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Sci Rep. 2016 Mar 15;6:23119. doi: 10.1038/srep23119.

Suppression of Structural Phase Transition in VO2 by Epitaxial Strain in Vicinity of Metal-insulator Transition.

Yang M1,2, Yang Y1,2,3, Hong B1,2, Wang L1, Hu K1, Dong Y1,2, Xu H4, Huang H3, Zhao J1, Chen H1, Song L1, Ju H1, Zhu J1, Bao J1, Li X4, Gu Y5, Yang T5, Gao X5, Luo Z1,2, Gao C1,2,3.

Author information

1
National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, China.
2
Collaborative Innovation Center of Chemistry for Energy Materials, University of Science and Technology of China, Hefei, Anhui 230026, China.
3
CAS Key Laboratory of Materials for Energy Conversion, Department of Materials Science and Engineering, University of Science and Technology of China, Hefei, Anhui 230026, China.
4
Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
5
Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China.

Abstract

Mechanism of metal-insulator transition (MIT) in strained VO2 thin films is very complicated and incompletely understood despite three scenarios with potential explanations including electronic correlation (Mott mechanism), structural transformation (Peierls theory) and collaborative Mott-Peierls transition. Herein, we have decoupled coactions of structural and electronic phase transitions across the MIT by implementing epitaxial strain on 13-nm-thick (001)-VO2 films in comparison to thicker films. The structural evolution during MIT characterized by temperature-dependent synchrotron radiation high-resolution X-ray diffraction reciprocal space mapping and Raman spectroscopy suggested that the structural phase transition in the temperature range of vicinity of the MIT is suppressed by epitaxial strain. Furthermore, temperature-dependent Ultraviolet Photoelectron Spectroscopy (UPS) revealed the changes in electron occupancy near the Fermi energy EF of V 3d orbital, implying that the electronic transition triggers the MIT in the strained films. Thus the MIT in the bi-axially strained VO2 thin films should be only driven by electronic transition without assistance of structural phase transition. Density functional theoretical calculations further confirmed that the tetragonal phase across the MIT can be both in insulating and metallic states in the strained (001)-VO2/TiO2 thin films. This work offers a better understanding of the mechanism of MIT in the strained VO2 films.

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