Graphene and related materials: from fundamental science to applications

Resume : Conventional photodetectors and solar cells based on semiconductors (or metal/semiconductor interfaces) suffer from two important performance limitations: they are insensitive to photons with energies lower than the band gap (or Schottky barrier height), while excess photon energy is converted into thermal energy and considered as loss. Here we introduce and experimentally demonstrate a novel way of detecting and harvesting infrared light: the photo-thermionic (PTI) effect. This mechanism overcomes both of the previous issues by combining unique thermal processes of graphene compared to metal, and original vertical extraction of carriers enabled by a van der Waals heterostructure geometry. In our graphene/WSe2/graphene devices, photoexcited carriers created in graphene upon near infrared light excitation redistribute their energy among other carriers to create a thermalized Fermi distribution of so-called hot electrons. This enables a significant fraction of them to be injected over the energy barrier at the graphene/WSe2 planar interface via thermionic emission, generating a photocurrent. We study a wide range of optical (wavelength, power, time delay) and electrical (bias voltage, gate voltage) parameters, and obtain excellent agreement with a simple model that provides a comprehensive understanding of the PTI effect. We therefore identify clear strategies for optimizing the efficiency of future PTI-based devices. http://arxiv.org/abs/1601.04197 - submitted

Resume : We show that a large SOI in graphene can be achieved in heterostructures with semiconducting transition metal dichalcogenides (TMD). Basic transport characterization of these heterostructures show high quality, with carrier mobility in graphene exceeding 10^5 cm^2/Vs, and the quantum Hall effect exhibiting the behavior expected for Dirac fermions. SOI is revealed by a weak anti-localization (WAL) effect at temperatures below 10 K, increasing in magnitude upon lowering T down to 250 mK. WAL is observed in all devices, irrespective of substrate materials (WSe2, WS2 and MoS2), thickness of graphene (mono-, bi-, thicker layer) and device mobility (elastic scattering time from 0.04 ps to 1 ps), demonstrating that graphene/TMD heterostructures are a reliable solution to enhance SOI in graphene. A quantitative analysis of mono-layer graphene data shows that the upper limit for the spin relaxation time extracted from WAL is 0.2-0.3 ps for all devices. In high mobility devices this value is smaller than the elastic scattering time, strongly suggesting that the induced SOI originates from a modification of the graphene band structure, and not from scattering at random potentials. This conclusion is consistent with electronic structure calculations, showing that interfacial interactions with WS2 do induce strong SOI in mono-layer graphene. These calculations also show that interfacial SOI can lead to the opening of a gap and result in a two-dimensional topological insulating state[1]. [1] Z. Wang, D.-K. Ki, H. Chen, H. Berger, A. H. MacDonald, A. F. Morpurgo, in: Nature Communications 6, 8339 (2015).

Resume : Two-dimensional materials are the most promising materials in science and technologies nowadays. Graphene is 2D semimetal with zero band gap, which displays amazing electronic, mechanical and optical properties. 2D MoS2 belongs to the transition metal dichalcogenides with the band gap about 1.6 eV depending of the thickness. Set of numbers of the layers of various 2D films allows creating van der Waals heterostructures by combining the layers between each other like in LEGO constructor. Weak van der Waals interaction between the layers is the cause of lack of effective charge transfer between the layers. To improve a weak interaction an individual metal atoms could be adsorbed on the layers surface before the creation of the hererostructure. Here the novel covalent heterostructures based on graphene and MoS2 was studied in details by means of ab initio calculations. Decoration process of MoS2 surface by Mo adatoms was studied firstly. It was found the strong binding between the MoS2 layer and molybdenum adatoms. Further the step by step decoration process and migration barrier of Mo adatom on the MoS2 surface were carried out to understand the origin of strong binding. Electronic properties during the decoration also were also studied. Finally the electronic properties of covalent graphene-Mo-MoS2 heterostructure were studied. Detailed partial density of states was constructed and the wave function distribution was calculated. This work was supported by the Russian Scientific Foundation (project no 14-12-01217). We are grateful to the 'Chebishev' and 'Lomonosov' supercomputers of Moscow State University and the Joint Supercomputer Center of the Russian Academy of Sciences for the possibility of using a cluster computer for our quantum-chemical calculations. This work was published in Physical Chemistry Chemical Physics journal in 2015.

Resume : At zero magnetic field, the absence of an energy gap separating conduction and valence bands of the system makes graphene and its multilayers highly susceptible to interactions very close to charge neutrality (CNP), leading to new interesting phenomena. These effects of interactions—which can only be accessed experimentally in ultraclean suspended devices with a very low charge inhomogeneity less than 10^10 cm^-2—include the renormalization of the Fermi velocity in monolayers and the occurrence of gapped, broken symmetry states in bilayers at zero magnetic field. Interestingly, the recent study on “Bernal-stacked” tetralayer graphene (4LG) [1] has shown that the system becomes highly insulating at CNP with characteristics analogous to the bilayers, and suggested that even thicker multilayers, whose behavior is expected to converge to that of graphite, can exhibit such a strong effect of interactions: that is, the opening of an energy gap at CNP in even multilayers (referred to as the even-odd effect). Here, we have realized ultraclean suspended hexa- and octalayer graphene, the thickest graphene multilayers whose transport properties have been studied in such a high quality, and revealed the occurrence of a highly insulating state close to CNP in both cases. Experiments clearly demonstrate that the behavior of these insulating states is remarkably similar to that found in bilayer and 4LG, which is fully consistent with the even-odd effect. Our study, therefore, clearly indicates that with extremely high quality, thick multilayer graphene—even if it is so thick to be considered as a graphite—can exhibit a strong effect of interactions which has interesting implications for multilayer-to-graphite crossover. [1] A. L. Grushina et al., Nature Communications 6 6419 (2015).

Resume : As technology has progressed, the trust of everyday interactions has inadvertently been undermined by the sophistication and availability of modern resources. To handle this issue, authentication strategies are implemented to provide proof of identities. Devices providing unique and reproducible fingerprints in response to an applied challenge can supply such identities. To generate these distinct signatures, physically unclonable functions (PUFs) are commonly utilised. The imperfect manufacturing process used to fabricate these devices provides structures that contain inherent randomness whilst containing a physical attribute that is simple to measure. Due to their physical nature, these structures do not rely on the privacy of stored secrets and can provide hard-to-predict unique identities for authentication in response to a challenge. However, the character of their classical design not only limits their size but also causes vulnerabilities in their security. In our recent work, we show that the fluctuations in the current-voltage spectra of resonant tunnelling diodes (RTDs) containing quantum wells presents a straightforward yet robust measurement that can function as a PUF without conventional resource restrictions. We have coined structures demonstrating variations due to quantum confinement QC PUFs – quantum confinement physical unclonable functions. As an alternative to the reported QC PUF, which relies on circuitry, we have devised a solution that uses an optical measurement by utilising the desired properties of two-dimensional materials. Here, we are interested in the variations in the photoluminescence from a given 2D flake that is dependent on the degree of oxidisation and density of imperfections at different areas of the flake. The practicality of such devices rely on scalability, so we have fabricated samples containing thin films of MoS2 and WS2 by the Langmuir-Blodgett technique, for the first time. These thin films show large-area photoluminescence where the intensity and linewidth depends highly on position. Importantly, these devices are impossible to clone or simulate, even with state-of-the-art technology. We have shown that it is possible to make optical PUF-like devices based on two-dimensional materials which operate at room-temperature, require the fewest resources and make use of quantum phenomena in a highly manufacturable device. Standard spectral analysis methods, when pertained to our QUFs, will facilitate consistent production of unpredictable unique identities which can be implemented in complex authentication schemes.

Resume : Coherent motion of the electrons in the Bloch states often breaks down for the interlayer conduction in layered materials where the interlayer coupling is significantly reduced by e.g. large interlayer separation. We found that the graphene layers are significantly decoupled by rotation, and the incoherent electron tunneling is the main interlayer conduction channel in twisted bilayer graphene [1]. In this regime, the interlayer conduction is determined by the overlap of the Dirac Fermi surfaces (FS) from each layer. This result implies that twisted bilayer graphene provides a double layer two dimensional electron gas with an extra layer degeneracy. Here we present broken symmetry quantum Hall states in high quality twisted bilayer graphene due to the lifting of the available degeneracies by electric and magnetic fields. References: [1] Youngwook Kim et al Phys. Rev. Lett. 110, 096602 (2013).

Resume : Two dimensional covalent organic frameworks (2D-COFs) are an exciting new class of planar ordered organic materials formed from the directed self-assembly of molecular building blocks. Depending on the chosen building blocks certain structures and functionalities will be obtained.[1] Triarylmethyls (TAMs) are stable open-shell molecules with great potential for numerous applications.[2] To date no 2D-COF has been reported based on open-shell molecules due to their inherent instability. However, TAMs are known to preserve their open-shell nature both in solution and on surfaces.[3] By means of accurate ab initio density functional calculations we have designed numerous TAM-based 2D-COFs. Further, by external strain, we show that the materials’ structures can be smoothly perturbed which, as we reported for single TAMs,[4] gives rise to a predictable variance in spin localization. Consequently, other important magnetic, optical and electrical properties of these 2D materials can also be finely tuned. [1] X. H. Liu, C. Z. Guan, D. Wang and L. J. Wan, Adv. Mater., 2014, 26, 6912–20. [2] R. Frisenda, R. Gaudenzi, C. Franco, M. Mas-Torrent, C. Rovira, J. Veciana, I. Alcon, S. T. Bromley, E. Burzurí and H. S. J. van der Zant, Nano Lett., 2015, 15, 3109–3114. [3] V. Mugnaini, A. Calzolari, R. Ovsyannikov, A. Vollmer, M. Gonidec, I. Alcon, J. Veciana and M. Pedio, J. Phys. Chem. Lett., 2015, 6, 2101–2106. [4] I. Alcon and S. T. Bromley, RSC Adv., 2015, 5, 98593–98599.

Resume : Lateral heterostructures of two-dimensional materials, such as hexagonal boron nitride (h-BN) and graphene, are of increasing interest for nanoelectronics applications. As in conventional three-dimensional epitaxy, lattice mismatch strain in lateral h-BN/graphene heterostructures may be relieved by formation of interfacial misfit dislocations. Here we study these misfit dislocations in the 2D h-BN/graphene system using continuum thin film mechanics theory and an atomistic model based on classical potentials. We show that misfit dislocations in this system take the form of either 5-7 or 8-6 cores, and that the choice depends on the local stoichiometry. Furthermore, we show that a strain relieving dislocation may switch its reconstruction from 8-6 to 5-7, or vice versa, through a process of vacancy or interstitial mediated climb. The energetic analysis of the dislocation at the interface also permits a simple evaluation of the critical thickness, or the size of the “film” domain (either h-BN or graphene) at which the system becomes unstable against the formation of an interface misfit dislocation, which is analogous to the classic Matthews-Blakeslee critical thickness condition in 3D thin film growth. The 2D critical thickness condition will be further discussed in the paper and is found to depend on the relative size of the h-BN and graphene domains, or in the terminology of 3D critical thickness theory, the film/substrate thickness ratio.

Resume : Layer-by-layer assembly from aqueous solutions was used to construct multilayer thin films (< 200 nm) comprised of polyethyleneimine and graphene oxide. These nanocoatings impart significantly reduced oxygen and carbon dioxide transmission rates when deposited on polyester thick film substrates. This thin film’s nanobrick wall structure also provides high gas selectivity for hydrogen. Low temperature (175 ºC) thermal reduction of these films improves the gas barrier properties (e.g., lower permeability than SiOx), even under high humidity conditions, and also increases their electrical conductivity to 1750 S/m. The flexible nature of the aforementioned thin films, along with their excellent combination of transport properties, make them ideal candidates for use in a broad range of electronics and packaging applications.

Resume : Single layer graphene (SLG) is an ultimately thin membrane made of sp2-hybridized carbon atoms with unique electronic properties and is considered an excellent candidate for future nano-electronics. The properties of this 2D material can be modified and tailored by inducing defects in the honeycomb lattice by collisions with energetic particles or by applying an external magnetic or electric field and splitting the well known double cone in the electronic structure around the Fermi energy. In our contribution we maximize the latter effect locally by investigating the electronic response to an extremely large external field, the Coulomb field of an approaching slow highly charged ion with charge states up to q=35. Collision studies of ions with freestanding SLG are also of fundamental interest in the field of ion-matter interaction, because as an atomically thin 2D material, SLG bridges the gap between atomic collisions in gaseous and those in solid targets. By studying the charge exchange and energy loss of transmitted ions by using an electrostatic analyser, we get information on the equilibration dynamics and energy loss. Charge equilibration times are derived from the mean exit charge state, i.e. the number of captured and stabilized electrons as a function of the incident charge state and ion velocity. Additionally, the energy loss of highly charged projectiles is found to be strongly enhanced and to increase quadratically with the incident projectile charge state.

Resume : The analysis of unprecedented high-resolution scanning tunneling microscopy (STM) images of graphene/Ni(111) shows the presence of different types of defects, manly due to carbon vacancies and partially filled with trapped Ni adatoms. We have proposed some structural models and verified their reliability on the basis of the energetics and the comparison between observed and simulated STM images, obtained from ab-initio density functional theory calculations. In particular, we have studied in details a triple-vacancy defect with one Ni atom trapped inside, that shows a peculiar dynamical behavior in the interaction with carbon monoxide. We have investigated and characterized also other defects, even more extended, extracting some general trend to predict their stability and their abundance. Preliminary results concerning their activity under the exposure of small molecules of environmental importance have been also obtained.

Resume : Efforts to turn molecular and atomic building blocks into functional materials have energized scientists and engineers and have greatly contributed to shape nanoscience and nanotechnology as we know them today. The development of nanoscience is a premise for new technological advances and scientific scrutiny has progressively shifted to translating nanoscience discoveries into technological realizations. However, the road from nanoscience to nanotechnology is a difficult one, as fundamental issues related to quality of interfaces, materials homogeneity and integration into existing technology must all be satisfactorily addressed. In this context, graphene has been touted as a miracle material where all these challenges could be met, especially given the extensive research activities devoted to its development. However, despite graphene's remarkable electronic properties, the lack of an electronic bandgap severely limits its potential for applications. In contrast to extended films, narrow strips of graphene are semiconductors due to quantum confinement, with a bandgap that can be tuned as a function of the nanoribbon width and edge structure. Atomically precise graphene nanoribbons can be obtained via a bottom-up approach based on the surface-assisted assembly of molecular precursors. In this talk, I will present the properties of graphene nanoribbon heterojunctions and heterostructures obtained by combining pristine hydrocarbon precursors with their nitrogen-substituted equivalents. I will present a number of computational and theoretical studies combined with experiments that suggest that these defect-free materials have a high potential for applications in photovoltaic and electronic applications.

Resume : 2D-layers, like graphene or a monolayer of hexagonal boron nitride (h-BN), enable the creation of new (hybrid)-materials, unforeseen reaction pathways or striking confinement effects. Three examples for this statement are given. (i) Room temperature deposition of atomic carbon on a 2D-layer moiré with an Ir(111) substrate results in the formation of a regular nanodiamond array with a pitch of 2.5 nm and extremely high thermal stability. The carbon cluster structure and the transformation of the clusters to graphene is discussed. (ii) The inertness of 2D-layers together with the confinement of the diffusion for the supplied reactands to two dimensions enables new reaction pathways in organo-metallic chemistry. As an example, it is shown how graphene and h-BN enable the growth of europium-cyclooctatetraene nanowires of micrometer length through supply of atomic Eu and cyclooctatetraene molecules under well-defined ultra high vacuum conditions. (iii) Using ion implantion and thermal processing highly pressurized precipitates of the implanted species can be created in the space between a 2D-layer and its substrate. Thereby new high temperature and high pressure reactions might come into reach. As an example for the high pressure in these precipitates, we demonstrate crystalline Xe underneath h-BN on Ir(111). Contributions to this work by H. Åhlgren, M.A. Arman, C. Busse, F. Craes, C. Herbig, F. Huttmann, W. Jolie, J. Knudsen, T. Knispel, J. Kotakoski, A.J. Martinez-Galera, A.K. Krasheninnikov, N. Schleheck, U.A Schröder, S. Simon, and P. Valerius are gratefully acknowledged.

Resume : Molecular dynamics simulations with LAMMPS [1] using empirical potentials [2] have been performed to study the mechanical properties of a graphene drumhead containing 674644 atoms, after irradiating with low energy (140 eV) Ar ions for different initial strains and doses. In particular, the mechanical properties are assessed by nanoindentation simulations using these irradiated graphene samples. We show how out-of-plane displacements can be modified by strain resulting in softening of the membrane under compression and stiffening under tension, decreasing and increasing the value of the 2D Young's modulus, respectively. Irradiation also induces changes in these mechanical properties of graphene. Interestingly, compressed samples, irradiated with low doses are stiffened by the irradiation while samples under tensile strain do not show significant changes in their mechanical properties. The above mentioned is in agreement with the results of Lee et al [3] that showed that the presence of ripples results in the softening of graphene since two mechanisms take place: initially ripples get smoothed, followed by C-C bond stretching. These results provide an alternative explanation of recent experimental measurements of an increase of E2D (stiffening) under irradiation [4] as a combination of applied strain and irradiation, and not as the sole results of defect production. [1] http://lammps.sandia.gov. S. Plimpton, Fast Parallel Algorithms for Short-Range Molecular Dynamics, J Comp Phys, 117, 1-19 (1995). [2] J. Tersoff, New empirical approach for the structure and energy of covalent systems, Phys. Rev. B 37, 6991 (1988). [3] S. Lee, Effect of Intrinsic Ripples on Elasticity of the Graphene Monolayer, Nanoscale Research Letters 10, 422 (2015). [4] G. Lopez-Polin et al., Increasing the elastic modulus of graphene by controlled defect creation, Nature Physics 11, 26–31 (2015).

Resume : Tailoring interfacial thermal transport in graphene-based nanoarchitectures is important for many applications including nanoelectronics, solid-state lighting, energy generation and nanocomposites.[1,2,3] We demonstrate that interfacial thermal conductance G can be fivefold enhanced by introducing covalent bonds at the interfaces using molecular dynamics simulations.[2,3] The simulations captured the trend of thermal transport enhancement with the increment of interfacial covalent bond density. The results confirm that the observed G enhancements at the interfaces are due to strong interfacial covalent bonds and resultant coupling in the atomic vibrational spectra near the interface. The spectral analysis indicates that the coupling between graphene out-of-plane motion and bonded linkage group motion at low frequencies serves as the most important channels for thermal transport across the interface. Thus, covalently bonding functionalization is an attractive approach to tune the heterointerfacial thermal transport in a variety of material systems. [1]Liu X., Zhang, G., Zhang Y.-W. Graphene-based thermal modulator. Nano Res. 2015, 8, 2755. [2]Liu X., Zhang, G., Zhang Y.-W. Thermal conduction across graphene cross-linkers. J. Phys. Chem. C 2014, 118, 12541. [3]Guo T., Sha Z.-D., Liu X., Zhang G., Guo T., Pei Q.-X., Zhang Y.-W. Tuning the thermal conductivity of multi-layer graphene with interlayer bonding and tensile strain. Appl. Phys. A 2015, 120, 1275.

Resume : In the last two years, we reached remarkable results in the theoretical and experimental study of surface morphology of graphene [1-3]. Graphene moir� superlattices formed on various hexagonal supports (e.g. 111 metal surfaces) exhibit convex (protruded) morphology [4]. In rare cases, suspected to be concave (nanomesh with periodic lattice of depressions) topography may exist [5]. However, the experimental verification of the topography convexity is difficult. The curvature of the surface topography can not be clearly specified by STM due to the bias voltage dependence of the measured convexity. Varying the bias voltage contrast inversion occurs which prevents the clearcut identification of the surface curvature. Using additional first principles DFT theoretical studies were only able to prove the existence of convex morphology e.g. on Ru(0001) [4]. Why is it important to know the precise topographic curvature of the graphene surface ? According to our present knowledge and assumptions convex and concave superlattices may exhibit different electronic structure properties such as LDOS or band structure. Moreover, the surface activity, such as the adsorption energy of various molecules and/or the local magnetic property of surface Carbon atoms may depend on the morphology of the superlattice. The most important results [1-3]: - The detailed description of the topography of moir� superlattices using a combined theoretical and STM approach [1-3]. The confirmation of the nanomesh morphology on Au(111). - The coexistence of convex and concave superlattices has been explored in the same image which rules out the presence of contrast inversion [3] - DFT calculations support the possible coexistence of various superlattices with different curvature due to the tiny energy difference between the various morphologies [3] - The Au(111) surface reconstructs upon graphene adsorption and exhibits an imprinted topography very similar to that of the moir� superlattice [3] - New, previously unexplored rotational misoriented moir� superlattices have been found by STM and analysed for graphene/Cu(111) [1] and for graphene/Au(111) systems [3] using new DFT-adaptive force fields which has been developed for this purpose in our Lab [1,2]. [1] P S�le, M Szendr?, C Hwang, L Tapaszt�, Rotation misorientated graphene moire superlattices on Cu(111): classical molecular dynamics simulations and scanning tunneling microscopy studies, Carbon 77, 1082-1089. (2014). [2] P S�le, M. Szendr?, Time-lapsed graphene moir� superlattice on Cu(111), Modelling and Simulation in Materials Science and Engineering 23:(2), 025001. (2015). [3] P. S�le, M. Szendr?, G. Magda, C. Hwang, L. Tapaszt�, Nanomesh type graphene superlattice on Au(111) substrate, Nano Letters, 15, 8295. (2015). [4] M. Batzill, The surface science of graphene: Metal interfaces, CVD synthesis, nanoribbons, chemical modifications and defects, Surf. Sci. Rep. 67, 83. (2012). [5] Yankowitz, M.; Xue, J.; LeRoy, B. J., Graphene on hexagonal boron nitride. J. Phys.: Condens. Matter 26, 303201. (2014), Woods, C. R.; Britnell, L.; Eckmann, A.; Ma, R. S.; Lu, J. C.; et al. Commensurate?incommensurate transition in graphene on hexagonal boron nitride. Nat. Phys. 10, 451. (2014). [6] Voloshina, E. N.; Fertitta, E.; Garhofer, A.; Mittendorfer, F.; Fonin, M.; Thissen, A.; Dedkov, Y. S. Electronic structure and imaging contrast of graphene moir� on metals. Sci. Rep. 3, 1072., (2013).

