Browsing by Author "Say, Wen C."

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A mechanism for the formation of annealed compact oxide layers at the interface between anodic titania nanotube arrays and Ti foil
(2009-06-01)
Chen, Chien-Chon
;
Say, Wen C.
;
Hsieh, Sheng-Jen
;
Diau, Eric Wei-Guang
;
應用化學系
We propose a mechanism for the growth of crystalline anodic titanium-oxide (ATO) nanochannel arrays based on thermodynamic considerations and structural imperfections. Both amorphous and crystalline ATO films were obtained from the anodization of a titanium foil. Amorphous ATO nanotubes have a single-layer form, which makes them inefficient for use in photo-catalytic and solar-cell applications. Annealed ATO nanotubes are considered non-stoichiometric if the effect of oxygen partial pressure on the composition is significant. The driving force behind growing crystalline ATO nanotubes is the drawing of oxygen from the atmosphere to the oxygen site, which consequently decreases the concentration of oxygen vacancies in the anatase phase. The small ionization energies of titanium ions produce the stoichiometric defects. A diagram showing Gibbs energy and Kroger-Vink notation to indicate the strong influence of the non-stoichiometric ATO structure is deduced.
Fabrication of bismuth nanoballs using thermal oil reflow
(2008-11-01)
Kuo, Chin-Guo
;
Chen, Chien-Chon
;
Hsieh, Sheng-Jen
;
Say, Wen C.
;
應用化學系
Sub-micron-size bismuth (Bi) balls with diameters between 100 and 2000 nm were formed on an anodic aluminum oxide (AAO) template using thermal expansion and thermal oil reflow processes. After centrifugal force separation, 100 nm size Bi balls were obtained. In addition, the ball density was approximately 6 x 10(7)/cm(2) on an AAO surface. Because of their round shape, the contact angle of the Bi nanoballs on the AAO surface was large after hot oil reflow, making it easy to remove them using ultrasound and to separate different sizes of balls using centrifugal force. (C) 2008 The Ceramic society of Japan. All rights reserved.