Abstract
Rhenium Disulphide (ReS2) differs fundamentally from other group-VI transition metal dichalcogenides (TMDs) due to its low structural symmetry, which results in its optical and electrical anisotropy. While the optoelectronic properties of ReS2 have been the subject of extensive study, little attention has been placed on the vertical and anisotropic growth of ReS2 during chemical vapor deposition. Although vertical growth has been observed in some TMDs under special conditions, vertical growth in ReS2 is very different in that it is highly spontaneous and substrate-independent. In this study, we discovered that the governing mechanism for ReS2 growth involves two distinct stages. In the first stage, ReS2 grows parallel to the growth substrate, consistent with conventional TMD growth. However, subsequently vertical growth is nucleated at points on the lattice where Re atoms are “pinched” together. At such sites, an additional Re atom binds with the two pinched Re atoms, leaving an under-coordinated S atom protruding out of the ReS2 plane. This under-coordinated S is “reactive” and binds to free Re and S atoms, initiating growth in a direction perpendicular to the ReS2 surface. We demonstrate the utility of such vertical ReS2 arrays in applications where high surface-to-volume ratio and electric-field enhancement are essential, such as surface enhanced Raman spectroscopy, field-emission and solar-based bacterial disinfection of water.