Resume : While graphene is a promising material for novel photonic devices due to its broadband optical absorption, ultrafast carrier dynamics and electrical tunability [1], the quantum efficiency of graphene devices is intrinsically limited by low absorption of graphene (2.3% of normal incident light). To enhance light-matter interaction, optical focusing elements such as plasmonic metal nanoparticles (NP) can be utilized [2]. Here, we report our recent results on the graphene plasmonic NP hybrid structures. Femtosecond pump−probe measurements of graphene nearby plasmonic gold nano-disc structures confirm the presence of a strong near-field interaction leading to hot carrier generation in the graphene; however, the results suggest that the hot carriers arise dominantly from direct photoexcitation in the graphene with a minimal contribution from charge transfer from the gold [3]. Asymmetric plasmon-nanobar electrical contacts are employed with a view to measuring the plasmon-induced hot carriers in graphene via the thermoelectric effect. The devices are characterized using a scanning photovoltage technique with both CW and pulsed excitation sources. Time-resolved photovoltage measurements are further employed to analyse the timescale of photovoltage generation. [1] T. Mueller et al. Nat Photonic 4, 297 (2010); [2] Z. Fang et al. Nanoletts 12, 3808 (2012); [3] Gilbertson, A. M. et al. Nano Lett. 2015, 15, 3458–3464.

Resume : In the past decade, carbon-based three-dimensional (3D) architectures have received increasing attention in science and technology due to their fascinating properties, such as huge surface area, macroscopic bulky shape and interconnected porous structures, enabling them to be one kind of most promising materials for water remediation. In this talk, I will summarize the recent development in design, preparation and applications of carbon-based 3D architectures and introduce our recent research progress on the preparation of carbon aerogels (CA) for water treatment. Three kinds of CA, which are made from graphene, raw cotton and waste paper, respectively, have been successfully used as novel, efficient and recyclable sorbents for oils and organic solvents. The CA can absorb a variety of oils and organic solvents with outstanding recyclability. The maximum sorption capacity is as high as 192 times the weight of CA. Compared with the sorption efficiency of commercialized products (e.g. activated carbon), the sorption efficiency of CA is extremely high. Moreover, it still possesses a high sorption capacity after five cycles by using distillation, burning or squeezing methods to recover the absorbed liquids. References [1] B. Chen, Q. Ma, C. Tan, T.-T. Lim, L. Huang, H. Zhang*, Small, 2015, 11, 3319. [2] H. C. Bi, X. Huang, X. Wu, X. H. Cao, C. L. Tan, Z. Y. Yin, X. H. Lu, L. T. Sun,* H. Zhang*, Small, 2014, 10, 3544. [3] H. C. Bi, Z. Y. Yin, X. H. Cao, X. Xie, C. L. Tan, X. Huang, B. Chen, F. T. Chen, Q. L. Yang, X. Y. Bu, X. H. Lu, L. T. Sun*, H. Zhang*, Adv. Mater., 2013, 25, 5916.

Resume : Recently, various materials have been employed to synthesize graphene-based composites or hybrids, from which, in particular, metal films and nanoparticles acquired a great relevance in view of applications in sensing and nanoelectronics. The extraordinary electrical properties of graphene layers can be drastically modified when contacted by metal films in nanoelectronic devices on the basis of the metal nature. In this work, we present an experimental characterization, by conductive atomic force microscopy (CAFM) measurements, of the nanoscale electrical properties of metal-graphene-metal contacts. In particular, starting from single layer graphene films grown on Cu, we deposited Au, Ag, Pd thin films of increasing thickness on the Cu/graphene substrate and we acquired, by CAFM, the current-voltage (I-V) characteristics for the Au/graphene/Cu Ag/graphene/Cu, Pd/graphene/Cu systems. The three systems present different behaviors, as extracted by the I-V characteristics: the Au/graphene/Cu system presents a rectifying electrical behavior with the graphene layer acting as a p-type semiconductor, the Pd/graphene/Cu system presents a rectifying electrical behavior with the graphene layer acting as a n-type semiconductor, and the Ag/graphene/Cu presents an ohmic behavior. These differences are discussed on the basis of the peculiar energy band diagram originating in the specific meta/graphene/Cu stack.

Resume : Separation has become one of the critical technologies to solve the problems that mankind faced including resource depletion and environmental issues. Comparing to other separation approaches, membrane separation is energy effective, continuous and can be integrated in small volume facilities, reducing the total cost of operation. In the past several decades, polymeric and inorganic membranes have been utilized for the separation and purification and even commercialized in industry, but a trade-off between permeability and selectivity has hindered the wide adoption of membrane in practical applications, requiring high operation cost. Because pore size determines the selectivity and because thickness of membrane affects the permeability of membrane, ideal membrane with high selectivity and high permeability can be realized as well controlled pores are generated in the film with nanometer thickness.Defect free graphene is a perfect barrier that even hydrogen molecules cannot penetrate across. On the other hand, both high flux and selectivity can be achieved as size controlled pores are introduced in the basal plane of graphene due to its two-dimensional atomic-scale thickness. Furthermore, low biofouling tendencies, chemical resistance and mechanical durability are considered as powerful advantages of graphene membrane to extend its lifespan. Thus, development of high-performance graphene membranes is regarded as one of the most important issues in graphene research. As in the case of currently available polymer membranes, the formation of nanometer pores (~ nm in size) on bulk-scale graphene is essential to realizing the mass production of high-performance graphene membranes. However, all previous graphene membranes have relied on the use of small quantity graphene with meso- or nanopore structures by using e-beam, ion beam exposure and thermal treatment with metal nano particles. Therefore, all previous graphenes are critically limited to the commercialization of the graphene membrane via cost-effective solution process. In this talk, a novel chemical method to fabricate the nano-porous graphene in bulk scale will be presented, showing the high selectivity to NaCl salt with dramatically enhanced permeance. Graphene film (20 nm thickness) made of this nanoporous graphene displays excellent water flux (~37 L·m-2h-1bar-1) at a low operation pressure (5 bar) and high rejection above 70 % to 0.2 M NaCl solution, which is dramatically advanced (30 times) than that of commercial nanofiltration membranes with ~50 % rejection.

Resume : The graphene has taken much attention to the researchers all around the world due to its excellent physical properties since Novoselov et al. firstly discovered graphene by using mechanical exfoliation method. However, the size and thickness of graphenes fabricated by mechanical exfoliation method is too small and thick, and thus this method remained challenging. Hence an alternative method for commercial graphene yield is required. In order to approach scalable and commercial aims, CVD is regarded as the optimal synthesis method, but the requirement for high temperature and metallic catalyst makes CVD less environmental friendly. Therefore, this study provides a refined green chemical liquid-phase exfoliation method to prepare graphene with alcohol-water mixture. Sonication of graphite powder in alcohol solution can yield graphene dispersions which contains numerous graphene sheets at micrometer scale, and they can be identified by the Raman spectroscopy and optical microscope. The concentration of dispersions is determined by the visible absorbance via Lambert – Beer’s law (A=abc). It shows the yield of graphene is about 2%. In order to examine the quality of the graphene dispersions, the solution was placed for a month and the concentration variation was measured every interval. The experimental parameters are optimized by adjusting mixture proportion, graphite mass and sonication time. The results show that alcohol-water mixture manufacture is environmental friendly, convenient and useful method to obtain graphene commercial. In the future, we will focus on improving the quality and controlling its layers.

Resume : Transition metal nitrogen carbon complexes (M–N-C) are considered as a promising ORR catalyst to replace Pt [1]. The M-N-C catalysts were synthesized by pyrolyzing mixture of metal, nitrogen and carbon at 400-1000°C. The ORR activity of M-N-C depend on the transition metal and carbon elements. Currently, Fe-N-graphene is regarded as highly active catalyst for ORR among other M-N-C materials [2-4] but still not comparable to that of commercial Pt/C, therefore, many efforts such as modification of structure, doping new atom to promote catalytic activity are in progress. The present work is to enhance oxygen reduction reaction (ORR) activity of transition metal–nitrogen–graphene catalysts through formation of edge site and doping S by facile ball milling method. The edge-activated S-doped Fe-N-graphene (EA-SFeNG) was successfully synthesized by simply mixing graphene oxide (GO), melamine as a nitrogen source, sulfur and iron acetate using ball milling, and then followed by pyrolysis treatment for 2 h at 700 ˚C, and then optimized to exhibit the best ORR catalytic performance. The ORR performance of the EA-SFeNG was measured to have the onset potential (Vonset: 1.02 VRHE) and the half wave potential (V1/2: 0.848 VRHE) that is comparable to those (Vonset: 1.05V, V1/2: 0.865V) of the commercial 20wt.% Pt/C. The S in the catalyst exists in the form of SOx, and the ball milling process increase edge sites in the catalysts, which acted as a highly ORR active site. It was demonstrated from the measurement of nanoscale work function by kelvin probe force microscopy that the work function of the EA-SFeNG catalyst is significantly reduced by the S doped and the active edge sites formed in the catalyst. Hence, the excellent ORR performance of the EA-SFeNG catalyst can be attributed to the increase in the defect density such as the doping S and the edge site in the graphene.

Resume : High pulse energy Q-switched erbium-doped fiber lasers have been demonstrated by polymer-free graphene saturable absorber (GSAs) coated on a fiber connector. This reduces non-saturable losses, making it suitable for high power operations. Graphene flakes were fabricated simply and cost-effectively by liquid phase exfoliation (LPE) method in which the graphite powder and solvent (sodium deoxycholate) were dissolved in DI water by sonication technique without chemical reaction. For ultrasonic times of 1, 2 and 4 hours, the measured intensity ratios (I2D/IG) of 2D and G bands and (ID/IG) of D and G bands in the Raman spectroscopy were (0.66, 0.68, 0.55) and (1.69, 1, 1.26), respectively. We obtained the best quality flakes for the ultrasonic time of 2 hours, with the largest I2D/IG and the smallest ID/IG, The transmittance of SA sample is 30% at 1560 nm. When the GSA was inserted in the erbium-doped fiber laser, self-starting Q-switched pulses were observed as the pumping power reaches 68 mW. As pumping power being increased from 68 to 250 mW, the Q-switched pulses show duration of 25.3 to 1.8 us, repetition rate of 7.6 to 30.5 kHz, and output power of 0.6 to 8.6 mW, corresponding to pulse energy of 78.9 to 282 nJ. The center wavelength and 3-dB bandwidth were measured to be ∼1566.5 nm and ∼0.4 nm, respectively. The Q-switched fiber laser can stably and continuously operate over 1 hours and even larger output power will be obtained by using a high-power pump laser.

Resume : Despite much effort put into the large scale production of graphene by chemical vapor deposition (CVD), there are still many challenges to be solved concerning the fundamentals of the growth itself. Isotopic labeling during CVD growth of graphene is a powerful tool to study the growth kinetics such as nucleation density and growth speed as a function of time. In particular, we investigate the question if there is a correlation between isotope grains and crystallographic grains, in short, if there is a grain boundary when the isotope locally changes. For this circumstances, we secured robust CVD growth methods to synthesize graphene with clearly separate isotope grains. Due to the isotopic sensitivity, Raman spectroscopy of the graphene sample reveals the isotopic distribution whereas dark field transmission electron microscopy distinguishes crystallographic orientations and therefore makes grain boundaries visible. Furthermore, we investigated different defect formation behavior of the isotopic modified graphene. The angstrom sized electron probe of a Nion UltraSTEM is used to observe the formation of defects with atomic resolution as a function of dose. The theoretical estimations of the required dose in order to create defects agrees with our experimental results. Therefore, we observed different defect densities in different regions of an isotopic mixed graphene sample.

Resume : The solar energy is converted to electrical power by a sequence of events: the absorption of light, the generation of charge carriers (electrons and holes), their spatial separation and transport to electrodes. Great attention has been given to quantum dots sensitized solar cells due to their promising conversion efficiency, their simple device fabrication process and their low cost. Zero-dimensional nanostructures have gained interest owing to their unique size related electronic properties, especially the tuning of their band gap. Different types of material that play the role of absorbing media should be studied tuning their band gap by changing their size or changing the degree of cation disorder. ITO and FTO have been widely used as window electrodes in solar cell devices. These TCOs, however, have many drawbacks such as limited availability of their constitutive raw materials (e.g. indium), instability in the presence of acid or base, limited optical transparency in the near-infrared region. ii The search for novel electrode materials with good stability, high transparency and excellent conductivity is therefore a critical goal for solar cells.iii Graphene, as a matter of fact, appears to have none of these drawbacks—and it is cheap and sustainable.iv In this presentation, the researchers will highlight the use of graphene as suitable material for solid-state quantum dots sensitized solar cells that harvest light over a wider range of the spectrum.

Resume : Since 2D materials such as graphene, h-BN and the transition metal dichalcogenides (TMDs) were discovered, there have been many studies on fabrication of 2D material-based device for next generation electronic devices [1-3]. As a supporting layer to transfer 2D material, poly (methyl methacrylate) (PMMA) is commonly used particularly for chemical vapor deposition (CVD) grown graphene. However, the residues of PMMA after the transfer, degrades graphene’s intrinsic electric properties [4]. Many groups have used annealing method to solve this problem, however, it was impossible to completely remove the residues of PMMA [5]. In this paper, we report the effect of CVD graphene property after mechanical cleaning method using contact-mode atomic force microscope (AFM). Some groups showed significant effects of mechanical cleaning method on the exfoliated graphene [6]. However, cleaning effect on CVD graphene cannot be the same as that on exfoliated graphene, owing to its grain structure including defect. To remove easily the residues, the samples were exposed to alcoholic solvent atmosphere such as ethanol and methanol. After that, AFM tip was contacted strongly on the sample surface and scanned several times to remove the residues of PMMA. The samples after the treatment were measured using Raman spectroscopy and different AFM modes such as CFM, LFM and EFM. In particular, transconductance properties associated with 2D material-based device were analyzed. Furthermore, we studied the effect of the grain boundary after removing residues. Reference 1. Geim, A. K.; Novoselov, K. S. Nat.Mater, 6, 183–191. (2007) 2. Dean, C. R. et al. Nat. Nanotechnol. 5, 722–726 (2010) 3. B. Radisavljevic, A. Radenovic, J. Brivio, Nat. Nanotechnol., 6, 147– 150, (2011) 4. A. Nourbakhsh, M. Cantoro, J. Phys. Chem. , 114, 6894–6900.(2010) 5. Yung-Chang Lin, Chun-Chieh Lu, and Po-Wen Chiu, Nano letter,12, 414-419.(2012) 6. Niclas Lindvall, Alexey Kalabukhov, and August Yurgens, JOURNAL OF APPLIED PHYSICS 111, 064904 (2012)

Resume : The smart window is a controllable glazing where transparent and opaque states can be switched by an electric field. The smart window has been expected to be a solution in diverse area to save energy for heating and cooling as blocking loss of the radiation heat by controlling the transparency of the windows. Among the various candidates of smart window materials, polymer-dispersed liquid crystal (PDLC) has come into wide use. PDLC is a mixture of UV curable polymer and a nematic liquid crystal. Indium tin oxide (ITO) which is widely used for transparent electrode materials and one of the base materials for PDLC is brittle and often requires an additional annealing process to improve the property as conducting materials. These weaknesses of ITO are barely suitable for flexible PDLC film. In this study, instead of using conventional transparent conducting film, we used the single-layer-graphene coated PET films as transparent electrodes. The single-layer-graphene was grown by thermal chemical vapor deposition and transferred onto the PET film. We confirmed its various properties such as transmittance, response time and impedance analysis.

Resume : We prepared a Ag-decorated graphene oxide catalyst (GOSH-Ag) and used for the decarboxylative addition and coupling reactions. This catalyst was easily prepared by depositing Ag nanoparticles on thiolated grapheme oxide (GOSH) surfaces. Transmission eletron microscopy indicated that the nanoparticles were well-dispersed and of a small, approximately 3.7 nm average size. Moreover, the adhered nanoparticles could not be separated from the GOSHs even after thorough washing and prolonged sonication. Suchstrong adhesion might result from the relatively high BE betweenAg and thiol groups. The supported catalyst displayed good catalytic activity under a low oxidized Ag loading (calc. 3.1 wt%). It could easily be separated and recovered from the reaction mixture and reused several times. The results suggest that sp2 carbon-based supports significantly influence catalytic activities in the decarboxylative cycloaddition reaction.

Resume : Graphene is atom-thick, 2D material which is flexible and has a large surface area about 2630 m2/g and high conductivity. [1] Due to these exceptional characteristics, researchers have great interest to incorporate graphene as ideal electrode in supercapacitors based applications. Conventionally grown graphene is no band gap material. In order to scale up its productivity, one needs to reduce graphene oxide (GO). Owing to flexible characteristics of graphene, it can be used in wearable or mobile devices and PCB. Even though CVD grown graphene has high conductivity compared with reduced graphene oxide (rGO), but rGO has high functionality due to its large surface area. In this work, we fabricated complex structure of CVD graphene and rGO to gain high capacitance. Graphene/rGO complex was synthesized on PET (polyethylene terephthalate) films to have flexibility of both materials. At first, CVD graphene was transferred to PET substrate, and 0.1 mg/ml GO/IPA solution was sprayed onto CVD graphene/PET films. A separator was sandwiched between two films by using an epoxy glue, and 1 M H2SO4 solution was infiltrated into the separator. We compared the graphene/rGO complex based super capacitors with bare graphene and rGO devices. The complex based supercapacitor was measured as highest capacitance of 3.2 mF, while bare graphene and rGO devices showed 50 to 90 μF and 5 to10 μF, respectively. Our comparative study confirms that complex based supercapacitors have much higher capacitance than the single component capacitors.

Resume : In membrane technology, bio-inspired approaches have attracted remarkable attentions to break through current technological issues. Biomimetic research navigates us to take a step forward in membrane technologies, particularly in the field of ion filtration and water purification. Aquaporin is a one of the most sophisticated channel in natural cells, and it selectively transports water molecules. In aquaporin water channels, there are several peptide motifs, called selectivity filter, that recognize water molecules to selectively transport it and reject other ions or molecules. As an attempt to make biomimetic water channels, peptide sequence is designed to have similarity with water selective filters found in many natural aquaporins. Using the designed peptide as an affinity ligand, water purification membrane was fabricated. Graphene oxide (GO) was used as a solid state matrix material for membrane. GO was functionalized with the peptide ligand and is the resulting functionalized GO was deposited on PC (poly carbonate) or MCE (mixed cellulose ester) supports. Water molecule recognition capability of the designed peptide sequence is successfully applied to water purification process and the fabricated affinity membrane showed enhanced water permeability maintaining rejection performances compared to pristine GO membranes.

Resume : Combining graphene with other materials can multiply its benefits by engineering the desired properties. Graphene-metal nanoparticle hybrid materials potentially display not only the unique properties of metal nanoparticles and those of graphene, but also additional novel properties due to the interaction between graphene and nanoparticles. In this work we prepared such new type of hybrid nanomaterials by transferring graphene onto polycrystalline gold nanoislands. We investigated the samples by STM and STS. After multiple annealing procedures we found that graphene induces surface re-crystallisation of the supporting gold nanoparticles. We showed that gold nanoislands, in turn, can be used to tailor the local electronic properties of graphene. Graphene on crystalline gold nanoislands exhibits moiré superlattices, which generate secondary Dirac points in the local density of states. Room temperature charge localization and anomalously large wavelength moiré patterns are observed. Such large wavelength moiré cannot be formed simply by the rotation misorientation of the crystal lattices. We show using DFT-adaptive molecular dynamics simulations that in such cases the graphene and the interfacial metallic layer is strained, leading to altered lattice constants in both graphene and the interfacial gold layer. These findings can open a route towards the realization of engineered graphene/metal surfaces with various moiré superlattices and tailored local electronic properties.

Resume : The physical properties of chemically synthesized polyaniline (PANI)/reduced graphene oxide (RGO) nanocomposites are investigated as a function of volume fraction of RGO. The characteristics Raman bands of each component demonstrate that RGO-reinforced PANI nanocomposites have been effectively prepared while FE-SEM, TEM and WAXRD are used for analyses of morphology and structure of the products. It is observed that electrical conductivity exhibits a percolation behavior where electrical transport follows a 2D conduction process. Unlike electrical conductivity, the effective thermal conductivity (k) obeys a linear relationship with the filler volume fraction. The results of thermal conductivity fitted by modified MG-EMA model imply that both in plane and through plane thermal transports could take place in the composites. The thermoelectric performance (ZT) is enhanced up to two orders of magnitude for 12.76 vol-% RGO nanocomposites compared to that of pure PANI. In addition, the evolution of volumetric heat capacity of the nanocomposites shows increasing behaviour with RGO loading which is a valuable characteristic for potential applications in high heat capacitive solid state materials. To assess the heat storage factor or heat absorption per unit area Q (J/m2) of the composites, an analytical model is proposed in this study. Owing to their relatively low thermal conductivity and their good heat storage capability, we believe that the composites could be used as the critical component of the thermal management devices or should find potential applications in the next generation of thermoelectric material.

