetration of the wave functions in the barrier and the wave function oscillations up to any surface roughness size while still having an analytic expression for the scattering probability. These probabilities are used in the multi‐subband Boltzmann equation, retrieving state‐dependent and self‐consistent relaxation times without numerical integration. Our approach allows for both accurate and fast simulations of metal nanowires with many subbands and substantial wave function spill‐over in the barrier.

5.4. W. Xintian, Critical phenomena of a single defect Xintian Wu1,2 and Yangyang Zhang1 1Department of physics, Beijing Normal University, Beijing, China; 2Theoretical physics section, Department of Physics, KU Leuven, Belgium We consider the critical system with a point defect and study the variation of thermodynamic quantities, which are the differences between those with and without the defect. Within renormalization group theory, we show generally that the critical exponent of the internal energy variation is the specific heat exponent of a pure system, and the critical exponent of the heat capacity variation is that for the temperature derivative of specific heat of a pure system. This conclusion is valid for


32/32

the isotropic systems with a short‐range interaction. As an example we solve the two dimensional Ising model with a point defect numerically. The variations of the free energy, internal energy and specific heat are calculated with bond propagation algorithm. At the critical point, the internal energy variation diverges with the lattice size logarithmically and the heat variation capacity diverges with size linearly. Near the critical point, the internal energy variation behaves as $\ln |t|$ and the specific heat variation behaves as $|t|^{‐1}$, where $t$ is the reduced temperature.

6. Physics Education

6.1. L. Bollen, Investigating students’ use of the divergence and curl in electrodynamics L. Bollen1, P. van Kampen2, M. De Cock1 1Department of Physics and Astronomy & 2LESEC, KU Leuven (Belgium) Understanding Maxwell's equations in differential form is a prerequisite to study the electrodynamic phenomena that are discussed in advanced electromagnetism courses. It is therefore necessary that students master the use of vector calculus in physical situations. In this light we investigated the difficulties students encounter with the divergence and curl of vector fields in mathematical and electromagnetic contexts, using a pretest post‐test design and conducting student interviews.

6.2. P. Coppens, Students and signals P. Coppens1, J. Van den Bossche2 and M. De Cock3 1Faculty of Engineering Technology, KU Leuven, Belgium; 2Faculty of Engineering Technology, KU Leuven, Belgium; 3Department of Physics and Astronomy, KU Leuven, Belgium As part of a PhD research project about learning in electronics laboratories, we interviewed second year electronics engineering students. Several of them seemed to have various problems related to signal properties. To verify how widespread these problems were, a questionnaire was administered to over 150 students at 3 campuses of the faculty of Industrial Engineering. The questions asked for different aspects of signals, including phase, frequency as well as Bode plots. Students showed that they do seem to understand the concept of a phase shift, although they have problems with its direction (or sign). They generally don’t have any idea what a signal with two frequencies looks like in the time domain. Bode plots also prove to be a problem for students, who don’t manage to construct one from a set of (dummy) measurements. Most of these problems persist after lab instruction. The analysis of student answers focuses on the solution method and thinking process rather than the result in terms of right or wrong. Therefore, a phenemographical approach is used. The poster shows the possible answers students gave, together with their train of thought as well as how ‘popular’ every option was.

Date post:	02-Jun-2020
Category:	Documents
Upload:	others
View:	0 times
Download:	0 times

Research@Dept2015 · Research@Dept 2015 Poster Abstract Book ‐ Updated version 2 ‐ 23/4/2015...

Documents