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 A1g 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 E2g1 and A1g 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 E2g1 and A1g modes, demonstrating the importance of three- and four- phonon anharmonicities.