Ion Beam Density Research Articles

The Intense Pulsed Ion Beam Treatment and the Titanium Nitride Coating of Hard Alloy for Cutting Tool

The aim of this work was to investigate adhesion increasing of titanium nitride coating deposited at hard alloy tool’s surface pretreated by intense pulsed ion beam of different energy density. Two alloys were treated by high-power pulsed ion beam of 1÷3.75 J/cm2 energy density. Analyzing the data obtained from tunnel microscopy, X-ray spectrum and measurements of surface relief geometry characteristics, such as roughness and profile length, we came to the following conclusion. First, the value of energy density of ion beam plays the key role in the formation of the relief and phase structure of the surface. Second, these two characteristics are almost independent of the initial characteristics of the irradiated alloys.Also, the article touches the results of scratch-test of the titanium nitride coating. The results demonstrate changes in wearing and destruction mode of the coating deposited at the tool treated by ion beam.

Generation of nonlinear Alfvén and magnetosonic waves by beam–plasma interaction

One-dimensional (1-D) and two-dimensional (2-D) hybrid simulations are carried out to study the interaction between a background plasma and an ion beam, whose velocity is parallel to the ambient magnetic field B0. It is found that the beam–plasma interaction and the associated wave evolution can be divided into four phases. The simulation results in phase 1 in the early stage of wave evolution are consistent with the linear theory. Right-hand nonresonant instabilities are present and dominant in cases with a relatively strong ion beam (e.g., the ratio of beam ion density to background ion density >0.06 for beam velocity =10VA, where VA is the Alfvén speed), while right-hand resonant instabilities are present in the weak beam cases. During phases 2 and 3, the waves grow to form nonlinear structure, and are then saturated. A detailed analysis shows that the wave evolution in these phases is through secondary instabilities associated with parametric decay or the wave modulation. In addition, it is shown for the first time from the self-consistent simulation that in the final phase, nonlinear shear Alfvén waves with right-hand polarization in the magnetic field are generated. The magnetohydrodynamic (MHD) wave conditions of the Alfvén mode are satisfied. These Alfvén waves propagate mainly with k⋅B0>0, and the dispersion relation ω=kVA cos α is satisfied, where α is the angle between the wave vector k and B0. On the other hand, fast magnetosonic/whistler waves and slow mode waves are formed in the final phase of weak beam cases. In the 2-D simulations, field-aligned filaments (with k∼k⊥) in the density and magnetic field can be present due to the 2-D effects, in addition to the Alfvén, fast, and slow modes. The heating rate of background ions and its dependence on the wave propagation direction are also examined.

Optimization of secondary ion mass spectrometry detection limit for N in SiC

Controlled changes in the Cs+ primary ion beam density and analytical expressions describing the sources (bulk concentration, memory effect, and adsorption of N from the residual vacuum) of secondary ion mass spectrometry analyte secondary ion intensities were used to determine the contributions to the N secondary ion intensity obtained during the analysis of trace levels of N in bulk SiC. This methodology allows the determination of N concentrations that can be substantially less than the apparent N secondary ion background intensity. It was shown that for the Cameca IMS-6F instrumental conditions used, memory effect is the main contributor to the N background signal. Taking into consideration the Cs+ beam diameter, the raster size, the diameter of the ion-extracted area, and the impurity secondary ion intensity, an optimized combination of primary ion beam current and raster size was determined that resulted in the best detection limit for N in bulk SiC. This detection limit for N in bulk SiC (∼6×1014 atoms/cm3) was obtained for a primary ion current of 100 nA, a raster size of 45 μm×45 μm, and a secondary ion extraction area diameter of 30 μm.

