Temperature Dependent Phonon Shifts in Single-Layer WS2

Atomically thin two-dimensional tungsten disulfide (WS2) sheets have attracted much attention due to their potential for future nanoelectronic device applications. We report first experimental investigation on temperature dependent Raman spectra of single-layer WS2 prepared using micromechanical exfoliation. Our temperature dependent Raman spectroscopy results shows that the E-2g(1) and A(1g) modes of single-layer WS2 soften as temperature increases from 77 to 623 K. The calculated temperature coefficients of the frequencies of 2LA(M), E-2g(1), A(1g), and A(1g)(M) + LA(M) modes of single-layer WS2 were observed to be -0.008, -0.006, -0.006, and -0.01 cm(-1) K-1, respectively. The results were explained in terms of a double resonance process which is active in atomically thin nanosheet. This process can also be largely applicable in other emerging single-layer materials.