Article pubs.acs.org/JPCC
Direct Growth of Graphene Films on Sapphire (0001) and (112̅0) Surfaces by Self-Catalytic Chemical Vapor Deposition Kosuke Saito and Toshio Ogino* Graduate School of Engineering, Yokohama National University, Tokiwadai 79-5, Hodogaya-ku, Yokohama 240-8501, Japan ABSTRACT: We investigated mechanism of the metal-catalystfree direct growth of graphene films in chemical vapor deposition on sapphire surfaces using three kinds of substrates, randomly stepped (0001), phase-separated (0001) and randomly stepped (112̅0). The graphene growth process includes pit formation in the early stage by hydrogen and methane mixed gas flow, appearance of catalytic action inside the pit, nucleation of graphene on the pit surfaces, and expansion and fusion of graphene films. It was found that the quality of graphene films depends on the crystallographic plane. In addition, even on an identical plane, a domain-selective growth mode was observed between domains with different stepterrace structures. This study indicates that morphology of the sapphire surface is crucial in direct growth of graphene films because a certain density of atomic-steps on the surface is favorable to nucleation of graphene films. boundaries of a Cu thin film to the substrate surface that was in contact with the catalyst Cu film.15 In this method, however, wet etching is still necessary to remove the Cu films. Toward a breakthrough of graphene device technology, metal-catalystfree direct growth of graphene films on insulating substrates is desired as an ideal graphene formation process. Recently, catalyst-free direct growth of graphene films on sapphire surfaces was realized and quality of the grown films was found to be comparable to that grown on metal catalytic surfaces.16−18 However, a major drawback of this process is the high growth temperature (>1500 °C), which is a serious problem in compatibility with the conventional device processes. Large-scale catalyst-free synthesis of graphene films has also been realized at relatively low temperatures (
