Neutral Atom Beam Research Articles

Neutral beam microscopy with a reciprocal space approach using magnetic beam spin encoding

The emerging technique of neutral beam microscopy offers a non-perturbative way of imaging surfaces of various materials which cannot be studied using conventional microscopes. Current neutral beam microscopes use either diffractive focusing or pin-hole scanning to achieve spatial resolution, and are characterised by a strong dependence of the imaging time on the required resolution. In this work we introduce an alternative method for achieving spatial resolution with neutral atom beams which is based on manipulating the magnetic moments of the beam particles in a gradient field, and is characterised by a much weaker dependence of the imaging time on the image resolution. The validity of the imaging approach is demonstrated experimentally by reconstructing one dimensional profiles of the beam which are in good agreement with numerical simulation calculations. Numerical simulations are used to demonstrate the dependence of the signal to noise on the scan resolution and the topography of the sample, and assess the broadening effect due to the spread of velocities of the beam particles. The route towards implementing magnetic encoding in high resolution microscopes is discussed.

Accelerated neutral atom beam (ANAB) and gas clustered ion beam (GCIB) treatment of implantable device polymers leads to decreased bacterial attachment in vitro and decreased inflammation in vivo

Accelerated neutral atom beam (ANAB) and gas clustered ion beam (GCIB) treatment of implantable device polymers leads to decreased bacterial attachment in vitro and decreased inflammation in vivo

Fast and cold negative ion and neutral atom beams from a water spray

High-power lasers are routinely used to generate energetic positively charged ions, and this paper reports on the observation of negative ions in these experiments. A large number of negative ions and neutral atoms at MeV energies was obtained from the interaction of a high intensity laser pulse with a water spray along with positive ions [Abicht et al., Appl. Phys. Lett. 103, 253501 (2013)]. Beams of negative ions and neutral atoms have the same properties as beams of positive ions. However, the mechanism of negative ion formation and acceleration is still under discussion. In order to gain more information about physics of generation negative ions and neutrals, we present a new experiment where all species, positive, negative ions, and neutrals, are spatially separated, and the electron capture and loss of each in water spray is evaluated. The formation of negative ions and neutral atoms of hydrogen and carbon with energies up to 140 keV and 1.2 MeV, respectively, is confirmed. It is suggested that the electrification of spray droplets plays a decisive role in these charge-exchange processes.

In-plasma analysis of plasma–surface interactions

During deposition, modification, and etching of thin films and nanomaterials in reactive plasmas, many active species can interact with the sample simultaneously. This includes reactive neutrals formed by fragmentation of the feed gas, positive ions, and electrons generated by electron-impact ionization of the feed gas and fragments, excited states (in particular, long-lived metastable species), and photons produced by spontaneous de-excitation of excited atoms and molecules. Notably, some of these species can be transiently present during the different phases of plasma processing, such as etching of thin layer deposition. To monitor plasma–surface interactions during materials processing, a new system combining beams of neutral atoms, positive ions, UV photons, and a magnetron plasma source has been developed. This system is equipped with a unique ensemble of in-plasma surface characterization tools, including (1) a Rutherford Backscattering Spectrometer (RBS), (2) an Elastic Recoil Detector (ERD), and (3) a Raman spectroscopy system. RBS and ERD analyses are carried out using a differentially pumped 1.7 MV ion beam line Tandetron accelerator generating a beam at grazing incidence. The ERD system is equipped with an absorber and is specifically used to detect H initially bonded to the surface; higher resolution of surface H is also available through nuclear reaction analysis. In parallel, an optical port facing the substrate is used to perform Raman spectroscopy analysis of the samples during plasma processing. This system enables fast monitoring of a few Raman peaks over nine points scattered on a 1.6 × 1.6 mm2 surface without interference from the inherent light emitted by the plasma. Coupled to the various plasma and beam sources, the unique set of in-plasma surface characterization tools detailed in this study can provide unique time-resolved information on the modification induced by plasma. By using the ion beam analysis capability, the atomic concentrations of various elements in the near-surface (e.g., stoichiometry and impurity content) can be monitored in real-time during plasma deposition or etching. On the other hand, the evolution of Raman peaks as a function of plasma processing time can contribute to a better understanding of the role of low-energy ions in defect generation in irradiation-sensitive materials, such as monolayer graphene.

