多孔奈米線之熱傳導分析

Abstract

本文主要是探討鑲嵌相異材料的鑲嵌式奈米線以及多孔隙的孔隙式奈米線之熱傳導行為。利用聲子輻射熱傳方程式(Equation of Phonon Radiative Transfer)描述聲子在直角座標系中，二維奈米結構裡強度的分布。當結構中存在兩種不同材料時，利用非彈性散異理論模式(Inelastic Diffuse Mismatch Model)，描述聲子通過相異材料界面所受到的界面熱阻。 鑲嵌式奈米線是利用兩種不同材料的奈米線，週期性排列而成的複合結構，其中雖然尺寸效應與界面熱阻的影響會增加熱阻，但因為嵌入的材料性質會使得整體熱傳導係數上升，進一步比較齊列式(Align)或交錯(Stagger)式複合奈米線對整體熱傳影響，結果顯示兩者誤差在3%以內，顯示材料排列方式對熱傳導性質影響有限。 多孔奈式奈米線中，假設孔隙中無任何形式的熱傳，因此聲子碰撞孔隙邊界後會發生鏡反射。齊列式多孔奈米線中，孔隙與孔隙間距高寬比會影響聲子散射強度，夾雜尺寸效應後使得此影響更為明顯。比較齊列(Align)和交錯(Stagger)兩種排列方式，當孔隙間距高寬比大於或等於1.33，則排列方式對熱傳導係數沒有影響；當孔隙間距高寬比小於1.33，則交錯式多孔奈米線較能有效攔阻聲子運動。

This study discusses microscale heat transfer phenomena in two dimensional nanostructures based on the microscopic heat transport theory. The phonon Boltzmann equation model is established to analyze the effects of the wire size on the thermal conductivity of nanocomposites of nanowires embedded in a host semiconductor material and nano porous silicon wire. First, we predict the thermal conductivity of the arranged in align and stagger rows nanocomposites of nanowires. The Inelastic diffuse mismatch model is utilized to simulate the phonon transfer across the interface between two different materials and the results show that the negligible sensitivity of thermal conductivity to wire arrangement. Second, we present the numerical analysis on estimating the thermal conductivity of nano porous silicon wire. It shows that the size between the pores affects the probability of the phonon collide with the pores boundary in align model. In stagger model, phonon will be blocked up the path through the wire. It also means that the larger size of the pores, the lower thermal conductivity of the wire. The results of this study can be used to direct the development of high efficiency thermoelectric materials.