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Title: Molecular Dynamics Simulations of the Time Evolution of Irradiation Induced Defects

Abstract

We present here molecular dynamics simulations of collision cascades in various metals irradiated with ions having the initial kinetic energy of 500 eV. We find that although during the collision cascade some regions of the sample become amorphous, after the thermal spike, the crystal starts to recrystallize. The multiple vacancy clusters tend to break into smaller fragments and to migrate towards the surface, leaving behind only a small number of defects.

Authors:
;  [1]
  1. Department of Physics, Ovidius University of Constanta, 900527 Constanta (Romania)
Publication Date:
OSTI Identifier:
21057260
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 899; Journal Issue: 1; Conference: 6. international conference of the Balkan Physical Union, Istanbul (Turkey), 22-26 Aug 2006; Other Information: DOI: 10.1063/1.2733458; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; COMPUTERIZED SIMULATION; CRYSTALS; EV RANGE; FRENKEL DEFECTS; IRRADIATION; KINETIC ENERGY; METALS; MOLECULAR DYNAMICS METHOD; PHYSICAL RADIATION EFFECTS; SURFACES; THERMAL SPIKES

Citation Formats

Sopu, Daniel, and Girtu, Mihai A. Molecular Dynamics Simulations of the Time Evolution of Irradiation Induced Defects. United States: N. p., 2007. Web. doi:10.1063/1.2733458.
Sopu, Daniel, & Girtu, Mihai A. Molecular Dynamics Simulations of the Time Evolution of Irradiation Induced Defects. United States. doi:10.1063/1.2733458.
Sopu, Daniel, and Girtu, Mihai A. Mon . "Molecular Dynamics Simulations of the Time Evolution of Irradiation Induced Defects". United States. doi:10.1063/1.2733458.
@article{osti_21057260,
title = {Molecular Dynamics Simulations of the Time Evolution of Irradiation Induced Defects},
author = {Sopu, Daniel and Girtu, Mihai A.},
abstractNote = {We present here molecular dynamics simulations of collision cascades in various metals irradiated with ions having the initial kinetic energy of 500 eV. We find that although during the collision cascade some regions of the sample become amorphous, after the thermal spike, the crystal starts to recrystallize. The multiple vacancy clusters tend to break into smaller fragments and to migrate towards the surface, leaving behind only a small number of defects.},
doi = {10.1063/1.2733458},
journal = {AIP Conference Proceedings},
number = 1,
volume = 899,
place = {United States},
year = {Mon Apr 23 00:00:00 EDT 2007},
month = {Mon Apr 23 00:00:00 EDT 2007}
}
  • In view of the important implications of excess electrons (EEs) interacting with CO{sub 2}–H{sub 2}O clusters in many fields, using ab initio molecular dynamics simulation technique, we reveal the structures and dynamics of an EE associated with its localization and subsequent time evolution in heterogeneous CO{sub 2}–H{sub 2}O mixed media. Our results indicate that although hydration can increase the electron-binding ability of a CO{sub 2} molecule, it only plays an assisting role. Instead, it is the bending vibrations that play the major role in localizing the EE. Due to enhanced attraction of CO{sub 2}, an EE can stably reside inmore » the empty, low-lying π{sup *} orbital of a CO{sub 2} molecule via a localization process arising from its initial binding state. The localization is completed within a few tens of femtoseconds. After EE trapping, the ∠OCO angle of the core CO{sub 2}{sup −} oscillates in the range of 127°∼142°, with an oscillation period of about 48 fs. The corresponding vertical detachment energy of the EE is about 4.0 eV, which indicates extreme stability of such a CO{sub 2}-bound solvated EE in [CO{sub 2}(H{sub 2}O){sub n}]{sup −} systems. Interestingly, hydration occurs not only on the O atoms of the core CO{sub 2}{sup −} through formation of O⋯H–O H–bond(s), but also on the C atom, through formation of a C⋯H–O H–bond. In the latter binding mode, the EE cloud exhibits considerable penetration to the solvent water molecules, and its IR characteristic peak is relatively red-shifted compared with the former. Hydration on the C site can increase the EE distribution at the C atom and thus reduce the C⋯H distance in the C⋯H–O H–bonds, and vice versa. The number of water molecules associated with the CO{sub 2}{sup −} anion in the first hydration shell is about 4∼7. No dimer-core (C{sub 2}O{sub 4}{sup −}) and core-switching were observed in the double CO{sub 2} aqueous media. This work provides molecular dynamics insights into the localization and time evolution dynamics of an EE in heterogeneous CO{sub 2}–H{sub 2}O media.« less
  • A series of molecular dynamics simulations using the embedded atom method is conducted to investigate crack propagation under mode I loading in a Ni single crystal with and without defects. The crack system (0 0 1)[1 0 0] in a slab of 160 000 atoms was studied. Defects consisting of lines of vacancies were introduced near the crack tip. Critical loads and strain energy distributions around the crack tip are obtained. Our results indicate that the critical strain necessary for crack propagation is dependent on the defect configuration and can either increase or decrease relative to the defect-free system.
  • Molecular dynamics simulations have been used to generate a comprehensive database of surviving defects due to displacement cascades in bulk tungsten. Twenty-one data points of primary knock-on atom (PKA) energies ranging from 100 eV (sub-threshold energy) to 100 keV (~780 × Ed, where Ed = 128 eV is the average displacement threshold energy) have been completed at 300 K, 1025 K and 2050 K. Within this range of PKA energies, two regimes of power-law energy-dependence of the defect production are observed. A distinct power-law exponent characterizes the number of Frenkel pairs produced within each regime. The two regimes intersect atmore » a transition energy which occurs at approximately 250 × Ed. The transition energy also marks the onset of the formation of large self-interstitial atom (SIA) clusters (size 14 or more). The observed defect clustering behavior is asymmetric, with SIA clustering increasing with temperature, while the vacancy clustering decreases. This asymmetry increases with temperature such that at 2050 K (~0.5 Tm) practically no large vacancy clusters are formed, meanwhile large SIA clusters appear in all simulations. The implication of such asymmetry on the long-term defect survival and damage accumulation is discussed. In addition, <100> {110} SIA loops are observed to form directly in the highest energy cascades, while vacancy <100> loops are observed to form at the lowest temperature and highest PKA energies, although the appearance of both the vacancy and SIA loops with Burgers vector of <100> type is relatively rare.« less