Resume : In this work, some results of materials based on graphene oxide-polymer-electron donor dopants for possible supercapacitor applications are shown. These systems include the use of graphene oxide combined with electrospun nylon-porphyrin or PANi-gold nanoparticles. Electrochemical and physicochemical characterization was performed for both systems. It is well known that conducting polymers such as PANi (polyaniline) has been used in supercapacitors due to its pseudocapacitance. On the other hand, gold nanoparticles have been introduced as electron donor to improve conductivity. The combination of graphene oxide and polymers showed resistive properties that when electric donors were included, the conductivity properties are greatly increased. Porphyrin has the ability to protonate/deprotonate in a reversible way, and their nanocomposite materials were characterized for the first time for super capacitors applications, between others. The results obtained are encouraging to pursue the best conditions in the development of these materials for supercapacitor applications

Resume : Graphene, a one atom thick sp2-hybridized carbon sheet, has attracted a great deal of scientific interest since its discovery by Geim and co-workers graphene holds enormous potential in a variety of applications, including electronic devices, transparent electrodes, super capacitors, sensors and composites . On the other hand, semiconductor based photocatalysts have attracted much attention over the world for environmental remediation, of which ZnO is considered as the most promising material due to its relatively high activity, nontoxicity, and low cost, have emerged as important components for building various optoelectronic and electronic devices especially photovoltaic ones . Graphene film was formed on the surface of ZnO nano wires arrays through in situ electrochemical reduction of a graphene oxide dispersion by cyclic voltammetry. The residual oxygen-containing groups and other structural defects such as sp3-hybridized carbons in the electrodeposited graphene were further removed by photo assisted reduction of the underlying ZnO nanowires, thus achieving the maximum restoration of π-conjugation in the graphene planes. Spectroscopic, electrochemical, and photo electrochemical techniques were used to characterize the graphène films, and the use of the resulting graphene–ZnO nanowires material in photocatalysis and photovoltaic was investigated.

Resume : Graphene oxide (GO) contains oxygen bearing functionalities. The removal of these groups producing reduced-GO (rGO) that shows substantial optical, electrical and chemical changes with respect to original GO. In recent years GO and rGO have shown several promising applicability in energy storage, water purification, sensing and biomedicine. Microstructuration of these materials enhance their properties and make possible their use in supercapacitors or in platforms for cell alignment. Laser interferometry has been widely used to induce periodic surface modification of thin films; spatially located heating occurs in the maxima of interference and the thin film is selectively transformed in those regions. In this work, GO was prepared by using a modified Hummers and Offeman method and thermal treatment was used to produce rGO films (thickness 9.61 ± 1.17 nm) on circular glass coverslips. We then use laser interferometry to produce a pattern of fringed channels with topography and a period of 9.4 microns on this rGO. Width and topography of these channels are controlled by the number of laser pulses. Optical transmittance (T) of the fringes was analyzed by a customized hyperspectral microscope. It is seen that, similar to non-irradiated rGO regions, T increases slightly as wavelength increase in regions corresponding to laser interference minima (i.e., non-transformed ones). Detailed analysis of the hyperspectral cube by using a principal component analysis method reveals UV-Visible absorption peaks located in the edge of the channels. These peaks can be related to chemical products used in the fabrication of the rGO films.

Resume : The electronic properties of the single layer graphene can be changed when double (triple) layer system, i.e. turbostratic graphene or so called twisted graphene (TG) is deposited. Many interesting phenomena are associated with TG: enhanced optical absorption, non-dispersive flat bands at the charge neutrality point related to confinement, enhanced photochemical reactivity, etc. We present experimental evidences of high degree of homogeneity graphene layers synthesized by atmospheric pressure chemical vapor deposition from alkane hydrocarbon precursor. TG was synthesized on Cu foils at 1050 ºC temperature employing different mixtures of N2 and H2 feed stock gases. Original transfer recipe on SiO2/Si substrates was proposed avoiding use of polymer. Samples were analyzed by micro-Raman (excitation wavelengths of 473 and 532 nm) and X-ray photoelectron spectroscopies. The blue shift for G and 2D bands were observed for both wavelengths. The positions, FWHM and intensity distribution of the 2D band proved the turobostratic (twisted) double layer structure of graphene growth at the low hydrogen feeding rate. The blue shift of G band positions and XPS study demonstrated the nitrogen doping of graphene. Homogeneity of the twisted graphene layer was proved by measurements of transmission coefficient of VIS-NIR light in the 400-1000 nm range. It was obtained that at the wavelength of 550 nm the transmission coefficient is equal to 94%, which corresponds to 2-3 graphene layers.

Resume : Electronic properties of graphene substantially depend on its interaction with a substrate. Recently, graphene-on-diamond structures (G on D) have attracted much attention. Theoretical efforts to predict interactions at the G on D interface vary and often contradict each other. Despite the technological importance of the G on D heterostructure a systematic experimental study related to the nature of interactions at the interface is missing. In our research we aim experimentally to realize various systems of graphene-on-diamond and investigate their properties. We design possible routes to obtain G on D hetero-system. A. Surface graphitization of diamond will undergo when annealed under high vacuum and temperatures ~1100 degC. At these temperatures, mobility of the carbon atoms facing vacuum is sufficient to reorganize into a more stable graphitic phase. B. Catalytic transformation of the diamond surface into graphene. Catalyst (Ni, Pt, etc.) dissolves carbon at elevated temperatures (700–900 degC). During cooling, dissolved carbon precipitates back on the surface of catalyst forming graphene. Variety of diamond substrates (single crystals in different orientations) will be tested for graphene growth. It is expected that, while the surface graphitization of diamond will lead to strongly bound graphene to diamond, transferring graphene from other surface onto diamond, on the other hand, will result in a poor interaction between these two carbon structures.

Resume : Thin Layers Graphene have been obtained at an interface between a metal film like Ni or Cu and transparent substrate like MgO (111) or quartz by carbon implantation into the metallic matrix near the interface followed by a heat treatment to migrate the carbon atoms directly at the interface and to graphenize the carbon interfacial layer. Finally the metallic layer is dissolved to recover a graphene on a transparent substrate. This preparation avoids the step of graphene films transfer. We have studied the process and we have stressed the importance of the metallic film epitaxied on MgO. Thus high quality graphene can be grown with Ni, reversely to Cu.

Resume : In this contribution, we report on two recent advances done in Grenoble [1] on CVD graphene. In the first study [2], we measure uniaxial strain fields in the vicinity of edges and wrinkles in graphene prepared by chemical vapor deposition on Co, by combining microscopy techniques and local vibrational characterization. These strain fields have magnitudes of several tenths of a percent and extend across micrometer distances. The nonlinear shear-lag model remarkably captures these strain fields in terms of the graphene–substrate interaction and provides a detailed understanding of strain-relieving wrinkles in graphene for distinct levels of graphene–substrate coherency. In the second study [3], we report on graphene formed on a Pt substrate using a modified hot-filament-assisted chemical vapor deposition setup, which does not require any control of crystal nucleation and orientation. The underlying growth mechanism includes a stage of structural evolution from nanocrystalline to microcrystalline graphene film. An enhanced recrystallization process in the graphene film is assessed by means of Raman spectroscopy and atomic resolution transmission electron microscopy. This process opens a new route to control the electrical properties of large-scale uniform graphene film. [1] http://2d.grenoble.cnrs.fr/ [2] "Strain relaxation in CVD graphene: wrinkling with shear lag”, Merijntje S Bronsgeest, Nedjma Bendiab, Shashank Mathur, Amina Kimouche, Harley T Johnson, Johann Coraux, Pascal Pochet Nano Lett. 15 (8) pp 5098–5104 (2015) [3] "CVD Graphene recrystallization as a new route to tune graphene structure and properties”, Anastasia V. Tyurnina, Hanako Okuno, Pascal Pochet, Jean Dijon submitted to Carbon (2015)

Resume : The presence of heavy metals in water may cause serious problems about the environment and humans life because of the high toxicity of heavy metals to humans and other living creatures. Arsenic is one of the most toxic and oncogenic chemical elements. Also, Arsenic can cause several serious health problems and skin cancer. Iron oxide based materials are very effective in the removal of arsenic. However, these adsorbents are difficult to control in water flow systems due to small particle size and in stability of iron oxide. To solve this problems and increase arsenic removal efficiency, many studied have been focused on graphene and Fe3O4 composites that have high surface area for increasing adsorption efficiency. For example, graphene oxide (GO)/carbon nano tube/Fe3O4 composites have high surface area and good adsorption efficiency. Also, mesoporous graphene/Fe3O4 gels suggest good arsenic adsorption efficiency because of high surface area. In this study, we synthesized the core shell structure of PS/positively charged reduced graphene oxide (rGO-NH3 )/negatively charged reduced graphene oxide (rGO-COO-)/graphene oxide by layer-by-layer assembly. Next, the surface of rGO-NH3 coated with GO that have many functional group for attaching Fe3O4. And, the surface of GO coated with the Fe3O4 nanoparticles. Field-emission scanning electron microscope (FE-SEM) analysis suggest the successful synthesis of morphology of PS/rGO/Fe3O4 composites. The elements and chemical bondings, chemical composition of surface on the PS/rGO/Fe3O4 composites were confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS). And, we checked arsenic adsorption efficiency of PS/rGO/Fe3O4 composites by arsenic adsorption analysis.

Resume : Single and few-layers graphene were grown by CVD on Steel (API X80) using ethanol as precursor at 1000oC, 400 mtorr. The substrates were first reduced in Hydrogen at the same temperature during 2 hours, 50 sccm. The samples were characterized by Raman spectroscopy performed with a laser of 473 nm wavelength and the Raman maps clearly show the formation of inhomogeneous coating of graphene with regions covered with a single-layer graphene or few-layers graphene, the last one covering the higher surface area of the sample. The samples were analysed by scanning electron microscopy and EDS using a FEG-SEM JSM- 6701F from JEOL. XPS was performed using an Mg Kα x-ray source and an Alpha 110 commercial hemispherical electron energy analyzer. The results indicate that the surface is covered with a carbon layer with a small amount of oxygen contamination. Nanoscale friction measurements were performed by Lateral Force Microscopy using a Park AFM NX10 with silicon nitride tips and 4 nN of applied load scanning at 0.3 Hz. Macroscale friction measurements were performed using a CTER tribometer in a low load regime (less than 2 N). In both cases, the friction coefficients obtained from the coated sample are lower than the one obtained from bare steel sample. Wear measurements were performed with a ball-on-disk contact geometry. The normal load was 1 N at a speed of 60 rpm. The graphene coating reduces the wear rate. This work is partially supported by Brazilian agencies CNPq and FAPERJ.

Resume : The deposition of various nano-materials onto graphene nanoplatelets (layers of graphene) is ideal for different applications. Deposition by radio frequency (RF) sputtering technique can degrade layers of graphene due to interaction of high energy sputtered particles and plasma species. By optimizing the deposition parameters, the level of damage to graphene layers can be controlled. In this scenario, niobium pentaoxide (Nb2O5) thin films deposited on graphene nanoplatelets (GNPs) powder by various deposition parameters like RF power, process pressures, deposition times and sample vibration frequency in argon atmosphere. The structural properties of the samples were investigated by X-ray diffraction (XRD) and Raman spectroscopy. For the chemical analysis of the samples X-ray photoelectron spectroscopy (XPS) was used. The interlayer d spacing of the GNPs calculated from the XRD pattern changes with Nb2O5. By increasing Nb2O5 contents through deposition parameters variation, defects on the surface of GNPs increased and basal planes of GNPs gradually lost their initial ordering, decreasing the degree of graphitization. Raman study revealed that both doping and tensile strain contributed shift of G and 2D bands to lower wave numbers in the Raman spectra. From the XPS analysis, we found that, with increasing RF power, low process pressure and increasing sample vibration frequency more Nb2O5 contents are intercalated into the GNPs system.

Resume : To date, a number of two-dimensional (2D) topological insulators (TIs) have been realized in Group 14 elemental honeycomb lattice, but all are inversion symmetric. Here, based on first-principles calculations, we predict a new family of 2D inversion asymmetric TIs with sizeable bulk gaps from 105 meV to 284 meV, in X2-GeSn (X=H, F, Cl, Br, and I) monolayers, making them in principle suitable for room-temperature applications. The nontrivial topological characteristics of inverted band orders are identified in pristine X2-GeSn with X=(F, Cl, Br, I), while for H2-GeSn, it undergoes a nontrivial band inversion at 8% lattice expansion. Topologically protected edge states are identified in X2-GeSn with X=(F, Cl, Br, I) as well as in strained H2-GeSn. More importantly, the edges of these systems, which exhibit single-Dirac-cone characteristics located exactly in the middle of their bulk band gaps, are ideal for dissipationless transport. Thus, Group 14 elemental honeycomb lattices make a fascinating playground for manipulation of quantum states.

Resume : Two-dimensional materials have been investigated extensively since the discovery of graphene. Among these, monolayer MoS2 is a semiconducting material with a direct band gap making it attractive for various applications. In addition to pristine structures of various 2D crystals, their usage in form of heterostructures has attracted a considerable interest [1]. On the other hand, the general approach for obtaining such heterostructures have been performed using transfer methods such as exfoliation. These approaches hinder the practical use of the technology due to the inherent limitations of transfer methods resulting in limited lateral size and introduction of contaminants into the structure. In this work, we demonstrate the first growth comparison and optimization study of MoS2 on both transferred and as-grown graphene. We investigate the effect of the two different approaches on MoS2 monolayer properties systematically. The process parameters such as growth temperature, process time, precursor ratio, ambient atmosphere and pressure have also been studied. The heterostructures are characterized by optical, scanning electron, Raman scattering and photoluminescence microscopies. The MoS2 flake sizes are observed to be larger than several micrometers and also the flake distribution over graphene is found to be almost uniform according to the SEM results, while MoS2 flakes are rarely observed on the oxide surface. [1] H. Lim et al., Chemistry of Materials, 2014 ,26 17, 4891-4903.

Resume : Fundamental understanding of carrier transport is needed for current graphene-based devices (e.g. graphene based FET’s or G-FET’s, solar cells) involving single G-layers grown directly over n- or p- type semiconductors (e.g. Si). In an ideal G/n-Si junction under reverse bias, carriers may (a) tunnel through the junction barrier with a non-zero tunneling probability and may (b) thermionically overcome the potential barrier at the junction. In this communication we are treating the latter, by proposing new modeling for thermally escaping carriers over the top of the barrier in the Landauer formalism frame. Our modeling considers incident carriers from the graphene side, with sufficient energy to overcome an ideal reverse-biased G/n-semiconductor contact. Specifically, we predict thermionic emission current directly related to (a) temperature as T^3/2 (b) applied bias (c) junction barrier and (d) Fermi level in the semiconductor EFs. We find a T3/2 -temperature dependence (instead of a T2-dependence of common bulk metal-semiconductor SB’s). The predicted current follows the standard Schottky diode model, with (i) a different Richardson’s constant and with (ii) an explicit dependence on the thickness of the graphene layer: JTH = (A*/d) T^3/2 exp [-(qFB-Efs)/kT] [exp (qV/kT)-1], where A*(A m-1 Kelvin^-3/2) is a new Richardson’s constant, d is the graphene layer’s thickness, qFBis the potential barrier at the G/n-Si contact relative to the graphene layer’s Fermi level, Efs is the quasi Fermi level in the n-semiconductor and V is the applied voltage. Our result is attributed to graphene’s DOS (density of states) linear dependence on energy, and resembles similar T-dependence of thermionic currents in 2-dimensional structures (thermal escape over the barrier of quantum wells in GaAs/AlGaAs multi-quantum wells and superlattices); the result agrees with standard thermionic emission of regular metal-semiconductor contacts, but differs in the temperature dependence.

Resume : Topological insulators (TIs) attract great amount of attention in the field of ultrafast photonics due to its graphene-like features. Here, we demonstrated the manipulation of operation states in erbium-doped fiber laser (EDFL) with Bi2Te3 (BT) film deposited on side-polished fiber (SPF) by pulse laser deposition. The BT-SPF provides highly polarization-sensitive absorption for evanescent fields. Three Raman peaks were observed at 59.1, 99.3, and 127.7 cm^−1, which are consistent with the vibrational modes of BT crystal. The transmission spectrum measured for the transverse electric mode is flat from 1.5 to 1.6 um with transmittance of 20%. Due to the asymmetrical geometry of the saturable absorber (SA), the polarization-dependent loss (PDL) of BT-SPF SAs is ~33 dB, while that of SPF before BT depositing is ~0.5 dB. EDFL can be tuned to operate at mode-locked (ML), Q-switched, and Q-switched ML (QML) states by inserting BT-SPF SA and adjusting the quarter-wave plate (QWP) or half-wave plate (HWP) of intracavity polarization controller at pump power of 140 mW. In ML operation, the pulse spacing, center wavelength, 3-dB spectral bandwidth and pulse width were ~50 ns, 1562.2 nm, ~7.93 nm and ~408 fs, respectively. Q-switched operation was realized by tuning QWP, with repetition rates of 5.6~23.5 kHz and pulse widths of 2.96~2.11 us, while QML operation is obtained by tuning HWP, with repetition rate and pulse width of about 74 kHz and 2.62 us. Switching between operation states could be attributed to BT-SPF SA, which plays the dual role of SA and polarizer of nonlinear polarization evolution.

Resume : One of the problematic aspects of graphene CVD growth on metal substrates is that graphene is capable to create rotational domains [4], separated by grain boundaries, sometimes even on a single crystal surface [5]. Grain boundaries worsen the electric properties of graphene [6], therefore the nucleation of differently orientated graphene islands is an undesirable phenomenon. An interesting feature is, that the number and the type of different existing orientations are very specific to the substrate (e.g.: on Cu(111) the most commonly known orientations are: R0°, R7°, but for Ir(111) we have R0°, R14°, R19°, R23°, R26°, R30°) [7]. Even today there is no such a physical model that can somehow clarify the very basic nature of these orientations: why only these orientations can appear, and what are the circumstances that influences the graphene to realize one or another? In order to understand these aspects we developed DFT-adaptive force-fields for CMD simulations with self-made parameter fitting code. Our force-field can reproduce remarkably the corrugated surface of the graphene (Moiré-pattern) [1-3]. With our CMD method supported by DFT calculations we were able to confirm the existence of new rotational domains on Cu(111)[1] and Au(111)[3] discovered by STM measurements. We also confirmed the coexistence of two types of surface topographies found on Au(111) [3]. By investigating the energetics and dynamics of graphene nanoislands we were able to make a simple model that can predict the possible orientations on substrates found by STM. References: [1] P. Süle, M. Szendrő, C. Hwang, L. Tapasztó, Carbon 77, 1082-1089 (2014). [2] P. Süle, M. Szendrő, Modelling Simul. Mater. Sci. Eng. 23(2), 025001 (2015). [3] P. Süle, M. Szendrő, G. Magda, C. Hwang, L. Tapasztó, Nano Letters 15, 8295 (2015). [4] M. Batzill, Surf. Sci. Rep. 67, 83 (2012). [5] Li Gao, Jeffrey R. Guest, Nathan P. Guisinger, Nano Letters 10(9), 3512-3516. (2010). [6] P. Vancso, et al., Applied Surface Science 291, 58-63 (2014). [7] H. Tetlow, et al., Physics Reports 542.3, 195-295 (2014).

Resume : Present work provides results of micro-Raman, and scanning atomic and Kelvin-probe force microscopy (AFM and KPFM) studies of gamma-irradiated graphene flakes on Ni. Graphene flakes with varied number of layers are synthesized on the Ni surface by thermal treatment in vacuum and rapid thermal annealing in nitrogen of “sandwich” structure such as amorphous a-SiC/Ni/SiO2/Si. The a-SiC/Ni layers were deposited by magnetron sputtering technique. It allowed us to obtain the graphene flakes with sizes about 20x20 μm covering about 80% of the Ni surface as confirmed by appearance of prominent G and 2D bands in the Raman spectra. Fabricated structures are subjected to gamma-radiation with doses up to 5x10^6 Rad in air. At the maximum dose of the gamma-irradiation a formation of new graphene-based structures on Ni surface such as “domes”, “stars”, and “rods” occurred. The obtained structures are investigated in details by confocal micro-Raman mapping, AFM and KPFM methods. Doublet structure of the graphene Raman G-band with components peaked at ~1571 сm^-1 and ~1596 cm^-1 is registered in the vicinity of the dome-like structures. The observed doublet behavior of the G-band is discussed in the relation with non-uniform doping of graphene with charge impurities, structural defects and elastic strains.

Resume : For good performance graphene and carbon nanotubes devices, clean and individualised dispersion is often desired. Many dispersion methods are known but sonication is the fastest and simplest. Both nanomaterials can be dispersed in organics, typically amides, particularly N-methylpyrrolidone (NMP). The solvation of the nanomaterials by amides has been previously attributed to the similar surface energies between the amides and sp2 carbon lattice. However, there are solvents with similar surface energies to amides that do not solvate them. Clearly, there is at least an extra parameter that has to be considered together with the surface energy theory when choosing a solvent for carbon nanomaterials. We have discovered that sonicating NMP rapidly produces organic nanoparticles which subsequently contaminate dispersions. AFM and UV-vis show that the concentration of the nanoparticles increases with sonication time. IR and 1H NMR confirm that the nanoparticles originated from sonochemical degradation and polymerisation of NMP. The organic contaminant should be considered in concentration determination and subsequent application since the data show that up to 70wt% of suspended mass could be organic contaminant. The organic species is likely to be polyamide which has a high affinity to both graphene and CNTs. Hence, the in situ sonochemical degradation & polymerisation of NMP may be responsible for the high dispersibility of the carbon nanomaterials.

Resume : With today’s aberration corrected machines, atomically resolved (scanning) transmission electron microscopy (TEM/STEM) has become a standard characterization technique for nanoscaled materials, especially in the evolving field of 2D-materials. However, a big limitation is beam damage because of the high required dose of energetic electrons. While reducing the acceleration voltage to 80 kV or below can prevent beam damage in pristine graphene, defects, functional groups or molecules on the surface are still strongly affected by energetic electrons. Our recently published algorithm makes it possible to reconstruct defects or single molecules on graphene from simulated STEM and TEM low-dose data. In this approach, the electron dose is distributed over many copies of the same structure which makes it possible to directly image the atomic configuration of highly beam-sensitive materials in the TEM. Depending on the dose, areas up to a few square micrometer have to be imaged with atomic resolution which corresponds to up to several thousand single single images. Acquiring such amounts of data efficiently is only possible via automated methods. We present such an approach implemented on our Nion UltraSTEM 100.

