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The aim of this Workshop is to gather the Researchers’ community dealing with nano-sized carbon

based materials, in order to share experiences and perspectives in the fields of synthesis,

characterization, theoretical modeling and possible applications of low-dimensional carbon structures.

The Workshop will give the opportunity to promote the cooperation among the research groups active

in this field, in order to establish a network of excellence that would mix fundamental research and

technological applications.

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- Low-dimensional carbon structures: nanotubes, fullerenes, linear chains, graphene, …

- Growth and fabrication methods

- Characterization (structural, electrical, …)

- Theoretical modeling

- Carbon-based nanomaterials for electronics, sensors and environmental applications

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Silvia Scalese Antonino La Magna

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Salvatore Bagiante Ioannis Deretzis

Markus Italia Giovanna Leanza Viviana Scuderi

Consiglio Nazionale delle Ricerche, Istituto per la Microelettronica e Microsistemi (CNR-IMM)

Catania (Italy)

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The Workshop is hosted at Palazzo Platamone (via Vittorio Emanuele 121), one of the hystorical

buildings of Catania (Italy), built in the XV Century and today hosting the council office of culture of

Catania. [for more information see: http://www.comune.catania.it/la_citt%C3%A0/culture/monumenti-

e-siti-archeologici/palazzo-platamone-convento-san-placido/storia/]

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Using electron diffraction for the precise determination of a nanotube structure (invited contribution)

Philippe Lambin Physics Department, FUNDP - University of Namur, 61 Rue de Bruxelles, B5000 Namur, Belgium Apart from manipulation and packaging problems, a real challenge for the application of nanostructures at the industrial level will be the quality control of samples, especially in large scale production plants. For instance, some applications of carbon and other nanotubes may require using samples with a predefined atomic structure. No technique exists today to produce single-walled nanotubes having a given pair of wrapping indices (n,m). Post-synthesis treatments have then to be developed to select those nanotubes that have the desired atomic structure. Techniques are regularly proposed and refined to do so, with more or less success. The "fishing" process used in post-synthesis sorting of nanotubes needs to be validated in a convincing way by resorting to the very few characterization tools available to probe the atomic structure of the product with reliable accuracy. One of them is micro Raman resonant scattering, another is electron diffraction. Diffraction taking place in a transmission electron microscope is an elemental physical process based on constructive interferences of the electronic plane wave by the sample atoms. In principle, diffraction is not subject to artifacts such as image construction or reconstruction. Being of geometric nature, the data obtained by diffraction do not rely either on any theoretical parameter. They are therefore of great interest for nanostructure metrology and sorting process calibration. However, this techniques yield information in reciprocal space, which needs to be interpreted. The interpretation of the electron diffraction pattern produced by an isolated nanotube is straightforward, for it reliably rests on the simple kinematics theory. Information on the diameter and helicity of a nanotube can be extracted from its diffraction pattern. For a single-walled nanotube, redundancy of information from well defined diffraction spots allows one to deduce a pair of (n,m) indices almost free of error, despite several unknown parameters such as wave-vector calibration and tilt angle of the sample in the microscope. Although much more difficult, the structure of double-walled nanotubes can also be resolved with high accuracy. This communication will demonstrate why and how all this is possible.

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SWNT nets: from on-site synthesis to device fabrication

Rita Rizzoli, Giulio Paolo Veronese, Francesco Suriano CNR - Istituto IMM, Via Gobetti 101, I - 40129 Bologna

Carbon nanotubes have been often addressed at as major candidates for beyond-Si technology, but the exploitation of their extraordinary electronic properties is still facing difficulties to go to large scale production of devices. Large scale manufacturing requires high processing speeds and high yield over large areas, which are still a big challenge for most nanomaterials and in particular for devices based on single isolated nano-objects. On the other hand, a viable hybrid Si-C technology for the fabrication of versatile platforms exploiting the collective properties of many SWNTs is mature for large area applications in gas and biological sensors or hybrid solar cells.

The Catalytic Chemical Vapor Deposition (C-CVD) of various types of Single-Walled Carbon Nanotubes (SWNTs) nets on silicon-based substrates has been investigated in order to develop a cheap and reliable technology for the integration of SWNTs based sensors in Si microsystems. The direct synthesis of SWNTs nets has been performed at T ≤ 900 C, using methane as C feedstock, directly between doped poly-Si electrodes or on patterned areas of SiO2/Si substrates before the evaporation of metallic (Pd, Ni, Au/Ti electrodes). The catalyst nanoparticles formation has been optimized in order to grow different kinds of nets: few SWNTs with a preferential orientation with respect to the electrodes or disordered SWNT nets of various densities between the electrodes. Each type of nanostructure has been fabricated both suspended and lying on the SiO2 film across the channel between the electrodes. The pattern of electrical contacts has been designed in order to allow combined electrical and structural characterizations inside a SEM chamber, using an in-situ nano-manipulation system, for low-noise reliable measurements.

Simple back-gate FETs based on these SWNT nets have been prepared and characterized as a testing tool for the set-up technology. Micro-Raman spectra of the SWNT nets combined with electrical and SEM characterizations of devices will be discussed. Corresponding author: Rita Rizzoli rizzoli@bo.imm.cnr.it

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Chemical vapor deposition growth of Carbon nanotubes: characterization and applications. M. Passacantando, V. Grossi and S. Santucci Dipartimento di Fisica, Università degli Studi dell’Aquila, via Vetoio (67100) Coppito (AQ) - Italy Different Carbon nanotubes (CNTs) have been synthesized at different temperature by chemical vapor deposition (CVD) using acetylene as precursor gas, in hydrogen or ammonia atmosphere, onto different substrates with Ni or Fe catalyst. These different samples were characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM) and Raman measurements to check their property and check the growth morphology of single or multi-wall nanotubes. Our presentation will be an exhibition about the different applications that these materials may have in the field of optoelectronics, and the study of electronic properties of individual CNTs that was made with the ability to use a nanomanipulation technique inside of our SEM. Corresponding author: Maurizio Passacantando maurizio.passacantando@aquila.infn.it

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CCVD production of few-walled carbon nanotubes by Fe-Co bimetallic catalysts supported on MgO: a spectro-microscopic investigation Enrico Maccallini,1 Alfonso Policicchio,1 Theodoros Tsoufis,2 Tommaso Caruso,1 Dimitrios Gournis2 and Raffaele G. Agostino1

1Physics Dep., Univ. of Calabria, cubo 31C, via P. Bucci, 87036, Arcavacata di Rende (Cs), Italy 2Dep. of Materials Science and Engineering, Univ. of Ioannina, GR-45110 Ioannina, Greece The CNT synthesis by CCVD is governed by the choice of carbon source, catalyst and growth temperature although in many studies other parameters, such as growth time [1], have been also proved to be crucial to the resulting carbon materials. Considering CCVD, the catalytical decomposition of hydrocarbon gases is realized making use of metal particles dispersed in different supports. In this framework, the utilization of MgO as supporting material minimizes the formation of amorphous carbon and the metal particles aggregation. In addition MgO can be removed from the carbon material by purification procedures without varying the chemical and physical properties of CNTs. On the other hand the use of bimetallic catalysts arises higher CNT production [2] with the synthesis of SWCNTs and/or DWCNTs [3, 4]. However CNT growth with few walls over Fe-Co catalysts supported on MgO using acetylene as carbon source still remains a challenge since mainly MWCNTs have been grown so far by pyrolytic decomposition of acetylene over Fe-Co catalysts supported on MgO. Fe-Co bimetallic catalysts supported on MgO were investigated for the CCVD synthesis of CNTs. Different %wt metal loadings were studied at various deposition temperatures and times. Characterization of the synthesized materials has been obtained by DTA-TGA, XRD, spectroscopy (Raman, UPS, EELS and STS) and microscopy (SEM, TEM and STM) techniques. The metal content is fundamental either for the yield and the structural quality of the grown CNTs either to tune the desired type of nanotubes synthesized. 2 %wt of Fe-Co catalysts favour the formation of SWCNTs and/or DWCNTs for deposition time and temperature 30 min and 800°C respectively. DTA-TGA and Raman measurements showed that these thin CNTs were synthesized at high amounts, with high graphitization degree and only small traces of amorphous carbon in the final product. The synthesis of CNTs bundles has been observed by TEM and individual CNTs with less than 2 nm outer diameter have been imaged by STM. Additional energy loss measurements at nanometric scale indicated that the synthesized CNTs are mainly single wall. Increasing the Fe-Co loadings to 10%wt resulted to the formation of MWCNTs. References [1]C. Oncel and Y. Yurum, Fullerenes Nanotubes and Carbon Nanostructures, 14, 17-37 (2006) [2]E. Flahaut, et al., Chemical Physics Letters, 300, 236-242 (1999) [3]J. F. Colomer, et al., Chemical Physics Letters, 317, 83-89 (2000) [4]B. C. Liu, et al., Chemical Physics Letters, 407, 232-235 (2005) Corresponding author: Enrico Maccallini, e-mail: enrico.maccallini@fis.unical.it

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Anchoring of SWCNT-SH on gold surface Vanna Torrisi (1), Giovanni Marletta (1), Tatiana Da Ros (2), Maurizio Prato (2) (1) Laboratory for Molecular Surface and Nanotechnology (LAMSUN), Dept. of Chemical Sciences-University of Catania and CSGI, Viale A. Doria 6, I-95125, Catania, Italy (2) Dept. of Pharmaceutical Sciences-University of Trieste and INSTM, Piazzale Europa 1, I-34127, Trieste, Italy The bottom-up approach is crucially important in the field of nanometer-sized devices and it leads to a variety of smart nanoscale building blocks. Among the various nanoscale building blocks, nanotubes and nanowires have been synthesized with desired physical properties to be incorporated in electronic and optical devices. Whereas the carbon nanotubes (CNTs) synthesis has been explored extensively, the effort to address CNTs onto specific locations of the substrates for the device fabrications has just begun. Many kind of interactions, among which molecular recognitions, were applied for positioning CNTs in specific regions on substrates. We report on the use of three anchoring strategies (A,B,C) of single-walled CNTs functionalised with thiols (SWCNT-SH), both involving the use of strong thiol-based chemical bonds. The length of used SWCNT-SH ranged from 10 nm to 10 µm. A)We employed mixtures of SWCNT-SH and alkane- or aromatic thiols to obtain the SWCNT-SH self-assembly onto polycrystalline Au surfaces. B) We performed the SWCNT-SH insertion within a previously self-assembled alkane-thiol monolayer. Finally, C) we carried out the direct micro contact printing of SWCNT-SH suspension onto gold coated substrates. The morphology of thiol films and SWCNT-SH/thiol systems has been studied by Atomic Force Microscopy. It was found that the direct printing of SWCNT-SH allows the positioning of CNT at the surface. Corresponding author: Vanna Torrisi, v.torrisi@unict.it

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Microscopic study of water condensation on carbon nanotubes and graphite. Tommaso Caruso, Enrico Maccallini, Alfonso Policicchio, Nicola Scaramuzza and Raffaele Giuseppe Agostino. Dipartmento di Fisica, Università della Calabria, cubo 31C, via P. Bucci, 87036, Arcavacata di Rende (CS), Italy An environmental scanning electron microscope (eSEM) was used to study water condensation on graphite and carbon nanotubes. The graphitic samples were both highly oriented pyrolytic graphite (HOPG) and polycrystalline graphite. The investigated CNTs instead were both aligned nanotubes (self assembled by SiC substrate decomposition) and not aligned ones. The “microscopic” water contact angle was evaluated from SEM images of condensed water droplets on the samples’ surfaces. The wetting results imaged by eSEM were compared to the macroscopic contact angle measured by the sessile drop method. The results were analyzed in term of the surface hydrophobicity and associated at the surfaces’ morphology, chemical state and nanostructuring. Corresponding author: Tommaso Caruso, e-mail: tommaso.caruso@fis.unical.it

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Technology for 300mm wafer scale growth of carbon nanotubes Ken Teo AIXTRON The integration of carbon nanotubes (CNT) on silicon-based substrates/devices require its deposition over a variety of wafer sizes, including the current production size of 300mm diameter wafers. This presentation discusses the development and scaling of CNT deposition equipment at AIXTRON. The horizontal flow and vertical flow techniques are compared. The simulation and measurement of gas flow and thermal distribution of the reactor are presented. Plasma enhanced chemical vapour deposition of cnt is discussed and techniques for obtaining improved plasma stability are explained. The use of a pre-heater is also characterised using mass spectroscopy. Finally, various growth results (SWNT, MWNT, VACNF, cvd graphene) achieved are shown and a 300mm wafer with CNT will be displayed.