Engineering of niobium surfaces through accelerated neutral atom beam technology for quantum applications

A major roadblock to scalable quantum computing is phase decoherence and energy relaxation caused by qubits interacting with defect-related two-level systems (TLSs). Native oxides present on the surfaces of superconducting metals used in quantum devices are acknowledged to be a source of TLS that decrease qubit coherence times. Reducing microwave loss by “surface engineering” (i.e., replacing the uncontrolled native oxide of superconducting metals with a thin, stable surface with predictable characteristics) can be a key enabler for pushing performance forward with devices of higher intrinsic quality factor. In this work, we present a novel approach to replace the native oxide of niobium (typically formed in an uncontrolled fashion when its pristine surface is exposed to air) with an engineered oxide, using a room-temperature process that leverages accelerated neutral atom beam (ANAB) technology at 300 mm wafer scale. This ANAB is composed of a mixture of argon and oxygen, with tunable energy per atom, which is rastered across the wafer surface. The ANAB-engineered Nb-oxide thickness was found to vary from 2 to 6 nm depending on ANAB process parameters. The modeling of variable-energy x-ray photoelectron spectroscopy data confirms the thickness and compositional control of Nb surface oxide by the ANAB process. These results correlate well with those from transmission electron microscopy and x-ray reflectometry. Since ANAB is broadly applicable to material surfaces, the present study indicates its promise for modification of the surfaces of superconducting quantum circuits to achieve longer coherence times.

Calibrating beam fluxes of a low-energy neutral atom beam facility.

Scientific detection and imaging instruments for low-energetic neutral atoms (ENA) onboard spacecraft require thorough pre-flight laboratory calibration against a well-characterized neutral atom beam source. To achieve this requirement, a dedicated test facility is available at the University of Bern, which is equipped with a powerful plasma ion source and an ion beam neutralization stage. Using surface neutralization, low-energy neutral atom beams of any desired gas species can be produced in the energy range from 3keV down as low as 10eV. As the efficiency of the neutralization stage is species and energy dependent, the neutralizer itself needs to be calibrated against an independent reference. We report on the calibration and characterization of this neutral atom beam source using our recently developed Absolute Beam Monitor (ABM) as a primary calibration standard. The ABM measures the absolute ENA flux independent of neutral species in the energy range from 10eV to 3keV. We obtain calibration factors of a few 100cm-2s-1 pA-1, depending on species at beam energies above about 100eV, and a power-law decrease for energies below 100eV. Furthermore, the energy loss of neutralized ions in the surface neutralizer is estimated from time-of-flight measurements using the ABM. The relative energy loss increases with ENA energy from low levels near zero up to 20%-35% at 3keV, depending on atomic species. Having calibrated our neutral beam source allows for accurate calibration of ENA space instruments.

Wall stabilization of high-beta anisotropic plasmas in an axisymmetric mirror trap

The stabilization of the ‘rigid’ flute and ballooning modes both with and without the effect of additional MHD anchors in an axisymmetric mirror trap, with the help of a perfectly conducting lateral wall, is studied using a model pressure distribution of a plasma with a steep-angle neutral beam injection at the magnetic field minimum. The calculations were performed for an anisotropic plasma in a model that simulates the pressure distribution during the injection of beams of fast neutral atoms into the magnetic field minimum. It is assumed that the lateral wall is an axisymmetric shell surrounding the plasma that follows the shape of the magnetic field line and is placed at a certain distance to the plasma border. It has been found that for the effective stabilization of the modes by the lateral wall only the parameter beta (β, ratio of plasma pressure to the magnetic field pressure) must exceed some critical value β crit. When combined with the conducting end plates imitating the MHD end stabilizers, there are two critical beta values and two stability zones and that can merge, making the entire range of allowable beta values stable. The dependence of the critical betas on the degree of plasma anisotropy, the mirror ratio, and the width of the vacuum gap between the plasma and the lateral wall is studied. In contrast to the previous studies focusing on a plasma model with a sharp boundary, we calculated the stability zones for a number of diffuse radial pressure profiles and several axial magnetic field profiles.

