Cross-Sectional Investigations of Spherical Colloidal Clusters from Submicrometer-Sized Silica Particles toward Designing Novel Photonic Materials

High Resolution Image Download MS PowerPoint Slide Interest has been rising in investigating spherical colloidal clusters for their potential application to optical materials, such as pigments and sensors. It is also interesting that the spherical colloidal clusters have various types of particle arrangements, including onion-like, icosahedral, and face-centered cubic (FCC) single crystal types. Generally, structural characterizations of cluster surfaces are often performed by scanning electron microscopy. In this study, we investigate structural arrangements in cross-sections through cluster cuts by using transmission electron microscopy. We prepared several spherical colloidal clusters under differing conditions and identified seven types of structures based on the cross-sectional observations. Some structures appear highly regular, whereas others have different degrees of disorders. The layered FCC domain type is of particular interest, as it is considered an intermediate structure in the crystallization of the FCC lattice. In this paper, we present a detailed structural analysis of this and other types of crystals.