Modification of SiO2, ZnO, Fe2O3 and TiN Films by Electronic Excitation under High Energy Ion Impact

It has been known that the modification of non-metallic solid materials (oxides, nitrides, etc.), e.g., the formation of tracks, sputtering representing atomic displacement near the surface and lattice disordering are induced by electronic excitation under high-energy ion impact. We have investigated lattice disordering by the X-ray diffraction (XRD) of SiO2, ZnO, Fe2O3 and TiN films and have also measured the sputtering yields of TiN for a comparison of lattice disordering with sputtering. We find that both the degradation of the XRD intensity per unit ion fluence and the sputtering yields follow the power-law of the electronic stopping power and that these exponents are larger than unity. The exponents for the XRD degradation and sputtering are found to be comparable. These results imply that similar mechanisms are responsible for the lattice disordering and electronic sputtering. A mechanism of electron–lattice coupling, i.e., the energy transfer from the electronic system into the lattice, is discussed based on a crude estimation of atomic displacement due to Coulomb repulsion during the short neutralization time (~fs) in the ionized region. The bandgap scheme or exciton model is examined.

Calculation of the sputtering coefficients of oxide films from the surface of a homogeneous material by medium-energy helium ions

The paper presents an analytical model for sputtering two-component layered inhomogeneous targets by bombardment with light ions. An analytical formula is obtained that makes it possible to calculate the total and partial sputtering yields of a binary layer of target inhomogeneity by light ions. The obtained formula is used to calculate the sputtering yields of oxide layers from the surface of a homogeneous substrate. The calculation results are in good agreement with the computer simulation data.

A novel setup to examine sputtering characteristics of mineral samples

<p>The surface of bodies without a thick atmosphere in outer space is exposed to the harsh space environment [1]. Space weathering alters its properties and leads to the formation of a tenuous exosphere. This elevated density of particles is coupled to the surface and therefore carries information about the latter. The BepiColombo mission aims to probe the composition of Mercury’s exosphere for the purpose of extracting this information [2]. However, this task requires precise models of exosphere formation [3]. Sputtering by solar wind ions is expected to be one of the main drivers for exosphere formation and models are therefore sensitive to sputtering inputs. So far, mainly simulation data are used, as experimental sputtering data for relevant materials are rare. Furthermore, available measurements have been typically performed with amorphous thin films due to use of the Quartz Crystal Microbalance (QCM) technique for sputtering measurements [4, 5]. Such a QCM is very sensitive to mass changes with resolutions in the sub mono-layer regime and is therefore an ideal tool for quantitative measurements of sputtering yields [6].</p><p>We introduce a new method for determining sputtering yields of more realistic samples, which allows to overcome the limitations of thin films while making use of the high sensitivity of QCMs. For this purpose, pellets pressed from minerals that are relevant for Mercury are used. The primary sample holder is placed on a xyzφ -manipulator, which enables switching between different samples and varying the irradiation angle α. A secondary quartz (C-QCM) is placed on an independently rotatable manipulator. This setup allows probing the angular distribution of sputtered particles by determining the mass change ∆m ion<sup>−1 </sup>in dependence on the angle α<sub>C</sub> between the sample and the C-QCM, which can lead to further improvement of exosphere models. Furthermore, mass changes of the irradiated sample due to ion implantation [7], can be untangled as only deposition of ejected particles contributes to the C-QCM signal. The use of pressed pellets enables a variation in sample parameters not accessible with thin films like crystal structure, surface roughness and porosity. Nonetheless, a QCM coated with the same material is installed on the primary sample holder in addition to the pellet for calibration.<br>First results with the Ca-pyroxenoid wollastonite (CaSiO3) and 2 keV Ar<sup>+</sup> ions are very promising. They indicate no difference in sputtering of the amorphous thin film and the pressed wollastonite pellet for Ar<sup>+</sup> irradiations. In a next step, solar wind ions will be used, which will improve the understanding of sputtering of realistic samples by solar wind ions. </p><p><strong>References</strong></p><p>[1] Hapke B.: J. Geophys. Res. Planet., 106, 10039, 2001.<br>[2] Milillo A., et al.: Planet. Space Sci., 58, 40, 2010.<br>[3] Wurz P., et al.: Planet. Space Sci., 58, 1599, 2010.<br>[4] Szabo P. S., et al.: Astrophys. J., 891, 100, 2020.<br>[5] Hijazi H., et al.: J. Geophys. Res. Planets, 122, 1597, 2017.<br>[6] Hayderer G., et al.: Rev. Sci. Instrum., 70, 3696, 1999.<br>[7] Biber H., et al.: Nucl. Instrum. Methods Phys. Res. B, 480, 10, 2020.</p>

