High-strain-induced local modification of the electronic properties of VO$_2$ thin films

TL;DR

This study demonstrates reversible control of VO2's semiconductor-metal transition through nanoscale mechanical pressure, revealing insights into pressure-induced electronic changes and nanoscale contact behavior for potential oxide electronic devices.

Contribution

It introduces a method to reversibly manipulate VO2's phase transition using atomic force microscopy, providing new understanding of pressure effects on electronic properties.

Findings

Reversible phase transition induced by nanoscale pressure.

Conductivity modulation by a factor of several during transition.

Identification of tunneling as the charge injection mechanism.

Abstract

Vanadium dioxide (VO2) is a popular candidate for electronic and optical switching applications due to its well-known semiconductor-metal transition. Its study is notoriously challenging due to the interplay of long and short range elastic distortions, as well as the symmetry change, and the electronic structure changes. The inherent coupling of lattice and electronic degrees of freedom opens the avenue towards mechanical actuation of single domains. In this work, we show that we can manipulate and monitor the reversible semiconductor-to-metal transition of VO2 while applying a controlled amount of mechanical pressure by a nanosized metallic probe using an atomic force microscope. At a critical pressure, we can reversibly actuate the phase transition with a large modulation of the conductivity. Direct tunneling through the VO2-metal contact is observed as the main charge carrier injection mechanism before and after the phase transition of VO2. The tunneling barrier is formed by a very thin but persistently insulating surfacelayer of the VO2. The necessary pressure to induce the transition decreases with temperature. In addition, we measured the phase coexistence line in a hitherto unexplored regime. Our study provides valuable information on pressure-induced electronic modifications of the VO2 properties, as well as on nanoscale metal-oxide contacts, which can help in the future design of oxide electronics.