Defining Laser-Induced Phase Transition and Thermal Response of VO2 by Raman Spectroscopy: A Comparative Study of Functional Nanostructures.

Vanadium dioxide (VO2) is a strongly correlated transition metal oxide that undergoes a reversible metal-insulator transition (MIT) accompanied by a structural phase transformation, making it highly sensitive to localized thermal excitation. The effect of Raman laser irradiation on the phase stability and oxidation behavior of VO2 materials fabricated via different methods is systematically investigated. VO2 powder prepared by Rapid Thermal Annealing (RTA) and three VO2 -based thin films deposited on Al2O3 substrates (VO2/PVP composite, sol-gel, and Reactive Biased Target Ion Beam Deposition (RBTIBD)) were characterized by X-ray diffraction (XRD), along with field-emission scanning electron microscopy (FE-SEM), UV-Vis-IR spectroscopy, temperature-dependent measurements to determine their thermochromic transition behavior, while Raman spectroscopy under controlled laser excitation was employed as a localized heating source to probe thermal response and phase stability. Under 638 nm excitation, VO2 powder rapidly oxidized to higher vanadium oxides at intermediate laser power, whereas the VO2/PVP thin film exhibited delayed oxidation, requiring higher power for complete transformation. In contrast, sol-gel and RBTIBD thin films analyzed using 532 nm excitation did not undergo oxidation but instead showed a fully reversible laser-induced phase transition between monoclinic VO2 (M) and rutile VO2 (R). This work establishes a clear correlation between fabrication method, microstructure, and laser-induced phase stability in VO2 materials.