Organizers
- Andrea Sand (Aalto University)
- Artur Tamm (University of Tartu)
Objectives
Particle radiation interacts with materials on a wide range of length and time scales. The multi- scale non-equilibrium nature makes radiation-induced processes exceptionally difficult to model. Molecular dynamics within a two-temperature framework (TTMD) has shown success for large- scale atomistic simulations of non-equilibrium effects in specific regimes [1], by treating electronic and ionic systems individually, with a coupling between the subsystems implemented in various ways. Ions and their interactions are treated explicitly, while electrons are represented in a continuum approximation retaining only heat capacity and heat conductivity realized through a heat diffusion equation [2,3]. Nevertheless, questions exist both regarding the implementation of the electronic subsystem, the interactions within the ionic system, and the coupling between the subsystems.
Probing the full range of effects experimentally is in many cases challenging. For example, the energy losses experienced by projectiles traveling through a material can be measured, but determining electronic stopping is challenging due to the synergistic effects of nuclear and electronic stopping. The nuclear and electronic stopping cannot be readily disentangled in experiments, especially for lower velocity and heavy projectiles [4]. Detailed investigations of low energy projectiles in different crystal orientations reveal trajectory-dependent effects which have yet to be fully understood [5], and as of yet have not been reproduced in modeling. Computational and experimental determination of electron-phonon coupling is often in disagreement [6]. Swift heavy ions are understood to cause a local rapid heating of the electronic system [7], a situation which is similar to that induced by ultra-fast laser pulses. The TTMD method has allowed predictions for instance of melting thresholds or heating rates in laser- irradiated metals, but is subject to limitations in applicability [8]. Finally, radiation induced collision cascades, where both electron-phonon coupling and electronic stopping are active [9,10], have yet to be experimentally probed at all, on the sub-nanosecond time scale at which these processes evolve. Hence modeling, while offering an essential tool for understanding and predicting effects that cannot be observed directly, proves challenging to validate for non- equilibrium processes that are active over a wide range of scales.
The aim of this workshop is to bring together researchers working on developing and implementing models of electron-ion interactions into large scale atomistic simulations, parametrizing such models through theory or first principles calculations, and researchers carrying out experimental investigations on a level that facilitates model validation. The topics that the workshop will cover include, but are not limited to:
- collision cascades, experimental and modeling
- swift heavy ions, experimental and modeling
- ultra-fast laser excitation, experimental and modeling
- electronic stopping, experimental and modeling
References
[1] A. Tamm, et al., Phys. Rev. B 94 (2016) 024305
[2] D.M. Duffy, et al., J. Phys.: Condens. Matter 19 (2007) 016207
[3] A. Tamm, et al., Phys. Rev. Lett. 120 (2018) 185501
[4] J. Ziegler, et al., NIMB 268 (2010) 1818–1823
[5] S. Lohmann, et al., Phys. Rev. Lett. 124 (2020) 096601
[6] Z. Lin,et al, Phys. Rev. B 77 (2008) 075133
[7] A. Kamarou, et al., Phys. Rev. B, vol. 73 (2006) 184107
[8] B. Rethfeld, et al., J. Phys. D: Appl. Phys. 50 (2017) 193001
[9] E. Zarkadoula, et al., Scripta Materialia 138 (2017) 124–129
[10] AE Sand, et al., J. Nucl. Mater. 456 (2015) 99-105
