Noble Gas Ions Research Articles

Optimizing the resistivity of colloidal SnO2 thin films by ion implantation and annealing

Tin oxide (SnO2) is a critical material for a wide range of applications, such as in perovskite solar cells, gas sensors, as well as for photocatalysis. For these applications the transparency to visible light, high availability, cheap fabrication process and high conductivity of SnO2 benefits its commercial deployment. In this paper, we demonstrate that the resistivity of widely colloidal SnO2 can be reduced by noble gas ion beam modification. After low energy argon implantation with a fluence of 4×1015 at.cm−2 at 25keV and annealing at 200°C in air, the resistivity of as-deposited film was reduced from (178±6)μΩcm to (133±5)μΩcm, a reduction of 25%. Hall effect measurements showed that the primary cause of this is the increase in carrier concentration from (8.1±0.3)×1020 cm−3 to (9.9±0.3)×1020 cm−3. Annealing at 200°C resulted in the removal of defect clusters introduced by implantation, while annealing at 300°C resulted in the oxidation of the films, increasing their resistivity. The concentration of oxygen vacancy defects can be controlled by a combination of low energy noble gas ion implantation and annealing, providing promising performance increases for potential applications of SnO2 where a low resistivity is crucial.

A review of ion scattering spectroscopy studies at liquid interfaces with noble gas ion projectiles

Ion scattering spectroscopy (ISS) is an analytical tool that provides direct structural, topographical, and atomic compositional information at interfaces when ions are used as projectiles. Since its development in 1967, ISS is commonly used to obtain quantitative information about solid interfaces. Over the last couple of decades, ISS has emerged as an important technique to probe liquid interfaces and their studies employing ISS has become not uncommon, more so with Neutral impact collision ion scattering spectroscopy (NICISS). Therefore, here the principle of ISS with a particular focus on NICISS and its data evaluation are summarised while reviewing some important studies at vapor-liquid interfaces that provide direct information for molecular orientation of liquids (including ionic liquids), composition and distribution of atoms (or solutes) and charges as a function of depth to gain vast variety of thermodynamical information. Employing ISS such information can be achieved with high depth resolution of ∼1–2 Å (depending on the nature of the experiment). These examples highlight the significance of ISS and show potential for its application for studies related to specific ion effects, atmospheric reaction in aerosol and sea water droplets, and even determining the fate of environmental pollutants like heavy metal ions and per-fluoroalkyl substances (PFAS). Furthermore, some limitations of ISS are also discussed relating to investigation of high-vapor pressure liquids and probing buried interfaces like liquid-liquid interfaces while presenting progresses made in probing solid-liquid interfaces.

Elucidation of discharge mechanisms in He- and Ar-flexible μ-tube plasmas by temporally and spatially resolved plasma optical emission phoresis spectroscopy

A Helium- and Argon-flexible μ-tube plasma (FμTP) driven by a square wave high voltage were investigated by means of temporally and spatially resolved spectroscopy to characterize the discharge mechanisms. These two discharge gases show different discharge behavior in the same FμTP-configuration. The mixtures of different concentration of propane in Ar were used as discharge gases to confirm the role of Ar+ in an Ar-FμTP by tuning the discharge behavior. It was demonstrated that, N2+ are mainly responsible for the excitation and ionization and only small amount of He+ are produced in a He-FμTP, whereas Ar-FμTP lives from Ar+. These ions as well as excited species do not propagate beyond the capillary during the negative half cycle, resulting in a negligible contribution for protonation in this half cycle. The present study proposes a new method to data analysis, Plasma Optical Emission Phoresis Spectroscopy, which allows to distinguish noble gas ions from excited noble gas species.

