A comparative molecular dynamics simulation study of collision cascades in two elemental semiconductors and five fcc metals is performed to elucidate how different material characteristics affect primary defect production during ion irradiation. By using simulations of full 400 eV-10 keV collision cascades and contrasting the results on different materials with each other, we probe the effect of the mass, melting temperature, material strength, and crystal structure on the modification of the material due to the cascade. The results show that the crystal structure has a strong effect on many aspects of damage production, while other material characteristics are of lesser overall importance. In all materials studied, isolated point defects produced by the cascade are predominantly interstitials. In semiconductors, amorphous clusters are produced in the cascade core, whereas in metals most of the crystal regenerates, leaving only small vacancy-rich clusters. Large interstitial clusters found in a few events in the heavy metals were observed to form by the isolation of a high-density liquid zone during the recrystallization phase of a cascade.

We discuss molecular-dynamics simulations of ion damage in silicon, with emphasis on the effects of ion mass and energy. We employ the Stillinger-Weber potential for silicon, suitably modified to account for high-energy collisions between dopant-silicon and silicon-silicon pairs. The computational cells contain up to ${10}^6$ atoms and these are bombarded by B and As atoms at incident energies from 1 keV up to 15 keV. We show that the displacement cascade results in the production of amorphous pockets as well as isolated point defects and small clusters with populations which have a strong dependence on ion mass and a weaker relationship to the ion energy. We show that the total number of displaced atoms agrees with the predictions of binary collision calculations for low-mass ions, but is a factor of 2 larger for heavy-ion masses. We compare the simulations to experiments and show that our results provide a clear and consistent physical picture of damage production in silicon under ion bombardment. We studied the stability of the damage produced by heavy ions at different temperatures and the nature of the recrystallization mechanism. The inhomogeneous nature of the damage makes the characterization of the process through a single activation energy very difficult. An effective activation energy is found depending on the pocket size. We discuss our results considering the Spaepen-Turnbull recrystallization model for an amorphous-crystalline planar interface. © 1996 The American Physical Society.

Planar shock waves in single-crystal copper were simulated using nonequilibrium molecular dynamics with a realistic embedded atom potential. The simulation results are in good agreement with new experimental data presented here, for the Hugoniot of single-crystal copper along $⟨100⟩$ . Simulations were performed for Hugoniot pressures in the range 2 GPa – 800 GPa, up to well above the shock induced melting transition. Large anisotropies are found for shock propagation along $⟨100⟩,⟨110⟩$ , and $⟨111⟩$ , with quantitative differences from pair potentials results. Plastic deformation starts at $U_p\gtrsim 0.75\mathrm{km}∕\mathrm{s}$ , and melting occurs between 200 and 220 GPa, in agreement with the experimental melting pressure of polycrystalline copper. The Voigt and Reuss averages of our simulated Hugoniot do not compare well below melting with the experimental Hugoniot of polycrystalline copper. This is possibly due to experimental targets with preferential texturing and/or a much lower Hugoniot elastic limit.

In this work, we introduce the Object Kinetic Monte Carlo (OKMC) simulator MMonCa and simulate the defect evolution in three different materials. We start by explaining the theory of OKMC and showing some details of how such theory is implemented by creating generic structures and algorithms in the objects that we want to simulate. Then we successfully reproduce simulated results for defect evolution in iron, silicon and tungsten using our simulator and compare with available experimental data and similar simulations. The comparisons validate MMonCa showing that it is powerful and flexible enough to be customized and used to study the damage evolution of defects in a wide range of solid materials.I. M.-B. wants to acknowledge funding of the project MASTIC (PCIG09-GA-2011-293783) by the Marie Curie Actions Grant FP7-PEOPLE-2011-CIG program. This work contributes to the Joint Programme of Nuclear Materials of the European Energy Research Alliance

The diffusion of He in irradiated $\alpha \text{−}\mathrm{Fe}$ is studied using a rate theory model addressing the effect of impurities. Ab initio values for the migration and binding energies of He, He-vacancy complexes, vacancy, and self-interstitial clusters are used to model desorption experiments of He-implanted $\alpha \text{−}\mathrm{Fe}$. Using the brute ab initio data yields a significant discrepancy with experimental measurements. On the other hand, good agreement is obtained when the vacancy migration energy is increased from the original ab initio value while the binding energies of vacancies with substitutional and interstitial helium are lowered. The presence of impurities, with carbon being the most likely candidate, is proposed as a justification for these effective energies. Our simulations also provide a detailed description of the diffusion mechanisms of He active under these particular experimental conditions.