nanosheets have proven to be promising candidates for ultrathin optoelectronic devices due to their direct narrow band-gap and the strong light–matter interaction. In addition, the marked in-plane anisotropy of TiS3
is appealing for the fabrication of polarization sensitive optoelectronic devices. Herein, we study the optical contrast of TiS3
nanosheets of variable thickness on SiO2
/Si substrates, from which we obtain the complex refractive index in the visible spectrum. We find that TiS3
exhibits very large birefringence, larger than that of well-known strong birefringent materials like TiO2
or calcite, and linear dichroism. These findings are in qualitative agreement with ab initio
calculations that suggest an excitonic origin for the birefringence and linear dichroism of the material.
Mapping the color of TiS3 flakes to their thickness. (a) Optical image of an exfoliated thin flake of TiS3 on 90 nm SiO2/Si substrate. (b) AFM topography of the same flake from panel (a). The thickness of the particular flake is 4.2 nm. (c–j) Optical images of flakes with different thickness and a colorbar with the colors of flakes with thickness up to 110 nm. The scale bars are 5 μm.