Selective gold nanoparticles formation by pulsed laser interference

摘要

Discontinuous Au films are prepared on glass substrates by pulsed laser deposition with two different metal coverages that lead to a film being formed by irregular coalesced nanoparticles (NPs) and to another film close to the percolation limit. The films are exposed to three interfering beams at different intensities produced by the fourth harmonic of a Nd:YAG laser (266 nm, 10 ns). Scanning electron microscopy and extinction spectra are used respectively to study the structural and optical properties before and after the laser structuring. Round metal NPs appear in the laser transformed areas due to melting followed by rapid solidification that is reflected in the extinction spectra by the appearance of a surface plasmon resonance around 530-540 nm. The areas with NPs are surrounded by non-transformed areas forming a periodic pattern that evolves from a 2D array to parallel lines when local laser intensity increases to cover the whole sample at high intensity. The accumulation of several pulses at low fluence can also transform the metal film almost completely by creating alternating areas having different NP dimensions. The accumulation of metal in some areas of the pattern is consistent with mass transport towards the lower temperature regions.