Metal-to-Insulator Phase Transition of Vanadium Oxide VO2

Abstract

Vanadium Oxide VO2 exhibits a first-order phase transition from insulator to metal at a characteristic temperature of 68°C with a pronounced hysteresis. The transition, often accomplished using heat currents or applied DC electric fields, induces the modification in electrical, optical and structural properties of the material. This thesis focuses on studying the phase transition of VO2 thin films prepared through Pulsed Laser Deposition (PLD) on Silicon Si(001) substrate, with emphasis on how deposition/annealing conditions may affect film quality, as in crystallinity, grain size, defect density, etc. Surface morphology was examined using Scanning Electron Microscopy (SEM), thickness and surface roughness using Stylus Profilometry. The core novelty is the use of temperature-dependent Raman spectroscopy (TD-Raman) as the primary probe of the phase transition. By tracking phonon modes through heating and cooling cycles, we extract hysteresis parameters, such as the transition temperature Tc, hysteresis width ∆T and transition amplitude ∆A via complementary metrics: An intensity-based ratio sensitive to bond character and a linewidth-based ratio sensitive to disorder and phonon scattering. In doing so, this work will link growth parameters to MIT functionality, enabling reproducible control of Tc and ∆T to help guide the design of low-power, heat-based neuromorphic devices.