# Spectroscopic properties of few-layer tin chalcogenides

## TL;DR

This study uses first-principles DFT calculations to predict the structural, electronic, and vibrational properties of few-layer SnS and SnSe, revealing phase transformations and changes in electronic band structure.

## Contribution

It provides new insights into the phase behavior and spectroscopic properties of layered SnS and SnSe during thinning, which were not previously characterized.

## Key findings

- Layered SnS and SnSe undergo phase transformation upon thinning.
- Electronic band gaps change from indirect to direct in few-layer forms.
- Distinct phonon signatures and surface vibrational states are identified.

## Abstract

Stable structures of layered SnS and SnSe and their associated electronic and vibrational spectra are predicted using first-principles DFT calculations. The calculations show that both materials undergo a phase transformation upon thinning whereby the in-plane lattice parameters converge to a pseudo-cubic phase, similar to the high-temperature behaviour observed for their bulk counterparts. The electronic properties of layered SnS and SnSe evolve to an almost symmetric dispersion whilst the gap changes from indirect to direct. Characteristic signatures in the phonon dispersion curves and surface phonon states where only atoms belonging to surface layers vibrate can also be observed for these materials.