Resume : Graphene blended with the conjugated polymer poly(3-hexylthiophene) (P3HT) is known to be able to work as an efficient absorber in organic solar cells. By its high charge mobility, graphene use in composite materials improves significantly their conductivity. Furthermore, charge separation in these materials is favored as graphene usually act as quencher in the fluorescence of the conjugated polymer and consequently enhances the performance of devices. Despite intensive investigations, the interactions between materials and the quenching process in P3HT/graphene composites has not been fully understood yet. In this work, we have fabricated and studied composites made of P3HT and graphene with different concentrations and qualities (expressed by the graphene weight per surface unit). Using optical spectroscopy including absorption, infrared, Raman and photoluminescence (steady state and time-resolved) we analyzed the electronic structure of the composites as a function of the graphene concentration and quality. Interactions between graphene and P3HT were observed in composite spectra as compared to those of separate components. Charge transfer process was also evidenced in composites, which was found to depend not only on the concentrations but also on the contact area of graphene in the conjugated polymer matrix. From the obtained results, we discussed the possible transfer mechanisms occurring in the composites.

Resume : At present time the works over development and producing of chemical acoustoelectronic sensors are actively carried out. It should be pointed the questions concerning the increasing of sensitivity, selectivity, working time of such sensors and widening their functional possibilities are very actual. One of the ways that allows solve these tasks is the search of the new gas-sensitive films. The using as the active element graphene and its derivatives will allow to develop whole set of different sensors for analysis of gases and liquids. This possibility is connected with the unique graphene property that allows change the wide of his forbidden zone by the modification of the film surface by using the different ligand groups. The paper proposes to use a film of graphene oxide deposited on a piezoelectric substrate, with the possibility of further reduction to graphene. The technology of deposition of films from polar and nonpolar solutions of synthesized graphene oxide by the spin-coating method has been developed. This method allowed get homogeneous dense coating from graphene oxide for further reduction to graphene and its modification. By using acoustoelectronic technology the influence of different gases on the physical properties of the films based on oxide graphene, graphene and its derivatives for development of sensitive sensor for various applications has been investigated. The work is supported by grant Russian Science Foundation #15-19-20046.

Resume : Understanding carrier transport through Graphene-oxide-semiconductor contacts is vital for graphene-based devices (e.g. FET geometries, solar cells). Carrier transport at G-oxide-semiconductor interfaces strongly depends on (a) carrier tunneling through oxide/n-semiconductor layers (b) thermionic carrier tunneling through the oxide in the semiconductor conduction band. Oxide layer tuning, for instance, plays a crucial role for carrier transport and overall solar cell performance; in graphene-FET geometries, typical modeling of carrier transport through oxide layers is dealt via standard quantum tunneling (exponential tunneling probability factors). In this communication we are proposing a new model combining thermionic emission and subsequent tunneling through an ultra-thin oxide layer. We demonstrate the feasibility of (i) thermionic emission of electrons leaving the graphene layer side with energies above the Schottky barrier qB (assumed much greater than kT and between G and n-Si) and quantum tunneling next through the oxide layer may occur. Most of the literature deals with such issues with relatively thick insulator barriers, however we propose a delta-function oxide layer and incorporate its tunneling probability T(E) ~ E/a, where E is the carrier density and a is related to the strength of the oxide's delta-barrier. We then incorporate the tunneling probability, in a Landauer-based frame for thermionic emission above the contact barrier at the interface. Between the linear density of states of graphene and the tunneling through the oxide/insulator layer (between G and n-Si), we find a combined thermionic/tunneling current that follows the standard Schottky barrier format, with the following additional details (a) strong T^3/2 dependence instead of T^2 for the usual bulk cases (b) exponential [exp(-(qB-Efsi)/kT)] where qB is the contact barrier, Efsi is the semiconductor's Fermi level, (c) direct dependence on the graphene layer thickness and (d) an overall different Richardson’s constant A*.

Resume : One barrier to progress in the field of carbon nanotube-incorporated devices is that current production methods generally create a mixture of nanotube types. However, as their metallic behaviour depends on their specific diameter and helicity, it becomes necessary to have fine control over the type of nanotube used, if device performance is to be optimised. Although selective synthesis methods have recently been developed, a possible way to overcome this barrier is to separate the mixture of nanotubes, based on their physical and electronic properties, post-production. A method of great interest is selective solvation due to both the minimal damage made to the carbon nanotube and its low-cost, scalable nature. This process utilises the fact that the characteristic electron affinities of the carbon nanotube, and the extent to which they become charged, vary depending on their structure. Calculations based on hybrid-exchange Density Functional Theory methods, as implemented in the CRYSTAL software package, have been used to document the behaviour of the electron affinities and ionisation potentials of carbon nanotube as a function of their diameter and helicity. Furthermore, the effect of varying length, and differing methods of edge termination, on these electronic properties will be discussed to help inform experimental efforts in developing novel nanotube separation techniques.

Resume : We present an analytical device model for graphene-nanoribbon field-effect transistor based gas detection. The gas detection is achieved by changing the conductivity of graphene-nanoribbon which influences directly the work function of the GNR-FET electrodes and so affect the metal/GNR junction transfer characteristics. A mathematical model is proposed to acquire an analytical understanding of the graphene-nanoribbon based gas detection mechanism. We have used NH3 as a prototype gas to be detected by the GNR-FET nanosensor and we have studied the corresponding current–voltage characteristics. When exposed to different gases concentration, Graphene-based gas sensor exhibits higher conductivity compared to that of GNR-FET based counterpart for similar ambient conditions without gas exposure. The proposed gas sensors show a sensitivity of almost 2.7% after exposure of 1ppm of NH3. These results make them appropriate candidates for use in gas sensing/measuring applications.

Resume : Ab-initio calculations, carried out with different basis sets, for the static longitudinal linear polarizability, αL, and second order hyperpolarizability, γL, of small doubly charged polyacetylene (PA) chains, are presented. The polarizabilities were calculated using the Hartree–Fock (HF) method while the electron correlation effects were included through the second-order Møller–Plesset perturbation theory (MP2). Positively and negatively charged bipolarons were studied. The results obtained for positive and negative chains show that the ionization state effect decreases more rapidly, as the chain length is increased, for αL than for γL. Or both types of charged chains, the incorporation of the electron correlation increase the αL, and γL values, as compared to the HF values. A comparison between the results obtained using the standard 6-31G basis set and augmented versions of this set, obtained by the addition of diffuse and polarization functions, shows that 6-31G basis set does not provide a good description of the negative chains studied here and that the addition of extra diffuse functions on the basis set is needed in order to obtain reliable estimates for polarizabilities, specially for γL. Key words : polarizabilities; hyperpolarisability; polyacetylene; bipolarons; correlation effects.

Resume : The graphene-like (GL) film was synthesized by hot-wall CVD technique between Ni and SiO2 layers on structure Ni-SiO2-Si with following dry mechanical removal of the Ni film from the substrate. Thickness of the Ni film was 110 nm. Heating of the structure was up to 760°C in stream of H2/N2 (4/3) gas and exposure in C2H2 for 10 min. Quality and structure of the GL film were analyzed by micro-Raman scattering spectroscopy (mRSS) with excitation by the 514 nm line of an Ar-Kr ion laser and AFM. The mRSS shown an appearance of narrow G (1600 cm-1) and D (1350 cm-1) bands with same amplitude and weakly pronounced 2D band (2700 cm-1) that denotes on existence of defect graphene structure. The AFM allowed us to determine a thickness of the film which was 0.6 nm, and RMS of surface roughness was 0.2 nm. Spectroscopic ellipsometry in range of wavelengths from 200 to 1600 nm was used for optical constants (n and k) determination. Reconstraction of the optical constants by Cauchy approach for GL film with thickness 0.6 nm and SiO2 layer with optical parameters, obtained on control sample, shown small changing of k (from 2.3 to 2.2) in the entire region of the wavelengths. Determined value of k is considerably higher than for graphene layers (about 1.5). Refractive index, n, in range from 500 to 1600 nm is changed from 2.2 to 2.6. Different models for optical constants reconstruction have been considered. Photoconductivity spectrum of the GL-SiO2-Si structure was also measured and discussed.

Resume : The nanoscopic properties of graphene have attracted a lot of scientific effort due their utiliza-tion as building blocks for the development of new hybrid nanostructures with well-defined di-mensions and behaviour. In fact, graphene sheets can be used as templates for the synthesis of novel intercalated carbon-based materials suitable for various applications among else in gas stor-age, gas/liquid separations, photocatalysis, bioimaging, optoelectronics, nanosensing and biology. In this work, graphene was combined with luminescent carbon-dots (C-dots) to form novel hybrid thin films. Our thin film preparation approach involves a facile and low cost layer-by-layer proce-dure that includes the formation of a hybrid graphene multilayer film hosting luminescent C-dots within its interlayer spacing. This new method, based on combining self-assembly with the Lang-muir-Schaefer technique, uses the graphene nanosheets as a template for the grafting of C-dots moieties in a bi-dimensional array, and allows for perfect layer-by-layer growth with control at the molecular level. Hybrid C-dot-based thin films deposited on hydrophobic substrates were charac-terized by photoluminescence, UV-Vis, X-ray diffraction, X-ray photoelectron and Raman spec-troscopies and atomic force microscopy. The results revealed the formation of a hybrid graphene film hosting luminescent C-dots within its interlayer spacing.

Resume : The aim of this work is the synthesis and characterization of single wall carbon nanotubes (SWCN) with phosphorus incorporated. Two temperatures (800 and 850 Celsius degrees) were used to produce the nanotubes in a vacuum chemical vapor deposition (CVD) system using as precursor the solid substance triphenylphosphine without any dilution in liquid. Raman spectroscopy and x-ray photoelectron spectroscopy (XPS) were used to characterize the samples. Raman spectroscopy were employed to show the signature of SWCN and a shift in Raman bands was observed due presence of phosphorus in the structure comparing with a reference sample without phosphorus. This shift can be related to changes in the electronic properties of the material. XPS spectra confirm the presence of phosphorus bonded to carbons atoms showing the phosphorus incorporation in carbon nanotubes.

Resume : Nowadays lots of materials are elaborated for microwave absorption applications. Carbon-based nanoparticles belong to those materials. Among these, graphene presents some distinctive features for electromagnetic radiation absorption, and thus microwave isolation applications. In this study, the dielectric and microwave absorption characteristics of epoxy resin loaded with graphene are presented from 2 GHz to 18 GHz. The real and imaginary parts of the complex dielectric constant ε* (ε* = ε’+j ε”) are retrieved from a dielectric kit. The microwave reflection and absorption levels of the samples are measured from a home-made free-space bench. The influence of various parameters, such as particle size (3 µm; 6-8 µm and 15 µm) and weight ratio (from 5% to 25%), is investigated and discussed. The sample loaded with the smallest graphene size (3 µm) and the highest weight ratio (25%) exhibits high loss tangent (tand=0.4) and dielectric permittivity ε’=12-14 in the 8-10 GHz frequency range. As expected, this sample also provides the highest absorption level: from 5 dB/cm at 4 GHz to 16 dB/cm at 18 GHz. Filling epoxy resin with the smallest graphene particles (3 µm-size) increases multiple microwave reflections into the composite material, and thus promotes high absorption level at microwaves.

Resume : Misfit layered compounds can be considered as inter-grown materials with a general formula [(MX)1 x]m[TX2]n, where M is rare earths, Pb, Sb, etc; T is Ti, V, Cr, Nb, etc. and X is S, Se. They constitute an heterostructure formed by the stacking of TX2 dichalcogenides layers with MX layers.1 In 2011, nanotubes based on the SnS-SnS2 system were synthetized for the first time in large amounts2. Later, the syntheses were generalized to many other systems. However, making these structures in the nano-size is rather challenging. Most of the misfit nanotubes reported in the earlier reports have wall thickness of more than a few dozen of nanometers. In order to improve the synthesis conditions, detailed structural and chemical analyses at the nanoscale are highly needed. In this work, few layers thick nanotubes based on the TbS-CrS2 system are reported. Their detailed structure and chemical composition are elucidated by different TEM techniques including high-resolution scanning TEM (HR-STEM) and spatially-resolved EELS (SR-EELS). Surprisingly, structural modulation and composition variation along the thin nanotubes axis were observed.3 In light of this new structural and chemical information, a growth mechanism for these nanotubes is proposed. In addition, we will also show how the coupling between HR-STEM, SR-EELS and DFT calculation can shed light not only on the atomic structure of misfit nanotubes but also on their opto-electronic properties.4 1. J. Rouxel, A. Meerschaut, and G. Wiegers, J. Alloys Compd. 229, 144 (1995) 2. G. Radovsky, R. Popovitz-Biro, M. Staiger, K. Gartsman, C. Thomsen, T. Lorenz, G. Seifert, and R. Tenne, Angew. Chem. Int. Ed. 50, 12316 (2011). 3. L.S. Panchakarla, L. Lajaunie, R. Tenne, R. Arenal. J. Phys. Chem. C (2015), In Press. 4. L.S. Panchakarla, L. Lajaunie, A. Ramasubramaniam, R. Tenne, R. Arenal, In preparation

Resume : Centimeter up to inch-sized single-crystal graphene has been successfully grown by catalytic chemical vapor deposition (CVD) on Cu and other metal substrates. However, previous attempts to grow large domains in graphene have been limited to isolated graphene single crystals rather than as part of an industrially useable continuous film. In this study, we demonstrate the CVD growth of continuous monolayer graphene with millimeter-sized domains within 80 min.[1] We obtain this by electropolishing and mild oxidation of the Cu foil and optimization of the CH4 supply. The Cu oxidation is found to be particularly efficient in drastically reducing the graphene nucleation density, in consistence with published results. However, there has been no adequate explanation for why the surface oxygen suppresses the nucleation density. We show by DFT that the opportunity for the hydrocarbons occupying the active sites on Cu surface is significantly reduced in the presence of the oxygen atoms, due to the differences between their chemisorption energy. In addition, the concentration of H2 in our work has been diluted to well below its lower explosive limit, which enhances the safety of industry-scale graphene-CVD processes. The as-grown graphene has been characterized by charge carrier mobility measurements, scanning electron microscope, electron diffraction study, and Raman mapping. The hole mobility reaches ~5,700 cm2V-1s-1, notably higher than the published results using similarly low concentrations of H2. This work helps improve the scalability and safety of industrial production of high quality graphene. It also deepens understanding of the role of oxygen in the graphene-CVD process. [1] Wu, X., Zhong, G., D'Arsié, L., Sugime, H., Esconjauregui, S., Robertson, A., & Robertson, J. Growth of Continuous Monolayer Graphene with Millimeter-sized Domains Using Industrially Safe Conditions. Accepted by Scientific Reports.

Resume : Graphene microelectronics will expectedly complement the mainstream Si technology, CMOS, instead of replacing it. The reason is cost-efficiency, but the available growth methods are not easily CMOS-integrable. Large area graphene that can be grown on Cu or on Ni must be transferred onto Si(001); this is problematical [1]. A process in which graphene grows directly on a Si wafer would be welcome; yet SiC formation makes this hard to realize. An approach bypassing some of these problems is chemical vapor deposition (CVD) on Ge substrates [2-6]. We discuss the results of ab initio density functional theory (DFT) calculations for the interaction between C, H, and Ge during deposition of C2H4 on Ge(001)-p(2×2). Ge dimer vacancies are found to play an important role in the process of graphene nucleation. [1] G. Lupina et al., Residual Metallic Contamination of Transferred CVD Graphene, ACS Nano, 9, 4776 (2015). [2] G. Wang et al. Direct growth of graphene film on Ge substrate. Sci. Rep. 3, 2465 (2013). [3] J. H. Lee et al., Wafer-scale growth of single-crystal monolayer graphene on reusable H-terminated Ge, Science 344, 286 (2014). [4] R. M. Jacobberger et al., Direct oriented growth of armchair graphene nanoribbons on Ge, Nature Comm. 6, 8006 (2015). [5] B. Kiraly et al., Electronic and Mechanical Properties of Graphene-Ge Interfaces Grown by CVD, Nano Lett. 15, 7414 (2015). [6] J. Dabrowski et al., Initial State of Graphene Growth on Ge(001) Surfaces, ECS Trans. 69, 345 (2015).

Resume : Catalytic chemical vapor deposition (CCVD) has long been recognised as the most promising technique for controlled synthesis of single-walled carbon nanotubes (SWNTs). However, understanding the nucleation-growth mechanisms of SWNTs remains a very difficult task limiting our ability to control the tube’s structure. In this context, understanding the key role played by carbon solubility in the catalyst particle seeding the nucleation and growth of SWNTs is an essential step towards a better knowledge and control on the growth mechanisms of SWNTs. To go beyond phenomenological approaches, we have performed simulations at atomic scale. Here, we use a carefully assessed tight binding model for nickel and carbon [1] to numerically investigate different aspects of the CCVD synthesis process. Grand canonical Monte Carlo calculations to model metal-carbon systems of the type NiC [1] have shown very accurate results. Among other thing, nanotube growth from Ni nanoparticles was very accurately described [2]. It was also noticed that solubility and wetting properties are important parameters in which regard the growth [3]. In the present work, we plan to expand this model to a more general metal-carbon systems studying the influence of the solubility on the thermodynamics properties metal-carbon nanoparticles along with the growth of carbon nanotubes. By considering metals with different solubilities, we highlight that controlling the level of dissolved carbon in catalytic particles is of key importance to enable nucleation and growth. [1] H. Amara, J.-M. Roussel, C. Bichara, J.-P. Gaspard and F. Ducastelle, Tight-binding potential for atomistic simulations of carbon interacting with transition metals: Application to the Ni-C system, Phys. Rev. B, 73, 014109 (2009) [2] M.-F. C. Fiawoo, A.-M. Bonnot, H. Amara, C. Bichara, J. Thibault-Pénisson and A. Loiseau, Evidence of Correlation between Catalyst Particles and the Single-Wall Carbon Nanotube Diameter: A First Step towards Chirality Control, Phys. Rev. Lett., 108, 195503 (2012) [3] M. Diarra, A. Zappelli, H. Amara, F. Ducastelle and C. Bichara, Importance of Carbon Solubility and Wetting Properties of Nickel Nanoparticles for Single Wall Nanotube Growth, Phys. Rev. Lett., 109, 185501 (2012)

Resume : The aim of the present work is understanding the role of the buffer layer, ambient conditions and growth parameters for attaining a full control on epitaxial graphene growth on SiC to obtain cm scale continuous coverage of ML graphene. To follow the aims a series of graphene samples was grown on Si face of SiC in an inductively heated furnace at a temperature ranging from 1700-1950°C, in vacuum, at argon ambient with different pressure, in Si rich ambient, and at different growth times. Buffer layer is a precursor for graphene formation and can strongly influence its quality; depending on the buffer layer integrity the graphene may contain defects. Graphene formation was analyzed in respect to step bunching and surface decomposition energy. The result showed that the buffer layer halts the step bunching process, which means the surface energy becomes uniform all over the substrate surface after the coverage by a buffer layer. Graphene samples grown at different argon ambient pressure prove that there is an optimal argon pressure yielding a large coverage of ML graphene. The temperature dependence of the buffer layer and ML graphene coverage is sublinear, suggesting that the formation process is surface kinetics limited. We have found that changing environment from C to Si rich resulted in disturbance of the buffer layer formation. Results of such surface manipulation will be presented along with optimal growth conditions for large scale growth of epitaxial graphene on SiC.

Resume : The commercial potential of 2D materials hinges on the development of growth and integration techniques that are scalable and allow an adequate level of structural control. Chemical vapor deposition (CVD) now dominates the carbon nanotube market and rapid progress is being made to develop it also for the manufacture of graphene and other 2D materials. A key challenge thereby is to increase the level of structural growth selectivity and control. With a focus on diverse applications in the electronics and display industry, we are developing integrated process rationales for these nanomaterials that are informed by a fundamental understanding of the catalytic growth process. This talk will focus on the scalable CVD of monolayer hexagonal boron nitride (h-BN) single crystals and our current understanding of the formation mechanisms of such compound 2D material on various catalyst systems [1,2]. Strategies for controlling the number of layers, stoichiometry, and crystal structure, i.e. domain size, connectivity, and orientation, will be compared to graphene CVD [3], and the potential of the direct CVD of various 2D heterostructures discussed. The talk thereby will also outline current challenges for integrated manufacturing and industrial device integration of these 2D materials. 1. Caneva et al., Nano Lett., DOI: 10.1021/acs.nanolett.5b04586 (2016). 2. Caneva et al., Nano Lett. 15, 1867 (2015). 3. Hofmann et al., J. Phys. Chem. Lett. 6, 2714 (2015).

Resume : Free-standing three-dimensional (3D) graphene structures have attracted increasing development due to their promise for a wide range of applications, ranging from bioelectronics to energy storage. The production of 3D graphene networks can be divided into two concurrent strands: formation of aerogels from liquid phase suspensions of graphene oxide, and chemical vapour deposition (CVD) of graphene on 3D metal preformed foams. The development of this second strand of graphene constructs has been limited so far by poor levels of structural control over the metal architectures and large feature size (in the micron or mm range). We have developed free-standing 3D CVD graphene monoliths with features in the sub-micron scale by additive manufacturing design of the metal scaffolds. The metal scaffolds are produced via laser melting of polymer photoresists using a Nanoscribe system, and then coated with nickel. Following removal of the photoresist and CVD graphene growth the nickel can be etched away giving the ultimate realization of a 3D graphene free-standing network. The structural resolution is controlled by the laser power, dwell time, and physical properties of the photoresists. While the walls thickness of the struts can be tuned by controlling the CVD growth conditions. The graphene 3D structures exhibit excellent electrical and mechanical properties determined by structure of the scaffold.

