Graphene Encapsulated Growth of 2D Materials

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Nontechnical description: The project explores the use of graphene encapsulated growth for the formation of single layer (also known as two dimensional) of traditionally three dimensional materials with a specific focus on materials that emit light in the ultraviolet range. The graphene encapsulated growth process, which was initially demonstrated for the synthesis of two dimensional gallium nitride, involves the diffusion and reaction of growth species within the ultrathin space that is present beneath graphene formed on silicon carbide. The research, which combines both experimental studies and molecular simulations, is aimed at developing a fundamental understanding of the synthesis process, aiming to achieve improved control and scalability, as well as to expand the technique to the synthesis of other two dimensional nitrides and oxides. The realization of large area, uniform and reproducible two dimensional nitride and oxide films impacts a range of technologies including quantum communication and computing, ultraviolet emitters and detectors and high frequency/high power electronics. The activities provide collaborative research opportunities for a graduate student, a postdoctoral scholar and several undergraduate students and also engages high school students from underrepresented groups and economically disadvantaged backgrounds.Technical description: The research focuses on fundamental studies of defects and growth chemistry relevant to the synthesis of two dimensional nitride and oxide films via graphene encapsulated growth within a metalorganic chemical vapor deposition environment. Experimental studies focus on controlling the type and density of defects in the graphene layer in order to understand their impact on the adsorption and reaction of gallium and nitrogen precursors as assessed by surface chemical analysis. Collaborative research employs atomic resolution characterization techniques including scanning tunneling microscopy and aberration-corrected scanning transmission electron microscopy with chemical analysis to provide detailed insights on defects and the structure and chemistry of synthesized materials. The experiments are supported by atomistic-scale simulations, which are used to study precursor thermal decomposition and adsorption on the graphene surface, species transport on and through the graphene layer and sub-surface reactions that lead to gallium nitride formation. To enable these simulations, the research team extends existing ReaxFF parameter sets to gallium/graphene systems and uses these, in conjunction with molecular dynamics and Monte Carlo techniques, to study chemical and diffusion events. The studies also extend the technique to investigate the synthesis of other two dimensional nitrides and oxides. The overall goal of the project is the development of graphene encapsulated growth as a general platform for the synthesis of novel two dimensional materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.