2,137 research outputs found
Historical review of computer simulation of radiation effects in materials
In this Article, I review the development of computer simulation techniques for studying radiation effects in materials from 1946 until 2018. These developments were often closely intertwined with associated experimental developments, which are also briefly discussed in conjunction with the simulations. The focus is on methods that either deal directly with the primary radiation damage generation event, or with such defects or phase changes that typically occur due to radiation. The methods discussed at some length are, in order of historical appearance: Reaction rate theory or rate equations (RE), Monte Carlo neutronics calculations (MCN), Metropolis Monte Carlo (MMC), Molecular Dynamics (MD), Binary Collision Approximation (BCA), Kinetic Monte Carlo (KMC), Discrete Dislocation Dynamics (DDD), Time-Dependent Density Functional Theory (TDDFT), and Finite Element Modelling (FEM). For each method, I present the origins of the methods, some key developments after this, as well as give some opinions on possible future development paths. (C) 2019 The Author. Published by Elsevier B.V.Peer reviewe
High energy collision cascades in tungsten: dislocation loops structure and clustering scaling laws
Recent experiments on in-situ high-energy self-ion irradiation of tungsten
(W) show the occurrence of unusual cascade damage effects resulting from single
ion impacts, shedding light on the nature of radiation damage expected in the
tungsten components of a fusion reactor. In this paper, we investigate the
dynamics of defect production in 150 keV collision cascades in W at atomic
resolution, using molecular dynamics simulations and comparing predictions with
experimental observations. We show that cascades in W exhibit no subcascade
break-up even at high energies, producing a massive, unbroken molten area,
which facilitates the formation of large defect clusters. Simulations show
evidence of the formation of both 1/2 and interstitial-type
dislocation loops, as well as the occurrence of cascade collapse resulting in
vacancy-type dislocation loops, in excellent agreement with experimental
observations. The fractal nature of the cascades gives rise to a scale-less
power law type size distribution of defect clusters.Comment: 6 pages, 3 figure
Cooperative mixing induced surface roughening in bilayer metals: a possible novel surface damage mechanism
Molecular dynamics simulations have been used to study a collective atomic
transport phenomenon by repeated Ar irradiations in the Ti/Pt interfacial
system. The ion-induced injection of surface atoms to the bulk, the ejection of
bulk atoms to the top layers together with surface erosion is strongly enhanced
by interfacial mixing. This process leads to a dense interfacial material, and
broadening of the interface region. The process scales with the relative
difference of the atomic masses. We find that surface roughening and
interfacial mixing is strongly coupled via an enhanced counterflow material
transport normal to the surface which might be a novel surface damage
mechanism. This cooperative phenomenon is active when the bilayer system is
subjected to a high dose ion irradiation (multiple ion irradiations) and leads
to surface cavity growth.Comment: 6 pages, 6 figures. accepted in Nucl. Instrum. Meth.
Does the thermal spike affect low-energy ion-induced interfacial mixing?
Molecular dynamics simulations have been used to obtain the three-dimensional
distribution of interfacial mixing and cascade defects in Ti/Pt multilayer
system due to single 1 keV impacts at grazing angle of incidence. The
Ti/Pt system was chosen because of its relatively high heat of mixing in the
binary alloy and therefore a suitable candidate for testing the effect of heat
of mixing on ion-beam mixing. However, the calculated mixing profile is not
sensitive to the heat of mixing. Therefore the thermal spike model of mixing is
not fully supported under these irradiation conditions. Instead we found that
the majority of mixing occurs after the thermal spike during the relaxation
process. These conclusions are supported by liquid, vacancy as well as adatom
analysis. The interfacial mixing is in various aspects anomalous in this
system: the time evolution of mixing is leading to a phase delay for Ti mixing,
and Pt exhibits an unexpected double peaked mixing evolution. The reasons to
these effects are discussed.Comment: 7 pages, 12 figures, Nucl. Instr. Meth. B211, 524. (2003
Channeling maps for Si ions in Si : Assessing the binary collision approximation
Simulations based on the binary collision approximation (BCA) are in principle less accurate than molecular dynamics (MD) simulations. In this work, we present a comprehensive comparison between BCA and MD for Si ions impinging on a (001)-Si surface by comparing "channeling maps", i.e., projected ranges of the ions as a function of incidence direction in a representative part of the angular space. We find quantitative differences to develop as the energy decreases below similar to 100 eV, but find qualitative agreement down to similar to 10 eV. Moreover, the quality of the BCA channeling maps depends on the implementation of the BCA, which is explained in terms of double-hits and missed collisions.Peer reviewe
Sputtering yields exceeding 1000 by 80keV Xe irradiation of Au nanorods
Using experiments and computer simulations, we find that 80 keV Xe ion irradiation of Au nanorods can produce sputtering yields exceeding 1000, which to our knowledge are the highest yields reported for sputtering by single ions in the nuclear collision regime. This value is enhanced by more than an order of magnitude compared to the same irradiation of flat Au surfaces. Using MD simulations, we show that the very high yield can be understood as a combination of enhanced yields due to low incoming angles at the sides of the nanowire, as well as the high surface-to-volume ratio causing enhanced explosive sputtering from heat spikes. We also find, both in experiments and simulations, that channeling has a strong effect on the sputtering yield: if the incoming beam happens to be aligned with a crystal axis of the nanorod, the yield can decrease to about 100
Molecular dynamics simulations of cascades in strained carbide inclusions embedded in alpha-iron
The effect of strain on the amount of point defects created in Fe and Cr carbide inclusions embedded in ferrite has been investigated. The spherical carbide inclusions consisted of either Fe3C or Cr23C6. Recoil energies from 100 eV to 3 keV and strains from -0.15 (compressive) to 0.01 (tensile) were used. The overall tendency is that the number of point defects - such as antisites, vacancy and interstitials - inside the carbide is lowered when the strain grows more negative (compressive). Outside the carbides, the number of defects is markedly higher for strongly compressive strains than for e.g. zero strain, especially at high energies. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.Peer reviewe
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