Publications (25)0 Total impact
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Article: Primary damage formation in molybdenum: a computer simulation study
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ABSTRACT: The primary damage formation in Mo is investigated using molecular dynamics (MD) simulation with embedded-defect (ED) and embedded-atom method (EAM) interatomic potentials. The former is similar in spirit to the latter but includes an approximate treatment of bond directionality in the many-body interaction. MD simulations are used to calculate threshold displacement energy as function of crystallographic orientation and displacement cascade evolution resulting from primary knock-on atoms (PKAs) with energies ranging from 0.5 up to 50 keV. The defect structures produced with increasing PKA energy are analysed and the results obtained are compared for the two potentials and with simulations from the literature for other bcc materials. The impact of temperature and inelastic losses on the cascade characteristics are also discussed. The ED approach is in better agreement with the experimental findings on threshold energy. It also predicts larger vacancy clusters as well as a larger fraction of clustered vacancies than the EAM does; this seems to be more consistent with experiment, however, on statistical grounds a definite assessment is not possible with the number of simulations performed. Inelastic losses coupled with the thermal spike affect the defect production in subtle ways, especially at the higher energies considered here. This does not seem to have been realized before and deserves to be studied more comprehensively. -
Article: Quantitative analysis of CTEM images of small dislocation loops in Al and stacking fault tetrahedra in Cu generated by molecular dynamics simulation
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ABSTRACT: The visibility of conventional transmission electron microscopy (CTEM) images of small crystalline defects generated by molecular dynamics (MD) simulation is investigated. Faulted interstitial dislocation loops in Al smaller than 2 nm in diameter and stacking fault tetrahedra (SFT) in Cu smaller than 4 nm in side are assessed. A recent approach allowing to simulate the CTEM images of computer generated samples described by their atomic positions is applied to obtain bright field and weak beam images. For the dislocation loop-like cluster it appears that the simulated image is comparable to experimental images. The contrast of the g(3.1g) near weak beam image decreases with decreasing size of the cluster but is still 20% of the background intensity for a 2 interstitial cluster. This indicates a visibility at the limit of the experimental background noise. In addition, the cluster image size, which is here always larger than the real size, saturates at about 1 nm when the cluster real size decreases below 1 nm, which corresponds to a cluster of 8 interstitials. For the SFT in Cu the g(6.1g) weak beam image is comparable to experimental images. It appears that the image size is larger than the real size by 20%. A large loss of the contrast features that allows to identify an SFT is observed on the image of the smallest SFT (21 vacancies). (C) 2000 Elsevier Science B.V. All rights reserved. -
Article: Microstructure and growth modes of stoichiometric NiAl and Ni3Al thin films deposited by rf-magnetron sputtering
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Article: Quantitative long-range-order measurement and disordering efficiency estimation in ion-irradiated bulk Ni3Al using cross-sectional conventional transmission electron microscopy
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ABSTRACT: Irradiation-induced disordering of bulk Ni3Al under 6 MeV Ni2+ irradiation is studied at room temperature. A self-consistent long-range-order quantification method for ion-irradiated intermetallics is presented using cross-sectional sample preparation and conventional transmission electron microscopy in selected area diffraction depth profiling mode. This method, which does not require the full assessment of dynamic diffraction image simulation information, is unique to precisely measure long-range-order as a function of depth or dose for a single total fluence. The disordering efficiency constant epsilon is estimated in the range 10.0 +/- 0.7/dpa for a total fluence of 10(14) cm(-2). (C) 2000 American Institute of Physics. [S0003-6951(00)03543-9]. -
Article: Modelling irradiation effects in fusion materials
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ABSTRACT: We review the current status of the European fusion materials modelling programme. We describe recent findings and outline potential areas for future development. Large-scale density functional theory (DFT) calculations reveal the structure of the point defects in α-Fe, and highlight the crucial part played by magnetism. The calculations give accurate migration energies of point defects and the strength of their interaction with He atoms. Kinetic models based on DFT results reproduce the stages of radiation damage recovery in iron, and stages of He-desorption from pre-implanted iron. Experiments aimed at validating the models will be carried out in the future using a multi-beam ion irradiation facility chosen for its versatility and rapid feedback.Fusion Engineering and Design.
