Robust band gap of TiS3 nanofilms.

First-principles calculations have been performed on the band structure of mono- and few-layer TiS3 nanofilms. It is found that the band gap character of the TiS3 films is quite robust, almost independent of layer thickness, vertical strain and stacking order, which is in sharp contrast to most other two-dimensional materials, such as MoS2. The robustness of the band gap originates from the location of the CBM and VBM states, which are at the center atoms of TiS3, and are thus unaffected by the layer-layer coupling. Such a property of TiS3 nanofilms promises good application potential in nanoelectronics and optoelectronics, and also makes TiS3 a good platform to study the electronic properties of a material in the two-dimensional limit.