Seven at One Blow: Particle Cluster Stability in a Single Plasmonic Trap on a Silicon Waveguide

Relying on localized surface plasmons, plasmonic nanotweezers enable trapping and handling nanoparticles in the near-field of nanoscale optical hotspots. hi this work, we uncover new functionalities offered by plasmonic nanotweezers integrated in hybrid photonic-plasmonic platforms. Using a periodic chain of gold nanorods coupled to a silicon photonic waveguide, we demonstrate the optical trapping of single dielectric nanobeads as well as the formation of well-defined self-assembled nanobead clusters. Based on experimental observations and particle tracking analysis, we measure the trapping efficiency and analyze the statistical trends of the clusters' topology and stability. We demonstrate that vacancy-free cluster configurations composed of four and seven beads benefit from an enhanced stability thanks to the concomitant actions of both the optical forces and the bead-waveguide electrostatic interactions. This effect could enable further optimization of integrated plasmonic nanotweezers for efficient particle assembly and manipulation at the nanoscale in future lab-on-a-chip applications.