Ion Sputtering Research Articles

Non-thermal escape of the martian CO[formula omitted] atmosphere over time: Constrained by Ar isotopes

The ion escape of Mars’ CO2 atmosphere caused by its dissociation products C and O atoms is simulated from present time to ∼4.1 billion years ago (Ga) by numerical models of the upper atmosphere and its interaction with the solar wind. The planetward-scattered pick-up ions are used for sputtering estimates of exospheric particles including 36Ar and 38Ar isotopes. Total ion escape, sputtering and photochemical escape rates are compared. For solar EUV fluxes ≥3 times that of today’s Sun (earlier than ∼2.6 Ga) ion escape becomes the dominant atmospheric non-thermal loss process until thermal escape takes over during the pre-Noachian eon (earlier than ∼4.0–4.1 Ga). If we extrapolate the total escape of CO2-related dissociation products back in time until ∼4.1 Ga we obtain a maximum theoretical equivalent to CO2 partial pressure of more than ∼0.4 bar through non-thermal escape during quiet solar wind conditions. However, surface–atmosphere interaction and/or extreme solar events such as frequent CMEs could have increased this value even further. By including the surface as a sink, up to 0.9bar, or even up to 1.8bar in case of hidden carbonate reservoirs, could have been present at 4.1Ga The fractionation of 36Ar/38Ar isotopes through sputtering and volcanic outgassing from its initial chondritic value of 5.3, as measured in the 4.1 billion years old Mars meteorite ALH 84001, until the present day, however, can be reproduced for assumed CO2 partial pressures of ∼0.01–0.4bar without, and ∼0.4–1.8bar including surface sinks, and depending on the cessation time of the Martian dynamo (assumed between 3.6 and 4.0 Ga) — if atmospheric sputtering of Ar started afterwards.

Determination of the characteristic magnetic pre-sheath length at divertor surfaces using micro-engineered targets on DiMES at DIII-D

The magnetic pre-sheath (MPS) length, L MPS, is a critical parameter to define the sheath potential, which controls the ion trajectory of low-Z species (D, T, He, and C), as well as the prompt re-deposition of high-Z species. To determine L MPS, we fabricated micro-trenches (30 × 30 × 4 μm) via focused ion beam milling on a silicon surface and exposed them to L-mode deuterium plasmas in DIII-D via the divertor material evaluation system (DiMES) removable sample exposure probe. The areal distribution of impurity depositions, mainly consisting of carbon, was measured by energy-dispersive x-ray spectroscopy (EDS) to reveal the deuterium ion shadowing effect on the trench floors. The carbon deposition profiles showed that the erosion was maximized for the azimuthal direction of φ = −40° (referenced to the toroidal magnetic field direction) as well as the polar angle of θ = 80°. A Monte Carlo equation-of-motion (EOM) model, based on a collisionless MPS, was used to calculate the azimuthal and polar deuterium ion angle distributions (IADs) at the surface for a range of L MPS = k × ρ i, where ρ i is the ion gyro radius and k = 0.5–4. Then, gross erosion profiles were calculated by a Monte Carlo micro-patterning and roughness (MPR) code for ion sputtering using as input the calculated azimuthal and polar IADs for each value of k. Good agreement with the experimental C deposition profiles was obtained for the case k = 2.5–3.5. This result is consistent with a previous kinetic modeling prediction of k ∼ 3, as well as previous analytical investigations that predicted the L MPS to be several ion gyro radii. A validation of theoretical sheath models supports its applicability to ITER and pilot plant divertors to successfully predict plasma–materials interactions.

