Control of Au Nanoparticles Structural and Optical Properties by Laser Radiation and Thermal Annealing

Abstract

The aim of this study is to show the possibility to control structural and optical properties of Au nanoparticles (AuNPs) by changing their size and concentration and make comparison between methods of their formation. 1.4 nm thick Au films were formed on borosilicate glass substrates by the vacuum evaporation method. AuNPs were formed on the surface of the substrate by two methods. First is the irradiation by the Nd:YAG laser pulses with intensities from 75 to 180 MW/cm2. Second is thermal annealing, at temperature T=400 °C and the time of curing was varied from 24 to 72 hours. The irradiation of Au film by laser leads to formation of AuNPs. The increase of intensity of laser radiation causes the disappearing of small Au nanoparticles and growing of big nanoparticles from 113-180 nm due to the agglomeration of small particles into big ones and, correspondingly, concentration of particles decreases. In contrast, thermal annealing at T=400 °C from 48 to 72 hours leads to the island formation with the non-spherical shape and their dividing into several islands according to the spinodal dewetting model. As a result, the mean diameter of AuNPs is decreased from 161 to 85 nm but concentration increases.