Browsing by Author "Sato, Tatsuo"

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Cathodic deposition of TiO2 thin films with supercritical CO2 emulsified electrolyte
(2013-08-01)
Chang, Tso-Fu Mark
;
Lin, Wei-Hao
;
Hsu, Yung-Jung
;
Chen, Chun-Yi
;
Sato, Tatsuo
TiO2 thin films were fabricated by cathodic deposition with a supercritical CO2 (sc-CO2) emulsified TiCl3 + NaNO3 electrolyte. Morphology and average grain size were evaluated by SEM, TEM and XRD. SEM micrographs showed that the TiO2 films fabricated by TiCl3 + NaNO3 electrolyte were porous, and the films were composed of particles and aggregates of the particles. Also, size of the particles increased when the sc-CO2 emulsified electrolyte was used. Average grain size of the TiO2 films was calculated using Scherrer equation. The average grain size was found to increase when the sc-CO2 emulsified electrolyte was used. In addition, both particle sizes observed from SEM and average grain size calculated using Scherrer equation were found to increase when pressure was increased from atmospheric pressure to 20 MPa. (c) 2013 Elsevier B.V. All rights reserved.
Effects of Fluorinated Surfactant in Cathodic Deposition of TiO2 Films with Supercritical CO2 Emulsified Electrolyte
(2014)
Chang, Tso-Fu Mark
;
Lin, Wei-Hao
;
Hsu, Yung-Jung
;
Sato, Tatsuo
;
Sone, Masato
Effect of a fluorinated surfactant, F(CF(CF3)CF2O)(3)CF(CF3)COO(CH2CH2O)CH3, in pore structure and grain size of the TiO2 films deposited cathodically was studied. Increase in pore size and decrease in grain size were observed when the fluorinated surfactant was used. When supercritical CO2 was introduced into the system, synergetic effect on increasing the pore size was observed. Also, grain coarsening was observed for the films deposited with supercritical CO2. Therefore, the fluorinated surfactant combining with supercritical CO2 demonstrated the ability to control morphology and grain size of the deposited TiO2 films at the same time. (C) 2014 The Electrochemical Society. All rights reserved.
Supercritical CO2-Assisted Electrochemical Deposition of ZnO Mesocrystals for Practical Photoelectrochemical Applications
(2013-12-05)
Lin, Wei-Hao
;
Chang, Tso-Fu Mark
;
Lu, Yi-Hsuan
;
Sato, Tatsuo
;
Sone, Masato
We have successfully developed an effective supercritical CO2 (sc-CO2) emulsion-assisted electrochemical approach for cathodic deposition of ZnO mesocrystals. The sc-CO2 was introduced along with a nonionic surfactant in the process to form emulsified electrolyte, which significantly increased the supersaturation degree and promoted the molecular diffusion to affect the crystal growth of ZnO. The deposition involved the generation of primary nanocrystals with substantially high surface energy, followed by the preferred attachment of the primary nanocrystals along an energetically favorable orientation to form ZnO mesocrystals. The as-deposited ZnO mesocrystals exhibited remarkable optical properties at room temperature in terms of prominent near band-edge emission and substantially long exciton lifetime, attributable to the highly oriented crystallinity of mesocrystals that effectively suppressed the nonradiative charge recombination to extend the exciton decay dynamics. As compared to the structures prepared without the addition of surfactant or sc-CO2, ZnO mesocrystals from sc-CO2 emulsion displayed greatly improved photoactivity toward photoelectrochemical water oxidation, revealing their promising potential as photoanodes in relevant photoelectrochemical processes. The current study delivers the first demonstration of directly depositing ZnO mesocrystals on conductive substrates, which paves the way for utilization of mesocrystals as practical electrodes in technologically important energy conversion fields, such as electrochemical cells, photovoltaic devices, as well as photoelectrochemical water splitting, where the advantageous structural characteristics of mesocrystals, i.e., high crystallinity and abundant porosity, can be fully exploited.