Physical properties of VO2 thin films grown on oxide substrates

Abstract

In this thesis, the structural phase transition (SPT) and metal–insulator transition (MIT) phenome na in vanadium dioxide (VO2) are systematically elucidated from two perspectives.

(1) the intrinsic structural defects and strain effects, and (2) the structural distortion and associated structural and chemical characteristics induced by atomic diffusion from the substrate interface.

Chapter 1 describes the background and objectives of the research, Chapter 2 summarizes the representative crystal structures of VO2 polymorphs (M1, R, M2, and T phases) and the intrinsic defect structures associated with their space groups. It also outlines the physical principles and complementarity of X-ray diffraction (XRD) and transmission electron microscopy (TEM) as the main analytical methods employed in this work.

Chapter 3 describes the growth process of VO2 thin films using the RF magnetron sputtering method and details the experimental procedures and analytical approaches, including three-dimensional reciprocal space mapping (3D-RSM), high-resolution TEM (HR-TEM), and hard X-ray pho toelectron spectroscopy (HAXPES). Chapter 4 investigates the thickness-dependent structural and electrical properties of VO2 thin films grown on Al2O3(0001) substrates. Using an in-situ multimodal X-ray analysis system combining 3D-RSM and electrical resistance measurements, the study quantifies the effects of strain relaxation and intrinsic defects on the relation between SPT and MIT. Chapter 5 focuses on the interfacial atomic diffusion in VO2 thin films grown on LaAlO3(111) substrates, and analyzes the resulting chemical composition variations, structural distortion, and the physical and chemical properties of a distinct insulating phase different from the M1 phase using 3D-RSM and HAXPES.

Finally, Chapter 6 discusses the findings from VO2 thin films grown on Al2O3(0001) and LaAlO3(111), emphasizing the contribution of this work to understanding the physical properties of VO2.