Monoclinic structures of niobium trisulfide

Two-dimensional titanium and zirconium trichalcogenides nanosheets with highly anisotropic optoelectronic properties. A serial of two-dimensional titanium and zirconium trichalcogenides nanosheets MX 3 (M = Ti, Zr; X = S, Se, Te) were investigated based on first-principles calculations. The evaluated low cleavage energy indicates that stable two-dimensional monolayers can be exfoliated from their bulk crystals in the experiment. Electronic studies reveal the very rich electronic properties in these monolayers, including metallic TiTe 3 and ZrTe 3 , direct band gap semiconductor, TiS 3 , and indirect band gap semiconductors, TiSe 3 , ZrS 3 and ZrSe 3 . The band gaps of all the semiconductors are between 0.57 and 1.90 eV, which implies their potential applications in nano-electronics. In addition, the calculated effective masses demonstrate the highly anisotropic conduction properties for all the semiconductors. Optically, TiS 3 and TiSe 3 monolayers exhibit good light absorption in the visible and near-infrared region, respectively, indicating their potential applications in optical devices. In particular, the highly anisotropic optical absorption of the TiS 3 monolayer suggests it could be used in designing nano-optical waveguide polarizers.

Titanium trisulfide (TiS3) is a promising layered semiconductor material. Several-mm-long TiS3 whiskers can be conveniently grown by the direct reaction of titanium and sulfur. In this study, we exfoliated these whiskers using the adhesive tape approach and fabricated few-layered TiS3 field-effect transistors (FETs). The TiS3 FETs showed an n-type electronic transport with room-temperature field-effect mobilities of 18-24 cm(2) V(-1) s(-1) and ON/OFF ratios up to 300. We demonstrate that TiS3 is compatible with the conventional atomic layer deposition (ALD) procedure for Al2O3. ALD of alumina on TiS3 FETs resulted in mobility increase up to 43 cm(2) V(-1) s(-1), ON/OFF ratios up to 7000, and much improved subthreshold swing characteristics. This study shows that TiS3 is a competitive electronic material in the family of two-dimensional (2D) transition metal chalcogenides and can be considered for emerging device applications.