| Summary: | 博士 === 國立中正大學 === 機械工程所 === 97 === Materials are composed of elementary particles: atoms/molecules. For a macroscopic system, its number of particles is huge and thus can be well modeled as a continuum. In contrast, as the size of the system shrinks down to the scale of submicron and below, the mesoscopic scale, the continuous behavior breaks down and its characteristics on discreteness is nontrivial.
In this study, molecular-dynamics simulations are used to analyze the details of energy transfer in a dielectric material. Results show that the resulting internal energy would transfer in a wave manner with locally superimposing the so-called elastic 1st sound wave and the thermal 2nd sound wave. Besides, an interface between two dielectric
layers would play a significant role on the net energy transfer, even if the two layers were only dissimilar a little bit in their potential functions. This interfacial influence is even more noticeable with existence of defects and impurities. Although lifting temperature would decrease the contact resistance and increase the resistance of the layers lies between an interface, the contact resistance is still comparable to the layer’s resistance as the systematic temperature is up to the melting.
The interfacial effects lead to a difficulty in measuring the thermal properties using SThM, especially for an ultra-thin film sample. Mathematical models governing the solid-solid point contact heat transfer, as well as the thickness dependent film thermal conductivity, were proposed. Results show that as the film thickness is down to submicron scale, it is the surface and interface effects, instead of intrinsic bulk property, dominate the resulting film conductivity. The tip-film contact resistance Ri and film resistance Rf through the expression of Ri/(Ri+Rf) determines the error of the measured conductivity. Thus, the probe approach is appropriate for film conductivity measurement only when Ri<< Rf.
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