Noble Gas Ions Research Articles

Scratching resistance of SiC-rich nano-coatings produced by noble gas ion mixing

SiC-rich nano-layers were produced at room temperature by applying ion beam mixing of various C/Si multilayer structures using argon and xenon ions with energy in the range of 40–120 keV and fluences between 0.25 and 3 × 1016 ions/cm2. The mechanical behavior of the layers was characterized by scratch test. The scratching resistance of the ion mixed samples has been measured by standard scratch test applying an atomic-force microscope with a diamond-coated tip (radius < 15 nm) and they were compared to that measured on Si single crystal. The applied load varied in the range of 4–18 μN. The scratching resistance of the samples correlated with the effective areal density of the SiC; with increasing effective areal density the scratch depth decreases. Above sufficiently high effective areal density of SiC the scratch resistance (hardness) of the produced layer was somewhat higher than that of single crystal silicon. Previously it has been shown that such layers have excellent corrosion resistive properties as well. These findings allow to tune and design the mechanical and chemical properties of the SiC protective coatings.

Absolute cross sections for He+ impact single ionization of noble gases

Absolute cross sections for He+ impact single ionization of noble gases

Monte Carlo simulations of noble gas ion beam sputtering yield of MgO, CaO, SrO, and BaO with various thin coatings in AC‐PDP cells

MgO is one of the popular materials to be used as protection of the phosphor layer from plasma damage and reduction of the discharge voltages in the alternating current–type plasma display panel (AC‐PDP) cells. However, one limitation on the AC‐PDP lifetime is plasma erosion of MgO barrier coating. In order to maintain or extend the lifetime of the AC‐PDP, we have applied potential materials such as alumina (α‐Al2O3), titanium dioxide (TiO2), and aluminum titanate (Al2TiO5) as a thin coating on the alkaline earth metal oxides. This review focuses on the effect of α‐Al2O3, TiO2, and Al2TiO5 on sputtering yields of MgO, CaO, SrO, and BaO bombarded by Ne+ and Xe+ ions in the energy range 100 to 300 eV. The SRIM‐2013 simulations have been compared with the available experimental data to test the validity of the model potential and to extract the surface binding energies. These energies are employed to obtain more realistic sputtering yields of MgO, CaO, SrO, and BaO coated with three different ceramic coatings. Our results have shown that the coated surfaces exhibit better erosion resistance than the uncoated surfaces. It is found that the Al2TiO5 coating provided superior protection against physical sputtering of the substrate; it will demonstrate better performance in comparison with α‐Al2O3 or TiO2 coating.

Charge Exchange Cross Sections for Noble Gas Ions and N2 between 0.2 and 5.0 keV

Charge transfer of an electron from a neutral atom to an ion is a fundamental interaction that plays a dominant role in the energy balance of atmospheric and astrophysical plasmas. The present investigation measured the charge exchange cross sections of noble gas ions (He + , Ne + , Ar + , Kr + ) with N 2 in the intermediate energy range 0.2–5.0 keV. The systems were chosen because there remains a lack of consensus amongst previous measurements and regions where there were no previous measurements. A description of the mechanical design for an electrically floated gas cell is described herein.

Symmetric charge exchange for intermediate velocity noble gas projectiles

Experimental measurements of the total charge exchange cross section for 0.2–5.0 keV noble gas ions (He+, Ne+, Ar+, Kr+) with neutral atomic targets of the same species have been performed. The results are compared to theoretical predictions across this energy range as well as to prior data where available. Including these new results into the fitting parameters of state-of-the-art models brings prior measurements at higher energies into agreement. Merits of the two competing theories are discussed in the context of the four noble gas ions He+ through Kr+.

