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

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.

Engineering the Near-Edge Electronic Structure of SnSe through Strains

“…Another important alternative is strain-engineering, which has long been used as an effective and predictable means for tuning the materials properties [11][12][13][14][15][16], including strain-induced structural phase transitions [17][18][19], indirect-direct band gap transition [11][12][13], and semiconductormetal transition [12,20]. Previous work [4,21,22] also demonstrated the possibility of applying strains to tune the thermoelectric power factor.…”

Nanoscale Phase Separation and Lattice Complexity in VO2: The Metal–Insulator Transition Investigated by XANES via Auger Electron Yield at the Vanadium L23-Edge and Resonant Photoemission

“…Actually, the scenario can be even more complex if we consider films of VO 2 . As pointed out by Fan et al [8], investigating thin and ultrathin VO 2 films grown on oriented TiO 2 substrates, the strain dynamics also play a role and, in these films, the MIT process is modulated continuously via the interfacial strain [9,12,13]. The presence and role of different phases and the relationship between the phase transition temperature and strain have been investigated during film growth.…”

“…Moreover, the interfacial strain strongly affects the electronic orbital occupancy, which changes also the electron-electron correlation and controls the phase transition temperature. Recently Mengmeng Yang et al [9] investigated the MIT mechanism in a 13 nm thick strained VO 2 film on TiO 2 . With temperature-dependent synchrotron radiation high-resolution X-ray diffraction data and Raman spectroscopy, the authors suggested that the structural phase transition in the temperature range near the MIT is suppressed by epitaxial strain, and the electronic transition triggers the MIT in strained films [9].…”

“…Around 67-68 • C, the vanadium dioxide undergoes the electronic metal-insulator transition upon heating or cooling with hysteretic behavior and a change in the electrical conductivity by several orders of magnitude, coupled to a Structural Phase Transition (SPT) from the monoclinic to the rutile phase. Since the discovery of the MIT transition more than 50 years ago by Morin and Westman [1,2], VO 2 has attracted a lot of interest because of its strong electron correlation; recently the interest has increased because of the wide number of different possible applications in optics, as detectors or sensors, and in novel memory devices based on the occurrence of the reversible MIT transition [5][6][7][8][9][10][11]. However, since its discovery, and even now, the nature of this electronic/structural transition remains an open question.…”

First‐Principles Calculations on the Group‐IIIA Elements X‐Doped (X = Ga, In, Tl) VO2

“…However, the application of VO 2 as a smart window material has three main challenges: a) lowering the T c to comfortable room temperature, b) increasing the visible light transmittance ( T lum ), and c) increasing the solar energy regulation ability (Δ T sol ). To obtain these aims, the researchers have tried many ways to regulate the performance of VO 2 , such as, doping with foreign elements, forming point defects, exerting external pressure, and designing of multi‐layer structures . Among these methods, the elemental doping is an effective way to change T c to comfortable room temperature by controlling the doping ratio.…”