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12

Graphene under strain: a combined continuum/atomistic picture (invited contribution)

Luciano Colombo Department of Physics - University of Cagliari, Cittadella Universitaria- 09042 Monserrato (Ca), ITALY A thorough theoretical picture about elastic properties of graphene and carbon nanoribbons, both under stretching and bending deformations, is presented and discussed by combining continuum elasticity theory and tight-binding atomistic simulations. As for stretching elasticity, the stress-strain nonlinear constitutive equation is worked out by continuum theory in both the small-strain and large-strain conditions. Then, by atomistic simulations we compute all the relevant linear and non-linear elastic moduli [1]. In particular, we discuss the physical meaning of the effective non-linear elastic modulus recently measured by nano-indentation of a free standing monolayer graphene sample [2], and we provide a robust interpretation of such an experiment. Through the stress-strain plot we also predict a very high failure stress, in excellent agreement with available experimental data reported in Ref. [2]. The corresponding effective three dimensional failure stress is then obtained to be as large as 130 GPa, exceeding that of most materials (even including multiwalled nanotubes). This result motivates the use of one-atom-thick carbon layers as possible reinforcement in advanced composites. As for bending elasticity, by continuum theory we identify the bending rigidity modulus and we characterize it in terms of the local curvature of a bended ribbon. Then, we calculate the above bending modulus by tight-binding atomistic simulations [3]. Finally, we investigate the elastic behavior of various curved nanoribbons, and we discuss the onset of nano-scale features which are out-of-rich of the continuum picture. In particular, we prove that atomic-scale relaxations upon bending induce an additional strain field of in-plane stretching, which provides new energy contributions. This intriguing result opens the problem of how to disentangle bending and stretching features, an especially important issue of considerable practical interest for small-width nanoribbons. To this aim we define a proof-of-concept computational procedure, based on a virtual process of unbending, and by means of it we put evidence on the stretching emergence in bended nanoribbons. We acknowledge financial and computational support by Cybersar (Cagliari, Italy), and computational support by CASPUR (Roma, Italy) [1] E. Cadelano, P. Palla, S. Giordano, and L. Colombo, Phys. Rev. Lett. 102, 235502 (2009). [2] C. Lee et al., Science, 321, 385 (2008). [3] E. Cadelano, S. Giordano, and L. Colombo, Phys. Rev. B 81, 144105 (2010).

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Numerical model for the electromechanical characterization of carbon nanotubes Antonio Pantano Università degli Studi di Palermo Dipartimento di Meccanica, Viale delle Scienze, 90128, Palermo, Italy Carbon nanotubes (CNTs) can be metallic or semiconductors depending simply on geometric characteristics [e.g., 1]. This peculiar electronic behavior, combined with high mechanical strength, make them potential building blocks of a new nano-electronic technology. Most discussions of the electronic structure of CNTs assume perfect cylindrical symmetry, but this is somewhat of an oversimplification. High resolution images of CNTs often disclose structural deformations such as bent, twisted, or collapsed tubes. These deformations may develop during growth, deposition, and processing, or upon interaction with other CNTs, and with surfaces and surface features such as electrodes. Deformations break the tube symmetry, and a change in their electronic properties should result. A computationally effective mixed finite element-tight-binding approach [2-7] able to simulate the electromechanical behavior of single and multiwall nanotubes used in nano-electronic devices is presented. The finite element (FE) computes the evolution of atomic coordinates with deformation and provides these coordinates to a tight-binding (TB) code, enabling computation and updating of the electrical conductivity. The TB code is engineered to realize dramatic computational savings in calculating deformation-induced changes in electrical transport properties of the nanotubes. The FE-TB computational approach is successfully validated in a simulation of laboratory experiments which had measured the changes in electrical conductivity of a multiwall carbon nanotube during mechanical deformation. References [1]. J. Bernholc et al, Annu. Rev. Mat. Res. 32 , 347 (2002) [2]. A. Pantano et al, Phys. Rev. Lett. 91, 145504 (2003) [3]. A. Pantano et al, J. Mech. Phys. Solids 52, 789 (2004) [4]. A. Pantano et al, J. of Eng. Materials and Technology Trans. ASME 126, 279-284 (2004) [5]. A. Pantano et al, J. of Applied Physics 92, 6756-6760 (2004) [6]. A. Pantano et al, ACS Nano 3, 3266–3272 (2009) [7]. A. Pantano. Chapter of the book “Trends in Computational Nanomechanics: Transcending Length

and Time Scales”. Springer , pp. 335-365. ISBN: 978-1-4020-9784-3. Corresponding author: Antonio Pantano, apantano@dima.unipa.it

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Strain effect on the electronic and plasmonic spectra of graphene F. M. D. Pellegrino (1,2,3,4), G. G. N. Angilella (1,2,4,3) and R. Pucci (1,3) 1 Dipartimento di Fisica e Astronomia, Università di Catania, Via S. Sofia, 64, I-95123 Catania, Italy 2 Scuola Superiore di Catania, Via S. Nullo, 5/i, I-95123 Catania, Italy 3 CNISM, UdR Catania, I-95123 Catania, Italy 4 INFN, Sez. Catania, I-95123 Catania, Italy Within the tight binding approximation, we study the dependence of the electronic band structure and of plasmonic spectra of a graphene single layer on the modulus and direction of applied uniaxial strain. While the Dirac cone approximation, albeit with a deformed cone, is robust for sufficiently small strain, band dispersion linearity breaks down along a given direction, corresponding to the development of anisotropic massive low-energy excitations. We recover a linear behavior of the low-energy density of states, as long as the cone approximation holds, while a band gap opens for sufficiently intense strain, for almost all, generic strain directions. Our calculation of the dielectric function is based on the random phase approximation (RPA), besides we consider local field effects (LFE), following the method developed by Hanke and Sham for the calculations of the dielectric response properties of crystalline systems. In this way we will take into account possible collective excitations of any wavelength as a function of the uniaxial strain. References [1] A. H. Castro Neto et al., Rev. Mod. Phys. 81, 109 (2009) [2] F. M. D. Pellegrino, G. G. N. Angilella and R. Pucci, Phys. Rev. B 80, 094203 (2010) [3] S. M. Choi et al., Phys. Rev. B 81, 081407 (R) (2010) [4] F. M. D. Pellegrino, G. G. N. Angilella and R. Pucci, Phys. Rev. B 81, 035411 (2010) [5] W. Hanke and L. J. Sham, Phys. Rev. Lett. 33, 582 (1974) [6] B. Wunch et al., New J. Phys. 8, 318 (2006) [7] E. H. Hwang and S. Das Sarma, Phys. Rev B 75, 205418 (2007) [8] A. Hill et al., EPL 87, 27005 (2009) [9] M. H. Gass et al., Nature Technology 3, 676 (2008) [10] T. Eberlein et al., Phys. Rev. B 77, 233406 (2008) [11] C. Kramberger et al., Phys. Rev. Lett. 100, 196803 (2008) [12] F. Liu et al., Phys. Rev. B 76, 064120 (2007) [13] K. S. Kim et al., Nature 457, 706 (2009) Corresponding author: Francesco M. D. Pellegrino – fmd.pellegrino@gmail.com

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Nanoscale modification of graphene electronic properties by ion irradiation F. Giannazzo (1), S. Sonde (1,2), V. Raineri (1), E. Rimini (1,3) (1) CNR-IMM, Strada VIII, 5, 95121, Catania (Italy) (2) Scuola Superiore di Catania, Via San Nullo, 5/i, 95123, Catania (Italy) (3) Dipartimento di Fisica ed Astronomia, Università di Catania, Via S. Sofia, 64, 95123, Catania (Italy) Graphene is the object of huge research interests, due to the interesting properties of its two dimensional electron gas (2DEG), like the giant intrinsic carrier mobility and coherence length and the high capacitive density, making it an attractive candidate for post-Si electronics. Recently, plasma treatments or ion irradiation have been proposed as methods to selectively tailor graphene electronic properties. In this work, we investigate in details the nanoscale changes in the electrostatic properties (quantum capacitance, Cq, and density of states, DOS) and in the carrier transport properties (electron mean free path and mobility) of graphene monolayers (GML) induced by ion irradiation. GML were exfoliated from highly oriented pyrolitic graphite (HOPG) and deposited on 100 nm SiO2 grown on n+ Si. Irradiation was carried out under high vacuum using 500 keV C+ ions at different fluences (1- 10×1013 cm-2). The interaction mechanisms between the high energy ions and graphene sheet are discussed. The role played by the interaction of GML with the SiO2 substrate during irradiation is also considered. The effect of lattice disorder due to irradiation on graphene electronic properties was locally investigated by scanning capacitance spectroscopy (SCS) [1,2]. Local capacitance measurements were carried out on the graphene/SiO2/n+Si capacitor. When an oscillating bias is applied between the Si backgate and the AFM tip in contact with graphene, the 2DEG manifests itself as a capacitor with capacitance Cq (quantum capacitance), which is strictly related to the local DOS. An accurate method to extract Cq from measured local C-V curves was demonstrated [1]. The maps of Cq values measured at different positions both on as-exfoliated and on irradiated GML at difference fluences were compared. The hystogram of Cq values on pristine GML exhibits a single narrow peak at ~0.8 �F/cm2, whereas on irradiated GML two distinct distributions are observed, the first one peaked at the same Cq of pristine GML and the second one (very broad) at ~1.6 �F/cm2. The latter distribution can be associated with nanoscale regions affected by the damage, which are locally probed by the tip. Comparing the relative area under the two peaks allows to evaluate the percentage of graphene surface affected by irradiation. Furthermore, the local electron mean free path (i.e. the average of the distances traveled by electrons between "few" subsequent scattering events) and mobility at different positions in the GML can be evaluated from the SCS data [2]. For pristine graphene the distribution of mobility values exhibits a single peak at ~8200 cm2V-1s-1. In irradiated graphene, in addition to a narrow peak at ~8200cm2V-1s-1, a broader distribution extending from ~5000 to ~7500 cm2V-1s-1 is obtained, which is associated to the locally damaged regions. References [1] F. Giannazzo, S. Sonde, V. Raineri, E. Rimini, Nano Lett., 9, 23 (2009). [2] F. Giannazzo, S. Sonde, V. Raineri, E. Rimini, Appl. Phy. Lett. 95, 263109 (2009). Corresponding author: e-mail: filippo.giannazzo@imm.cnr.it