Soft ionization mechanisms in flexible µ-tube plasma—elucidation of He-, Ar-, Kr-, and Xe-FµTP

The soft ionization mechanism of helium-based plasma seems to be understood while it still remains challenging in argon-based plasma, although many studies have used argon plasmas as a soft ionization source with good ionization efficiencies. In this study, helium, argon, krypton, and xenon were fed into the same discharge geometry, a flexible micro-tube plasma (FµTP), to determine the ionization mechanisms. The FµTPs operated with the named noble gases obtained comparable ionization efficiencies by MS measurements. The optical emission results showed that N2+ were the dominant ions within the helium-FµTP and noble gas ions were dominant for the other plasmas. These ions support the development of excitation and eventually stop at the end of the capillary. Therefore, Penning ionization and charge transfer between plasma and ambient air/analytes in the open atmosphere have been proven not to be the primary soft ionization mechanism. Furthermore, it was found that photoionization played a minor role in soft ionization. Using helium as a diagnosis gas in front of the discharge capillary nozzle of the FµTP, where the sample is usually positioned, shows that helium can be ignited by all of these FµTPs. This demonstrates that the excitation of a diagnosis gas as well as the ionization of analytes is independent of the type of the discharge gas. An alternative mechanism that a transient potential created by the ions is responsible for the soft ionization is subsequently proposed.

Numerical simulation and experimental characterization of the TRIUMF-FEBIAD cathode temperature for optimizing the ion source performance

The FEBIAD ion source is routinely used to produce radioactive ions of halogens, molecules, and noble gases in several ISOL facilities worldwide. At TRIUMF, an extensive numerical and experimental campaign has been performed to fundamentally understand the source while improving its reliability and overall performance. Particularly, the cathode temperature has been studied by pyrometric measurements, Schottky analysis and numerical simulations to properly understand the electron emission driving the ionization. The temperature values found are consistent within the error bars and confirm the equivalence of the methodologies used. The findings can be used as part of a numerical ionization model for more realistic electron emission and the benchmarked thermal model can be used to propose novel and more robust geometries.

Permanent magnet ECR ion source and LEBT dipole for single-ended heavy ion ToF-ERDA facility

We present the status of the ion source and low energy beam transport prototyping for a single-ended heavy ion time-of-flight elastic recoil detection analysis equipment. The environmentally friendly concept is based on a permanent magnet ECR ion source and dipole magnet on a 500 kV platform without SF6 insulation, producing high charge state noble gas ion beams, e.g. 3–6 MeV argon. The ion fluxes of Ar6+–Ar12+ achieved with the CUBE-ECRIS permanent magnet minimum-B quadrupole ion source exceed 1-10 particle nA required for the low energy ToF-ERDA application. The CUBE-ECRIS can produce over 1 particle nA krypton and xenon beams up to charge states Kr19+ and Xe24+, which enables extending the scope of the ToF-ERDA application. The integration of an adjustable-field permanent magnet dipole into the CUBE-ECRIS test stand at the JYFL accelerator laboratory is described briefly.

Evaluation of the ionization of noble gases under the effect of an electric field for the generation of useful energy

This work originated from the demand presented by an electric power transmission company and addresses a possible solution for the sector by exploring alternatives to extend the flight time of drones in the inspection of transmission lines. This original article demonstrates the use of the electromagnetic field of a transmission line to generate useful electrical power at the terminals of a bulb containing argon gas. It is an unprecedented application in power transmission. In this work, the tests based on a proof of concept are documented, where the results obtained were satisfactory and still allowed to connect an LED through the constructed arrangement. It is observed that the continuity of this research can provide scalability for applications whose main source of ion excitation is given from the energy dissipated as electric field loss in high-voltage lines.

Spectromicroscopy Study of Induced Defects in Ion-Bombarded Highly Aligned Carbon Nanotubes.

Highly aligned multi-wall carbon nanotubes were investigated with scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) before and after bombardment performed using noble gas ions of different masses (argon, neon and helium), in an ultra-high-vacuum (UHV) environment. Ion irradiation leads to change in morphology, deformation of the carbon (C) honeycomb lattice and different structural defects in multi-wall carbon nanotubes. One of the major effects is the production of bond distortions, as determined by micro-Raman and micro-X-ray photoelectron spectroscopy. We observe an increase in sp3 distorted bonds at higher binding energy with respect to the expected sp2 associated signal of the carbon 1s core level, and increase in dangling bonds. Furthermore, the surface damage as determined by the X-ray photoelectron spectroscopy carbon 1s core level is equivalent upon bombarding with ions of different masses, while the impact and density of defects in the lattice of the MWCNTs as determined by micro-Raman are dependent on the bombarding ion mass; heavier for helium ions, lighter for argon ions. These results on the controlled increase in sp3 distorted bonds, as created on the multi-wall carbon nanotubes, open new functionalization prospects to improve and increase atomic hydrogen uptake on ion-bombarded multi-wall carbon nanotubes.

