Substrate-induced microstructure effects on the dynamics of the photo-induced Metal-insulator transition in VO₂ thin films

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We investigate the differences in the dynamics of the ultrafast photo-induced metal-insulator transition (MIT) of two VO₂ thin films deposited on different substrates, TiO₂ and Al₂O₃, and in particular the temperature dependence of the threshold laser fluence values required to induce various MIT stages in a wide range of sample temperatures (150 K - 320 K). We identified that, although the general pattern of MIT evolution was similar for the two samples, there were several differences. Most notably, the threshold values of laser fluence required to reach the transition to a fully metallic phase in the VO₂ film on the TiO₂ substrate were nearly constant in the range of temperatures considered, whereas the VO₂/Al₂O₃ sample showed clear temperature dependence. Our analysis qualitatively connects such behavior to the structural differences in the two VO₂ films.