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Interferometric transmission electron microscopy characterization of the structural and electronic properties of graphene membranes. Luca Ortolani (1) , Vittorio Morandi (1), Florent Houdellier (2), Etienne Snoeck (2), Marc Monthioux (2) 1. CNR IMM-Bologna, Via Gobetti, 101 40129 Bologna, Italy. 2. CNRS CEMES, 29 Rue Jeanne Marvig, 31055 Toulouse, France. Graphene is a two-dimensional crystal of carbon atoms arranged in a honeycomb lattice, and this peculiar atomic structure provides this material with unusual and interesting physical and chemical properties, like extremely high electronic carriers mobility, low spin-orbit coupling and ultimate mechanical stiffness [1]. The characterization of the structural and electronic properties of graphene membranes is the subject of an intense study by the material science community since its isolation in 2004, and transmission electron microscopy (TEM) established as an essential tool due to its elevated spatial resolution and sensitivity [2, 3]. We will present our recent results on the structural and electronic characterization of graphene membranes, using advanced low-voltage aberration-corrected interferometric TEM methods, like electron holography [4] and Geometric Phase Analysis [5]. In particular, we will show that electron holography has been pushed to its actual resolution limits to map the distribution of electrostatic crystal charges in individual graphenes, and to investigate valence charge redistributions due to inter-layers bonding and surface atoms under-coordination in few-graphenes membranes and carbon nanotubes. We will also present a novel method for the 3D reconstruction of few-graphenes membranes folds and undulations, providing maps of sub-nanometric height variations from the Geometric Phase Analysis of the apparent lattice deformations in individual high-resolution images of the membranes. References: [1] C. Soldano et al., Carbon 48, 2127-2150 (2010) [2] J. Meyer et al., Nano Lett. 8, 3582-3586 (2008) [3] C. Girit et al., Science 323, 1705-1708 (2009) [4] H. Lichte et al., Annu. Rev. Mater. Res. 37, 539-588 (2007) [5] M.J. Hytch et al., Ultramicroscopy 74, 131-146 (1998) Corresponding author: Luca Ortolani, E-mail: ortolani@bo.imm.cnr.it

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Raman spectral effects of edge disorder and strain distribution in monolayer graphene E. Cazzanelli a,b, M. Castriota a,b, D. Pacilè a, L. Papagno a, Ça�lar O. Girit c, Jannik C. Meyer c , Alex Zettl c and G. Mariotto d a: Department of Physics, University of Calabria, 87036-Arcavacata di Rende, ITALY b: Laboratory LICRYL CNR-INFM, 87036-Arcavacata di Rende, ITALY c: Department of Physics, University of California, 94720-Berkeley (CA), USA d: Faculty of Sciences, University of Verona, Strada le Grazie 15, 37134-Verona, ITALY Graphene sheets of different thickness, including single layers, were deposited by a standard exfoliation method [1] on SiO2/Si substrate and were characterised by optical microscopy and micro-Raman spectroscopy [2], by using different excitation wavelengths, from red (647.1 nm) to deep blue (454.5 nm). A remarkable dependence on the spatial position has been found for the peak frequency of the 2D overtone band, occurring in the region 2600-2700 cm-1 within single-layer (1L) structures. The G band frequency does not change appreciably, while the apparent bandwidth of this band can increase strongly. The maximum observed variation of 2D frequency, within single-layer domains, is more than 20 cm-1, for spatial displacements of the order of 10 micrometers, at constant excitation wavelength. Frequency shifts of this order of magnitude have been observed, both in the case of 1L flakes exhibiting high degree of order (i.e.: D band absent or barely detectable) as well as in the cases of a highly disordered 1L structures (very strong D band near the region borders and appreciable intensity inside), this latter occurring when 1L regions share borders with 2L and 10 L regions. On the contrary, no significant spatial variation of 2D peak frequency has been found for two-layer (2L) or thicker structures. These experimental results, compared with a recent Raman study under uniaxial stress [3], suggest a strain variation within the as-deposited 1L graphene sheets, whose amount can explain both the observed frequency shift of the 2D-band and the apparent broadening of the G band, which can be interpreted as an unresolved splitting due to stress-induced symmetry decrease. [1] K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I.V. Grigorieva, A. A. Firsov, Science 306, 666 (2004) [2] M. Castriota, E. Cazzanelli, D. Pacilè , L. Papagno, C. O. Girit, J. C. Meyer, A. Zettl, M. Giarola and G. Mariotto ; Diamond & Related Materials 19, 608 (2010) [3] T.M.G. Mohiuddin, A. Lombardo, R. Nair, A. Bonetti, G. Savini, R. Jalil, N. Bonini, D. M. Basko, C. Galiotis, N. Marzari, K.S. Noselov, A. K. Geim, A. C. Ferrari; Cond. Matter.mtrl- sci, arXiv:0812.1538v1, 8 December 2008

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Carbon nanostructures grown by plasma processes in liquid environments (invited contribution)

Giuseppe Compagnini Dipartimento di Scienze Chimiche, Università di Catania Viale A. Doria 6 Catania 95125, Italy Carbon-based materials are currently considered to be key elements in nanotechnology for the ability of carbon atoms to accommodate various degree of confinements, thus creating structures frequently referred to as zero-dimensional (fullerenes), one-dimensional (nanotubes) and two dimensional (graphene)[1]. Since the discovery of the first all-carbon nano-system, the central role of hot carbon vapours in the formation and growth of these appealing structures was clearly described. Indeed many synthetic approaches involve plasmas generated by pulsed-laser irradiation or arc discharge between electrodes[2]. In this frame, the use of suitable liquids (or solutions) as an environment in which the produced plasma can be confined, gives the possibility to tailor the process and discover new and intriguing synthetic possibilities[3]. This work intends to give a comprehensive view in this field through the presentation of some “in liquid” laser ablation and arc discharge experiments in which carbon materials are involved and intend to highlight the formation of new appealing carbon species in view of their future applications. A general discussion will be also provided through the comparison of the above mentioned phenomena with other energetic processes in condensed matter such as those obtained by the irradiation of carbon solids with energetic particles. References [1] T.D.Burchell “Carbon materials for advanced technologies” (Pergamon, Amsterdam, 1999) [2] G.Compagnini, et al. Journal of Physical Chemistry C 112, 20301 (2008) [3] V.Scuderi, et al. Carbon 47, 2134, 2009 Corresponding author: Giuseppe Compagnini - email:gcompagnini@unict.it

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Multi-wall carbon nanotubes and carbon hybrid systems by arc discharge in liquid nitrogen. Viviana Scuderi (1), Salvatore Bagiante (1,2), Giuseppe Compagnini (3), Luisa D’Urso (3), Santo Gibilisco (2), Vittorio Privitera (1) and Silvia Scalese (1) (1) Istituto per la Microelettronica e Microsistemi - Consiglio Nazionale delle Ricerche, Zona Industriale VIII Strada 5, I-95121 Catania, Italy (2) Dipartimento di Fisica e Astronomia, Università di Catania via S. Sofia 64, I-95123 Catania, Italy (3) Dipartimento di Scienze Chimiche, Università di Catania, Viale A. Doria 6, I-95125 Catania, Italy Arc discharge is commonly used for the synthesis of carbon nanotubes [1-2], even though is still poorly understood as concerns the process itself and the role of the discharge parameters on the formation of different kinds of nanostructures. We have investigated the effects of the experimental parameters on the structural quality of the multiwall carbon nanotubes (MWCNTs) [3] and the distribution of nanostructures in the carbon deposit produced by arc discharge [4]. A suitable combination of these parameters allowed to control the synthesis of MWCNTs and/or MWCNT/linear C-chain hybrid systems [5-6] In particular, depending on the applied voltage, it is possible to synthesize MWCNTs with an innermost tube diameter smaller than 1 nm, as confirmed by the presence of active Radial Breathing Modes (RBMs) observed in Raman spectra and by Transmission Electron Microscopy analysis. References [1] S.H. Jung et al, Appl. Phys. A 76, 285 (2003) [2] I. Alexandrou et al, J. Chem. Phys., 120, 1055 (2004) [3] S. Bagiante et al, Phys Status Solidi B 247 (4) 884 (2010) [4] S. Scalese et al, J. Appl. Phys. 108, 064305 (2010) [5] S. Scalese et al, J. Appl. Phys. 107 (1) 014304-1 (2010) [6] V. Scuderi et al, Carbon 47 (8) 2134 (2009) Corresponding author. Viviana Scuderi. E-mail address: viviana.scuderi@imm.cnr.it

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Hydrogen adsorption at high pressure in carbon nanostructures: equilibrium and kinetic properties Enrico Maccallini, Alfonso Policicchio and Raffaele Giuseppe Agostino Physics Department, Univ. of Calabria, cubo 31C, via P. Bucci, 87036, Arcavacata di Rende (Cs), Italy H2 is recognized as an ideal energy carrier even though it is not yet commercially used. A major limitation in this direction is the development of an easy and efficient storage process. Scientific research is focusing its efforts in the synthesis and characterization of nanoporous materials for H2 storage. The use of these materials, instead of a H2 storage as a cryogenic liquid or a extremely compressed gas, would resolve the safety problems and reduce the costs of the H2 transport systems. The use of nano-structured materials is based on the use of physical interactions between adsorbent and adsorbate (van der Walls forces) to achieve an easy sorption and release of the gas. However, to reach the H2 density target values indicated by the Department of Energy (DOE) of the United States of America [1], which sets the gravimetric capacity of hydrogen as 6 weight%, we need the 'tuning' of porous materials (pores size and distribution, specific active surface area), the use of lightweight materials and the functionalization of the pore walls for an effective hydrogen adsorption and release. In this framework, the hydrogen adsorption properties of graphite-based materials have been investigated using a Sievert-type volumetric apparatus [2] with which we collect the adsorption isotherms and the relative kinetic behavior. The investigated carbon-based samples have low (activated carbon and cellulose), medium (carbon nanotubes) or high (graphene) specific surface areas. The isotherms were recorded up to 8 MPa and at different temperatures (77 K and ambient temperature). The asymptotic adsorbed H2 amount seems to be mainly related to the specific surface of samples. However, in graphene samples at high pressures, we find a selective adsorption allowing the access to the internal surfaces. The results of repetitive adsorption/desorption cycles show the mechanical stability of these materials. Furthermore, different adsorption kinetics are observed according to the samples porosity. In particular, we observed much faster molecular hydrogen diffusion in graphene samples than in the carbon nanotubes and activated carbon/cellulose ones. The equilibrium adsorption properties and the relative kinetics are linked to the morphological and structural properties revealed through the SEM, XRD and BET techniques. References [1]National Hydrogen Energy RoadmapUnited States Department of Energy, results from the National Hydrogen Energy Roadmap Workshop, Washington DC, April 2-3 2002. http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/national_h2_roadmap.pdf [2]R. G. Agostino, et al., submitted (2010) Corresponding author: Agostino Raffaele Giuseppe, e-mail: raffaele.agostino@fis.unical.it

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Dynamical phase diagram for chiral quasi particles in a noisy environment

Giuseppe Falci, Elisabetta Paladino, Antonio D’Arrigo and Marco Berritta MATIS-INFM-CNR Catania

