Gap Effect on Electric Field Enhancement and Photothermal Conversion in Gold Nanostructures.Plasmonic optical tweezers and thermophoresis are promising tools for nanomaterial manipulation.  In addition, a temperature gradient is also generated by the photothermal conversion, and thermophoretic force is then generated.  Here, we focused on the effect of the gap width between nanostructures on the optical radiation pressure and thermophoretic force.  The simulation results show that the electric field is locally enhanced according to the gap width, but the effect on the temperature rise due to the photothermal heating is small.  This fact suggests that the gap effect between the nanostructures is particularly dominant in nanomanipulation using optical force, whereas it has little effect in nanomanipulation using thermophoresis.
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