Total Sputtering Yield Research Articles

Differential sputtering yield measurement of ion grid materials by novel arch array system

In this experimental study the differential sputtering yield and total sputtering yield of ion thruster grid materials (Mo and C/C composite) under low-energy ion bombardment has been investigated. A novel combinable aluminum arch array is developed to determine the spatial distributions of sputtered atoms in different azimuthal angles. The quartz crystal microbalance (QCM) method is used to validate the typical distribution profile of sputtered atoms at the 180° azimuthal angle. The distribution characteristics of sputtered atoms as well as the specific regions of maximum differential sputtering yield under different incident energies, incident angles and ion species (Xe, Kr, Ar) have been discussed. The sputtering resistance performance of C/C composite materials have been compared with Mo metal by measuring the total sputtering yield. The spatial distributions of C/C differential sputtering yield are found highly anisotropic even under normal incidence, a multi-region discontinuous distribution characteristic of maximum differential sputtering yield have been observed in C/C composite material. The experimental results about the spatial distribution of sputtered atoms are of great importance for establishing the sputter-redeposition models of grid apertures to accurately predict the evolution of grid morphology and lifetime of ion thruster.

Molecular dynamics study of surface binding energy and sputtering in W-V alloys

This article used molecular dynamics to simulate the surface binding energy of W1-xVx (x = 0, 0.0625, 0.125, 0.25, 0.3125, 0.5) alloys along the (100) direction, considering the volume effect. The results showed that forming an alloy between W and V significantly improved the surface binding energy of W within the simulated proportion range, and the surface binding energy of W increased with increasing V proportion. However, when the simulated surface binding energy was input into the Monte Carlo program (SRIM-2013) to calculate the sputtering yield of W-V alloys, it was found that the alloy with V only greatly reduced the sputtering yield of W in the alloy, and the total sputtering yield of the alloy was higher than that of pure tungsten. Therefore, W still had the best anti-sputtering ability in the simulated material. The obtained results provided a reference for the selection of plasma-facing materials in future nuclear fusion.

Establishing a Best Practice for SDTrimSP Simulations of Solar Wind Ion Sputtering

Solar wind (SW) ion irradiation on airless bodies can play an important role in altering their surface properties and surrounding exosphere. Much of the ion sputtering data needed for exosphere studies come from binary collision approximation sputtering models such as TRansport of Ions in Matter and its more recent extension, SDTrimSP. These models predict the yield and energy distribution of sputtered atoms, along with the depth of deposition and damage of the substrate, all as a function of the incoming ion type, impact energy, and impact angle. Within SDTrimSP there are several user-specific inputs that have been applied differently in previous SW ion sputtering simulations. These parameters can influence the simulated behavior of both the target and sputtered atoms. Here, we have conducted a sensitivity study into the SDTrimSP parameters in order to determine a best practice for simulating SW ion impacts onto planetary surfaces. We demonstrate that ion sputtering behavior is highly sensitive to several important input parameters including the ion impact angle and energy distribution and the ejected atom surface binding energy. Furthermore, different parameters can still result in similarities in the total sputtering yield, potentially masking large differences in other sputtering-induced behaviors such as the elemental yield, surface concentration, and damage production. Therefore, it is important to consider more than just the overall sputtering behavior when quantifying the importance of different parameters. This study serves to establish a more consistent methodology for simulations of SW-induced ion sputtering on bodies such as Mercury and the Moon, allowing for more accurate comparisons between studies.

Molecular dynamics simulation of surface phenomena due to high electronic excitation ion irradiation in amorphous silica

We studied by means of an atomistic model based on molecular dynamics the thermal evolution of surface atoms in amorphous silica under high electronic excitation produced by irradiation with swift heavy ions. The model was validated with the total and differential yields measured in sputtering experiments with different ions and ion energies showing a very good quantitative prediction capability. Three mechanisms are behind the evolution of the surface region: (1) an ejection mechanism of atoms and clusters with kinetic energy exceeding their binding energy to the sample surface, which explains the experimentally observed angular distributions of emitted atoms, and the correlation of the total sputtering yield with the electronic stopping power and the incidence angle. (2) A collective mechanism of the atoms in the ion track originated by the initial atom motion outwards the track region subsequently followed by the return to the resulting low-density region in the track center. The collective mechanism describes the energy dissipation of bulk atoms and the changes in density, residual stress, defect formation and optical properties. (3) A flow mechanism resulting from the accumulation and subsequent evolution of surface atoms unable to escape. This mechanism is responsible for the crater rim formation.Graphic Evolution of the molecular dynamics simulation of amorphous silica for 12 keV/nm electronic stopping power with a hot cylinder of radius 3.0 nm and an incidence angle of 20º

