探索一維熱傳導之現象

Investigations of One Dimensional Heat Transport

吳奇勳(Chi-Hsun Wu)

指導教授 ： 陳智泓

共同指導教授 ： 張之威(Chih-Wei Chang)

國立臺灣大學/理學院/應用物理所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.02203

摘要

為探討聲子在熱傳導之機制,近年許多研究對低維度熱傳系統的實驗及理論多有探討,但基於高長度奈米物質製程上困難以及訊號強度隨長度遞減的問題,長度對聲子傳遞熱的影響的實驗仍是缺乏的。然而,由於奈米碳管製程技術的進步,現以氣流導向的化學氣相沉積法已能長出長至半米的單壁奈米碳管9,加之本實驗室所研發之高鑑別率的兩倍頻熱傳導量測方法10,使近似一維度的熱傳導實驗能夠完成。本文探討熱導率在奈米碳管隨長度的關係以及提出了量測熱傳導不對稱性之新的實驗方法。
在論文的一部分,將介紹奈米碳管的特性及製程,以及實驗樣品的製備和實驗原理。而後在第二章,我們量測不同長度(2μm~1mm)奈米碳管之熱導率,發現了其值隨長度發散的現象。這個現象打破了傅立葉定律的描述, 有助於我們對熱傳導理論有新的了解。我們亦將從各種方面嚴格檢視我們實驗結果,包含了對輻射熱發散,接觸電阻,量測電訊號之頻率影響多加探討,確立實驗結果的可靠信。
論文的第三章,我們提出了量測熱傳導不對稱性的四倍頻法,理論上其可大幅改進傳統測量方法。此方法相關的參數之間的關係被探討,並提供樣本量測結果。雖然仍有些問題需要克服,但我們認為此方法極有潛力在熱傳導不對稱性上帶給我們更多的發現。

關鍵字

聲子 ； 奈米碳管 ； 熱傳導 ； 熱導率 ； 傅立葉定律 ； 化學氣相沉積法 ； 異常熱傳導

並列摘要

To investigate the mechanism of phonon in thermal transport, recently, many researches have studied1, both experimentally and theoretically, on heat conduction in low dimensional systems, but due to the difficulties of synthesis of long-length nanomaterial and the decay of signal with the length, the experiments on length dependence of heat conduction by phonons are still few. After the improvement on the synthesis of carbon nanotube (CNT), single wall carbon nanotube (SWCNT) with length about half meter can be produced by flow guided chemical vapor deposition9. Besides, the highly sensitive double frequency ( 2 ω ) method we invented10 made the experiment of heat conduction in quasi-one dimensional system possible. In this thesis, we investigated the length dependence of thermal conductivity and proposed a new method to measure the asymmetric phenomena on heat conduction.
In the second chapter of the thesis, the properties and synthesis of CNT will be introduced, followed by the sample preparation and experimental principle. In chapter three, we measured the thermal conductivity of CNTs with different length (2μm~1mm), and verified that the thermal conductivity diverges with increasing length. This phenomenon violates the Fourier’s law, which may help us understand thermal transport theory better. We also check our result carefully in many aspects, including the discussion on radiation heat dissipation, contact resistance, the frequency dependence of electric signals, to ensure the validity of experimental results.
In the fourth chapter, we proposed a 4ω method for detecting asymmetric heat conduction, which can theoretically improve traditional method significantly. The details of this method are discussed, and the experimental results are provided. Although there are some mysteries need to be understood, we believe that this method is promising for bringing new findings on asymmetric heat conduction.

並列關鍵字

phonon ； carbon nanotube ； heat conduction ； thermal conductivity ； Fourier’s law ； chemical vapor deposition ； anomalous heat conduction

參考文獻

1 Wingert, M. C. et al. Thermal conductivity of ge and ge-si core-shell nanowires in the phonon confinement regime. Nano letters11, 5507-5513 (2011).

2 Li, D. Y. et al. Thermal conductivity of individual silicon nanowires. Appl. Phys. Lett.83, 2934-2936 (2003).

3 Li, D. Y., Wu, Y., Fan, R., Yang, P. D. & Majumdar, A. Thermal conductivity of Si/SiGe superlattice nanowires. Appl. Phys. Lett.83, 3186-3188 (2003).

4 Hochbaum, A. I. et al. Enhanced thermoelectric performance of rough silicon nanowires. Nature451, 163-165 (2008).

5 Chen, R. K. et al. Thermal conductance of thin silicon nanowires. Phys. Rev. Lett.101, 105501 (2008).