Roll-to-Roll Graphene Synthesis by Using Microwave Plasma Chemical Vapor Deposition at Low Temperature
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Roll-to-Roll Graphene Synthesis by Using Microwave Plasma Chemical Vapor Deposition at Low Temperature Takatoshi Yamada, Masatou Ishihara, Jaeho Kim, Masataka Hasegawa and Sumio Iijima Nanotube Research Center, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba 305-8565, Japan ABSTRACT We reported continuous depositions of grahene films on copper foils with A4 width using roll-to-toll microwave plasma chemical vapor deposition (MWPCVD) technique. A pair of winder and unwinder was built into an MWPCVD apparatus. Surface-wave plasma enabled us to deposit large-area graphene film (substrate stage is of 480 mm x 300 mm) at temperatures below 400 ºC. In Raman spectra, G- and G’-band attributed to graphene were obtained. In addition, Dand D’-band originated from defects and/or edges were detected. These results suggested that the obtained graphene films consisted of flake boundaries and defects. After the transferring graphene onto the polyethylene terephthalate film, uniform transmittance and sheet resistance were confirmed. INTRODUCTION Transparent conductive films are used in a lot of modern electronic and optoelectronic applications such as solar cells, displays and touch screens. Currently, most of these commercial transparent conductive films are made from indium tin oxide (In2O3:Sn, ITO). Due to the limited supply of indium, the search for a material that replaces ITO is one of the key technologies to be solved. Graphene is considered to be an appropriate material for transparent conductive film, that substitutes ITO, because graphene consists of carbon atoms. In addition, an ideal mono-layer graphene has a transmittance of 97.7 %, an electron mobility of 200,000 cm2/Vs at room temperature and a thermal conductivity of 5,000 W/mK. Thus, transparent conductive films have been demonstrated by graphene based films [1-3]. There are two techniques to fabricate graphene transparent conductive films. The thermal chemical vapor deposition (CVD) on metal catalysts [1] and the reduction of graphene oxide [2] were reported for the syntheses of graphene films. However, high temperature and the long process time are the remaining problems in both methods for the mass production of graphene. For the development of transparent conductive films based on graphene, it is necessary to develop a continuous production of graphene films as well as depositions of high quality films. Roll-to-roll process is commonly used for industrial mass productions for thin film deposition. It was reported to transfer graphene films to polymer support from copper (Cu) substrate using a roll-to-roll process [3]. CVD within the roll-to-roll process is expected for continuous deposition process of graphene films. However, it has not yet been established due to the high process temperature of about 1000 ºC and long process time that takes a few tens of minutes, both of which are necessary for the thermal CVD of graphene. In order to establish a roll-to-roll CVD technique of graphene films, lowering the deposition temp
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