Lasemi, N., Liedl, G., & Rupprechter, G. (2022, October 25). Multi-pulse femtosecond laser ablation of Au-coated Ni foil in various fluids: A way to produce hierarchical periodic surface structures and nanomaterials [Keynote Presentation]. Functional Materials 2022, Bratislava, Slovakia.
Femtosecond laser ablation in liquids can be used for surface engineering to generate laser-induced periodic surface structures (LIPSS) or for nanomaterial production. Both have a variety of applications in optics, electronics, catalysis and medicine. In fact, LIPSS is the preliminary process to generate nanoparticles. That´s why several monomodal and multimodal nanoparticles were detected while they were embedded or trapped on nanoripples. After applying several consecutive fs pulses on metals, the absorption of laser energy by surface electrons leads to the formation of hot and excited electron gas while the lattice system stays cold, as explained by the two-temperature model. Since the fs pulses are shorter than the electron-lattice relaxation time (10−10 to 10−12 s), a surface goes through a reorganization followed by hydrodynamic instabilities, phase transformations and formation of self-organized micro/nanostructures. However, the expected results can be affected by the ablation environment, thus the nature of the fluid plays an important role for the morphology of the laser-treated areas, type/frequency/orientation of hierarchical features, the composition of the ripples/crates/nanoparticles, crater width/depth/volume and specific ablation rate. For analyses of either LIPSS or craters, the highest resulting microstrain was measured for butanol. Also, LIPSS on butanol went through lattice deformation and increased cell volume. For NiAu nanoparticles, a lowest Stokes radius was observed in butanol. This can result from the formation of a thin graphite shell around the nanoparticles which prevents particles from further diffusion. Moreover, an imperfect graphite layer was detected by confocal Raman spectroscopy on LIPSS areas for butanol.
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Research Areas:
Materials Characterization: 30% Photonics: 33% Surfaces and Interfaces: 37%