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Artificially stacked transition metal dichalcogenide (MX₂) films show ultra-low thermal conductance along out-of-plane directions. The ultra-low thermal conductance is attractive for thermoelectric energy conversion. However, the relationships between out-of-plane heat and electrical conductivity across MX₂ films are still under debate because of the limitations of the measurement techniques. A time-domain thermoreflectance (TDTR) method is one of the techniques that can determine the thermal conductivity of thin films in the out-of-plane direction. In conventional TDTR setups, Al is used as the thermal transducer, but we developed a TDTR system where Au is used as a thermal transducer (Au-TDTR). Au can be also used as electrodes to evaluate the electrical characteristics of the sample. In this study, we investigated out-of-plane heat and electrical characteristics of four-layered (4L) MoS₂ films with different interfacial coupling by annealing process.

The electrical and thermal conductance of the pristine film are estimated to be 0.32 MS/m² and 9 MW/m²K, respectively. Both the thermal conductance and the electrical conductance increased with vacuum annealing temperature, implying the strengthen of the interfacial coupling between the layers. When we apply the vacuum annealing with the temperature of 350 °C, the electrical and thermal conductance become 0.53 MS/m² and 20 MW/m²K, respectively. In the presentation, the details of this study will be discussed.