Study of the dependence of light ion sputtering yields of carbon-modified surface titanium layers on their thickness

A theoretical sputtering model based on two mechanisms is used in this work to investigate the dependence of light ion sputtering yields of carbon-modified surface titanium layers on their thickness. The model used allows not only to correctly describe the nonlinear dependence of the sputtering yields on the layer thickness, but also to analyze the resulting dependencies. Calculations of the total sputtering yields of helium and hydrogen ions of surface layers of titanium modified with carbon are given in comparison with the results of computer simulations.

Total and Differential Sputtering Yields Explored by SRIM Simulations

Total sputtering yield and spatial distributions of sputtered atoms are important for numerous deposition techniques. We performed SRIM (Stopping and Range of Ions in Matter) simulations to analyze the total sputtering yield and angular distribution of sputtered atoms for a range of single-element target materials. The simulations were conducted for normal argon ion incidence in the 300–1200 eV range and at an oblique angle for selected ion energies. We examined the total and differential sputtering yields for the transition metals in the periods 4–6 and groups 4–6 (Ti, V, Cr; Zr, Nb, Mo; Hf, Ta, and W) and group 11 (Cu, Ag, and Au) of the periodic table, and other materials that are relevant to sputtering (B and C; Al and Si). For the transition metals, the total sputtering yield increases with the group of the periodic table. The elements in group 4 (i.e., Ti, Zr, and Hf) have the lowest sputtering yield, while the elements in group 11 (i.e., Cu, Ag, and Au) exhibit the highest sputtering yield. The angular distribution of the sputtered atoms shows a cosine distribution for the transition metal atoms. The angular distribution of the sputtered atoms for the oblique ion incidence is more asymmetric for the lower ion energies, while for the higher ion energies, the atoms are sputtered more symmetrically. The symmetry also depends on the group of the periodic table and the atomic mass of the target material. The elements in group 11 show the most symmetric distribution, while the elements in group 4 experience the most asymmetric distribution. Furthermore, in an individual group, the distribution becomes more symmetric with heavier target elements. We also examined in detail the influence of the surface binding energy, atomic mass, and ion energy on the total sputtering yield. These parameters were analyzed with regard to the simplified analytical formula for the total sputtering yield, which was derived by Sigmund. This formula was modified by introducing a power fitting parameter, which accounts for the non-linear sputtering yield dependence on the ion energy. The equation provided good estimates for the total sputtering yield of the transition metals that were sputtered by argon ions with energies up to 1200 eV.

Low energy Xe+ sputter yields for alumina, Hiperco 50, and boron nitride

Electric thruster materials are often subject to erosion during normal device operation. As a result of the ion sputtering process, surface properties can be affected or the underlying material may be exposed, possibly compromising performance and/or lifetime. It is therefore important to know both the energy and angle dependence of total sputter yield for relevant materials so that these effects can be predicted. In this study, we have obtained limited datasets on three materials with applications in electric propulsion development, thruster-spacecraft integration, and other technological areas—alumina, Hiperco 50, and HP boron nitride—in order to augment the material properties database. For each case, angular profiles were obtained at a single ion incidence energy, and energy dependence was explored at normal incidence. The datasets have been least squares fitted, and the results were interpreted.

SPUTTERING OF GOLD AND COPPER SURFACES UNDER LOW ENERGY CESIUM IONS

To use gold and copper ions for ion implantation through 1-MV pelletron accelerator, gold and copper targets were bombarded with low energy cesium ions applying source of negative ions by cesium sputtering (SNICS). This work aims to investigate the cluster dynamics of these noble metals in a low energy range so that optimized data can be obtained for the use of these cluster ions in ion implantation. Negative ions including monomers and clusters of both metals were detected which were mass analyzed. Cu clusters up to Cu[Formula: see text] and gold clusters up to Au[Formula: see text] were emitted. The minimum energy of cesium ions to produce enough cluster ions so that they could be detected by a mass analyzer has been determined. The data was analyzed to measure sputtering yield, total sputtering yield and normalized number density of different sputtered species. In this energy range, the sputtering behaviors of Cu remain almost constant but in the case of Au there is a slight increase in cluster sputtering probability with an increase in incident ion energy. The sputtering yield of clusters decreases according to the power-law, i.e. [Formula: see text]. Power law exponent in the case of copper has an average value of [Formula: see text] whereas exponent in the case of gold clusters changes from 3.5 to 6.

