The isolation of graphene and other materials of atomic thickness has generated enormous interest in two-dimensional (2D) crystals. Single layers cleaved from layered materials such as graphite, boron nitride, and molybdenum disulfide (MoS2) have been studied extensively, both experimentally and theoretically. 2D MoS2 and other semiconducting Transition Metal Dichalgogenides (TMDCs) exhibit novel optoelectronic properties, different from their bulk counterparts, and metallic states at their edges [1]. We present first-principles calculations on four representative TMDCs, MoS2, MoSe2, WS2, WSe2, in various 1D nanoribbon configurations. We compare the thermodynamic stability and the electronic structure of the 2D bulk and 35 different quasi-1D nanoribbons for each of the four materials. We use Density-Functional-Theory (DFT) as implemented by the open-source package GPAW[2]. In each case, we perform calculations for the total energy and the band structure and we consider the reconstructions of the zigzag metal-terminated edge by adding different amounts of chalcogen adatoms. The 1D structures we investigated have positive edge energies when the chalcogen chemical potential is close to the energy of the bulk chalcogen phase, and negative edge energies for higher chemical potential values. We find that the reconstruction with two chalcogen adatoms per edge metal atom is the most stable under usual experimental conditions and that all 1D nanoribbon structures consist of a semiconducting bulk bounded by edges with metallic character [3].
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