Abstract
The productivity of nanoparticles formed by laser ablation of gold-silver and iron-gold alloy as well as copper and iron-nickel alloy targets in water is correlated with the formation of laser-induced surface structures. At a laser fluence optimized for maximum nanoparticle productivity, it is found that a binary alloy with an equimolar ratio forms laser-induced periodic surface structures (LIPSS) after ablation, if one of the constituent metals also form LIPSS. The ablation rate of nanoparticles linearly depends on the laser fluence if LIPSS is not formed, while a logarithmic trend and a decrease in productivity is evident when LIPSS is formed. To cancel LIPSS formation and recover from this decrease, a change to circularly polarized light is performed and an increase in nanoparticle productivity of more than 30% is observed.
Highlights
Laser ablation offers a broad application platform, which can be used for generating colloidal nanoparticles [1,2] and/or to induce surface structures such as “Laser induced periodic surface structures” (LIPSS) or ripples [3,4,5,6,7]
Comparing the scanning electron microscope (SEM) images, it is evident that alloys of iron with nickel or gold are forming laser-induced periodic surface structures (LIPSS) while alloys that contain an equimolar amount of silver (i.e. Fe50Ag50 and Au50Ag50) are not forming any LIPSS at the applied laser fluences
For this surface the reflectivity was measured to be 10.39% ± 1.06%, it is 20% lower than the reflectivity of a surface that showed LIPSS. This finding strongly supports the result, that without LIPSS on the target surface the absorption and the ablation efficiency significantly increases. To further support this interesting finding which directly relates to nanoparticle productivity, we have extended this study to a further material that is not forming LIPSS structures at a fluence of 2.72 J/cm2
Summary
Laser ablation offers a broad application platform, which can be used for generating colloidal nanoparticles [1,2] and/or to induce surface structures such as “Laser induced periodic surface structures” (LIPSS) or ripples [3,4,5,6,7]. While in many LAL-related studies the focus is placed on the effect of the ambient liquid, the utilized laser or the material properties of the ablation target, the surface structure of the target which apparently changes during ablation is generally neglected For aspects such as the nanoparticle productivity [27,28,29] (i.e. the ablation rate) the surface structure needs to be considered, since the ablation rate is strongly related to the (evolving) optical properties of the target [2]. To shed light onto the interplay between LIPSS and LAL and their opposing fluence-trends, LIPSS formation on several metal targets are studied in this study Due to their relevance in plasmonics [33,34,35], biomedicine [36,37] and catalysis [38,39] the alloy systems of iron-gold and gold-silver as well as their constituent metals are studied in detail for different fluences and compositions and eventually correlated to nanoparticle productivity
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