Thermal conductivity and mechanical properties of soda-lime glass with interfacially connected Au layer fabricated via sputtering and spark plasma sintering

ABSTRACT Glass is used for various substrates, but its thermal conductivity and mechanical properties are lower than ceramics. In this paper, we propose a new process for fabricating heat conduction paths using a small amount of metal. Au was coated on soda-lime glass powder via ion sputtering for 0, 20, 40, and 60 min, and the resultant powders were sintered via spark plasma sintering. The Au nanolayers precipitated between the soda-lime glass domains and were well connected to each other. Their thickness increased with increasing sputtering time. The thermal conductivity was enhanced by 10% with a small amount of precipitation less than 0.28 vol%, mainly resulting from the well-connected highly conductive Au nanolayers. The hardness and toughness were hardly affected by the precipitation of Au.

Preliminary results of positive ion mass spectrometry based on a 2.45 GHz ECR ion source and a non-metallic gas target

Positive-ion mass spectrometry (PIMS) is a positive-to-negative ion conversion metrology that just operated on the opposite of traditional accelerator mass spectrometry (AMS) on high-precision radiocarbon dating. With a higher efficient simple structure plasma ion sources instead of AMS sputter ion sources, lower ion energy (tens keV) in place of MeV, and limited footprint facility, PIMS will be a powerful competitor to AMS in the future. To precisely measure 14C, interference of molecular isobars (such as 12CH2, 13CH) will be eliminated with higher charged ions (charge state ≥ 3; molecular cations 12CH2 2+ is metastable, can be eliminated by higher stripping pressure.), nitrogen will be eliminated inside the charge-exchange cell (CXC) through charge exchanging with target gas. To demonstrate the probability of PIMS with a 2.45 GHz ECR ion source, an experiment was launched at Peking University (PKU). A compact permanent magnet 2.45 GHz ECR ion source is designed to produce carbon ions from CO2. A CXC unit was installed after the extraction system and ethylene is chosen as charge exchange gas. Preliminary experiments prove that more than hundreds of microamp of C2+ beam can be produced with this ECR source. By injecting ethylene into CXC, several microamp C- beam was detected and the C2+ ions charge exchange efficiency to C- ions can reach close to 5%.

Effect of Surface Morphology Changes on Optical Properties of Silicon Nanowire Arrays.

The optical properties of silicon nanowire arrays (SiNWs) are closely related to surface morphology due to quantum effects and quantum confinement effects of the existing semiconductor nanocrystal. In order to explore the influence of the diameters and distribution density of nanowires on the light absorption in the visible to near infrared band, we report the highly efficient method of multiple replication of versatile homogeneous Au films from porous anodic aluminum oxide (AAO) membranes by ion sputtering as etching catalysts; the monocrystalline silicon is etched along the growth templates in a fixed proportion chemical solution to form homogeneous ordered arrays of different morphology and distributions on the surface. In this system, we demonstrate that the synthesized nanostructure arrays can be tuned to exhibit different optical characteristics in the test wavelength range by adjusting the structural parameters of AAO membranes.

Relative straggle of sputtering parameters as a potential measure of power conversion efficiency of Perovskite materials

The growing demand for electricity necessitates the development of time-efficient computational methods in search of better solar energy-harvesting materials. One challenge has been ways to improve the power conversion efficiencies (PCEs) of potential harvesters.In this paper, an ion sputtering approach was used to study the problem of estimation of the power conversion efficiencies (PCEs) of perovskite solar device materials through their surface sputtering signatures. This rests on a hypothesis that the similarity between the phenomenon of photon excitation from light-sensitive absorbers, leading to electricity generation, and ejection of energetic particles from sputtered surfaces, could be exploited to estimate PCE. Hence, a Monte Carlo (MC) simulation of the sputtering of surfaces of perovskite materials with energetic ions was performed; and a number of quantities that could be used for the estimation of PCE were calculated. The results indicated that the relative straggle of surface sputtering parameters of the materials could be an effective measure of the theoretical maximum power conversion efficiencies of these materials. In particular, the relative straggle of the projected range of the ions in the respective materials was found to be close to reported experimental results of PCEs in the literature.

Microstructural Variation of Clay during Land Subsidence and the Correlation between Macroscopic and Microscopic Parameters.