DMFCI-Universita’ degli studi di Catania, Italy We consider a particle whose free dynamics obeys the two-dimensional Dirac-Weyl equation [1], as quasi-particles in grapheme [2], and we study the effect of coupling to a time-dependent uniform field, which may have both deterministic and stochastic parts, or even be quantized. We find an exact mapping, wherethe pseudospin only is coupled anisotropically to a general quantum field. Impolementing an effective driven two-level atom, subject to classical or quantum noise. The “atom” is coupled dispersively with a continuous conserved degree of freedom (the total momentum), yielding conditional dynamics and entanglement. The atomic analogy suggest that is possible to control the dynamics of the pseudospin of the quasiparticle with protocols of quantum optics, operated by electrostatic coupling only. In chiral quasiparticle system, as in grapheme, this allows quantum control of photocurrents. We apply the theory to wave-particle motion and study how classical/quantum noise modify the phenomena of Spin Separation (SS) and Zitterbewegung (ZB) [1,3,4,5]. This latter is one of the striking manifestations of the coherent chiral pseudospin dynamics, and due to zero-gap it may have macroscopic size. Moreover it determines fundamental phenomena as the residual conductance at the Dirac point and the Quantum Hall Effect [2,4,6]. We derive the exact master equation for the pseudospin and present results in the an exactly solvable case of white noise [5,7], obtaining a generalized Lindblad master equation. It is seen that non-secular dynamics, which determines overdamped components of the motion is very important, contrary to the standard case in atomic physics. We also point out that overdamped ZB can be understood in terms of the quantum Zeno effect [8], and derive a phase diagram in the space of the parameters [7]. For special one-dimensional “longitudinal” preparations of the wavepacket we derive an exact result for arbitrary spectral density of the quantum noise [5]. It is seen that pseudospin dynamics is extremely sensitive to low-frequency components of the quantum noise, showing that the behavior near the Dirac points must be determined from out of equilibrium dielectric properties. References [1] W. Greiner, Relativistic quantum mechanics, Springer, 2003. [2] A.H. Castro Neto et al., Rev. Mod. Phys. 81 (2009) 109. [3] J. Cserti et al., Phys. Rev. B 74, 172305 (2006); J.Schliemann, D.Loss, R.M.Westervelt, Phys. Rev. B 73, 085323, (2006); J.Schliemann et al., Phys. Rev. Lett. 94, 206801 (2005 [4] J.Y. Vaishnav et al., Phys. Rev. Lett. 100, 153002 (2008) [5] G. Falci, M. Morello, M. �rapheme, A. D’Arrigo, E. Paladino, Physica E 42, 584 (2010). [6] M.I. Katsnelson, Eur. Phys. J. B 51, 157 (2006). [7] M. �rapheme, E. Paladino, M. Morello, A. D’Arrigo and G. Falci, subm. To Phys. Rev. E, 42, 584 (2010); and M. Berritta, E. Paladino, A. D’Arrigo and G. Falci In: Physics and Control 2009 – IPACS Library p. 1987. [8] P. Facchi et al., Phys. Rev. A 71 022302 (2005). Corresponding author: Giuseppe Falci, e-mail: gfalci@dmfci.unict.it

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Graphene nanostructures and interfaces for (nano)electronics applications: ab initio calculations Giovanni Cantele, Ivo Borriello Domenico Ninno CNR-SPIN and University of Napoli “Federico II” – Physical Sciences Department, Compl. Univ. M.S. Angelo, Via Cintia, I-80126, Napoli, Italy Since its discovery, �rapheme, a single plane of carbon atoms with honeycomb arrangement, has emerged as one of the most promising materials for a variety of applications ranging from (nano)electronics to window electrodes for solid-state dye-sensitized solar cells, solid-state sensors, hydrogen storage and others [1]. The two-dimensional structure, amenable to lithographic techniques, made possible single graphene nanoribbon patterning, with defined width and orientation. Electronic-structure calculations have shown that edge states emerge in zigzag-edge graphene nanoribbons (ZGNRs); the resulting peak in the density of states at the Fermi level induces a magnetic instability that leads to a ground state with antiferromagnetic ordering, where the spins on the two ribbon edges opposite orientations. In this work some recent results [2] on the electronic properties of functionalized ZGNRs and �rapheme/metal interfaces are shown, with the aim of elucidating potential applications in spin-valve and nanoelectronics devices. In particular, since edge terminations, passivations, and defects play a key role in the performance of graphene, we characterize the avenues available to control electronic and spin transport with chemical functionalizations or defects following hydrogenation or treatment with ion or electron beams. We use an original approach, based on the chemically accurate and minimal basis of maximally localized Wannier functions, suitable to describe the electronic structure and ballistic transport in large-scale nanostructures. It is shown that defects in spin-polarized ZGNRs can be effectively used to remove the unpolarized conduction channels in the bulk of the ribbon, while preserving edge states. The resulting asymmetry between the spin-up and spin-down channels makes these systems ideal candidates for spin-polarized transport with a very high degree of spin polarization. As a next step, we are investigating the effects of a metallic substrate, needed to either support or contact graphene nanoribbons devices. At this purpose, a recent route for the covalent graphene immobilization on metallic substrate is being explored, elucidating the role of the metal Fermi level on the material doping. REFERENCES [1] A.K. Geim, Science 324, 1530 (2009) [2] G. Cantele et al., Nano Lett. 9, 3425 (2009) Corresponding author: Giovanni Cantele, e-mail: giovanni.cantele@na.infn.it

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Pairing symmetry of superconducting graphene F. M. D. Pellegrino (1,2,3), G. G. N. Angilella (1,2,3,4), R. Pucci (1,3) (1) Dipartimento di Fisica e Astronomia, Universit`a di Catania, Via S. Sofia,64, I-95123 Catania, Italy. (2) Scuola Superiore di Catania, Via S. Nullo, 5/i, I-95123 Catania, Italy. (3) CNISM, UdR Catania, I-95123 Catania, Italy. (4) INFN, Sez. Catania, I-95123 Catania, Italy The possibility of intrinsic superconductivity in alkali-coated graphene monolayers has been recently suggested theoretically. Here, we derive the possible pairing symmetries of a carbon honeycomb lattice and discuss their phase diagram. We also evaluate the superconducting local density of states (LDOS) around an isolated impurity. This is directly related to scanning tunneling microscopy experiments, and may evidence the occurrence of unconventional superconductivity in graphene. Corresponding author: G. G. N. Angilella (giuseppe.angilella@ct.infn.it).

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Atomistic quantum transport modeling of junctions between metallic contacts and pure/defected graphene nanoribbons Ioannis Deretzis (1) , Gianluca Fiori (2), Giuseppe Iannaccone (2), Antonino La Magna (1) (1) CNR-IMM, Z.I. VIII Strada 5, 95121 Catania, Italy (2) Dipartimento di Ingegneria dell’Informazione, Università di Pisa, Via G. Caruso 16, 56122 Pisa, Italy We perform self-consistent quantum transport calculations for metal-graphene nanoribbon heterojunctions, by means of a coupled Schrödinger/Poisson approach. Attention is paid on both the chemical aspects of the interface bonding as well the one-dimensional electrostatics along the ribbon length. We study quantities that are inherently correlated with Schottky junctions, like depletion length scales, charge transfer and barrier heights. Simulation outcomes show that band bending and doping effects strongly influence the transport properties, giving rise to conductance asymmetries and a selective suppression of quantum quantization. Junction electrostatics and p-type characteristics drive the conduction mechanism in the case of high work function Au, Pd and Pt electrodes, while contact resistance becomes dominant in the case of Al. On the basis of this analysis we evaluate the capability of the various metals to form transparent contacts on graphene. We moreover discuss the effects of backscattering due to the presence of vacancies. Results highlight the importance of confinement and geometry on the shaping of the local density of states around the defects that can lead to important alterations on the conduction process, giving rise to impurity-like pseudo gaps in the conductance distribution [1]. [1] I. Deretzis, G. Fiori, G. Iannaccone, and A. La Magna, Phys. Rev. B 81, 085427 (2010) Corresponding author: Ioannis Deretzis Email: ioannis.deretzis@imm.cnr.it

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Rapid identification of graphene flakes: Alumina does it better Patrizia De Marco (1,2) , Michele Nardone (2), Annalisa Del Vitto (3), Mauro Alessandri (3), Sandro Santucci (1,2), Luca Ottaviano (1,2) (1) Dipartimento di Fisica, Università dell’Aquila, Via Vetoio, 67100, Coppito-L’Aquila, Italy (2) CNR-SPIN L’Aquila, Via Vetoio, 67100, Coppito-L’Aquila, Italy (3) Numonyx Agrate Brianza, Milano, Italy Nowadays graphene is one of the hottest systems under investigation in materials science and condensed matter physics. The micro-mechanical exfoliation of HOPG yields to graphene flakes with various thicknesses that, once deposited on a dielectric substrate, can be rapidly identified by white light contrast analysis via an optical microscopy survey. 300 nm thick SiO2/Si(100) is widely recognized as a good substrate to rapidly locate exfoliated graphene flakes. Very recently, it has been demonstrated that 72 nm thick Al2O3/Si(100) shows an optical contrast that is 3 times higher than the one observed on 300 nm thick SiO2 [1]. We report a systematic investigation of the colour contrast (CC) of Graphene (one, two and three layers) on 50, 72 and 80 nm thick Al2O3/Si(100) and 100 and 300 nm thick SiO2/Si(100). The CC is determined by the analysis of optical microscopy images taken under white light illumination. A corresponding assignment of graphene in the single, double and try layer phase is made with micro-Raman spectroscopy. A quantitative evaluation allows to conclude that the color contrast between 72 nm alumina and graphene is significantly larger than the one between 300 nm silicon oxide and graphene (by a factor 2.2, 2.0 and 3.3 for the single, double and tri-layer graphene flakes respectively). Moreover, data indicate that, to increase the visibility, the use of a red or a green light is preferable [2]. [1] L. Gao et al, ACS Nano 2, 1625 (2008) [2] P. De Marco et al, Nanotechnology (in press) Corresponding author: Patrizia De Marco, patrizia.demarco@aquila.infn.it

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Role of graphene /substrate interface on the local transport properties of the twodimensional electron gas S. Sonde (1,2), C. Vecchio (1,2), F. Giannazzo (1), R. Yakimova (4), V. Raineri (1), E. Rimini (1,3) 1CNR-IMM, Stradale Primosole, 50, 95121, Catania, Italy. 2Scuola Superiore di Catania, Via San Nullo, 5/i, 95123, Catania, Italy. 3Dipartimento di Fisica ed Astronomia, Università di Catania, Via S. Sofia, 64, 95123 Catania, Italy. 4IFM, Linkoping University, Linkoping, Sweden Graphene is currently the object of large research efforts, owing to the remarkable properties of the two-dimensional electron gas (2DEG), like the giant intrinsic carrier mobility. Since electrons in graphene are confined to a plane of atomic thickness, the transport properties (electron mean free path and mobility) are affected substantially by the surrounding environment, in particular by the interface with the substrate. In the present work we applied a recently demonstrated scanning probe method (based on Scanning Capacitance Spectroscopy, SCS, [1,2]) to “locally” probe the transport properties (electron mean free path l and mobility �) of graphene obtained with different preparation methods and on different substrates, i.e. graphene exfoliated from HOPG and deposited on SiO2 (DG/SiO2) and SiC (DG/SiC), and epitaxial graphene grown on SiC (EG/SiC). Epitaxial growth of graphene on SiC was carried out in Ar environment in an inductively heated reactor at a temperature of 2000 °C [3], or in a commercial furnace at temperature from 1600 to 1700 °C. Highly doped 4H-SiC (0001) substrates, 8° off, with of a lowly doped (~1014 cm-3) epilayer were used. The number of graphene layers obtained for fixed process conditions was determined by cross-section transmission electron microscopy. Graphene obtained by mechanical exfoliation of HOPG was also deposited on the surface of a pristine sample of the same 4H-SiC wafer and on the surface of a SiO2/Si sample. Measurements on these three kinds of samples allowed to clarify the role of the interface with the substrate and of the dielectric properties of the substrate on graphene transport properties. First, dedicated test structures have been fabricated both on EG on SiC (EG/SiC), and on deposited graphene on SiC (DG/SiC) and on SiO2 (DG/SiO2), to measure � and l on macroscopic scale. The results of macroscopic measurements were compared with those of local measurements by SCS. The local electron mean free path was measured on arrays of different tip positions on EG/SiC, on DG/SiC and DG/SiO2. For the same carrier density in the graphene sheets (~1011 cm-2), l on DG/SiC is on average about two times than on DG/SiO2. This difference can be explained in terms of the different permittivities of SiC and SiO2 and of the different coupling of the 2DEG with surface polar phonons in SiO2 and SiC. On EG/SiC l is on average ~0.45 times that on DG/SiC, and a much larger spread in the l values is observed from point to point. This difference can be ascribed to a large and inhomogeneous density (from ~1012 to ~1013 cm-2) of positive charges which is present at EG/4H-SiC (0001) interface [3] and is instead absent at DG/SiC interface. [1] F. Giannazzo, S. Sonde, V. Raineri, E. Rimini, Nano Lett., 9, 23 (2009). [2] F. Giannazzo, S. Sonde, V. Raineri, E. Rimini, Appl. Phy. Lett. 95, 263109 (2009). [3] S. Sonde, F. Giannazzo, V. Raineri, et al., Phy. Rev. B 80, 241406(R) (2009). Corresponding author: e-mail: sushant.sonde@imm.cnr.it