Resume : Graphene and doped graphene materials new synthesis routes are an attractive prospective. Especially, nitrogen doping has been an effective way to tailor the properties of graphene and make them attractive in a wide range of potential applications [1]. Recently, pulsed laser deposition of graphene has been shown to be effective in electrochemistry and biosensors applications [2] . This work reports graphene and N-doped graphene synthesis by femtosecond pulsed laser deposition. The nitrogen doping and structural changes have been studied systematically by various characterization techniques. The X-ray photoelectron spectroscopy has been performed to elucidate the C-N bonding information and N content in doped graphene. Doping of graphene decreased the 2D peak intensity compared to the pure graphene, and Raman mapping confirmed that the doping is homogeneous. The crystalline size (La) of N-doped graphene decreased with doping. The N atoms are evidenced by XPS to mainly pyridinic-N type nitrogen structure, with a N doping content up to 3 at.%. The surface morphology of films was studied by Scanning electron microscopy and Atomic force microscopy. This simple, fast and low temperature approach offers directly pyridinic-type of N bonding with high N content. This type of grown N-doped graphene could be a promising material in electrochemical sensors, electrochemical energy devices, bioelectronics and biosensors applications. References 1. Wang, H., Maiyalagan, T. & Wang, X. Review on Recent Progress in Nitrogen-Doped Graphene: Synthesis, Characterization, and Its Potential Applications. ACS Catal. 2, 781–794 (2012). 2. P. Fortgang et al. Robust electrografting on self-organized 3D graphene electrodes. ACS Appl. Mater. Interfaces (2015). doi:10.1021/acsami.5b10647

Resume : For most practical applications, metal nanoparticles (NPs) need to be supported on a substrate that can act as a deposition template for growing them in regular arrays. This prevents sintering at high temperatures, a process that would deactivate the catalytic devices. The Moire' pattern due to the small lattice mismatch between graphene and Ir(111) works as an efficient template for the ordered growth of some transition metal NPs. With the help of ab-initio calculations performed for adsorption of monomers and small clusters of Cu, Pt, and Ir, we explain the behavior of different metals, predicting results in agreement with the available experimental findings and identifying the criteria for the suitability of a metal to form ordered nanocluster arrays. Moreover, preliminary results indicate that even materials that do not form cluster superlattices can be grown through the application of cluster seeding using properly chosen metals.

Resume : Layered two-dimensional (2D) nanomaterials interact primarily via van der Waals bonding, which has created new opportunities for nanoelectronic heterostructures that are not constrained by epitaxial growth. However, it is important to acknowledge that van der Waals interactions are not limited to interplanar interactions in 2D materials. In principle, any passivated, dangling bond-free surface interacts with another via non-covalent forces. Consequently, the emerging layered 2D nanomaterials can be integrated with a diverse range of other materials, including those of different dimensionality, to form van der Waals heterostructures. This talk will explore mixed dimensional combinations of 2D + n-D (n = 0, 1 and 3) materials, thus significantly expanding the van der Waals heterostructure concept. In order to efficiently explore the vast phase space for mixed dimensional heterostructures, our laboratory employs solution-based additive assembly. In particular, constituent nanomaterials (e.g., carbon nanotubes, graphene, transition metal dichalcogenides, black phosphorus, and boron nitride) are isolated in solution, and then deposited into thin films with scalable additive manufacturing methods (e.g., inkjet, gravure, and screen printing). By achieving high levels of nanomaterial monodispersity and printing fidelity, large-area device arrays are incorporated into complex circuits and systems such as static random access memory (SRAM). Furthermore, by integrating multiple nanomaterial inks into heterostructures, unprecedented device function is realized including anti-ambipolar p-n heterojunctions and gate-tunable memristors. In addition to technological implications for nanoelectronics and optoelectronics, this work allows the exploration of several fundamental issues including band alignment, doping, trap states, and charge/energy transfer across previously unexplored mixed dimensional heterointerfaces.

Resume : Invention of graphene has stimulated research of diverse 2D materials. The most recent trend in materials science is the design of artificial 3D crystals, consisting of separate 2D layers, assembled together (vdW heterostructures - 2D HEX). The presently dominating approach for 2D HEX fabrication is assembling of separate flakes into a stack. While the highly desirable direct growth of 2D HEX can be realized via the van der Waals epitaxy through accurate growth parameters tuning and proper substrate choice. Graphene (Gr), being a dangling bonds free surface can serve as appropriate substrates for vdW epitaxy. We have studied vdW epitaxy of thin metal oxide films (ZnO, Ga2O3) on Gr/SiC. It is revealed, that despite the low growth temperature and large difference in lattice parameters, the films deposited possess advanced crystal properties (i. e. are strain-free, with no in-plane epitaxial relationship and are weakly attached to the substrate). Furthermore, an unusually high ultraviolet and visible photoluminescence was observed from the ZnO/Gr/SiC heterostructures in contrast to identical samples on conventional substrates (Si and SiC). The phenomena observed are explained with the graphene role as a dangling bond free substrate and a back reflector of a Fabry-Perot cavity which is formed at a certain thickness of the ZnO layer. We show evidence that graphene has a strong potential as a substrate for vdW epitaxy of metal oxides, leading to 2D HEX with added functionality.

Resume : One of the main advantage for applications of graphene and related 2D materials is that they can be produced on large scales by liquid phase exfoliation. The exfoliation process shall be considered as a particular fragmentation process, where the 2D character of the exfoliated objects will influence significantly fragmentation dynamics as compared to standard materials. The production of large quantities of 2D materials in solution with well-controlled morphological properties of the nanosheets (i.e. area, lateral size and shape) is not only a technological challenge but also a fundamental one, because several scientific aspects still need to be clarified for a detailed understanding of the fragmentation mechanisms and the control of the final products. Furthermore, it is necessary to develop fast and reliable protocols to measure and analyze a large number of 2D objects and well as to find a set of “robust” parameters to achieve an accurate multi-scale description of the system. Here we show how these problems can be fruitful solved by using a statistical approach. In particular, the study of the distribution of the morphological parameters such as area and shape represents the key-factor i) to understand the physical mechanisms of the fragmentation in liquid,[1] ii) to test the theoretical models and iii) to explore the mechanical and the structural properties of both the starting material and the final fragments.[2] Recently, we developed a fast and automatic procedure based on topographic images to measure, one by one, the exact shape and size of thousands of nanosheets obtained by exfoliation and fragmentation in general.[3] Previously tested on low-dimension materials such as boron nitride flakes, here we used the procedure to monitor the time evolution of the area and the shape distribution of 2D single sheets of graphene oxide (GO) in water during extended sonication treatment (i.e 100 hours). Combining the analysis of images acquired with different techniques such as Fluorescence (FM), Scanning Electron (SEM) and Atomic Scanning Probe (AFM) microscopies, we monitored the distribution of the 2D fragments in the suspension studying the morphological parameters from the millimeter to the nanometer scale. In particular, we showed that the quantitative analysis of the fragments distributions on multi-scale provides to measure the mechanical properties of the GO single sheet such as the Young’s modulus and the fracture strength. Moreover, the analysis of the fragment distributions gives detailed information on the dynamics of the 2D fragmentation providing direct evidence of different regimes given by the interplay of two breaking mechanisms, such as core fragmentation and peripheral erosion. Showing unambiguously the coexistence of different GO sheets, we describe the GO suspensions as a blend of large sheets together with small debris fragments (similar to fulvic oxides), casting a new light on the results reported in the last years on this topic.[4-6] Finally, based on the high-skewed size-distribution of the GO sheets, we propose a new approach to parametrize the polydispersity of the 2D materials. The capability to monitor and to control the morphological and the mechanical properties at nanoscale of large quantities of 2D materials in solution will pave the way towards using these materials as fillers for industrial-scale production of graphene- and 2D-based composites. References [1] D.E. Grady, Int. J. Fract., 163 (2010) 85. [2] H. Yasuyuki. Shock Wave Science and Technology Reference Library, Vol. 3. Springer Berlin Heidelberg, London | Heidelberg, 2009. [3] K. Kouroupis-Agalou et al., Nanoscale, 6 (2014) 5926. [4] J. P. Rourke et al., Angewandte Chemie-International Edition, 50 (2011) 3173. [5] H. R. Thomas et al., Chem Mater, 25 (2013) 3580. [6] I. Rodriguez-Pastor et al., Carbon, 84 (2015) 299. [7] This research was supported by Graphene Flagship (Grant Agreement No. 604391).

Resume : Graphene properties are strongly affected by the underlying substrate making the integration of graphene into commercial devices still challenging. Here, we transfer large area, single-layer CVD graphene on Si (100) and c-plane sapphire substrates followed by the growth of vertically aligned, high crystal and optical quality GaN nanorods on top of graphene using metal-organic vapor phase epitaxy (MOVPE). The contributions of doping and strain induced in graphene by substrates and MOVPE process are separated based on the 2D vs G frequency representation extracted from Mapping Raman Spectroscopy. After the transfer, graphene on sapphire exhibits a lower doping level than graphene on Si, which is attributed to less substrate-induced charge doping. This initially lower doping level enables a higher incorporation of nitrogen atoms in the graphene lattice on sapphire than on Si from the ammonia gas used during GaN epitaxy. Although more nitrogen doping should result in larger compressive strain, graphene on sapphire is less strained because of a smaller difference in the thermal expansion coefficients of graphene and sapphire as compared to silicon. The Raman results are further supported by X-ray Photoelectron Spectroscopy and electrical measurements, the latter showing a nearly ohmic contact between the highly doped graphene and GaN nanorods. Our work advances the integration of wurtzite GaN on cubic Si using graphene as a lattice matched buffer layer for optical applications.

Resume : Transition-metal chalcogenides (TMC) are widely investigated materials for perspective utilisation in nanoelectronic and optoelectronic devices, especially as 2D systems. The prototypical TMC, MoS2, in the forms of mono- and multi-layers is already well-known and its electronic properties are well-understood, with direct band gap characteristic of monolayers, giant spin-orbit coupling in non-centrosymmetric systems, or modulations of these properties using strain or external electric field. However, the plethora of 2D TMC materials is very large and many systems exhibit similarly interesting band structure signatures. Among others, we would like to present our results on MX materials (M = Ga, In; X = S, Se, Te) with honey-comb symmetry, showing e.g. the effect of quantum confinement on the electronic properties of these layered systems.

Resume : Hybrid devices based on graphene and sensitizer materials have provided a promising platform to detect light in the infrared, visible and near UV ranges; in particular, the use of colloidal semiconductor nanocrystals (NCs) has given very good results [1]. Here, photoexcited charges in the NCs are transferred to graphene, inducing a sizeable change in its resistivity. Therefore, it is possible to exploit the high absorption in the NCs and high mobility in graphene in a device with high photoconductive gain. However, the relaxation processes of photoexcited charges can be slow and limit high frequency performance of the device. We report on photodetectors based on CVD-graphene field-effect transistors and a thin film of CdS NCs, deposited onto it by spin coating. The spectral response follows the NCs absorption, with high sensitivity in near UV range, and a maximum responsivity of about 40000 A/W. Using a pulsed laser at 349 nm, we could detect ns-pulses up to 2 kHz repetition rate, thus showing that fast relaxation processes are active in parallel to slow mechanisms, and can be exploited for fast detection [2]. We discuss the charge transfer mechanisms from NCs to graphene, as well as the role of surface states and adsorbed molecules. Finally, we discuss the use of different materials to extend the operating wavelength range. [1] G. Konstantatos et al., Nat. Nanotechnol., 7 (2012) 363. [2] D. Spirito et al., J. Phys. Chem. C, 119 (2015) 23859.

Resume : I will show several recent experiments with 2D materials that have been treated for the generation of defects, synthesized in amorphous form, deformed and strained via local probes, or decorated with molecules. The first part concerns the study of these systems by high-resolution scanning transmission electron microscopy, which reveals structural modifications at the atomic level and also can be used to introduce disorder or even controlled displacements. Among other things, we have studied the transition from a crystalline to an amorphous 2D material, traced the diffusion of a vacancy in graphene, showed a controlled displacement of silicon impurities in graphene and created lateral hetero-structures of ordered and disordered twodimensional carbon. I will also show a new approach to image radiation-sensitive molecular species on graphene, based on distributing the dose over many identical structures, besides sandwiching and using low energies. In the second part, I will discuss a novel approach to study free-standing membranes by dual-probe scanning tunneling microscopy (STM), where two STM tips are brought into contact with the graphene membrane from opposing sides. At the closest point, the two tips are separated only by the thickness of the membrane. The interaction of the two probes across the membrane provides insights to both the membrane properties as well as to the fundamental interactions between the probe and the material.

Resume : The studies of the physical properties of two-dimensional materials, and speficically phosphorene, are currently among the hottest research areas in solid state physics. At the same time, while defects are present in all materials, very little is known about the presence of defects in phosphorene. Defects in other 2D materials have been studied using transmission electron microscopy (TEM), but the electron beam can also produce additional defects. Indeed, while few-layer flakes of the material has been characterized using TEM, monolayer phosphorene has proven more problematic and very little is known about its response to electron irradiation. Using first-principles atomistic simulations, we study production and dynamics of defects in single phosphorene sheets under impacts of energetic electrons, and among other characteristics, assess atom displacement energy. The knowledge of this quantity is important not only for damage minimization during TEM experiments, but also in the context of top-down engineering of phosphorus nanostructures using focused electron beam. To this end, we also consider energetics and the radiation stability of nanoribbon edges down to the limit of single-atom thin phosphorus chains.

Resume : The translation of two-dimensional (2D) nanomaterials such as graphene, hexagonal Boron-Nitride (h-BN) or Molybdenum Disulfide (MoS2) into real world applications critically hinges on seamless and industrially scalable integration of the novel 2D materials with a wide range of other established functional non-2D (nano-)materials such as metals, metal-oxides or organic semiconductors. The resulting structural, chemical and electronic interfacing effects remain however largely elusive, in particular on the atomically resolved level. This precludes rational 2D/non-2D integration process design. Here, we show how atomically-resolved scanning transmission electron microscopy (STEM), combined with bright-field and dark-field transmission electron microscopy (TEM) techniques, provides the critically required physical and mechanistic insights: We examine atomic layer deposition (ALD) of the important high-k dielectric HfO2 on chemical vapour deposited (CVD) graphene and identify HfO2 nucleation modes on graphene. We further study - as an alternative to CVD - physical vapour deposited (PVD) MoS2 layers on CVD graphene and evidence electron-beam induced MoS2 crystallisation and the possibility of epitaxial MoS2-graphene integration. Finally, we discuss the use of (S)TEM to study the competing effects of epitaxy and preferential nucleation in the growth of organic semiconductor molecule films on CVD graphene [Appl. Phys. Lett. 106, 103101 (2015)].

Resume : 2D transition metal dichalcogenides (MX2, M = transition metal e.g Nb, Mo, Ti X= chalcogen e.g S, Te, Se) are of great interest due to some of their unique properties including metal-insulator transitions and charge density waves (CDW) which are often observed as a function of temperature, pressure, and doping.[1] The structure of the charge density wave is very sensitive to crystalline defects and can be destroyed by these defects.[2] Here we report on the interaction of commensurate charge density waves (CCDW) and nearly commensurate charge density waves (NCCDW) with anionic point defects in 1T-TaSe2 and 1T-TaS2 generated by electron beam irradiation. By using atomic resolved high resolution transmission microscopy (HRTEM) we show the loss of CDW long range order as a result of the interaction with S and Se vacancies generated by the electron beam irradiation. We discuss the loss of long range order as a result of the possible interaction between the CDW and the Friedel oscillations arising from the point defects. [1] J. A. Wilson, F. J. Di Salvo, and S. Mahajan, Adv. Phys. 50, 1171 (2001). [2] H. Mutka, L. Zuppiroli, P. Molonie, and J. C. Bourgoin,“Charge-density waves and localization in electron irradiated 1T-TaS2”, Phys. Rev. B 23, pp5030-5037, 1981.

Resume : We present a comprehensive study of the effects of the defects produced by electron irradiation on the electrical and crystalline properties of graphene and MoS2 monolayers. We realized electrical devices from monolayer MoS2 or graphene crystals suspended on a 50nm SiNx membrane. The devices are exposed to electron irradiation inside a 200kV transmission electron microscope (TEM) and we perform in situ conductance measurements[1] and subsequently ex-situ raman cartography. We correlate the damage to the crystalline lattice measured by diffraction with the observed decrease in the conductivity of the devices and the variation in the Raman phonon modes. The change in the diffraction pattern is fitted to a kinematic model. The variation of the phonon modes is fitted to DFT simulations. The evolution of the conductivity with the defect concentration is explained in the percolation theory framework, using a resistance network model. [1] Towards sensitive graphene nanoribbon-nanopore devices by preventing electron beam induced damage. M. Puster, J. A. Rodriguez- Manzo, A. Balan, M. Drndic. ACS Nano,10.1021/nn405112m.

Resume : Properties of low-dimensional material highly depend on its atomic structure with defects and boundaries. Formations and evolutions of atomic defects and boundaries are of general interest for the wide range of researches. Point defects and edge structures of graphene have been intensively studied with atomic precision in the last decade. Here I present some new examples for atomic-scale imaging and spectroscopy of various low-dimensional materials with interrupted periodicities. Nitrogen defects and their chemical dynamics of graphene are now studied at individual atom basis [1]. Defects and phase transitions of single-layered dichalcogenides (MX2) are corroborated in situ [2, 3]. Also dynamic behaviours of various new 1D structures inside carbon nanotubes are investigated [4, 5, 6]. Eventually single atom magnet at graphene atomic defects will be discovered [7]. [1] Y.-C. Lin et al., Nano Letters, 15 (2015) pp.7408-7413 [2] Y.-C. Lin et al., Nature Communications, 6:6736 (2015) [3] Y.-C. Lin,et al., ACS Nano (2015) in press DOI: 10.1021/acsnano.5b04851 [4] R. Senga et al., Nature Materials 13 (2014) pp. 1050-1054 [5] L. Tizei et al., Phys. Rev. Lett., 114 (2015) 197602 [6] R. Senga and K. Suenaga, Nature Communications, (2015) 6:7943 [7] Y.-C. Lin et al., Phys. Rev. Lett., 115 (2015) 206803

Resume : Hybrids of 2D materials are expected to become building blocks of next generation nanoelectronic devices. In order to investigate the properties of graphene - MoS2 hybrids, MoS2 sheets (monolyer to few layers) were grown by chemical vapour deposition (CVD) on highly ordered pyrolytic graphite (HOPG) and MoS2 sheets were covered by CVD grown graphene. We investigated the crystallographic orientation of the nanostructures and determined the preferred relative orientation during the growth. The vertical stacking of the different 2D materials yielded moiré patterns in the atomic resolution images. Topographic artefacts arising from the complex electronic structure caused by stacking were identified in the images taken at positive and negative biases. The electronic properties of these nanohybrids were investigated using Current Imaging Tunneling Spectroscopy. Significant differences were found at MoS2 flake edges and grain boundaries; therefore these features are expected to have a very important influence on the performance of nanoelectronic devices. We have also performed STM nanolithography to cut less than 20 nm wide MoS2 ribbons.

Resume : For printed electronics graphene based-inks have several advantages over metal-based inks such as lower cost, chemical stability and flexibility of final structures. However, as a downside, the conductivity of printed graphene structures is still far from that of printed metal structures requiring extensive post-treatments to achieve a sheet resistances of at least 5 Ω□⁻¹. As a consequence, applications aiming at utilizing graphene conductors should be designed anew on account of the higher sheet resistance. Here, we present the design, fabrication and performance study of graphene screen printed radio-frequency identification devices (RFID) realized on temperature sensitive flexible substrates. We demonstrate printing of graphene RFID antennas using an earlier described highly conductive graphene ink that was prepared by the gelation of highly concentrated graphene dispersions.^[1] To achieve sheet resistance of 5 Ω□⁻¹ and lower we utilize a post-treatment of screen-printed graphene structures comprising photonic annealing and subsequent compression rolling^[2] leading to mechanically stable, flexible, and bending-fatigue resistant devices with a reading range of up to 4 m.^[3] [1] K. Arapov et al., Adv. Funct. Mater. 2015, 10.1002/adfm.201504030. [2] K. Arapov, G. Bex, R. Hendriks, E. Rubingh, R. Abbel, G. de With, H. Friedrich, 2016, submitted [3] K. Arapov, K. Jaakkola, V. Ermolov, G. Bex, E. Rubingh, S. Haque, H. Sandberg, R. Abbel, G. de With, H. Friedrich, 2016, submitted

Resume : We have developed a new biocompatible nanocomposite material composed of reduced graphene oxide (RGO) and poly acrylic acid (PAA) to achieve RGO functionalized PAA (RGOPAA). The photothermal capability of RGOPAA was demonstrated at 808 and 1064 nm near infrared (NIR) wavelength to kill HeLa cells and S. aureus. RGOPAA exhibits wide range of NIR adsorption in both first (650~950 nm) and second biological window (1000-1300 nm). The photothermal heating curves of RGOPAA showed similar temperature profiles at 808 and 1064 nm wavelength. Confocal laser scanning microscopy images revealed successful internalization of RGOPAA into HeLa cells while the MTT assay and heat shock protein expression studies revealed that the cytotoxicity of HeLa cells was mainly attributed from the heat generation of graphene upon photoirradiation. In addition, the photothermal studies were also demonstrated in the pathogenic bacteria, S. aureus, which revealed excellent killing efficiencies. RGOPAA shows a flat and extended absorption in the NIR I and II window, with superior light absorbing capability, a remarkable light to heat conversion property, excellent mechanical property and thermal conductivity, which protects it from reshaping under laser heat. Overall RGOPAA exhibits excitation wavelength independent photothermal therapy in the NIR region covering both biological windows and can be a robust and economic photothermal reagent to combat against cancer and pathogens.