Effect of noble gases ion implantation on the life time of WC-Co tools usedin wood-based material machining

Effect of noble gases ion implantation on the life time of WC-Co tools used in wood-based materialmachining. The results of the investigations on the tool life of WC-Co tools, implanted with three noble gas ions,i.e. helium, neon and argon, are presented in the comparison with the virgin tools and tools implanted withnitrogen ions. The surface modification of the tools was preceded by the modelling of the depth profiles of theimplanted elements. The implantation of the ions of noble gases resulted in an improvement in tool tool life, inthe range from 5 to 49%.

Transient to steady-state morphology evolution of carbon surfaces under ion bombardment: Monte Carlo simulations

Molecular dynamics (MD) simulations have established the sputtering yields of carbon under the low-energy bombardment of noble gas ions. Here, we upscale these MD results to account for the evolving surface morphology and sputtering yield with ion fluence using a Monte Carlo model, which considers the shadowing of the incident ion flux, redeposition of sputtered carbon material, and secondary sputtering induced by the surface impact of carbon sputterants. Results show that initially rough surface morphologies are consistently smoothened and flattened by a normal ion flux, resulting in sputtering yields that approach MD predictions. Under a highly oblique ion flux, however, the activation of multiple cooperative roughening and smoothening mechanisms at different scales lead to the formation of characteristic surface steps at the microscale, with steady-state sputtering yields that are up to an order-of-magnitude lower than MD predictions. While the observed surface features and the ensuing sputtering yield at steady-state are generally not sensitive to the initial surface morphology, the initial morphology controls the ion fluence to attain steady-state. We discuss surface design strategies to delay and abate sputtering.

Quantitative Measurement of Positive and Negative Ion Species Ejected from a Li–O–H Surface by Hydrogen and Noble Gas Ion Irradiation

Quantitative Measurement of Positive and Negative Ion Species Ejected from a Li–O–H Surface by Hydrogen and Noble Gas Ion Irradiation

Efficient radioactive gas detection by scintillating porous metal–organic frameworks

Natural and anthropogenic gas radionuclides such as radon, xenon, hydrogen and krypton isotopes must be monitored to be managed as pathogenic agents, radioactive diagnostic agents or nuclear activity indicators. State-of-the-art detectors based on liquid scintillators suffer from laborious preparation and limited solubility for gases, which affect the accuracy of the measurements. The actual challenge is to find solid scintillating materials simultaneously capable of concentrating radioactive gases and efficiently producing visible light revealed with high sensitivity. The high porosity, combined with the use of scintillating building blocks in metal–organic frameworks (MOFs), offers the possibility to satisfy these requisites. We demonstrate the capability of a hafnium-based MOF incorporating dicarboxy-9,10-diphenylanthracene as a scintillating conjugated ligand to detect gas radionuclides. Metal–organic frameworks show fast scintillation, a fluorescence yield of ∼40%, and accessible porosity suitable for hosting noble gas atoms and ions. Adsorption and detection of 85Kr, 222Rn and 3H radionuclides are explored through a newly developed device that is based on a time coincidence technique. Metal–organic framework crystalline powder demonstrated an improved sensitivity, showing a linear response down to a radioactivity value below 1 kBq m−3 for 85Kr, which outperforms commercial devices. These results support the possible use of scintillating porous MOFs to fabricate sensitive detectors of natural and anthropogenic radionuclides.

