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

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 MoS2 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 MoS2 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 MoS2, 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.