Browsing by Author "Klein, Dominic"

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Open Access
Atomistic simulation of ultra-short pulsed laser ablation of Al : an extension for non-thermalized electrons and ballistic transport
(2022) Eisfeld, Eugen; Förster, Daniel; Klein, Dominic; Roth, Johannes
For our model material aluminum, the influence of laser pulse duration in the range between 0.5 and 16 ps on the ablation depth is investigated in a computational study with a hybrid approach, combining molecular dynamics with the well known two-temperature model. A simple, yet expedient extension is proposed to account for the delayed thermalization as well as ballistic transport of the excited electrons. Comparing the simulated ablation depths to a series of our own experiments, the extension is found to considerably increase the predictive power of the model.
Open Access
Laser ablation of covalent materials
(2023) Klein, Dominic; Roth, Johannes (Apl. Prof. Dr.)
Ultra-fast laser ablation is the process of material removal from solid surfaces by pulsed sub-picosecond laser irradiation. In contrast to longer pulse durations, ultra-fast laser ablation shows the distinguishing feature of the timescale of excitation being below the timescale of consequent material heating. Excited charge carriers distribute the thermal energy over a larger volume than the optical penetration depth suggests, while the lattice remains in a cold state. Spatial energy distribution is followed by a fast carrier-lattice energy relaxation, which induces overheated and meta-stable states of matter. These meta-stable states are induced simultaneously in the laser-affected zone, forcing the material to relax in a variety of mechanisms, ranging from ultra-fast melting over hydrodynamic expansion to material ejection in a complex mixture of chunks, droplets or vapor. While a multitude of publications successfully study the laser irradiation induced material dynamics of metals, we investigate laser ablation of covalent materials. In contrast to metals, covalent materials show a band gap, excitation-dependent carrier heat conduction and strong excitation-dependent interatomic bonding strengths, rendering the theoretical description of such materials a difficult task. However, it also gives rise to a number of unique dynamics like non-thermal melting, Coulomb explosions and altered carrier heat conduction due to charge carrier confinement. In this work we choose silicon as our prototypical covalent material and perform molecular dynamics simulations of laser irradiated silicon, while applying an excitation-dependent interatomic potential. We present new parametrizations of the optical properties, as well as the extension of established charge carrier transport models for silicon, which are both tailored for the application on large scale massive multi-parallel high-performance computers. Finally we observe and characterize the novel and non-thermal ablation mechanics of laser irradiated silicon.
Open Access
Molecular dynamics simulations of the laser ablation of silicon with the thermal spike model
(2021) Klein, Dominic; Eisfeld, Eugen; Roth, Johannes
The purpose of this work is to model laser ablation of silicon on an atomistic scale in combination with a mesoscale model for the description of the electron-phonon interaction and an electron-temperature dependent interaction potential. The well-known continuum two-temperature model (TTM) for solids with highly excited electrons is extended from metals to silicon by explicitly taking charge carrier transport effects into account (nTTM). This is accomplished by the drift-diffusion limit of the Boltzmann-transport equation leading to the so called thermal-spike model (TSM). The model is further enhanced by extending the static modified Tersoff potential to a dynamical carrier excitation dependent interaction potential. We compare the TSM and nTTM with regard to physical correctness, numerical stability and applicability in the context of large-scale massive parallel high performance computing.
Open Access
Prozessmodellierung in der additiven Fertigung : Molekulardynamische Simulation als Ansatz zur Optimierung der additiven Qualität
(2023) Müller, Sarah; Klein, Dominic; Öhlschläger, Fabio; Roth, Johannes; Westkämper, Engelbert