Frequency-domain Raman method to measure thermal diffusivity of one-dimensional microfibers and nanowires
Frequency-domain Raman method to measure thermal diffusivity of one-dimensional microfibers and nanowires
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频域拉曼法测量一维微纤维和纳米线的热扩散率
DOI：
10.1016/j.ijheatmasstransfer.2019.01.057
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发表时间：
2019-05
影响因子：
5.2
通讯作者：
Zhang Xing
中科院分区：
文献类型：
--
作者：
Li Qinyi;Takahashi Koji;Zhang Xing
单个微纳米材料的热性能测量一直是非常具有挑战性的，而测量方法的发展对于微纳米尺度传热的实验研究至关重要。在此，我们提出了一种非接触式频率域拉曼方法来测量单个一维微纤维和纳米线的热扩散率，而不需要知道激光吸收率。利用余弦波调制激光对样品进行加热，同时通过样品的拉曼波段位移检测激光强度加权的时空平均温度。建立了考虑高斯激光分布和接触热阻的周期性加热瞬态热传导模型，并在频域上进行了解析求解。通过改变激光调制频率和光斑大小，可以通过归一化技术消除激光吸收系数，提取出高灵敏度的热扩散系数。通常，如果热扩散率为10−4m2/s，我们需要使用10 Hz的调制频率来测量毫米长的微光纤，使用~ MHz的频率来测量微米长的纳米线。我们还证明了任何一种周期激光调制都可以被分解成一系列余弦模式，并且很容易用这种频域方法分析，这可以大大拓宽瞬态拉曼技术的应用范围。
Thermal property measurement of individual micro- and nano-materials has been very challenging and the development of measurement methods is crucial for the experimental investigation of microscale and nanoscale heat transfer. Here we present a noncontact frequency-domain Raman method to measure thermal diffusivity of individual 1D microfibers and nanowires without the need of knowing laser absorptivity. Cosine-wave modulated laser is used to heat the sample, while the laser-intensity-weighted spatiotemporal average temperature is simultaneously detected from the sample’s Raman band shift. Transient heat conduction models under periodic heating are established and analytically solved in the frequency domain with considerations of the Gaussian laser distribution and thermal contact resistance. By varying the laser modulation frequency as well as the laser spot size, we can eliminate the laser absorptivity by a normalization technique and extract the thermal diffusivity with high sensitivity. Typically, if the thermal diffusivity is on the order of 10−4m2/s, we need to use the modulation frequencies on the order of 10 Hz to measure millimeter long microfibers, and ∼MHz frequencies to measure micrometer long nanowires. We also demonstrate that any kind of periodic laser modulation can be decomposed to a series of cosine modes and readily analyzed by this frequency-domain approach, which can greatly broaden the applications of transient Raman techniques.
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