Formation of AgCl Cubic Crystals Induced by Shrinkage of Sol–Gel Silica Film

Abstract

Growth of AgCl cubic crystals at the surface of sol–gel silica films containing AgCl nanocrystals and poly(ethylene glycol)/ethylene glycol as diffusion-controlled media has been successfully demonstrated. Crystals were grown during the shrinking of the film when it was exposed to air at room temperature, and both size and shape of the crystals were found to be dependent on the film thickness. When the film thickness was in the range of 70–250 nm, cubic shaped crystals with size between 120 and 250 nm were produced. These cubes exhibited predominant {200} facets as indicated by the electron beam diffraction patterns. Spherical crystals with size and height between 200 and 400 nm were observed when film thickness was in the range of 250–400 nm, while elliptical crystals were found on films thicker than 400 nm. Crystals were not grown when the film thickness was <25 nm. These results suggest that sol–gel silica films can be utilized as a nanocrystal reservoir to grow crystals of desired size and shape with their locations controlled by the pattern of the film.