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

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.

Formation of Periodic Surface Structures by Multipulse Femtosecond Laser Processing of Au-Coated Ni in Various Fluids

“…A liquid thickness of 12 mm was used in all cases; thus the initial pulse duration (30 fs) broadened due to the pulse traveling from air/glass to liquid. Nevertheless, the final pulse duration (Table S1) did not exceed the femtosecond range. , …”

“…Also, atomistic modeling confirmed the existence of different shapes for Au nanoparticles considering their thermal stabilities. 67 In fact, these trapped cubic nanoparticles are frozen molten droplets ejected from the surface during phase explosion 56 and material reorganization. Then, as a result of fast cooling processes, these cubic and octahedral shapes are well preserved.…”

“…For hexane, the crystallite size was intermediate, but the microstrain was highest. Since the largest self-organized structures were detected for hexane ( Figure 6 j; Table 1 ) along with several small and large nanoparticles ( Figure 5 f), the pronounced fs laser-induced phase explosion 56 may thus trigger a higher accumulation of deformation zones during consecutive pulses.…”

“…Nevertheless, the final pulse duration (Table S1) did not exceed the femtosecond range. 55,56 The orientation of LIPSS on Au-coated Ni is typically perpendicular to the horizontal beam polarization. In previous work with the same femtosecond system, this orientation was also observed on steel.…”

Defect-Rich CuZn Nanoparticles for Model Catalysis Produced by Femtosecond Laser Ablation

“…Based on previous studies, such fluences avoid unwanted nonlinear processes. 49,56,59 BF-TEM micrographs of CuZn nanoalloys (Figure 4a) synthesized at 1.6 J cm −2 revealed a bimodal size distribution. Larger NPs had a mean size of 38 nm, the small ones were 2 nm (for a size distribution analysis, see Figure S11ab).…”