SnS Nanoflake-Based Field Effect Transistor with an Anisotropic Gate Effect and a Polarization-Dependent Raman Response

SnS has attracted intensive attention because of the strong anisotropic electric and optical properties along the in-plane zigzag and armchair directions. In this work, SnS nanoflakes with the lateral sizes varying from 3 to 112 mu m and thicknesses varying from 2.7 to 305.4 nm were synthesized by controlling the growth temperature and time of chemical vapor deposition. With the thickness was decreased from 22.4 to 3.2 nm, obvious red shifts were observed in the "waving" and "breathing" vibration modes along the normal direction of the (010) plane and the "NaCl" type vibration along the in-plane zigzag direction. Meanwhile, the "NaCl" type vibration along the armchair direction shows a distinct blue shift. The intensity of the vibrations along the two typical inplane directions are also highly in-plane anisotropic and thickness-dependent. The anisotropic electrical properties of SnS thin films were also studied using back-gated multiple-electrode SnS nanostructured field effect transistors. Interestingly, the gate effect is nearly absent along the zigzag direction, while the output characteristic along the armchair direction shows a strong gate effect. The zigzag/armchair conductance ratio reaches as high as 31 when V-D = -8 V at V-g = 0 V, which may pave the way for future optoelectronic applications with high anisotropic optical response and electrical transport.