Strain Effect on Metal–Insulator Transition and Electronic Structure of Epitaxial VO2 Thin Films: Comparative Structural, Transport, and Optical Studies

초록

Extensive studies of structural, transport, and optical conductivity properties have been considered one of the most suitable approaches to investigate the phase transition-induced electronic structure changes of strongly correlated electron systems. Here, we report the effect of strain on the metal–insulator transition (MIT) and electron correlation in VO2 thin films. Stoichiometric VO2 thin films (~10 nm thickness) with different strain states were epitaxially grown on TiO2(001) and Al2O3(0001) substrates using a pulsed laser deposition. Fully strained VO2/TiO2 and relaxed VO2/Al2O3 both have a critical carrier density of ~ 1019 cm−3 and exhibit the monoclinic-rutile structural phase transition near the MIT temperature. The lowest lying optical transition of d|| → π* in the insulating state transforms into a Drude peak in the metallic state. The effective plasma frequency of VO2/TiO2 is found to be slightly larger than that of a VO2 single crystal. These results suggest that the MIT in 10 nm-thick VO2 films should originate from electron–phonon and electron–electron interactions, and the electron correlation should be related to the strain-induced orbital occupancy and bandwidth changes. © 2026 Wiley-VCH GmbH.

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