Plasmonic nanostructures, which allow light focusing at the deep subwavelength scale, and colloidal nanoparticles with unique optoelectronic properties are nowadays fabricated with nanometer precision. However, to fully control and exploit nanoscale light–matter interactions in hybrid plasmonic–nanophotonic devices, both materials must be assembled in heterostructures with similar precision. Near-field optical forces have recently attracted much attention, as they can precisely trap and position nanoparticles at plasmonic hotspots. However, long-range attraction and the surface bonding of nanoparticles usually require other specific techniques, such as electrothermal heating and surface chemical treatments. This Letter reports on the optical trapping and deposition of dye–molecule nanoparticles in the nanogap of a gold antenna. The nanoparticles are captured by focusing a near-infrared laser beam on a targeted plasmonic antenna. This single-step deposition process requires only a few seconds under 1.4–1.8 MW·cm –2 continuous-wave illumination and shows a polarization dependence smaller than expected. Fluorescence and electronic microscopy observations suggest that nanoparticle deposition arises from a trade-off between optical and thermal effects.

International audienceBy analyzing the thermal motion of fluorescent dielectric microbeads trapped in the near-field of a silicon nanocavity, we investigate the influence of the bead's size and the trapping laser power on the shape of the optical trap and the "effective" trap stiffness. We demonstrate that the trapping potential is proportional to the subwavelength patterns of the electromagnetic near-field intensity distribution for unexpectedly large Mie particle sizes. More especially, we show that mapping the trapping potential experienced by a 500 nm diameter bead reveals the nanopattems of the cavity resonant mode. This result highlights how photonic force microscopy in nanotweezers can provide an elegant way to image evanescent fields at the nanoscale via the thermal motion of optically trapped fluorescent microprobes