| 1. |
- Akram, Nadeem, 1980-
(author)
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Transmission of slow highly charged ions through nano-structures
- 2012
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Doctoral thesis (other academic/artistic)abstract
- This thesis is based on experimental investigations of transmitting slow highly charged ions through nano-structures of various cross-sections. Transmission through rhombic and rectangular nanocapillaries in muscovite and phlogopite mica, respectively, is used to study the guiding and shaping of highly charged ion beams. The two-dimensional angular distributions of the transmitted ions reveal that slow highly charged ion beams are tailored into rectangular and rhombic shapes after passing through the capillaries of rhombic and rectangular cross-sections, respectively. These transmission profiles are maintained for tilt angles within the geometrical opening angle of the capillaries. The ‘incident charge-dependent’ time evolution of the transmission profiles indicates that the tailored shape comes from the image force experienced by the traversing ions and the deposited charge by the incident ions moves the transmission profiles towards higher observation angles with respect to the beam direction. Transmission is also observed for tilt angles larger than the geometrical opening of the capillaries and evidence of charging-up of capillary walls was seen. Other incident charge-dependent features including the increase in angular width and shift of transmitted angular distributions were also observed. Starting from initially charged capillaries, it was found that the deposited charge must be distributed uniformly along the capillary walls to maintain the tailored rhombic shape through rectangular capillaries. In this thesis, a technique is presented which is successfully employed to investigate directly the formation of charge patches on the walls of a glass capillary by imaging the visible photons emitted due to impact of ions on the walls. These tapered glass capillaries were applied in biological studies of cell damage by ion impact and the technique provides a new way to directly observe the development of ion-guiding in these capillaries. With the help of this technique the mechanism of ion-guiding can be controlled and optimized. We also review the transmission characteristics of slow highly charged ions through nanometer thick foils and present the results of transmission of slow highly charged ions through ultra-thin carbon nano-sheets of molecular layer thickness. The observed energy loss is smaller than the calculated one using SRIM and agrees rather well with the Firsov model. The transmitted ions also keep their initial charge state up to 98% in a complete contradiction to the electron capture rate predicted by the classical over-the-barrier model. The results suggest that the energy loss of slow highly charged ions in such thin sheets is due to the electronic excitations, without charge exchange inside the target.
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| 2. |
- Aumayr, Friedrich, et al.
(author)
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Roadmap on photonic, electronic and atomic collision physics : III. Heavy particles
- 2019
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In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 52:17
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Journal article (peer-reviewed)abstract
- We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of the ICPEAC conference. Roadmap III focusses on heavy particles: with zero to relativistic speeds. Modern theoretical and experimental approaches provide detailed insight into the wide range of many-body interactions involving projectiles and targets of varying complexity ranging from simple atoms, through molecules and clusters, complex biomolecules and nanoparticles to surfaces and crystals. These developments have been driven by technological progress and future developments will expand the horizon of the systems that can be studied. This Roadmap aims at looking back along the road, explaining the evolution of the field, and looking forward, collecting nineteen contributions from leading scientists in the field.
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| 3. |
- Biber, Herbert, et al.
(author)
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Solar wind Helium ion interaction with Mg and Fe rich pyroxene as Mercury surface analogue
- 2020
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In: Nuclear Instruments and Methods in Physics Research Section B. - : ELSEVIER. - 0168-583X .- 1872-9584. ; 480, s. 10-15
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Journal article (peer-reviewed)abstract
- The surface of Mercury is continuously exposed to impinging solar wind ions. To improve the understanding of space weathering and exosphere formation, a detailed investigation of the ion-surface interaction is necessary. Magnesium and iron rich pyroxene (Ca,Mg,Fe)(2)[Si2O6] samples were used as analogues for Mercury's surface and irradiated with He+ ions at solar wind energies of 4 keV. Several regimes of implantation and sputtering were observed there. The total estimated mass of implanted He coincides with the mass decrease due to He outgassing during subsequent Thermal Desorption Spectroscopy measurements. Comparison to established modeling efforts and SDTrimSP simulations show that a He saturation concentration of 10 at.% has to be assumed. A complete removal of He is observed by heating to 530 K. On the surface of Mercury, temperatures between about 100 K and 700 K are expected. This temperature will therefore influence the implantation and release of He into Mercury's exosphere.
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| 4. |
- Kantre, Karim-Alexandros, et al.
(author)
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Combined in-situ ion beam analysis and thermal desorption spectroscopy for studying deuterium retention in tungsten
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Other publication (other academic/artistic)abstract
- We demonstrate a combinatory approach integrating ion implantation followed by thermal annealing and simultaneous in‑situ ion beam analysis with thermal desorption spectroscopy to be used for investigating the retention of deuterium in tungsten. All sample preparation, modification and analysis steps are performed in a single system. Atomic and molecular deuterium ions of 3 keV were implanted into tungsten bulk samples with highest doses significantly exceeding 1x1022 ions/m2. We demonstrate depth profiling of different hydrogen species by elastic recoil detection analysis, while the outgassing rate of molecular deuterium was simultaneously monitored by thermal desorption spectroscopy in different annealing processes (continuous and stepwise temperature ramping) from room temperature up to ≈1400 K. No pronounced narrow peaks were detected in the thermal desorption spectra regardless of the annealing procedure. The combination of the two techniques in a full in‑situ approach is shown capable to identify the distinct retention behavior of deuterium at different temperatures and in different reservoirs, e.g. located close to the surface and deuterium diffused deeper in the material from a single sample. Simultaneously, protium was detected in small amounts close to the sample surface. Ex-situ scanning electron microscopy analysis confirmed blister formation induced by ion implantation, and a recovery of the initial surface morphological aspect after high temperature annealing, confirming the analogy of our model system to earlier comprehensive ex‑situ studies.
