CC BY
9LMI-I-6
Multistep phase transitions in X-ray free-electron-laser irradiated solids
N. Medvedev1
institute of Physics Czech Academy of Sciences, Department of Radiation and Chemical Physics, Prague, Czech Republic
This talk will briefly review the results of our theoretical research on damage mechanisms in various materials irradiated with femtosecond X-ray free-electron-laser pulses at fluences ranging from mild excitation of the target to warm dense matter formation. Various damage mechanisms are discussed on examples of insulators (e.g. diamond [1]), semiconductors (e.g. silicon [2]), metals (e.g. gold). They are studied with the developed hybrid approach, XTANT (X-ray-induced Thermal And Nonthermal Transitions [3]), which includes nonequilibrium kinetics of electrons modeled within a combination of the Monte Carlo simulation and Boltzmann kinetic approach, nonthermal effects in the atomic system traced within tight-binding molecular dynamics, and nonadiabatic coupling between the systems.
We analyze the effects of thermal melting of targets as a result of electron-ion energy exchange; nonthermal phase transitions due to modification of the interatomic potential (such as nonthermal melting in silicon or solid-solid phase transition in irradiated diamond); spallation or ablation at higher fluences due to detachment of sample fragments; and a complex multistep kinetics of warm dense matter formation [4]. As a result, we demonstrate that diamond upon femtosecond pulse irradiation turns into graphite within 150-200 fs, in a very good agreement with experimental data [1]. Silicon [2], as well as AlAs [5], can melt both, thermally or nonthermally, into two different liquid phases. We also find that the electron-ion (electron-phonon) coupling parameter can be accessed in highly-excited samples via pump-probe time-resolved measurements of optical properties [2].
References
[1] F. Tavella, H. Hoppner, V. Tkachenko, N. Medvedev, F. Capotondi, T. Golz, Y. Kai, M. Manfredda, E. Pedersoli, M. J. Prandolini, N. Stojanovic, T. Tanikawa, U. Teubner, S. Toleikis, and B. Ziaja, High Energy Density Phys. 24, 22 (2017).
[2] N. Medvedev, Z. Li, V. Tkachenko, and B. Ziaja, Phys. Rev. B 95, 014309 (2017).
[3] N. Medvedev, V. Tkachenko, V. Lipp, Z. Li, and B. Ziaja, 4open 1, 3 (2018).
[4] N. Medvedev and B. Ziaja, Sci. Rep. 8, 5284 (2018).
[5] N. Medvedev, Z. Fang, C. Xia, and Z. Li, Phys. Rev. B 99, 144101 (2019).
