GOALI: Ultrafast Phase Transition and Critical Issues in Structure-Property Correlations of Vanadium Oxide

North Carolina State University, Raleigh NC

Investigators

Abstract

This project impacts profoundly infrared camera and smart sensors based upon bolometer imaging arrays that can be monolithically integrated with silicon integrated circuits and operated at or above room temperature. By improving the reliability and sensitivity of uncooled bolometer arrays, it is hoped that every soldier in the field will have another tool with which to ?own the night? and maintain technological and operational superiority. Professor Narayan plans to work closely with ORNL and Kopin Corporation to transition the basic knowledge into practical devices. This work involves training of graduate and undergraduate students at NCSU, and collaborations with NC A&T University to attract minority students into the graduate program at NCSU. The outreach will also involve an annual ASM International-sponsored Summer School for rising high school seniors. This research deals with the very interesting phenomenon ? an ultrafast phase transition from monoclinic to the tetragonal structure of vanadium oxide (VO2). The principal investigator (PI) will study the role of epitaxy in determining the properties of VO2, a material that exhibits a sharp semiconductor-to-metal transition in bulk form. The transition is associated with energy release (associated, at least in part, with the deformation associated with the transition) that destroys the bulk material. The supposition is that the thin film and its substrate will be able to accommodate the transition without failure due to heat dissipation in the substrate. Of course, the substrate will also impose mechanical boundary conditions that will influence the temperature and "sharpness" of the transition. Furthermore, the detailed microstructure of the epitaxial, textured or amorphous film will influence the nature of the transition. The PI will address the synthesis and processing of vanadium oxide thin films with increasing grain size through to high-quality single-crystal on sapphire and silicon substrates. High-quality single crystal films with controlled strain will be grown by domain matching epitaxy paradigm on substrates with a large lattice misfit, where critical thickness is less than a monolayer and the films are relaxed from the beginning. These epitaxial films should exhibit a sharp transition, large amplitude, and very small hysteresis, similar to bulk single crystals of vanadium oxide. To obtain efficient and reliable infrared camera and smart sensors, the PI will strive to control and optimize the sharpness and amplitude of the transition, and the hysteresis upon heating and cooling.