Interlayer Vibronic Interactions and Phonon Anharmonic Decay in Few-Layer WS2 Nanoflakes

Temperature-dependent (TD) Raman spectroscopy has been utilized to probe the phonon anharmonicity in few-layer WS2, focusing on interlayer interactions and Davydov splitting under resonance excitation. In this study, spectroscopic measurements were conducted across a wide temperature range of 200-600 K using a laser with an excitation wavelength of 633 nm. The splitting in the out-of-plane A(1g) mode due to weak interlayer interactions in few-layer WS2 was observed to be prominent at low temperatures. The first-order temperature coefficients corresponding to the peak positions of E-2g(1) and A(1g) modes indicate the softening of Raman modes with an increase in temperature. The quantification of quasi-harmonic and anharmonic contributions to phonon mode softening has been primarily identified by using thermodynamic relations. Furthermore, a semi-quantitative model has been employed to investigate the TD frequency shift and peak width of E-2g(1) and A(1g) modes, demonstrating the importance of three- and four- phonon anharmonicities.