Preparation and characterization of indium tin oxide films formed by oxygen ion beam assisted deposition

Indium tin oxide (ITO) films were produced by low-energy oxygen ion beam assisted electron-beam evaporation. The dependence of surface morphology, electrical and optical properties on evaporation rate, oxygen ion beam energy and density, as well as substrate temperatures was characterized by atomic force microscopy, X-ray photoelectron spectroscopy, Hall-effect and optical transmittance measurements. The results show that high-quality ITO films (resistivity of 7.0×10 −4 Ω cm, optical transmittance above 85% at wavelength 550 nm, surface roughness of 0.6 nm in root mean square) can be obtained at room temperature.

Mini rf-driven ion sources for focused ion beam systems

Mini rf-driven ion sources with 1.2 cm and 1.5 cm inner chamber diameter have been developed at Lawrence Berkeley National Laboratory. Several gas species have been tested including argon, krypton, and hydrogen. These mini ion sources operate in inductively coupled mode and are capable of generating high current density ion beams at tens of watts of absorbed rf power. Since the plasma potential is relatively low in the plasma chamber, these mini ion sources can function reliably without any perceptible sputtering damage of the chamber wall. The mini rf-driven ion sources will be combined with electrostatic focusing columns, and are capable of producing nanofocused ion beams for micromachining and semiconductor fabrications.

Dust acoustic solitary waves and double layers in a dusty plasma with an arbitrary streaming ion beam

The effects of variable dust charge, dust temperature and an arbitrary streaming ion beam on small amplitude dust acoustic waves are investigated. It is found that both compressive and rarefactive solitons as well as double layers exist. There exists a critical ion beam velocity below which the ion beam is unable to generate solitons. Korteweg–de Vries (KdV) equations with third and fourth-order nonlinearity at the critical values are derived and the properties of dust acoustic solitary waves are discussed. In the vicinity of the critical values, KdV-type with mixed nonlinearity is obtained. The quite dense positive ion, the dust temperature, the ion beam density, mass ratio and temperature govern the existence of dust acoustic waves. The findings of this investigation may be useful in understanding laboratory plasma phenomena and astrophysical situations.

Conceptual design of beam-ion profile diagnostics for the DIII-D tokamak

Three diagnostic concepts that measure the radial profile of deuterium beam ions are assessed. One diagnostic exploits 3 MeV protons that are lost on their first orbit. Since beam-plasma reactions usually predominate in the discharges of interest, the beam-ion density profile can be inferred from the d-d fusion reaction profile. The relatively modest plasma current (∼1.6 MA) implies that a significant fraction of the charged d-d fusion reaction products are unconfined. The second diagnostic employs a neutron collimator. For this diagnostic, neutron scattering is a major concern. Both fusion product diagnostics are sensitive to uncertainties in the thermonuclear rate, so the anomalous beam-ion transport must exceed DB≳1.0 m2/s to be detectable. The third diagnostic employs an array of natural diamond detectors that is configured to measure the signal from beam ions that charge exchange with neutrals in a modulated heating beam. The sensitivity to uncertainties caused by pitch-angle scattering of the beam ions can be minimized by a prudent choice of detection angle. Because of attenuation of the escaping neutrals the effective resolution is DB∼0.5 m2/s.

Mechanical properties of zirconium films prepared by ion-beam assisted deposition

Zirconium nitride films were prepared by ion-beam assisted deposition on single-crystal silicon substrates. The films were synthesized by depositing the zirconium vapor from an electron-beam source, under the irradiation of nitrogen ions from an arc ion source. Transport ratio of Zr to N was varied from 1.0 to 3.0 by controlling the deposition rate of Zr. The ion beam density was kept constant, 0.2 mA/cm 2. The ion beam energy was varied between 0.5 and 2.0 keV. The films were characterized by X-ray diffraction (XRD) and Auger electron spectroscopy. Hardness of the films was measured by the nano-indentation tester. The tribological behavior of films was evaluated by the ball-and-disk tribometer, under the normal load of 2 N and the relative sliding speed of 10 mm/s. The steel balls were used as a counter material. Formation of ZrN was recognized in XRD pattern for all deposition conditions. Depth profiles measured by X-ray photoelectron spectroscopy showed that the composition ratio of Zr to N was uniform in the inside of film. The hardness of the films increased with decreasing the transport ratio. Tribological properties of films are also discussed.

