Physical properties and phase transition of VO2 thin films grown on LaAlO3(111)

Abstract

Controlling the metal-insulator transition (MIT) in VO2 thin films requires a fundamental understanding of the physical and chemical properties at the film-substrate interface, such as interfacial mixing, local oxygen stoichiometry, and metastable intermediate polymorphs arising from lattice-level shear/tilt distortions. With threedimensional X-ray reciprocal-space mapping and hard X-ray photoelectron spectroscopy (HAXPES), we explore the structural and electronic evolution of VO2 thin films deposited on LaAlO3(111) during the MIT. We find that diffusion of La atoms from the LaAlO3 substrate generates La-enriched and La-deficient VO2 grains in the film, leading to the stabilization of an intermediate triclinic (T) phase that coexists with the monoclinic (M1) phase. Compared to the M1 phase, the T phase exhibits a higher MIT temperature and a distinct lattice-distortion pathway. HAXPES measurements reveal a distinct chemical state of La-containing VO2 grains in the interfacial region, which nevertheless exhibit typical MIT behaviors. Our findings demonstrate that cation interdiffusion can influence the formation of VOA polymorphs and their structural transition pathways, thereby providing valuable insights into the relationship between phase transition mechanisms and interfacial properties in VOA.