二氧化鈦奈米複合結構之電容與光催化特性研究

Abstract

二氧化鈦奈米管陣列為具有高化學穩定性、光電轉換特性之高比表面積結構，無論是應用於複合電容之領域，或是利用光催化特性應用於太陽能之領域，其皆扮演重要的角色。本研究嘗試以二氧化鈦奈米管陣列結構作為模板開發具有特殊結構之複合電容，並嘗試改善介電材料與奈米管結構之複合品質來提高電容表現。另一方面，本研究將不同陽極處理階段數之二氧化鈦奈米管陣列進行退火處理，藉由維持較完整的奈米管陣列結構來提升光觸媒對於可見光的催化活性。 在複合電容方面，本研究以陽極處理法製備高比表面積之二氧化鈦奈米管陣列結構，並透過濕化學蝕刻以及水熱法製程來調整結構以及化學組成，最後以原子層沉積法填入二氧化鉿完成二氧化鈦與高介電材料複合結構之製備。各項分析結果之搭配，我們發現較短的奈米管陣列結構，可在縮小尺度的情況下僅犧牲小部分之電容表現且介電材料二氧化鉿與奈米管陣列結構之接觸面積為影響電容表現之重要指標。電容表現之貢獻機制中，二氧化鈦材料在界面處之空乏區寬度變化所貢獻之空間電荷極化為影響電容表現之重要機制。 本研究在光催化特性探討方面，同樣是以陽極處理法所製備二氧化鈦奈米管陣列為模板，在不同溫度下進行退火處理後，較高的退火溫度雖然可具有較高的氧空缺濃度與氮摻雜程度、以及較高比例的Rutile相，進而降低較多的能隙值，但高溫的退火過程亦會使奈米管陣列結構有坍塌的現象而減少照光面積。本研究發現在紫外光波段下，一階段的陽極處理搭配較低溫之退火有比較好的表現；而兩階段的陽極處理搭配較高溫的退火將能在可見光波段下有良好的光催化能力。

Titania nanotube arrays (TNTs) is playing an important role in the field of composite capacitor and improvement of the efficiency of water splitting because of its high chemical stability and high aspect ratio. In this study, we try to develop the unique composite capacitor with special nanostructure from the TNTs. On the other side, The TNTs from one-step or two-step anodization was going through annealing treatment with different temperature. The optical and photoelectric properties to visible light of these photocatalysts would be improved when maintaining complete nanotube arrays structure. To produce composite capacitor, we synthesize TNTs with high aspect ratio from anodization treatment. The structure and chemical composition can be tuned by the combination of wet-etching process and hydrothermal treatment. Filling the nanotube arrays with HfO2 by ALD to produce the composite structure of TiO2 and high-K materials. From the results of several analysis, we found that the shorter nanotube arrays can scale down only with little decreased capacitance. The contact area of high-K material and nanotube arrays structure is the important index of the capacitor performance. And among the polarization mechanisms we proposed, space charge polarization from the width variation of the depletion layer is the most important.one. The other topic of this study is to investigate the photocatalytic ability of the annealed anodized TNTs. Higher annealing temperature can induce higher concentration of oxygen vacancies, extent of nitrogen doping and the ratio of rutile phase, and these are known as band gap narrowing factors. However, higher annealing temperature will make TNTs sintered to become rutile film layer and collapsed, which decreasing irradiated area. In conclusion, one-step anodized TNTs combining the low temperature annealing can perform well under UV light. The better photocatalytic performance can be achieved by the combination of two-step anodized TNTs and higher annealing temperature.