| 1. |
- Popok, Vladimir, 1966, et al.
(författare)
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Formation of surface nanostructures on rutile (TiO2): comparative study of low-energy cluster ion and high-energy monoatomic ion impact
- 2009
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Ingår i: Journal of Physics D. - : Institute of Physics. - 0022-3727 .- 1361-6463. ; 42:20, s. 205303-
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Tidskriftsartikel (refereegranskat)abstract
- The formation of nanostructures on rutile (TiO2) surfaces formed after the implantation of kiloelectronvolt-energy Ar+n cluster ions and megaelectronvolt- to gigaelectronvolt-energy multiply charged heavy ions (Iq+, Taq+ and Uq+) is studied. Despite the differences in stopping and energy transfer mechanisms between the kiloelectronvolt-energy cluster ions and megaelectronvolt-energy monoatomic ions, their impacts lead to a similar type of surface damage, namely craters. For the cluster ion implantation the craters are caused by the multiple-collision effect (dominated by nuclear stopping) and the high density of energy and momentum transferred to the target, while for the case of megaelectronvolt multiply charged ions the craters are probably formed due to the Coulomb explosion and fast energy transfer caused by the electronic stopping. At ion energies in the gigaelectronvolt range, nanosize protrusions, so-called hillocks, are observed on the surface. It is suggested that electronic stopping leads to the formation of continuous tracks and the transferred energy is high enough to melt the material along the whole projectile path. Elastic rebound of the tension between the molten and solid state phases leads to liquid flow, expansion and quenching of the melt, thus forming the hillocks. Atomic force microscopy measurements carried out under different environmental conditions (temperature and atmosphere) suggest that the damaged material at the nanosize impact spots has very different water affinity properties (higher hydrophilicity or water adsorption) compared with the non-irradiated rutile surface.
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| 2. |
- 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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| 3. |
- Vuckovic, Sasa, 1974, et al.
(författare)
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Laser ablation source for formation and deposition of size-selected metal clusters
- 2008
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 79:7
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Tidskriftsartikel (refereegranskat)abstract
- This work describes construction of a source and optimisation of its parameters for production of cluster ion beams using material ablation by the second harmonic of a Nd:YAG laser (532 nm). The influence of different source parameters such as carrier gas pressure, laser power, delay time between gas, and laser pulses as well as nozzle configuration on the cluster formation are studied. For the current experiments the laser ablation cluster source was optimized for production of Co cluster ions. Clusters with n up to 150 atoms are registered by a time-of-flight mass spectrometer. Deposition of size-selected Co50 clusters with kinetic energies in the interval of 250–4850 eV/cluster on highly ordered pyrolytic graphite is studied. At the highest impact energies the clusters are implanted. Craters and well-like structures can be seen by scanning tunneling microscopy at impact spots. A decrease in cluster kinetic energy leads to formation of bumplike structures which probably represent damaged graphite areas with incorporated Co atoms. Further decrease in the cluster impact energy to the level of 450–250 eV/cluster creates condition for so-called cluster pinning when the cluster constituents are intact but the energy transferred to the graphite is still enough to produce radiation defects to which the cluster is bound.
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| 4. |
- 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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