準分子雷射處理對於二氧化鈦奈米管陣列之型態與結構之影響

Abstract

結晶型二氧化鈦奈米管陣列(TNAs)近年來受到廣大的矚目與應用；其中在各種結晶技術中，準分子雷射退火由於其快速與低溫的特性，而成為受重視的退火技術。而在此研究中，將對於雷射退火之功率(fluence) 與頻率 (number of laser pulses)等退火條件對於二氧化鈦奈米管陣列的結晶性，表面形態和電子架構進行研究與討論。 在此研究中，以0.5 wt% NH4F和3 wt% H2O 的乙二醇(ethylene glycol, EG)溶液為電解質，進行陽極處理以形成高深寬比的二氧化鈦奈米管陣列。實驗在室溫下使用兩個電極式電化學系統(陰極為SS304不鏽鋼),在20V恆定的直流電壓為反應24小時。之後，在室溫與大氣下進行二氧化鈦奈米管陣列之準分子雷射退火。處理完之樣品將以X光繞射 (XRD)、掃描電子顯微術(SEM) , X光近緣結構(XANES) 與以及拉曼光學進行材料分析與討論。 XRD 結果顯示準分子雷射之頻率少於9000 shots，在功率為0.067 和0.133 Jcm-2之間所形成的TNAs 為anatase 相，當從0.133 Jcm-2增加到0.4 Jcm-2時，TNAs 的相轉變成anatase 和rutile 相。另外，TNAs 以雷射在0.1 Jcm-2的功率下，頻率少於9000時將從非晶相改變到anatase。換句話說，當頻率比9000高時，在TNAs上的雷射退火從非晶相轉變到anatase 和rutile相。FESEM 表面型態顯示TNAs 表面的損害隨著功率增加與頻率增加而更加嚴重。經由上述結果，雷射所引起的相轉變機制將以雷射理論和結晶動力學來討論。另外，TNAs結晶像的定量分析將使用XRD 結果與理論加以計算與討論。此外，我們將提出一種新實驗方式來降低表面損壞和改進準分子雷射並增加的TNAs的結晶性. 最後，在此研究中，以準分子雷射進行二氧化鈦奈米管陣列退火處理功率在大於或等於0.042 Jcm-2時，較低的價數：二價(TiO)以及三價(Ti2O3)也會因退火處理轉變成四價(TiO2) 。

Crystallization of TiO2 nanotube arrays (TNAs) has received extensive interest for their attractive applications. Among various crystallization techniques, excimer layer annealing is one of prominent technologies because it is a fast and effective low-temperature annealing technique for forming crystalline TNAs. The influence of laser annealing conditions such as fluence and number of laser pulses on the crystallinity, surface morphology and electronic structure of TNAs were investigated. In this study, TiO2 nanotube arrays with high aspect-ratio have been prepared by anodic oxidation in an electrolyte including ethylene glycol, 0.5 wt% NH4F, and 3 wt% H2O. All anodization experiments were carried out at room temperature using a two-electrode electrochemical cell consisting of a stainless steel foil (SS304) as the cathode and a Ti foil as the anode, at constant DC potential at 20 V for 24 hours. Subsequently, TNAs were irradiated by laser in air at room temperature. Samples are analyzed using following techniques: X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-Ray Near Edge Spectroscopy (XANES), and Raman Spectroscopy. The XRD results show that TNAs annealed by laser at fluence between 0.067 and 0.133 Jcm-2 under 9000 shots yield anatase phase, while at fluence from 0.133 to 0.4 Jcm-2, 9000 shots, TNAs possess both of anatase and rutile phases. In addition, TNAs annealed by laser at fluence of 0.1 Jcm-2 and shots less than 9000 will be transformed from amorphous to anatase. On the other hand, when shots are higher than 9000, laser annealing on TNAs leads to phase transformation from amorphous to anatase and rutile. FESEM images show that damage of TNAs surface increases with increasing fluence as well as the number of shots. Moreover, the mechanism for laser-induced structural transformation will be proposed in terms of laser-matter theory and crystallization kinetics. In addition, the phase composition of TNAs has been calculated based on XRD results and the matrix flushing method. Then, a new experimental mode was designed to reduce the surface damage as well as improve the crystallinity of TNAs induced by ELA. Finally, ELA process with fluences at 0.042 Jcm-2 or above results in all of lower charge state Ti+2 (TiO) and Ti+3 (Ti2O3) of Ti cations transferred toTi4+ (TiO2). The physical mechanisms responsible for this conclusion were proposed.