Thickness dependent anisotropy of in-plane Raman modes under different temperatures in supported few-layer WTe2

Tungsten ditelluride (WTe2) has attracted extensive interest because of promising magnetic, electrical, and thermal properties, such as non-saturable large magnetoresistance, pressure-induced superconductivity, and low thermal conductivity, owing to the heavy atomic mass and low Debye temperature. Here, we report the thickness dependence of anisotropic in-plane Raman modes under different temperatures in supported few-layer WTe2. With angle-resolved Raman spectroscopy, supported few-layer WTe2 reveals a temperature-related anisotropy in Raman modes, and the highest degree of anisotropy is obtained between zigzag and armchair directions, which could be resulted from the different phonon group velocities along these directions. In addition, as the thickness of the WTe2 nanosheet decreases from bulk to 10 nm, the anisotropic ratio (χzigzag/χarmchair) increases from 1.09 to 1.45. Such enhancement in the anisotropic ratio could result from the thickness-dependent surface scattering in supported few-layer WTe2. Our study provides guidance to regulate the anisotropy ratio in thermoelectrical and optoelectronic devices, which might inspire the innovation of functional two-dimensional devices in the future.