Ion beam sputtering of silicon: Energy distributions of sputtered and scattered ions

The properties of sputtered and scattered ions are studied for ion beam sputtering of Si by bombardment with noble gas ions. The energy distributions in dependence on ion beam parameters (ion energy: 0.5–1 keV; ion species: Ne, Ar, Xe) and geometrical parameters (ion incidence angle, polar emission angle, and scattering angle) are measured by means of energy-selective mass spectrometry. The presence of anisotropic effects due to direct sputtering and scattering is discussed and correlated with process parameters. The experimental results are compared to calculations based on a simple elastic binary collision model and to simulations using the Monte-Carlo code sdtrimsp. The influence of the contribution of implanted primary ions on energy distributions of sputtered and scattered particles is studied in simulations. It is found that a 10% variation of the target composition leads to detectable but small differences in the energy distributions of scattered ions. Comparison with previously reported data for other ion/target configurations confirms the presence of similar trends and anisotropic effects: the number of high-energy sputtered ions increases with increasing energy of incident ions and decreasing scattering angle. The effect of the ion/target mass ratio is additionally investigated. Small differences are observed with the change of the primary ion species: the closer the mass ratio to unity, the higher the average energy of sputtered ions. The presence of peaks, assigned to different mechanisms of direct scattering, strongly depends on the ion/target mass ratio.

Hybrid refractive-diffractive microlenses in glass by focused Xe ion beam

The combination of refractive and diffractive components in a single optical element provides miniaturization of optical systems and enhancement of their performance. Thus, hybrid singlet lenses with diffractive structures added on top of the refractive curved surface were shown to have reduced chromatic and spherical aberration. Optical systems based on such hybrid lenses have reduced dimensions as they require fewer lenses for aberrations-correction. Diffractive elements provide additional possibilities of light manipulation and enable the realization of miniaturized multifocal systems, spectrometers, and other devices. Glass hybrid lenses are typically realized by diamond turning or glass moulding. These techniques, however, are not applicable for the fabrication of lenses in brittle materials or microlenses (hundreds of micrometers in diameter or less). On the other hand, direct writing techniques, such as focused ion beam (FIB) milling (typically Ga), offer a high resolution and flexibility of patterning on curved lens surfaces made of a great variety of materials. The disadvantages of FIB milling are its slow speed and Ga implantation that may alter or degrade the optical performance of fabricated components. FIB systems based on high brightness plasma ion sources provide more than an order of magnitude increase in milling rates with noble gas ions (e.g., Xe) compared with Ga FIBs. Here, the authors demonstrate the feasibility of rapid, direct milling of hybrid refractive-diffractive microlenses in glass using &amp;gt;60 nA of Xe ion current. Microlenses with up to 300-μm diameter were milled and diffraction gratings were realized on top of their curved surfaces. The performance of the lenses was characterized by mapping the transmitted intensity at different positions. Due to the introduction of diffraction gratings on the surface of the lenses, their optical performance is modified with the emergence of additional focal spots spatially separated by distances consistent with the theoretical and simulated values. The results indicate the applicability of the plasma focused ion beam systems for rapid fabrication of high-quality hybrid optical elements directly in hard substrates.

Laser-Induced Fluorescence Measurements of the Noble-Gas Atom and Ion Densities in a Mirror System

The densities of NeI atoms and XeII ions in the PS-1 mirror system were measured by the method of laser-induced fluorescence (LIF). Schemes of levels for LIF measurements of the density are proposed. Models for numerical processing of the obtained LIF signals are developed. The electron temperature and plasma density were also measured using Langmuir probes.

The regularities of surface corrugation of polyacrylonitrile based carbon fibers under high-fluence ion irradiation

