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Thermal transport from nanoscale heat-sources and in nano-structured materials.

机译：来自纳米级热源和纳米结构材料的热传递。

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摘要

Nano-structured materials find practical applications in microelectronics, optoelectronics, micro-mechanical-electrical systems, thermoelectric energy-conversion and lab-on-a-chip devices, to name a few. Fundamental research on thermal transport properties at length scale where the classical transport laws are not applicable anymore and the effective transport properties of nano-structured materials are affected primarily by the characteristic length and interface properties in these low-dimensional materials is crucial for engineering high performance devices. Even though reduction in thermal conductivity within a nano-structure has been extensively studied, experimental investigation of heat-dissipation from a nanoscale heat-source or "hot-spots" to its bulk surrounding substrate has been virtually unexplored. A technique based on joule heating thermometry was developed to capture the non-equilibrium thermal transport across nanowires deposited on silicon substrate. Employing this technique the effect of heater size on the effective thermal conductivity of bulk substrate was shown for the first time in silicon as a function of temperature. The effective thermal conductivity of bulk silicon substrate, measured by a heater-wire with characteristic width ∼ 96 nm, varied from a strongly reduced value of 57 W/mK at 300 K to only 77 W/mK at 80 K in sharp contrast to that of bulk silicon which ranges from 148 W/mK--1292 W/mK for the same temperature range. A proof-of-concept demonstration of the DC measurement of thermal resistance from nanowires using AFM based 'moving' probe technique was performed. Extensive study on improving the spatial resolution to map any local variation of thermal resistance along the length nanoscale heat-source is the objective of future studies.;The second part of the thesis investigates thermal transport in two nanostructured materials, polymer infiltrated aligned carbon nanotube arrays and Si/SiC superlattices. Thermal transport in polymer infiltrated multiwalled carbon nanotubes arrays showed at least 600% enhancement in thermal conductivity of the nano-composite compared to the matrix. Aligning the tubes is critical to limit the scattering at the nanotube-polymer interface and obtain the measured enhancement along the alignment direction. Nevertheless, in the next system investigated (superlattice system), resistance across multiple interfaces stemming from numerous interface-phonon scattering usually proves beneficial in enhancing thermoelectric figure of merit. Temperature dependent thermal conductivity of Si/SiC superlattices was studied for the first time employing a differential 3? method. Results showed a strong reduction in the cross-plane thermal conductivity varying from 1--2 W/mK which much smaller than that of the constituent materials. Estimations of the relative contributions of interface and intrinsic layer thermal resistance based on microscopic phonon transport models indicated that mean free path reductions within the superlattice layers were responsible for the observed experimental trends. The phonon mean free path was strongly reduced by structural disorder in each of the superlattice layers as confirmed by high resolution transmission electron microscopy.
机译：纳米结构材料在微电子，光电子，微机电系统，热电能量转换和片上实验室设备等方面都有实际应用。在不再适用经典传输定律且纳米结构材料的有效传输特性主要受这些低尺寸材料的特征长度和界面特性影响的长度尺度上的热传输特性的基础研究中，这对工程高性能至关重要设备。尽管已经广泛研究了纳米结构内的导热率降低，但是实际上还没有进行从纳米级热源或“热点”到其周围的大体积衬底散热的实验研究。开发了一种基于焦耳加热测温的技术，以捕获沉积在硅基板上的纳米线之间的非平衡热传输。利用这种技术，首次显示了加热器尺寸对大块衬底有效导热率的影响，该影响是温度随硅的变化而变化的。通过特征宽度约为96 nm的加热丝测量的块状硅衬底的有效导热率，从300 K时的57 W / mK的强烈降低值到80 K时的77 W / mK的大幅降低，与之形成鲜明对比。在相同温度范围内，大块硅的数量范围为148 W / mK--1292 W / mK。进行了使用基于AFM的“移动”探针技术对纳米线的热阻进行直流测量的概念验证。广泛研究提高空间分辨率以绘制热阻沿纳米尺度热源的任何局部变化的图谱是未来研究的目标。本论文的第二部分研究了两种纳米结构材料中的热传递，聚合物渗入排列的碳纳米管阵列和Si / SiC超晶格。与基质相比，聚合物渗透的多壁碳纳米管阵列中的热传输显示出纳米复合材料的导热系数至少提高了600％。对准管是限制在纳米管-聚合物界面处的散射并获得沿对准方向测得的增强作用的关键。但是，在下一个研究的系统（超晶格系统）中，由大量界面声子散射引起的跨多个界面的电阻通常被证明有助于提高热电性能。 Si / SiC超晶格的温度依赖性导热系数是首次使用差分3？方法。结果表明，横断面热导率大大降低，范围从1--2 W / mK，远小于构成材料的热导率。基于微观声子传输模型的界面和本征层热阻的相对贡献估计表明，超晶格层内的平均自由程减少是观察到的实验趋势的原因。高分辨率透射电子显微镜证实，每个超晶格层中的结构紊乱都大大降低了声子平均自由程。

著录项

  • 作者

    Mazumder, Monalisa.;

  • 作者单位

    Rensselaer Polytechnic Institute.;

  • 授予单位 Rensselaer Polytechnic Institute.;
  • 学科 Engineering Chemical.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 113 p.
  • 总页数 113
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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