Trapping and Deposition of Dye-Molecule Nanoparticles in the Nanogap of a Plasmonic Antenna.

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.

Seasonal variations in coastal debris on Awaji Island, Japan.

The subject of our study was Awaji Island, an island located in the west of Japan that is surrounded by sea and that has serious problems relating to coastal debris. We conducted a long-term investigation focusing on three beaches and evaluated the results. The study was designed to develop an understanding of the actual situation, to inform local citizens, and raise their concerns about the problem of debris with a view to taking action against it. We obtained the following results: the amount, type, and ratio of debris changed according to weather and ocean conditions; debris also differs according to geographical conditions; social and economic activities of the surrounding area influence the type of debris encountered. Following this study, we have continued our investigation, and are continuing to gather data. At the same time, it is important to spread our ideas and enlighten people so as to encourage them not to dump debris. We hope that these actions manage to raise the level of consciousness among local citizens and to expand their anti-debris activities.