关键词: 石墨烯, 化学气相沉积, 绝缘衬底, 气相助剂

Abstract:

Utilizing a direct chemical vapor deposition approach to synthesize graphene on insulating substrates has received enormous attention to date in both scientific and technological realms. In contrast to the graphene growth on metal substrates, the catalytic inertness of insulators toward feedstock decomposition and the high energy barrier for carbon fragment migration on the insulating surface result in not only high density of grain boundaries but also a low growth rate. Thus-obtained graphene film is usually accompanied by massive defects and limited crystal quality, which adversely affect the physical integrity and electrical performance of the fabricated graphene-based device. In this respect, various strategies have been adopted to modify the direct growth processes of graphene, e.g., sacrificial metal catalysis approach, self-terminating confinement approach and near-equilibrium growth approach. Among these mentioned above, the gaseous-promotor-assisted growth methodology has proven to be a beneficial way in enhancing crystal quality and augmenting the growth rate of graphene. For the gaseous-promotor-assisted chemical vapor deposition route, the gaseous promotor can not only regulate the composition/content of active carbon species in the gas-phase reaction process but also promote the surface migration and growth reactions. In this contribution, we review the recent advances in gaseous-promotor-assisted direct growth of graphene with high crystallinity, optimized uniformity, and enhanced growth rate on insulating substrates. First of all, we provide a systematic description of the growth behavior of graphene on insulators, including both the surface and gas-phase reactions combined with elementary steps during the growth process. We then summarize developed strategies aiming to achieve the direct growth of high-quality graphene via the assistance of gaseous promotors, with special emphasis on the effects and mechanisms of the growth process. The types of promotors commonly used in the gaseous-promotor-assisted strategy can be divided into metallic and non-metallic vapor species. These gaseous promotors can play influence on the feedstock decomposition, graphene nucleation, and enhance the enlargement and merging of individual domains. The corresponding mechanisms of the strategy can be classified into three parts: (1) The existence of highly concentrated metallic vapor species can promote thermal decomposition of carbon feedstock, which is the key to the growth of high-quality graphene; (2) The introduction of oxygen-containing species can effectively reduce the nucleation density, etch the amorphous carbon, leading to a high-quality, uniform growth of graphene film. In addition, hydroxylation of substrate through oxygen-containing species weakens the binding energy between the graphene edge and surface of the substrate, facilitating carbon fragment migration to evolve uniform monolayer graphene film; (3) The appearance of silicon and fluorine species reduces the growth kinetic barrier for carbon feedstock migrating onto the graphene edge to form the honeycomb lattice, which ensures the ultrafast growth of graphene on insulating substrates. Finally, we describe existed challenges and present future perspectives on the direct growth of high-quality graphene on insulating substrates to stimulate more efforts devoted to direct graphene growth and ultimate applications. We hope this review can propel in-depth comprehension of the direct growth of graphene on insulators by gaseous-promotor-assisted strategy, and pave the way for the development and applications of graphene materials.

Key words: Graphene, Chemical vapor deposition, Insulating substrate, Gaseous-promotor