Phonon scattering mechanism in van der Waals heterostructures comprising of MoS2 and WS2 nanosheets

Abstract

In this work, the effect of temperature on the phononic modes (E12g and A1g) of few-layered MoS2 and WS2 nanosheets and their van der Waals heterostructure has been investigated in the temperature regime: 80–600 K. The E12g and A1g modes showed a red-shift with an increase in temperature and exhibited non-linear temperature dependency above 300 K for the constituent nanosheets and their co-stacked heterostructure. A physical model comprising of both thermal and volume effects, is used to quantitatively understand the origin of non-linear temperature dependency of E12g and A1g modes. The observed non-linearities in the phononic modes is well described by the higher-order phonon scattering as a consequence of greater amount of sulphur vacancies in the nanosheets as compared to the bulk counterparts. However, the MoS2-WS2 heterostructure exhibited higher structural stability (lesser sulphur vacancies) as compared to its constituent counterparts owing to the enhanced van der Waals coupling at the hetero-interface and subsequently it decreases with rise in temperature.