The nonlinear deformation, visco-elasto-plasticity and other macroscopic properties of soil are the concentrated manifestations of its microstructural state. In order to study the microstructural characteristics and variations of the clay under the action of additional stress caused by groundwater exploitation, borehole sampling was carried out on the clay layers at different depths in a typical land subsidence area. Consolidation tests, freeze-drying, ion sputtering, and scanning electron microscope (SEM) were conducted in order to scan and analyze the microstructure of the test samples at different scales. The Particles and Cracks Analysis System (PCAS) was used to quantify the microscopic parameters, the variations of the microstructural parameters with consolidation loads at different sizes were revealed, and the correlation between the macroscopic and microscopic parameters were discussed. The results show that: (1) the microstructural characteristics of soils with different buried depths have directivity, to a certain extent; (2) as the consolidation load increases, the average unit area and average form factor of the soil microstructure generally decrease, the structural arrangement of the unit gradually tends to be orderly, and the average pore area, apparent void ratio and the number of pores generally show a decreasing trend; (3) under the action of a consolidation load, when the microstructure at a relatively large scale is basically stable, the microstructure at a smaller scale will continue to adjust; (4) the apparent void ratio has a good linear regression relationship with the conventional void ratio, and the apparent void ratio has a good exponential growth relationship with the compressibility.

Electron reflectivity from clean and oxidized steel surface

This paper aims to elucidate the effect of an air‐formed native oxide covering mild steel surface on the contrast in the scanning electron microscopy (SEM) images obtained with the landing energy from 5 keV down to 0 eV. Part of the mild steel surface was in‐situ cleaned by Ar+ ion sputtering process in order to remove native oxide from the surface. It enabled us to observe the oxide‐free and the naturally oxidized area on the mild steel surface simultaneously in the SEM micrographs. Presence of the native oxide starts to play a role in the SEM images acquired at landing energy below roughly 3 keV. Contrast between differently oriented grains situated inside the area covered by the native oxide starts to be negligible with landing energy decreasing below 3 keV, up to some ultra‐low values where the contrast increases again. Total reflectivity contrast between the clean and the oxidized area increases exponentially with landing energy decreasing below 3 keV. The reflectivity‐versus‐energy curves of the cleaned and the naturally oxidized mild steel surface are markedly different. The reflectivity of the electrons is correlated with the density of states (DOS), as is demonstrated at very low landing energies. Sensitivity of the very low‐energy electrons to the electronic structure was verified by comparison of the experimental data with the simulations of reflectivities, band structure, and DOS. The theoretical predictions are based on the density‐functional theory calculations and they have been performed in energy range corresponding to specular reflectivities of the Fe‐BCC (001) orientation. We have also observed that close to the mirror condition, that is, near‐zero landing energies, the primary electrons become sensitive to the surface potential differences caused by the work function differences of clean and native oxide‐covered steel surfaces.

Effects of Cs+ and Arn+ ion bombardment on the damage of graphite crystals

Intercalation mechanisms and diffusion or segregation phenomena in graphitic materials play a crucial role in different applied science fields. The investigation of such phenomena is usually accomplished through depth profiling experiments. Ar-GCIBs (Argon- Gas Cluster Ion Beams) are commonly adopted for in-depth concentration profiling of organic or soft materials; on the other hand, cesium ions are in general more suitable for the sputtering of inorganics. During such experiments, the beam-target interaction could alter chemistry and structure of the material. In this work, we define the optimal conditions in terms of both sputtering ion source and energy to preserve the crystal features. HOPG was used as a model system to compare morphological, physical, and chemical effects induced by different Arn+ clusters, and ultra-low energy Cs+ beam during ToF-SIMS (Time of Flight Secondary Ion Mass Spectrometry) depth profiling experiments. We demonstrated, through in-situ AFM (Atomic Force Microscopy) analysis, that the monoatomic Cs+ beam alters to a lower extent the HOPG structure. On the contrary, Ar-GCIBs strongly modify the graphite surface basal plane and underlying layers. However, HOPG crystals treated with the cesium monoatomic source undergo a chemistry modification leading to the formation of graphite oxide (GOx) together with the presence of hydrogen, and cesium adducts.

