Laser-Induced Translative Hydrodynamic Mass Snapshots: Noninvasive Characterization and Predictive Modeling via Mapping at Nanoscale

Abstract

Nanoscale thermally assisted hydrodynamic melt perturbations induced by ultrafast laser energy deposition in noble-metal films produce irreversible nanoscale translative mass redistributions and results in formation of radially-symmetric frozen surface structures. We demonstrate that the final three-dimensional (3D) shape of the surface structures formed after re-solidification of the molten part of the film is governed by incident laser fluence and, more importantly, predicted theoretically via molecular dynamics modeling. Considering the underlying physical processes associated with laser-induced energy absorption, electron-ion energy exchange, acoustic relaxation and hydrodynamic flows, the theoretical approach separating "slow" and "fast" physical processes and combining hybrid analytical two-temperature calculations, scalable molecular-dynamics simulations, and a semi-analytical thin-shell model was shown to provide accurate prediction of the final nanoscale solidified morphologies, fully consistent with direct electron-microscopy visualization of nanoscale focused ion-beam cuts of the surface structures produced at different incident laser fluences. Finally, these results are in reasonable quantitative agreement with mass distribution profiles across the surface nanostructures, provided by their noninvasive and non-destructive nanoscale characterization based on energy-dispersive x-ray fluorescence spectroscopy, operating at variable electron-beam energies.

Laser Printing of Plasmonic Nanosponges

“…This guarantied identical coupling of the incident ns-laser pulse energy to all types of metal films under study ( Figure 1a). Such laser pulse induces thermalisation of charge carriers in the metal film that results in its local melting accompanied by detachment from the substrate via relaxation of the thermal-generated stress or evaporation at the interface between the film and the substrate [31,32]. At a pulse energy that is smaller than the ablation threshold (F th ≈ 0.17 J/cm 2 ), detached metal shell resolidifies before its rupture forming parabola-shaped surface protrusion (also (Figure 2c), while the smaller nanopores far from the rim walls preserve spherical-like geometry.…”

“…The ionisation potential of Au is 9.23 eV while that of nitrogen is 14.53 eV (for O -13.62 eV). The laser pulse driven avalanche ionisation of gold is seeding the energy deposition which is evolving into run away ablation (melting, evaporation, ionisation).The general geometry of the surface structure produced by direct laser ablation is defined by the laser irradiation parameters (fluence, pulse width and beam profile[42]) as well as by the thickness/composition of the metal film[32,43]. Our results clearly show that advanced chemical engineering of the metal film composition gives additional degree of freedom allowing to modify morphology of the laser-printed structures at the nanoscale, namely, incorporate the nanopores and control their density.…”

Enhancement of X-ray emission from nanocolloidal gold suspensions under double-pulse excitation

“…This provides a moderate enhancement of the optical near-fields as shown further by numerical simulations. The incident fluence of the main pulse used in the present study significantly exceeds both the ablation threshold for bulk gold [ 39 ] as well as the fragmentation thresholds for gold colloidal nanoparticles in water [ 40 – 41 ]. It should be stressed out that the increase of the effective size of the laser spot due to filamentation can significantly reduce the incident fluence [ 3 – 4 ].…”

Biomimetic Anti-Adhesive Surface Microstructures on Electrosurgical Blade Fabricated by Long-Pulse Laser Inspired by Pangolin Scales

“…In the capillary stage, the surface tension slowed down the moving liquid film and finally stopped its motion to form the micro-riblets radially distributed along the arc microstructure that was the part of the crater edge in the groove. Finally, the molten surface structures recrystallized, and the shape of the splashing morphology was immobilized due to the cooling effect [23][24][25].…”