Ion beam synthesized of VO₂ nano-crystals show a sharp metal-insulator phase transition (MIT) with an extremely wide and tunable temperature hysteresis loop of up to 50°C with strong superheating and supercooling. By elastic strain, doping and intentional defect generation we manipulate the MIT phase transition and its dynamics. Controlling and engineering these effects, potential applications in extremely fast electro-optical memory and switching technologies can be envisaged: i.e. Bistable thermochromic gratings have been prepared and characterized in close cooperation with Huber Krenner. These nanocrystals can be cycled more than 104 times through the MIT without any sign of degradation of their optical properties.

(left) Transmission electron microscopy (TEM) image; (right) Temperature hysteresis of the metal-insulator transition

VO₂ micro-/nano-crystals are grown from V₂O₅ melt by capillary transport and decomposition. We study the growth on different amorphous and crystalline dielectric and metal surfaces. The metal-insulator phase transition (MIT) and dynamics of phase transition and bimorphs are imaged by polarization microscopy and µ-Raman spectroscopy.

(left) VO₂ nano-crystal/Ir (300nm/30nm) bimorph actuator (temperature sweep up); (right) Phase boundary evolution during temperature cycle of a fully clamped VO₂ micro-crystal

Growth mechanism of fully clamped VO₂ crystal