Radiation-induced phase separation in nanostructured Hf-In-C ternary thin films under irradiation with 200 keV Ar+ ion beam

Thin films consisting of 17 groups of Hf/In/C multilayers cyclically alternating layers of Hf, In and C each with a thickness of 4–5 nm were synthesized by ion sputtering using a 25 keV Ar+ ion beam with 400 µA current and targets made of pure hafnium, indium and carbon. The films were subsequently annealed in vacuum at 120°C for 24 hours to induce intermixing of elements phases, their interaction, and formation of the Hf-In-C nanostructures (including the Hf2InC MAX phase). After fabrication, a part of the pristine (as deposited) samples was irradiated by 200 keV Ar+ ions at high fluences 1015 and 1017 cm−2. Both samples (as prepared and irradiated) were analyzed by IBA nuclear analytical methods, as well as by AFM and TEM microscopic techniques, and by XPS and profilometry to understand the microstructural evolution. Moreover, nanoindentation analysis was performed to assess the effects of ion irradiation on the microstructure and mechanical properties of the films. The experimental results showed that thin Hf-In-C nanostructured films can be formed by ion sputtering with promising mechanical parameters. The irradiated Hf-In-C films were found to be resistant only up to a fluence of about 1015 Ar cm−2. At higher fluences it degrades, and Hf2InC transforms to the binary HfC0.95 phase due to sublimation of In. At 1017 cm−2 the original matrix (including M2AX) is destroyed, and instead, a mixture of MX binary phases (e.g. HfC0.95) and crystalline oxides (e.g. HfO2 and In2O3) are formed.

Effect of the Magnetospheric Plasma Interaction and Solar Illumination on Ion Sputtering of Europa’s Surface Ice

AbstractFor the entire ion energy range observed at Europa, we calculate spatially resolved maps of the surface sputtering rates of H2O, O2, and H2 from impacts by magnetospheric ions. We use the perturbed electromagnetic fields from a hybrid model of Europa’s plasma interaction, along with a particle‐tracing tool, to calculate the trajectories of magnetospheric ions impinging onto the surface and their resultant sputtering yields. We examine how the distribution of the sputtering rates depends on the electromagnetic field perturbations, the angle between the solar radiation and the corotating plasma flow, and the thickness of the oxygen‐bearing layer within Europa’s surface. Our major findings are: (a) Magnetic field‐line draping partially diverts the impinging ions around Europa, reducing the sputtering rates on the upstream hemisphere, but allowing for substantial sputtering from the downstream hemisphere. In contrast, zero sputtering occurs in much of the downstream hemisphere with uniform electromagnetic fields. (b) If the oxygen‐bearing surface layer is thin compared to the penetration depth of magnetospheric ions, thermal ions dominate the O2 sputtering rates, and the region of strongest sputtering is persistently located near the upstream apex. However, if the oxygen‐bearing layer is thick compared to the penetration depth, energetic ions sputter the most O2, and the location of maximum sputtering follows the sub‐solar point as Europa orbits Jupiter. (c) The global production rate of O2 from Europa’s surface varies by a factor of 3 depending upon the Moon’s orbital position, with the maximum particle release occurring when Europa’s Sun‐lit and upstream hemispheres coincide.

