鍺誘發二氧化鈦奈米線成長機制及其應用之研究; Germanium Enhanced Titanium Dioxide Nanowires Growth Mechanism and its Applications

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Title:	鍺誘發二氧化鈦奈米線成長機制及其應用之研究;Germanium Enhanced Titanium Dioxide Nanowires Growth Mechanism and its Applications
Authors:	林子傑;Lin,Tzu-chien
Contributors:	材料科學與工程研究所
Keywords:	二氧化鈦;奈米線;鍺;場發效應;TiO2;Nanowires;Ge;Field emission
Date:	2013-07-15
Issue Date:	2013-08-22 11:44:15 (UTC+8)
Publisher:	國立中央大學
Abstract:	在過去十幾年裡，因為二氧化鈦有著優異的特性，例如：低成本、化學穩定性、無毒、良好的催化效應等，而被廣泛的研究。除此之外，一維的二氧化鈦奈米線可以提供較大的面積讓電子電洞對做結合以及在一維方向上傳遞電子並結合，這使二氧化鈦奈米線常常被應用在觸媒、感測器、染料敏化太陽能電池、鋰電池等等。而在製備二氧化鈦奈米線主要有兩種最為普遍的方式，分別為水熱法以及利用熱蒸鍍的方式配合固-液-氣的成長機制來做製備，雖然以水熱法製備二氧化鈦奈米線是相對簡單，反應的溫度只需要100℃左右的溫度就能完成反應，但在低溫下完成的奈米線，其結晶度是不足的，必須經過後續複雜的處理來改善結晶性的問題。除此之外，利用固-液-氣的成長機制來製備二氧化鈦奈米線必須先利用金屬催化物幫助奈米線的元素產生共析現象，才有辦法完成奈米線的成長，會使得奈米線的頭部會殘留金屬催化物，而這樣的殘留物會造成奈米線的導電率與能隙的改變，破壞了材料原有的特性。在本論文中提出了一種利用元素鍺做為催化物誘發二氧化鈦奈米線，以直接的方式成長含有大範圍、均勻性高且不含金屬催化物殘留的二氧化鈦奈米線並討論不同厚度的鍺以及不同溫度下對奈米線成長造成的影響。藉由實驗結果得知材料的結構總共包含的四大部分，有頂部至底部分別為：二氧化鈦奈米線、二氧化鈦晶粒層、二氧化鍺晶粒層以及最底部的鈦金屬板。在二氧化鈦奈米線成長機制的探討會利用X-ray繞射分析儀、掃描式電子顯微鏡、穿透式電子顯微鏡以及拉曼光譜分析材料的成分分佈、晶體結構、試片表面形貌以及奈米線的表面形貌，進而得知鍺元素在實驗中扮演的角色。本論文最後量測二氧化鈦奈米線的場發性質、光催化性質以及潤濕性，讓人意外的，二氧化鈦奈米線有著相當不錯的場發性質，而在光催化性質以及潤濕性也得到良好性質，皆有著不錯的表現。 Titanium dioxide has been widely studied over the past decades owing to its excellent properties of low cost, chemical stability, nontoxicity, catalysis and so on. Additionally, one-dimensional TiO2 nanowires can provide a large surface area for effectively collecting photons or electrons. Meanwhile, enabling charge transfer along single direction thus the facilitation of carrier collections. TiO2 nanowires are frequently used in catalysis, sensors, dye-sensitized solar cells, Li-ion batteries and so on. Among them, hydrothermal method and thermal evaporation with VLS mechanism are two typical synthetic methods for preparing TiO2 nanowires. However, hydrothermal method needs to be followed by complex post-treatment in order to improve the poor crystallinity. Using the VLS mechanism also remain the metal-catalysts on the top of TiO2 nanowires. Therefore, this research investigated Ge to enhance directly synthesis of large scale, uniform, well-aligned and free-catalyst TiO2 nanowires on the Ti substrate at various temperatures and thickness of Ge layer by horizontal tube furnace. The material structure included the TiO2 nanowires, TiO2 layer, GeO2 layer and Ti foil. It shows that the growth mechanism of TiO2 nanowire substrates utilize the x-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM) and Raman spectroscopy, which pertain to the composition distribution, crystal structure, surface morphology and nanowire morphology to obtain the function of Ge in this research. Finally, the results provided a new catalytic effect of Ge on the growth TiO2 process, which enhance directly synthesis of large scale, uniform, well-aligned and free-catalyst TiO2 nanowires on the Ti substrate. We figure out the function of Ge to play in the reaction. Additionally, the TiO2 nanowires display an outstanding field emission property, well photocatalytic activity and wettability.
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