| 1. |
- Biber, H., et al.
(author)
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Sputtering Behavior of Rough, Polycrystalline Mercury Analogs
- 2022
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In: The Planetary Science Journal. - : Institute of Physics (IOP). - 2632-3338. ; 3:12
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Journal article (peer-reviewed)abstract
- The solar wind continuously impacts on rocky bodies in space, eroding their surface, thereby contributing significantly to the exosphere formations. The BepiColombo mission to Mercury will investigate the Hermean exosphere, which makes an understanding of the precise formation processes crucial for evaluation of the acquired data. We therefore developed an experimental setup with two microbalances that allows us to compare the sputter behavior of deposited thin solid layers with that of real mineral samples in the form of pressed powder. In addition, this technique is used to study the angular distribution of the sputtered particles. Using 4 keV He+ and 2 keV Ar+ ions, the sputter behavior of pellets of the minerals enstatite (MgSiO3) and wollastonite (CaSiO3) is studied, because these minerals represent analogs for the surface of the planet Mercury or the Moon. Pellets of powdered enstatite show significantly lower sputter yields than thin amorphous enstatite films prepared by pulsed laser deposition. 3D simulations of sputtering based on surface topography data from atomic force microscopy show that the observed reduction can be explained by the much rougher pellet surface alone. We therefore conclude that sputter yields from amorphous thin films can be applied to surfaces of celestial bodies exposed to ion irradiation, provided the effects of surface roughness, as encountered in realistic materials in space, are adequately accounted for. This also implies that taking surface roughness into account is important for modeling of the interaction of the solar wind with the surface of Mercury.
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| 2. |
- Szabo, P.S., et al.
(author)
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Energetic neutral atom (ENA) emission characteristics at the moon and mercury from 3D regolith simulations of solar wind reflection
- 2023
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In: Journal of Geophysical Research - Planets. - : American Geophysical Union (AGU). - 2169-9097 .- 2169-9100. ; 128:9
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Journal article (peer-reviewed)abstract
- The reflection of solar wind protons as energetic neutral atoms (ENAs) from the lunar surface has regularly been used to study the plasma-surface interaction at the Moon. However, there still exists a fundamental lack of knowledge of the scattering process. ENA emission from the surface is expected to similarly occur at Mercury and will be studied by BepiColombo. Understanding this solar wind backscattering will allow studies of both Mercury's plasma environment as well as properties of the hermean surface itself. Here, we expand on previous simulation studies of the solar-wind-regolith interaction with 3D grains in SDTrimSP-3D to compare the predicted scattering energies and angles to ENA measurements from the Moon by the Chandrayaan-1 and IBEX missions. The simulations reproduce a backward emission toward the Sun, which can be connected to the geometry of the regolith grain stacking. In contrast, the ENA energy distribution and its Maxwellian shape is mostly connected to the solar wind velocity. Our simulations also correctly describe a lunar ENA albedo between 10% and 20% and support its decrease with solar wind velocity. We further expand our studies to illustrate how BepiColombo will be able to observe ENAs at Mercury using hybrid simulations of Mercury's magnetosphere as an input for the complex surface precipitation patterns. We demonstrate that the variable ion precipitation will directly influence ENA emission from the surface. The orbits of BepiColombo's Mercury Planetary Orbiter and Mercury Magnetospheric Orbiter/Mio spacecraft are shown to be suitable to observe ENA emission patterns both on a local and a global scale.
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| 3. |
- Szabo, P. S., et al.
(author)
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Experimental Insights Into Space Weathering of Phobos : Laboratory Investigation of Sputtering by Atomic and Molecular Planetary Ions
- 2020
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In: Journal of Geophysical Research - Planets. - : AMER GEOPHYSICAL UNION. - 2169-9097 .- 2169-9100. ; 125:12
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Journal article (peer-reviewed)abstract
- Investigating the space weathering of the Martian moon Phobos represents an important step toward understanding the development from its origin to its present-day appearance. Depending on Phobos' orbital position, its surface is continuously sputtered by the solar wind and planetary ions that originate in the Martian atmosphere. Based on Mars Atmosphere and Volatile Evolution measurements, it has been proposed that sputtering by planetary O+ and O-2(+) ions dominates in the Martian tail region, where the planet mostly shadows Phobos from the solar wind. In these models, uncertainties for sputtering yield inputs still exist due to the lack of sufficient analog experiments. Therefore, sputtering measurements with O+, O-2(+), C+, and CO2+ ions between 1 and 5 keV were performed using augite samples as Phobos analogs. The experimental results for O+ irradiations show smaller mass changes than predicted by SDTrimSP simulations, which probably can be attributed to O implantation enabled by the Fe content of the target. Sputtering with O-2(+) and CO2+ in the low keV range shows no deviations in the sputtering yields attributable to molecular effects. Therefore, CO2+ ions will most likely be negligible for the sputtering of Phobos according to the current understanding of ion fluxes on the Martian moon. Ultimately, our experiments suggest that the sputtering contribution on Phobos by O ions is about 50% smaller than previously assumed. This does not change the qualitative outcome from previous modeling stating that planetary O ions are by far the dominant sputtering contribution on Phobos in the Martian tail region.
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| 4. |
- Cupak, C., et al.
(author)
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Absence of synergistic effects in quasi-simultaneous sputtering of tungsten by Ar and D ions
- 2023
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In: Nuclear Materials and Energy. - : Elsevier. - 2352-1791. ; 35
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Journal article (peer-reviewed)abstract
- A quartz crystal microbalance was used to experimentally study the erosion of tungsten during rapidly alternating bombardment with 2 keV argon and deuterium projectiles. A key goal was to investigate whether the mean sputtering yield of the alternating irradiation can be predicted from data for sputtering yields of single ion species. In addition, influences by residual gas pressure in the UHV experiment and variable ion fluxes have been studied. Our results show that the mean sputtering yield of irradiations with alternating ion species can be well predicted for a range of different fluence ratios as a simple superposition of individual sputtering yields, weighted by the respective relative fluences. This finding supports that no synergistic sputtering effects were relevant in the investigated low-flux regime.
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| 5. |
- Cupak, C., et al.
(author)
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Sputter yields of rough surfaces : Importance of the mean surface inclination angle from nano- to microscopic rough regimes
- 2021
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In: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 570
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Journal article (peer-reviewed)abstract
- The roughness of a surface is known to have a strong influence on the sputtering process. Commonly used 1D Monte Carlo codes for calculating sputter yields show good agreement with experimental data only for comparably flat surfaces, whereas local ion incidence angles, shadowing and redeposition influence the sputter yields in both magnitude and angular dependence on rough surfaces. In the present work, we therefore investigated tungsten samples of largely different roughness, characterised by atomic force and confocal microscopy. A highly sensitive quartz crystal microbalance was used to determine sputter yields during ion irradiation. Low ion fluences were applied to ensure that the surface morphology did not change during irradiation. The results were used to benchmark our new ray-tracing simulation code SPRAY, which can take microscopy images without limitations in size as input. SPRAY was furthermore applied to perform systematic simulations for artificially roughened and computer-generated surfaces. A clear result was that the governing parameter for description of the sputtering behaviour is the mean value of the surface inclination angle distribution, rather than the commonly used root mean square roughness. Our simulations show that this parameter is universally applicable for a wide range of different surface structures.
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