Improved sensitive conductive sponge sensors with tunnel-crack broadening for pressure, humidity and temperature sensing applications

Nanocrack-based flexible sensors can be fabricated on various stretchable substrates for different applications, such as strain, humidity and temperature sensing. As the initial width of the nanocrack has a great influence on the sensitivity of the flexible nanocrack based sensor, there still are great demands to further improve the sensitivity by broadening the width of the nanocrack. Therefore, we propose a simple method of expanding the width of nanocracks on three-dimensional (3D) conductive sponge sensor by acid etching, which can be used to enhance the sensitivity of pressure, humidity and temperature sensing. The acid-etched tunnel-cracked nickel networks on polyurethane sponge (ATNNPS) samples were prepared by ion sputtering nickel conductive networks on the polyurethane sponge, followed by mechanical compression and acid etching. ATNNPS served as a sensitive platform for pressure, humidity, and temperature sensing, and offered good mechanical elasticity and high compressibility. ATNNPS exhibited a piezoresistive sensitivity of 257.5 kPa-1, which was over 3000 times higher than that of an unetched sample. Similarly, acid etching increased the humidity and temperature sensitivities by over 46,000 times (69.96 kΩ/1%RH) and 41 times (TCR=1.770 °C-1), respectively. This enhanced sensitivity was attributed to efficient adjustment of the initial width of the nanocracks in the conductive network, as tunnel resistance has an exponential relationship with nanocrack width. ATNNPS-based sensors offer appropriate sensing properties, low cost, easy fabrication, and the application potential is shown by using it in a proof-of-principle setup for speech recognition, pulse wave monitoring and automatic switch.

Research on measuring method of pumping speed for miniature sputter ion pump

In this work, a new calibration apparatus, which employs the flowmeter method and the orifice method, was developed to get the low pumping speed of the miniature sputter ion pump (SIP), and the two methods were compared in the measurement of the low pumping speed. A low pumping speed of the order of 10-4 m3 s−1 was calibrated in the pressure range of 10-6 Pa to 10-2 Pa, and the combined standard uncertainty was 4.5–8.8% for nitrogen. The measurement results of the spinning rotor gauge (SRG) and the extractor gauge (IE514) were contrasted, and it can be found that the measurement error of the extractor gauge is obvious. Hence a method to measure the pumping speed and the outgassing rate of the extractor gauge is introduced, and the influence of the extractor gauge on the measurement was evaluated in the pressure range of 10-6 Pa to 10-4 Pa. The low pumping speed of the miniature SIP, which is a single-cylinder diode SIP, was calibrated in these high purity gases (N2, He, and Ar), and the flowmeter method performs better than the orifice method.

Facile fabrication of defect-induced 2D-stanene/stanene-oxide nano-sheet structure material through etching of SnOx thin film by the process of successive Ar+ ion sputtering

Facile fabrication of defect-induced 2D-stanene/stanene-oxide nano-sheet structure material through etching of SnOx thin film by the process of successive Ar+ ion sputtering

Variation of Surface Nanostructures on (100) PbS Single Crystals during Argon Plasma Treatment

The nanostructuring of the (100) PbS single crystal surface was studied under varying argon plasma treatment conditions. The initial PbS single crystals were grown by high-pressure vertical zone melting, cut into wafer samples, and polished. Subsequently, the PbS single crystals were treated with inductively coupled argon plasma under varying treatment parameters such as ion energy and sputtering time. Plasma treatment with ions at a minimum energy of 25 eV resulted in the formation of nanotips with heights of 30–50 nm. When the ion energy was increased to 75–200 eV, two types of structures formed on the surface: high submicron cones and arrays of nanostructures with various shapes. In particular, the 120 s plasma treatment formed specific cruciform nanostructures with lateral orthogonal elements oriented in four <100> directions. In contrast, plasma treatment with an ion energy of 75 eV for 180 s led to the formation of submicron quasi-spherical lead structures with diameters of 250–600 nm. The nanostructuring mechanisms included a surface micromasking mechanism with lead formation and the vapor–liquid–solid mechanism, with liquid lead droplets acting as self-forming micromasks and growth catalysts depending on the plasma treatment conditions (sputtering time and rate).

