Fast Atom Research Articles

Receiver Calorimeter of Fast Atom Beam Injector in Megawatt Range

Receiver Calorimeter of Fast Atom Beam Injector in Megawatt Range

Electrical properties of Si/diamond heterojunction diodes fabricated by using surface activated bonding

We evaluated the current–voltage ( I-V ) and temperature-dependent I-V characteristics of n + -Si/p-diamond heterojunction diodes (HDs) fabricated by using surface activated bonding and Ru/p-diamond Schottky barrier diodes (SBDs). Both types of diodes were fabricated on diamond surface that was activated using a fast atom beam of Ar. Their room-temperature reverse-bias characteristics were explained using the trap-assisted tunneling model, wherein the surface activation process affects the carrier transport across the Si/diamond and Ru/diamond interfaces. In addition, we compared the electrical properties of n + -Si/p-diamond HDs and Ru/p-diamond SBDs with those of previously fabricated p + -Si/p-diamond HDs and Al/p-diamond SBDs. A correlation between the barrier heights and the work function of the contact materials (n + -Si, p + -Si, and Ru) was observed. • We fabricated n + -Si/p-diamond heterojunction diodes (HDs) and Ru/p-diamond Schottky barrier diodes (SBDs) on a diamond surface activated using a fast atom beam (FAB) of Ar. • The reverse-bias characteristics of HDs and SBDs were explained by the trap-assisted tunneling model. • The S factors of HDs and SBDs after annealing at 703 K and 873 K were close to 0.7 and 0.6, respectively, which suggested that the partially “pinning-free” interfaces were formed thank to FAB irradiation.

Spectrometer with Diamond Detectors for Diagnosing Fast Atoms at Tokamak with Reactor Technologies (TRT)

Spectrometer with Diamond Detectors for Diagnosing Fast Atoms at Tokamak with Reactor Technologies (TRT)

Revealing pre-breakdown processes of a single-gap pseudospark switch triggered from the anode side

Pseudospark switch is a special kind of low-pressure (typically 1–100 Pa) high-voltage pulsed discharge switch with the hollow electrode configuration. This paper experimentally investigates the pre-breakdown processes of a single-gap pseudospark switch triggered from the anode side. The species and contents of impurities on copper electrode surface are firstly analyzed, which mainly include C, N and O. Then, at the same conditions, the trigger delay and jitter of triggering from the anode side are significantly higher than the cathode side, as well as the minimum voltage and pressure that the switch can be triggered. The evolution of the discharge region of the pseudospark switch triggered from the anode side is observed by the ICCD camera for the first time in the literature. The time-resolved images show that the luminescence firstly appears in the hollow anode where the trigger discharge happens and then in the hollow cathode, the cathode hole, the main gap and the anode hole successively, which is completely different from triggering from the cathode side. Finally, a model considering the migration and collisions of ions and fast atoms is established, and it points out that the ion flux from the hollow anode plays an important role in triggering from the anode side. The key processes also include the formations of the positive space charge column inside the hollow cathode and the intense secondary electron emission as an electron source for the main gap.

Molecular dynamics study of the growth of ZnOx films

Crystalline zinc oxide thin films are important due to a combination of optical transparency, electrical conductivity, and piezoelectric and pyroelectric properties. These functional properties are improved with increasing perfection of the crystalline structure. In this paper, classical molecular dynamics with a reactive force field was used to simulate the atom-by-atom growth of ZnOx films on a crystalline template. Contrary to previous modeling studies, the effect of a wide range of process parameters (elemental ratio x, kinetic energy of arriving atoms, and fraction of fast atoms in the particle flux) on the film crystallinity was investigated. All the parameters were found to have a significant impact. Counterintuitively, the highest crystal quality was obtained for slightly overstoichiometric films with x > 1. The results provide a quantitative insight into the role of individual deposition parameters, and the identification of their optimum values facilitates a further improvement of the film properties.

Particle-in-cell simulations of the direct-current argon breakdown process in the 10–300 kV range

