| 1. |
- Samela, J., et al.
(author)
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Argon cluster impacts on layered silicon, silica, and graphite surfaces
- 2007
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In: European Physical Journal D. ; 43, s. 181-184
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Journal article (peer-reviewed)abstract
- Seven structures of covalently bonded materials are used as targets of 6 keV Ar12 cluster bombardment in classical molecular dynamics simulations. Energy deposition, cratering and Ar ranges are compared and remarkable differences are found between the structures. In particular, bombardment of a thin 2 nm silica layer on top of the Si(111) surface is shown to behave quite differently from bombardment of pure Si.
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| 2. |
- Samela, J., et al.
(author)
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Comparison of silicon potentials for cluster bombardment simulations
- 2007
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In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. ; 255:1, s. 253-258
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Journal article (peer-reviewed)abstract
- We have compared three common silicon potentials for molecular dynamics simulations of cluster bombardment of silicon structures. The potentials tested are Stillinger–Weber, Tersoff III and EDIP. We have also tested one variation of Stillinger–Weber and a variation of Tersoff III potential to see how small modifications of parameter values affect collision cascade and crater geometries. Single ion sputtering yields are compared to experimental values. In simulations, Si(1 1 1) surfaces are bombarded with 1–60 keV Ar12 clusters. The potentials give almost similar overall description of collision cascades at different energies. However, measurable quantities like sputtering yields and crater sizes vary considerably between potentials and even between different parametrisations of the same potential.
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| 3. |
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| 4. |
- Henriksson, Krister O. E., et al.
(author)
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Annihilation of craters : Molecular dynamic simulations on a silver surface
- 2007
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 76:24, s. 15 p.-
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Journal article (peer-reviewed)abstract
- The ability of silver cluster ions containing 13 atoms to fill in a preexisting crater with a radius of about 28 angstrom on a silver (001) target has been investigated using molecular dynamics simulations and the molecular-dynamics-Monte Carlo corrected effective medium potential. The largest lateral distance r between crater and ion was about three times the radius of the preexisting crater, namely, 75 angstrom. The results reveal that when r < 20 angstrom and r>60 angstrom the preexisting crater is partially filled in, and for other distances there is a net growth of the crater. The lattice damage created by the cluster ions, the total sputtering yield, the cluster sputtering yield, and simulated transmission electron microscopy images of the irradiated targets are also presented.
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| 5. |
- Henriksson, Krister O. E., et al.
(author)
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Crater annihilation on silver by cluster ion impacts
- 2007
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In: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 255:1, s. 259-264
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Journal article (peer-reviewed)abstract
- Using the MD/MC-CEM potential we have investigated the impacts of 20 keV Ag-13 cluster ions on (001) silver surfaces having one initial crater. This one was made in the zeroth ion impact. The degree of annihilation of the initial crater was investigated as a function of the lateral distance r(i) between the crater and the ion. The impact points were selected randomly inside a circular area with a radius of 75 angstrom centered on the crater. To reduce the total number of simulations, the circular area was divided into annuli. The initial and final atomic positions in the impact simulations were analyzed and the degree of annihilation of the initial crater was determined. The results indicate that for r <= 60 angstrom there is a net growth of the initial crater, and for distances r is an element of (60,80) angstrom there is a small net filling of the crater.
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| 6. |
- Henriksson, Krister O. E., et al.
(author)
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Difference in formation of hydrogen and helium clusters in tungsten
- 2005
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 87:16
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Journal article (peer-reviewed)abstract
- The experimentally observed large difference in the depths of hydrogen and helium clusters formed in tungsten still lacks a fundamental explanation. Using density functional theory calculations, molecular dynamics simulations, and kinetic Monte Carlo calculations, we show that the fundamental mechanism behind the different clustering depths is significantly different behaviors of interstitial H and He atoms in W: H-H states are unstable for small interatomic distances whereas He-He states are strongly bound.
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| 7. |
- Henriksson, Krister O. E., et al.
(author)
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Fragmentation of clusters sputtered from silver and gold : Molecular dynamics simulations
- 2005
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 71:1
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Journal article (peer-reviewed)abstract
- Using molecular dynamics simulations and the embedded atom method (EAM) potential we have investigated the sputtered atom clusters produced by 15 keV xenon impacts on silver and 20 keV xenon impacts on gold. Ejected clusters were simulated for long times, up to 0.01-1 mus, in order to investigate the fragmentation of nascent clusters. The size distributions of nascent and final clusters were calculated and fitted to an inverse power law, resulting in exponents close to 2 and 3, depending on the range of the cluster sizes used. These values are in agreement with other simulations and experiments. The results show that clusters are subject to a dramatic breakup, which makes the size of the largest sputtered cluster go down by a factor of 2-4. Despite this, the exponent in the power law does not change very much from the size distribution of nascent to that of final clusters. Considering the uncertainties, the exponent of the final size distribution is 1.0-1.7 times the exponent of the nascent size distribution.
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| 8. |
- Henriksson, Krister O. E., et al.
(author)
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Molecular dynamics simulations of helium cluster formation in tungsten
- 2006
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In: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 244:2, s. 377-391
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Journal article (peer-reviewed)abstract
- Molecular dynamics simulations of helium implantation into single-crystalline tungsten at 0 and 300 K have been performed. Non-damaging ion energies of 50, 100 and 200 eV were used. Clusters containing up to the order of 100 He atoms were formed. These clusters were nucleated athermally, via the creation of (111) crowdion interstitials and interstitial dislocation loop punching. Ruptures of He clusters were observed, but no associated ejection of W atoms.
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| 9. |
- Henriksson, Krister O. E., et al.
(author)
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Sticking of atomic hydrogen on the tungsten (001) surface
- 2006
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In: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 600:16, s. 3167-3174
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Journal article (peer-reviewed)abstract
- The sticking of hydrogen atoms with kinetic energies in the range 0.003-10 eV on a clean (001) tungsten surface has been investigated using molecular dynamics simulations. The atoms are found to stick to the surface at 0 and 300 K, with a sticking coefficient smaller than 0.6 for kinetic energies higher than 3 meV. The adsorption sites for H on the W(001) surface are also presented. The dominant site is in perfect agreement with the experimentally found bridge site.
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| 10. |
- Henriksson, Krister O. E., et al.
(author)
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The depths of hydrogen and helium bubbles in tungsten : A comparison
- 2006
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In: Fusion science and technology. - 1536-1055 .- 1943-7641. ; 50:1, s. 43-57
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Journal article (peer-reviewed)abstract
- The role of self-trapping and defect trapping of hydrogen and helium implanted into tungsten has been investigated using density functional theory (DFT) calculations, molecular dynamics simulations, and kinetic Monte Carlo simulations (KMCSs). The potential energy curves of hydrogen or helium pairs were obtained by molecular dynamics, and the energy of the most essential states was checked with DFT Under assumptions of bubble formation due to trapping by similiar impurity atoms (self-trapping) or defects, KMCSs were carried out using parameters from implantation experiments. The results indicate that self-trapping plays no (or a very small) role in hydrogen bubble formation, whereas helium bubbles form due to strong self-trapping.
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