Dust sputtering within the inner heliosphere: a modelling study

The aim of this study is to investigate through modelling how sputtering by impacting solar wind ions influences the lifetime of dust particles in the inner heliosphere near the Sun. We consider three typical dust materials, silicate, Fe0.4Mg0.6O, and carbon, and describe their sputtering yields based on atomic yields given by the Stopping and Range of Ions in Matter (SRIM) package. The influence of the solar wind is characterized by plasma density, solar wind speed, and solar wind composition, and we assume for these parameter values that are typical for fast solar wind, slow solar wind, and coronal mass ejection (CME) conditions to calculate the sputtering lifetimes of dust. To compare the sputtering lifetimes to typical sublimation lifetimes, we use temperature estimates based on Mie calculations and material vapour pressure derived with the MAGMA chemical equilibrium code. We also compare the sputtering lifetimes to the Poynting–Robertson lifetime and to the collision lifetime. We present a set of sputtering rates and lifetimes that can be used for estimating dust destruction in the fast and slow solar wind and during CME conditions. Our results can be applied to solid particles of a few nanometres and larger. The sputtering lifetimes increase linearly with the size of particles. We show that sputtering rates increase during CME conditions, primarily because of the high number densities of heavy ions in the CME plasma. The shortest sputtering lifetimes we find are for silicate, followed by Fe0.4Mg0.6O and carbon. In a comparison between sputtering and sublimation lifetimes we concentrate on the nanodust population. The comparison shows that sublimation is the faster destruction process within 0.1 AU for Fe0.4Mg0.6O, within 0.05 AU for carbon dust, and within 0.07 AU for silicate dust. The destruction by sputtering can play a role in the vicinity of the Sun. We discuss our findings in the context of recent F-corona intensity measurements onboard Parker Solar Probe.

Dust sputtering within the inner heliosphere

The aim of this study is to investigate how sputtering by impacting solar wind particles influence the lifetime of dust particles in the inner heliosphere near the Sun. We consider three typical dust materials: silicate, Fe0.4Mg0.6O and carbon and describe their sputtering yields based on atomic yields given by the Stopping and Range of Ions in Matter (SRIM) package. The influence of the solar wind is characterized by plasma density, solar wind speed and solar wind composition and we assume for these parameters values that are typical for fast solar wind, slow solar wind and CME conditions to calculate the sputtering lifetimes of dust. To compare the sputtering lifetimes to typical sublimation lifetimes we use temperature estimates based on Mie calculations and material vapour pressure derived with the chemical equilibrium code MAGMA. We also compare the sputtering lifetimes to the Poynting-Robertson lifetime and to the collision lifetime. We present a set of sputtering rates and lifetimes that can be used for estimating dust destruction in the fast and slow solar wind and during CME conditions. Our results can be applied to solid particles of a few nm and larger. The sputtering lifetimes increase linearly with size of particles. We show that sputtering rates increase during CME conditions, primarily because of the high number densities of heavy ions in the CME plasma. The shortest sputtering lifetimes we find are for silicate, followed by Fe0.4Mg0.6O and carbon. In a comparison between sputtering and sublimation lifetimes we concentrate on the nanodust population. The comparison shows that sublimation is the faster destruction process within 0.1 AU for Fe0.4Mg0.6O, within 0.05 AU for carbon dust and within 0.07 AU for silicate dust. The destruction by sputtering can play a role in the vicinity of the Sun. We discuss our findings in the context of recent F-corona intensity measurements onboard Parker-Solar-Probe.

DEUTERIUM TRAPPING AND SPUTTERING OF TUNGSTEN COATINGS EXPOSED TO LOW-ENERGY DEUTERIUM PLASMA

Processes of sputtering, surface modification and deuterium retention of tungsten coatings were studied under the influence of low-energy (500 eV) deuterium plasma with fluence (21024 D+/m2) at room temperature. The method of cathodic arc evaporation was used to deposit W and WN-coatings on stainless steel. Results of erosion studies indicated that the sputtering yields for coatings WN and W are 3.110-3 and 4.810-3 at./ion, respectively, and at least two times larger compared to bulk W but almost an order of magnitude smaller compared to ferritic martensitic steels. The total D retentions of W coatings were on the order of 51019 D/m2 and around one orders of magnitude lower than that of WN.