Direct-current ionization breakdown in argon at very high voltage on the low-pressure branch of the Paschen curve is studied by means of kinetic simulation. The employed particle-in-cell/Monte Carlo collision model tracks the motion of electrons, ions and fast neutral atoms, as well as their collisions with the background gas. Secondary electron emission due to the bombardment by ions and fast atoms, as well as backscattering of different species on the electrode surfaces are also consistently accounted for. To validate the model, we compare the Paschen curve predicted by kinetic simulations against published experimental results as well against the prediction of a reduced (fluid) model. The model is then applied to predict, for the first time, the low-pressure branch of the Paschen curve for argon gas in the 10–300 kiloVolt range of applied voltage. One of the findings is the existence of a turning point on the Paschen curve at and , where is the breakdown voltage and the reduced pressure is the product of the gas pressure with the inter-electrode distance. According to our analysis, the presence of the turning point is due to the phenomena of electron and ion runaway in high electric field. We further investigate the role of the heavy species (i.e. ions and fast neutral atoms) in sustaining the Townsend discharge at high voltage and thus setting the breakdown threshold. Specifically, the role of fast atoms is significant over the entire low-pressure branch of the Paschen curve due to their contribution to both ionization and secondary electron emission. Also, the ions, as the precursor for the fast atoms, show an important influence on the latter process. The newly predicted low-pressure branch of the Paschen curve for argon at high voltage should provide an essential reference for the design of high-voltage devices, e.g. circuit breakers in electrical power transmission.

Helium electron beam rf plasma for low-k surface functionalization

A complex simulation approach is applied to determine optimal conditions for the functionalization of low-k materials in e-beam rf discharge generated by 1 keV electron beam in He. The possibility and mechanisms of methyl group elimination from low-k surfaces with low-energy He ions and fast He atoms are studied with ab initio dynamic density functional theory-based simulations. The effect of gas pressure, rf voltage, and rf frequencies on the ion energy and angle distribution functions is analyzed using a 1D Particle-in-Cell Monte Carlo model. The relative contribution of fast atoms in the surface functionalization is estimated. Ion fluxes on the 2D trench walls and bottom are calculated with the developed analytical approach.

A quantum-mechanical investigation of O(3P) + CO scattering cross sections at superthermal collision energies

ABSTRACT The kinetics and energetic relaxation associated with collisions between fast and thermal atoms are of fundamental interest for escape and therefore also for the evolution of the Mars atmosphere. The total and differential cross sections of fast O(3P) atom collisions with CO have been calculated from quantum mechanical calculations. The cross sections are computed at collision energies from 0.4 to 5 eV in the centre-of-mass frame relevant to the planetary science and astrophysics. All the three potential energy surfaces (3A′, 3A″, and 2 3A″ symmetry) of O(3P) + CO collisions separating to the atomic ground state have been included in calculations of cross sections. The cross sections are computed for all three isotopes of energetic O(3P) atoms collisions with CO. The isotope dependence of the cross sections are compared. Our newly calculated data on the energy relaxation of O atoms and their isotopes with CO molecules will be very useful to improve the modelling of escape and energy transfer processes in the Mars’ upper atmosphere.

Coupling plasma physics and chemistry in the PIC model of electric propulsion: Application to an air-breathing, low-power Hall thruster

This work represents a first attempt to include the complex variety of electron-molecule processes in a full kinetic particle-in-cell/test particle Monte Carlo model for the plasma and neutral gas phase in a Hall thruster. Particular emphasis has been placed on Earth’s atmosphere species for the air-breathing concept. The coupling between the plasma and the gas phase is self-consistently captured by assuming the cold gas approximation and considering gas-wall and gas recycling from the walls due to ion neutralization. The results showed that, with air molecular propellants, all the most relevant thruster performance figures degraded relative to the nominal case using Xe propellant. The main reasons can be ascribed to a reduced ionization cross-section, a larger gas ionization mean free path due to lighter mass air species, and additional electron collisional power losses. While vibrational excitations power losses are negligible, dissociation and electronic excitations compete with the ionization channel. In addition, for molecular oxygen, the large dissociation leads to even faster atoms, further reducing their transit time inside the discharge channel. Future studies are needed to investigate the role of non-equilibrium vibrational kinetics and metastable states for stepwise ionization.

Decay time extension of terahertz electromagnetic waves emitted from coherent longitudinal optical phonons in GaAs epitaxial layers with the use of fast atom bombardment

We succeeded in extending the decay time of terahertz electromagnetic waves from coherent longitudinal optical (LO) phonons in GaAs epitaxial layers with the use of fast atom bombardment, a treatment method for introducing defects and/or disorders at the surface. The decay time becomes long, up to 4.81 ± 0.15 ps, with the bombardment time of 4.0 min. This value is 2.4-times larger than the decay time of 2.04 ± 0.04 ps of the reference sample (untreated sample). We attribute the origin of the present phenomenon to the fact that the reduction of the photogenerated carrier scattering effect on the coherent LO phonon, which is caused by the presence of the surface defects and disorders formed by the fast atom bombardment, results in the extending of the decay time of the terahertz wave from the coherent LO phonon.

A setup for grazing incidence fast atom diffraction.

