Revealing anisotropy and thickness dependence of Raman spectra for SnS flakes

Abstract

In this work, we have successfully synthesized SnS flakes with different thicknesses and systematically investigated their polarization-dependent Raman properties. It is found that the different Raman mode of SnS shows distinctly anisotropic thickness dependence. For B_3g mode, the polar plot of Raman intensities is insensitive to the flake thickness. However, the behavior of A_g mode is entirely different. Under parallel polarization configuration, with decreasing the flake thickness, the maximum Raman intensity of A_g mode changes from the armchair direction to the zigzag direction with 514.5 nm excitation. The results can be understood by the complex Raman tensor owing to the large absorption of SnS. Moreover, under the perpendicular polarization configuration, the Raman intensity of A_g mode along 45° direction becomes apparently different from that along 135° direction. Our finding not only deepens the understanding of anisotropic Raman properties of SnS but also provides inspiration for further studies on the other 2D IV–VI materials.