The regularities of surface corrugation of polyacrylonitrile based carbon fibers reinforcing composite KUP-VM has been studied experimentally after high-fluence 30 keV Ne+, 20 and 30 keV Ar+, 30 keV N2+ ion irradiation at target temperatures ranging from 100 to 600 °C. It was found that periodic corrugated structure parameters, such as the angles of the inclination β of the corrugations and their fraction on the fiber surface have strong temperature dependences. The periodicity of corrugations for all used ions slightly decreases with increasing temperature and is of the order of hundreds of nanometers. For neon and argon ions the corrugation inclination angles and the fraction in contrary of nitrogen ions show minima at the temperatures near 400 °C which corresponds to the minimum of radiation-induced dimensional changes in carbon materials. The depth of the minima at 400 °C depends on the competition of the processes of ion-induced plastic deformation of carbon materials and ion bombardment sputtering. For nitrogen ions the inclination angles increase with temperature so that at temperature ∼270 °C they reach maximum values ∼40°, staying at this level at subsequent temperature elevation up to 600 °C. The qualitative difference in the temperature dependences of fiber corrugation for noble gas ions and nitrogen ones is connected to nitrogen chemical activity and the creation of CN bonds under nitrogen ion implantation.

Ionization‐Facilitated Formation of 2D (Alumino)Silicate–Noble Gas Clathrate Compounds

AbstractThe nanoscale confinement of noble gases at noncryogenic temperatures is crucial for many applications including noble gas separations, nuclear waste remediation, and the removal of radon. However, this process is extremely difficult primarily due to the weak trapping forces of the host matrices upon noble gas physisorption. Herein, the formation of 2D clathrate compounds, which result from trapping noble gas atoms (Ar, Kr, and Xe) inside nanocages of ultrathin silica and aluminosilicate crystalline nanoporous frameworks at 300 K, is reported. The formation of the 2D clathrate compounds is attributed to a novel activated physisorption mechanism, facilitated by ionization of noble gas atoms. Combined X‐ray photoelectron spectroscopy (XPS) and density functional theory (DFT) studies provide evidence of an initial ionization process that significantly reduces the apparent trapping barrier. Noble gas ions become neutralized upon entering the cages, and their desorption requires unprecedentedly high temperatures, even in ultrahigh vacuum conditions. From 2D aluminosilicate films these temperatures are 348 K (Ar), 498 K (Kr), and 673 K (Xe). DFT calculations also predict that Rn can be trapped in 2D aluminosilicates with an even higher desorption temperature of 775 K. This work highlights a new ionization‐facilitated trapping mechanism resulting in the thinnest family of clathrates ever reported.

On the Dynamic Annealing of Ion-Induced Radiation Damage in Diamond under Irradiation at Elevated Temperatures

The structure and properties of the near surface layer of diamond after high-fluence irradiation at elevated temperatures with 30-keV Ar+, Ne+, N+, $${\text{N}}_{{\text{2}}}^{ + }$$ and C+ ions are studied. Dynamic annealing at temperatures above 500°С results in recrystallization of the diamond phase only in the case of irradiation with carbon ions, and irradiation with impurity ions causes graphitization of the ion-modified layer of diamond. According to Raman spectroscopy and reflection high-energy electron diffraction data, a nanographite structure is formed in the modified layer when irradiated with noble-gas ions. When irradiated with carbon ions, diamond grows and recrystallizes with a thin (~1 nm) graphite-like layer on the surface. In the case of nitrogen ions, a graphite layer is observed up to 720°С. Graphite-like layers on the surface of diamond are thermostable and, according to X-ray photoelectron spectroscopy, are layers of sp2 carbon. The Raman spectroscopy of visible light shows the different optical transparency of ion-induced structures on the surface of diamond, which correlates with the resistivities. The diamond structure disordered during ion irradiation at room temperature and the nanographite structure are more transparent than the graphite structure.

The impact of surface oxidation on energy spectra of keV ions scattered from transition metals

Studying the initial stages of surface oxidation is of great relevance to understand how oxygen alters the physical and chemical properties at the interface of the host material to the environment and is therefore, crucial for improvement in manifold technological applications. We investigated the influence of surface oxygen on ion spectra recorded for keV noble gas ions backscattered from metal surfaces in low energy ion scattering (LEIS). Initially pure Zn and Ta surfaces, chosen for their well-characterized properties in ion-neutralization in LEIS, have been oxidized and ion spectra for pure and oxidized surfaces have been compared. Oxygen on the surface significantly influences shape and intensity of the backscattered ion spectrum at all energies: for both metal systems, the surface scattered ion yield of the metal is drastically decreasing under oxygen presence. The observed decrease, however, cannot be explained by the reduction in the surface areal density of the metal constituents exclusively. At least for Zn an additional significant change in charge exchange behavior is necessary to explain the observations. In contrast to the generally observed decrease in the yield of ions scattered from the outermost surface, the change in shape and intensity of the reionization background are found to show opposing trends and different energy dependencies for Zn and Ta.

