Thickness-dependent Raman active modes of SnS thin films

Abstract

Tin sulfide (SnS) thin films have been reported to show strong layer number dependence on their ferroelectricity and Raman spectra. Identifying the number of layers and stacking structures is crucial for optoelectronic device fabrication. Here, we theoretically study the electronic and phononic properties of SnS thin films using first-principles calculations. We identify the characteristic Raman active phonon modes and their dependence on the number of layers and stacking sequences. The clear separation between surface modes and bulk modes is clarified for SnS thin films. In addition, we have clarified the relation between stacking structures and Raman active modes for bilayer SnS. Our results will serve the experimental characterization of such thin monochalcogenide systems through Raman spectra and will expedite their device fabrication.