Xe Ion Bombardment Research Articles

An experimental study on the degradation of the C12A7 hollow cathode

Emitter overheating is by far the greatest problem limiting the performance of novel C12A7 hollow cathodes. To explore the failure operating point and degradation mechanism of the C12A7 hollow cathode, microscopic analyses of a degraded electride emitter after 10 h of thermal electron emission are presented in this paper. The morphology and composition variation of overheated electride emitters by scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction indicate the melting and decomposition of electride of the surface layer. The monitored temperature of the electride emitter during the C12A7 hollow cathode operation shows that to avoid overheating the electride emitter, the average current density allowed should be about 64 mA mm−2 for the C12A7 hollow cathode in its current configuration. Experimental results of the heaterless C12A7 hollow cathode demonstrate that xenon (Xe) ion bombardment can remove the insulating layer and restore the thermionic emission capability for less degraded emitters. Based on experimental results and microscopic characterization, the depletion and degradation mechanisms of electride emitters during the hollow cathode operation are discussed.

The effects of swift Xe ion bombardment on the amorphous structure of a VITROPERM type alloy

Influence of swift Xe ion irradiation (ion energy of 11.1 MeV/u, ion fluences from 2.5 × 1012 to 1.0 × 1013 ions/cm2) on the local structural arrangement of a VITROPERM alloy is investigated using synchrotron-based X-ray diffraction, Fe and Nb K-edge X-ray absorption spectroscopy, and 57Fe Mössbauer spectroscopy techniques. The obtained data show an increase of structural disordering due to ion bombardment. However, no alterations in pairwise interatomic lengths are observed. The irradiation-induced structural modifications can be removed by an appropriate post-irradiation heat treatment. We suggest that the microscopic origin of changes induced by the swift heavy ions could be similar to the structural modifications caused by severe plastic deformation.

Observation of sputtering of yttrium from Y2O3 ceramics by low-energy Ar, Kr, and Xe ion bombardment in microwave-excited plasma

Y2O3 ceramics were immersed in microwave-excited Ar, Kr, and Xe plasmas, and the sputtering of yttrium atoms from Y2O3 ceramics as a result of low-energy (range of approximately 10 eV) Ar, Kr, and Xe ion bombardment was observed. The amount of sputtered yttrium atoms well correlated with the ion bombardment energy estimated by Langmuir probe measurement. The estimated sputtering yield was 10−5 or less for such a low ion bombardment condition.

Microstructure and nanoindentation of the CLAM steel with nanocrystalline grains under Xe irradiation

This work presents an early look at irradiation effects on China low activation martensitic (CLAM) steel with nanocrystalline grains (NC-CLAM steels) under 500keV Xe-ion bombardment at room temperature to doses up to 5.3displacements per atom (dpa). The microstructure in the topmost region of the steel is composed of nanocrystalline grains with an average diameter of 13nm. As the samples were implanted at low dose, the nanocrystalline grains had martensite lath structure, and many dislocations and high density bubbles were introduced into the NC-CLAM steels. As the irradiation dose up to 5.3dpa, a tangled dislocation network exists in the lath region, and the size of the bubbles increases. X-ray diffraction results show that the crystal quality decreases after irradiation, although the nanocrystals obviously coarsen. Grain growth under irradiation may be ascribed to the direct impact of the thermal spike on grain boundaries in the NC-CLAM steels. In irradiated samples, a compressive stress exists in the surface layer because of grain growth and irradiation-introduced defects, while the irradiation introduced grain-size coarsening and defects gradients from the surface to matrix result in a tensile stress in the irradiated NC-CLAM steels. Nanoindentation was used to estimate changes in mechanical properties during irradiation, and the results show that the hardness of the NC-CLAM steels increases with increasing irradiation dose, which was ascribed to the competition between the grain boundaries and the irradiation-introduced defects.

Influence of Xe Ion-Bombardment on the Substrate Microstructure and the Residual Stresses of Tin Coatings Deposited by Plasma Reactive Sputtering onto AISI 4140 Steel

The seek for sustainability in the global economic scenario has led to the need for developing materials that provide higher productivity, greater speed of operation, extended lifetimes and enhanced surface finishing of engineering parts. To achieve these goals it is essential to modify the metal surface with respect to its behavior in situations of friction, wear and oxidation at high temperatures. In this work, we studied the impact of different surface treatment strategies involving atomic peening with Xe ions and low temperature plasma nitriding on the surface microstructure of AISI 4140steel and the consequences of those surface treatments on the residual stresses of TiN coatings deposited onto the pre-treated substrates. The results show that ion bombardment at 1000 eV leads to mainly sputtering of surface material and no appreciable surface activation could be obtained for the subsequent plasma nitriding treatment. In the sample subjected to simple plasma nitriding, the highest nitride content was found and a Ti-enriched transition zone deposition appears to build up during the coating deposition. Accordingly the residual stresses of the TiN coatings deposited onto the nitrided steel surface were significantly lower in comparison to those encountered in the coatings grown on the non-treated, only bombarded and bombarded followed by nitriding substrates.

