Modeling Time‐Resolved Kinetics in Solids Induced by Extreme Electronic Excitation

Abstract

The authors present a concurrent Monte Carlo (MC)-molecular dynamics (MD) approach to modeling matter response to excitation of its electronic system at nanometric scales. The two methods are combined on-the-fly at each time step in one code, TREKIS-4. The MC model describes the arrival of irradiation (a photon, an electron, or a fast ion). It traces induced cascades of secondary electrons and holes, and their energy exchange with atoms due to scattering. The excited atomic system is simulated with an MD model. An efficient way is proposed to account for nonthermal effects in the electron-atom energy transfer in covalent materials via the conversion of the potential energy of the electronic ensemble into the kinetic energy of atoms. Such a combined MC-MD approach enables a time-resolved tracing of the excitation kinetics of both, the electronic and atomic systems, and their simultaneous response to a deposited dose. As a proof-of-principle, it is shown that the proposed method describes atomic dynamics after X-ray irradiation in good agreement with tight-binding MD. The model also allows gaining insights into the atomic system behavior during the energy deposition from a nonequilibrium electronic system excited by an ion impact.

Non-thermal structural transformation of diamond driven by x-rays

“…The effective x-ray dose D eff is calculated as follows: where E is the pump pulse energy, w x is the pump horizontal x-ray focus (width at the 1/e level), w y is the pump vertical x-ray focus (width at the 1/e level), λ e is the electron cascade size at the pump photon energy of 7 keV (0.41 μ m according to Refs. 20 and 33 ), λ x is the x-ray penetration depth at the pump photon energy, and ρ a is the atomic density. The pump pulse energy is evaluated from the pump pulse intensity observed by the spectrometer, which is then normalized by the signal of a beamline intensity monitor and corrected by the reflectivity of the Kirkpatrick–Baez focusing mirrors.…”

Frontiers, challenges, and solutions in modeling of swift heavy ion effects in materials

“…168 Figures 9-11 present the mean free paths (MFPs) for elastic and inelastic scatterings of electrons in alumina, calculated with the CDF-based cross sections in MC code TREKIS-4. 169 At low energies, when the electron scatters on phonons or plasmons (collective modes of the target), the scattering probability increases approximately linearly with the electron velocity. As the velocity approaches the characteristic velocity of the scattering centers (∼tens of eV for scattering on electrons), the incident electron is seeing the target as an ensemble of individual scattering centers.…”

“…Inelastic electron mean free path in Al 2 O 3 , calculated with TREKIS. 5,6,169 Total MFP, scattering on the valence band electrons, and on all deep shells are shown.…”

“…Electron mean free paths of different processes in Al 2 O 3 , calculated with TREKIS. 5,6,169 Bremsstrahlung cross section is calculated according to Ref. 41. section with the modified Molier screening parameter [Eq.…”

Electronic nonequilibrium effect in ultrafast-laser-irradiated solids

“…The impact ionization and (quasi-)elastic scattering processes are included. The impact ionization is modeled with the binary-encounter Bethe (BEB) cross-section [35], or, alternatively, with the linear response theory [36]. The elastic scattering is modeled with the screened Rutherford (Mott) cross-section with the modified Molier screening parameter [37].…”