Browsing by Author "Lu, Yang-Ming"

Now showing 1 - 2 of 2

Effects of oxygen partial pressure on structural and gasochromic properties of sputtered VOx thin films
(2013-10-01)
Jang, Wei-Luen
;
Lu, Yang-Ming
;
Lu, Ying-Rui
;
Chen, Chi-Liang
;
Dong, Chung-Li
VOx films were deposited by radio-frequency reactive magnetron sputtering from a vanadium target in an Ar-O-2 gas mixture and pure O-2. For the films deposited in the gas mixture, the Ar flow rate was controlled at 20 sccm and the oxygen flow rate was controlled at 1, 3, and 5 sccm, respectively. A thin (similar to 5 nm) Pt layer was deposited on the VOx thin films as a hydrogen catalyst. The long-range structural order, short-range atom arrangement, and gasochromic properties of the deposited films were studied. The grazing incidence X-ray diffraction (GIXRD) results indicate that the deposited films are amorphous. Lamellar structures were found at oxygen flow rates of 3 sccm and above. The X-ray absorption spectroscopy (XAS) results show that the short-range atom arrangement of the lamellar VOx thin films is similar to that of crystal V2O5. The GIXRD and XAS results show that the film obtained with the gas mixture and at an oxygen flow rate of 1 sccm did not significantly change after exposure to hydrogen, whereas the other films exhibited decreased interlayer distance, oxidation state, and crystallinity. The color of the films changed from light or deep yellow to gray. The results suggest that the gasochromic properties of the VOx thin films are related to the V2O5-like atom arrangement and the interlayer distance of the lamellar structure. The films deposited with an oxygen flow rate of 3 sccm and above can be applied to H-2 gas sensors. (C) 2013 Elsevier B. V. All rights reserved.
Local geometric and electronic structures of gasochromic VOx films
(2014)
Jang, Wei-Luen
;
Lu, Yang-Ming
;
Chen, Chi-Liang
;
Lu, Ying-Rui
;
Dong, Chung-Li
VOx films were deposited by radio-frequency reactive magnetron sputtering from a vanadium target at room temperature. Local atomic and electronic structures of the films were then modified by thermal annealing. The oxidation state and structural and gasochromic properties of the films were elucidated by X-ray absorption spectroscopy. Analytical results indicate that the as-deposited VOx films were amorphous with mixed V4+ and V5+ valences. The amorphous VOx had a disordered and expanded lamellar structure resembling that of polymer-intercalated V2O5 gels. VOx films were crystallized into orthorhombic V2O5 at 300 degrees C, and the lamellar structure was eliminated at 400 degrees C. Additionally, the gasochromic reaction reduced the vanadium valence via intervalence transitions between V5+ and V3+. Moreover, removing the lamellar structure reduced the gasochromic rate, and the gasochromic reaction transformed the V2O5 crystalline phase irreversibly into an H1.43V2O5 phase. Based on the results of this study, amorphous VOx with a lamellar structure is recommended for use in H-2 gas sensors.