Resume : In this work we perform a thermoelectric (TE) material survey of the full family of group VI TMDs (MoS2-WTe2) produced by solution processing methods. Full ZT characterisation (σ, S and κ) has been carried out in the temperature range around room temperature. Whilst recent theoretical studies show such materials may make for promising TE materials, no experimental TE studies exists for this set of materials produced by such an approach previously. In addition to its many well-known existing benefits, solution processing can be particularly beneficial for producing films of TE material as they inherently contain a high interface density; which serves to attenuate the lattice component of the thermal conductivity. Here we have applied size selection methods of the commercial TMD powders dispersed in NMP to remove the smallest flakes which are known to be more prone to oxidation in atmosphere. Films of 100 µm thickness have been formed by vacuum filtration onto PTFE membranes which are then cut into 1 cm2 pieces before being hot pressed at a pressure of 65 kN at 150 oC for 10 minutes, in order to densify the porous networks normally characteristic of solution processed films. This has the added benefit of boosting the obtainable electrical conductivity by a full two orders of magnitude in all cases, concomitantly enhancing the power factor. This work highlights the most promising of this family of solution processed layered materials for thermoelectric applications in their bulk form, in addition to informing which ones may be most suitably combined to make higher ZT nanocomposites in the future.

Resume : Graphene, like carbon nanotube networks, can be modified to produce a wide variety of properties [1]. The ability to switch charge carriers from electrons to holes suggests that graphene could be useful for thermoelectric applications. We discuss the temperature-dependent thermoelectric properties of freestanding few-layer graphene/polyvinylidene fluoride composite thin films as measured by Corey Hewitt in David Carroll’s group [2]. We also analyze the thermoelectric and conduction properties of carbon nanotube networks and composites to identify the mechanisms occurring in different types of material, and how improved properties might be attained for flexible thermoelectric fabrics [3]. We discuss modelling of how carbon nanotube networks can be prepared with negative thermopower (as measured experimentally[4]) instead of the more usual positive thermopower in order to improve thermoelectric power generation from stacks of alternating thermopowers [3]. We compare the observed electron transport properties to those of other carbon-based materials of different types and investigate the role of disorder. [1] V. Skakalova and A,B. Kaiser (ed.), Graphene: properties, preparation, characterisation and devices (Woodhead/Elsevier), pp 400 (2014). [2] C.A. Hewitt, A.B. Kaiser, S. Roth, M. Craps, R. Czerz and D.L. Carroll, Synthetic Metals 165, 56 (2013). [3] C.A. Hewitt, A.B. Kaiser, S. Roth, M. Craps., R. Czerz and D.L. Carroll, Nano Lett. 12, 1307 (2012). [4] C.A. Hewitt, A.B. Kaiser, S. Roth, M. Craps., R. Czerz and D.L. Carroll, J. Appl. Phys. 114, 083701 (2013).

Resume : Surface-enhanced Raman scattering (SERS) provides high sensitivity and selectivity on molecule detection, making it attractive for biomedical and chemical detections. Generally there are two mechanisms to influence the SERS enhancement: electromagnetic mechanism (EM) created by the metals with surface plasmon resonance (SPR) property and chemical mechanism (CM) due to the charge transfer between the molecule and the substrate. Consequently, the rational design and development of synthetic method to produce nanostructures with controllable EM and CM properties will lead to important advances on both fundamental study and innovative applications for SERS-based biomedical detections. Graphene nanoribbons (GNRs) represent a new structure of carbon nanomaterials which have exceptional physical and chemical properties, making them can be potentially used in the applications of energy, composites, biomedical and electronics. Here we report a controllable synthesis of Ag/GNR composites using a two-step reaction route. First, we synthesized and functionalized GNRs by a facile carbon nanotube chemical unzipping. The functionalization of GNRs could be tuned by controlling reaction conditions (temperature, time, and oxidant concentration), confirming by scanning electron microscopy and X-ray photoelectron spectroscopy characterizations. Ag NPs can be decorated onto the GNRs surface through a wet-chemical-based redox reaction. In our present experiment, we found that the distribution of Ag NPs can be further controlled by controlling the reaction conditions. Detailed materials characterizations including transmission electron microscopy and UV-Vis spectroscopy show that Ag/GNR composites were successfully synthesized in our experiment. We further systematic studied the Raman response of the Ag/GNR composite using Rhodamine 6G (R6G) as the Raman probe molecules. The result indicates that the Ag/GNR composite shows superior SERS performance with low detection concentration of 10^-8 M of R6G and high enhance factor (EF) of 2.1×10^8.

Resume : Graphene is a two-dimensional material that possesses many unique properties, such as, high thermal conductivity and high electrical conductivity, which make it desirable in electronic devices. Unfortunately, the lack of a bandgap in this material is an obstacle for its exploitation. There is a sustained research effort to develop methods for opening and controlling the bandgap of graphene. A promising approach results from the demonstration that a bandgap can form by applying strain. In this work, we propose a computational analysis of the effects of periodic strains (corrugations) on the properties of graphene using density functional theory (DFT) calculations. To this end, the Quantum Espresso software is adopted using generalised gradient approximation (GGA) to DFT, a plane wave basis set, and Vanderbilt ultrasoft pseudopotentials. In this work, we assume graphene to be corrugated on specific substrates due to fabrication methods found in previous works. Knowing the periodic ripples of the substrates we can construct unique unit cells to help determine required parameters for reliable results (e.g. energy cutoff and k-points). After that, calculations on strained graphene allow us to document trends in band structure and electronic properties. Moreover, we discuss the potential addition of adsorbates on the wrinkled graphene, in order to explore the effects of wrinkling on the chemical and electronic structure. The long term aim of this work is to establish the role that mechanical modifications of graphene can have in making it a flexible and effective material for application in electronic devices.

Resume : Recently, we demonstrated that graphene can provide an efficient far-field shielding against microwave radiations [1] allowing one to achieve up to 50% absorption of the incident radiation, depending on the number of graphene sheets and doping level. Here we discuss different possibilities to enhance graphene/polymer absorption ability in wide frequency range, from microwaves to THz, up to perfect, 100%, absorption. For that substrate of proper thickness and dielectric properties suppoted graphene sample, as well as an optimal incidence angle of electromagnetic radiation can be used. We demonstrate both theoretically [2] and experimentally that the increase of the grain size of the CVD graphene from 20 to 400 microns does not affect the electromagnetic interference shielding performance of graphene/polymer heterostructure. The possibilities to tune electromagnetic response of graphene/polymer sandwich by mechanical strengths and deformations are also addressed in this communication. The work was carried out within the framework of the FP7- FET Flagship 604391 Graphene, and supported by H2020 project 644076 CoExAN, IRSES-2012-318617 FAEMCAR. AP acknowledges FP7 project FP7-316633 POCAONTAS. 1. K. Batrakov et al, Scientific Reports 4, Article number: 7191 (2015) 2. Michaël Lobet et al Nanotechnology 26, 285702 (2015)

Resume : Recently graphene and graphene-based hybrid materials have attracted much attention due to unique chemical and physical properties. To develop an appropriate understanding of the properties of these hybrid materials, it is necessary to address the material preparation and the structural and defect issues as well as their influence on the performance in a wide range of applications such as photovoltaics, catalysis, optoelectronics, nanoelectronics, energy and hydrogen storage. In this work we studied the interaction of monolayer graphene and graphene nanoplatelets with Nb2O5 and TiO2, by means of X ray photoelectron (XPS) and micro-Raman spectroscopies, Rutherford backscattering spectrometry (RBS). Both oxides were deposited by RF sputtering. In particular, the structural modification and strain induced in graphene during the layer deposition processes as well as the electron properties at the interface between graphene and the metal oxide were investigated. Raman analysis revealed the occurrence of both doping and strain in oxide-decorated graphene, while XPS analysis showed graphene doping evidenced by shifts of the Fermi level correlated with the oxide amount on graphene. The effect of hydrogenation of the Nb2O5-graphene hybrid material was studied as well, by means of RBS, elastic recoil detection analysis and XPS analyses, which showed an hydrogen uptake directly linked to the graphene decoration extent.

Resume : Graphene is known to have a negative thermal expansion coefficient at cryogenic temperature. The influence of the graphene additive on alumina matrix composites fabricated by colloidal process is reported for the first time. The temperature-dependent increase in hardness is accompanied by a substantial increase in fracture toughness with decreasing temperature from 293 K to 77 K. The optimum composition of graphene is obtained at 1.0 vol% because of the effect of residual stresses, originating from the thermal expansion mismatch between graphene and alumina. The above results could contribute to further study of materials toughened by graphene at cryogenic temperature, which suggested that graphene/alumina composites can be a structural material for cryogenic application.

Resume : In bimetallic nanoparticles, composed of two different metal elements, the particle size and the structure of bimetallic nanoparticles can affect their catalytic properties including activity and selectivity of catalysts. So it is important to understand growth mechanism of bimetallic nanoparticles. The best way to prove growth mechanism of nanostructures is direct observing by in situ transmission electron microscopy (TEM). However, due to most chemical reactions occur in liquid phase, it is difficult to observe by normal method. General TEM is not suitable for observing liquid specimen due to high vacuum environment in a TEM. To overcome this problem, previous studies using several type of liquid cell with silicon nitride viewing window. However, silicon nitride layers with thick thickness and liquid surrounding the sample are main challenges for atomic-level resolution imaging. A novel graphene liquid cell that encapsulating liquid between two layers of graphene is expected that could enable atomic-level resolution observation of liquid specimens including chemical reaction or nucleation and growth due to outstanding characteristics of graphene. Graphene, a one atom thick planar sheet of carbon atoms, can provide a high contrast images in a TEM and sealing any type of material including liquid and gas phase materials because of high flexibility. In this work, in order to observe growth behavior of Au-Pd core-shell nanoparticle, we employed the graphene liquid cell electron microscopy and modified the method of graphene liquid cell fabrication suitable for water-based liquid samples. We prepared graphene liquid cell samples for TEM using few layer graphene sheets instead of monolayer graphene sheets to minimize leakage of liquid. Non-spherical Au nanoparticles were used as seeds to clearly observe change of Au-Pd core-shell nanoparticle shape and to study orientation relationship between Au core and Pd shell. Pd growth solution and Au nanoparticles were directly encapsulated between free-standing few layer graphene sheets to increase the yield of liquid cells. We confirmed water-based Pd growth solution and Au nanoparticles successfully trapped between graphene sheets and observed growth of Pd on Au seed nanoparticles with atomic-level resolution in a TEM. We also demonstrated that growth behavior of Pd shells depend on the shape of Au seed nanoparticles.

Resume : Graphene has two-dimensional (2-d) honeycomb structure. Due to the unique properties of graphene (electrical conductivity, optical transparency, thermal conductivity and echanical strength), it has diverse field of applications ranging from electronic devices, sensors, batteries, printable inks, to composite materials etc. Graphene could be produced either by top-down (chemical/mechanical exfoliation) or bottom-up (chemical vapor deposition (CVD)) approaches. Although it is possible to obtain high quality large-area, monolayer graphene with bottom-up CVD process, such process is rather costly to be used for general applications [1]. In case of top-down (chemical exfoliation) produced graphene, industrial scale production is possible, yet further reduction process is mandatory because graphene has oxidized during exfoliation process. Graphene oxide produced with chemical exfoliation could be reduced using thermal annealing, chemical reagent reduction, photo catalyst reduction, and laser scribing etc. Annealing temperature required for thermal annealing is not compatible with flexible devices, and reduction induced by chemical reaction normally involves toxic chemicals [2-3]. In the present work, we show that reduced graphene electrodes could be spontaneously fabricated by exposing stencil mask-covered GO films to Xe lamp irradiation. The process does not involve excess amount of heat; could be performed on flexible substrates including paper filters. Only with flash (order of ~ms) light annealing, C/O ratio of the system increased from ~2.14 to ~116. Electron microscopy analysis, spectroscopy (XPS, Raman analysis), electrical and electrochemical characterization of the electrodes spontaneously formed by flash annealing were performed with irradiation power dependent manner as well.

Resume : Surface plasmon polaritions (SPPs) are hybrid photon-electron waves that exist on metallic surfaces. The hybrid nature of SPPs allows control of light in nanoscale dimensions. Thus, exploiting SPPs has led to a great advancement in many areas such as subwavelength waveguides, photovoltaics, and molecular sensors. Silver is one of the most widely studied metals to create and manipulate SPPs. However, the exploitation of silver has been restricted due to the oxidation of the surfaces causing SPP losses during the propagation. Here, we address the oxidation problem of silver surfaces by coating of graphene layers on the surfaces. High-quality graphene layers are synthesized by chemical vapor deposition and then transferred on single-crystalline silver surfaces. The oxygen and water in the surroundings can be effectively blocked by the graphene layers, avoiding the deterioration of silver surfaces. The SPP propagation lengths on the bare and coated silver surfaces are measured and their variation due to the oxidation is examined. The silver surfaces covered with graphene layers exhibit strong resistance to the oxidation without significant decrease in the SPP propagation length while a conventional passivation method using SiO2 layers suffers from an increase in SPP losses. The coating of graphene layers on metal surfaces will therefore provide highly enhanced performance for plasmonic devices.

Resume : Despite the recent progress in the fabrication of field emitters based on graphene nanosheets, their morphological and electrical properties, which affect their degree of field enhancement as well as the electron tunnelling barrier height, should be controlled to allow for better field-emission properties. Here we report a method that allows the synthesis of graphene-based emitters with a high field-enhancement factor and a low work function. The method involves forming monolithic three-dimensional (3D) graphene structures by the freeze-drying of a highly concentrated graphene paste and subsequent work-function engineering by chemical doping. Graphene structures with vertically aligned edges were successfully fabricated by the freeze-drying process. Further, their number density could be controlled by varying the composition of the graphene paste. Al- and Au-doped 3D graphene emitters were fabricated by introducing the corresponding dopant solutions into the graphene sheets. The resulting field-emission characteristics of the resulting emitters are discussed. The synthesized 3D graphene emitters were highly flexible, maintaining their field-emission properties even when bent at large angles. This is attributed to the high crystallinity and emitter density and good chemical stability of the 3D graphene emitters, as well as to the strong interactions between the 3D graphene emitters and the substrate.

Resume : Graphene and carbon nanotubes (CNTs) are unique carbon materials with exceptional properties , such as ultrahigh charge carrier mobility[1, 2], gigantic thermal conductivity[3], extremely large surface area[4], exceptional mechanical strength, and flexibility[5], arising from the purely sp2 hybrid carbon structures with abundant delocalized π-electrons[6, 7]. However, pristine carbon nanomaterials, such as graphene, is a zero-band-gap material, making it difficult to be used in many applications required materials with a band gap. There are several methods to modify the properties of carbon nanomaterials, and heteroatom doping has been demonstrated as an effective method to control the band gap in carbon nanomaterials. Recent theoretical and experimental studies have suggested that heteroatom-doped carbon nanomaterials including CNTs and graphenes as novel materials with exceptional properties for applications including nanoelectronics, energy storage[8], fuel cells[9], and electrochemical sensing[10]. However, current synthesis methods of heteroatom-doped carbon nanomaterials usually involve complicated vacuum systems, making it difficult to enable industrial-scale production. Consequently, the development of a controllable synthesis of heteroatom-doped carbon nanomaterials at atmospheric pressure will lead to important advances on both scientific studies and innovation applications. Here we demonstrate an atmospheric-pressure, solution-assisted substitution method to produce heteroatom-doped carbon nanomaterials with varying heteroatoms including boron (B), sulfur (S), nitrogen (N), and phosphorus (P). The heteroatom-doped carbon nanomaterials were produced by heating the mixture of heteroatom precursor and pristine carbon nanomaterials under argon (Ar) atmosphere from 400 to 1200 oC for 1 to 4h at atmospheric pressure. We found that heteroatom concentrations in the nanotubes could be tuned by controlling the reaction temperature and time, confirming by the X-ray photoelectron spectroscopy (XPS) and Raman characterizations. Detailed XPS characterization indicated that the doping atoms were successfully doped into the sp2 graphene lattice of carbon nanomaterials. The high-resolution XPS (XPS) result reveals several C-X-O (X=B, S, N, P) doping configurations existed in our as-produced samples. The systematic Raman characterization was performed and shown the ratio of the D- and the G- bands (ID/IG) was increased for the as-produced samples, indicating the defect densities due to the doping process can be controlled in our method. Thin-film electrical conductance characterization using four-point probe method suggested the electrical conductances of the as-prepared heteroatom-doped carbon nanomaterials were significantly improved by heteroatom doping, making them useful materials for electrochemical-base applications. Our study provides a methodology to systematically study the physical and chemical properties of heteroatom-doped carbon nanomaterials. It is also noteworthy from a practical point of view that the developed atmospheric-pressure synthesis method is amenable to industrial-scale production since it avoids the need for a vacuum system. Reference [1] A. Javey, J. Guo, Q. Wang, M. Lundstrom, H. Dai, Ballistic carbon nanotube field-effect transistors, nature 424 (2003) 654-657. [2] A.K. Geim, K.S. Novoselov, The rise of graphene, Nature materials 6 (2007) 183-191. [3] S. Berber, Y.-K. Kwon, D. Tománek, Unusually high thermal conductivity of carbon nanotubes, Physical review letters 84 (2000) 4613. [4] A. Peigney, C. Laurent, E. Flahaut, R. Bacsa, A. Rousset, Specific surface area of carbon nanotubes and bundles of carbon nanotubes, Carbon 39 (2001) 507-514. [5] M.-F. Yu, O. Lourie, M.J. Dyer, K. Moloni, T.F. Kelly, R.S. Ruoff, Strength and breaking mechanism of multiwalled carbon nanotubes under tensile load, Science 287 (2000) 637-640. [6] P. Avouris, Graphene: electronic and photonic properties and devices, Nano letters 10 (2010) 4285-4294. [7] S. Gupta, K. Dharamvir, V. Jindal, Elastic moduli of single-walled carbon nanotubes and their ropes, Physical Review B 72 (2005) 165428. [8] J. Han, L.L. Zhang, S. Lee, J. Oh, K.-S. Lee, J.R. Potts, J. Ji, X. Zhao, R.S. Ruoff, S. Park, Generation of B-doped graphene nanoplatelets using a solution process and their supercapacitor applications, ACS nano 7 (2012) 19-26. [9] L. Qu, Y. Liu, J.-B. Baek, L. Dai, Nitrogen-Doped Graphene as Efficient Metal-Free Electrocatalyst for Oxygen Reduction in Fuel Cells, ACS Nano 4 (2010) 1321-1326. [10] Y. Wang, Y. Shao, D.W. Matson, J. Li, Y. Lin, Nitrogen-doped graphene and its application in electrochemical biosensing, ACS nano 4 (2010) 1790-1798.

Resume : In the fabrication of active materials for a supercapacitor, the major reduction methods of graphene oxide are thermal reduction, photo-reduction including laser reduction, and chemical reactive reduction. Among them, the photo reduction method(xenon-lamp method) has been focused on an effective reduction method since it has advantages of reducing graphene oxide (GO) within several milliseconds, consuming less energy, and being able to deoxidize GO adhered to any substrates. However, it has a limit in reduction depth of GO and surface roughness after photo-exposed. In this study, we introduced the multi-process of photo and thermal reduction to deoxidize GO with the thickness of more than 20㎛ for supercapacitor electrodes. The GO films were prepared with a doctor blade and reduced by light irradiation for a few milliseconds at room temperature under ambient condition. They are followed by heat treatment and under Ar/H2 3.5% gas condition to deoxidize the bottom of non-reduced GO by a light. The GO and rGO films were analyzed by XPS, XRD, and Raman spectroscopy to find out the chemical properties. The electrical properties of supercapacitors were measured by a 4 point probe and a cyclic voltammetry. The fabrication method combined with photo and thermal reductions is able to offer the possibility to a continuous coating by a roll to roll process.

Resume : The antibacterial activity and possible toxicity of laser-irradiated graphene oxide (iGO) were investigated. Graphene oxide was prepared by the modified Hummers methods and the iGO solutions were prepared by pulsed visible laser-irradiation of the initial GO solution in water. Antibacterial activity was tested on Escherichia coli and showed to be higher for GO irradiated at least for three hours, which seems to be correlated to the resulting morphology of laser treated GO and independent of the kind and amount of oxygen functionalities. X-ray photoelectron spectroscopy, Raman spectroscopy, dynamic light scattering and scanning electron microscopy (SEM) show a reduction of the GO flakes size after the laser irradiation, preserving a considerable content of oxygen at reasonable concentration to make the iGO solutions highly dispersible in water. This effect is essential to have a good interaction between nanomaterials and bacteria in water. SEM images of the bacteria after the exposure to the iGO flakes confirm a membrane damage after interaction with the laser-modified morphology of GO. The efficient antibacterial properties and the absence of toxicity make iGO a promising green option dedicated to water purification application.

Resume : Routes to produce large area graphene are important for application-driven device manufacture. Chemical vapour deposited (CVD) graphene is one such route, but CVD graphene growth is substrate limited and subsequent transfer techniques are required for integration with existing silicon technologies. One area that has potential importance is the use of graphene in biological or chemical sensing, either in terms of graphene-enhanced Raman spectroscopy (GERS) or surface-enhanced Raman spectroscopy (SERS); the latter when graphene is integrated with metallic nanostructures. The role of substrate preparation for these processes has not been widely studied. In our work CVD graphene is transferred using a standard wet transfer technique onto three different gold nanodisc decorated Si/SiO2 substrates: untreated, oxygen plasma treated, and h-BN coated. Raman spectroscopy as a characterisation technique provides information about purity, number of layers, stress/strain and electrical doping of the graphene. In the vicinity of the gold nanodiscs, Raman peaks are enhanced by SERS, but they can also be shifted due to increased temperature around the concentrated electric fields, and due to doping by the proximity to gold. In this presentation we study the influence of each of these effects by combination of Kelvin probe microscopy and Raman spectroscopy in areas of the samples where the disc arrays are situated and in areas of pristine transferred graphene. Laser induced changes in graphene/substrate morphology can also produce irreversible differences in doping, the implications of which will also be discussed.

