奈米尺度下材料表面光學行為分析與應用之研究

Abstract

奈米科技指的是對於奈米尺度下之特性加以研究、設計以及應用。本論文將探討材料於奈米尺度下之表面光學行為與其應用，包括設計不同的奈米結構以應用於環境淨化之光催化反應，以及碳化矽之原子級表面性質分析。在第一部份，我們開發出一奈米干涉共振腔結構，有效提升結構上金奈米粒子與氮摻雜二氧化鈦（N-TiO2）之吸收，增加可見光催化效率之元件。此結構可使入射光源得以被有效吸收，增加電子電洞對的產生，而N-TiO2與金奈米粒子之複合結構可以更加提高可見光催化的效果。另一方面，我們提出了單位光觸媒量反應效率之計算，光觸媒的使用量雖少但反應效率高，並且比較了不同文獻中之反應效率。 而在論文第二部份，本研究結合了光源之光效應與熱效應，並將之運用於光催化反應。我們利用奈米鐘乳石結構，可以有效吸收95%以上的寬頻光源並將之轉換為熱能，而此結構再結合N-TiO2，可在可見光下快速進行光熱催化反應。明顯優於一般基板與商用P25 TiO2粉末，可以快速的分解亞甲藍。 在論文最後一部份中，利用拉曼散射及可見光譜等非破壞光學檢測方式，檢測碳化矽之各種原子級表面性質，包括晶體型態、載子濃度、雜質、微孔洞及表面極性分析。其中微孔洞的分析是利用不同景深之拉曼雷射與物鏡搭配，可以從拉曼強度及波數的變化預估微孔洞之位置。在表面極性的判定，則使用減光法的方式。達到縮小拉曼訊號的來源深度，可以成功區分碳化矽晶片表面上只有單個原子層厚的矽面與碳面。

Nanotechnology is the study, design, manipulation and application of matter in nanoscale. In recent years, the properties of materials in nanoscale have attracted great attention in different fields. In this thesis, we studied the optical behaviors and applications of materials surface within nanoscale region. The main topics of the thesis include designing different nanostructures for photocatalytic reaction and analysing the surface behaviors of silicon carbide in atomic scale. In the first part, we developed an interference effect based nanocavity structure which could efficiently enhance the absorption of gold nanoparticles and N-doped TiO2 on the cavity structures. The nanocavity based structure could be applied for enhancing visible light photocatalytic reaction. Ihe cavity would increase the absorption of incident light and could effectively generate electron-hole pairs on the structures. Therefore, the combination of N-TiO2, gold nanoparticles, and nanocavity structure could dramatically enhance the efficiency of visible light photocatalytic reactions. We further calculated the photocatalytic efficiency of per unit amount of photocatalyst, and compare the result with previous studies. The result demonstrated that the amount of photocatalyst used in this study is few, however, the photocatalytic efficiency is very high. In the second part of the thesis, we combined the optical and thermal effects from light source and applied that to enhance the photocayalytic reaction. By using a nano-stalactites structure, up to 95% of the incident light could be absorbed and further converted to heat. Therefore the N-TiO2 on nanostructures could quickly react with methylene blue under visible light by photothermal-catalytic reaction. We found the reaction rate of the N-TiO2 on nanostructure was much higher than the commerical P25 TiO2 nanoparticles based samples. In the last part, we used non-destructive optical analysis methods including Raman scattering spectroscopy and visible-IR spectroscopy to analysis the surface properties of silicon carbide within nanoscale. The analyses included the polytypes, carries concentrations, impurities, micropipes and surface polarity of silicon carbide. By combining laser with different object lenses, the position of micropipes could be determined. In this study, we found the characterization surface polarity of silicon carbide could be conducted by attenuated power of Raman laser. With reduced power of Raman laser, the penetration depth could be effectively decreased, and the Raman signal contributed by surface region of SiC would be largely increased. By this method, we could successfully identify the silicon face or carbon face with atomic layer thickness on the surface of a silicon carbide wafer .