Electronic Properties and Chemical Reactivity of TiS₂ Nanoflakes

Abstract

Transition metal dichalcogenides have a laminar structure, with strongly covalently bonded layers weakly interacting through van der Waals forces. They are of special interest also because of their unique properties once exfoliated in nanoflakes. We analyze the microstructure of oxidized TiS2 nanoflakes with atomically resolved scanning transmission electron microscopy and propose a comprehensive model for their reactivity by means of first-principles simulations. In particular we find that reaction to water proceeds from the edges of the flake, while it is thermodynamically possible but kinetically hindered in the middle, unless it is initiated by the presence of a surface vacancy. Importantly O substitution for S allows fine-tuning control of the flake bandgap, paving the way for the use of TiS2-xOx alloys as surface catalysts and photovoltaic materials.