Resume : Recently, graphene flakes including graphene oxides (GOs) and reduced graphene oxides (rGOs) have been paid attention mainly due to various kinds of possible applications. Here, we like to briefly introduce how to effectively prepare mass production of the materials and their possible applications such as energy storage devices including supercapacitors and Li ion batteries. For the high performance supercapacitor, to achieve both a high surface area and high pore volume of the electrodes at the same time becomes a crucial issue. We like to report new idea on how to increase the surface area of GO/rGO as well as the pore volume of the non-stacked GO/rGO 3D structure. In addition, for the fast charging and discharging, we like to present novel idea on how to fabricate highly dense and vertically aligned reduced graphene oxide (VArGO) electrodes involving simple hand-rolling and cutting processes of the rolled graphene papers. Finally, we like to also introduce new applications with hetero-atom doped rGO flakes.

Resume : Recently, graphene quantum dots (GQDs) have attracted much attention due to their advantageous properties featuring a large surface area, low cytotoxicity and good solubility. They show strong quantum confinement that induces efficient, blue/green photoluminescence (PL), which can be further tuned over the whole visible range. In the report we discuss the optical properties of GQDs synthesized by different processes. Green emitting GQDs are prepared by the oxidative cleavage of graphene oxide to introduce hydroxyl groups in the dots. For blue emitting GQDs, the precursor is subjected to redox reactions under hydrothermal or solvothermal conditions. We observe high-intensity PL emission bands that are tunable over a range of 1.8 – 3.0 eV and that in an ensemble blue-shift with increasing excitation energy. We also investigate the possible intraband transitions using ultrafast transient induced absorption (TIA) spectroscopy. The time-dependent evolution of absorption spectra provides information on inter- and intraband relaxation and recombination processes within the excited states of QDs. This is done by probing intraband transitions of free carriers generated by the pump pulse. We discuss possible implications of these findings for new applications of GQDs for photovoltaic and light emitting devices.

Resume : Graphene thin films on Diamond-like carbon (DLC) films have been obtained on Si or transparent substrates like quartz or glass by pulse laser deposition (PLD) of carbon at ambient temperature followed by either thermal annealing performed in Ultra High Vacuum condition up to 1273 K or laser treatment. The surface formation of a graphene-like film on top of the DLC, soon described in Appl. Phys. A, Materials Science & Processing, 71, 433–439 (2000), has been investigated as a function of many parameters of the PLD and post-PLD process (like fluence, DLC thickness, annealing temperature). The roughness of the films was find lower than 1 nm set over a rather large surface area, as checked by atomic-force microscopy and Raman imagery. The formation of graphene films on top of DLC have been characterized by different techniques including X-ray photoemission (XPS), Auger electron (AES) and electron-energy-loss (ELS) spectroscopies, and Raman scattering. Under optimized conditions these films can exhibit high conductivity, transmission and work function performances, so that it can achieve high figure of merit (conductivity of transparency) as transparent conductors.

Resume : We report for the first time, a novel coating method on Love wave devices, leading the highway for a new generation of acoustic components in plenty of technological applications, especially as environmental sensors. Functional oxide thin films such as Graphene Oxide (GO) layers were deposited by inkjet printing method. Devices with several (1 to 10) layers of GO, between the Inter-Digitated Transducers (IDTs) and over almost the entire top surface of the device, were studied, both experimentally and theoretically with a 3D finite element modeling tool. It was shown that enhanced properties were offered by amalgamating ultra-thin GO films with SiO2 and thus leading to optimized surface acoustic wave propagation. Indeed, SiO2 has been widely chosen in numerous works [1] and plenty of applications [2] as a guiding layer material, since it provides an appropriate surface, chemically more stable than polymer guiding layer materials. Then, the operational frequency was increased and the insertion losses were decreased whilst adding each new layer of GO on SiO2 resulting in an improved guiding layer. Furthermore, due to the exceptional properties of GO and among them the effective surface, it was recently shown [3] that, similar devices have a great potential as vapor detectors, allowing unmatched sensitivities. With such improved GO-on-SiO2 films, this method can meet the requirements of high demanding gas, liquid or biological sensing applications. In addition, inkjet-printed GO also offers an easy way of functionalization by chemically tailoring its properties, which may allow to customize conveniently generic multisensor chips for selectivity purposes. References [1]. Länge, K., Rapp, B. E., & Rapp, M. (2008). Surface acoustic wave biosensors: a review. Analytical and bioanalytical chemistry, 391(5), 1509-1519. [2]. Jakoby, B., & Vellekoop, M. J. (1997). Properties of Love waves: applications in sensors. Smart materials and structures, 6(6), 668. [3]. Nikolaou, I.; Hallil, H.; Dejous, C.; Rebiere, D.; Deligeorgis, G.; Conedera, V., "Inkjet - Printed graphene layer by layer on SAW devices for gas detection applications," in SENSORS, 2015 IEEE , vol., no., pp.1-4, 1-4 Nov. 2015, doi: 10.1109/ICSENS.2015.7370509.

Resume : A 2D carbon structure called quasi-graphite phase (QGP) has been predicted by first-principles simulations [1]. The structure is a graphene bilayer, linked by parallel rows of 3D hybridized bonds. The structure resembles a 2D package of nanotubes, with the electronic and vibrational properties intermediate between graphitic layers and nanotubes. The structure was suggested to be very resistant to the action of external loads and high temperatures. Here we demonstrate that QGP is a special implementation of a broader class of structures based on graphene stacks interlinked by chemical bonds. We report the effects of strain and temperature on atomic structures, thermal stability and mechanical properties of such systems, including QGP itself. The modeling techniques involve Molecular Dynamics simulations and first principles calculations of cohesive energies of various QGP modifications that differ in the hybridization modes of atoms linking graphene layers. All these modifications have very similar cohesive energy. The transition between the structures is relatively easy and can be achieved e.g. by appropriate elastic loading. However, both the stiffness of QGP modifications and their response to the action of high temperatures are strongly different. This opens a possibility to manipulate the mechanical behavior of QGP layers by varying their strain state. [1] M.G. Ganchenkova et al. Phys.Rev.B, 78, 195421 (2008).

Resume : The potential of graphene field effect transistors (GFETs) for high frequency (HF) electronics has been recently demonstrated by several groups using exfoliated graphene, SiC-based graphene and chemical Vapor Deposition (CVD) based graphene [1]. In parallel, graphene is being explored for large scale electronics on flexible substrates via CVD growth on metal foils associated with transfer methods. This progress is driven by the perspective to develop flexible radio frequency electronic. However, the combination of these two properties, namely high speed and flexibility, remains an open challenge. In particular for the viable development of fast and flexible electronic applications in the areas of portable/wearable communicating devices with low power consumption, this combination should be achieved with a source of material and fabrication processes adapted flexible substrate [2-5]. One of the major challenges comes from the fabrication since it is difficult to adapt conventional transistors fabrication processes to thermal limits imposed by the flexible substrates. In this work, we report the development and full characterization of GFETs on a Kapton substrate. The developed process is based on a low-temperature technology utilizing an Aluminum bottom gate with a native oxide on top. The CVD graphene is made by Graphenea, and shows hole mobility of 2500 cm2/V-1s-1 which is extracted from Hall measurement. The contact resistance of 192 ohm.µm is obtained by using pure gold contact. A large number of transistors with different gate length (Lg= 100 nm, 200 nm and 300 nm) and different gate width (W= 12 µm, 24 µm and 50 µm) has been successfully fabricated with high yield (greather than 80%) on Kapton. The DC measurement shows high current density (around 0.5 mA /um, normalized by gate width). The current is limited by the thermal conductivity of the flexible substrate. Using a thermal camera, we observe that when the substrate temperature is above 150°C, device performances begin to decrease. The dynamic characterization is performed by measuring S-parameters from Network Analyzer. The best measured characteristics (without any de-embedding) shows a current gain cut-off frequency (ft) of 39 GHz and a maximum oscillation frequency (fmax) of 13.5 GHz for transistors with 100 nm gate length and 12 µm gate width. This performance corresponds to state of the art for flexible GFETs and is maintained under strain values up to 0.5%. The outstanding results obtained in this work demonstrate that our full fabrication process exhibits great potential for graphene based flexible transistors. Keywords: Graphene, Field effect transistors, flexible, high frequency [1] Schwierz, F. Proc. IEEE 2013, 101, 1567–1584. [2] Sire, C.; et al. Nano Lett. 2012, 12, 1184–1188. [3] Petrone, N.; et al. ACS Nano 2015, 9, 8953–8959. [4] Yeh, C. H.; et al. ACS Nano 2014, 8, 7663–7670. [5] Lee, J.; et al. ACS Nano 2013, 7, 7744–7750.

Resume : Piezoelectricity is a unique material property, which enable us to convert mechanical energy into electrical one or vice versa. Two dimensional IIA/IIB-VI group oxides are expected to have great potential due to their non-centrosymmetric structure and intrinsic large band gaps. In order to investigate the piezoelectric properties of monolayer IIA/IIB-VI group oxides (MO where M= Be, Mg, Ca, Sr, Ba, Zn and Cd), density functional perturbation theory (DFPT) and Berry's Phase approximation based calculations were held. e11, piezoelectric stress and d11, piezoelectric strain coefficients were calculated. Increasing and decreasing piezoelectric trends were found for IIA and IIB group oxide structures, respectively, according to row number of the atoms. The results reveal that II-VI family oxide structures are strong candidates for future atomically thin piezoelectric applications.

Resume : Hydrogenated graphene is an interesting system for both fundamental research and applications. Indeed, the H adatom is an almost ideal resonant scattering centre for graphene electronic systems, acting as a quasi-vacancy in the honeycomb structure of the pz orbitals. As a consequence, the controlled introduction of variable densities of H adatoms in graphene could produce 2D materials with a tailored disorder and new electronic and magnetic properties. However, during the hydrogenation, chemisorbed hydrogen atoms diffuse and interact due to the relatively strong and long-range effective H-H interactions. Therefore, the atomistic configuration and the related electronic states of the resulting material can be strongly modified by the process parameters. We have theoretically studied the electronic properties of hydrogenated graphene using a statistical analysis of a large number of sequential process simulations and non-equilibrium Green Function (NEGF) calculations. The hydrogenation process of graphene is simulated by an ab-initio calibrated Monte Carlo method considering configuration dependent absorption, diffusion and desorption kinetics. Our combined KMLC-NEGF methodology predicts that H atoms reorganize in complex correlated structures and the disorder state critically depends on the process conditions. We demonstrate how conductance distribution, localization features and scaling behavior are correlated to the process parameters.

Resume : Graphene, a single atom thick material with carbon atoms arranged in a honeycomb lattice has been gathering a lot of attention due to its special electrical and mechanical properties [1, 2]. Over the years, Chemical vapor deposition (CVD) of graphene has evolved as an interesting route to produce graphene films over large areas [3, 4]. However, the transfer of large area graphene remains a challenge as it results in polymeric residues and wrinkles. While thermal annealing is routinely performed to reduce polymeric residues, there is a possibility that it can lead to strain, thereby limiting graphene's electrical properties [5]. Here, we show that treating CVD graphene with Hexamethyldisilazane (HMDS) can lead to improved electrical transport characteristics. By performing large area Raman characterization, we observe a downshift of the G and 2D peak positions after HMDS treatment. The electrical transport measurements show a shift in graphene's charge neutrality point (CNP) from a highly p-doped to an almost undoped state with the CNP located close to zero gate voltage after HMDS treatment [6]. References : [1] K.S. Novoselov et al., "A roadmap for graphene", Nature 490, 192-200 (2012). [2] K.S. Novoselov et al., "Electric field effect in atomically thin carbon films" Science 306, 666–669 (2004). [3] A. Reina et al., "Large area, few layer Graphene films on arbitrary substrates by CVD" Nano Lett. 9, 30 (2009). [4] T. Kobayashi et al., "Production of 100m long high quality graphene", Appl. Phys. Lett. 102, 023112 (2013). [5] J. E. Lee, et al., "Optical separation of mechanical strain from charge doping in graphene", Nat. Commun. 3, 1024 (2012). [6] K.Thodkar et al, CPEM 2016 submitted.

Resume : Despite recent market’s interest, direct grown of graphene onto metals is still very difficult to be obtained. However, the advent of a green and direct process of graphene formation on metallic surfaces would be a big technological step. In this work, graphene layers are directly grown on different metals like iron cast, copper and low carbon stainless steel by laser annealing using various carbon sources. The laser treatment heats the surface up to its melting point, leading the carbon atoms to diffuse in the liquid phase regime. During the resolidification step, C atoms are segregated to the surface generating a self-structured graphenic layer. Different carbon sources, deposited by spin coating (graphite particles, graphene nano-pellets and polymers) and various laser sources (pulsed excimer and CW (DPSS) lasers from UV to near IR) are compared in order to optimize the surface properties. Complementary techniques helped to characterize the graphene in the ways of structure (Raman), morphology (SEM), adhesion (scotch tape), electromagnetic properties (Rsheet, Hall effect).In situ temperature measurements are compared to LAX model simulations. The efficiency of each “laser/carbon source” combination in terms of adhesion, structure, electromagnetic and anti-corrosion properties of the generated coating layer is improved by fine matching the characteristics of laser sources (wavelength, scanning speed, overlap and energy levels) to the various metals properties.

Resume : In 21th century, heavy metal ion pollution has become a major concern to our civilization. Rapid industrialization increases different toxic heavy metals including mercury in the ground water and contaminates it. Similarly, iodide anion has also very essential role in controlling micro nutrition, neurological and thyroid gland function for human growth. Therefore, selective detection of both mercury (Hg2+ ) and iodide (I–) ion is an important area of research. Among different techniques, fluorescence detection has become very popular due to its simple instrumentation, cost-efficiency, fast and high sensitivity. In the present work, we have functionalized weak emissive GO at the epoxy sites by nucleic acid base thymine through normal SN2 mechanism ensuing a new luminescent material. We have successfully used it to detect Hg2 and I– ions in aqueous medium by fluorescence turn-off-on process. Here, the complete quenching of fluorescence intensity occurs selectively after addition of 40 µM Hg2+ solution and also regained by addition of 80 µM iodide salts in aqueous medium. This material is also very sensitive towards both mercury and iodide ions down to their nano molar concentrations. The density functional theory (DFT) calculations also help us to understand the structural stability and the nature of interactions between fluorophore T–rGO, Hg2+ and I– ions during this ‘turn-off-on’ selective fluorescence sensing.

Resume : The physical integrity of graphene during transfer and fabrication processes and the long-term stability of graphene devices are key issues that must be resolved in order to make graphene commercially applicable. Improved stability has been attained by encapsulating graphene devices with a protection layer. So far, this method has been widely reported for exfoliated hBN material [1], with limited attention to scalability. In this work, we report a novel hBN-assisted transfer method that enables a polymer-free transfer process and subsequent top encapsulation of large-area CVD-grown graphene. We demonstrate that the CVD hBN layer that is utilized in this transfer technique acts as a buffer layer between the graphene film and supporting polymer layer. We show that the resulting graphene layers possess lower doping concentration, and improved carrier mobilities compared to graphene films produced by conventional transfer methods onto untreated SiO2/Si, SAM-modified and hBN covered SiO2/Si substrates. Moreover, we show that the top hBN layer used in the transfer process acts as an effective top encapsulation resulting in improved stability to ambient exposure. The transfer method is applicable to other CVD-grown 2D materials grown on copper foils, thereby facilitating the preparation of van der Waals heterostructures with controlled doping. [1] L. Wang et al., Science 2013, 342, 614.

Resume : Differential reflection (DR) spectroscopy is a powerful tool to probe energy relaxation of photoexcited carriers and has been applied extensively to investigate the ultrafast dynamics of charge carriers in graphene. Particular interest has been recently devoted to the studies with probe photon energies close to the Fermi energy of graphene, where the sign of the DR signal can be inverted [1]. This effect allows non-invasive determination of the Fermi energy with high accuracy and can be exploited for the development of the novel high speed optoelectronic devices. In this work, we use optical nondegenerate pump-probe measurement to provide an insight into the effects of substrate interactions and doping on the graphene carrier dynamics in the vicinity of the Fermi level. The CVD graphene was transferred on different substrates, namely quartz and Si/SiO2 with varying oxide thickness (native oxide, 90nm and 300 nm). To increase the doping level, the samples were treated using thermal annealing in vacuum and oxygen plasma treatment. The change in the sign of the DR signal is explained in terms of interference effects analysed by transfer-matrix method. [1] Shi, S.-F. et al. Nano Lett. 2014, 14, 1578–1582.

Resume : Graphene has attracted significant interest due to its extraordinary properties and tailoring these properties of graphene is important for next generation electronic, optical, and mechanical applications. Both chemical and physical techniques have been studied for such modification. The physical techniques include confinement of size and varying number of graphene layers. Such physical techniques need highly sophisticated instruments but their reproducibility is poor. Among chemical techniques, surface functionalization is one of the promising method for modifying graphene properties. However, chemical method has inherent limitation in temporospatial distribution of dopant. Atomic force microscope and scanning tunneling microscope are utilized for the control of adatoms locally on the graphene surface. However, in these methods the modifications are restricted to nanoscale level. In this study, we report the synthesis of clean and good quality single layer graphene oxide (SLGO) by thermal oxidization of single layer graphene (SLG). Then, we controlled the coverage of oxygen adatoms in SLGO using physical method via electromigration technique. Raman mapping was utilized to differentiate the graphene and graphene oxide loci in SLGO samples. Finally we demonstrate the implication of adatom migration on the properties of graphene.

Resume : The properties of carbon nano-structured materials, carbon nanotubes (CNTs), thermo-extended graphite (TEG), can be efficiently functionalized by addition of non-carbon components. The N(B)-doped carbon nanotubes (CNTs) are intensively studied at present as components of carbon/oxide composites for various practical applications. Efficient functionalization is possible if peculiarities of chemical bonding between the carbon and oxide components are well understood. Computational modeling of molecular adsorption on the CNT surface is the most suitable research method which can provide this understanding. Molecular oxyanions XO42- (X = Cr, Mo, W) are constituents of a large variety of oxide inorganic compounds which are widely used now as luminescent materials. In the work we consider adsorption of XO42- molecular oxyanions on the surfaces of un-doped and N(B, Al)-doped CNTs and graphene. The DFT-based geometry-optimized calculations of the electronic structure of CNTs with adsorbed oxyanions were carried out by Gaussian 03 program package [1]. Relaxed geometries, binding energies between oxy-anions and adsorbents, energy barriers for desorption, electronic wave-function contours were calculated. Obtained results were analyzed together with experimental data on the luminescence of carbon (MCNT, TEG)/oxide composites. [1] M.J. Frisch, G.W. Trucks, H.B. Schlegel, et al. // Gaussian 03 (Gaussian, Inc., Wallingford, CT, 2003).

Resume : Single-wall carbon nanotubes are known for their exceptional properties, which are expected to give rise to innovative applications. However, SWNTs are produced as a poly-disperse mixture of nanotubes with different lengths, diameters and chiralities. The nanotube population depends on the synthesis parameters and always contains both metallic and semiconducting chiralities. It is highly desirable to be able to selectively extract the nanotubes with the targeted properties. We report an effective polymer-assisted technique for the high-selectivity separation of semiconducting SWNTs with their fundamental optical transition centred at 1550 nm. For applications, the concentration and alignment of the nanotubes are also of great importance. We used a modified evaporative self-assembly approach that can deposit concentrated SWNT with configurations varying from random to highly-oriented networks. We characterize the samples with optical and electrical measurements. The absence of residual metallic single walled carbon nanotubes is proved by absorption measurement and resonant Raman spectroscopy and is confirmed by electrical measurements on nanotube transistors. Asymmetric (Pd and Sc) contacts and local gates are also implemented. We elaborate configurations enabling photo-detection and electroluminescence, which pave the way to exploit s-SWNTs for optoelectronic at telecom wavelengths ranges. This work was funded by the European Union through the FP7 Project CARTOON (Contract FP7 -618025).

Resume : Thermoelectric phenomena of novel nanomaterials are currently of a great interest due to a possibility of conversion of thermal energy into electric one at nanoscale. Recently, ultra-thin graphene nanoribbons (GNRs) have been obtained by chemical synthesis [1]. However, these nanostructures appear to be wide-gap semiconductors, which prevents them from being good thermoelectric materials. We demonstrate that this problem may be overcome by structure modification. Calculations show, that the gap can be considerably narrowed. in presence of substitution atoms (N,Al) or by functionalization with chemical groups containing nitrogen and oxygen. Electronic, magnetic and transport properties of modified nanoribbons have been investigated using theoretical methods based on ab-initio calculations and non-equilibrium Green function formalism. Conventional and spin thermoelectric phenomena have been determined for a variety of functionalized or doped nanoribbons. Numerical calculations performed in a wide region of temperatures for GNRs of different atomic structure show that conventional Sc and spin Ss, Seebeck coefficients, and especially the spin efficiency described ZTs, can achieve high values even at room temperatures. Interestingly, the maximum of ZTs only weakly depends on temperature, which makes the system interesting for applications in spintronic devices. [1] J. Cai at. al., Nature vol. 466, 470-474 (2010).

