Interplay between Anharmonic and Lattice Effects in MoS2 Nanoflowers: Probing through Temperature-Dependent Raman Spectroscopy

Raman spectroscopy has been utilized to understand the structural and vibrational properties of MoS2 nanoflowers. The temperature-dependent Raman shifts of E-2g(1) and A(1g) modes of MoS2 nanoflowers have been quantified using 633 nm laser excitation in the temperature range 173-498 K. The softening of E-2g(1) and A(1g) modes with the increase in temperature has been observed. The experimental results indicate that both modes vary linearly with temperature. Further, by using a semiquantitative model, individual contributions of true anharmonic and quasi-harmonic parts to the temperature-dependent Raman shifts of both modes have been quantified. The true anharmonicity was found to be more dominating than quasi-harmonicity. The three-and four-phonon processes determined the true anharmonicity, while the thermal expansion coefficient plays a major role in quantifying the quasi-harmonic contribution. In this work, we have shown the variation in the behavior of quasi-harmonicity by considering the thermal expansion as a function of temperature and its correlation in quantifying the three-and four-phonon parts.

Automated summary

Raman spectroscopy was used to investigate the structure and vibrational properties of MoS2 nanoflowers. The study observed a softening of the E-2g(1) and A(1g) modes with increasing temperature, and found a linear relationship between these modes and temperature. Using a semiquantitative model, the study quantified the contributions of true anharmonicity and quasi-harmonicity to the temperature-dependent Raman shifts. It was observed that true anharmonicity had a greater influence, while the thermal expansion coefficient played a major role in the quasi-harmonic contribution. The study also demonstrated the variation in quasi-harmonicity behavior with temperature.