Relative In-flight Response of IBEX-Lo to Interstellar Neutral Helium Atoms

The IBEX-Lo instrument on the Interstellar Boundary Explorer (IBEX) mission measures interstellar neutral (ISN) helium atoms. The detection of helium atoms is made through negative hydrogen (H−) ions sputtered by helium atoms from the IBEX-Lo’s conversion surface. The energy spectrum of ions sputtered by ISN helium atoms is broad and overlaps the four lowest IBEX-Lo electrostatic analyzer (ESA) steps. Consequently, the energy response function for helium atoms does not correspond to the nominal energy step transmission. Moreover, laboratory calibration is incomplete because it is difficult to produce narrow-energy neutral atom beams that are expected for ISN helium atoms. Here, we analyze the ISN helium observations in ESA steps 1–4 to derive the relative in-flight response of IBEX-Lo to helium atoms. We compare the ratios of the observed count rates as a function of the mean ISN helium atom energy estimated using the Warsaw Test Particle Model (WTPM). The WTPM uses a global heliosphere model to calculate charge exchange gains and losses to estimate the secondary ISN helium population. We find that the modeled mean energies of ISN helium atoms, unlike their modeled fluxes, are not very sensitive to the very local interstellar medium parameters. The obtained relative responses supplement the laboratory calibration and enable more detailed quantitative studies of the ISN helium signal. A similar procedure that we applied to the IBEX-Lo observations may be used to complement laboratory calibration of the next-generation IMAP-Lo instrument on the Interstellar Mapping and Acceleration Probe (IMAP) mission.

Surface Modifications of High-Performance Polymer Polyetheretherketone (PEEK) to Improve Its Biological Performance in Dentistry.

This comprehensive review focuses on polyetheretherketone (PEEK), a synthetic thermoplastic polymer, for applications in dentistry. As a high-performance polymer, PEEK is intrinsically robust yet biocompatible, making it an ideal substitute for titanium-the current gold standard in dentistry. PEEK, however, is also inert due to its low surface energy and brings challenges when employed in dentistry. Inert PEEK often falls short of achieving a few critical requirements of clinical dental materials, such as adhesiveness, osseoconductivity, antibacterial properties, and resistance to tribocorrosion. This study aims to review these properties and explore the various surface modification strategies that enhance the performance of PEEK. Literatures searches were conducted on Google Scholar, Research Gate, and PubMed databases using PEEK, polyetheretherketone, osseointegration of PEEK, PEEK in dentistry, tribology of PEEK, surface modifications, dental applications, bonding strength, surface topography, adhesive in dentistry, and dental implant as keywords. Literature on the topics of surface modification to increase adhesiveness, tribology, and osseointegration of PEEK were included in the review. The unavailability of full texts was considered when excluding literature. Surface modifications via chemical strategies (such as sulfonation, plasma treatment, UV treatment, surface coating, surface polymerization, etc.) and/or physical approaches (such as sandblasting, laser treatment, accelerated neutral atom beam, layer-by-layer assembly, particle leaching, etc.) discussed in the literature are summarized and compared. Further, approaches such as the incorporation of bioactive materials, e.g., osteogenic agents, antibacterial agents, etc., to enhance the abovementioned desired properties are explored. This review presents surface modification as a critical and essential approach to enhance the biological performance of PEEK in dentistry by retaining its mechanical robustness.

Combined Treatment of Parts Produced by Additive Manufacturing Methods for Improving the Surface Quality

To improve the quality of a part manufactured by the additive method, it is necessary to eliminate the porosity and high roughness of its surface, as well as to deposit a coating on it. For this purpose, in the present work, we studied the combined processing in a gas discharge plasma of complex shape parts obtained by the additive manufacturing method, which includes explosive ablation of surface protrusions when voltage pulses are applied to the part immersed in the plasma; polishing with a concentrated beam of fast neutral argon atoms at a large angle of incidence on the surface of the part, and magnetron deposition of a coating on it with assistance by fast argon atoms. Combined processing made it possible to completely get rid of porosity and reduce the surface roughness from Ra ~ 5 µm to Ra ~ 0.05 µm.

