Laser annealing of bimetal thin films: A route of fabrication of composite nanostructures

The paper presents results on laser nanostructuring of bimetallic thin films. The thin films are deposited by classical on-axis pulsed laser deposition technology by using targets consisted of two sections composed of different metals. Using this technique gold/nickel or gold/silver thin films are deposited on quartz substrate. By changing the area of the different sections of the target, thin films with different concentrations of the two metals are obtained. The as fabricated films are then annealed by nanosecond laser pulses delivered by Nd:YAG laser system operated at λ = 355 nm. The modification of the produced films is studied as a function of the parameters of the incident irradiation as pulse number and laser fluence, the composition of the thin films, and characteristics of the environment. It is found that the laser annealing may lead to nanostructuring of the films as at certain conditions the thin films are decomposed into a monolayer of nanoparticles with narrow size distribution. The performed EDX analyses indicated that the fabricated particles are composed by a bimetallic system of the basic metals used. The extinction spectra of the obtained structures show plasmon excitations as the resonance wavelength can be efficiently tuned in a wide range by changing the ratio of the basic metals in the films. The obtained structures can be used in SERS and magneto-optics.