Combined Effect of Temperature Induced Strain and Oxygen Vacancy on Metal‐Insulator Transition of VO2 Colloidal Particles

Vanadium dioxide (VO2) is a promising material in the development of thermal and electrically sensitive devices due to its first order reversible metal-insulator transition (MIT) at 68 °C. Such high MIT temperature (TC) largely restricts its widespread application which could be enabled if a straightforward tuning mechanism were present. Here this need is addressed through a facile approach that uses the combined effects of temperature induced strain and oxygen vacancies in bulk VO2 colloidal particles. A simple thermal annealing process under varying vacuum is used to achieve phase transformation of metastable VO2(A) into VO2(M2), (M2+M3), (M1) and higher valence V6O13 phases. During this process, distinct multiple phase transitions including increased as well as suppressed TC are observed with respect to the annealing temperature and varied amount of oxygen vacancies respectively. The latent heat of phase transition is also significantly improved upon thermal annealing by increasing the crystallinity of the samples. This work not only offers a facile route for selective phase transformation of VO2 as well as to manipulate the phase transition temperature, but also contributes significantly to the understanding of the role played by oxygen vacancies and temperature induced stress on MIT which is essential for VO2 based applications

Tuning the optical coupling between molecular dyes and metal nanoparticles by the templated silica mineralization of J-aggregates

cited By 9International audienceSupramolecular porphyrin aggregates are used as a template for the higher-order assembly of fluorophore–dielectric–metal hybrid nanostructures in which the optical properties of the molecules are modulated by the finely tuned coupling to localized plasmons. First, J-aggregates are encapsulated inside a dielectric silica shell of well-controlled thickness, which reinforces mechanically the template and serves as a precise optical coupling spacer. The silicified J-aggregates are then decorated with gold or silver nanoparticles. UV–visible and fluorescence spectroscopies show that the presence of metal nanoparticles induces a marked enhancement of the J-aggregate fluorescence when the silica thickness is tuned to 7–12 nm, whereas a significant quenching is measured when the dielectric thickness is sub-2 nm. Interestingly, the enhancement is maximized when oxidized silver nanoparticles are placed very close to the J-aggregates