Metallic nanoparticles (NPs) have many potential applications such as heterogeneous catalysts, gas sensors, optical waveguides, optical switches and etc. One of the future candidates to produce nonlinear optical devices is nanocomposite (NC) systems made of metal NPs embedded in a dielectric matrix for their fast response and strong nonlinear absorption.
In this work, we compare formation of heat treated Ag NPs in silica matrix synthesized by co-sputtering and sol-gel methods. Also, the effect of heating temperature on the optical absorption of the films as well as particle size and chemical state of the prepared Ag NPs has been studied.
Ag-SiO2NC films with 2 mol% Ag were grown on quartz glass substrates by reactive RF magnetron co-sputtering. The as-deposited films were annealed at 400, 600 and 800°C for 1h in an Ar+H2 atmospheres. In the sol-gel method; the Ag-SiO2NC films were synthesized by dipping the soda lime substrates in a sol containing 1.6 mol% of AgNO3/TEOS followed by a drying process at 100°C in air. Then the samples heat-treated at different temperatures of 200, 300 and 400°C.
The optical UV-visible spectroscopy for the films synthesized by the sol-gel method indicated that by increasing the annealing temperature, the absorption peak has a blueshift from 456 to 416 nm wavelength and an intensity reduction due to size variation of Ag NPs and formation of AgOx NPs. For the co-sputtered samples the absorption peak observed at 400 nm. Increasing the annealing temperatures resulted in more intensive and narrower peaks with no shift. In addition, XPS measurements showed that the Ag NPs were in metallic state for both dried (100°C) sol-gel samples (93% Ag0, 6% Ag+, and 1%Ag2+) and reduced (800°C) sputtered samples (97.6% Ag0, 2.4% Ag+). Also XPS and AFM analyses showed that by increasing the annealing temperature surface concentration of the sol-gel Ag NPs with 25 nm in size decreased indicating their diffusion into the substrate, while for the sputtered Ag NPs with crystalline size of about 15 nm their concentration increased. |