Interfacial thermal resistance between nm-thick MoS2 and quartz substrate: A critical revisit under phonon mode-wide thermal non-equilibrium

Abstract

2D materials experience a cascading energy transfer under intense laser irradiation, which leads to a strong thermal non-equilibrium between energy carriers, especially between optical (OP) and acoustic (AP) phonon branches. In previously reported Raman optothermal techniques, this non-equilibrium effect is neglected that leads to very large physics errors in interface thermal resistance characterization. Here, the optical phonon temperature rises of both in-plane and out-of-plane modes of nm-thick MoS 2 films supported on quartz substrate are determined using a steady-state Raman, and the non-equilibrium between OP-AP and their energy coupling factor are characterized by controlling the heating domain and precise calculation of Raman signal and subsequently absorbed laser power by using a transfer matrix method. It is concluded that the OP-AP temperature difference under laser heating area could be as high as ~45% of the total OP temperature rise probed by Raman. The interfacial thermal resistance ( R ″ tc ) between MoS 2 and quartz is reevaluated by considering this non-equilibrium effect, and it is observed that neglecting it could lead to R ″ tc over-prediction by ~100%. By determining R ″ tc using both Raman modes of MoS 2 , it is observed that due to the ballistic and diffusive phonon transport and difference of interface thermal resistance among phonon modes, the flexural optical mode has a higher temperature rise than the longitudinal/transverse optical modes. This agrees well with atomistic modeling results of other 2D materials, e.g. graphene on BN. • First time distinguishing of LO/TO and ZO phonon temperatures of supported MoS 2 . • First time determination of OP-AP energy coupling factor of supported MoS 2 . • Intrinsic interfacial thermal resistance measurement under phonon non-equilibrium. • ZO mode has a much higher temperature rise than the LO/TO modes.