Anisotropic layered semiconductors have attracted significant interest due to the huge possibility of bringing new functionalities to thermoelectric, electronic and optoelectronic devices. Currently, most reports on anisotropy have concentrated on black phosphorus and ReS2, less effort has been contributed to other layered materials. In this work, two-dimensional (2D) orthorhombic SnS flakes on a large scale have been successfully synthesized via a simple physical vapor deposition method. Angle-dependent Raman spectroscopy indicated that the orthorhombic SnS flakes possess a strong anisotropic Raman response. Under a parallel-polarization configuration, the peak intensity of Ag (190.7 cm(-1)) Raman mode reaches the maximum when incident light polarization is parallel to the armchair direction of the 2D SnS flakes, which strongly suggests that the Ag (190.7 cm(-1)) mode can be used to determine the crystallographic orientation of the 2D SnS. In addition, temperature-dependent Raman characterization confirmed that the 2D SnS flakes have a higher sensitivity to temperature than graphene, MoS2 and black phosphorus. These results are useful for the future studies of the optical and thermal properties of 2D orthorhombic SnS.

In-plane anisotropy in optical, electronic and thermal properties of two-dimensional (2D) materials has attracted significant interest because of the huge potential applications for developing novel devices. In this work, outstanding angle-dependent Raman property of layered SnSe nano-plates is obtained via polarized Raman system and it is confirmed that the Raman polarization directions of two A modes (130 cm and 150 cm) are consistent with specific crystalline directions (zigzag direction or armchair direction) of SnSe flakes under parallel polarization configuration at home temperature and low temperature. Furthermore, the SnSe nano-plate devices show excellent angle-resolved photo-response at home temperature and low temperature (150 K) with a 90° cycle period and the polarized directions are also along zigzag direction and armchair direction, which is ascribed to the unique in-plane asymmetric crystal structure. These prominent in-plane anisotropic properties provide a precise and rapid method to determine the crystal orientation of SnSe nano-flakes and open up the new applications of 2D asymmetric structure materials.