Author(s): Mineo Hiramatsu
Graphene-based materials such as carbon nanotube (CNT) and graphene itself have attracted much attention due to their emerging applications. Graphenebased materials can be syn-thesized by several plasma enhanced chemical vapor deposi-tion (PECVD) techniques on heated substrates. For example, plane graphene can be formed by low-pressure PECVD on Cu and Ni in the remote plasma configuration. However, excess flux of carbon precursors causes supersaturation and ion bom-bardment induces the defects. Previously a microwave-excited non-equilibrium atmospheric pressure plasma source with a high electron density of ~1015 cm-3 and low electron temperature of ~1 eV was applied to the synthesis of CNTs. This type of plasma has a great potential for realizing the new material processing because the larger amount of radicals is estimated by a few orders of magnitude compared with the conventional low-pressure and high-density plasmas. Furthermore, the effect of ion bombardment on the growing surface can be removed due to the high-pressure operation. Here, microwave-excited atmospheric pressure plasma employing He/H2/CH4 mixture was applied to the synthesis of graphene-based materials. A schematic of an atmospheric pressure PECVD system is shown in Fig. 1. The microwave (2.45 GHz) propagates from the top of the deposition chamber to the micro-slit electrode. The micro-slit electrode width is 0.2 mm. Formation of plane graphene was carried out on Cu substrate for 10- 300 sec at a microwave power of 100 W, the total pressure of 1 atm, and substrate temperature of about 700 ËδC. In spite of the localized plasma shape, graphene was formed uniformly on the whole substrate. Moreover, the number of graphene layers did not increase even in the increase of the formation period. Results indicated that the self-limiting growth of few-layer graphene could be attained on the Cu substrate by the supply of long-lived hydrocarbon radicals without ion bombardment using atmospheric pressure plasma.
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