All-optical positioning of single and multiple Au nanoparticles on surfaces using optical trapping

Plasmonic metal nanoparticles have recently generated significant interest in both fundamental and applied nanoscience. An emerging area of interest within plasmonics is the study of optical forces on metal nanoparticles. These forces can be used to manipulate and assemble particles into useful geometries. In this work Au nanoparticles are optically trapped and deposited onto surfaces using both focused beam (gradient) as well as total internal reflection (TIR) based optical trapping. In the case of focused beam trapping, single spherical Au nanoparticles can be rapidly deposited to arbitrary locations on a surface with high spatial precision (similar to 100 nm). By controlling both the particle stability and the surface chemistry, large areas (10's of mu m(2)) can be patterned with Au nanoparticles. For TIR-based trapping, dense arrays of high-aspect ratio Au bipyramids with spot sizes similar to 10 mu m(2) are deposited on surfaces. Au bipyramids are deposited via a plasmon-selective photothermal heating mechanism. Both of these methods are fast (patterning large areas in minutes) and require no lithography or scanning probes.