Simulation of ion irradiation of crystalline and amorphous targets tokamak-reactor first wall materials

An overview of results concerning simulation of various processes which occur due to atomic bombardment of crystalline and amorphous solids is presented. With the use of original computational codes, the following data were obtained: reflection coefficients, projected energy losses and ranges of ions in solids, channeling data as well as sputtering yield and its dependence on incident angle of bombarding particles for Be-W and Ne-W combinations. Be, C and W targets were studied as these are among the plasma-facing materials in tokamaks, including ITER. The emphasis was made on atom-target combinations which lack reliable experimental data. Experimental data on other materials were used to verify calculations. A significant influence of the interaction potential used on the simulation results is shown. The reviewed results are tied by a common subject a study of interaction of plasma ions and first-wall materials of a tokamak-reactor and also by a common method of study the use of an original computational code. Keywords: scattering, ion sputtering, interaction potential, energy release.

Interaction of molecular oxygen ions with copper surface: features of the energy spectra of sputtered and backscattered ions

An experimental study on the energy spectra of ions emitted from the surface of a polycrystalline Cu target under the bombardment by 2 keV O2+ molecular ions was carried out. Sputtered atomic ions Cu+ and O+ were prevailed among the positively charged secondary ions, and among the negative ions, in addition to sputtered ions Cu-, CuO2-, O-, and O2-, intense elastically and inelastically backscattered O-, and O2+ ions were revealed. Keywords: energy spectra, ion sputtering, backscattered ions, charge exchange.

Ionization probability of atoms sputtered under bombardment of metal surface with single and multiply charged ions

The processes of ionization of atoms sputtered under bombardment of clean metal surface by singly and multiply charged ions with kinetic energy of several keV were studied. Within the framework of simple phenomenological model of ion formation, the relaxation of local electron excitation in metal was taking into account. Analytical expressions for estimation of ionization probability of sputtered atoms was obtain. It was shown, that in comparison with singly charged ions, bombardment of metals with multiply charged ions results to significant increase of ionization probability of sputtered atoms due to more efficient excitation of electrons and increase of relaxation time of this excitation. Keywords: ion sputtering, ionization probability, multiply charged ions, Auger electrons, collision cascades, secondary ion mass spectrometry.

Solar Wind Ion Sputtering of Sodium from Silicates Using Molecular Dynamics Calculations of Surface Binding Energies

Abstract For nearly 40 yr, studies of exosphere formation on airless bodies have been hindered by uncertainties in our understanding of the underlying ion collisional sputtering by the solar wind (SW). These ion impacts on airless bodies play an important role in altering their surface properties and surrounding environment. Much of the collisional sputtering data needed for exosphere studies come from binary collision approximation (BCA) sputtering models. These depend on the surface binding energy (SBE) for the atoms sputtered from the impacted material. However, the SBE is not reliably known for many materials important for planetary science, such as plagioclase feldspars and sodium pyroxenes. BCA models typically approximate the SBE using the cohesive energy for a monoelemental solid. We use molecular dynamics (MD) to provide the first accurate SBE data we are aware of for Na sputtered from the above silicate minerals, which are expected to be important for exospheric formation at Mercury and the Moon. The MD SBE values are ∼8 times larger than the Na monoelemental cohesive energy. This has a significant effect on the predicted SW ion sputtering yield and energy distribution of Na and the formation of the corresponding Na exosphere. We also find that the SBE is correlated with the coordination number of the Na atoms within the substrate and with the cohesive energy of the Na-bearing silicate. Our MD SBE results will enable more accurate BCA predictions for the SW ion sputtering contribution to the Na exosphere of Mercury and the Moon.

Formation of inhomogeneous oxide and suboxide layers on an ultra-thin metal film by multiple oxidation and ion sputtering

A technique of controlled formation of multilayer oxide and suboxide layers on a thin metal film. An opportunity of controlled generation of films containing an ultra-thin suboxide layer inside a higher oxide layer and films being a periodic layered structure with alternating oxide layers of various oxidation levels. A structure containing alternating ultra-thin layers of higher oxide and suboxide layers on a niobium film. Keywords: metal-oxide films, controlled film formation, layer chemical and phase profiling, X-ray photoelectron spectroscopy.