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Orion Plus: exploiting He-Ion Microscope imaging and nano-modification capabilities Giulio Lamedica Assing SpA Via E Amaldi 14, 00015 Monterotondo (RM) The need for more precise image information of samples coming from fields such as materials analysis, semiconductor processing, and life sciences have pushed the boundaries of charged particle microscopy. The Orion Plus microscope has been developed that uses a beam of helium ions which is focused and scanned across the sample. In principle, and in its applications, it is similar to a traditional scanning electron microscope (SEM). However, the source technology, the sample interaction, and the contrast mechanisms are distinctly different. The helium ion source offers high brightness and a small energy spread, and hence allows the beam to be focused into very small probe sizes. Here are presented high resolution carbon nano tubes images and nano-modification capabilities on graphene demonstrating the outperforming capability of the Orion Plus He-Ion microscope. Acknowledgement: Zeiss NTS Corresponding Author: Giulio Lamedica: g.lamedica@assing.it

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Clean carbon nanotubes: From single-electron quantum dots to high quality nanomechanical resonators

(invited contribution) Gary A. Steele TU Delft, The Netherlands In conventional nanotube devices, nanotubes are first deposited on the surface of a substrate and subsequently patterned to make nanoscale devices. While this process is very flexible, it has the disadvantage that the nanotube can become contaminated and damaged by chemical and electron beam processing. Here, we present results from a new type of clean nanotube device that avoids all possible damage to the nanotube by growing it in the last step of fabrication. By eliminating disorder, we achieve a new level of control over single electrons in a carbon nanotube, tuning continuously from a single quantum dot (“artificial atom”) to a double dot (“artificial molecule”) for a single electron or hole confined in the nanotube. Studying this tunability, we observe a curious type of tunneling that is analogous to Klein tunneling in relativistic quantum mechanics. Clean carbon nanotubes also exhibit spectacular mechanical properties as nanomechanical resonators with quality factors exceeding 10^5. Here, we study the coupling of this motion a quantum dot embedded in the nanotube. We find that this coupling is remarkably strong, dominating the dynamics of the mechanical motion.

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Carbon nanotubes based electron guns to improve the performances of Electron Cyclotron Resonance Ion Sources

Rita Rizzoli (1), Giulio Paolo Veronese (1), Fabrizio Odorici (2), Luciana Malferrari (2), Marco Cuffiani (3), Santo Gammino (4), Luigi Celona (4), David Mascali (4,5), Nadia Gambino (4,6), Rosalba Miracoli (4,7), Tiziana Serafino (8)

(1) CNR - Istituto IMM, Via Gobetti 101, I - 40129 Bologna (2) INFN - Sezione di Bologna, Viale B. Pichat 6/2, I- 40127 Bologna (3) Dipartimento di Fisica, Università di Bologna, Viale B. Pichat 6/2, I - 40127 Bologna (4) INFN - Laboratori Nazionali del Sud, via S. Sofia 62, I - 95123 Catania (5) CSFNSM, Viale A. Doria 6, I - 95125 Catania (6) Dip. di Metodologie Fisiche e Chimiche per l’Ingegneria, Università di Catania, Viale A. Doria 6, I - 95125 Catania (7) Dip. di Fisica e Astronomia, Università di Catania, via S. Sofia 64, I - 95123 Catania (8) Università di Messina, Ctr.da Papardo-Sperone, I - 98100 Messina

One of the crucial issues for the plasma stability within Electron Cyclotron Resonance (ECR) ion sources is the so-called electron starvation. The injection of auxiliary electrons into the magnetic trap is then necessary to obtain an electron density large enough for efficient ionization of the low-gas-pressure plasma. Moreover, the plasma quasi-neutrality is responsible of large ion losses onto the plasma chamber wall, unless the electron deficit is reduced. By exploiting field emission electron sources based on carbon nanotube (CNT) arrays, an alternative method to provide additional electrons to the plasma core has been proposed. Good quality CNTs are grown by Catalytic Chemical Vapor Deposition inside vertically aligned nanopores of an anodic alumina template prepared on a Si substrate, which provides the back contact to the CNTs. These electron guns, tested within an ECR ion source, have been able to inject electrons in the plasma and increase the plasma density and thus the total extracted ion current. In addition, a relevant reduction of the number of “high energy” electrons (above 100 keV) has been observed, which is even more important, because such hot electrons, coming out when large power and high frequencies are used, have detrimental effects on the source stability and reliability. The fabrication of CNTs based electron guns, their behaviour in plasma environments and preliminary results in terms of variations in the extracted charge state distribution and X-ray spectra from the ECR ion source will be presented. The structural and electrical characterizations of these CNTs based sources, performed by micro-Raman spectroscopy, SEM observations and field emission measurements both before and after their testing in plasma environments, will be also discussed. Corresponding author: Rita Rizzoli rizzoli@bo.imm.cnr.it

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Direct synthesis of hybrid nanostructures based on multi-walled C nanotubes for high-performance polymer composite applications Elpida Piperopoulos (1), Saveria Santangelo (2), Giuliana Faggio (2), Giuliana Gorrasi (3), Maurizio Lanza (4), Signorino Galvagno (1), Giacomo Messina (2), Candida Milone (1) (1) Dept. of Industrial Chemistry and Materials Engineering, University of Messina, I-98166 Messina, Italy (2) Dept. of Mechanics and Materials, University “Mediterranea” of Reggio Calabria, I-89122 Reggio Calabria, Italy (3) Dept. of Chemical and Food Engineering, University of Salerno, I-84084, Italy (4) CNR, Inst. for Chemical Physical Processes, Messina Section, I-98158 Messina, Italy Multi-walled C nanotubes (MWCNTs) are very attractive candidates for a lot of advanced nanotechnology applications, ranging from nanoelectronics [1] to reinforcing [2] and flammability retardancy [3] of polymers. Catalysed chemical vapour deposition (CCVD) is broadly preferred for their bulky production [4]. Present work deals with MWCNT-based hybrids, prepared by direct CCVD growth of MWCNTs on suited supports, to be incorporated in a polymeric matrix so as to finally obtain polymeric composites with improved physical properties and enhanced performances. CCVD in 1:1 isobutane/hydrogen atmosphere is carried out at moderate temperature (600–700°C) over Fe-catalysts reduced at different temperatures (500–700°C). Besides to the conventional silica and alumina (SiO2 and Al2O3) catalyst supports, also alkaline earth metal oxides (MgO, CaO, SrO or BaO) and montmorillonite (MM) are utilised. Catalysts employed and carbonaceous deposits obtained are systematically characterised by the use of several techniques (XRD, TPR, SEM, TEM, TGA and Raman spectroscopy), in order to investigate the influence of catalyst specifics on reaction yield, selectivity and characteristics (crystallinity, purity and thermal stability) of the grown MWCNTs. The crystalline perfection of MWCNTs synthesised over sodium-exchanged MM catalysts (Na+-MM) is outstanding; it is the highest ever reported in literature for similarly grown nanotubes [5]. Poly-L-Lactide Acid (PLLA) samples loaded with MWCNTs/MM and MWCNTs/Na+-MM hybrids become semiconductive. However, PLLA-MWCNTs/Na+-MM exhibits a lower percolation threshold than PLLA-MWCNTs/MM (1.35wt% against 2.80wt%) and at given filler load undergoes a larger conductivity enhancement: for 5wt% filler, the increase if of 9 instead of 6 orders of magnitude with respect to the pristine insulating PLLA (σ =1 10–10S/m). References [1] J. Robertson, G. Zhong, S. Hofmann et al., Diam. Rel. Mater. 18, 957 (2009). [2] A.M.K. Esawi, M.M. Farag, Mater. Design 28, 2394 (2007). [3] S. Fu, P. Song, H. Yang, Y. Jin et al., J. Mater. Sci. 45, 3520 (2010). [4] G.Messina, V.Modafferi, S.Santangelo et al., Diam. Rel. Mater. 17, 1482 (2008). [5] T. Tsoufis, L. Jankovic, D. Gournis et al., Mat. Sci. Eng. B 152, 44 (2008). Corresponding author: Saveria Santangelo - e-mail address: saveria.santangelo@unirc.it.

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Percolation behavior of MWNT/epoxy composites: from the statistical to the dynamic threshold Gabriella Faiella, Vincenza Antonucci, Mauro Zarrelli, Michele Giordano Institute for Composite and Biomedical Materials (IMCB) – National Research Council (CNR) P.le E. Fermi 1 80055 Portici (NA) - Italy Polymer composites possessing conductive electrical properties are typically produced by dispersing conductive particles within the insulating matrix. In this field, carbon nanotubes (CNTs) have been considered ideal candidates to be used as fillers because of their exceptional electrical properties. The transition from an insulating to a conducting behavior is known as percolation and the concentration at which this drop occurs is named percolation threshold. The statistical theories describing this phenomenon consider random fillers distribution and static particles not allowed to move within the hosting matrix. However, many experimental results showed that a percolation threshold much lower than the predicted statistical one can be measured in CNTs composites [1, 2]. This percolation threshold reduction is due to the occurrence of strong interactions between tubes and between tubes and matrix, that induce agglomeration phenomena driven by external forces such as temperature and shear. In a previous work [3], authors described how it is possible to obtain a fine tuning of the insulator to conductor transition in multiwalled-epoxy carbon nanotubes (MWNTs) composites at a fixed nanotubes concentration through the development of different tubes network morphologies induced by the variation of process parameters. Here a study of the electrical percolation behavior of MWNTs-epoxy composites having different tunable electrical properties has been carried out by varying process parameters, such as sonication time and curing temperature. Two types of pristine nanotubes have been used and a fine tuning of the composites electrical conductivity with process parameters has been observed for both the types of nanotubes. A notable result of this work consists in the possibility to tune the percolation threshold of the composites in a wide range of concentration, from values two orders of magnitude below the theoretical one up to it. References should be listed as below [1] C.A. Martin et al., Comp. Sci. Technol. 64, 2309-2316 (2004). [2] J.Z. Kovacs et al., Comp. Sci. Technol. 67, 922-928 (2007). [3] G. Faiella et al., Appl. Phys. Lett. 95, 153106-153108 (2009). Corresponding author: Gabriella Faiella – gabriella.faiella@imcb.cnr.it

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The effect of the aspect ratio of carbon nanotubes on their effective reinforcement modulus in an epoxy matrix. Alfonso Martone, Cristina Formicola, Gabriella Faiella, Mauro Zarrelli and Michele Giordano CNR-National Research Council, IMCB-Institute for Composite and Biomedical Materials, P.le E. Fermi 1, 80055 Portici, Italy The potentiality of carbon nanotubes as reinforcement for polymer matrix is primarily due to the exceptional high intrinsic modulus of these carbonaceous structures of the order of 1TPa and their very high aspect ratio. Several studies [1] have sought to verify the reinforcement effect of CNT on the mechanical properties of polymer matrices. Nanotubes reinforcement effects, indeed, depend by their amount within the hosting matrix but also by their state of dispersion [2]. CNT aggregation or networking, in fact, may become a defect causing a loss of the theoretical enhancement of the mechanical properties for the final composites. As a matter of fact, when high aspect ratio tubes are individually hosted inside a matrix, they can display the maximum efficiency in stress transfer with matrix; networking, instead, may lead to either a reduction of the effective aspect ratio, therefore decreasing the stress loading efficiency and the presence of weak points of adhesion among nanotubes. These two features, surely cause a reduction of the expected theoretical reinforcement effect. In addition, increasing nanotube content, the clustering on the different dimension scales, typical of the multi-scale structures of nanotube agglomerates, may also represents a further reduction of the expected mechanical performances [3]. In this work, we have been investigated the reinforcement efficiency of different multi-walled carbon nanotubes (MWCNT) aerospace epoxy composites, paying attention at two main aspects: the behavior at very low concentration in respect to the percolation limit and the effect of nominal aspect ratio of a series of nanotubes [4-5]. Final results have revealed a critical volume fraction inversely related to the CNT aspect ratio, which separates at least two limiting behaviors: for higher content the reinforcement effect drops while for lower concentrations, the maximum efficiency of CNR reinforcement is achieved. Such a behavior results in accordance with the percolative threshold theory for tubes. References [1] D. Qian et al., Appl. Phys. Lett. 76, 2868-70 (2000) [2] E. T. Thostenson et al., Compos. Sci. Technol. 65, 491-516 (2005) [3] A. Martone et al., Compos. Sci. Technol., 70, 1154-1160, (2010) [4] G. Faiella et al., Appl. Phys. Lett. 95, 153106 (2009) [5] G. Stauffer, Introduction to percolation theory, Taylor & Francis, London (1985). Corresponding author: Alfonso Martone alfonso.martone@imcb.cnr.it

