Study of the phase evolution, metal-insulator transition, and optical properties of vanadium oxide thin films

• Published in: Optical materials express 2016-11, Vol.6 (11), p.3609-3621
• Main Authors: Huang, Taixing, Yang, Lin, Qin, Jun, Huang, Fei, Zhu, Xupeng, Zhou, Peiheng, Peng, Bo, Duan, Huigao, Deng, Longjiang, Bi, Lei
• Format: Article
• Language: English
• Subjects: Confocal; Metal-insulator transition; Microscopy; Optical properties; Oxygen; Partial pressure; Thin films; Vanadium oxides
• ISSN: 2159-3930; 2159-3930
• DOI: 10.1364/OME.6.003609

VO sub(2) thin films featuring a metal-insulator transition (MIT) at 68 [degrees]C with a large reversible tunability of the optical property have attracted great interest recently. Due to the complex phase and valence states of the vanadium oxides, understanding the microstructure and optical properties of this material with different oxygen stoichiometries has been challenging. In this study, we show that confocal Raman microscopy mapping can resolve the phase distribution in a large vanadium oxide thin film sample area, therefore providing a useful tool for a structure-property relationship study of this material. A new Raman peak at 166 cm super(-1) is observed in oxygen rich VO sub(2) films, which forms micron size islands in the films, and is attributed to the characteristic peak of V super(4+)/V super(5+) mixed valence states. The mixed valence state structure exists in a large oxygen partial pressure window during thin film fabrication. By joining the structural analysis and optical constants fitted by the Drude-Lorentz model using effective medium theory, the influence of different phases and valence states to the optical constants of the vanadium oxide thin films is clearly observed. These results provide in-depth understanding of the structure-optical property relationship of vanadium oxide thin films.