ECR plasma source for heavy ion beam charge neutralization

Highly ionized plasmas are being considered as a medium for charge neutralizing heavy ion beams in order to focus beyond the space-charge limit. Calculations suggest that plasma at a density of 1–100 times the ion beam density and at a length ∼0.1–2 m would be suitable for achieving a high level of charge neutralization. An Electron Cyclotron Resonance (ECR) source has been built at the Princeton Plasma Physics Laboratory (PPPL) to support a joint Neutralized Transport Experiment (NTX) at the Lawrence Berkeley National Laboratory (LBNL) to study ion beam neutralization with plasma. The ECR source operates at 13.6 MHz and with solenoid magnetic fields of 1–10 gauss. The goal is to operate the source at pressures ∼10−6 Torr at full ionization. The initial operation of the source has been at pressures of 10−4–10−1 Torr. Electron densities in the range of 108 to 1011 cm−3 have been achieved. Low-pressure operation is important to reduce ion beam ionization. A cusp magnetic field has been installed to improve radial confinement and reduce the field strength on the beam axis. In addition, axial confinement is believed to be important to achieve lower-pressure operation. To further improve breakdown at low pressure, a weak electron source will be placed near the end of the ECR source. This article also describes the wave damping mechanisms. At moderate pressures (> 1 mTorr), the wave damping is collisional, and at low pressures (< 1 mTorr) there is a distinct electron cyclotron resonance.

Using masks to obtain uniform ion etch rates

For milling over large areas there is need for broad ion beam sources with a uniform etch rate profile. Currently uniform ion beam density is obtained in the central portion of the ion source by manipulating the grids and the magnets in the ion source. We have designed and implemented specially shaped hard masks to a rotating substrate holder. This mask is able to transform the Gaussian etch rate profile of a 150-mm-diam Oxford ion source to a flat profile. The flat profile decreases the etch rate in the central portion while maintaining the same etch rate along the edge. The deviation in the ion beam etch rate is within 5% in the flat region.

Nonlinear charge and current neutralization of an ion beam pulse in a pre-formed plasma

The propagation of a high-current finite-length ion beam in a cold pre-formed plasma is investigated. The outcome of the calculation is the quantitative prediction of the degree of charge and current neutralization of the ion beam pulse by the background plasma. The electric and magnetic fields generated by the ion beam are studied analytically for the nonlinear case where the plasma density is comparable in size with the beam density. Particle-in-cell simulations and fluid calculations of current and charge neutralization have been performed for parameters relevant to heavy ion fusion assuming long, dense beams with length lb≫Vb/ωb, where Vb is the beam velocity, and ωb is the electron plasma frequency evaluated with the ion beam density. An important conclusion is that for long, nonrelativistic ion beams, charge neutralization is, for all practical purposes, complete even for very tenuous background plasmas. As a result, the self-magnetic force dominates the electric force and the beam ions are always pinched during beam propagation in a background plasma.

Surface nitridation processes and non-linear behaviour of the reactive magnetron discharge with titanium target

Recently, a model was proposed to explain the non-linearity of the V– I characteristics of the reactive magnetron discharge with a Ti-cathode in an Ar–N 2 gas mixture. It accounts for the rapid development of an additional (lower impedance) metal–target discharge, which is coupled in parallel to the existent one, after outrunning a current threshold. Here, we employed various surface science techniques to confirm the connection between mentioned non-linearity and target nitridation-versus-sputtering processes. Surface atomic N/Ti ratios were measured for different N 2 pressures, and ion current densities using X-ray photoelectron spectroscopy, Auger electron spectroscopy and low-energy ion scattering spectroscopy. Systematic experiments showed that while the nitridation enhancement process plays a significant role at lower current densities, the sputtering process becomes predominant after outrunning a critical current density. Taking into account the checked scaling effect of pressure and ion beam density, we were able to correlate the mentioned critical current density with the threshold currents in the V– I plots.

