一維材料之非局域性熱傳導現象

Abstract

近年來，有理論和實驗指出低維度材料有著特殊的熱傳導現象。這本篇論文中，我們將探討一維材料包含矽鍺均勻合金奈米線和奈米碳管在室溫下的熱傳導非局域性效應。前者是傳統認知的波動型(彈道型)熱傳導現象6，然而後者確是異常型的熱傳導現象7，兩者皆在一維尺度上不遵守古典的傅立葉熱傳導現象。理論上來說非局域性效應會在彈道式熱傳導被顯現。因此，為了更進一步探索這兩種特殊的熱傳導性質，我們使用微米尺度的三端點量測裝置(約10微米至150微米)進行非局性效應的探討。 論文第一部份，我們將陳述熱傳導的背景並簡單的介紹實驗中會使用到的實驗技巧包含掃描式電子顯微鏡、溫度係數量測已及聚焦離子束系統。 論文第二部分，我們主要探討在矽鍺奈米線內波動型熱傳導所具有的非局域現象並做定量和定性上的分析，並發現其非局域大小可達30%。在對照實驗上，我們量測氧化鎵奈米線，因為其熱傳導現象屬於傅立葉古典的熱擴散方式，實驗上證明無非局域性效應的發生。最後意外地，我們在矽奈米線中也發現疑似非局域性效應 論文第三部分，我們探討單壁奈米碳管的異常熱傳導現象是否有非局域效應的發生，我們使用兩倍頻率的分析方式量測進而發現長度為150微米時發現並無非局域熱傳導現象的發生。

Recently, there are many studies suggesting the presence of unusual thermal transport in low dimensional systems. In this thesis, we will investigate non-local effect of one-dimensional materials, including Silicon-Germanium (Si-Ge) and Carbon Nanotube (CNT) at room temperature. The former is conventional ballistic thermal conduction6, whereas the latter belongs to anomalous thermal conduction7. Both of them are known to violate the Fourier’s law of thermal conduction and display a length-dependent thermal conductivity. In order to investigate the non-local property of thermal transport, we used thee-terminals thermal devices separated by various distances (10μm~150μm). In the first part of the thesis, we will provide the background knowledge and have a brief introduction to thermal device and experiment techniques, including SEM skill, temperature coefficient measurements and Focused Ion Beam techniques. In the second part of the thesis, we will mainly analyze heat flow in ballistic regime and calculate thermal conductance in Si-Ge alloy nanowire. The non-local effect value we discovered is at least 30%. Additionally, we measured 〖Ga〗_2 O_3 nanowires as a controlled experiment for its diffusive, local thermal transport. Interestingly, we also found that the non-local phenomena could exist in Silicon nanowire. In the third part of the thesis, we hope to investigate whether the anomalous thermal transport observed in single-wall carbon nanotube (SWCNT) could have similar non-local effect. We employed a 2ω measurement methods and found that for a length of SWCNT exceeding 150μm, its thermal transport is almost local.