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.

Argon cluster‐ion sputter yield: Molecular dynamics simulations on silicon and equation for estimating total sputter yield

Argon Gas Cluster‐Ion Beam sources have become widely‐used on X‐ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) instruments in recent years, but there is little reference data on sputter yields in the literature as yet. Total sputter yield reference data is needed in order to calibrate the depth scale, of XPS or SIMS depth profiles. We previously published a semi‐empirical ‘Threshold’ equation for estimating cluster total sputter yield from the energy‐per‐atom of the cluster and the effective monatomic sputter threshold of the material. This has been shown to agree extremely well with sputter yield measurements on a range or organic and inorganic materials for clusters of around a thousand atoms. Here we use the molecular dynamics (MD) approach to explore a wider range of energy and cluster size than is easy to do experimentally to high precision. We performed MD simulations using the ‘Large‐scale Atomic/Molecular Massively Parallel Simulator’ (LAMMPS) parallel MD code on high‐performance computer (HPC) systems. We performed 1150 simulations of individual collisions with a silicon (100) surface as an archetypal inorganic substrate, for cluster sizes between 30 and 3000 argon atoms and energies in the range 5 to 40 eV per atom. This corresponds to the most important regime for experimental cluster depth‐profiling in SIMS and XPS. Our MD results show a dependence on cluster size as well as energy‐per‐atom. Using the exponent previously suggested by Paruch et al., we modified the Threshold model equation published previously to take this into account. The modified Threshold equation fits all our MD results extremely well, building on its success in fitting experimental sputter yield measurements.This work is submitted to the volume dedicated to Dr. Martin P Seah, MBE, who was a great influence on the early career of one of the authors (PJC) and who himself made many valuable contributions to the literature on sputtering as it relates to surface and interface analysis.

The sputtering of radiolytic O2 in ion irradiated H2O-ice

Charged particle bombardment alters the physical and chemical properties of extraterrestrial icy surfaces by simultaneously producing radiolytic products and sputtered material. To better understand these phenomena, we measure the total sputtering yield of H2O-ice induced by 0.5–5 keV Ar+ at temperatures between 40 and 120 K, using microbalance gravimetry as our analytical tool. In addition, we also estimate the sputtered flux of radiolytic products formed during irradiation and in both cases find good agreement with comparable laboratory studies. At 120 K, we find that the O2/H2O sputtered ratio increases nearly linearly with the ion range suggesting that the ions are stopping at depths where O2 is still efficiently being produced below the surface. Furthermore, we find that although theoretical models appear to over predict our O2 sputtering yields by about a factor of three, we can make a small adjustment to this model, which improves the agreement between the model and the laboratory data significantly. This empirical adjustment may have implications for models of energetic processing that occurs on extraterrestrial icy surfaces, such as Europa, where low-energy ions are thought to be the primary source producing O2 from sputtering of the surface H2O-ice.

Energy distributions of the particles sputtered by gas cluster ions. Experiment and computer simulation

We present experimental studies and computer simulations of the energy distributions of the particles sputtered from copper and molybdenum with gas cluster ions. Both experimental and simulated distributions were found to be narrower than ones known for atomic ion sputtering. It was shown that the distributions of sputtered atoms obtained by molecular dynamics simulations can be well described in frames of the thermal spike theory. For a given cluster energy, its size and the target material properties determine the parameters of the distributions. Including into consideration sequential cluster impacts on the target surface resulted in changes both in energy and angular distributions of sputtered matter and as well in total sputtering yield. Experimentally measured distributions well matched the ones simulated in “sequential” mode.