Alternative approach to the numerical synthesis of the dense-ion-beam focusing systems.

An alternative approach has been developed to the numerical synthesis of ion-beam focusing systems that prepare the dense laminar ion beams with the required profile of the ion trajectories. Conventionally an ill-posed synthesis problem arises in such cases, and only low-density beams with no magnetic field are treated. Instead, we compute both the electric and magnetic fields by considering two well-posed problems, the first for the equivalent potential Q and the second for the electric potential U. An analytical solution for Q for the specific case of an axial system has been found and a self-consistent method of satisfying the axial boundary conditions for Poisson's equation in U is described. It is shown that the beam can be focused while preserving its laminar structure and the required profile when applying various superpositions of both the electric and magnetic fields.

The sp 3 bond fraction in carbon films prepared by mass-separated ion beam deposition

Amorphous carbon films were prepared by mass-separated ion beam deposition (MSIBD), and the sp 3 bond fraction was examined by electron energy loss spectroscopy. In previous studies, the carbon ion current was low, and the vacuum pressure during deposition was insufficient. There seems to be an influence of residual hydrogen gas, and damage to the film by the high-speed neutral species produced by the charge exchanging with residual gas molecules during ion transportation. In this study, an MSIBD system was developed with a high ion current density under ultra-high vacuum conditions. Typical carbon ion beam density was 0.2 mA/cm 2 at an energy of 100 eV under a vacuum pressure of 6×10 −7 Pa. The sp 3 bond fraction of the carbon film, which was prepared under a vacuum pressure of 10 −5 Pa during deposition, was 34%. However, that of the film prepared under 10 −7 Pa reached 83%. It was thought that the impact of the high-speed neutral carbon species on the films accounts for the degradation of the sp 3 bond fraction. The dependence of the sp 3 bond fraction on the carbon ion energy was examined. The maximum sp 3 bond fraction of 84% is obtained at an ion energy between 75 and 100 eV.

Methane to Methanethiol Conversion by FeS+. A Combined Experimental and Theoretical Study†

The reaction of FeS+ with methane is examined by guided ion beam mass spectrometry and density functional theory employing the B3LYP/6-311+G* level of theory. For the FeS+/CD4 system examined in the experiments, two major product ions, Fe+ and FeSD+, are observed along with minor channels leading to FeCD3+, FeSCD3+, and FeSCD+. All products are formed in endothermic processes. The measured thresholds for the formations of Fe+ and FeSD+ are compared with computational data as well as literature thermochemistry. In the theoretical approach, two competing reaction mechanisms for the formation of Fe+, concomitant with neutral methanethiol, are investigated and used to interpret the experimental data. The lowest-energy path involves a formal 1,2-addition of H3C−H across the Fe+−S bond to generate a CH3FeSH+ insertion intermediate. This bond activation step involves spin inversion from the sextet to the quartet surface en route to the products. The occurrence of the second conceivable pathway resulting in formation of HFeSCH3+ as an intermediate can be ruled out because of the high-energy demand associated with overcoming the insertion barrier along this pathway.

Ion-beam–plasma electromagnetic instabilities

It is well known that ion-beam–plasma interactions can destabilize right- and left-hand polarized electromagnetic waves. Owing to the fact that these instabilities have mostly been studied numerically by solving the hot-plasma dispersion relation, their fluid nature has often gone unnoticed. Choosing the ion background to be the rest frame, it is shown that the right-hand polarized instabilities are the result of a merging of the magnetosonic/electron-cyclotron branch of the dispersion relation with the ion beam. For any given ion-beam density and sufficiently large beam velocity, there are always two right- and two left-hand polarized instabilities leading to forward-propagating electromagnetic waves. It is also shown that all right-hand polarized instabilities are resonant instabilities, satisfying ω−kU+Ωp ≈ 0 around their maximum growth rate (ω and k are the frequency and the wavenumber respectively, U is the beam velocity, and Ωp is the proton gyrofrequency). Likewise, when the two left-hand instabilities are simultaneously present, they are also resonant instabilities satisfying ω ≈ Ωp. The high-frequency right-hand resonant instability (ω [Gt ] Ωp) has a maximum growth rate that depends only on the ratio between the beam density and the total density. The range of the unstable spectrum decreases with increasing beam velocity, leading to highly monochromatic radiation.

