Formation of bimetallic gold-silver nanoparticles in glass by UV laser irradiation

Abstract

Experimental technique for preparing of space arranged arrays of bimetallic AuAg nanoparticles in the near-surface region of glass, exhibiting surface plasmon resonance (SPR) characteristics varying in the wider ranges comparing to monometallic Au, Ag particles or corresponding thin films, is presented together with the structural characterization of the obtained particles. The suggested technique is based on the UV laser irradiation (λ = 193 nm) of the glass surface preliminary doped with silver ions and then sputter coated by a thin gold layer. Optical extinction spectra of the prepared AuAg/glass samples demonstrated strong dependence of SPR upon the number of laser pulses applied. The relationship “SPR characteristics – particles structure and composition – synthesis conditions” was studied using transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray fluorescence (XRF) method and X-ray absorption fine structure (XAFS) spectroscopy. The latter provided the structural information on AuAg bonds, which directly evidenced on the formation of bimetallic AuAg nanoparticles in AuAg/glass samples. The XAFS derived values of structural parameters of AuAu and AuAg bonds allowed to visualize the distribution of gold and silver over the volume of representative AuAg nanoparticle and to suggest the most plausible cluster models of the architecture of such particle for the prepared AuAg/glass samples. It was revealed that the core-shell architecture of Au@Ag particles (Au-core, Ag-shell) is the most plausible in AuAg/glass samples prepared by the low number of laser pulses, while the structure of disordered solid solution is suitable for AuAg particles in samples prepared by ∼ 50 and more pulses. Calculations of contributions into experimental optical extinction spectra of AuAg/glass samples from particles with the revealed composition, size and architecture were performed to prove that the proposed structural models of nanoparticles are not in contradiction with the observed optical properties of the samples.