Ion beam sputtering of germanium – Energy and angular distribution of sputtered and scattered particles

The energy and angular distributions of scattered and sputtered particles produced by ion beam sputtering of a Ge target under variation of geometrical (incidence angle of primary ions and emission angle of secondary particles) and ion parameters (ion species (Ar, Xe) and energy (0.5–1.5keV) are presented.Several sets of Ge thin films are deposited and their thickness is measured by profilometry to determine the angular particle flux distribution of the sputtered particles. The particle flux distributions are of cosine-like shape and tilted in forward direction and the tilt of the maximum position increases with decreasing energy of the primary ions and increasing incidence angle.The energy distributions of the sputtered and the scattered ions are measured with an energy-selective mass spectrometer. The average energy of the sputtered ions increases with increasing incidence angle of the primary ions and with increasing emission angle, but is nearly unaffected by the species of the primary ions and their energy. The energy distribution of the scattered Ar ions reveals high energetic maxima that originate in direct scattering between Ar/Ge and Ar/Ar and which shift with increasing emission angle to higher energies. For Xe ion bombardment, there are only maxima for Xe/Xe scattering observed.All experimental data are compared with Monte Carlo simulations done with the well-known TRIM.SP code.

Diamond-like carbon sputtering by laser produced Xe plasma

The sputtering of diamond-like carbon (DLC) was investigated using Xe ion bombardment from the laser plasma X-ray source (LPX). The LPX we developed uses a solid Xe target and emits UV–X-rays and Xe ions. Using the LPX as an ion source, we measured etching depths of DLC, Ru, and Au films using a quartz crystal microbalance (QCM) to determine their ion sputtering rates at incident angles of 0° and 70°. The calculated results by the SRIM code were able to predict the measured results, except for the case of the DLC film at 0° incident. Our measured result indicated that the DLC sputtering at 0° was ten times larger than previously reported data, in which an ion gun was used. We consider that the difference was a characteristic effect of the laser plasma, and can be explained as a synergistic effect of ion bombardment and UV radiation from the Xe plasma.

Heavy-ion-induced modification of structural and mechanical properties of carbon-nanotube aerogels

We study the effect of 2MeV Xe ion bombardment at room temperature on the microstructure and mechanical properties of cross-linked carbon-nanotube-based nanoporous carbons. Irradiation causes a gradual densification and a decrease in the surface roughness of monoliths, an increase in Young’s modulus and failure stress, a decrease in the failure strain, and smoothening of nanoligament surfaces. Our results demonstrate a potential of heavy-ion bombardment for a controlled modification of nanoporous carbons.

Molecular dynamics study on low-energy sputtering of carbon material by Xe ion bombardment

The low-energy sputtering of carbon material under Xe ion bombardment is studied through the molecular dynamics (MD) simulation. For the normal incidence of Xe, the MD result of sputtering yield almost agrees with the experimental result by Williams et al. (AIAA-2004-3788). However, the experimental result shows a less incident angle dependence than the MD result because the experiment performed on a rough surface. It is found that the sputtered particles have memory of the projectile because the sputtered particles by the low-energy projectile undergo only a few collisions before the ejection. Low density of an amorphous carbon surface brings the decrease of the sputtering yield and the increase of high-energy sputtered atoms.

Kr and Xe ions implanted on the surfaces of Mo, Hf, Ta, W, Re, Au and platinum group elements

Kr and Xe ion bombardment experiments were conducted on Mo, Hf, Ta, W, Re, Au, and five platinum group elements. The implanted Kr and Xe ions were detected, and their concentrations were determined by X-ray photoelectron spectroscopy (XPS) using synchrotron radiation. In the case of 5d transition metals, the binding energies of Kr2p3/2, Xe3d3/2, and Xe3d5/2 in the target metals correlate with the number of d electrons of metals. Furthermore, the Xe concentration in the 5d transition metals correlates with atomic number, but there is no such correlation for Kr. The observed trend for the Xe concentration can approximately be reproduced by a theoretical calculation that takes sputtering yield into consideration. The retentivities of Kr and Xe are defined as the ratio of the experimental and theoretical surface concentrations. Although there is no correlation between retentivity and the atomic number of the target metal, the elastic energies in the cases of Kr and Xe atoms implanted in metals positively correlate with the corresponding retentivities. If the activation energy of noble-gas diffusion in the target metals can be represented in terms of the elastic energy, the noble-gas retentivity can be qualitatively explained.

