Modeling of Nonthermal Solid‐to‐Solid Phase Transition in Diamond Irradiated with Femtosecond x‐ray FEL Pulse

Medvedev, Nikita; Tkachenko, Victor; Ziaja, Beata

doi:10.1002/ctpp.201400026

Cited by 23 publications

(33 citation statements)

References 73 publications

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“…The Monte Carlo (MC) method is used to describe the transient nonequilibrium kinetics of high-energy electrons and their secondary cascading as well as the photoabsorption and Auger decays of atomic deep-shell holes [19,25,26,29,30]. More details on the Monte Carlo model and the cross sections used can be found in [19,38]. The cross sections used for electron scattering in silicon can be found in Ref.…”

Section: A Hybrid Modelmentioning

confidence: 99%

Thermal and nonthermal melting of silicon under femtosecond x-ray irradiation

2015

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As is known from visible-light experiments, silicon under femtosecond pulse irradiation can undergo so-called "nonthermal melting" if the density of electrons excited from the valence to the conduction band overcomes a certain critical value. Such ultrafast transition is induced by strong changes in the atomic potential energy surface, which trigger atomic relocation. However, heating of a material due to the electron-phonon coupling can also lead to a phase transition, called "thermal melting." This thermal melting can occur even if the excited-electron density is much too low to induce nonthermal effects. To study phase transitions, and in particular, the interplay of the thermal and nonthermal effects in silicon under a femtosecond x-ray irradiation, we propose their unified treatment by going beyond the Born-Oppenheimer approximation within our hybrid model based on tight-binding molecular dynamics. With our extended model we identify damage thresholds for various phase transitions in irradiated silicon. We show that electron-phonon coupling triggers the phase transition of solid silicon into a low-density liquid phase if the energy deposited into the sample is above ∼0.65 eV per atom. For the deposited doses of over ∼0.9 eV per atom, solid silicon undergoes a phase transition into high-density liquid phase triggered by an interplay between electron-phonon heating and nonthermal effects. These thresholds are much lower than those predicted with the Born-Oppenheimer approximation (∼2.1 eV/atom), and indicate a significant contribution of electron-phonon coupling to the relaxation of the laser-excited silicon. We expect that these results will stimulate dedicated experimental studies, unveiling in detail various paths of structural relaxation within laser-irradiated silicon.

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Section: A Hybrid Modelmentioning

confidence: 99%

Thermal and nonthermal melting of silicon under femtosecond x-ray irradiation

2015

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“…Later, if the density of excited electrons overcomes a certain fraction of the total number of valence band electrons (∼1.5% for diamond), the electronic band structure undergoes significant changes, with the most prominent effect of the band gap collapse [29]. For above-threshold doses, band gap collapse is clearly visible on the time scale of the transmission decrease.…”

Section: Diamondmentioning

confidence: 99%

“…For above-threshold doses, band gap collapse is clearly visible on the time scale of the transmission decrease. However, it can also occur before the final drop of the transmission to zero, because it takes some time for atoms to relax into a new equilibrium state of graphite [29]. That is reflected by an occurrence of a transient plateau in the transmission curve mentioned above.…”

Section: Diamondmentioning

confidence: 99%

“…Amorphization of silicon can occur via thermal and non-thermal melting [29]. The estimated threshold dose for silicon melting is ∼ 0.65 eV/atom, when solid silicon transforms into a low-density liquid (LDL).…”

Section: Siliconmentioning

confidence: 99%

“…Heating of atoms by electron-phonon coupling is necessary to accomplish the transition. This usually takes up to a few picoseconds [29].…”

Section: Siliconmentioning

confidence: 99%

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Transient Changes of Optical Properties in Semiconductors in Response to Femtosecond Laser Pulses

2016

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Abstract:In this paper we present an overview of our theoretical simulations on the interaction of ultrafast laser pulses with matter. Our dedicated simulation tool, X-ray induced Thermal And Non-thermal Transitions (XTANT) can currently treat semiconductors irradiated with soft to hard X-ray femtosecond pulses. During the excitation and relaxation of solids, their optical properties such as reflectivity, transmission and absorption, are changing, affected by transient electron excitation and, at sufficiently high dose, by atomic relocations. In this review we report how the transient optical properties can be used for diagnostics of electronic and structural transitions occurring in irradiated semiconductors. The presented methodology for calculation of the complex dielectric function applied in XTANT proves to be capable of describing changes in the optical parameters, when the solids are driven out of equilibrium by intense laser pulses. Comparison of model predictions with the existing experimental data shows a good agreement. Application of transient optical properties to laser pulse diagnostics is indicated.

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

Medvedev

Akhmetov

Rymzhanov

et al. 2022

Advcd Theory and Sims

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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.

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Modeling of Nonthermal Solid‐to‐Solid Phase Transition in Diamond Irradiated with Femtosecond x‐ray FEL Pulse

Cited by 23 publications

References 73 publications

Thermal and nonthermal melting of silicon under femtosecond x-ray irradiation

Thermal and nonthermal melting of silicon under femtosecond x-ray irradiation

Transient Changes of Optical Properties in Semiconductors in Response to Femtosecond Laser Pulses

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

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