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Nanoindentation on polyvinylbutyral (PVB) carbon nanotubes composites Mauro Giorcelli (1) , Sunil Bhardwaj (2), Alberto Tagliaferro(1) (1) Politecnico di Torino, c.so Duca degli Abruzzi 24, 10129 Torino (2) Istituto Officina dei Materiali - CNR, National Laboratory TASC, Basovizza, 14 Km.163.5 I-34149 Trieste, Italy Instrumented indentation testing was used to evaluate the variation in mechanical properties of polyvinylbutyral (denoted as PVB) when of multi walled carbon nanotube in different percentage were added. The nanotubes were prepared using a chemical vapour deposition technique and successively added as filler in PVB. Hardness and elastic modulus were measured on the samples. The variations in elastic modulus and hardness obtained using nanoindentation showed quantifiable differences between the various composite specimens. In particular an addition of 0,1 wt% of carbon nanotubes increase the hardness of about 20% with respect to pure PVB. The changes in the observed stiffness and breaking strength were also evaluated and discussed. References [1] Xiao-Feng LI et al., in Composite Science and Technology 68 (2008): Mechanical properties of epoxy-based composites using coiled carbon nanotubes pp.2876-2881 [2] Bhushan B, Li X. in Int Mater Rev (2003) 8: Nanomechanical characterization of solid surfaces and thin films pp.125–64. Corresponding author: Mauro Giorcelli mauro.giorcelli@polito.it

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Ultra-clean carbon nanotubes for optoelectronic devices Salvatore Bagiante (1,2), Gary A. Steele (3), Gilles Buchs (3), Silvia Scalese (1), Valery Zwiller (3) and Leo P. Kouwenhoven (3). (1) Istituto per la Microelettronica e Microsistemi, Consiglio Nazionale delle Ricerche, Zona Industriale VIII strada n. 5, Catania 95121, Italy. (2) Dipartimento di Fisica e Astronomia Università di Catania, Viale A. Doria 6, Catania 95125, Italy. (3) Kavli Institute of NanoScience, Delft University of Technology, PO Box 5046, 2600 GA, Delft, The Netherlands. Single-walled carbon nanotubes (SWNTs) are a new class of material with potentially useful properties for building electronic devices [1]. In addition, semiconducting SWNTs are direct bandgap materials and thus they may be useful for photonics and optoelectronic applications [2]. This study has been focalized to create an optoelectronic device using ultra clean carbon nanotubes (CNT). Ultra-clean means that our nanotubes are grown on the chip in the last step of the process and they have exceptional electrical mechanical and optical properties. We report the characterisation of different metals for contacting our ultra-clean carbon nanotubes, after many tests we have found different metals that are good candidates as ambipolar, p-type contact. Electrical measurements have been performed and we have observed that drain current changes when different bias are applied to the gates. The device has been characterized by scanning photocurrent microscopy (SPCM). This technique constitutes a very useful tool to study the spatial variations of the potential along suspended nanotubes for different gates voltages under laser excitation. SPCM, compared with other analytical techniques (e.g SEM, AFM), allows the individuation of a suspended SWCNT without altering its characteristics. With this technique we have seen as it is possible to have a precise doping spatial control in the nanotube. [1] M. Dresselhaus et al., Carbon Nanotubes: Synthesis, Structure Properties and Applications, ed- ited by (Springer, Berlin, 2001). [2] Phaedon Avouris et al., Nature Photonics, 2 , 341-350 (2008).

Corresponding author. Salvatore Bagiante. E-mail address: salvatore.bagiante@imm.cnr.it

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Optical Trapping of Nanotubes and Graphene O.M. Maragò(1), R. Saija(2), P.G. Gucciardi(1), M.A. Iatì(1), G. Calogero(1), F. Borghese(2), P. Denti(2), P.H. Jones(3) (1) Istituto per i processi chimico-fisici del CNR (U.O. Messina), Messina, Italy (2) Dip. di Fisica della Materia e Ingegneria Elettronica, Università di Messina, Messina, Italy (3) Department of Physics and Astronomy, University College London, London, UK Optical Tweezers, instruments based on a tightly focussed laser beam, have been used to trap, manipulate, control and assemble dielectric particles, single atoms, cells, metal and semiconduncting nanostructures, leading to a real optical revolution in Physics, Biology and Nanotechnology. In particular optical trapping of one-dimensional nanostructures has great potential for top-down organization of complex nano-assemblies [1-7] and increased space and force resolution in photonic force microscopy [1,5,8]. Their small transverse size is the key to achieve nanometric resolution, while an axial dimension in the micron range ensures stable trapping and force sensing in the femtonewton regime. Here we review our recent results on optical trapping and force sensing with nanotubes and graphene [3-6,9]. We show how to extract the distribution of both centre-of-mass and angular fluctuations from three-dimensional tracking of optically trapped nanotubes [5]. The optical force and torque constants can be measured from auto and cross-correlation of the tracking signals [5,6]. This allows us to isolate the angular Brownian motion [5]. We demonstrate that nanotubes enable nanometre spatial, and femto-Newton force resolution in photonic force microscopy [1,5,8] by accurately measuring the radiation pressure in a double frequency optical tweezers. Furthermore we use correlation function analysis to study the rotational dynamics of light driven nanorotors made of nanotube bundles [6]. We then extend our results to study trapping and dynamics of individual graphene flakes in solution. Finally, we show how to integrate optical trapping with Raman and photoluminescence spectroscopy. We demonstrate the use of these Raman and photoluminescence Tweezers to study nanotubes and graphene flakes in solution [9]. References [1] Maragò, O.M, Jones P.H., Gucciardi P.G. Photonic Force Microscopy: From Femtonewton Force Sensing to Ultra-Sensitive Spectroscopy, in “Scanning Probe Microscopy in Nanoscience and Nanotechnology”, ed. B. Bushan, Springer-Verlag (2010). [2] Nakayama, Y. et al. Nature 447, 1098-1102 (2007). [3] Borghese, F. et al. Phys. Rev. Lett. 100, 163903 (2008). [4] Maragò O.M. et al., Physica E 40, 2347-2351 (2008). [5] Maragò, O.M. et al. Nano Lett. 8, 3211-3216 (2008). [6] Jones, P.H. et al. ACS Nano 3, 3077 (2009). [7] Neves A.A.R. et al., Opt. Express 18, 822 (2010). [8] Florin E. L., et al., J. Struct. Biol. 119, 202 (1997). [9] Maragò O.M. et al., Submitted (2010). Corresponding author: O.M. Maragò, marago@me.cnr.it

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Micro-Raman study of transition metal oxide/carbon-nanotubes hybrid nanostructures for gas sensing applications Domenico Alfieri (1), Lidia De Luca (1), Andrea Donato (1), Nicola Donato (2), Giuliana Faggio (1), Giacomo Messina (1), Giovanni Neri (3), Nicola Pinna (4), Saveria Santangelo (1), Pietro Tripodi (1) (1)Department of Mechanics and Materials, University “Mediterranea” of Reggio Calabria, I-89122 Reggio Calabria, Italy (2)Department of Matter Physics and Electronic Engineering, University of Messina, I-98166 Messina, Italy (3)Department of Industrial Chemistry and Materials Engineering, University of Messina, I-98166 Messina, Italy

(4)Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal Transition metal oxide/carbon nanotubes (TMO/CNTs) hybrids are a new class of materials with promising applications in many technological fields, including gas sensing [111]. Present work deals with NO2 and H2 sensing devices, fabricated using respectively vanadia/CNTs and titania/platinum/CNTs hybrid nanostructures, prepared by different synthetic approaches, as active sensor components. Vanadia/CNTs are obtained via a modified approach to the atomic layer deposition (ALD) that allows the homogeneous coating of CNTs with nanometer thick films of TMOs [222]. Titania/platinum/CNTs are obtained by wetness impregnation of titania/CNTs prepared by sol-gel method [333]. In order to more deeply understand the sensing properties of the considered hybrid nanostructures, a systematic investigation by micro-Raman spectroscopy is carried out. As concerns “as prepared” vanadia/CNTs, the obtained results demonstrate that the composition of the coating layer is V2O4 with a marked degree of amorphousness. Moreover, the thermal treatment (25–375 °C) carried after synthesis primarily affects the oxide coating-layer that is responsible for the sensing properties. The best sensor-performance is obtained at the temperature (~220°C) at which the oxide layered-structure exhibits the highest structural order. As concerns titania/CNTs, the results show that, in a wide range of nominal C/Ti molar ratio (from 0.3 to 17.0) only the anatase phase of titania is formed. Theoretical calculations based on phonon confinement reveal that the small grain size (about 5 nm) of TiO2 crystallites is fully responsible for the large blue shift (~10 cm–1) and broadening (~20 cm–1) of the lowest-frequency Raman mode with respect to bulk anatase. On the basis of the results obtained, hypotheses on the sensing mechanisms operating on these nanostructured hybrid materials have been formulated. References [111] T. Ueda, K. Takahashi, F. Mitsugi, T. Ikegami, Diam. Rel. Mater. 18, 493 (2009). [222] E. Rauwel, G. Clavel, M.-G. Willinger et al., Angew. Chem., Int. Ed. 47 3592 (2008) [333] L.DeLuca, A.Donato, G.Apa, S.Santangelo et al., “AISEM Conference”, Messina (Italy), Febr. 8−10, 2010 Corresponding author: Saveria Santangelo - e-mail address: saveria.santangelo@unirc.it.

