Vol.9 No.3 2017

Research paper−124−Synthesiology - English edition Vol.9 No.3 pp.124–138 (Feb. 2017) attempt to develop high throughput plasma-enhanced CVD for high quality graphene.[8]-[16] 2 Preparation of a substrate for graphene synthesis and suppression of impurity incorporation.In the case of CVD of graphene using a copper foil substrate, surface cleaning technique of copper foil before CVD is especially important. Also in the case of plasma-assisted CVD (plasma CVD), it is necessary to prevent contamination such as impurities released from the reaction chamber by plasma exposure, particularly silicon, which originate from the quartz of antenna units for exciting plasma.Commercially available copper foil surfaces are subjected to anticorrosive treatment in order to prevent oxidation. Moreover, even foil with anticorrosive treatment has a surface that is still covered with a thin copper oxide layer. For high-quality graphene synthesis, it is necessary to remove these copper oxide and anticorrosive treatment carefully. In thermal CVD of graphene, electrolytic cleaning and successive high-temperature treatment at about 1000 °C of the copper foil substrate in the reaction chamber are effective for removing copper oxide and the anticorrosive treatment layer. Furthermore, in order to atten the copper foil surface, chemical polishing (CMP) before electrolytic cleaning and annealing treatment is effective.[17][18] On the other hand, electrolytic cleaning is a wet process and thus there is a possibility of recontamination before CVD. Therefore, cleaning methods consistent with CVD are desirable. 1 IntroductionGraphene[1] is a single atomic sheet in which carbon atoms are arranged in a hexagonal honeycomb lattice. Graphene has a very unique band structure (zero bandgap, linear dispersion), and thereby it shows brilliant electronic and optical characteristics such as extremely high carrier mobility and light absorption which does not depend on wavelength. (2.3 % absorption per layer.) Moreover graphene has the property of exibility which indium tin oxide (ITO)[2] does not possess, and an attempt has been made to use a few layers of graphene(FLG) as transparent electrodes in such devices as exible organic light-emitting diode (OLED), solar batteries, and displays.For transparent electrode application of graphene, it is necessary to establish production technology of high quality and high throughput for large area graphene. Among the various methods of graphene production such as mechanical exfoliation of bulk graphite,[1][3] exfoliation of graphene oxide in liquid phase,[4] thermal decomposition of SiC,[5] etc., chemical vapor deposition (CVD) on catalytic transition metal surfaces, in particular on a copper surface, has great promise as a production method for transparent electrode application. Recently, high conductivity graphene has been synthesized on copper substrates by energetic development of the thermal CVD method.[6][7] On the other hand, since throughput of the thermal CVD method is insufficient, synthesis time needs to be significantly shortened for transparent electrode application. In this paper, we report an - Toward a high throughput process-The current trend in graphene synthesis is to use thermal chemical vapor deposition(CVD) at the temperature of 1000 °C or higher. For industrial use of graphene as transparent conductive lms, higher throughput of graphene synthesis is necessary. We were among the rst to adopt the plasma-enhanced CVD method, and have developed a process of high-speed large-area deposition for transparent conductive lm applications. The development and a method to remove impurities from the process are presented in this paper. We report improvement in graphene lm quality and other properties by decreasing the nucleus density using plasma-enhanced CVD.High quality and large-area graphene synthesis with a high growth rate using plasma-enhanced CVDKeywords : Graphene, plasma CVD, large area synthesis, high growth rate, high throughput, transparent electrode [Translation from Synthesiology, Vol.9, No.3, p.124–138 (2016)]Masataka Hasegawa1,2*, Kazuo Tsugawa2, Ryuichi Kato2, Yoshinori Koga2, Masatou Ishihara1,2, Takatoshi Yamada1,2 and Yuki Okigawa1,21. Nanomaterials Research Institute, AIST Tsukuba Central 5, 1-1-1 Higashi, Tsukuba 305-8565, Japan *E-mail: , 2. Technology Research Association for Single Wall Carbon Nanotubes, Graphene Division Tsukuba Central 5, 1-1-1 Higashi, Tsukuba 305-8565, JapanOriginal manuscript received March 10, 2016, Revisions received April 27, 2016, Accepted May 26, 2016

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