Near-Infrared Femtosecond Laser Ablation of Au-Coated Ni: Effect of Organic Fluids and Water on Crater Morphology, Ablation Efficiency and Hydrodynamic Properties of NiAu Nanoparticles.

Niusha Lasemi,Günther Rupprechter,Dominik Eder,Gerhard Liedl

doi:10.3390/ma14195544

Abstract

Scanning electron microscopy (SEM) and profilometry of the crater morphology and ablation efficiency upon femtosecond laser ablation of Au-coated Ni targets in various fluids revealed a pronounced dependence on the ablation medium. For ethanol, a sufficient ablation efficiency was obtained, whereas for 2-butanol a higher efficiency indicated stronger laser–target interaction. Hierarchical features in the crater periphery pointed to asymmetrical energy deposition or a residual effect of the Coulomb-explosion-initiating ablation. Significant beam deviation in 2-butanol caused maximum multiple scattering at the crater bottom. The highest values of microstrain and increased grain size, obtained from Williamson–Hall plots, indicated the superposition of mechanical stress, defect formation and propagation of fatigue cracks in the crater circumference. For n-hexane, deposition of frozen droplets in the outer crater region suggested a femtosecond-laser-induced phase explosion. A maximum ablation depth occurred in water, likely due to its high cooling efficiency. Grazing incidence micro X-ray diffraction (GIXRD) of the used target showed residual carbon and partial surface oxidation. The produced nanoparticle colloids were examined by multiangle dynamic light scattering (DLS), employing larger scattering angles for higher sensitivity toward smaller nanoparticles. The smallest nanoparticles were obtained in 2-butanol and ethanol. In n-hexane, floating carbon flakes originated from femtosecond-laser-induced solvent decomposition.

Highlights

Nanoparticle (NP) generation by laser ablation in liquids was first reported in 1987 [1]
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Summary

Introduction

Nanoparticle (NP) generation by laser ablation in liquids was first reported in 1987 [1]. During pulsed laser ablation in liquid (PLAL), several processes (e.g., ionization of matter, plasma evolution, cavitation creation, bubble expansion and collapse, nanoparticle formation and secondary processes) occur sequentially or simultaneously [13,14]. The interaction of a femtosecond laser beam with a target results in local material vaporization and the formation of a high-temperature plasma plum. Since the molten layer of the target and the plasma plum are in direct contact with the liquid, a supercritical temperature liquid can be formed that assists the formation of a short-lived and hemispherical membrane, a so-called cavitation bubble [14], in which primary and secondary nanoparticles are generated and encapsulated [15]. Agglomeration, particle diffusion and ripening processes occur after the cavitation collapse [16]

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Results

Conclusion