Titanium trisulfide (TiS3): a 2D semiconductor with quasi-1D optical and electronic properties

Abstract

We present characterizations of few-layer titanium trisulfide (TiS3) flakes which, due to their reduced in-plane structural symmetry, display strong anisotropy in their electrical and optical properties. Exfoliated few-layer flakes show marked anisotropy of their in-plane mobilities reaching ratios as high as 7.6 at low temperatures. Based on the preferential growth axis of TiS3 nanoribbons, we develop a simple method to identify the in-plane crystalline axes of exfoliated few-layer flakes through angle resolved polarization Raman spectroscopy. Optical transmission measurements show that TiS3 flakes display strong linear dichroism with a magnitude (transmission ratios up to 30) much greater than that observed for other anisotropic two-dimensional (2D) materials. Finally, we calculate the absorption and transmittance spectra of TiS3 in the random-phase-approximation (RPA) and find that the calculations are in qualitative agreement with the observed experimental optical transmittance.

Emerging in‐plane anisotropic two‐dimensional materials

“…Compared to BP and group IV monochalcogenides GeS and GeSe, the quasi‐one‐dimensional structure of the group IVB trichalcogenide TiS 3 has a much larger anisotropic absorption ratio. As shown in Figure F, the transmittance of the RGB channels is clearly strong polarization dependent, and the transmission ratio between b‐axis ( y ‐direction) and a‐axis ( x ‐direction) can up to 30 . Besides, the optical contrast under polarized light is also anisotropic, which can be approved by the optical images in Figure F.…”

“…Reproduced with permission from ref. Copyright 2016, Nature Publishing Group. G, Calculated absorption spectra of bulk TiS 3 with field parallel to a‐axis (solid line) and b‐axis (dashed line).…”

“…Reproduced with permission from ref. Copyright 2016, Nature Publishing Group. H, Polarization‐resolved reflection spectra of 3 L ReS 2 with 15° intervals from 5° to 170°.…”

“…The anisotropic optical absorption of triclinic ReS 2 and ReSe 2 has also been studied . Typical polarization‐resolved reflection spectra for 3 L ReS 2 is presented in Figure H, three exciton peaks 1, 2, and 3 are indicated by arrows, showing clear anisotropy, in which excitons 1 and 2 exhibit maximum values at an angle of ∼15 and ∼50° between light polarized direction and b‐axis, respectively . This is different from BP, GeS, and GeSe that show maximum absorptions along the principal axes.…”

Selectively tunable optical Stark effect of anisotropic excitons in atomically thin ReS2

“…We emphasize that such advantages basically originate from the unique in-plane crystal anisotropy of group VII TMDs, which is absent in group VI 2D TMDs (for example, MoS 2 , MoSe 2 , WS 2 and WSe 2 ). Of course, group VII TMDs are not the only material family exhibiting anisotropic property of excitons; there are several systems possessing anisotropic excitonic properties (such as carbon nanotubes (CNTs) and black phosphorus (BP))12303132. However, both of them lack polarization-dependent exciton selectivity so that energy-selective optical Stark effect cannot be expected.…”