基于拉曼光谱的纳米线热输运特性研究

Nanowires have great promising applications in micro/nano electronics, photoelectric conversion and thermoelectric conversion due to their excellent merits. Thermophysical properties of nanowires and thermal transport characteristics in nanoscale are the fundamental parameters for the thermal design of micro/nano devices. However, due to the size effects, thermophysical properties of nanowires are significantly different from their corresponding bulk values. Moreover, the thermometry methods applied in macro scale no longer meet the requirement of nanowire measurements. The project aims at measuring the thermophysical properties of nanowires, studying the length dependent thermal transport characteristics, and finally providing the guidance for thermal design of micro/nano devices. Two novel noncontact methods, laser flash-Raman spectroscopy methods and “T” type Raman method will be proposed and the properties of nanowires will be measured in the temperature range from 200 K to 500 K, including thermal diffusivity, thermal conductivity, and laser absorption coefficient. Using the advantage that the focused submicron laser spot from Raman system serve as both local heater and local temperature sensor, length dependent thermal conductivity of individual FWCNT and phonon transport characteristics in confined space at different temperature will be studied.

纳米线材以其优异的性能在微纳电子、光电转换和热电转换等领域有着巨大的应用潜力。纳米线的热物性和纳米尺度下的热输运特性是微纳器件热设计的关键，然而由于尺度效应的存在，纳米线的热物性和热输运特性与其对应的体材料相比发生了显著的变化。另外，宏观尺度下的热物性测量技术不能适用于纳米线的热物性测量。项目旨在准确测量纳米线热物性，研究纳米线热输运的尺度效应，为微纳器件热设计提供依据。项目拟开发拉曼闪光法和非接触式“T”形拉曼法，在200-500 K温度区间非接触式测量单根纳米线的热扩散率、热导率和激光吸收系数；利用拉曼光谱的聚焦亚微米光斑同时进行局部加热和局部测温功能，实现利用同一根少壁碳纳米管（FWCNT）研究热导率随热输运特征长度的变化规律，揭示不同温度条件下声子在受限空间内的输运特性。

纳米线材以其优异的电学、光学和热学性能在前沿科技领域有着巨大的应用潜力。纳米线的热物性和纳米尺度下的热输运特性是微纳器件热设计的关键，然而由于尺度效应的存在，纳米线的热物性和热输运特性与其对应的体材料相比发生了显著的变化。然而，宏观尺度下的热物性测量技术不能适用于纳米线的热物性测量。本研究利用拉曼光谱的非接触式局部加热和测温功能，开发具有广泛适用性的非接触式测量微纳米线热物性的方法，研究热导率随热输运特征长度的变化规律。本研究开发了拉曼闪光法并进一步提出了差分拉曼闪光法，通过比较单根直径为10 μm的白金线热扩散率的测量值与标准值验证了该方法的可行性，进一步利用已验证的差分拉曼闪光法研究了平均直径为385 nm的硅纳米线（SiNW）热扩散率随温度的变化规律，结果表明纳米线热扩散率显著低于体材料值。开发了“T”形拉曼法，通过测量白金线（d=25 μm）热导率验证了该方法的可行性，利用该方法测量了单根石墨纤维（d=17 μm）和单根碳化硅纳米线（d=465 nm）的热导率。在不同环境温度下测量了同一根单壁碳纳米管（SWCNT，d=1.33 nm）不同长度悬架段的热导率，结果表明热导率随特征长度的增大先增加后收敛于定值。温度对热导率的影响随样品特征长度的缩短而减弱。