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Field effect devices on graphene exfoliated from graphite and on graphene epitaxially grown on SiC C. Vecchio (1,2), S. Sonde (1,2), F. Giannazzo (1), F. Roccaforte (1), V. Raineri (1), S. Di Franco (1), C. Bongiorno (1), E. Rimini (1,3) 1CNR-IMM, Stradale primosole, 50, 95121, Catania, Italy. 2Scuola Superiore di Catania, Via San Nullo, 5/i, 95123, Catania, Italy. 3Dipartimento di Fisica ed Astronomia, Università di Catania, Via S. Sofia, 64, 95123 Catania, Italy. Graphene has generated a lot of interest in the research community due to its outstanding electronic properties, like very high carrier mobility, which could open the way to the fabrication of innovative transistors operating at very high frequencies. Currently several methods have been demonstrated to obtain single few layers of graphene, like the mechanical or chemical exfoliation from highly oriented pyrolitic graphite (HOPG) and the growth of epitaxial graphene (EG) on SiC by controlled graphitisation of the surface at high temperatures (1200 –2000 °C) in inert gas ambient. Among these different synthesis methods, mechanical exfoliation of HOPG has produced high crystalline quality graphene samples, which can be deposited on several materials (deposited graphene (DG)). Epitaxial growth by thermal annealing of SiC has the advantage to yield single layer (SL) or few layers (FL) of graphene directly on a semiconductor substrate. Epitaxial graphene (EG) typically cover an entire wafer, thus allowing large scale fabrication of graphene based devices. In the present work, the elementary micro- and nano-fabrication steps necessary to the fabrication of field effect devices based on DG and EG have been investigated, i.e. lateral isolation of graphene structures by O2 plasma etching, deposition of different dielectric layers working as gate material, deposition of contacts for source/drain and gate electrodes. Epitaxial growth of graphene on SiC was carried out in Ar environment in an inductively heated reactor at a temperature of 2000 °C [1], or in a commercial furnace at temperature from 1600 to 1700 °C. Highly doped 4H-SiC (0001) substrates, 8° off, with of a lowly doped (~1014 cm-3) epilayer were used. The efficiency of the different fabrication steps has been investigated by electrical characterization of opportunely designed test structures fabricated both on DG and EG. The insulation between individual adjacent devices (obtained using oxygen plasma) has been first verified. Then transmission line model (TLM) and van der Pauw structures have been used to measure the specific contact resistance �c of metal/graphene ohmic contacts and the sheet resistance of the SL or FL of graphene. The leakage current through the gate dielectric on graphene has been also checked. Furthermore, since EG grows on the oriented step bunching on SiC, the current transport in graphene between electrodes having different orientations with respect to the steps has been studied. All of these elementary fabrication steps have been integrated to obtain field-effect devices on few-layer graphenes. The current–voltage characteristics of these devices were measures and the channel mobility and the extrinsic transconductance has been extracted. The field effect channel mobility was compared with the Hall mobility measured on Van der Pauw structures. [1] S. Sonde, F. Giannazzo, V. Raineri, et al., Phy. Rev. B 80, 241406(R) (2009). Corresponding author: e-mail: carmelo.vecchio@imm.cnr.it

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Transport properties of alkali-doped carbon nanotube mats M. Barberio, A. Bonanno, P. Barone, R. Vasta, F. Xu Physics Department, University of Calabria and INFN, Research Unit of Cosenza 87036 Arcavacata di Rende, Italy Carbon nanotubes (CNT) are very promising nano-objects due to their exceptional properties. CNT are elongated-shape members of the fullerene family. The properties of CNT derive from their simple, rigid, nanometre-scale structure: a simple layer of carbon atoms rolled up to form a long cylinder. In particular the electronic and electrical properties are strongly influenced by tube diameter and chirality (which characterize the rolling directions) [1]. For instance, it is known that in a SWNT mat, the ratio between the conducting and semiconducting CNT is 1:2 and that semiconducting species show a band gap with an energy depending on diameter/chirality ratio [1]. Recently, CNTs have been studied for possible applications in new electronic devices (nanotips for field emission display and for scanning probe microscopy, field effect transistors, supercapacitors), in chemical sensors and in hydrogen storage materials[2-5]. In this framework, the analysis of the electrical transport properties of cleaned or doped CNTs assumes a primary role. In this context, doping of CNTs bundles with either donors or acceptors is expected to shift the Fermi energy Ef in the electronic band structure, providing valuable insight into the electronic conduction mechanism [6]. The study of such modifications in electric transport properties can lead to new device applications and to innovative chemical sensors (e.g. SWNT mat can be used as detector for small concentrations of gases). In this paper we present a comprehensive study of transport properties modification of Single-Wall Carbon Nanotube (SWNT) and Multi-Wall Carbon Nanotube (MWNT) interacting with alkali metals. We report resistivity measurements of SWNT mats as a function of Na, K, Cs and Li doping. References

1. S.J. Tans, M.H. Devoret, H. Dal, A. Thess, R.E. Smalley, L.J. Geerligs, C. Dekker, Nature 386 (1997) 474.

2. M. Bockrath, D.H. Cobden, J. Lu, A.G. Rinzler, R.E. Smalley, L. Balents, P.L. McEuen, Nature 397 (1999) 598.

3. R. S. Lee, H. J. Kim, J. E. Fischer, A. Thess, and R. E. Smalley, Nature 388, 255-257. 4. J. E. Fischer, H. Dai, A. Thess, R. Lee, N. M. Hanjani, D. L. Dehaas, and R. E. Smalley. Phys.

Rev. B 55, R4921 (1997). 5. J. Hone, I. Ellwood, M. Muno, Ari Mizel, Marvin L. Cohen, A. Zettl, Andrew G. Rinzler and R.

E. Smalley Phys. Rev. Lett. 80, 1042 (1998). 6. L. Grigorian, K. A. Williams, S. Fang, G. U. Sumanasekera, A. L. Loper, E. C. Dickey, S. J.

Pennycook, and P. C. Eklund, Phys. Rev. Lett. 80, 5560 (1998). Corresponding author: Marianna Barberio, marianna.barberio@fis.unical.it

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Linear carbon chains inside multiwalled carbon nanotubes and their temperature evolution, investigated by Raman spectroscopy.

Enzo Cazzanelli 1,2, Marco Castriota 1,2, Lorenzo Caputi 1,3, Anna Cupolillo 1,3, Luigi Papagno 1,3 and Gino Mariotto 4

1:Dipartimento di Fisica, Università della Calabria, 87036-Arcavacata di Rende (Cosenza), ITALY; 2: LICRYL (CNR-INFM) e CEMIF.CAL, Università della Calabria; 3: Istituto Nazionale di Fisica Nucleare, Gruppo collegato di Cosenza 4: Dipartimento di Informatica, Università di Verona, Strada le Grazie 15, 37134- Verona, ITALY

Multiwalled carbon nanotubes have been synthesized on graphite cathodes by arc discharge, in He atmosphere, either by using a catalytic Ni-Cr mixture or without catalysts [1, 2]. SEM investigations indicate the presence of nanotubes. Raman peaks due to first-order longitudinal optic modes of linear carbon chains (L bands) with sp hybridization (carbyne), encapsulated inside the nanotubes, are found in the wavenumber range 1780-1870 cm-1, together with the typical bands of MWCNT, as reported also in previous investigations on carbon nanotubes grown in different atmosphere [3, 4]. They show variable intensity and shapes in different regions of the analysed samples. In some zones of samples obtained by using the catalyst, a very high concentration of linear carbon chains is found, as indicated by the intensity of the L band, which turns out remarkably stronger than the G band of the host nanotubes. In these zones the second order Raman scattering of the linear chains is clearly observed, too [5, 6]. The wavenumbers of 2L overtones are slightly lower than the exact doubling of one-phonon peak values, and this fact is discussed in terms of the existing theoretical predictions for the chain mode dispersion curve [7, 8]. The temperature dependence of the first-order modes of linear carbon chains is studied up to about 1000 K: a reversible strong decrease of relative intensity of L band is observed [2] and this behaviour is interpreted as a reversible change of the bond configuration of the chains from polyynic to cumulenic [7] . [1] E. Cazzanelli, L. Caputi, M. Castriota, A. Cupolillo, C. Giallombardo and L. Papagno; Surface Science 601, 3926 (2007) [2] E. Cazzanelli, M. Castriota, L. Caputi, A. Cupolillo, C. Giallombardo and L. Papagno; Phys. Rev. B 75, 121405 (2007) [3] Y. Ando, X. Zhao, H. Kataura, Y. Achiba, K. Kaneto, M. Tsuruta, S. Uemura, S. Iijima; Diam.& Relat. Mater. 9, 847 (2000) [4] X. Zhao, Y. Ando, Y. Liu, M. Jinno, T. Suzuki; Phys. Rev. Lett. 90, 187401-1, (2003) [5] A. Cupolillo, M.Castriota, E.Cazzanelli, L.Caputi, C. Giallombardo, G. Mariotto, and L. Papagno; J. Raman Spectroscopy 39, 147 (2008) [6] M. Castriota, E. Cazzanelli, L. Caputi, A. Cupolillo, C. Giallombardo, L. Papagno and G. Mariotto; Diamond and Related Materials 17, 1716 ( 2008) [7] A. Milani, M. Tommasini, M. Del Zoppo, C. Castiglioni, and G. Zerbi; Phys. Rev. B74, 153418 (2006) [8] S. Yang, M. Kertesz, V. Zólyomi, J. Kürti; J. Phys. Chem. A 111, 2434 (2007)

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First principle study of impurities in graphene: HF , DFT and MP2 methods comparison Giuseppe Forte (1), Antonio Grassi (1), Giuseppe Marcello Lombardo (1), Giuseppe Angilella (2), Renato Pucci (2) (1) Dipartimento di Scienze Chimiche, Facoltà di Farmacia, Università di Catania, Viale A. Doria 6, I-95126 Catania, Italy (2) Dipartimento di Fisica e Astronomia, Università di Catania, Via S. Sofia, 64, I-95123 Catania, Italy From a theoretical point of view, the effects on the electronic structure of graphene due to the presence of vacancies, local impurities, and substitutional impurities have been studied by Pereira et al. [1], by using a tight-binding Hamiltonian with a local potential U. These authors have found general trends in the low–energy spectrum of graphene connected with localized zero modes, resonances and gaps induced by the above mentioned defects. In the present work we have followed a ‘molecular’ approach to study impurity effects, on the electron structure, in graphene. This is thought as the limiting case of an infinitely large cluster of benzene rings. Therefore, we study several carbon clusters, with increasing size, from phenalene, including three benzene rings, up to coronene 61, with 61 benzene rings. The impurities considered were a vacancy, and a substitutional proton. We performed HF, DFT and MP2 calculations, using the a double zeta basis set, in order to evaluate the correlation effects [2]. With increasing cluster size in the absence of impurities, we find a decreasing energy gap, here defined as the HOMO–LUMO difference. In the case of a vacancy, the gap does not decrease appreciably in HF and MP2, whereas it is substantially reduced in the case of a substitutional proton whatever method is adopted. The presence of an impurity invariably induces an increase of the density of states near the HOMO level. A very large value of the energy gap was found in the case of HF and MP2, while DFT results gives a more realistic description of the electronic properties when compared to the experiment. Such difference becomes less evident by increasing the size of the cluster. [1] V.M. Pereira, J.M.B. Lopes dos Santos, A.H. Castro Neto, Phys. Rev. B 77, 115109, (2008). [2] J. Martin, N. Akerman, G. Ulbricht, T. Lohmann, J.H. Smet, K. von Klitzing, A. Yacoby, Nat. Phys. 4, 144, (2008). Corresponding author: Giuseppe Forte, gforte@unict.it

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Structuring of single wall carbon nanotubes / poly(3-hexylthiophene) nano-composites at air/water interphases

Gianfranco Sfuncia, Giovanni Li Destri and Giovanni Marletta Laboratory for Molecular Surfaces and Nanotechnology (LAMSUN) - Department of Chemical Sciences – University of Catania and CSGI – Viale A.Doria 6 – Catania – Italy In the present work we report the peculiar nanostructuring based onto the Langmuir technique of composite poly(3-hexylthiophene)/single wall carbon nanotubes (P3HT/SWCNTs) at the air/water interfaces studied by, Langmuir isotherms, atomic force microscopy (AFM) and optical absorption measurements. P3HT is indeed known to effectively promote the solubility of SWCNTs in organic solvents via �-stacking interactions with the SWCNT walls [ref.]. In particular, the composite systems P3HT/SWCNTs have shown to be a promising candidate as active layer in plastic solar cells, due to the very efficient photo-induced electron transfer from the donor (P3HT) to the acceptor (SWCNT) [ref.]. Moreover, Langmuir technique, i.e. formation of a molecular film at the air/water interface, may provide an effective approach for the self-nanostructuring of P3HT/SWCNTs composites in view of the peculiar nanometric scale of the forces driving the formation of Langmuir films. The phase behaviour of these composites has been followed by studying the Langmuir isotherms which shows a reversible compression process at low surface pressures while a marked hysteresis, i.e an irreversible compression process, at higher surface pressure values. Regarding the morphology, when P3HT/SWCNTs composites are spread at the air/water interface, both isolated and bundle nanotubes, covered by wrapped P3HT, are detected. By then, compressing the system, SWCNTs start to interact and aggregate forming microscopic quasi-circular hybrid aggregates laying onto an homogeneous polymer film. Further compression of the system makes such aggregates to grow both in terms of amount and size with nanotubes probably buried inside. The Langmuir technique is therefore a promising approach to produce microscopic P3HT/SWCNTs hybrid aggregates. The appropriate chose of experimental conditions may indeed allow to tune the size of aggregates as well as the amount of SWCNTs in each of them and thus to control the photophysical properties of the system. References [1] T. Schuettfort et al, Nanotechnology 21, 025201 (2010) [2] T. Schuettfort et al., Nano Letters 9, 3871(2009) Corresponding author: Giovanni Li Destri, giolides@unict.it