He ion beam density effect on damage induced in SiC during Rutherford backscattering measurement

The damage generation of a 3.5 MeV 4He + analyzing beam in 4H-SiC during Rutherford backscattering spectrometric (RBS) measurement was studied by channeling effect measurements (RBS/C). A dose rate dependence of the minimum yield ( χ min) was found, i.e., higher damage accumulation occurs with higher dose rate. On the other hand, the dose dependence shows that in the applied dose range (⩽3 × 10 17 ions/cm 2) there is an effective dose region where χ min increases with dose, whereas it almost remains unchanged outside of this range. The behavior of analyzing beam induced damage was also discussed according to RBS observations.

Experiments with a microwave plasma as a cathode for cold or hot reflex discharge ion source

A microwave plasma cathode (MPC) was developed to replace the thermionic filaments of the cold or hot reflex discharge ion source (CHORDIS) ion source for operation with reactive gases. Experiments with our MPC showed its long lifetime and its capability of high-current electron emission. Two new types of antennae are presented. Different electron extraction apertures were used, but the best results were obtained with an extraction aperture of 6 mm in diameter. Ion beam currents for different oxygen pressures and different discharge voltages are presented and discussed. The gas pressure proved to be a critical parameter in respect to the extracted ion beam densities and beam noise. Total ion current densities of 16.8 mA/cm2 were obtained for oxygen. We are also presenting an experiment where the MPC-CHORDIS system was used as a tool to study the influence of the beam noise on the space charge compensation at the GSI Darmstadt injection beam line.

Surface modification of aluminum and chromium by ion implantation of nitrogen with a high current density ion implanter and plasma-source ion implantation

Results of ion implantation of nitrogen into electrodeposited hard chromium and pure aluminum by a high-dose ion-beam source are presented and compared to plasma-source ion implantation. The large-area, high current density ion-beam source can be characterized, with respect to surface modification use, by a uniform emitted dose rate in the range of 1016 to 5 × 1017 N cm−2 min−1 over an area of <100 cm2 and with acceleration energies of 10–50 keV. The implantation range and retained dose (measured using ion-beam analysis), the surface hardness, coefficient of friction, and the change in the wear coefficient (measured by nanohardness indentation and pin-on-disk wear testing) that were obtained with an applied dose rate of ∼1.7 × 1017 N cm−2 min−1 at 25 kV are given, and they are compared to results obtained with plasma-source ion implantation.

Ion and electron characteristics in auroral density cavities associated with ion beams: No evidence for cold ionospheric plasma

Low‐density cavities associated with upgoing ion beams were identified in the auroral regions over two decades ago. In order to understand the waves, double layers, and solitary structures observed within these cavities, accurate measurements of the plasma distribution function are required. Although measurements by DE 1 indicated that these cavities were composed primarily of hot plasma in the form of ion beams, plasma sheet ions, and inverted V electrons, later reports from Viking showed these cavities contained a cold plasma component whose density was an order of magnitude larger than the hot component. Recent measurements by the FAST satellite contrast sharply with the Viking results and support the earlier DE 1 observations. Regions of upgoing ion beams observed by FAST are shown to contain little or no cold plasma. The hot electron densities (>100 eV) and the combined plasma sheet ion and upgoing ion beam densities (>30 eV) agree remarkably well. Furthermore, no cold ions (0–30 eV) are measured at low energies by the mass spectrometer, which precludes the presence of significant (>20%) cold electrons to preserve charge neutrality. Characteristics of the plasma for 11 ion beam events are tabulated.