Light propagation in photonic clusters of spherical particles assembled with micromanipulation method

In self-assembled multilayer arrays of micrometer-sized spheres which include small amount of fluorescent particles, unique six-dot-triangular and seven-dot-hexagonal patterns have been known to appear in the fluorescence microscopic image. Although it has been suggested that these patterns correspond to local domain structures, i.e., face centered cubic (fcc) or hexagonal closed packing (hcp), no convincing evidence has been presented. In this study, we fabricated well-controlled photonic clusters by use of micromanipulation and investigated the relation between the propagation patterns and the domain structures. While the minimum fcc and hcp clusters exhibited the triangular and hexagonal patterns, respectively, it was also found that the propagation patterns are dependent on the size of the clusters.