Determination of intrinsic thermal expansion coefficient of VO2 film via interface engineering

Abstract

The strong coupling between thermal and epitaxial strain in as-grown vanadium dioxide (VO2) thin films obscures the underlying physical mechanisms and impedes precise device control. Here, we circumvent epitaxial strain by fabricating a freestanding VO2 membrane and determine its intrinsic in-plane thermal expansion coefficient (TEC) as (5.3 ± 0.4) × 10−6 K−1 from 298 to 80 K using a noncontact optothermal Raman technique integrated with a three-substrate approach. By engineering the TEC mismatch at the material–substrate interface, we quantitatively analyze the resulting strain conditions and show that substantial compressive strain lowers the laser power threshold (Fth) for triggering metal–insulator transition (MIT) in the VO2 film. This work provides a general strategy to decouple thermal strain from epitaxial strain effects, enabling precise manipulation of phase transitions in correlated oxide films.