Structural and Optical Characterization of Decahedral-Type Spherical Colloidal Clusters

Abstract

Spherical colloidal clusters have attracted considerable attention, owing to their potential as optical materials. Interestingly, they exhibit a rich variety of particle arrangements, such as face-centered cubic (fcc) and icosahedral types, whose characteristics have been hitherto unexplored. This study focuses on the evaluation of spherical colloidal clusters with decahedral structures. First, the particle arrangement is evaluated using electron microscopy, and a quantitative structural model is constructed based on the observed surface and cross section details. Second, the clusters are analyzed using optical methods, and various reflection patterns are observed, such as teardrop and half-moon patterns, depending on the orientation of the clusters. A quantitative analysis performed based on the structural model and reflectance measurements reveals two origins of the observed wavelength-selective reflection, namely, reflection from the stacked particle layers, which can be modeled as the {111} plane of an fcc lattice and that from the twin boundaries between two fcc crystals. The twin-boundary-based reflection mechanism is primarily observed in spherical colloidal clusters with other structure types. The presented detailed structural and optical analyses will aid in understanding the formation processes of various types of spherical colloidal clusters.