Substrate-induced microstructure effects on the dynamics of the photo-induced Metal-insulator transition in VO$_2$ thin films

TL;DR

This study compares how substrate-induced microstructure influences the ultrafast photo-induced metal-insulator transition in VO₂ thin films, revealing substrate-dependent temperature behaviors of transition thresholds.

Contribution

It provides new insights into substrate effects on VO₂ thin film MIT dynamics, highlighting structural influences on threshold fluence temperature dependence.

Findings

VO₂/TiO₂ film shows temperature-independent transition thresholds.

VO₂/Al₂O₃ film exhibits clear temperature dependence of thresholds.

Structural differences qualitatively explain the observed behaviors.

Abstract

We investigate the differences in the dynamics of the ultrafast photo-induced metal-insulator transition (MIT) of two VO$_2$ thin films deposited on different substrates, TiO$_2$ and Al$_2$O$_3$, 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 VO$_2$ film on the TiO$_2$ substrate were nearly constant in the range of temperatures considered, whereas the VO$_2$/Al$_2$O$_3$ sample showed clear temperature dependence. Our analysis qualitatively connects such behavior to the structural differences in the two VO$_2$ films.