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

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.Materials Science and Engineerin

The Future of Radiology Consultation

A more collaborative approach to consultation is one that every radiologist concerned about the future of radiology should be eager to embody

Carbon-assisted chemical vapor deposition of hexagonal boron nitride

We show that in a low-pressure chemical vapor deposition (CVD) system, the residual oxygen and/or air play a crucial role in the mechanism of the growth of hexagonal boron nitride (h-BN) films on Ni foil 'enclosures'. Hexagonal-BN films grow on the Ni foil surface via the formation of an intermediate boric-oxide (BOx) phase followed by a thermal reduction of the BOx by a carbon source (either amorphous carbon powder or methane), leading to the formation of single-and bi-layer h-N. Low energy electron microscopy (LEEM) and diffraction (LEED) were used to map the number of layers over large areas; Raman spectroscopy, time-of-flight secondary ion mass spectrometry (ToF-SIMS), x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) were used to characterize the structure and physical quality of the ultra-thin h-BN film. The growth procedure reported here leads to a better understanding and control of the synthesis of ultra-thin h-BN films

Quantum Optics and Photonics

Contains reports on nine research projects.National Science Foundation (Grant PHY82-10369)Joint Services Electronics Program (Contract DAAG29-83-K-0003)U.S. Air Force - Office of Scientific Research (Contract F49620-82-C-0091)Litton Guidance and Control SystemNational Science Foundation (Grant PHY82-10369

Uniform wafer-scale synthesis of graphene on evaporated Cu (111) film with quality comparable to exfoliated monolayer

Monolayer graphene has been grown on crystallized Cu (111) films on standard oxidized Si 100 mm wafers. The monolayer graphene demonstrates high uniformity (>97% coverage), with immeasurable defects (>95% defect-negligible) across the entire wafer. Key to these results is the phase transition of evaporated copper films from amorphous to crystalline at the growth temperature as corroborated by X-ray diffraction and electron backscatter diffraction. Noticeably, phase transition of copper film is observed on technologically ubiquitous oxidized Si wafer where the oxide is a standard amorphous thermal oxide. Ion mass spectroscopy indicates that the copper films can be purposely hydrogen-enriched during a hydrogen anneal which subsequently affords graphene growth with a sole carbonaceous precursor for low defect densities. Owing to the strong hexagonal lattice match, the graphene domains align to the Cu (111) domains, suggesting a pathway for increasing the graphene grains by maximizing the copper grain sizes. Fabricated graphene transistors on a flexible polyimide film yield a peak carrier mobility ~4,930 cm2/Vs

Quantum Optics and Photonics

Contains reports on nine research projects.U.S. Air Force - Office of Scientific Research (Contract F49620-82-C-0091)Joint Services Electronics Program (Contract DAAG29-83-K-0003)National Science Foundation (Grant PHY82-10369)Litton Guidance and Control Syste

Submicron Structures Technology and Research

Contains reports on fourteen research projects.Joint Services Electronics Program (Contract DAAG29-83-K-0003)U.S. Navy - Office of Naval Research (Contract N00014-79-C-0908)National Science Foundation (Grant ECS82-05701)Semiconductor Research Corporation (Grant 83-01-033)U.S. Department of Energy (Contract DE-ACO2-82-ER-13019)Lawrence Livermore National Laboratory (Contract 2069209)National Aeronautics and Space Administration (Contract NAS5-27591)Defense Advanced Research Projects Agency (Contract N00014-79-C-0908)National Science Foundation (Grant ECS80-17705)National Aeronautics and Space Administration (Contract NGL22-009-638

Submicron Structures Technology and Research

Contains reports on ten research projects.Joint Services Electronics Program (Contract DAAG29-83-K-0003)Joint Services Electronics Program (Contract DAAL03-86-K-0002)National Science Foundation (Grant ECS82-05701)National Science Foundation (Grant ECS85-06565)Lawrence Livermore Laboratory (Subcontract 2069209)National Science Foundation (Grant ECS85-03443)U.S. Air Force - Office of Scientific Research (Grant AFOSR-85-0154)National Aeronautics and Space Administration (Grant NGL22-009-638)National Science Foundation (through KMS Fusion, Inc.)U.S. Navy - Office of Naval Research (Contract N00014-79-C-0908