Application of keV-energy proton scattering for thin film analysis

Hydrogen ions are not widely used in low or medium-energy ion scattering spectroscopy. However, in certain cases, the use of non-destructive hydrogen ions with low nuclear stopping may provide additional information compared with noble gas ions. In this work, we describe in situ analysis of nanometer layer deposition of Au on Si and vice versa using keV-energy proton scattering spectroscopy. Ion beam sputtering and thermal evaporation were used for deposition of surface layers. The maximum thickness of deposited layers was measured with X-ray photoelectron spectroscopy and surface profiler. The accuracy of in situ surface layer thickness determination with energy spectra of scattered protons is discussed.

Defect sizing, separation, and substrate effects in ion-irradiated monolayer two-dimensional materials

Precise and scalable defect engineering of 2D nanomaterials is acutely sought-after in contemporary materials science. Here we present defect engineering in monolayer graphene and molybdenum disulfide (MoS$_2$) by irradiation with noble gas ions at 30 keV. Two ion species of different masses were used in a gas field ion source microscope: helium (He$^+$) and neon (Ne$^+$). A detailed study of the introduced defect sizes and resulting inter-defect distance with escalating ion dose was performed using Raman spectroscopy. Expanding on existing models, we found that the average defect size is considerably smaller for supported than freestanding graphene and that the rate of defect production is larger. We conclude that secondary atoms from the substrate play a significant role in defect production, creating smaller defects relative to those created by the primary ion beam. Furthermore, a similar model was also applied to supported MoS$_2$, another promising member of the 2D material family. Defect yields for both ions were obtained for MoS$_2$, demonstrating their different interaction with the material and facilitating comparison with other irradiation conditions in the literature.

Xenon solubility and formation of supercritical xenon precipitates in glasses under non-equilibrium conditions

Estimates of noble gas solubility in glasses and minerals are important to understand the origin of these gases, particularly xenon, in the atmosphere. However, technical difficulties and ambiguities in quantifying the dissolved gases introduce large uncertainties in the solubility estimates. We present here the use of transmission electron microscopy (TEM) with in-situ noble gas ion implantation as a non-equilibrium approach for noble gas solubility estimates. Using a suitable Xe equation of state and Monte-Carlo simulations of TEM images, a clear distinction between Xe filled precipitates and empty voids is made. Furthermore, implantation-induced changes in the solubility are estimated using molecular dynamics simulations. These studies allow us to evaluate the xenon solubility of irradiated and pristine silica glasses and monitor in-situ the diffusion-mediated dynamics between the precipitates and voids — otherwise impossible to capture. On exceeding the solubility limit, supercritical xenon precipitates, stable at least up to 1155 K, are formed. The results highlight the high capacity of silicates to store xenon and, predict higher solubility of radiogenic xenon due to the accompanying radiation damage.

Luminescence of Noble Gases and Their Mixtures Under Nanosecond Electron-Beam Excitation

Luminescence spectra in the range 200–970 nm were studied for He, Ne, Ar, Kr, and Xe and Ar–Kr, Ar–Xe, and Kr–Xe mixtures under 5-ns electron-beam excitation. Emission intensity distributions over noble-gas 2p-levels were obtained. It was concluded that the main process for populating atomic levels was not dissociative recombination of molecular noble-gas ions with electrons. The emission intensity of heteronuclear ionic noble-gas molecules was noticeably less (relative to the intensities of the atomic lines) than for ion-beam excitation.

