Thermionic Emission of Electrons from Gold Nanoparticles by Nanosecond Pulse-Laser Excitation of Interband

Gold nanoparticles exhibit optical absorption bands assignable to a broad interband in the UV region and a narrow intraband (surface plasmon band) in the 520 nm wavelength region. The gold nanoparticles were multiply ionized in an aqueous solution of sodium dodecyl sulfate when excited by a tightly focused nanosecond pulsed laser at 532 nm resonant to the intraband or at 355 nm resonant to the interband. Although the absorbance at 355 nm is almost comparable with the absorbance at 532 nm, gold nanoparticles with higher charge states were formed when the interband at 355 nm was excited. Our experimental findings and the theoretical prediction by Grua et al. ( Phys. Rev. B 2003, 68, 035424) lead to the conclusion that electrons are predominantly released from the gold nanoparticles through thermionic emission by the excitation of the interband, whereas excitation of the surface plasmon band hardly contributes to the ionization processes.