Laser annealing of bimetal porous structures produced by PLD in open air

This work presents experimental results on laser annealing of bimetal structures produced by pulsed laser deposition in air at atmosphere pressure. The initial structures are deposited in open air by laser ablation of a rotating target consisting of two sections – Au and Ag. The ablation process is carried out by nanosecond pulses delivered by a Nd:YAG laser system emitting the wavelength of 355 nm. In open air, the laser ablation results in the formation of nanoparticles (NPs) and NP aggregates; during a prolonged deposition, these grow on the substrate into a 3D porous structure. The as-deposited structures are then annealed by laser pulses using the same laser system. The morphology of the annealed samples is studied in relation to the laser processing by varying the laser fluence and the number of the laser pulses. It is found that under certain conditions, the laser annealing leads to the formation of a 2D array of bimetal NPs on the substrate. The optical response of such structures composed by noble metals (such as Au and Ag) or their alloys is associated with a strong absorption in the visible spectral range known as surface plasmon resonance. Special attention is paid to the influence of the annealing parameters on the optical properties of the samples prepared.