Effect of inhomogeneities and substrate on the dynamics of the metal-insulator transition in VO$_2$ thin films

TL;DR

This study investigates how substrate material and microstructure influence the ultrafast thermal recovery dynamics of VO₂ thin films undergoing a photo-induced metal-insulator transition, revealing significant differences based on substrate choice.

Contribution

It introduces a theoretical model linking microstructure and interface thermal conductivity to recovery times, validated by experimental measurements on different substrates.

Findings

Recovery time differs by two orders of magnitude between substrates

Microstructure and interface thermal conductivity significantly affect recovery dynamics

A simple analytic relationship relates recovery time to film parameters

Abstract

We study the thermal relaxation dynamics of VO$_2$ films after the ultrafast photo-induced metal-insulator transition for two VO$_2$ film samples grown on Al$_2$O$_3$ and TiO$_2$ substrates. We find two orders of magnitude difference in the recovery time (a few ns for the VO$_2$/Al$_2$O$_3$ sample vs. hundreds of ns for the VO$_2$/TiO$_2$ sample). We present a theoretical model that accurately describes the MIT thermal properties and interpret the experimental measurements. We obtain quantitative results that show how the microstructure of the VO$_2$ film and the thermal conductivity of the interface between the VO$_2$ film and the substrate affect long time-scale recovery dynamics. We also obtain a simple analytic relationship between the recovery time-scale and some of the film parameters.