| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 104 === In recent years, studies show materials embedded with high-density interfaces are potential candidates for thermoelectric devices due to their low thermal conductivities and acceptable power factors. Yet, the detailed mechanism of the phonon transmission through the interface is still unclear. This study aims at exploring the transport phenomena of phonons through the Si/Ge alloy interfaces in use of the molecular dynamics simulation. Also targeted are the involved thermal boundary resistance (TBR) and the effects of the interface thickness and composition on TBR.
In this study, the Stillinger-Weber (SW) potential was used to describe the interaction among Si and Ge atoms. Two interface thicknesses, 10UC and 2UC, were attempted. The simulation results show that as the Ge atomic concentration ( ) increases, the TBR associated with the 10UC-interface increases first, peaks at =0.5, and decreases thereafter. On the other hand, the variation trend of the TBR associated with the 2UC-interface appears to be W-shaped; two local minimums, even below the TBR of the perfectly smooth interface, are observed at =0.1 and 0.9.
For illumination, wave-packet numerical experiments were designed and performed. The investigation indicates that except the very long longitudinal wave, the variation trend of the transmissivity of the longitudinal waves against the Ge concentration is V-shaped, minimized at =0.5, consistent with the variation trend of the TRB associated with the 10UC-interface and implying the dominance of the mass difference scattering in determining the TBR. Furthermore, the polarization change and inelastic scattering were both observed as waves passed through the alloy interfaces, thereby allowing more phonons to transmit. When the mass difference scattering is weak (i.e. thin alloy interface and low mass difference), the above two mechanisms possibly lead to a TBR smaller than the TBR associated with the perfectly smooth interface. This explains the observed W-shaped variation trend of the TBR associated with the 2UC-interface against the Ge concentration.
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