Synthesis and characterization of size-controlled vanadium dioxide nanocrystals in a fused silica matrix

Vanadium dioxide single-crystal precipitates with controlled particle sizes were produced in an amorphous, fused SiO2 host by the stoichiometric coimplantation of vanadium and oxygen ions and subsequent thermal processing. The effects of the vanadium dioxide nanocrystal size, nanocrystal morphology, and particle/host interactions on the VO2 semiconductor-to-metal phase transition were characterized. VO2 nanoparticles embedded in amorphous SiO2 exhibit a sharp phase transition with a hysteresis that is up to 50 degreesC in width-one of the largest values ever reported for this transition. The relative decrease in the optical transmission in the near-infrared region in going from the semiconducting to the metallic phase of VO2 ranges from 20% to 35%. Both the hysteresis width and the transition temperature are correlated with the size of the precipitates. Doping the embedded VO2 particles with ions such as titanium alters the characteristics of the phase transition, pointing the way to control the hysteresis behavior over a wide range of values and providing insight into the operative physical mechanisms. (C) 2002 American Institute of Physics.