Local geometric and electronic structures of gasochromic VO sub(x) films

• Published in: Physical chemistry chemical physics : PCCP Vol. 16; no. 10; pp. 4699 - 4708
• Main Authors: Jang, Wei-Luen, Lu, Yang-Ming, Chen, Chi-Liang, Lu, Ying-Rui, Dong, Chung-Li, Hsieh, Ping-Hung, Hwang, Weng-Sing, Chen, Jeng-Lung, Chen, Jin-Ming, Chan, Ting-Shan, Lee, Jyh-Fu, Chou, Wu-Ching
• Format: Journal Article
• Language: English
• Published: 01.02.2014
• Subjects: Amorphous structure; Annealing; Electronic structure; Lamellar structure; Magnetron sputtering; Phase transformations; Vanadium; Vanadium pentoxide
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c3cp54773f

VO sub(x) 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 VO sub(x) films were amorphous with mixed V super(4+) and V super(5+) valences. The amorphous VO sub(x) had a disordered and expanded lamellar structure resembling that of polymer-intercalated V sub(2)O sub(5) gels. VO sub(x) films were crystallized into orthorhombic V sub(2)O sub(5) at 300 degree C, and the lamellar structure was eliminated at 400 degree C. Additionally, the gasochromic reaction reduced the vanadium valence via intervalence transitions between V super(5+) and V super(3+). Moreover, removing the lamellar structure reduced the gasochromic rate, and the gasochromic reaction transformed the V sub(2)O sub(5) crystalline phase irreversibly into an H sub(1.43)V sub(2)O sub(5) phase. Based on the results of this study, amorphous VO sub(x) with a lamellar structure is recommended for use in H sub(2) gas sensors.