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

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

High quality graphene synthesized by atmospheric pressure CVD on copper foil

International audienceGraphene 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

Sensitization of ZnO nanowire arrays with CuInS < sub>2 < /sub> for extremely thin absorber solar cells < sup>a) < /sup&gt

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Graphene-HfO2_2-based resistive RAM memories

International audienceGraphene, a two dimensional material with remarkable electronic properties, has attracted a huge interestamong scientist during the last decade. We report the fabrication of Graphene-HfO$_2$-based resistive RAM memories.We insert graphene layers between the oxide layer and the gold top electrode resulting in stabilization of alow resistance state stability without applied voltage, contrary to behaviour observed for identical graphene freememory devices. Graphene here is used as an oxygen reservoir and contribute to the switching mechanis