Sputtering of LiF and other halide crystals in the electronic energy loss regime

Sputtering experiments were performed by irradiating LiF, NaCl, and RbCl crystals with various swift heavy ions like S, Ni, I, Au with energies between 60 and 210 MeV, C60 clusters between 12 and 30 MeV or Pb ions between 730 and 6040 MeV. Sputtered species are collected on arc-shaped catchers and subsequently analyzed by elastic recoil detection analysis or Rutherford backscattering analysis. The study focuses on angular distributions and total yields for LiF and covers a broad range of experimental parameters including cleaved or rough sample surfaces, ion fluence, beam incident angles, and different ion velocities leading to electronic energy loss (Se) values from 5 to 45 keV/nm. In most cases, the angular distribution has two components, a jet-like peak perpendicular to the surface sample superimposed on a broad isotropic cosine distribution whatever is the beam incident angle. The observation of the jet depends mainly on the surface flatness and angle of ion incidence. However, the jet does not appear clearly when irradiated with C60 cluster. The sputtering yield is stoichiometric and characterized by huge total yields of up to a few 105 atoms per incident ion. The yield follows a power law as function of electronic energy loss, Y follows an exponential law with Sen with n ~ 4. While the azimuthal symmetry for sputtering is observed at low ion velocity (~1 MeV/u), it seems to be lost at high velocity (>4 MeV/u). The data provide a comprehensive overview how the angular distribution and the total sputtering yield scale with the energy loss, beam incidence angle and ion velocity. Complementary experiments have been done with NaCl and RbCl targets confirming the observation made for LiF.

Sputtering yields of tantalum by hydrogen ions in the energy range of 3–11 keV

ABSTRACTThe total sputtering yield of 6 nm thick polycrystalline tantalum films resulting from H2+ ion bombardment, at normal incidence, has been determined. For this purpose, we study the evolution of the energy loss of protons transmitted through very thin films of tantalum following bombardment with controlled doses of H2+. The energy of the incident ions ranges from 3 to 11 keV. Our method allows us to determine how to find the limit of the thin film surface contamination which is important for stopping power measurements of pure samples. It also allows to prepare films of predetermined variable thickness.

Effect of random surface orientation on W sputtering yields

In this study, we investigate the sputtering yield of tungsten surfaces by energetic particles, focusing on the effect of surface orientation and the incoming irradiation angle, by means of molecular dynamics. We develop a simulation approach to simulate sputtering from completely random surface orientations. This allows obtaining the sputtering yields averaged over a sufficiently large number of orientations, to obtain statistically significant yields representative of a polycrystalline sample with random grain orientations. We find that the total sputtering yield is dependent on the surface orientation, and that the results for random surfaces are clearly different from that of any of the low-index ones or their average. The different low index surfaces and the random surfaces also showed that the sputtering yield is dependent on the incoming angle of the ion. The outgoing angle of the sputtered tungsten atoms was observed to be very sensitive to the surface orientation. Different features on the tungsten surface were observed to drastically affect the sputtering yield at certain angles.

Erosion and deuterium retention of CLF-1 steel exposed to deuterium plasma

In recent years reduced activation ferritic martensitic steel has been proposed as the plasma-facing material in remote regions of the first wall. This study reports the erosion and deuterium retention behaviours in CLF-1 steel exposed to deuterium (D) plasma in a linear experimental plasma system as function of incident ion energy and fluence. The incident D ion energy ranges from 30 to 180 eV at a flux of 4 × 1021 D m−2 s−1 up to a fluence of 1025 D m−2. SEM images revealed a clear change of the surface morphology as functions of incident fluence and impinging energy. The mass loss results showed a decrease of the total sputtering yield of CLF-1 steel with increasing incident fluence by up to one order of magnitude. The total sputtering yield of CLF-1 steel after 7.2 × 1024 D m−2 deuterium plasma exposure reduced by a factor of 4 compared with that of pure iron, which can be attributed to the enrichment of W at the surface due to preferential sputtering of iron and chromium. After D plasma exposure, the total deuterium retention in CLF-1 steel samples measured by TDS decreased with increasing incident fluence and energy, and a clear saturation tendency as function of incident fluence or energy was also observed.