Low-Energy Ion Scattering Intensities from Supported Nanoparticles: The Spherical Cap Model

Supported nanoparticles are of great importance to many technologies like fuel processing and chemical synthesis using catalysts and electrocatalysts, energy storage and generation using fuel cells and batteries, electrochemistry, magnetic information storage, and more. Low-energy ion scattering spectroscopy (LEIS) with noble gas ions like He+ is a powerful tool for the characterization of nanoparticles dispersed across flat support surfaces due to its ability to probe the elemental composition in the topmost atomic layer of a surface, providing quantitative information regarding the size and number density of nanoparticles. In this work, we present a derivation of the LEIS intensities expected from nanoparticles and the support material as a function of the average particle size, their number per unit area, and their contact angle with the support when modeled as spherical caps of the nanoparticle material dispersed over the surface of a flat support. The model assumes that the ion intensities are determined only by the physical blocking of linear ion trajectories and independent of the tilt angle of the local surface relative to the incident and scattered ion directions, an assumption we support by quantitative modeling of published data which tested tilt-angle effects. The model is a generalization to arbitrary contact angles of the hemispherical cap model, which assumes 90° contact angle and has been widely used to model spectroscopic signals in LEIS (and also in Auger and photoelectron spectroscopies) during nanoparticle growth. This new model quantitatively reveals how LEIS signals are sensitive not only to the diameter and number density of the nanoparticle but also to their contact angle (or height/diameter ratio). With the use of additional data (e.g., from microscopy or adsorption microcalorimetry), the model presented here will enable more accurate determination of the average size, shape, and number density of supported nanoparticles based on LEIS intensity measurements.

Probability of ionization of the noble gas atoms and ions for high harmonic generation

Radiation produced in high-order harmonic generation (HHG) process can be utilized to generate attosecond pulses. According to the semi-classical theory of HHG, the maximum emitted photon energy is [Formula: see text]. The ionization potential ([Formula: see text] and ponderomotive energy ([Formula: see text], play important roles in the generated photon energy; therefore, choosing the material and field for HHG is important. Here, investigating the probability of ionization of material in laser and plasmonic field for HHG is important. The ionization probability of noble gases atoms and ions was investigated. Using Ammosov–Delone–Krainov (ADK) model formulas, the parameters for ions and atoms were determined. The results show that helium is the most suitable noble gas atom for HHG in both fields. After ionizing the atoms, the ionization potential increases significantly, and the ionization probability also decreases. Then, ions are better than their corresponding atoms for HHG. Among noble gas atoms and ions, the helium ion is the most suitable for HHG. In addition, the plasmonic field increases the ponderomotive energy and decreases the probability of ionization for all atoms, as shown by the simulation. Then, extreme ultraviolet (XUV) high-energy photon can be efficiently generated using noble gas ions.

Monte Carlo Simulation of Alkaline Earth Metal Oxides Protective Layers Bombarded With Ne+ or Xe+ in Plasma Display Panels

One of the major components of commercial plasma display panel (PDP) cells is the magnesium oxide (MgO) protective layer. In order to obtain both lower discharge breakdown voltage and higher energy efficiency in the cells, other alkaline Earth metal oxides have been extensively studied as alternatives to MgO. Another important factor in the life-extending of PDP is resistance to ion sputtering. In this article, the Monte Carlo simulation program Stopping and Range of Ions in Matter (SRIM)-2013 was applied to study the behavior of the sputtering yield, vacancies/ions, backscattered ions, ion range, lateral and radial projection, energy loss due to ionization, vacancies, and phonons, of MgO, calcium oxide (CaO), SrO, and barium oxide (BaO) as a function of incident angle for Ne <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{+}$ </tex-math></inline-formula> and Xe <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{+}$ </tex-math></inline-formula> ion beam. It is discovered that CaO, SrO, and BaO protective layers increase the number of backscattered ions from surfaces when they are hit by noble gas ions. They resist sputtering and vacancies better than the MgO protective layer.

Nanoscale pattern formation produced by ion bombardment of a rotating target: The decisive role of the ion energy.

We study the nanoscale patterns that form on the surface of a rotating sample of an elemental material that is bombarded with a broad noble gas ion beam for angles of incidence θ just above the critical angle for pattern formation θ_{c}. The pattern formation depends crucially on the ion energy E. In simulations carried out in the low-energy regime in which sputtering is negligible, we find disordered arrays of nanoscale mounds (nanodots) that coarsen in time. Disordered arrays of nanodots also form in the high-energy regime in which there is substantial sputtering, but no coarsening occurs close to the threshold angle. Finally, for values of E just above the sputter yield threshold, nanodot arrays with an extraordinary degree of hexagonal order emerge for a range of parameter values, even though there is a broad band of linearly unstable wavelengths. This finding might prove to be useful in applications in which highly ordered nanoscale patterns are needed.

