Real-time study of gold nanoparticles formation by pulsed laser annealing

Full text: The synthesis of metallic nanoparticles (NPs) either covered or embedded in transparent dielectric materials has recently received great attention for its possible applications as plasmonic structures. There are several methods to synthesize metal NPs such as chemical synthesis, photoreduction, thermal and laser annealing among others. The formation of NPs on the surface of different substrates by laser annealing results from the irradiation with nanosecond laser pulses of metal thin films grown previously on these substrates. The main advantages of this method include high precision of nanoparticles placement, room temperature processing in atmospheric conditions and freedom of chemical wastes and lithography requirements. Moreover, it has been shown than for a laser fluences above a threshold, the NPs can be implanted into glass substrates. This work focuses on the fabrication of gold NPs on both glass and fused silica substrates via laser annealing of Au films using a Nd:YAG laser (355 nm of wavelength and 7 ns of pulse duration). This study is aimed at the better understanding of the mechanisms involved during the annealing. For this, real-time optical absorption, laser beam deflection and pulsed photoacoustic measurements were used to monitor the formation of the NPs as a function of the laser fluence and the number of pulses. The influence of the film thickness, the laser repetition rate and the background pressure on the characteristics of the NPs was also studied. The obtained NPs were characterized by SEM, AFM and UV-Vis optical absorption. The current assessment shows that the annealing induces physical processes with duration of hundreds of microseconds. (author)