Single-layer Molybdenum disulfide (MoS_2) appears to be a promising material for next generation nanoscale applications because of its low-dimensionality and intrinsic direct band-gap of about 1.9 eV. Several experimental groups have reported novel electronic and transport properties of single layer MoS_2 and other transition metal dichalcogenides, which may be further tuned through alloying , defects, doping, and coupling to substrate. In this talk I will present results from joint theoretical and experimental investigations which provide a framework for manipulating the functionality of this material. My emphasis will be on evaluation of binding energies of optical excitations (excitons and trions) using a density matrix based time dependent density functional theory method which takes into account long ranged exchange-correlation found necessary to provide reasonable agreement with experimental data. The effect of a monolayer support such as graphene, hexagonal boron nitride and silicene on the electronic structure and characteristics of optical excitations in monolayer transition metal dichalcogenides will be examined. Optical excitations in heterostructures consisting of monolayers of two different transition metal dichalcogenides will also be highlighted. I will also address the issue of tuning catalytic properties of single layer MoS_2 through vacancies and other defects. Possible technological applications of these materials will also be discussed. Work done in collaboration with D. Le, V. Turkowski, T. Rawal, N. Nayyar, A. Ramirez, L. Bartels and P. Dowben and supported in part by US Department of Energy.
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