We describe a UHV setup for grazing incidence fast atom diffraction (GIFAD) experiments. The overall geometry is simply a source of keV atoms facing an imaging detector. Therefore, it is very similar to the geometry of reflection high energy electron diffraction experiments used to monitor growth at surfaces. Several custom instrumental developments are described making GIFAD operation efficient and straightforward. The difficulties associated with accurately measuring the small scattering angle and the related calibration are carefully analyzed.

A Brief Review on Liquid Chromatography-Mass Spectrometry/LCMS and its Application

Liquid Chromatography- Mass Spectrometry is a powerful analytical technique having high Sensitivity and Specificity. LC-MS combines the separation capabilities of Liquid Chromatography with the mass analysis capabilities of Mass Spectrometry. Liquid Chromatography separates the mixture, which is having multiple components, and then Mass Spectrometry provides the Spectral information which is used to identify each separated component. Interfaces are used in LC-MS system to transfer the maximum amount of analyte, remove a significant portion of the mobile phase, and preserves the chemical identity. Different types of Interfaces are used which include Atmospheric-Pressure Ionization, Electrospray Ionization, Atmospheric Pressure Chemical Ionization, Thermospray and Plasma Spray Ionization, Particle Beam Ionization, Continuous Flow Fast Atom Bombardment. LC-MS having a wide range of application in various field which include Pharmaceutical, Drug Development, Forensic Science, Cosmetic, Petrochemistry, Environment, Food Analysis, Biochemical Application. In this article Principle, Instrument and Application are discussed briefly.

Study of fast atoms in molecular gas plasma via emission spectroscopy

Fast atoms are generated in reactions of ions with the molecular gas in laboratory and astrophysical plasma. In hydrogen they are observed in the emission spectra via Excessive line broadening. Energetic atoms also occur in astrophysical plasma in hydrogen, nitrogen and oxygen. The proposal here is that low pressure discharges can be used to simulate the phenomena in certain space plasma. In this study, we have used a special configuration of the electrode system, to obtain energetic atoms in plasma of three types of diatomic gases (H2, O2, N2). Emission spectroscopy was used to detect the atoms and measure their velocity. Energy analysis was performed to obtain atoms’ distributions and evaluate the mean energy of atoms. This was compared to the potential energy available from the electric field. The field acceleration model, previously established for hydrogen, was extended to nitrogen and oxygen. We suggest, that the same method of analysis can be applied for astrophysical plasma spectrum.

The investigation of dynamic heterogeneity in lead silicate liquid via molecular dynamic simulation

The structure and dynamics of liquid lead silicate with a wide range of PbO ratio are done by molecular dynamics methods. The simulated result shows that the pair radial distribution functions (PRDFs) are in good agreement with the results of previous studies. Our calculated data indicates that the system exists regions of fast and slow atoms determined via the mean square displacement (MSD) in the same interval. The exhibition of dynamical heterogeneity (DH) is also found in this paper.

Alkaline-earth metal(II) complexes of salinomycin – spectral properties and antibacterial activity

Abstract In the present paper the synthesis and structural characterization of alkaline-earth metal(II) complexes of the polyether ionophorous antibiotic salinomycinic acid (SalH.H2O) are discussed. The complexes [M(Sal)2(H2O)2] (M = Mg2+, 1; Ca2+, 2; Sr2+, 3; Ba2+, 4) were obtained reacting salinomycinic acid and Et4NOH with the corresponding metal(II) salts at metal-to-ligand-to-base molar ratio of 1:1:1. The spectral properties of 1–4 were characterized using infrared spectroscopy, fast atom bombardment-mass spectrometry, nuclear magnetic resonance and elemental analysis data. The crystallinity degree and morphology of complex 2 were studied by X-ray powder diffraction and transmission electron microscopy. The biometal(II) salinomycinate complexes 1 and 2 possess an enhanced antimicrobial activity compared to the parent antibiotic against Gram-positive bacteria. The comparison between the effectiveness of the complexes, reported here, and the already known isostructural coordination species of salinomycin and monensin (MonH.H2O), revealed that magnesium(II) and calcium(II) monensinates appear to be promising antibacterial agents against Bacillus subtilis, Bacillus cereus and Micrococcus luteus.