Combining Experiments and Modelling to Understand the Role of Potential Sputtering by Solar Wind Ions

<p>In the absence of a protecting atmosphere, the surfaces of rocky bodies in the solar system are affected by significant space weathering due to the exposure to the solar wind [1]. Fundamental knowledge of space weathering effects, such as optical changes of surfaces as well as the formation of an exosphere is essential for gaining insights into the history of planetary bodies in the solar system [2]. Primarily the exospheres of Mercury and Moon are presently of great interest and the interpretation of their formation processes relies on the understanding of all space weathering effects on mineral surfaces.</p><p>Sputtering of refractory elements by solar wind ions is one of the most important release processes. We investigate solar wind sputtering by measuring and modelling the sputtering of pyroxene samples as analogues for the surfaces of Mercury and Moon [3, 4]. These measurements with thin film samples on Quartz Crystal Microbalance (QCM) substrates allow recording of sputtering yields in-situ and in real time [5]. For the simulation of kinetic sputtering from the ion-induced collision cascade we use the software SDTrimSP with adapted input parameters that consistently reproduce measured kinetic sputtering yields [4, 6].</p><p>This study focuses on investigating the potential sputtering of insulating samples by multiply charged ions [7]. Changes of these sputtering yields with fluence are compared to calculations with a model based on inputs from SDTrimSP simulations. This leads to a very good agreement with steady-state sputtering yields under the assumption that only O atoms are sputtered by the potential energy of the ions. The observed decreasing sputtering yields can be explained by a partial O depletion on the surface [4]. Based on these findings expected surface composition changes and sputtering yields under realistic solar wind conditions can be calculated. Our results are in line with previous investigations (see e.g. [8, 9]), creating a consistent view on solar wind sputtering effects from experiments to established modelling efforts.</p><p> </p><p><strong>References:</strong></p><p>[1]          B. Hapke, J. Geophys. Res.: Planets, <strong>106</strong>, 10039 (2001).</p><p>[2]          P. Wurz, et al., Icarus, <strong>191</strong>, 486 (2007).</p><p>[3]          P.S. Szabo, et al., Icarus, <strong>314</strong>, 98 (2018).</p><p>[4]          P.S. Szabo, et al., submitted to Astrophys. J. (2020).</p><p>[5]          G. Hayderer, et al., Rev. Sci. Instrum., <strong>70</strong>, 3696 (1999).</p><p>[6]          A. Mutzke, et al., “SDTrimSP Version 6.00“, IPP Report, (2019).</p><p>[7]          F. Aumayr, H. Winter, Philos. Trans. R. Soc. A, <strong>362</strong>, 77 (2004).</p><p>[8]          H. Hijazi, et al., J. Geophys. Res.: Planets, <strong>122</strong>, 1597 (2017).</p><p>[9]          S.T. Alnussirat, et al., Nucl. Instrum. Methods Phys. Res. B, <strong>420</strong>, 33 (2018).</p>

Ion weathering of the surface of the Martian moon Phobos as inferred from MAVEN ion observations

<p>Phobos is the closest of the two moons of Mars and its surface is not only exposed to ions coming from the solar wind (mainly protons H+ and alpha particles He<sup>++</sup>), but is also bombarded by ions coming from Mars itself (mainly atomic and molecular oxygen ions O<sup>+</sup> and O<sub>2</sub><sup>+</sup>). Space weathering at Phobos would be intimately linked to the planetary atmospheric escape if Martian ions significantly alter the properties of the moon’s surface.<br />In this presentation, the long-term averaged ion environment seen by the surface of Phobos (omnidirectional and directional fluxes, and composition) is constructed from 4 years of ion measurements gathered in-situ by the NASA MAVEN mission. The MAVEN spacecraft repeatedly crossed the orbit of Phobos from January 2015 to February 2019 and was uniquely suited to unprecedently observe ions there with its three ion instruments: SWIA, STATIC, and SEP. These three experiments together constrain the entire range of ion kinetic energies that impact Phobos, from cold ions of a few eV to solar energetic ions of several MeV. In addition, the STATIC instrument (1 eV to 30 keV) is able to discriminate the mass of the observed ions by measuring their time-of-flight. This capability is important to understand the weathering of the surface of Phobos, as for instance the effect on the surface of a precipitating heavy molecular oxygen ion is significantly different from the one of a proton.<br />The relative importance of Martian and solar wind ions is in turn assessed from the observed ion omnidirectional fluxes for two space weathering effects: (1) surface sputtering, which is computed by using ion specie and energy-dependent sputtering yields available in the literature and (2) the production of vacancies inside the regolith grains, which is estimated with the SRIM software. (1) We find that Martian ions dominate solar wind ions in sputtering the surface of Phobos when the moon crosses the Martian magnetotail. We also reveal that molecular oxygen O<sub>2</sub><sup>+</sup> ions sputter as much as or more from the surface of Phobos than atomic O<sup>+</sup> ions. (2) Martian heavy ions significantly contribute to the production of vacancies in the uppermost nanometer of Phobos regolith grains. Finally, MAVEN directional flux measurements are used to study the anisotropy of the bombarding ion fluxes at Phobos, which we find implies an asymmetric weathering of the surface: the near side (always facing Mars) is primarily weathered by Martian ions, whereas the far side is primarily altered by solar wind ions. </p>