Compression of a Beam of Fast Argon Atoms for Surface Polishing

The results of studying a beam source of fast argon atoms obtained by neutralizing charges of accelerated ions during their flight through an accelerating grid in the form of a set of plane–parallel plates are presented. Ions are accelerated from the plasma emitter by a voltage of negative polarity at the grid, fly into the gaps between its plates, and, when approaching their surfaces, cause the emission of electrons that neutralize the ion charge. The equivalent beam current of fast atoms emitted from the grid is up to 90% of the current in its circuit, and their energy is equal to the ion energy that corresponds to the accelerating voltage between the plasma emitter and the grid. To increase the beam current density of fast atoms on the treated surface, the sections of the grid plates facing the plasma emitter are made in the form of a segment of a circle. The movement of ions and fast atoms that are formed inside the grid to the center of this circle makes it possible to reduce the beam width by an order of magnitude and increase the flow density of fast atoms without reducing the angle of their incidence on the treated surface. The beam compression significantly improves the efficiency of polishing a surface with a beam of fast neutral argon atoms with an angle of incidence on the surface of 80°.

Absolute beam monitor: A novel laboratory device for neutral beam calibration.

Instruments recording Energetic Neutral Atoms (ENAs) for space applications require thorough laboratory calibration in a dedicated test facility providing a neutral atom beam. Accurate knowledge of the neutral beam intensity and energy is central for the laboratory calibration procedure. However, until recently, the quantification of the neutral atom beam intensity in the low-energy range below a few 100eV was based on relative measurements with standard detectors of approximately known detection efficiencies for neutral atoms. We report on the design and development of a novel calibration device dedicated to determining the ENA beam flux in an absolute manner in the energy range from 3keV down to about 10eV. This is realized by applying ENA scattering at a surface and coincident detection of scattered particles and created secondary electrons. Moreover, the neutral beam energy is determined by a time-of-flight measurement. The applied measurement principle relies on very low background signals. The observed background count rates are in the range 10-2 s for the individual channels and about 10-5 s for coincidence events. The background is, thus, at least two, typically four, orders of magnitude lower than the signal rate for neutral atom beams in the foreseen energy range. We demonstrate a concrete application using the absolute flux calibration of a laboratory neutralization stage.

An ion-atom merged beams setup at the Cryogenic Storage Ring.

We describe a merged beams experiment to study ion-neutral collisions at the Cryogenic Storage Ring of the MaxPlanck Institute for Nuclear Physics in Heidelberg, Germany. We produce fast beams of neutral atoms in their ground term at kinetic energies between 10 and 300keV by laser photodetachment of negative ions. The neutral atoms are injected along one of the straight sections of the storage ring, where they can react with stored molecular ions. Several dedicated detectors have been installed to detect charged reaction products of various product-to-reactant mass ranges. The relative collision energy can be tuned by changing the kinetic energy of the neutral beam in an independent drift tube. We give a detailed description of the setup and its capabilities, and present proof-of-principle measurements on the reaction of neutral C atoms with D2 + ions.

Multi-Chord Beam Diagnostics of Plasma at the GOL-NB Device

—A multi-chord beam diagnostic system for an open multiple-mirror trap GOL-NB is described. The system is based on a 10 keV ribbon beam of fast neutral hydrogen atoms generated by a wide-aperture ion injector with an arc plasma source. The plasma linear density profile is calculated from the attenuation of the beam after passing through the plasma. This paper discusses the design of the diagnostics and its capabilities, and also presents the measured profiles of the linear plasma density in the experiment on filling the trap with the starting plasma. The modernized version of diagnostics and the expected increase in its resolution are described. The prospects of using the Charge eXchange Recombination Spectroscopy (CXRS) method on the existing element base are evaluated.

Accelerated Neutral Atom Beam (ANAB) Modified Polypropylene for Reducing Bacteria Colonization Without Antibiotics.

