Necklace-shaped Au–Ag nanoalloys: laser-assisted synthesis and nonlinear opticalproperties

Abstract

Here in this paper, necklace-shaped Au–Ag nanoalloys (NAs) have been synthesized by alaser-based approach. A chain of Ag nanoparticles (NPs), which were joined togetherwith Au junctions, was formed upon copper vapor laser (CVL) irradiation of acolloidal mixture of Ag and Au NPs; while the corresponding NPs were separatelyprovided by laser ablation of gold and silver targets in deionized water by a 1064 nmQ-switched Nd:YAG laser. Dependence of the NAs development process on the CVLirradiation time in three distinct stages of as-mixed, nucleation and complete formation hasbeen systematically studied by UV–vis optical absorption spectroscopy analysisas well as by transmission electron microscopy (TEM), which was exploited tovisually confirm the NAs evolution through the process. Furthermore, the x-rayphotoelectron spectroscopy (XPS) technique was accurately employed to determine thesynthesized alloy content. On the other hand, using the open-and closed-apertureZ-scan technique, the nonlinear absorption (NLA) as well as nonlinear refraction (NLR)changes in Au–Ag NAs were investigated through their formation. The deduced resultsfrom the nonlinear optical properties of the colloidal NAs in the mentioned stages wereinterpreted considering the spectroscopic and microscopic observations. The total change ofindividual Au and Ag NPs saturable absorption (SA) into the reverse saturableabsorption (RSA) behavior was concluded through the evolution into Au–Ag NAs.