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Abstract Very large areas of graphene (until 4 inch) are grown by chemical vapor deposition technique using copper foil as a catalyst. Because of its low cost, copper seems to be a good substrate for that. Besides graphene monolayers growth, we performed Raman spectroscopy investigation coupled with HRTEM and electrical measurements to point out its properties for devices. The technological lock remains the transfer of the graphene onto a specific substrate.
Graphene is the one-atom thin layer of sp2-bonded carbon atoms with a hexagonal symmetry lattice. This symmetry, gives graphene a peculiar electronic band structure where the valence and the conduction bands touch at six K points of the reciprocal lattice and the energy dispersion E(q) is linear. More, graphene has attracted much attention due to its remarkable electronic, optical and mechanical properties. It possesses many fascinating properties including massless Dirac electronic structure , high mobility and an extraordinary high thermal conductivity . As a result of those proprieties, graphene is a promising candidate for many applications, such as solar cells , terahertz transistors , ultrafast photo-detectors , gas sensors , MEMS and NEM devices, touch screens and many others. However, before developing Graphene based devices, it is critical to master the synthesis of large area of graphene with good quality. Several methods have been developed to synthesize this material: mechanical exfoliation, sublimation of Si from SiC substrates, Chemical vapor deposition (CVD) . However the only way that has the promise of becoming a manufacturable technology is CVD. The advantage of this method compared to mechanical exfoliation is that continuous films can be grown on the centimeter scale with single crystal domain size as high as 10 micrometers and low cost for industry. It is reproducible and the films can then be transferred to several substrates.
The growth of graphene is optimized using different experimental conditions (temperature, CH4/H2/Ar flowrates, pressure and time) to minimize the density of defects shown on 1D band on Raman spectra and also to keep graphene growing as monolayers, multilayers or isolated hexagonal single layers . For that we use a commercial BM4GB CVD/PECVD 4 inch reactor from Aixtron manufacturer.
Although it is necessary to synthesize large layers of graphene, it is also requires to transfer these films without deteriorating their qualities. We focus now our efforts onto the transfer of the graphene layers on several substrates such as silica, silicon, III-V compounds, SLG (bottle glass), BK7, Pyrex 7740 and also on metallic films. As widely described in the literature, we use usual polymers to protect the graphene during the wet etching of copper. At the end of the transfer process, the polymer is removed by using a solvent.
The first experiments on graphene based devices show that the CVD graphene have a huge potential for many applications. The node of this technique is the transfer of the material onto a specific substrate. The actual state of the art doesn’t guarantee free defect surface after transfer as we see on Raman maps. To improve the quality remains important but the control of the final quality after transfer is the big challenge.
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