Ion mass dependence of irradiation-induced damage accumulation in KTaO3

Damage production and amorphization resulting from the interaction of medium-energy (from 40 to 480 keV) noble-gas ions (from He to Kr) with potassium tantalate (KTaO3) are determined using ion channeling measurements. A disorder accumulation model has been fit to the maximum damage concentration versus ion fluence to extract the cross sections for direct-impact and defect-stimulated amorphization, and the results indicate that defect-stimulated amorphization is the dominant mechanism. These cross sections exhibit a strong dependence on the calculated cross sections for displacing lattice atoms, indicating a dominant contribution of nuclear interactions to the defect production and amorphization processes under the irradiation conditions used in this study. These experimental findings, along with the model fits, suggest that the difference in recoil spectra between He and the other heavier ions may be the main driving force for the decreased damage efficiency observed for He ions, which results in a reduced rate of damage accumulation.

New Resonance Ionization Mass Spectrometry Scheme for Improved Uranium Analysis.

Resonance ionization mass spectrometry (RIMS) combines tunable laser spectroscopy with mass spectrometry to provide a high-efficiency means of analyzing solid materials. We previously showed a very high useful yield of 24% for analysis of uranium using three lasers to excite and ionize atoms sputtered from metallic uranium and uranium dioxide. A new resonance ionization scheme using only two lasers achieves a higher useful yield of 38% by accessing both the ground electronic state and a low-lying electronic state of atomic uranium that is significantly populated by sputtering. The major loss channel in analyzing uranium dioxide is the formation of UOx molecules during sputtering. Prebombardment of the surface with 3 keV noble gas ions prior to analysis reduces the surface and results in a sputtered flux with a greatly enhanced proportion of atomic U. This method of surface reduction results in uranium useful yields as high as 6.6% for uranium dioxide analysis, compared to 2% from previous work.

Monte Carlo simulations of MgO and Mg(OH) 2 thin films sputtering yields by noble-gas ion bombardment in plasma display panel PDP

Abstract MgO is known to be a material suitable for barrier coating of commercial plasma display panel (PDP) cells owing to its excellent electrical insulating property, good resistance to sputtering, large secondary-electron emission coefficient and high transmittance. It is also a valuable information for improving the efficiency and the lifespan of the PDP. However, the effect of moisture emitted from the wall and phosphor materials of the PDP cells, an Mg(OH)2 is formed on the top surface of an MgO protective layer. In this work, the Monte Carlo simulation program SRIM-2013 was applied to calculate the sputtering yields of magnesium hydroxide Mg(OH)2 by low-energy noble-gas ion bombardment. The comparison between results obtained by Monte Carlo simulation and those obtained by experiments is elucidated in this paper. Furthermore, the surface binding energies for MgO and Mg(OH)2 layers on sputtering yield are discussed. It is found that the sputtering yield of Mg(OH)2 is generally lower than that of MgO at each incident energy. On the other hand, the sputtering yield depends on the properties of both the incident particle and the target.

Concurrent segregation and erosion effects in medium-energy iron beam patterning of silicon surfaces

We have bombarded crystalline silicon targets with a 40 keV Fe+ ion beam at different incidence angles. The resulting surfaces have been characterized by atomic force, current-sensing and magnetic force microscopies, scanning electron microscopy, and x-ray photoelectron spectroscopy. We have found that there is a threshold angle smaller than 40° for the formation of ripple patterns, which is definitely lower than those frequently reported for noble gas ion beams. We compare our observations with estimates of the value of the critical angle and of additional basic properties of the patterning process, which are based on a continuum model whose parameters are obtained from binary collision simulations. We have further studied experimentally the ripple structures and measured how the surface slopes change with the ion incidence angle. We explore in particular detail the fluence dependence of the pattern for an incidence angle value (40°) close to the threshold. Initially, rimmed holes appear randomly scattered on the surface, which evolve into large, bug-like structures. Further increasing the ion fluence induces a smooth, rippled background morphology. By means of microscopy techniques, a correlation between the morphology of these structures and their metal content can be unambiguously established.