Hydrogen-induced structural transition in single layer ReS2

By performing density functional theory-based calculations, we investigate how structural, electronic and mechanical properties of single layer ReS2 can be tuned upon hydrogenation of its surfaces. It is found that a stable, fully hydrogenated structure can be obtained by formation of strong S-H bonds. The optimized atomic structure of ReS2H2 is considerably different than that of the monolayer ReS2 which has a distorted-1T phase. By performing phonon dispersion calculations, we also predict that the Re-2-dimerized 1T structure (called 1T(Re2)) of the ReS2H2 is dynamically stable. Unlike the bare ReS2 the 1T(Re2)-ReS2H2 structure which is formed by breaking the Re-4 clusters into separated Re-2 dimers, is an indirect-gap semiconductor. Furthermore, mechanical properties of the 1T(Re2) phase in terms of elastic constants, in-plane stiffness (C) and Poisson ratio (v) are investigated. It is found that full hydrogenation not only enhances the flexibility of the single layer ReS2 crystal but also increases anisotropy of the elastic constants.