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 E¹_2g 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), E¹_2g, 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