[论文解读] Temperature dependence of electrical and thermal conduction in single silver nanowire

Zhe Cheng, Longju Liu+2 more|arXiv (Cornell University)|Nov 27, 2014

Nanomaterials and Printing Technologies参考文献 30被引用 6

一句话总结

本研究采用稳态电热法，将温度降至35 K，研究了单根银纳米线的温度依赖性电输运与热输运特性。与体相银相比，其电电阻率提高了四倍，热导率降低了55%，德拜温度降低36%（151 K），表明声子显著软化；同时，较大的剩余热阻表明晶界处电子散射占主导地位。

ABSTRACT

Silver nanowires have great application potential in fields like flexible electronic devices, solar cells and transparent electrodes. It is critical and fundamental to study the thermal and electrical transport properties in a single silver nanowire. In this work, the thermal and electrical transport in an individual silver nanowire is characterized down to 35 K with the steady state electro-thermal technique. The results indicate that, at room temperature, the electrical resistivity increases by around 4 folds compared from that of its bulk counterpart. After fitting the temperature dependent electrical resistivity curves with the Bloch-Grüneisen formula, the Debye temperature (151 K) of the silver nanowire is found 36% lower than that (235 K) of bulk silver, confirming strong phonon softening. The thermal conductivity is reduced by 55% compared with that of its bulk counterpart at room temperature and this reduction becomes larger as the temperature goes down. To explain the opposite trends of thermal conductivity (\k{appa}) ~ temperature (T) of silver nanowire and bulk silver, a unified thermal resistivity is used to elucidate the electron scattering mechanism. A large residual unified thermal resistivity for the silver nanowire is observed while that of the bulk silver is almost zero. The same trend of variation against T indicates that the silver nanowire and bulk silver share the same phonon-electron scattering mechanism. Additionally, due to phonon-assisted electron energy transfer across the grain boundaries, the Lorenz number of the silver nanowire is found much larger than that of bulk silver and decreases with decreasing temperature.

研究动机与目标

• 理解单根银纳米线在低温下的基本热输运与电输运特性。
• 量化银纳米线在电电阻率与热导率方面偏离体相银行为的程度。
• 识别导致纳米线中输运性能降低的内在散射机制。
• 研究晶界与电子-声子相互作用在调控热输运与电输运中的作用。

提出的方法

• 采用稳态电热法测量单根银纳米线从35 K到室温的电输运与热输运性能。
• 将温度依赖的电电阻率数据拟合至Bloch-Grüneisen公式，以提取德拜温度。
• 通过施加电流下测得的电压与温度梯度计算热导率。
• 采用统一热阻模型，比较纳米线与体相银中电子散射的贡献。
• 分析洛伦兹数以评估电子-声子耦合及能量传递效率。
• 与体相银对比结果，以分离尺寸效应与微观结构的影响。

实验结果

研究问题

• RQ1 单根银纳米线的电电阻率如何随温度变化？与体相银相比有何差异？
• RQ2 银纳米线热导率降低的根源是什么？与体相银相比。
• RQ3 银纳米线的德拜温度与体相银相比如何？这对其声子软化意味着什么？
• RQ4 晶界在纳米线中电子散射与热阻中起什么作用？
• RQ5 银纳米线中的洛伦兹数与Wiedemann-Franz定律的偏离程度如何？其随温度如何变化？

主要发现

• 在室温下，银纳米线的电电阻率比体相银高出约四倍。
• 银纳米线的德拜温度为151 K，比体相银的235 K低36%，表明存在显著的声子软化。
• 在室温下，纳米线的热导率比体相银降低55%，且在低温下降低程度进一步加剧。
• 纳米线中观察到较大的剩余统一热阻，而体相银中几乎为零，表明晶界处存在强烈的电子散射。
• 纳米线中的洛伦兹数显著高于体相银，且随温度降低而减小，表明晶界处存在声子辅助的电子能量传递。
• 纳米线与体相银在热导率上呈现相反的温度趋势，这一现象通过统一热阻模型得到解释，证实了共享的电子-声子散射机制。