Interplay between electronic and structural transitions in VO₂ revealed by ellipsometry

Temperature-dependent spectroscopic ellipsometry measurements, combined with AFM investigations, have been performed to reveal the interplay between the structural and electronic phase transitions during the insulator-to-metal transition in VO$2$ thin films with different thicknesses. A comprehensive analysis of the macroscopic optical response in the framework of an anisotropic Bruggeman effective medium approximation yields the hysteretic shape evolution of the metallic inclusions and the changes in film roughness due to the structural transitions during a temperature cycle. The authors show that the structural modifications in the material across the transition affect the metallic cluster shape in the vicinity of the percolation threshold, leading to an altered absorption by the localized plasmon resonances. The structural changes are supported by AFM measurements and can be explained by the particular strain present in different films.