以非平衡態分子動力學方法研究奈米鋁線的聲子熱導率

Abstract

我們利用非平衡態分子動力學方法來研究奈米接面的聲子熱傳導性質，也考慮在低溫時，基於Bose-Einstein distributions的量子修正。在塊材的情形，熱導率與材料的形狀無關；但與此不同的是，奈米接面的熱導率是與長度和截面積有關係的。為此，我們計算了連接在兩個熱儲之間的奈米鋁線，我們系統性的研究在不同的溫度下，熱導率與長度和截面積的關係。我們觀察到在低溫時，熱導率與溫度為正比關係，而高溫時，熱導率與溫度的關係相對比較弱。在我們計算的所有溫度下，熱導率隨著截面積和長度的增加而上升。我們也觀察到在高溫時，奈米接面會變的不穩定，高溫會使得奈米結構變成錐狀，也因其幾何結構的關係而降低熱導；甚至奈米接面也可能斷裂。

We investigate the phonon’s thermal current in nanoscale junctions using classical nonequilibrium molecular dynamics simulations. The quantum mechanical corrections due to Bose-Einstein distributions are also considered in low-temperature regime. The thermal conductivity of bulk material is a material specific property which is independent of the size of sample. In sharp contrast, the thermal conductivity is relevant to the lengths and cross sections in nanoscale junctions. To see this point, we calculate the thermal conductivity of aluminum nanowires connecting to two temperature reservoirs. We systematically investigate the dependence of thermal conductivity on lengths and cross-sectional areas in aluminum nanowires in a wide range of temperatures. We observe that the thermal conductivity is proportional to temperature in the low-temperature regime, while the dependence of thermal conductivity on temperature is relatively weak in the high-temperature regime. For all temperature ranges, the thermal conductivity increases with the increasing nanowire cross-sectional area, and increases with the increasing nanowire length. We also observe instability of nanojunctions in the high-temperature regime due to thermal fluctuations. High temperatures can result in a cone shape structure in the aluminum nanowires which decrease the magnitudes of thermal conductivity due to geometrically constriction, and can even break nanojunctions.