Thickness-Dependent Characterization of Chemically Exfoliated TiS 2 Nanosheets.

Monolayer TiS is the lightest member of the transition metal dichalcogenide family with promising applications in energy storage and conversion systems. The use of TiS has been limited by the lack of rapid characterization of layer numbers via Raman spectroscopy and its easy oxidation in wet environment. Here, we demonstrate the layer-number-dependent Raman modes for TiS. 1T TiS presents two characteristics of the Raman active modes, A (out-of-plane) and E (in-plane). We identified a characteristic peak frequency shift of the E mode with the layer number and an unexplored Raman mode at 372 cm whose intensity changes relative to the A mode with the thickness of the TiS sheets. These two characteristic features of Raman spectra allow the determination of layer numbers between 1 and 5 in exfoliated TiS. Further, we develop a method to produce oxidation-resistant inks of micron-sized mono- and few-layered TiS nanosheets at concentrations up to 1 mg/mL. These TiS inks can be deposited to form thin films with controllable thickness and nanosheet density over square centimeter areas. This opens up pathways for a wider utilization of exfoliated TiS toward a range of applications.