Temperature dependent Raman investigations of few-layered WS2 nanosheets

Abstract

We studied the temperature dependent phononic response of few-layered liquid phase exfoliated WS2 nanosheets using Raman spectroscopy over a wide temperature range from 80 to 600 K. We find that the E12g (in-plane) and A1g (out-of plane) modes follow a systematic red shift with increase in temperature and exhibits weak non-linear temperature dependence in the temperature range of 350–600 K. The first-order temperature coefficients are found to be −0.0111 cm−1 K−1 and -0.0103 cm−1 K−1 for E12g and A1g modes, respectively. From our analysis which is based on a semi-quantitative model, we find that at higher temperatures the non-linear temperature dependence of E12g and A1g modes primarily originates from the an-harmonic effects of three-phonon process as a consequence of creation of S vacancies in the WS2 nanosheets. The thermal expansion contribution is mainly dominant in low temperature region.