Synthesis of Au-Ag alloy nanoparticles with Au/Ag compositional control in SiO(2) film matrix

Au-Ag alloy nanoparticles with tunable atomic ratios have been generated in SiO(2) film matrix using a new two layer (TL) approach. Two successive overlapping coating layers of similar thickness were deposited on silica glass substrates using Au- and Ag-incorporated inorganic-organic hybrid silica sots, respectively. The Au and Ag concentrations in the individual layers were varied to obtain the desired Au-Ag alloys of different compositions. Four sets of such TL coating assemblies were prepared from the following pair of sots: (i) 4 equivalent mol.% Au-96% SiO(2) and 2 equivalent mol.% Ag-98% SiO(2), (ii) 3 equivalent mol.% Au-97% SiO(2) and 2 equivalent mol.% Ag-98% SiO(2), (iii) 3 equivalent mol.% Au-97% SiO(2) and 3 equivalent mol.% Ag-97% SiO(2), and (iv) 2 equivalent mol.% Au-98% SiO(2) and 3 equivalent mol.% Ag-97% SiO(2) and subjected to UV (2.75 J/cm(2)) and heat-treatments (450-550 degrees C) in air and H(2)-N(2) atmospheres for the generation of Au-Ag alloy nanoparticles of approximate compositions Au(0.66)Ag(0.33), Au(0.6)Ag(0.4), Au(0.5)Ag(0.5), and Au(0.4)Ag(0.6), respectively. After UV-treatment, individual Au and Ag nanoparticles were formed in the respective layers. The heat-treatment (450-550 degrees C) induces interlayer diffusion of Au and Ag to each other with the generation of Au-Ag alloy nanoparticles, and as a result, Au-Ag alloy surface plasmon resonance (SPR) absorptions were observed in between the Ag- and Au-SPR absorption positions in the visible spectra. The expected alloy compositions are formed through several intermediate alloy nanoparticles, which can also be arrested by controlling the annealing parameters. The alloy formations were monitored by UV-VIS, FTIR, XRD, EDAX, and TEM studies