Low energy ion bombardment of metal nanoclusters on graphite

Molecular dynamics simulations of 100 eV Ar and Xe ion bombardment of copper clusters, which consisted of 13 and 39 Cu atoms on a (0 0 0 1) graphite surface, have been performed. Energy distributions of backscattered Ar and Xe ions were analyzed. The influence of the cluster size on the Ar and Xe ion energy distributions are discussed.

Effect of xenon bombardment on ruthenium-coated grazing incidence collector mirror lifetime for extreme ultraviolet lithography

The effect of energetic xenon ion bombardment on the extreme ultraviolet (EUV) reflectivity performance of mirrors is of vital importance for the performance of discharge- and laser-produced plasma extreme ultraviolet lithography sources. To study these effects, we measured absolute and relative reflectivities at the National Institute of Standards and Technology and the Interaction of Materials with Particles and Components Testing facility to quantify the effects of singly ionized Xe ion bombardment on the reflectivity of Ru EUV collector mirrors. Results show that unity sputtering is reached at Xe+ energies near 400–500eV. The Xe+-induced sputter yield decreases an order of magnitude with only a 60% decrease in energy. Incident angle-dependent data of Xe+ bombardment show that the sputter yield is weakly dependent on angle at energies near 1keV. Dynamic measurements of in situ EUV reflectivity during Xe+ irradiation show that the oxygen state of the reflecting mirror has a significant effect on reflectivity performance. For example, 13.5nm light reflecting from an oxygen-rich mirror results in over a 40% loss in reflectivity. These studies also found that the surface roughness increased only at the atomic scale (subnanometer scale) when exposed to energetic Xe+ and thus did not contribute to EUV reflectivity losses except for cases of very high fluences (>1016cm−2).

Surface modification of MgAl2O4 and oxides with heavy ions of fission fragments energy

In this paper we report on results of surface modification in several candidate materials for inert matrix fuel hosts (MgAl2O4, MgO and Al2O3) induced by (0.5–5)MeV/amu Kr, Xe and Bi ion bombardment in the fluence range of 2×1010–1012ions/cm2. The size and shape of nanoscale hillock-like defects, each of which was created by the impact of a single ion, have been studied by using atomic force microscopy (AFM) technique. It was found that mean hillock height on sapphire and spinel surfaces depends linearly on the incident electronic stopping power. The hillocks are highest in MgAl2O4, having a lower threshold for the lattice disorder in the bulk material via relaxation of electronic excitations. As a possible reason for the hillocks formation, the plastic deformation due to the defects created by the Coulomb explosion mechanism in the target subsurface layer is suggested.

Luminescent and aging characteristics of blue emitting (Ca 1− x,Mg x)Al 2Si 2O 8:Eu 2+ phosphor for PDPs application

We have evaluated thermal stability and aging property of a blue color-emitting phosphor, CaAl 2Si 2O 8:Eu 2+ (CAS:Eu 2+), synthesized by conventional solid-state reaction method. When both CAS:Eu 2+ and BaMgAl 10O 19:Eu 2+ (BAM) were baked in air at 500 °C for 20 min, the decrease of photoluminescence (PL) intensity of CAS:Eu 2+ was lower than that of BAM. The aging property of CAS:Eu 2+ was also better than that of BAM. Due to its rigid structure and unlimited framework of silicon–oxygen and aluminum–oxygen around Eu 2+ ions, Eu 2+ ions were protected from outer oxidizing atmosphere and plasma discharge. After analysis of aging property and thermal stability, the differences of these thermal stability and aging property of CAS:Eu 2+ from those of BAM were ascribed to its crystal structure which plays a role of a shield for Eu 2+ ions against oxidation atmosphere and Xe ion bombardment.

The Lifetime Distribution of Cluster Ions from Sputtering Ion Source

The lifetime distribution of silver and mercury-silver binary cluster ions from a sputtering ion source was investigated. The cluster ions were produced by 10 keV Xe ion bombardment on a mercury-silver amalgam for mercury-silver binary clusters, and a silver plate for silver clusters. The fragmentation rates were obtained from experimental data at several positions of the mass spectrometer. The lifetime distribution was calculated using fragmentation rates. The distribution was found to be rather power functional than exponential, because of the wide distribution of lifetimes for cluster ions. The cluster ion, Hg12Ag+, which might have an icosahedron structure turned out to be more stable than neighboring clusters.

Size Distribution and Dissociation Patterns of Iron-Sulfur Binary Cluster Ions from Sputter Ion Source.

