奈米材料熱電的傳輸性質

奈米材料在近幾年受到極大的重視,不論是在理論計算或實驗結果都顯示出低維度材料具有與塊狀材料迥異的物理特性，特別是關於在低維度材料之中之聲子與電子以及聲子與介面間的交互作用為一非常有趣之研究課題。我們將針對奈米材料中的電傳導性質以及熱傳導性質進行量測，已期能深入了解其基本的物理特性。技術可以算是最廣泛被應用在一維以及二維的材料熱傳導研究的量測技術。我們架設了兩組不同的量測法分別可以對薄膜以及單一奈米線進行熱傳導率的實驗量測。相較於其他的量測方法，技術可提供更多的量測資訊，這對於了解在低維度材料中電子與聲子的行為有著極重要的幫助。在二維系統中，我們選擇了CuFeSe2薄膜做為我們的研究對象，我們製備了一系列的高結晶度CuFeSe2薄膜，並利用技術精準的量測薄膜的熱傳導性質以及西貝克係數，在此研究結果中我們發現此一系列薄膜的熱傳導與其結晶度有著非常高的相關性，結晶性越好的薄膜其熱傳導性質也越好。且由薄膜與基板的介面所貢獻的熱阻也經過仔細的分析並由結果中扣除，以得到精確的薄膜熱傳導係數。而在一維的系統中，我們也製備了一系列單晶的Bi2-xSbxTe3-y 奈米線(線徑由150到890奈米)做為我們熱電性質的研究對象，在此系統中，我們發現了聲子與表面的散射增強了，而且此增強的強度是隨著奈米線的線徑縮小而增加的，此一現象在由聲子所貢獻的熱傳導現象中非常的顯著，由其是在低溫的區域，由於聲子的平均自由徑增加了，因而表面散射對於聲子所貢獻的熱傳導造成更明顯的抑制作用。而利用我們所設計的量測平台，同一根奈米線的西貝克係數以及電傳導特性也可同時被量測出來。結果指出影響奈米線的西貝克係數以及電阻率的主要因素是來自於組成成分差異所造成。

關鍵字

奈米；熱傳導；熱電；薄膜；鉍碲

並列摘要

The low-dimensional materials exhibit a lot of innovative behaviors different from the bulk materials. The interactions of phonon-electron, phonon-interface, and phonon-grain boundary in low dimension materials attracted a lot of attentions in the research society. This initiated my motivation to investigate the electrical and thermodynamic properties in low dimensional systems for understanding their fundamental physics. One important measuring technique is the 3ω method, which can be applied to evaluate the thermal conductivity for low dimensional systems. In this work, the techniques have been developed to measure the cross-plane and in-plane thermal conductivity of a thin film and the longitudinal direction thermal conductivity of an individual nanowire. By comparison with other methods, the techniques yield more information, which is very helpful for understanding the behavior of phonon and electron in low dimension materials. For two-dimensional system, we have measured the cross-plane thermal conductivity of CuFeSe2 thin film which is considered to be the photoelectric material. The results indicate thermal conductivity of the films is strongly dependent on film crystallization, the better crystallization the higher thermal conductivity. In the meantime, the interfacial thermal resistance between film and substrate should also be taken into account for obtaining accurate total thermal conductivity. For one-dimensional system, a series of single crystalline Bi2-xSbxTe3-y nanowires (150 - 890 nm) were fabricated for the thermoelectric properties measurement. The phonon thermal conductivity decreases as the wire diameter reduces at low temperatures, indicating the enhancement of boundary scattering in one-dimensional system. The Seebeck coefficient and electrical resistivity were also measured for the same nanowire subsequently. The results show the Seebeck coefficient and electrical resistivity are greatly dependent on the composition of the nanowires.

並列關鍵字

nanowire ； thermal conductivity ； thermoelectric ； thin film ； BiSbTe ； Bi1-xSbxTe3

參考文獻

3 B. Yang, J. L. Liu, K. L. Wang, and G. Chen, " Simultaneous Measurements of Seebeck Coefficient and Thermal Conductivity Across Superlattice," Applied Physics Letters 80 (10), 1758-1760 (2002).

5 T. Borca-Tasciuc, A. R. Kumar, and G. Chen, " Data Reduction in 3 Omega Method for Thin-film Thermal Conductivity Determination," Review of Scientific Instruments 72 (4), 2139-2147 (2001).

6 L. D. Hicks and M. S. Dresselhaus, "Thermoelectric Figure of Merit of a One-dimensional Conductor," Physical Review B 47 (24), 16631-16634 (1993).

7 Yu-Ming Lin, Xiangzhong Sun, and M. S. Dresselhaus, "Theoretical Investigation of Thermoelectric Transport Properties of Cylindrical Bi Nanowires," Physical Review B 62 (7), 4610-4623 (2000).

8 Akram I. Boukai, Yuri Bunimovich, Jamil Tahir-Kheli, Jen-Kan Yu, William A. Goddard Iii, and James R. Heath, " Silicon Nanowires as Efficient Thermoelectric Materials," Nature 451 (7175), 168-171 (2008).

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奈米材料熱電的傳輸性質

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