Oxygen stoichiometry controlled sharp insulator-metal transition in highly oriented VO2/TiO2 thin films

• Published in: Current applied physics 2018, 18(6), , pp.652-657
• Main Authors: Im, Ji-Seok, Anoop, Gopinathan, Sohn, Min Kyun, Kang, Dae Joon, Jeong, Sang Yun, Lee, Sanghan, Jo, Ji Young
• Format: Article
• Language: English
• Subjects: Correlated oxide; Insulator-metal transition (IMT); Oxygen stoichiometry; Phase transformation; Vanadium dioxide; 물리학
• ISSN: 1567-1739; 1878-1675
• DOI: 10.1016/j.cap.2018.03.022

The insulator-metal transition (IMT) in vanadium dioxide (VO2) which occurs above room temperature (67 °C) is highly sensitive to atomic defects caused by oxygen stoichiometry. The strained growth and the degree of oxygen deficiency in VO2 epitaxial films result in lowering of transition temperature below room temperature as well as the broadening of transition parameters such as transition width and hysteresis width, which limit its application potential. Here we demonstrate the growth of highly oriented strain-relaxed VO2 thin films on (001)-oriented TiO2 substrates at various oxygen partial pressures, exhibiting the narrow transition and hysteresis width. The cross-sectional transmission electron microscopy and x-ray diffraction analyses of the films reveal the highly oriented growth of insulating monoclinic VO2. The IMT parameters associated with temperature-dependent phase transition vary with the oxygen partial pressure used during the deposition. The presence of multiple and mixed valence states of vanadium in the films was confirmed by Raman and XPS analyses. We have achieved a narrow transition width (2.3 °C) and hysteresis width (1.2 °C) through controlling the oxygen stoichiometry during the growth of VO2/TiO2 films. •Highly oriented epitaxial VO2 films were grown on (001)-oriented TiO2 substrate.•Insulator to metal transition (IMT) parameters of the VO2 film varies with the oxygen stoichiometry.•IMT in VO2 varied depending on the degree of crystallinity and microstructure of the films.•The VO2 film grown at high deposition oxygen pressure showed a sharp transition with a narrow hysteresis width.