Solar Wind Sputtering Rates of Small Bodies and Ion Mass Spectrometry Detection of Secondary Ions

AbstractSolar wind interactions with the surfaces of asteroids and small moons eject atoms and molecules from the uppermost several nanometers of regolith grains through a process called sputtering. A small fraction of the sputtered species, called secondary ions, leave the surface in an ionized state, and these are diagnostic of the surface composition. Detection of secondary ions using ion mass spectrometry (IMS) provides a powerful method of analysis due to low backgrounds and high instrument sensitivities. However, the sputtered secondary ion yield and the atomic composition of the surface are not 1‐to‐1 correlated. Thus, relative yield fractions based on experimental measurements are needed to convert measured spectra to surface composition. Here available experimental results are combined with computationally derived solar wind sputtering yields to estimate secondary ion fluxes from asteroid‐sized bodies in the solar system. The Monte Carlo simulation code SDTrimSP is used to estimate the total sputtering yield due to solar wind ion bombardment for a diverse suite of meteorite and lunar soil compositions. Experimentally measured relative secondary ion yields are analyzed to determine the abundance of refractory species (Mg+, Al+, Ca+, and Fe+) relative to Si+, and it is shown that relative abundances indicate whether a body is primitive or has undergone significant geologic reprocessing. Finally, estimates of the sputtered secondary ion fluxes are used to determine the IMS sensitivity required to adequately resolve major element ratios for nominal orbital geometries.

Kinetic and potential sputtering of an anorthite‐like glassy thin film

AbstractIn this paper, we present measurements of He+ and He+2 ion‐induced sputtering of an anorthite‐like thin film at a fixed solar wind‐relevant impact energy of ~0.5 keV/amu using a quartz crystal microbalance approach (QCM) for determination of total absolute sputtering yields. He+2 ions are the most abundant multicharged ions in the solar wind, and increased sputtering by these ions in comparison to equivelocity He+ ions is expected to have the biggest effect on the overall sputtering efficiency of solar wind impact on the Moon. Our measurements indicate an almost 70% increase of the sputtering yield for doubly charged incident He ions compared to that for same velocity He+ impact (14.6 amu/ion for He+2 vs. 8.7 amu/ion for He+). Using a selective sputtering model, the new QCM results presented here, together with previously published results for Ar+q ions and SRIM results for the relevant kinetic‐sputtering yields, the effect due to multicharged‐solar‐wind‐ion impact on local near‐surface modification of lunar anorthite‐like soil is explored. It is shown that the multicharged‐solar‐wind component leads to a more pronounced and significant differentiation of depleted and enriched surface elements as well as a shortening of the timescale over which such surface‐compositional modifications might occur in astrophysical settings. In addition, to validate previous and future determinations of multicharged‐ion‐induced sputtering enhancement for those cases where the QCM approach cannot be used, relative quadrupole mass spectrometry (QMS)‐based measurements are presented for the same anorthite‐like thin film as were investigated by QCM, and their suitability and limitations for charge state‐enhanced yield measurements are discussed.

In situ plasma sputtering and angular distribution measurements for structured molybdenum surfaces

We present in situ sputtering yield measurements of the time-dependent erosion of flat and micro-architectured molybdenum samples in a plasma environment. The measurements are performed using the plasma interactions (Pi) Facility at UCLA, which focuses a magnetized hollow cathode plasma to a material target with an exposure diameter of approximately 1.5 cm. During plasma exposure, a scanning quartz crystal microbalance (QCM) provides angular sputtering profiles that are integrated to estimate the total sputtering yield. This technique is validated to within the scatter of previous experimental data for a planar molybdenum target exposed to argon ion energies from 100 to 300 eV. The QCM is then used to obtain in situ measurements during a 17 h exposure of a micro-architectured-surface molybdenum sample to 300 eV incident argon ions. The time-dependent angular sputtering profile is shown to deviate from classical planar profiles, demonstrating the unique temporal and spatial sputtering effects of micro-architectured materials. Notably, the sputtering yield for the micro-architectured sample is initially much less than that for planar molybdenum, but then gradually asymptotes to the value for planar molybdenum after approximately 10 h as the surface features are eroded away.

BN/BNSiO2 sputtering yield shape profiles under stationary plasma thruster operating conditions

Quartz Crystal Microbalance (QCM) is used to measure the volumetric and total sputtering yield of Boron Nitride (BN) and Boron Nitride Silicon Dioxide (BNSiO2) bombarded by Xenon ions in the energy range of 100 eV to 550 eV. Sputtering yield shape profiles are reported at various angles of incidence 0-85° with surface normal and compared with modified Zhang model. The yield shape profile is found to be symmetric at normal incidence and asymmetric at oblique incidence. Both the materials show a sudden jump in the sputtering yield above 500 eV and at an angle of incidence in the range of 45-65°. Erosion of BN at as low as 74 eV ion energy is predicted using generalized Bohdansky model. BNSiO2 show a marginally higher sputtering yield compare to BN.