Shape Evolution of Two-Dimensional Au Hexagonal Nanoplates into Pseudo Three-Dimensional Oblate Spheroids

Herein, we report a seed-mediated synthetic method for pseudo three-dimensional oblate spheroids with structural complexity where concave and convex nanofeatures are formed simultaneously through manipulation of the growth directions. By exploiting hexagonal Au nanoplates as a seed material that consists of two Au(111)-faceted basal planes and side-by-side alternating arrangement of six Au(111) and six Au(100) side facets, we identified three growth patterns via a combination of kinetic and thermodynamic controls, leading to concomitant formation of concavity and convexity of the crystal facets. We denote the respective ellipsoidal nanoplates as convex or concave oblate spheroids. Various types of six-fold oblate spheroids were synthesized with high homogeneity in size, shape, and yield, and their optical responses in the ensemble were investigated. Given the many types of complex seed nanocrystals available, the suggested synthetic scheme using two-dimensional nanoplates as a seed will pave the way for the design of highly complex and sophisticated nanoparticles, especially where surface curvature is the main interest.