High-Strain-Induced Local Modification of the Electronic Properties of VO Thin Films.

Vanadium dioxide (VO) 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 toward mechanical actuation of single domains. In this work, we show that we can manipulate and monitor the reversible semiconductor-to-metal transition of VO 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 VO-metal contact is observed as the main charge carrier injection mechanism before and after the phase transition of VO. The tunneling barrier is formed by a very thin but persistently insulating surface layer of the VO. 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 VO properties, as well as on nanoscale metal-oxide contacts, which can help in the future design of oxide electronics.