Optical Trapping with Pillar Bowtie Nanoantennas

Plasmonic nanoantennas make effective optical tweezers, owing to their characteristic field enhancement and confinement properties which produce large near-field intensity gradients. The trapping dynamics of plasmonic nanotweezers are strongly affected by their resonant optical absorption, which can produce significant heating and induce rapid convective flows in the surrounding fluid medium. We here consider a new class of plasmonic nanotweezers based on an array of elevated bowtie nanoantennas (BNA), whereby BNAs are suspended on optically transparent, 500-nm tall silica pillars. We discuss how the plasmonic properties of these pillar-BNAs (pBNAs) can be manipulated in large areas of 80 x 80-micron using low-input power densities. This modification in local plasmonic properties is expected to result in a much more complex optical trapping landscape. We also find that the temperature increase in the pBNAs is more than 10x higher than in comparable substrate-bound structures (for the same input intensity), in which the substrate acts as a heat sink that mitigates temperature increase, and we investigate the role of this enhanced thermo plasmonic heating on plasmonic trapping dynamics.