Engineering Tip-to-Tip Cubic Assemblies of Octahedral Nanoparticles for Enhanced Generation of Near-Field Electromagnetic Hot Spots

Abstract

Engineering unique architectures at the nanoparticle and colloidal scales represents a promising strategy for harnessing physicochemical interparticle interactions, particularly to enhance nearfield light focusing. Although electric fields tend to concentrate at regions of high curvature, such as sharp tips, the presence of the latter features alone does not substantially strengthen the nearfield enhancement. Instead, directly assembling two sharp tips in a tip-to-tip configuration represents an effective way to maximize near-field focusing by generating highly localized electromagnetic "hot spots". To achieve this goal, we introduce an innovative approach for obtaining a tip-to-tip assembly of octahedral nanoparticles. This strategy involves encapsulating solid octahedral nanoparticles within cubic shells, serving as structural building blocks, to form point contacts between the flat surfaces of the cubic shell and the sharp tips of the octahedron. By arranging these distinctive structures in a serial configuration, we achieve a controlled tip-to-tip alignment. Within this architecture, the inner tips induce charge concentration on the flat planes, while the serial arrangement further enhances near-field focusing across adjacent building blocks. This configuration exhibits distinct near-field characteristics compared to assemblies composed of simple solid cubes or isolated octahedral nanoparticles, thus providing a novel strategy for optimizing near-field interactions in nanoscale systems.