The project addresses the science that underpins the reversible switch from insulating to metallic behavior in extremely thin vanadium dioxide. The goal of this research is to determine what happens at the nanometer scale during the thermally driven transition, and how to control it. Understanding and controlling transitions between the various possible phases of vanadium dioxide will enable advances to be made in the development of energy-efficient computers, and smart windows that regulate the heating and cooling of buildings. Extended international visits to Bremen University in Germany to perform experiments complement the development of joint on-line courses between universities in Binghamton and Bremen. Undergraduate researchers from underrepresented minorities are involved with the research activities, including dedicated field trips to national research facilities, such as Brookhaven National Laboratory. A K-12 educational outreach to attract younger students to science and engineering employs on-line video demonstrations and infographics.
TECHNICAL DETAILS: The abrupt metal insulator transition of vanadium dioxide is an archetypal example of the complex interplay between the electrons and the lattice. A structural phase transition accompanies the electronic transition, which can be triggered by small thermal perturbations near room temperature. Additional phases are expected to exist during the transition or may be stabilized by strained thin films. However, the exact nature and presence of these phases is a hot topic of debate. The advent of high quality ultrathin films, newly developed nanoscale spectromicroscopy techniques, and recent sophisticated computational studies present an ideal opportunity to explore these phases. Nanoscale resolution spectromicroscopy techniques can determine exactly and simultaneously the electronic and geometric configurations in phase-separated regions that coexist through the phase transitions of vanadium dioxide. The research objective is to determine whether the structural and electronic phase transitions in nanoscale vanadium dioxide are intrinsically decoupled, as suggested by the presence of intermediate states, or whether the material can be tailored to be so by strain and doping. Measured parameters, such as lattice constants, density of states, and vanadium coordination are used as inputs and constraints for band structure calculations of vanadium dioxide. Students, at both the graduate and undergraduate level, are being trained in cutting-edge low-energy/photoelectron electron microscopy and small-spot X-ray spectroscopy at national research facilities in the US and abroad.