The size distribution of iron-sulfur binary cluster ions, FenSm+ (n=1-36, m=1-23), was investigated using secondary ion mass spectrometry (SIMS). The dissociation patterns, n=2-26, m=1-17, were also investigated by varying the acceleration voltage of secondary ions step by step. Iron-sulfur binary cluster ions were produced by 10 keV Xe ion bombardment on a pyrite (FeS2) sheet and were mass-analyzed by a sector type mass spectrometer. Judging from the size distribution observed in mass spectra, the composition ratio n/m of the cluster ions gradually tended to increase as the cluster size became larger. The dissociation patterns of small size tended to yield the FenSn+ (n=2, 4, 6) and FenSn-1+ (n=7, 8, 9) which might be more stable structure. As the cluster size became larger, the dissociation mainly occurred by emitting Fe or S2. Dissociation patterns of FenSm+ suddenly changed at FenSM+ which had maximum peak intensity in the series of FenSm+ for the fixed n. In case of m≤M, Fe emission occurred and S2 emission for m>M

UHV-STM study on ion-assisted deposition

Ion-assisted deposition is widely used for ultra high quality films. It is necessary to understand the role of ion bombardment during film formation. The apparatus which combines the Variable Temperature Scanning Tunneling Microscope (VT-STM) and an ion source in ultra high Vacuum (UHV) have been constructed. Ion bombardment effects on surfaces and nucleation and growth have been studied with the apparatus at various temperatures. In order to reveal the role of ion bombardment during film formation, ion bombardment effects at each stage of film formation have been investigated. After annealing of a Si(1 1 1) sample at 400°C, with Ge atoms deposited to a few Å, the formation of many islands of Ge on that surface was observed. These islands did not separate or coalesce into step edges when the surface with the Ge islands was irradiated by Xe ions with V a=5 kV and Dose=1.3×10 13 ions/cm 2. At this stage, the ratio of Xe + ion flux to the flux of deposited Ge atoms was about 1/100 and the mean number of defects formed by single Xe ion was about 30, so that the total number of defects was only about 1/3 of the deposited Ge atoms and the islands were stable. The stability of the Ge islands obtain in this study indicates that the Xe ion bombardment may take effects on the growth kinetics either at a higher ion dose or at an earlier stage of the film formation.

The role of cascade atoms in the zero-fluence and the low-bombarding-energy isotope sputtering

Influence of cascade atoms on the preferential emission of isotopes during sputtering has been studied by a static Monte Carlo simulation program, for zero-fluence and low-energy (below 1 keV) Xe ion bombardment of a 63Cu 0.5 65Cu 0.5 target. Calculations show that the probabilities of the sputtered cascade atoms of 63Cu and 65Cu are over 80%. The calculations also show that towards the surface, the momentum flux of the cascade atoms of 63Cu is much more than that of 65Cu. The momentum asymmetry in the collision cascade plays a dominating role in preferential emission of the lighter 63Cu atoms in the near-normal direction during low-bombarding-energy 63Cu– 65Cu sputtering.

A comparison between the irradiation damage response of spinel and zirconia due to Xe ion bombardment

Abstract The mechanical properties of Xe-implanted spinel and cubic zirconia surfaces, as determined by nano-indentation measurements, are distinct and the differences can be related to their microstructures. Upon Xe 2+ ion irradiation to high dose at cryogenic temperature (120 K), the Young’s modulus of irradiated spinel falls dramatically until the modulus is only about 3/4 the un-irradiated value. The maximum modulus occurs concurrent with the formation of a metastable crystalline phase of spinel. The subsequent elastic softening at higher Xe 2+ doses is an indication of the onset of amorphization of the spinel. Xe-implanted zirconia surfaces behave differently, in all cases showing almost no change in elastic modulus with increasing Xe 2+ ion dose. This is consistent with microstructural observations of Xe-implanted zirconia crystals which, unlike spinel, show no change in crystal structure with increasing ion dose. The hardness of both spinel and zirconia increases slightly for low Xe 2+ ion doses. At higher doses, zirconia shows little change in hardness, while the hardness of the implanted spinel falls by more than a factor of two. The initial increase in hardness of both spinel and zirconia is consistent with point defect accumulation and the precipitation of small interstitial clusters, while the drop in hardness of spinel at high Xe 2+ ion doses is due to the formation of an amorphous phase.

Simulations of self-affine roughening and ripple formation on ion bombarded amorphous carbon surfaces

Sputtering roughening and ripple formation on amorphous carbon surfaces bombarded by 2, 5 and 10 keV Ar- and Xe-ions are studied by using Monte Carlo simulations, where sputtering is treated in detail by simulating the entire collision cascades and the surface relaxation is described by a Wolf-Villain-type model. The simulations show that bombarded surfaces have self-affine topography on a scale comparable to the cascade dimension, and on larger scales ripples are formed on the surface. In case of the Ar-ion bombardment the wavelength of the ripples depend on the magnitude of the diffusion and on the orientation of the beam as predicted by the continuum theories. In case of the Xe-ion bombardment ripples with well-defined wavelengths were found only at an angle of incidence 60°. In all cases the ripple wavelength was found to increase with the increasing bombarding energy.