Synthesis of graphene and h-BN by chemical vapor deposition and their transfer process

[摘要] Since graphene was discovered as an existing form by isolating from graphite in 2004, intense research and developments have been devoted to exploring this unique material; eventually, they pioneered a research field of 2-D materials including hexagonal boron nitride (h-BN) and transitional metal dichalcogenide (TMDC). In particular, the excellent material properties of graphene fascinated engineering fields to use it as a device component of applications such as RF-device or photodetector. Among various synthesis methods, metal-catalyzed chemical vapor deposition (CVD) has been the main process of 2-D materials because of their high film quality, scalability, and low production cost. In this thesis, I address challenging issues yet to be solved by separating the CVD process into two parts: synthesis and transfer. First, in the synthesis part, Cu-mediated CVD processes will be mainly discussed. Throughout an in-depth understanding of the growth mechanisms, I demonstrate a process to increase the domain size of graphene in sub-mm scale; and present a novel atmospheric CVD process to obtain a pristine monolayer graphene through an understating of a role of hydrogen. Besides, a method to cvaiuatc the domain size is presented through a moderate oxidation. With the knowledge accumulated in this part, the thesis scope is extended to the growth of h-BN and to the use of Pt as a new growth substrate for both 2-D materials to gain better quality. In the transfer of 2-D materials, it is highly required to preserve the original quality of 2-D materials when transferred onto a target substrate. In this respect, I analyze the effect of various steps in the poly(methyl methacrylate) (PMMA)-supported wet transfer on graphene samples. Afterwards, a transfer process is proposed to result in a clean graphene surface and to suppress hole-doping in graphene. In addition, by selecting a new supporting polymer, I demonstrate a route to transfer 2-D materials that allows reducing the density of wrinkles and enabling a conformal coating on uneven target substrates. The addressed questionings and proposed solutions in this thesis will provide criteria in the preparation of other 2-D materials beyond graphene and h-BN prepared by CVD processes.

[发布机构] Massachusetts Institute of Technology