Regular Assembly of Polymer Nanoparticles by Optical Trapping Enhanced with a Random Array of Si Needles for Reconfigurable Photonic Crystals in Liquid

We report the optical trapping of many particles with feasible laser powers by the nanostructured semiconductor-assisted (NASSCA) trapping technique. Furthermore, we have found that the random array of silicon needles with spacings substantially smaller than the nanoparticle sizes is advantageous not only for the trapping force-field enhancement but also for the realization of close-packed assembly of nanoparticles. This counterintuitive approach is promising for the realizations of collective structural orders such as reconfigurable photonic crystals in liquid, which have been often regarded to require either top-down templates or full self-assembly beyond control.