Simultaneous tunablility of electronic and phononic gap in SnS$_2$ under normal compressive strain

Ever since the discovery of graphene, 2D materials have emerged as an attractive field of research. Here, using density functional theory based calculations, we show tunability in the electronic structure of mono to multilayered SnS$_2$ under biaxial tensile (BT), biaxial compressive (BC), and normal compressive (NC) strains. We obtain a reversible semiconductor to metal (S-M) transition in mono to multilayered SnS$_2$ without changing the nature of the band gap (i.e. indirect). For the stability analysis with applied strain, we use bilayer (2L-)SnS$_2$ as our prototype system. Surprisingly, under a high NC strain, 2L-SnS$_2$ does not exhibit unstable modes. The phonon spectra of 2L-SnS$_2$ shows a gap in the optical region, which, most interestingly, increases with applied NC strain. Such a simultaneous tunability of the electronic as well as phononic properties of SnS$_2$ under applied strain can be exploited in many applications such as pressure sensors, micromechanical resonators, frequency filters, and in many other multi-physics devices.