Abstract
We report on the fabrication of spherical Au spheres by pulsed laser treatment using a KrF excimer laser (248 nm, 25 ns) under ambient conditions as a fast and high throughput fabrication technique. The presented experiments were realized using initial Au layers of 100 nm thickness deposited on optically transparent and low cost Borofloat glass or single-crystalline SrTiO3 substrates, respectively. High (111)-orientation and smoothness (RMS ≈ 1 nm) are the properties of the deposited Au layers before laser treatment. After laser treatment, spheres with size distribution ranging from hundreds of nanometers up to several micrometers were produced. Single-particle scattering spectra with distinct plasmonic resonance peaks are presented to reveal the critical role of optimal irradiation parameters in the process of laser induced particle self-assembly. The variation of irradiation parameters like fluence and number of laser pulses influences the melting, dewetting and solidification process of the Au layers and thus the formation of extremely well shaped spherical particles. The gold layers on Borofloat glass and SrTiO3 are found to show a slightly different behavior under laser treatment. We also discuss the effect of substrates.
Highlights
Nanoparticle (NP) plasmonics have gained importance in recent years in a variety of applications
We investigated the influence of laser fluence, laser pulse numbers and substrate materials on the ns-laser assisted particle formation
The fabricated single spheres, which were formed during a self-assembling process show Localized Surface Plasmon Resonance (LSPR) spectra dependent on the particle size
Summary
Nanoparticle (NP) plasmonics have gained importance in recent years in a variety of applications. Utilizing a laser for ablating a solid target or for heating or melting a layer by optical absorption extremely high energy is focused on and will be introduced into the metal These technologies are used, for instance, to turn spherical nanoparticles into spheroid shape[18], to prepare alloyed nanoparticles[19,20] or to produce nanoparticles in liquids or gaseous environment[21,22,23,24] by ablation or melting. A lot of different parameters like the target or layer material with its optical penetration depth, the layer thickness when an deposited continuous layer on a substrate should convert into particles, the ambient medium of the target or of the layer, the wavelength, the laser fluence, the pulse duration and the pulse number affect the particle formation process and the results in NP size and size distribution. We investigated the influence of laser fluence, laser pulse numbers and substrate materials on the ns-laser assisted particle formation
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