Browsing by Author "Hsu, Ming-Yi"

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Microstructure and Composition of TiO(2) Nanotube Arrays Fabricated with HF and NH(4)F Electrolytes and Their Evolution during Annealing
(2011-01-01)
Hsu, Ming-Yi
;
Yang, Wei-Chun
;
Teng, Hsisheng
;
Leu, Jihperng
;
材料科學與工程學系
The evolution of microstructure and composition of titanium dioxide (TiO(2)) nanotube arrays fabricated with hydrofluoric acid (HF) and NH(4)F electrolytes as a function of annealing temperature up to 400 degrees C was investigated and compared using X-ray diffraction, scanning electron microscopy, and X-ray absorption near-edge structure spectroscopy. Results showed that TiO(2) nanotube arrays grown in HF electrolyte contained 90% amorphous TiO(2) and 10% lower oxidation states of titanium from Ti(2+) (TiO) and Ti(3+) (Ti(2)O(3)) cations. After annealing at 400 degrees C, TiO(2) nanotube arrays underwent charge transfer and phase transformation to 93% anatase phase, 6% amorphous TiO(2), and 1% suboxides. In contrast, as-grown TiO(2) nanotube arrays using NH(4)F electrolyte possessed less amorphous TiO(2) (82%) but more suboxides (18%) due to lower oxygen ion formation from scanty 3 wt % of H(2)O addition. Its onset temperature of phase transformation was found to be higher than TiO(2) nanotube arrays prepared by HF solution. Moreover, when annealed to 400 degrees C, the crystallinity of TiO(2) nanotube arrays increased only by 86% for the anatase phase. The lower anatase phase could be attributed to the formation of (NH(4))(2)TiF(6) type compounds presumably formed by the reaction of TiF(6)(2-) and NH(4)(+) ions dissociated from NH(4)F. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3533388] All rights reserved.
Microstructure and Composition of TiO2 Nanotube Arrays Fabricated with HF and NH4F Electrolytes and Their Evolution during Annealing
(2011-01-01)
Hsu, Ming-Yi
;
Yang, Wei-Chun
;
Teng, Hsisheng
;
Leu, Jihperng
;
材料科學與工程學系
The evolution of microstructure and composition of titanium dioxide (TiO2) nanotube arrays fabricated with hydrofluoric acid (HF) and NH4F electrolytes as a function of annealing temperature up to 400 degrees C was investigated and compared using X-ray diffraction, scanning electron microscopy, and X-ray absorption near-edge structure spectroscopy. Results showed that TiO2 nanotube arrays grown in HF electrolyte contained 90% amorphous TiO2 and 10% lower oxidation states of titanium from Ti2+ (TiO) and Ti3+ (Ti2O3) cations. After annealing at 400 degrees C, TiO2 nanotube arrays underwent charge transfer and phase transformation to 93% anatase phase, 6% amorphous TiO2, and 1% suboxides. In contrast, as-grown TiO2 nanotube arrays using NH4F electrolyte possessed less amorphous TiO2 (82%) but more suboxides (18%) due to lower oxygen ion formation from scanty 3 wt % of H2O addition. Its onset temperature of phase transformation was found to be higher than TiO2 nanotube arrays prepared by HF solution. Moreover, when annealed to 400 degrees C, the crystallinity of TiO2 nanotube arrays increased only by 86% for the anatase phase. The lower anatase phase could be attributed to the formation of (NH4)(2)TiF6 type compounds presumably formed by the reaction of TiF62- and NH4+ ions dissociated from NH4F. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3533388] All rights reserved.
Structural and morphological transformations of TiO2 nanotube arrays induced by excimer laser treatment
(2012-02-29)
Hsu, Ming-Yi
;
Nguyen Van Thang
;
Wang, Chih
;
Leu, Jihperng
;
材料科學與工程學系
The structural and morphological transformations of TiO2 nanotube arrays (TNAs) treated by excimer laser annealing (ELA) were investigated as a function of the laser fluence using parallel and tilted modes. Results showed that the crystallinity of the ELA-treated TNAs reached only about 50% relative to that of TNAs treated by furnace anneal at 400 degrees C for 1 h. The phase transformation starts from the top surface of the TNAs with surface damage resulting from short penetration depth and limited one-dimensional heat transport from the surface to the bottom under extremely short pulse duration (25 ns) of the excimer laser. When a tilted mode was used, the crystallinity of TNAs treated by ELA at 85 degrees was increased to 90% relative to that by the furnace anneal. This can be attributed to the increased area of the laser energy interaction zone and better heat conduction to both ends of the TNAs. (c) 2011 Elsevier B.V. All rights reserved.
TiO2 Nanowires on Anodic TiO2 Nanotube Arrays (TNWs/TNAs): Formation Mechanism and Photocatalytic Performance
(2012)
Hsu, Ming-Yi
;
Hsu, Hsin-Ling
;
Leu, Jihperng
;
材料科學與工程學系
;
Department of Materials Science and Engineering
TiO2 nanowires connected directly with TiO2 nanotubes arrays (TNWs/TNAs) were successfully fabricated with a mixture of ethylene glycol and water that contained NH4F electrolyte via a one-step method without mechanical stirring. The morphology of the TNWs/TNAs structure was investigated by changing the anodizing voltage and processing time to elucidate its formation mechanism. Well-developed anodic oxide nanowires are only observed under specific anodizing voltage and processing time conditions. The evolution of TNWs follows four stages: (1) thinning of the tube wall thickness with high roughness near the TNA mouths, (2) forming strings of through holes in the upper section of the TNAs, (3) splitting into nanowires, and (4) collapsing and further thinning of nanowires. For photocatalytic application, TNWs/TNAs film demonstrated a better photocatalytic performance than regular TNAs due to higher surface area predominantly and improved charge transport. Moreover, TNWs/TNAs film (20 nm wire/40 nm pore diameter) achieved a performance comparable to that of the film made from TiO2 nanoparticles. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.063208jes] All rights reserved.