奈米尺度晶粒之碲化鉛薄膜的超低熱傳導率

Abstract

本論文主要在研究碲化鉛薄膜的熱傳導率，之前的研究顯示當材料大小接近於奈米尺度時，聲子會受到邊界散射導致材料的熱傳導率隨著尺寸降低而下降。在此研究中，我們沉積三種不同厚度的奈米尺度晶粒之碲化鉛薄膜，並以3 omega方法量測其熱傳導率。結果顯示在室溫下厚度為280 nm之薄膜的熱傳導率為0.29 W/m-K。此值僅是塊材尺度之碲化鉛之熱傳導率(k=2.4 W/m-K)的0.13倍，且碲化鉛薄膜之熱傳導率隨著晶粒尺寸下降而下降。其原因乃由於奈米尺度的晶粒限制聲子平均自由徑而造成熱傳導率隨著晶粒尺寸下降。另外，熱傳導率在300 K至500 K時，幾乎維持一定值，其原因可能是聲子的平均自由徑已接近原子之間的間距而不再改變，故限制熱傳導率為定值。

This study aims to investigate thermal conductivity of PbTe thin films with nano-scale grain size. Previous studies have shown that the effect of boundary scattering is more significant in nano-scale than in bulk, resulting in the decrease of thermal conductivity with decreasing system size. In this study, three omega method was adopted to measure the thermal conductivity of PbTe thin films with varying film thickness. The thermal conductivity of PbTe thin films decrease with decreasing grain size as a result of increased grain boundary scattering. A thermal conductivity of 0.29W/m-K was obtained for the 280 nm thick film at 300K, which is about 0.13 times of that of bulk PbTe. Furthermore, the thermal conductivity is temperature independent at high temperature, which may be due to that the phonon mean free path is already close to the spacing between atoms.