Surface morphology and carbon structure effects on sputtering: Bridging scales between molecular dynamics simulations and experiments

Experiments report large scatter in the sputtering yield of carbon materials under the bombardment of low-energy noble gas ions. Here, we conduct scale-bridging molecular dynamics (MD) simulations on the xenon bombardment of carbon substrates across ion energies of 75 eV to 2 keV, and at ion incidence angles of 0°–75°, to resolve uncertainties in the sputtering data. Results show rapid amorphization of the carbon subsurface with ion bombardment, but the structural characteristics (sp/sp2/sp3 bond proportion, atomic density) eventually plateau once steady-state sputtering is achieved. In addition, we obtain virtually indistinguishable “steady-state” amorphous structures across the range of ion energies and ion incidence angles, as well as for several different carbon structures, which suggests that the steady-state sputtering yield data is independent of the initial carbon structure and prior sputtering history. By accounting for changes in the local incidence angle, surface shielding, and redeposition of the sputterants associated with surface morphology effects, we demonstrate that the sputtering predictions from MD are in perfect agreement with prior experiments across the range of ion energies and incidence angles. Using a Bayesian approach based on the MD data, we calibrate the parameters of a semi-empirical sputtering model for different surface morphologies.

Corrosion resistance of tungsten carbide-rich coating layers produced by noble gas ion mixing

Tungsten carbide (WC) belongs to the class of protective coatings due to its good mechanical properties and corrosion resistance. Herein WC-rich coating layers have been produced by irradiating C/W multilayers with noble gases at room temperature. The in-depth concentration distributions after ion irradiation have been measured by Auger electron spectroscopy depth profiling. The corrosion resistance of the formed layers has been tested in 3.5 wt% NaCl solution. It has been shown that the growth of the WC-rich layer started at the interfaces and with increasing fluence the separately growing layers coalesced. With the coalescence of the layers the corrosion resistance of the system suddenly increased. To describe this phenomenon the term effective areal density has been introduced. If the effective areal densities of WC were lower and higher than 550 (1/nm2) and 1200 (1/nm2), the corrosion current densities were 0.5 and 0.08 (µA/cm2), resp. The in-depth distribution of the WC-rich layer and thus the corrosion resistance could be tailored by varying the projectiles, fluences, energies and initial layer structure. The maximum corrosion resistance found was better than that of stainless steel and WC cermet. The effective areal densities could be predicted by TRIDYN simulations allowing the design of corrosion resistive coatings.

Why are physical sputtering yields similar for incident ions with different masses?—physical sputtering yields of the Lennard–Jones system

Plasma etching of nano-meter-scale complex structures for semiconductor device manufacturing requires a deeper understanding of etching mechanisms. For example, it is known experimentally that the sputtering yield of a material tends to have weak dependence on the mass of incident ions except for extremely light ions such as helium. To understand this property, the sputtering yield of a system of atoms interacting with Lennard–Jones (LJ) potentials was evaluated with molecular dynamics simulation. As the simplest possible case involving two atomic species, a single-element face-centered-cubit (fcc) LJ solid surface interacting with purely repulsive atoms was examined, which emulates a solid surface sputtered by noble-gas ions. The sputtering of such a system at specific incident ion energy depends only on two parameters, i.e. the mass ratio and a parameter representing the relative interaction range between the surface atom and the incident ion. For real materials of our concern used in plasma etching, the range of these two parameters was found to be relatively limited. It was also found that the physical sputtering yield of the LJ system weakly depends on the mass ratio in this relatively narrow parameter range. Because the simple model predicts the weak yield dependence on the incident ion mass, it is considered as a generic property of physical sputtering, independent of the detailed atomic interactions of the surface material and incident ion species.

Ionization of Noble Gases Under the Effect of an Electric Field for the Generation of Useful Energy

Ionization of Noble Gases Under the Effect of an Electric Field for the Generation of Useful Energy