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

Abstract

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.