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

Abstract

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 °C 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.

Nanothermochromics: Calculations for VO2 nanoparticles in dielectric hosts show much improved luminous transmittance and solar energy transmittance modulation

“…[125][126][127] There is a tendency that limited dimensions decreases c and widens the hysteresis in nanocrystalline films 46,48,[128][129][130][131][132][133][134][135] and nanorods. 27,28,81,90,118 This may be associated with internal stress in the particles. However, the empirical data are not entirely consistent and we prefer not to discuss the differences between particles and thin films in detail.…”

“…56 The incorporation of VO 2 in polymer matrices 57,58 has been demonstrated too. Nanoparticles of VO 2 with more or less symmetrical shapes have been made by wet chemistry, [59][60][61][62][63][64][65][66] 74 There are also numerous works on nanorods ͑nanowires͒ of VO 2 prepared by wet chemistry, [75][76][77][78][79][80][81][82] gas phase synthesis, 32,[83][84][85][86][87][88][89] ion implantation of vanadium and oxygen ions followed by annealing, [27][28][29]90 and by thermal oxidation of V; 33,91 these particles can be represented as higheccentricity prolate particles. VO 2 : W nanorods have been deposited by wet chemistry 92 and VO 2 : Mo nanorods have been made by a sol-gel based technique.…”

“…In fact, experimental work on such nanoparticles has soared during recent years. We first note that VO 2 nanoparticles occluded in a silica matrix have been fabricated via reduction in a glass containing V 2 O 5 by use of hydrogen, 53,54 ion implantation of vanadium and oxygen ions in a silica host, 27,28 and sol-gel deposition. 55 Very well controlled nanostructures have been made by introduction of VO 2 into the voids of synthetic opal comprised of SiO 2 nanospheres.…”

“…The third problem has to do with the fact that the thermochromic reflectance modulation in VO 2 films is strong only in the near-infrared and at wavelengths for which the solar radiation is weak, which means that the modulation of the solar energy throughput between a low-temperature and a high-temperature state is modest; typically it is ϳ5% for a VO 2 film though, exceptionally, it can run up to 10%-15% in a well designed TiO 2 / VO 2 / TiO 2 / VO 2 / TiO 2 structure. 22,23 VO 2 -based nanoparticles of various types have received much interest in recent work, as discussed at length below, and there are a number of demonstrations that clear-cut thermochromic effects can be observed; data have been obtained for nanostructures made by ion implantation followed by annealing, [27][28][29] ion beam lithography and pulsed laser deposition, 30,31 ultrasonic spray and laser pyrolysis, 32 molten salt synthesis, 33 and aqueous chemistry. 34 Our present study demonstrates that nanoparticles dispersed in a dielectric host have advantages over what a thin solid film can offer.…”

Structure and Properties of Nanoparticles Formed by Ion Implantation

“…One example of "smart" nanocomposite material developed by ion implantation is nanocrystalline VO 2 embedded in a SiO 2 matrix (Fig. 7) [85]. VO 2 is a transition-metal oxide that shows abrupt changes in electronic and optical properties at 67…”