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| 2. |
- Samela, J., et al.
(författare)
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Argon cluster impacts on layered silicon, silica, and graphite surfaces
- 2007
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Ingår i: European Physical Journal D. ; 43, s. 181-184
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Samela, J., et al.
(författare)
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Comparison of silicon potentials for cluster bombardment simulations
- 2007
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. ; 255:1, s. 253-258
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Popok, Vladimir, 1966, et al.
(författare)
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Stopping of energetic argon cluster ions in graphite: Role of cluster momentum and charge
- 2010
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Ingår i: PHYSICAL REVIEW B. - 1098-0121. ; 82:20
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Tidskriftsartikel (refereegranskat)abstract
- We show that the implantation depth for argon clusters in graphite scales linearly with cluster momentum. A plot of implantation depth versus the momentum scaled with the projected surface area of the cluster falls on the same universal plot as that shown for semiconductor and metallic clusters, thus providing a universal scaling law for cluster implantation. Molecular dynamics simulations provide some insight to the mechanisms behind the empirical observation.
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| 5. |
- Popok, Vladimir, 1966, et al.
(författare)
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Stopping of energetic cobalt clusters and formation of radiation damage in graphite
- 2009
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Ingår i: Physical Review B. ; 80:20
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of energetic (up to 200 eV/atom) size-selected Con clusters with HOPG is studied both experimentally and theoretically. Etching of the radiation damage areas introduced by cluster impacts provides a measure of the depth to which the collision cascades are developed and allowes a comparison of these data with the molecular dynamics simulations. Good agreement between the experimental results and modelling is obtained. It is shown that the projected range of the cluster constituents can be linearly scaled with the projected momentum (the cluster momentum divided by surface impact area). With decrease of cluster energies to ca. 10 eV/atom the transition from implantation to pinning is suggested. It is found that even after quite energetic impacts residual clusters remain intact in the shallow graphite layer. These clusters can catalyse reaction of atmospheric oxygen with damaged graphite areas under the thermal heating that leads to the formation of narrow (5-15 nm) random in shape surface channels (trenches) in the top few graphene layers. Thus, small imbedded Co nanoparticles can be used as a processing tool for graphene.
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| 6. |
- Samela, J., et al.
(författare)
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Origin of complex impact craters on native oxide coated silicon surfaces
- 2008
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Ingår i: Physical Review B. ; 77
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Tidskriftsartikel (refereegranskat)abstract
- Crater structures induced by impact of keV-energy Ar cluster ions on silicon surfaces are measured with atomic force microscopy. Complex crater structures consisting of a central hillock and outer rim are observed more often on targets covered with a native silicon oxide layer than on targets without the oxide layer. To explain the formation of these complex crater structures, classical molecular dynamics simulations of Ar cluster impacts on oxide coated silicon surfaces, as well as on bulk amorphous silica, amorphous Si, and crystalline Si substrates, are carried out. The diameter of the simulated hillock structures in the silicon oxide layer is in agreement with the experimental results, but the simulations cannot directly explain the height of hillocks and the outer rim structures when the oxide coated silicon substrate is free of defects. However, in simulations of 5 keV/atom Ar12 cluster impacts, transient displacements of the amorphous silicon or silicon oxide substrate surfaces are induced in an approximately 50 nm wide area surrounding the impact point. In silicon oxide, the transient displacements induce small topographical changes on the surface in the vicinity of the central hillock. The comparison of cluster stopping mechanisms in the various silicon oxide and silicon structures shows that the largest lateral momentum is induced in the silicon oxide layer during the impact; thus, the transient displacements on the surface are stronger than in the other substrates. This can be a reason for the higher frequency of occurrence of the complex craters on oxide coated silicon.
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| 7. |
- Vuckovic, Sasa, 1974, et al.
(författare)
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Pinning of size-selected Co clusters on highly ordered pyrolytic graphite
- 2009
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Ingår i: European Physical Journal D. ; 52:1-3, s. 107-110
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Tidskriftsartikel (refereegranskat)abstract
- Deposition and implantation of size-selected Co50±5 cluster ions on/in highly ordered pyrolytic graphite (HOPG) have been performed. Cobalt clusters were produced by laser ablation using the second harmonic (532 nm) of a Nd:YAG laser. They were deposited/implanted with energies of 250-4850 eV/cluster and examined using scanning tunneling microscopy (STM). For the highest energies the clusters created craters and wells with residual clusters at the bottom of the wells. Decrease of the impact energy led to formation of bumps which consist of damaged graphite areas mixed with fragmented cobalt clusters. Further decrease of the impact energy to 250-450 eV/cluster probably corresponds to the so-called pinning regime, when the impacting cluster creates defects in the surface layer and becomes bound to them. The transition from implantation to pinning with a decrease of impact energy was confirmed by etching experiments showing the depth of the damage introduced by the cluster collisions with HOPG.
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