For this first time, this study utilized Accelerated Neutral Atom Beam (ANAB) technology to modify polypropylene to inhibit bacteria colonization in vitro after 24 hours without the use of drugs or antibiotics. Specifically, ANAB was designed and used to increase the surface energy of polypropylene to be closer to that of two critical proteins (mucin and casein) contained in bodily fluids that if adsorbed to a material surface can decreased bacteria colonization. Materials were characterized using atomic force microscopy demonstrating an expected greater surface roughness and surface area for the ANAB-treated samples compared to controls. A wide range of gram-positive, gram-negative, and antibiotic resistant bacteria were tested here (including Staph. epidermidis, Staph. aureus, MRSA, multi-drug resistant E. coli, and Pseudomonas aeruginosa) and demonstrated on average an over a 3-log reduction in bacteria after 24 hours. Further, this study confirmed a greater adsorption of mucin and casein on ANAB-treated polypropylene as the mechanism to decrease bacteria colonization. Lastly, this study utilized an aggressive cleaning procedure and showed strong durability of the ABAN-treated surfaces. This study is important as it demonstrates a way to potentially decrease polypropylene based implant infections using ANAB modification without using antibiotics.

Accelerated Neutral Atom Beam (ANAB) Modified Poly-Ether-Ether-Ketone for Increasing In Vitro Bone Cell Functions and Reducing Bacteria Colonization Without Drugs or Antibiotics.

Poly-ether-ether-ketone (PEEK) has become the spinal implant material of choice due to its radiolucency, low elastic modulus, manufacturability, and mechanical durability. However, studies have highlighted less that optimal cytocompatibility properties of conventional PEEK leading to decreased bone growth and/or extensive bacteria infection. In order to improve the surface properties of PEEK for orthopedic applications, here, Accelerated Neutral Atom Beam (ANAB) technology was used to modify PEEK and such samples were tested In Vitro for osteoblast (bone-forming cell) functions and bacterial colonization. Results showed significantly improved osteoblast responses (such as deposition of calcium containing mineral as well as alkaline phosphatase, osteocalcin, osteopontin, and osteonectin synthesis) on ANAB modified PEEK compared to controls due to optimized surface energy from nanostructured features and greater exposure of PEEK chemistry. ANAB treatment enhanced protein absorption (specifically, mucin, casein, and lubricin) to the PEEK surface and consequently significantly reduced bacterial (including methicillin resistant Staph. aureus (or MRSA), E. coli, and Staph. epidermidis) colonization. Collectively, this study introduces ANAB treated PEEK as a novel material that should be further studied for a wide range of improved orthopedic applications.

Accelerated neutral atom beam (ANAB) modified polyethylene for decreased wear and reduced bacteria colonization: An in vitro study

Ultra-high molecular weight polyethylene (UHMWPE) model implants were modified using accelerated neutral atom beam (ANAB) technology and tested for in vitro wear properties and bacteria colonization. Material characterization studies using atomic force microscopy (AFM), surface energy, and in vitro protein adsorption events were also conducted to better understand the mechanism behind such wear properties and bacteria colonization. ANAB modified UHMWPE showed significantly reduced wear properties compared to controls due to nanostructured features, greater surface energy, and improved adsorption of lubricin, a synovial fluid lubricating protein. There was significantly greater adsorption of proteins known to reduce bacteria colonization (specifically, mucin, casein, and lubricin) after 4 h on UHMWPE after ANAB treatment. Such changes in initial protein events led to significantly decreased bacteria (including methicillin resistant Staph. aureus (or MRSA), Staph. aureus, E. coli, multi-drug resistant E. coli, Pseudomonas aeruginosa and Staph. epidermidis) colonization after 24 h without resorting to antibiotic use.

