Formation of Gold Nanonetworks and Small Gold Nanoparticles by Irradiation of Intense Pulsed Laser onto Gold Nanoparticles

Gold nanoparticles with an average diameter of ∼20 nm were prepared in water by laser ablation at 1064 nm against a gold metal plate in it. The gold nanoparticles thus prepared in water and those mixed with an aqueous solution of sodium dodecyl sulfate (SDS) were irradiated with an intense pulsed laser at 532 nm. The products in the solution were examined by transmission electron microscopy (TEM) and optical absorption spectroscopy. The TEM images of the products revealed that gold nanonetworks and much smaller gold nanoparticles were produced selectively by a proper choice of the laser fluence and the SDS concentration. The optical absorption spectra measured simultaneously showed that the gold nanonetworks have an optical absorption in the wavelength longer than 600 nm which is assignable to longitudinal plasma oscillation of the gold nanonetworks, while the smaller gold nanoparticles (clusters) have an absorption band in the visible to the UV region. Taking advantage of those characteristic absorption bands, we constructed a two-dimensional mapping which illustrates the formation of the gold nanonetworks and the smaller nanoparticles as functions of the laser fluence and the SDS concentration.