Gap mode induced laser trapping of silver nanoparticles on thiophenol-covered silver substrates

Chiaki Iida, Keitaro Akai, Junichi Murakami, Masayuki Futamata
Silver nanoparticles (AgNPs) with radius of ∼20 nm were optically trapped and immobilized on thiophenol (TP)-covered Ag films under a gap mode resonance with extremely weak power density of ∼1 μW/μm2 at 532 nm. Intensity of Raman scattering from TP markedly increased with the accumulation of AgNPs. Trapping efficiency of AgNPs for p-polarization was 2-4 times higher than that for s-polarization. The observed optical trapping and immobilization were theoretically rationalized using a dipole-dipole coupling under a gap mode and van der Waals interaction between AgNPs and Ag films, which facilitate to fabricate versatile substrates for surface enhanced Raman scattering.

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