ДОСЛІДЖЕННЯ СПЕКТРУ АТОМІВ Zn I В ТРИПЛЕТНИХ РІДБЕРГІВСЬКИХ СТАНАХ

Purpose: This work aims at investigating the zinc atoms in the triplet preionization – Rydberg states. The energy levels of atoms having two electrons outside the closed shell were studied mainly by the optical spectroscopy methods. However, just using the microwave spectroscopy to measure the frequency of transitions between the two Rydberg states allows to increase the accuracy of measurements in two or more orders of magnitude. Disign/methodology/approach:A line of three dye lasers is used to excite the zinc atoms into the triplet Rydberg states with a predetermined set of quantum numbers. The radiation of the first two of them is transformed into the second harmonic in nonlinear crystals. Dye lasers are excited by the radiation of the second harmonic of one YAG: ND3+ laser. All three radiations are reduced to the zone of interaction with the laser and the microwave radiation, which is located between the plates of the ionization cell, where the pulsed electric field is created. The excited Rydberg atoms are recorded with the field ionization procedure. The beam of neutral atoms is created by an effusion cell under the vacuum conditions, the residual pressure does not exceed 10-5 mm Hg. A pulsed electric field of some certain intensity results inionization of atoms excited by microwave radiation and in acceleration of electrons, which have appeared in the direction of the secondary electron multiplier, though being insufficient for ionization of atoms excited only by the laser radiation and which are initial for interaction with microwaves. By scanning the microwave radiation frequency with the given step and measuring the signal intensity of the secondary electron multiplier, the excitation spectrum of the atoms under study can be obtained. Findings: Using the created laser-microwave spectrometer, the frequencies of the F→D, F→F and F→G transitions between the triplet Rydberg states of zinc atoms were measured. From the analysis made of the transition frequencies, the quantum defect decomposition constants were obtained by the Ritz formula for the D, F, and G states of zinc atoms. Conclusions: The frequencies of the F→D, F→F and F→G transitions between the triplet Rydberg states of zinc atoms were measured that allowed obtaining the quantum defect decomposition constants according to the Ritz formula for the D, F and G states of zinc atoms, that in turn had allowed to calculate the energy of these terms and the transition frequencies at least in two orders of magnitude more accurately as against the similar measurements made by the optical spectroscopy. Key words: zinc atom, triplet states of atoms, Rydberg states, laser excitation, microwave radiation

Spatial characteristics of luminous hydrocarbon pellet clouds in the large helical device

This study analyzes the dependences of the size of the luminous region of hydrocarbon pellet cloud on the ablation rate, as well as on the ambient plasma electron density and temperature. The data were obtained in a series of experiments where spherical solid polystyrene pellets with a diameter of ≈900 μm at a speed of ≈450 m s−1 were injected into hydrogen plasma of the large helical device. The ambient plasma with an electron temperature of 0.5–1.5 keV and a density of (1–7) × 1019 m−3 was maintained by injection of neutral atom beams with total the heating power of 3–14 MW. A scaling law was derived for determining the transverse size of the cloud’s luminous region from the known values of the pellet’s current radius as well as the values of the density and temperature of the ambient plasma at the place of image acquisition. The interdependencies between various dimensions of the luminous region obtained in the line spectrum are established. The presence of such dependences makes it possible to describe the dimensions of the luminous region comprehensively by means of the scaling law for its transverse size.

Surface Quality of Metal Parts Produced by Laser Powder Bed Fusion: Ion Polishing in Gas-Discharge Plasma Proposal

Additive manufacturing has evolved over the past decades into a technology that provides freedom of design through the ability to produce complex-shaped solid structures, reducing the operational time and material volumes in manufacturing significantly. However, the surface of parts manufactured by the additive method remains now extremely rough. The current trend of expanding the industrial application of additive manufacturing is researching surface roughness and finishing. Moreover, the limited choice of materials suitable for additive manufacturing does not satisfy the diverse design requirements, necessitating additional coatings deposition. Requirements for surface treatment and coating deposition technology depend on the intended use of the parts, their material, and technology. In most cases, they cannot be determined based on existing knowledge and experience. It determines the scientific relevance of the analytical research and development of scientific and technological principles of finishing parts obtained by laser additive manufacturing and functional coating deposition. There is a scientific novelty of analytical research that proposes gas-discharge plasma processing for finishing laser additive manufactured parts and technological principles development including three processing stages—explosive ablation, polishing with a concentrated beam of fast neutral argon atoms, and coating deposition—for the first time.