RADIATION-INDUCED SURFACE MIGRATION OF TUNGSTEN: CHANNELING ALONG ATOMIC STEPS

The interaction of accelerated helium atoms with the atomic-smooth surface of tun+gsten single crystals was investigated using the low-temperature field-ion microscope, equipped with the source of helium atoms with an energy of 5 keV together with the techniques of molecular dynamics. It was observed the effect of the surface channeling of fast atoms of a target along the surface steps which occurs as a result of the collision cascade induced by the incident projectile. A substantial part of these displaced atoms in the target gains momentum oriented along the < 111 > close-packed crystallographic directions. The fine morphology of the trajectory of an excited tungsten atom reveals the transverse oscillations of the W atom normally to the < 111 > surface atomic step. The rate of the kinetic energy loss during the surface channeling of fast tungsten atoms does not exceed 0.4 eV/Å. This provides relatively large displaced surface atom ranges along the close-packed atomic steps. The found out results can be regarded as a special case of the correlation mechanism of the radiation-induced surface mass transfer.

Reduced Thermal Resistance of Membrane Fabry-Perot Laser Bonded on Si Through Room-Temperature, Surface-Activated Bonding Assisted by a-Si Nano-Film

A membrane distributed-reflector (DR) laser bonded on a Si substrate is a promising light source for on-chip optical interconnection, as it features a low threshold current and enough output power. Benzocyclobutene (BCB) adhesive wafer-bonding or hydrophilic bonding technologies have been used to integrate the membrane laser with Si. However, the thermal conductivity of BCB is low, which results in a high thermal resistance of the membrane laser, and the process of both bonding technologies requires annealing. Thus, the bonded wafer accumulated thermal stress. In this study, we introduce a chemical mechanical polishing (CMP) process to flatten the wafer surface and investigate the surface activated bonding (SAB) based on an Ar fast atom beam (FAB) assisted by an a-Si layer to achieve a room temperature bonding. Based on this room temperature bonding technology, a membrane Fabry-Perot (FP) laser is demonstrated for the first time, and its thermal characteristics are measured. A higher optical saturation current (55 mA) was obtained compared to that of the conventional membrane FP laser (40 mA) with a 2-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula>-thick BCB bonding layer. From the lasing wavelength variation against the heat dissipation power and temperature, it was found that a reduction in thermal resistance of approximately 50&#x0025; (240 K/W to 120 K/W) was achieved by eliminating the BCB layer; the simulation results also showed the same trend.

Plasma-Beam Processing of Tools Made of SiAlON Dielectric Ceramics to Increase Wear Resistance When Cutting Nickel–Chromium Alloys

This research aimed at an increase in wear resistance of round cutting plates manufactured with SiAlON dielectric ceramics through deposition of wear-resistant coatings. To increase effectiveness of the coatings, their adhesion was improved by the removal of defective surface layers from the cutting plates before the deposition. As the depth of caverns and grooves appearing on the cutting plates due to manufacturing by diamond grinding reached 5 µm, a concentrated beam of fast argon atoms was used for the removal of defective layers with a thickness exceeding the depth of caverns and grooves. At the equal angles of incidence to the front and back surfaces of the cutting wedge amounting to 45 degrees, two-hour-long etching of rotating cutting plates provided removal of defective layers with thickness of ~10 µm from the surfaces. After the removal, the cutting edge radius of the plates diminished from 20 to 10 µm, which indicates the cutting plates’ sharpening. Wear-resistant TiAlN coatings deposited after the etching significantly improve the processing stability and increase wear resistance of the cutting plates by not less than 1.7 times.

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.

Stereocalpin B, a New Cyclic Depsipeptide from the Antarctic Lichen Ramalina terebrata.

Stereocalpin B, a new cyclic depsipeptide (1), and a new dibenzofuran derivative (3), were isolated from the Antarctic lichen, Ramalina terebrata (Ramalinaceae), along with a known cyclic depsipeptide (2). The structures of new compounds were characterized by comprehensive spectrometric analyses; high-resolution fast atom bombardment mass spectrometry (HR-FABMS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Stereocalpin B (1) existed in a rotameric equilibrium, which was confirmed using nuclear Overhauser effect spectroscopy (NOESY)/exchange spectroscopy (EXSY) spectrum. Absolute configurations of the amino acid units in 1 were assigned using the advanced Marfey’s method and subsequent NOESY analysis of the 5-hydroxy-2,4-dimethyl-3-oxo-decanoic acid residue confirmed the complete stereochemistry of 1. Compounds 1-3 exhibited moderate antimicrobial activities against E. coli, with the IC50 values ranging from 18–30 μg/mL. Compound 2 exhibited cell growth inhibition against HCT116 cell lines, with the IC50 value of 20 ± 1.20 μM, and compounds 1 and 2 also showed potent anti-inflammatory activities against lipopolysaccharide (LPS)-induced RAW264.7 macrophages with the IC50 values ranging from 5–7 μM.