High quality graphene synthesized by atmospheric pressure CVD on copper foil

Graphene was synthesized at 1000°C by Atmospheric Pressure Chemical Vapor Deposition on copper foil from methane diluted in argon and hydrogen. The influence of the main synthesis parameters was studied on 2x2 cm2 foils in order to obtain continuous monolayer graphene without crystalline defect. The uniformity, crystal quality and number of layers of graphene were analyzed by Raman spectroscopy and Scanning Electronic Microscopy. First, an increase of the annealing pre-treatment duration induced an increase of the average size of copper grains, leading to larger graphene flakes of higher crystallinity presenting a lower number of layers. Similar evolutions of graphene characteristics were observed when decreasing the methane concentration to 20 ppm, whereas an increase of run duration led to a loss of graphene quality and to a higher number of graphene layers, confirming that graphene formation is not self-limiting on copper. An optimum hydrogen/methane ratio was found, quite different from other results of the literature, probably due to differences in the copper pre-treatment step. Finally, an optimized three steps process was developed to form monolayer continuous graphene of high quality, successfully transposed to 7x7 cm2 substrates after a reactor scale-up

Nano-Architecture of nitrogen-doped graphene films synthesized from a solid CN source

New synthesis routes to tailor graphene properties by controlling the concentration and chemical configuration of dopants show great promise. Herein we report the direct reproducible synthesis of 2-3% nitrogen-doped ‘few-layer’ graphene from a solid state nitrogen carbide a-C:N source synthesized by femtosecond pulsed laser ablation. Analytical investigations, including synchrotron facilities, made it possible to identify the configuration and chemistry of the nitrogen-doped graphene films. Auger mapping successfully quantified the 2D distribution of the number of graphene layers over the surface, and hence offers a new original way to probe the architecture of graphene sheets. The films mainly consist in a Bernal ABA stacking three-layer architecture, with a layer number distribution ranging from 2 to 6. Nitrogen doping affects the charge carrier distribution but has no significant effects on the number of lattice defects or disorders, compared to undoped graphene synthetized in similar conditions. Pyridinic, quaternary and pyrrolic nitrogen are the dominant chemical configurations, pyridinic N being preponderant at the scale of the film architecture. This work opens highly promising perspectives for the development of self-organized nitrogen-doped graphene materials, as synthetized from solid carbon nitride, with various functionalities, and for the characterization of 2D materials using a significant new methodology

Synthesis of Large Area Graphene by Solid Carbon Source

International audienc

Large scale catalytic growth of grapheme on nickel for transparent conductive electrodes

International audienc

Synthesis of Large Area Graphene by Solid Carbon Source

International audienc

Nanomechanical mapping of graphene layers and interfaces in suspended graphene nanostructures grown via carbon diffusion

Graphene’s remarkable mechanical, electronic and thermal properties are strongly determined by both the mechanism of its growth and its interaction with the underlying substrate. Evidently, in order to explore the fundamentals of these mechanisms, efficient nanoscale methods are needed that enable observation of features hidden underneath the immediate surface. In this paper we use nanomechanical mapping via ultrasonic force microscopy that employs MHz frequency range ultrasonic vibrations and allows the observation of surface composition and subsurface interfaces with nanoscale resolution, to elucidate the morphology of few layer graphene (FLG) films produced via a recently reported method of carbon diffusion growth (CDG) on platinum-metal based substrate. CDG is known to result in FLG suspended over large areas, which could be of high importance for graphene transfer and applications where a standalone graphene film is required. This study directly reveals the detailed mechanism of CDG three-dimensional growth and FLG film detachment, directly linking the level of graphene decoupling with variations of the substrate temperature during the annealing phase of growth. We also show that graphene initially preferentially decouples at the substrate grain boundaries, likely due to its negative expansion coefficient at cooling, forming characteristic “nano-domes” at the intersections of the grain boundaries. Furthermore, quantitative nanomechanical mapping of flexural stiffness of suspended FLG “nano-domes” using kHz frequency range force modulation microscopy, uncovers the progression of “nano-domes” stiffness from single to bi-modal distribution as CDG growth progresses, suggesting growth instability at advanced CDG stages

Fabrication of quantum dots sensitized ZnO nanowires for extremely thin solar cells

International audienc

ZnO Nanowire arrays sensitization with different absorber materials for fabrication of nanostructured solar cells

International audienc

Experimental study of nucleation and growth mechanisms of graphene synthesized by Low Pressure Chemical Vapor Deposition on copper foil

During the past 40 years, the fields of micro-electronic, energy and communication devices have experienced an unbelievable evolution. To continue these progresses, the development of multifunctional materials presenting a broad range of properties such as high electronic and thermal conductivities, high transparency and good mechanical properties is needed. Graphene, a hexagonal arrangement of carbon atoms forming a one-atom thick planar sheet could match these demands. Several methods can be used for graphene synthesis, even though Chemical Vapor Deposition (CVD) on catalytic surfaces is foreseen to be the most compatible one with industrial requirements. Indeed, CVD graphene with an electronic conductivity of 7350 cm²V-1s-1, an electrical resistance of 30 Ω/sq and a transparency of 90% has already been obtained.1 However, these values are still far from the theoretical ones announced by physicists, because graphene grows as randomly oriented domains in which scattering at the boundaries leads to lower physical properties. The CVD formation of graphene on Cu substrates has long been considered to be surface-mediated and selflimiting due to the very low carbon solubility in Cu, thus leading to single layers formation. However, numerous studies in 2011 have shown that this is true only in a small window of deposition conditions, especially for methane partial pressure2. As a consequence, the control of graphene thickness and crystalline uniformity on large surface areas still remains elusive and needs a better understanding of the mechanisms of graphene nucleation and growth. In this framework, the present study consists in synthesizing graphene on copper foils (25 mm thick, 99,999% Alfa Aesar) by CVD from methane diluted in hydrogen and argon at 0.5 Torr of total pressure. The operating temperature was fixed at 1000°C. Scanning electron microscopy (SEM), optical microscopy and Raman spectroscopy measurements were carried out to investigate the quality and extend of graphene sheets