First-principles study of the sulfur K and L2,3 edges of transition metal disulfide monolayers, MS2 (M=Mo, W and Re)

By means of the energy loss near edge structure (ELNES) analysis, the electronic structures of layered transition metal disulfides were studied. In the framework of full potential linearized augmented plane wave method, ELNES spectra of sulfur K and L-2,L-3 edges of layered MoS2, WS2 and ReS2 have been calculated at magic angle conditions, and compared with those of bulks and the only existing experimental line structure. Compared to the bulks, the energy differences between the main peaks in sulfur K and L-2,L-3 edges of monolayers decrease due to the slightly larger bond lengths that it can be used as a fingerprint for monolayers. Sulfur K edges in monolayers include some main features originated from electron transition to p(z) (pi) and p(x) + p(y) (sigma) states and their hybridization. The overall dispersions of the sulfur L-2,L-3 edges in all cases are similar to the D-symmetry density of states. The first two features in L-2,L-3 edge of bulks and monolayers can be attributed to electron transition of sulfur 2p to the both unoccupied 3s-like states of sulfur and 4d states of transition metal atoms. Due to the considerable amount of s states at the energy position of a shoulder like structure in L-2,L-3 edge of both bulks and monolayers, these structures can be assigned to the sulfur 2p electron transition to unoccupied sulfur 3s states. The other features at higher energies are due to the transition of sulfur 2p electrons to the D-symmetry states of sulfur. In addition, due to the considerable energy band gaps, it seems that the use of core-hole approximation is essential for accurate reproduction of ELNES features of transition metal disulfides. (C) 2015 Elsevier B.V. All rights reserved.