Resume : Radioactive environments generate microstructural changes and mechanical properties deterioration in the materials that constitute nuclear reactors. In addition, the presence of trapped helium degrades the behavior of the materials and promotes the embrittlement of these [1]. Therefore, finding a material capable of minimizing the radiation damage is very desirable. Graphene has become one of the most important materials in the field of nanoscience due to its many applications. The reduced thickness, the high mechanical strength and the impermeability for He of this material [2], in addition to its mechanical, thermal and chemical stability, make graphene a potential candidate for the shielding of nuclear reactors against radiation prolonging its shelf life [3]. The present work focuses on the adsorption of helium on graphene. To study the saturation and diffusion of helium on graphene, we have employed density functional theory (DFT). The calculations have been performed with the Quantum Espresso code. In order to study the saturation of He as close as possible to reality, we have added helium atoms successively over the graphene sheet varying their positions, and relaxing the system, with the objective of finding out the atom arrangement with the minimum energy [4]. Moreover, the most favorable diffusion paths of He on graphene have been studied. An electronic structure analysis has been carry out to explain and understand more in detail the results obtained. The conclusions of this work may allow us to consider the possibility of graphene acting as a nanomembrane, for the storage and retention of He, which can be of importance in complex nuclear fusion systems as ITER (International Thermonuclear Experimental Reactor). References [1] Trinkaus H., Singh B.N., 2003 Helium accumulation in metals during irradiation – where do we stand? J. Nucl. Mater., 323, 229–242 (2003). [2] Leenaerts O., Partoens B., Peeters F.M., Graphene: A perfect nanoballoon, Appl. Phys. Lett., 93, 193107 (2008). [3] Topsakal M., Şahin H., S. Ciraci, Graphene coatings: An efficient protection from oxidation, Phys. Rev. B, 85, 155445 (2012). [4] Buldum A., Tetiker G., First-principles study of graphene-lithium structures for battery applications, J. Appl. Phys., 113, 154312 (2013).

Resume : Graphene, a single carbon atom thickness 2D material, has been intensively studied because of its incredible and interesting physical, chemical, and electrical properties. One of the applications of graphene is integration with semiconductor materials to overcome physical and chemical limitation of current semiconductor technology. Lots of research about graphene-semiconductor hybrid systems have been developed. Combining with Si material, for examples, new type of graphene transistor, barristor, was invented.[1] In this presentation, we introduce growth of low dimensional Ge @graphene nanostructures.[2, 3] The Ge, one of the representative semiconductor materials in group IV, is fascinated due to the high electrical conductivity with high carrier mobility. However, it is well known that reliability of Ge is poor due to the unstable oxide layer. In order to resolve it, we synthesized Ge@G nanostructures using conventional CVD process and we confirmed that reliability enhancement of it compared with pure Ge nanostructures. This growth approach serves an important point for future semiconductor-graphene hybrid for nanoelectronic devices applications REFERENCES: [1] Yang et al., “Graphene Barristor, a Triode Device with a Gate-Controlled Schottky Barrier ”, Science, Vol. 336, pp 1140-1143, 2012. [2] Lee et al., “Reliability Enhancement of Germanium Nanowires Using Graphene as a Protective Layer: Aspect of Thermal Stability”, ACS AMI, Vol. 6, pp 5069-5074, 2014. [3] Lee et al., “Wafer-scale growth of single-crystal Monolayer Graphene on Reusable Hydrogen- terminated Germanium”, Science, Vol. 344, pp 286-289, 2014.

Resume : Availability of clean and fresh water is becoming a serious challenge. Rapid industrialization, booming global populations and global warming have led to huge stress on ever depleting sources of fresh water. Heavy metal ions like mercury, arsenic, lead, chromium and cadmium; organic matter and high salt concentration are the major contaminants which make water unfit for human utilization. Moreover, high cost and energy inputs render most desalination and waste water treatment processes non-attractive for potable water supply. However, with advancements in carbon nanotechnology the scenario is changing rapidly. Graphene oxide (GO) has an intrinsic hydrophilic nature due to the presence of oxygen containing functional groups in its basal plane. This makes GO a very good absorbent of metal ions and organic matter from water. Further, the wide inter-planar distance between stacked GO layers and the micro-pores in GO act as capillary channels which allow only water molecules to pass through thus desalinating water. Chemical functionalization of GO further improves its absorbance towards selective contaminants. However, independent use of GO as a filter or membrane is not commercially feasible, moreover, GO being partially water soluble keeps on passing into the purified water. Thus, water-soluble GO can be coated on sand to create core-shell granules that find use in filtration columns readily. High temperature heat treatment of these composite granules above 700 °C in inert atmosphere strongly bonds graphitic layers to the silica rich surface. This work focusses on a gravity driven multi-action GO-Sand composite based water filter which can directly provide purified and desalinated potable water without the use of electricity. Firstly, graphitic layers were grown on poly-dispersed sand granules by de-caramelization of cane sugar (a popular di-saccharide) and subsequent heat treatment at 750 °C in Ar atmosphere. Following which these graphene coated granules were activated by sulphuric acid and partially oxidized by nitric acid treatments to obtain GO coated sand granules. Upon segregation, different sizes of granules were used for different layers of the filter. The filter is divided into eight layers having complementary action. First layer is for initial desalination and comprises of non-functionalized coarse GO coated granules. Second to sixth layers are for chromium (IV), cadmium, mercury, lead and arsenic ion removal respectively which contain chemically functionalized or hybrid granules specific to respective ions. Seventh layer is a silver nanoparticle decorated granule layer for disinfection and anti-bacterial action. Lastly, the eighth layer contains very fine granules (~ 100 μm) for removing very finely dispersed organic matter and for final desalination. In the second layer 2, 6 diamino pyridine functionalization was done for Cr(VI) removal from acidic water solution. The extra pyridinic nitrogen lone pair is responsible for this decontamination. Third and fourth layers are thiol functionalized using diazonium chemistry for mercury and cadmium removal. Zero-valent iron nanoparticles are decorated on GO in fifth layer for lead elimination. Lastly, arsenic removal is facilitated by ferric hydroxide cross links developed in the GO layers using hydrogen peroxide. Initial results have shown desalination up to 40% using only the top layer.

Resume : We investigate tunneling across non doped twisted bilayer graphene. Femi line in twisted bilayer graphene at zero-energy is transformed into two separated points positioned along the transverse direction of the reciprocal space. We show that this change in the topology of low-energy band-structure affects drastically the zero-energy transmission resonances. We report the appearance for a magic twist parameter of a new kind of transmission resonances: Fabry-Pérot like resonance in addition to the Klein-like resonances characterizing the perfectly Bernal stacked bilayer graphene at zero-energy. This unusual transmission resonance shows a strong dependence on the orientation of the reservoirs interfaces and the twisted bilayer strip.

Resume : Two graphene layers generally stack over the common AB or Bernal stacking configuration. Recently, it has been reported that rotationnal stacking defects can occur in natural and synthetic graphene bilayer systems. Here we theoretically investigate how a rotational mismatch between the two layers of a bilayer graphene could affect the quantum transport. Starting from the four-band low-energy Hamiltonian, we report a calculation of the conductivity and the Fano factor F in twisted bilayer graphene within the Landauer-Buttiker approach. Then we discuss the effect of the stacking default and the orientation of the electrodes on the pseudo-diffusive regime (F =1/3) around the Dirac point. We found that the range of energies which this pseudo-diffusive regime holds can be suppressed for a specific stacking default. We show that the pseudo-diffusive transport is related to the interference between the electron and hole states.

Resume : Graphene and graphene based materials have attracted a lot of interest due to their unique properties such as large surface area, high adsorption capacity and excellent electron transfer rate, which make them an excellent aspirants for environmental pollutant remediation application. Recently, graphene oxide (GO) has investigated extensively as it comprise of various functional groups, making it highly hydrophilic and water soluble, which makes it applicable for supporting metal oxides particles. The incorporation of metal oxides on GO has become a proficient way to prepare the environment friendly composite, where the metal oxide improves its properties by utilizing the advantage of graphene. In this work, binary/ternary metal oxide (TiO2/Fe3O4) based composite of GO are synthesized for removal of toxic methylene blue (MB) and As(III) from wastewater. The nanocomposites consist the properties of each constituent like, TiO2 nanoparticles degrades the pollutant, rGO provides the pathway to increase the surface area as well as suppress the recombination of charge carriers in TiO2, and Fe3O4, being a magnetic material, increases the adsorption capabilities of rGO towards the heavy metal impurities and also helps in magnetic separation. A systematic study has been done to investigate the photocatalytic activity under visible and UV light irradiation for MB and adsorption of As(III) metal ions by analyzing their adsorption isotherm and adsorption kinetics models, respectively.

Resume : Traditionally, the detecting dynamic range of a CMOS image sensor could not be wide. Under weak light, the photocurrent output from the Si photodiode (PD) in a pixel is too small and large transimpedance amplification of the signal is necessary. But under strong light, the amplified signal output can be saturated very easily. So, typical CMOS image sensors have poor performance under both weak and strong light conditions. This drawback in dynamic range can be avoided by directly sensing the photovoltage rather than the photocurrent of the PD. Similar to human eyes, the photovoltage bears a natural logarithmic function of light intensity. Thus, the detecting dynamic range can be very wide. It has been shown in literature [1] that, due to the unique energy band structure of graphene, a PD composed of Si and graphene is quite sensitive to weak light when the photovoltage sensing mode is used. The photovoltage responsivity of the Si/graphene PD is as high as 20 MV/W at 10 nW incident light power. Therefore, this PD has good potential in image sensor application, especially for detecting images in dark environment, if it can be integrated into the CMOS technologies. For this purpose, the present work attempts to directly combine a poly-Si/graphene PD and the sensing MOSFET of a pixel to form a single, integrated device which can be called as PD-Oxide-Semiconductor FET (PDOSFET). This integration can make the photovoltage sensing very efficient. The key feature of the new PDOSFET is that a single-layer graphene has been inserted between the gate oxide and the gate poly-Si of a MOSFET. The poly-Si not only is the gate terminal material but also serves as part of the poly-Si/graphene PD on top of the gate oxide. Under illumination, the poly-Si absorbs light energy and generates electron-hole pairs. One type of carriers accumulate in the graphene and a photovoltage is set up across the poly-Si/graphene junction. The channel current of the FET is modulated by the potential of graphene. The FET can be connected as a source follower to directly transmit the photovoltage signal. Experimental PDOSFET samples have been designed, fabricated, and tested. When the light intensity was 49000 lux, the voltage shift on graphene was measured to be 0.8 V. And measurements further showed that the photovoltage does vary logarithmically with light intensity, which facilitates wide detecting dynamic range. The successful demonstration of PDOSFET opens the door of image sensor application for graphene. [1] An, X., Liu, F., Jung, Y. J., & Kar, S. "Tunable graphene–silicon heterojunctions for ultrasensitive photodetection." Nano Letters 13.3 (2013): 909-916.

Resume : In traditional semiconductors, grain boundaries (GBs) are scattering sites for majority carriers and degrade transport via the formation of large electrostatic barriers. Such effects are amplified by the reduced charge screening in low dimensional materials. Two-dimensional transition metal dichalcogenides (TMDs) including MoS2 are one class of low-dimensional semiconductors that show promise for high-performance electrical and electro-optical applications as well as emerging soft electronics. Large-area monolayer TMDs grown via chemical vapor deposition inevitably possess grain boundaries between randomly oriented grains. However, the electrical transport characteristics of TMD GBs are still under debate, suffering from the large device-to-device mobility variation and poor single-domain carrier mobility, and most importantly, lacking of correlation between the transport property and GB atomic structure. Here, we overcome these difficulties by directly correlating 4-probe transport measurements across single GBs with both high-resolution transmission electron microscopy (TEM) imaging of the measured devices and first-principles calculations. Utilizing an inert-environment fabrication procedure, we observed a unique ? (misorientation angle)-dependent field effect mobility, and unexpectedly, larger ? leads to a higher mobility. The precise boundary locations, orientations, and atomic structures were assessed by TEM. Using the density functional calculations for the ?-dependent band structures, the calculated electrostatic barriers were correlated with experimentally determined barriers so as to provide a clear understanding of the underlying transport dependences of the GBs.

Resume : Chemical Vapor Deposition (CVD) and Rapid Thermal Annealing (RTA) are used to grow graphene and amorphous carbon on pre-patterned Ni electrodes as passivation layers. Chemical and composition analysis confirm that the carbon film strongly reduces the surface oxidation of the Ni. For testing charge injection into a p-type polymer semiconductor, electrical performances measured in three-terminal devices integrating such electrodes as source and drain provide insight into the quality of the interface between ferromagnetic contact and organic semiconductor. RTA-processed electrodes exhibit the lowest interface resistance for hole injection into organic transistor devices, on par with benchmark gold electrodes1. These results indicate that our approach presents an attractive strategy for the fabrication of solution-processed organic devices of potential applicability for spintronics2. 1 D., Braga, et al., Appl. Phys. Lett. 2010, 97, 193311. 2 T. Verduci, C.-S. Yang, L. Bernard, G. Lee, S. Boukari, E. Orgiu, P. Samorì, J.-O Lee, B. Doudin, Adv. Mater. Interfaces, Accepted.

Resume : Graphene nanoribbons (GNRs) with zigzag edge orientation have a magnetic insulating ground state with antiparallel spin orientation between the two edges [1]. However, external conditions like doping and temperature can significantly modify their electronic and magnetic properties. In this work we have performed electronic structure and magnetic ordering calculations on GNRs by applying the mean-field theory for an extended Hubbard Hamiltonian including the effect of temperature and finite doping. Within the framework of this approximation we have investigated the influence of the temperature, carrier density as well as the width and edge orientation of GNRs on their electronic and magnetic properties. We found that ribbons with zigzag edge orientation possess spin polarized edge states with both antiferromagnetic (AF) and ferromagnetic (FM) coupling between opposite edges. The calculations also reveal a strong correlation between the electronic and magnetic properties of zigzag GNRs, AF ribbons displaying semiconducting, while FM ribbons showing metallic behavior in excellent agreement with our experimental findings [2]. Our calculations further reveal that the sharp metal – semiconductor transition does not only happen as a function of ribbon width but also through varying the charge carrier concentration. This finding can be exploited for a novel magnetically mediated switching mechanism in GNR based field-effect transistors. 1. Y.-W. Son, et al., Phys. Rev. Lett. 97, 216803 (2006). 2. G. Zs. Magda, et al., Nature 514, 608-611 (2014).

Resume : Graphene nanoribbons are prone to in-plane bending even when supported on flat substrates. However, the amount of bending that ribbons can stably withstand remains poorly known. Here, by using molecular dynamics simulations, we study the stability limits of 0.5-1.5 nm wide armchair graphene nanoribbons subject to pure bending. We observe that buckling instability limits maximum curvatures below ~10 deg/nm, which roughly coincides the limit for maximum curvature sustainable by the substrate interactions alone. Both of these stability limits lower when ribbons widen. The results agree with recent experiments and are understood via transparent elasticity models.

Resume : In this presentation, electro-mechanical and optical properties of suspended graphene structure will be introduced. Micro contact transfer method is applied to realize the suspended grapheme structures. Basic mechanical resonance behaviors were studied by optical interferometry method. Xylophone like suspended graphene ribbon structure was prepared for studying length dependence of mechanical properties. Various mechanical behaviors, such as frequency tuning, non-linearity of graphene structure will be discussed in this presentation. The potential application of the graphene xylophone structure for RF component will be suggested. Our recent result on visible light emission from the suspended graphene ribbon structures will be presented. The mechanical properties before and after light emission of graphene were studied by comparing their resonance behaviors.

Resume : Graphene is increasingly explored as a platform for developing novel separation technologies. This interest has arisen because it is a maximally thin membrane that, once perforated with atomic accuracy, may allow ultrafast and highly selective sieving of gases, liquids, dissolved ions and other species of interest. However, a perfect graphene monolayer is impermeable to all atoms and molecules under ambient conditions. The same behavior might reasonably be expected in the case of other atomically thin crystals. Here we report transport and mass spectroscopy measurements which establish that monolayers of graphene and hexagonal boron nitride (hBN) are highly permeable to thermal protons under ambient conditions, whereas no proton transport is detected for thicker crystals such as monolayer molybdenum disulphide, bilayer graphene or multilayer hBN [1]. Further, we show that monolayers of graphene and boron nitride can be used to separate hydrogen ion isotopes. Deuterons permeate through these crystals much slower than protons, resulting in a separation factor of 10 at room temperature [2]. The observed results show that one-atom thick crystals are subatomic selective membranes, turning them into promising candidates for use in many hydrogen-based and isotope separation technologies. References: [1] S. Hu, et al. Proton Transport through One-Atom Thick-Crystals. Nature 516, 227–230 (2014). [2] M. Lozada-Hidalgo, et al. Sieving Hydrogen Isotopes through Two Dimensional Crystals. Science 351, 6268 (2016).

Resume : Graphene's two dimensional nature, highly sensitive unique electrical properties and low intrinsic noise characteristics make it a prime candidate for the creation of a new generation of molecular sensors. The long standing target of molecular sensing is to develop sensors with single molecule sensitivity and capability of selective determination of the detected molecules. Although graphene sensors have been demonstrated to be extremely sensitive, their selectivity remains a major problem for their practical use. Here we demonstrate that graphene field-effect transistors (GFETs) are able to measure distinct, coverage dependent, conductance signatures upon adsorption of small organic molecules in vacuum. This method allows for electronic discrimination of individual DNA nucleobases on GFETs, providing a first step towards graphene based electronic DNA sequencing. The existence of molecule specific signatures in electronic transport measurements was verified by independent synchrotron-based X-ray photoelectron spectroscopy (XPS) measurements. To get a deeper insight into the origin of the sensing mechanism and molecular recognition in GFET measurements we performed ab initio electronic structure calculations using density functional theory (DFT). The molecular recognition was found to be closely linked with specific noncovalent molecular interactions with graphene. The absorption of molecules resulted in the electronic structure change of graphene which is driven by complex interplay between molecule-graphene and intermolecular interactions, interface dipole moment, charge transfer, work function change and screening effects. These effects open up a range of new opportunities for molecular recognition in electronic sensor devices.

Resume : Graphene has potential for the realization of novel devices, such as printable antennas, touch screens and electrodes in (opto)electronic or storage devices [1-3]. However the current graphene production routes (sonication and high shear-mixer) give low concentrations of few layer graphene (<0.2 mg/ml) [4] and require time consuming centrifugation to remove the non-exfoliated particles [4]. Here we exfoliate graphite in aqueous surfactant solutions (sodium deoxycholate) using a microfluidic processor at a shear rate of 8.6x10^7 s^-1. Using a flow rate of 120 ml/min we get 1 mg/ml single/few layers graphene (20% of single layer) with a production rate of 65 mg/h. This rate, for the same energy input (100 MJ/m^3), starting graphite concentration (50 mg/ml) and volume (~200 ml) is 50% higher than reported values for a high-shear mixer [4] and 1500% times higher than sonication [4]. Unlike sonication or shear mixer, in microfluidization all the material is uniformly exposed to intensive shear, thus the centrifugation step can be avoided and graphene nanoplatelets (GNPs) (mean thickness of 12 nm) can be produced (concentration of 80 mg/ml at a rate of 7.2 g/h). We use these to formulate conductive inks by adjusting the rheology for blade coating or screen printing (viscosity of hundreds of mPas). We employ sodium carboxymethylcellulose (CMC) as a binder and as rheology modifier, reducing the viscosity from 600 mPas at 100 s^-1 to 160 mPas at 1000 s^-1 (thixotropic behaviour) thus making the ink easier to coat or print.The sheet resistance of the films prepared by blade coating is down to 2.2 Ohm/sq for 25 μm thickness, which enables the printed patterns to act as a metal at microwave frequencies. This allows us to fabricate flexible passive radio-frequency identification (RFID) antennas with a read range of 145 cm (865-868 MHz) which is comparable with printed copper or silver RFID tags [5], but more stable than copper, which is prone to oxidation [6], and cheaper than silver [6]. [1] A. C. Ferrari et al. Nanoscale 7, 4598 (2015) [2] F. Bonaccorso et. al. Nature Phot. 4, 611 (2010) [3] F. Bonaccorso, et. al. Science 347, 1246501 (2015) [4] K. R. Paton et al. Nature Materials 13, 624 (2014) [5] K. Koski et al. Int J Adv Manuf Technol 62, 167 (2012) [6] S. Magdassi et al. Materials 3, 4626 (2010)

Resume : Single-wall carbon nanotubes are known for their exceptional properties, which are expected to give rise to innovative applications. However, SWNTs are produced as a poly-disperse mixture of nanotubes with different lengths, diameters and chiralities. The nanotube population depends on the synthesis parameters and always contains both metallic and semiconducting chiralities. It is highly desirable to be able to selectively extract the nanotubes with the targeted properties. We report an effective polymer-assisted technique for the high-selectivity separation of semiconducting SWNTs with their fundamental optical transition centred at 1550 nm. For applications, the concentration and alignment of the nanotubes are also of great importance. We used a modified evaporative self-assembly approach that can deposit concentrated SWNT with configurations varying from random to highly-oriented networks. We characterize the samples with optical and electrical measurements. The absence of residual metallic single walled carbon nanotubes is proved by absorption measurement and resonant Raman spectroscopy and is confirmed by electrical measurements on nanotube transistors. Asymmetric (Pd and Sc) contacts and local gates are also implemented. We elaborate configurations enabling photo-detection and electroluminescence, which pave the way to exploit s-SWNTs for optoelectronic at telecom wavelengths ranges. This work was funded by the European Union through the FP7 Project CARTOON (Contract FP7 -618025).

Resume : The high catalytic activity of metallic MoS2 edges for the hydrogen evolution reaction (HER) has led to substantial effort in increasing the edge concentration of catalyst materials. The 2H basal plane is less active for HER because it is less conducting and therefore possessing less efficient charge transfer kinetics. We developed novel electrochemical microcells that allow us to measure the activity of individual nanosheets having their edges being alternatively exposed or covered. Thanks to this unique set-up, the catalytic activity of metallic 1T and semiconducting 2H phase MoS2 nanosheets can be directly investigated. We found that catalytic properties of MoS2 are primarily governed by the electrical coupling between the nanosheets and the substrate. The catalytic activity of the basal plane of 2H MoS2, which has been thought to be poorly active, can approach the activity of the metallic edges by engineering the contact resistance of the 2H phase of MoS2 basal plane with overpotential and Tafel slopes values of ~ -0.1 V and 50 mV/dec respectively. Our results provide new insights into the role of contact resistance and charge transport for improving the performance of 2D MoS2 nanosheet catalysts for hydrogen evolution.