Two-dimensional materials synthesis, characterization, and devices : working with hexagonal boron nitride and graphene

Chou, Harry
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Two dimensional materials have unique properties that are anisotropic in-plane and out-of-plane. They further exhibit unique properties when they are thinned down to an isolated monolayer or a few layers. These properties have the potential to greatly impact applications in energy, computing, construction, medicine, and other industries. Many researchers have published many reports working with two dimensional (2D) materials. This dissertation describes work which has contributed to the body of research around 2D materials synthesis, characterization, and device applications primarily with graphene and hexagonal boron nitride. Graphene is a hexagonal lattice of carbon atoms which is stable in ambient down to a single monolayer. Hexagonal boron nitride is an isomorph of graphene but with boron and nitrogen atoms on the lattice instead of carbon. Chemical vapor deposition (CVD) synthesis processes have shown to be replicable and capable for obtaining 2D materials of high quality, and experimenting with process conditions has improved the understanding about the synthesis mechanisms occurring. The objective of my 2D materials synthesis work is, broadly, to better understand the mechanisms during growth for graphene and h-BN. The growth mechanism has multiple of forces acting on it, in competition, and many of them are detailed in chapter 2. Growing the body of research and knowledge about 2D materials requires us to have techniques to characterize these materials accurately and precisely. It is important to develop and demonstrate new characterization techniques which are tailored for 2D materials. In chapter 3, the research done in characterizing 2D materials and interfaces between hetero-layers will be presented. Devices which take advantage of the dimensionality and confinement within a layer of 2D material, or multiple materials, have shown high performance in a variety of applications. The range for 2D materials device applications is continually expanding and increasing in complexity. In chapter 4, research will be presented which returns to the relatively simple system of graphene to try and apply its many unique properties for a few different photovoltaic devices.