Structural and morphological transformation of titania nanotube arrays induced by excimer laser treatment

• Main Authors: Nguyen, Van Thang, 阮文勝
• Other Authors: Leu, Jihperng (Jim)
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/71895360560426640337

碩士 === 國立交通大學 === 材料科學與工程學系 === 99 === 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.