Laser ablation of silver in aqueous solutions of organic species : probing Ag nanoparticle−adsorbate systems evolution by surface-enhanced raman and surface plasmon extinction spectra

Abstract : Laser ablation (LA) of a Ag target in aqueous solutions of some strongly adsorbing ions resulted in formation of chemically modified Ag nanoparticles (NPs). A prospective development of this approach into a one-pot synthesis of hybrid Ag NPs−organic species systems is conditioned by assessment of the factors affecting the hybrid system formation and stability during LA. In this study, intermittent LA of a Ag target accompanied by fragmentation of growing Ag NPs was carried out in aqueous solutions of 2,2′-bipyridine and/or of a cationic free-base porphyrin with nanosecond laser pulses of 1064 and 532 nm wavelengths. Ag NP/organic adsorbate systems resulting from each of the individual stages of the LA process were probed by SERS (surface-enhanced Raman scattering) and SPE (surface plasmon extinction) spectral measurements. The morphologies of selected systems were visualized by TEM (transmission electron microscopy). The efficiency of Ag NP fragmentation during LA (which corresponds to the efficiency of laser pulse absorption by the NPs) and the rate of the organic molecules' thermal desorption from the surfaces of Ag NPs heated by the laser pulse absorption have been recognized as crucial factors affecting the hybrid system stability.