Raman Spectroscopy Insights into the Size-Induced Structural Transformation in SnSe Nanolayers

Abstract

Raman spectroscopy is used to probe the structural changes in [SnSe]m[MoSe2]n ferecrystal thin films as a function of m, the number of bilayers of SnSe. In spite of the interleaved structure in the intergrowths, Raman spectra can be described as a superposition of spectra from the individual components, indicating that the interaction at the interface between the components is relatively weak. Analysis of room-temperature Raman spectra indicate that the MoSe2 layers separating the SnSe layers are nanocrystalline in all of the samples studied, with little change as the number of Se-Mo-Se trilayers (n) or SnSe bilayers (m) increases, reflecting the rotational disorder between adjacent trilayers. A thickness-dependent, continuous transition occurs in the SnSe layer as m is increased, from a pseudotetragonal structure when the layers are thin to a bulk-like orthorhombic SnSe structure when the SnSe layer thickness is increased. Polarization analysis of the Raman scattering from these materials allows the symmetry evolution of the SnSe layers through this transition to be determined.

Plasma-assisted synthesis and pressure-induced structural transition of single-crystalline SnSe nanosheets

“…As shown in Fig. 4, the initial and high-pressure phases exactly match the orthorhombic structure with the space group of Pnma (62) and Cmcm (63), respectively. This phase transition sequence is consistent with the previous experimental 33 and theoretical 37 studies on bulk SnSe.…”

Spectroscopic properties of few-layer tin chalcogenides

“…As can be seen in figure 2, when reducing the number of layers, the in-plane lattice parameters (a and b) converge, and are almost identical for the monolayer case of SnSe. This behaviour mirrors experimental studies on heterostructures containing SnSe slabs [32] and the high-temperature behaviour of both compounds [3,4]. The monolayer of SnS also rectifies, but its a/b ratio does not converge to 1: we find a small dynamical instability for perfect square in-plane parameters (see Supplemental information).…”

Recent Advances in SnSe Nanostructures beyond Thermoelectricity

“…In addition, the Raman peaks intensity observed for perpendicular polarization is higher than that for parallel polarization. The Raman spectrum of [SnSe] m [MoSe 2 ] n was experimentally studied by Ludemann et al [144] The change of Raman scattering with thickness decrease implied that the phase of SnSe transitioned from an orthorhombic (Pnma) to a tetragonal Bravais lattice structure. Due to limitations in the preparation technology, the experimental observation of the Raman spectrum of few-layer SnSe alone has not yet been reported.…”