Phase stability of the earth-abundant tin sulfides SnS, SnS2, and Sn2S3

The various phases of tin sulfide have been studied as semiconductors since the 1960s and are now being investigated as potential earth-abundant photovoltaic and photocatalytic materials. Of particular note is the recent isolation of zincblende SnS in particles and thin-films. Herein, first-principles calculations are employed to better understand this novel geometry and its place within the tin sulfide multiphasic system. We report the enthalpies of formation for the known phases of SnS, SnS2, and Sn2S3, with good agreement between theory and experiment for the ground-state structures of each. While theoretical X-ray diffraction patterns do agree with the assignment of the zincblende phase demonstrated in the literature, the structure is not stable close to the lattice parameters observed experimentally, exhibiting an unfeasibly large pressure and a formation enthalpy much higher than any other phase. Ab initio molecular dynamics simulations reveal spontaneous degradation to an amorphous phase much lower in energy, as Sn(II) is inherently unstable in a regular tetrahedral environment. We conclude that the known rocksalt phase of SnS has been mis-assigned as zincblende in the recent literature

Photovoltaic behavior of nanocrystalline SnS/TiO2

10.1021/jp9075756Journal of Physical Chemistry C11473256-325

Theoretical and Experimental Investigations on the Growth of SnS van der Waals Epitaxies on Graphene Buffer Layer

We present theoretical and experimental investigations on the growth of SnS van der Waals epitaxies (vdWEs) on graphene buffer layer (GBL). Local density approximation (LDA) was used to evaluate the bond length disorder, binding energies, and growth orientations for SnS deposited on crystalline semiconductor substrates with and without the GBL. Strong bond length disorder is observed for SnS deposited directly on GaAs substrates, whereas in the case where a GBL is used the disorder is substantially reduced. First-principle calculations indicate two favored growth orientations for SnS deposited on GBL resulting in 12 distinct peaks in the azimuthal hard X-ray diffraction (HXRD) scan due to the structural symmetry of the GBL. The results stipulate formation of strong chemical bonds at the GaAs/SnS interface while the interaction between SnS and the underlying GBL is dominated by vdW force. Nevertheless this vdW force is shown to be strong enough to induce favored nucleation orientations for the SnS and is essential for the observed improvement in the crystallinity of the films