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| 5. |
- Lohmann, Svenja, 1990-
(author)
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Electronic excitation, luminescence and particle emission : Studying ion-induced phenomena in ToF-MEIS
- 2018
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Licentiate thesis (other academic/artistic)abstract
- Medium energy ion scattering (MEIS) is an experimental technique for the high-resolution depth profiling of thin films. Commonly, ions with energies between several ten to a few hundred keV are employed as probes, and backscattered particles are detected. Apart from scattering, keV ions can upon their interaction with matter induce luminescence, electron emission and the sputtering of neutrals and ions. However, research on this secondary particle emission in the medium energy regime is scarce. Thus, this thesis aims to perform a systematic analysis of 1) ion-induced photon emission and 2) the sputtering of positive ions in a time-of-flight (ToF) MEIS set-up. A significant fraction of photons exhibits energies of only a few eV, which is on the order of typical valence transitions in solids. The dependence of the photon yield on several experimental parameters is studied. By analysing the dependence on the employed geometry, it is concluded that photons are produced along the whole trajectory of the incident ion. Furthermore, the photon yield shows a strong material dependence, which seems to be subject to matrix effects. To study the sputtering process, mass spectrometry was integrated into an existing ToF-MEIS set-up. The secondary ions exhibit very low initial kinetic energies and, therefore, need to be accelerated by a sufficiently high voltage. Then, atomic and molecular ions originating both from the employed target material and surface contaminations can be detected. Whereas experimental evidence suggests a predominantly electronic sputtering process for species adsorbed to the surface, target bulk constituents seem to be sputtered by nuclear collision cascades.
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| 6. |
- Szabo, Paul S., et al.
(author)
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Dynamic Potential Sputtering of Lunar Analog Material by Solar Wind Ions
- 2020
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In: Astrophysical Journal. - : IOP PUBLISHING LTD. - 0004-637X .- 1538-4357. ; 891:1
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Journal article (peer-reviewed)abstract
- Pyroxenes ((Ca, Mg, Fe, Mn)(2)Si2O6) belong to the most abundant rock forming minerals that make up the surface of rocky planets and moons. Therefore, sputtering of pyroxenes by solar wind ions has to be considered as a very important process for modifying the surface of planetary bodies. This is increased due to potential sputtering by multiply charged ions; to quantify this effect, sputtering of wollastonite (CaSiO3) by He2+ ions was investigated. Thin films of CaSiO3 deposited on a quartz crystal microbalance were irradiated, allowing precise, in situ, real time sputtering yield measurements. Experimental results were compared with SDTrimSP simulations, which were improved by adapting the used input parameters. On freshly prepared surfaces, He2+ ions show a significant increase in sputtering, as compared to equally fast He+ ions. However, the yield decreases exponentially with fluence, reaching a lower steady state after sputtering of the first few monolayers. Experiments using Ar8+ ions show a similar behavior, which is qualitatively explained by a preferential depletion of surface oxygen due to potential sputtering. A corresponding quantitative model is applied, and the observed potential sputtering behaviors of both He and Ar are reproduced very well. The results of these calculations support the assumption that mainly O atoms are affected by potential sputtering. Based on our findings, we discuss the importance of potential sputtering for the solar wind eroding the lunar surface. Estimated concentration changes and sputtering yields are both in line with previous modeling for other materials, allowing a consistent perspective on the effects of solar wind potential sputtering.
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| 7. |
- Ueda, Kiyoshi, et al.
(author)
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Roadmap on photonic, electronic and atomic collision physics : I. Light-matter interaction
- 2019
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In: Journal of Physics B. - : IOP PUBLISHING LTD. - 0953-4075 .- 1361-6455. ; 52:17
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Journal article (peer-reviewed)abstract
- We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of the ICPEAC conference. In Roadmap I, we focus on the light-matter interaction. In this area, studies of ultrafast electronic and molecular dynamics have been rapidly growing, with the advent of new light sources such as attosecond lasers and x-ray free electron lasers. In parallel, experiments with established synchrotron radiation sources and femtosecond lasers using cutting-edge detection schemes are revealing new scientific insights that have never been exploited. Relevant theories are also being rapidly developed. Target samples for photon-impact experiments are expanding from atoms and small molecules to complex systems such as biomolecules, fullerene, clusters and solids. This Roadmap aims to look back along the road, explaining the development of these fields, and look forward, collecting contributions from twenty leading groups from the field.
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