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Oxygen sensing properties of SnO2/CNTs heterostructures Nicola Donato (1), Mariangela Latino (2), Nicola Pinna (3), Catherine Marichy (3), Giovanni Neri (4) (1)Department of Matter Physics and Electronic Engineering, University of Messina, I-98166 Messina, Italy (2)Dept. of Chemical Science and Technologies, University of Tor Vergata, I- 00173 Roma, Italy

(3)Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal (4)Department of Industrial Chemistry and Materials Engineering, University of Messina, I-98166 Messina, Italy SnO2-based gas sensors are commercial devices largely used in industrial and domestic safety, environmental monitoring, process control and so on [1]. In order to enhance the performance of these sensors, metal oxide nanostructures have been reported to be more effective than bulk counterparts [2]. However, often it is difficult to obtain these nanostructures and control their shape, size and morphology. By using carbon nanotubes (CNTs) as template, and with the aid of a novel atomic layer deposition (ALD) coating approach, an easy way to prepare metal oxide/carbon nanotubes heterostructures has been proposed [3]. Previously, we already explored the very promising sensing properties of these heterostructures, investigating the V2O4/CNTs samples [4]. Here, we report some preliminary data on SnO2/CNTs samples. The morphology of these hybrid samples is characterized by a overlayer formed by SnO2 anchored on the surface of carbon nanotubes. Both the external and internal walls of CNTs are covered. Changing the ALD deposition parameters, SnO2/CNTs heterostructures with different SnO2 coating thickness, varying from 2 to 37.5 nm, have been obtained. Oxygen sensing tests revealed that, on SnO2/CNTs samples, O2 addition results in a strong change of the baseline resistance. Specifically, in oxygen the sensors resistance increases over that measured in nitrogen, whereas no response was registered on the bare CNTs. This behavior was explained considering the n-type behavior of SnO2, which dominate the sensing mechanism. It is believed that the improved sensing properties are related to the heterojunction barrier formed at the interface of the n-SnO2/p-CNTs heterostructure. Moreover, it was noted a marked influence of the SnO2 coating thickness on the resistance baseline and oxygenresponse of the sensors. On the basis of characterization and sensing data reported, a hypothesis, involving the space-charge layer model and concerning as these sensors works, was formulated. References [1] Gas Sensors, G. Sberveglieri (Ed.), Kluwer, The Netherlands, 1992. [2] A. Kolmakov, Y. Zhang, G. Cheng, and M. Moskovits, Advanced Materials, 15, 997 (2003). [3] E. Rauwel, G. Clavel, M.-G. Willinger et al., Angew. Chem., Int. Ed. 47, 3592 (2008) [4]] M. G. Willinger, G. Neri, E. Rauwel, A. Bonavita, G. Micali, N. Pinna, Nano Letters 8, 4201 (2008) Corresponding author: Giovanni Neri - e-mail address: neri@ingegneria.unime.it.

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Selective growth of forest-like carbon nanotube layers for gas sensors applications M. Penza(1) , R. Rossi(1), M. Alvisi(1), N. Donato(2), M. Latino(3), Giovanni Neri (4) (1)ENEA, Brindisi Technical Unit of Technologies for Materials, PO Box 51 Br-4, I- 72100 Brindisi, Italy. (2)Department of Matter Physics and Electronic Engineering, University of Messina, I-98166 Messina, Italy. (3)Dept. of Chemical Science and Technologies, University of Tor Vergata, I-00173 Roma, Italy. (4)Department of Industrial Chemistry and Materials Engineering, University of Messina, I-98166 Messina, Italy.

Carbon nanotubes (CNTs) based sensors have attracted recently great attention, due to their promising potential in many applicative fields, such as in the biomedical and environmental monitoring [1, 2]. The control of the deposition of nanotubes on the sensor substrate is a fundamental step in their fabrication, in order to achieve the desired characteristics of reproducibility of the sensor performance. Moreover, a strong adhesion of nanotubes to the substrate is required to avoid loss of sensitive material, and consequently of stability, during long-term operations. In this communication we investigated the direct growth of carbon nanotubes on alumina substrates with a 200 µm spacing platinum interdigitated structure, for making resistive sensors. Radio Frequency-discharge Plasma Enhanced Chemical Vapour Deposition (RF-PECVD) was used for the CNTs growth as follows. First, an iron catalyst layer, with a thickness of 2.5 nm, was deposited by sputtering onto the interdigitated alumina substrate, without use of any mask. Fe-coated alumina substrate was placed in a RF-PECVD stainless-steel reaction chamber and treated at 600°C in a H2 plasma to promote the formation of iron catalyst particles. Successively, acetylene (C2H2) was introduced into the chamber mixed with H2. After cooling at room temperature, SEM observations have shown the growth of “forest-like” CNTs, vertically-aligned to the interdigitated substrate surface. Interestingly, CNTs were observed only on the bare Al2O3 surface, i.e. in regions of the substrate not covered with Pt electrodes. SEM observation also showed that carbon nanotubes at Al2O3/Pt interface are still aligned and have good contact with the platinum layer, which is important for electronic device applications. Electrical measurements have shown very low Pt electrode-CNTs contact resistance values, confirming SEM observation and further indicating the efficacy of the selective deposition method. We attributed the preferential CNTs growth on the alumina surface to the fact that, on Al2O3 surface, diffusion of iron is minimized and allows the formation of a high density of uniformly dispersed catalyst nanoparticles to act as nucleation sites for well-aligned CNTs, whereas the platinum electrode surface does not support the CNTs growth. A sensing study on the properties of the CNT/metal interface prepared by this method is currently underway. References [1] N Sinha and J T W Yeow, IEEE Trans. Nanobiosci. 4, 180 (2005). [2] M Penza, R Rossi, M Alvisi and E Serra, Nanotechnology 21, 105501 (2010). Corresponding author: Giovanni Neri - e-mail address: neri@ingegneria.unime.it.

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Radial breathing modes in Raman spectra of multi-wall carbon nanotubes Viviana Scuderi (1), Salvatore Bagiante (1,2), Ioannis Deretzis (1), Antonino La Magna (1), Giuseppe Compagnini (3), Santo Gibilisco (2), Nicolò Piluso (1), Vittorio Privitera (1) and Silvia Scalese (1) (1) Istituto per la Microelettronica e Microsistemi - Consiglio Nazionale delle Ricerche, Zona Industriale VIII Strada 5, I-95121 Catania (Italy). (2) Dipartimento di Fisica e Astronomia, Università di Catania via S. Sofia 64, I-95123 Catania (Italy). (3) Dipartimento di Scienze Chimiche, Università di Catania, Viale A. Doria 6, I-95125 Catania (Italy). In the last 20 years, multiwall carbon nanotubes (MWCNTs) were synthesized by different techniques, such as arc-discharge in gaseous or in liquid environment [1-2], chemical vapour deposition [3], laser ablation [4], RF magnetron sputtering [5]. In this work, MWCNTs produced by arc discharge in liquid nitrogen were studied by Raman Spectroscopy using three laser energies. Active Radial Breathing Modes (RBMs), originating from the innermost tubes, show a selective response according to the different laser energies. Atomistic calculations correlate such behavior with optical transitions in the presence of strong electronic localizations, spatially confined in few neighbouring walls. We argue that the observation of RBM modes depends on the laser-energy in MWCNTs as in SWCNTs, albeit less stringent selectivity rules hold for MWCNTs, due to the interaction between neighbouring walls. References [1] S. Farhat et al, J Chem Phys 115 (14) 6752 (2001) [2] S. Bagiante et al, Phys Status Solidi B 247 (4) 884 (2010) [3] Y.Y. Wei et al, Appl Phys Lett 78 (10) 1394 (2001) [4] P.C. Eklund et al, Nano Letters 2 (6) 561 (2002) [5] S. Scalese et al, J Appl Phys 102 (2007) 114905 Corresponding author. Viviana Scuderi. E-mail address: viviana.scuderi@imm.cnr.it

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Electronic structure and quantum transport calculations of epitaxial graphene nanoconstrictions grown on SiC substrates Ioannis Deretzis and Antonino La Magna CNR-IMM, Z.I. VIII Strada 5, 95121 Catania, Italy We present an electronic structure and quantum transport study of epitaxial graphene nanoconstrictions grown on SiC substrates, by means of first-principles-parameterized calculations. Within an atomistic description of the graphene layer and the substrate we evidence the role of the graphene-SiC interface for the conducting capacity of the studied systems. In the case of Si-terminated SiC we show that a strong Fermi level pinning effect arises from dangling interface bonds, which is independent from the width of the considered nanostructures. Such phenomenon compromises the role of one-dimensional confinement, giving rise to an intrinsic metallic behavior in these structures [1]. Finally we discuss quantum transport implications that arise from the particularity of epitaxial systems and compare their transport features with those of suspended graphene. [1] I. Deretzis and A. La Magna, Appl. Phys. Lett. 95, 063111 (2009) Corresponding author: Ioannis Deretzis Email: ioannis.deretzis@imm.cnr.it

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Morphology and distribution of carbon nanostructures in a C deposit produced by arc discharge in liquid nitrogen. Viviana Scuderi (1), Salvatore Bagiante (1,2), Santo Gibilisco (2), Giuseppe Faraci (2), Nicolò Piluso (1), Francesco La Via (1), Vittorio Privitera (1) and Silvia Scalese (1) (1) Istituto per la Microelettronica e Microsistemi, Consiglio Nazionale delle Ricerche, Zona Industriale VIII strada n. 5, Catania 95121, Italy. (2) Dipartimento di Fisica e Astronomia Università di Catania, Viale A. Doria 6, Catania 95125, Italy. Arc discharge is commonly used for the synthesis of carbon nanotubes, even though not so much is known as concerns the process itself and the role of the discharge parameters on the formation of different kinds of nanostructures. We have investigated the formation and the morphology of the C deposit on the cathode, after arc discharge between two graphite electrodes immersed in liquid nitrogen. The deposit consists of disordered carbon structures at the bottom and on the external part of the deposit, forming like a bowl, that contains randomly oriented carbon nanotubes (CNTs), aggregated in several pillars in the internal part and on top[1]. [1] S. Scalese et al, J. Appl. Phys. 108. 064305 (2010)

Corresponding author: Silvia Scalese. E-mail address: silvia.scalese@imm.cnr.it

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The symbol of Catania is u Liotru, or the Fontana dell'Elefante, assembled in 1736 by Giovanni Battista Vaccarini. It portrays an ancient lavic stone elephant and is topped by an Egyptian obelisk from Syene.

The Sicilian name u Liotru is a phonetic change of Heliodorus, a nobleman who, after trying without success to become bishop of the city, became a sorcerer and was therefore condemned to the stake. Legend has it that Heliodorus himself was the sculptor of the lava elephant and that he used to magically ride it in his fantastic travels from Catania to Constantinople. Another legend has it that Heliodorus was able to transform himself into an elephant.

The presence of an elephant in the millenary history of Catania is surely connected to both zooarcheology and popular creeds. In fact, the prehistoric fauna of Sicily from the Upper Paleolithic, included dwarf elephants.

The Catanian Museum of Mineralogy, Paleonthology and Vulcanology holds the integral unburied skeleton of an Elephas falconeri in an excellent state of conservation. The first inhabitants of Etna molded such lavic artifact to idolize the mythical proboscidian.