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Tuesday 18 July 2017

MESA+ Colloquium by Nikita Medvedev

Date: 18 July
Time: 11.00 hrs
Room: Carré, Hal B - 2F

Various damage mechanisms in EUV/X-ray irradiated solids by Nikita Medvedev 1,2

  1. Department of Radiation and Chemical Physics, Institute of Physics, Czech Academy of Sciences, Na Slovance 2, 182 21 Prague 8, Czech Republic
  2. Laser Plasma Department, Institute of Plasma Physics, Czech Academy of Sciences, Za Slovankou 3, 182 00 Prague 8, Czech Republic

Abstract

In this talk I present modeling techniques and results on damage formation in solids irradiated with femtosecond free-electron Extreme-UV and X-ray laser pulses. The main results are obtained with the developed hybrid model XTANT (X-ray-induced Thermal And Nonthermal Transitions [1,2]), which combines Tight Binding formalism, Molecular Dynamics, Monte Carlo simulations, and Boltzmann equations into one numerical code. It reveals different mechanisms of material damage, namely: (i) thermal melting of materials such as silicon [1]; (ii) nonthermal melting in Si [1], or solid-solid phase transition in carbon, e.g. ultrafast graphitization of diamond [2]; (iii) Coulomb explosion of molecular crystal of C60, and ablation of amorphous carbon. Influence of various channels of electron-lattice energy exchange will be presented. Comparison of calculated transient optical properties [3] with experimental ones measured in pump-probe experiments provides a possibility to benchmarks theoretical frameworks and approximations used in the numerical models. For example, it is demonstrated that in case of semiconductors, shrinkage of the band gap due to atomic heating allows to extract information on electron-phonon coupling with femtosecond resolution in a broad range of electron temperatures [4]. At the end, I will briefly discuss other possibilities and advantages of combined and multi-scale models, such as combination of Two-Temperature Model with Monte Carlo simulations and Molecular Dynamics.

  1. N. Medvedev, Z. Li, B. Ziaja, Physical Review B. 91 (2015) 54113.
  2. N. Medvedev, H.O. Jeschke, B. Ziaja, Physical Review B. 88 (2013) 224304.
  3. V. Tkachenko, N. Medvedev, Z. Li, P. Piekarz, B. Ziaja, Physical Review B. 93 (2016) 144101.
  4. B. Ziaja, N. Medvedev, V. Tkachenko, T. Maltezopoulos, W. Wurth, Scientific Reports. 5 (2015) 18068.