Increase In Ion Current Density Research Articles

Effect of plasma nitriding ion current density on tribological properties of composite CrAlN coatings

CrAlN coatings were synthesized on pre-plasma nitrided M2 high speed steels using different ion current densities. The effect of plasma nitriding pretreatment on the microstructures and tribological properties of composite CrAlN coatings had been studied. The results showed that the nitriding efficiency could be significantly enhanced by higher ion current density. The thickness of nitrided layer increased from 43 μm to 63 μm with the increase of ion current density. The nitrided layers without either compound layer or grain boundary precipitation were produced with all experimental ion current densities. Radial cracks also appeared at the Rockwell-C indentation edge of the composite CrAlN coating due to the conformal effect. Moreover, radial cracks of the composite coatings originated from the hard and brittle nitrided layer. The highest interfacial adhesion of the composite CrAlN coating reached 105 N. Furthermore, the wear resistance of CrAlN coating was improved by combining nitriding pretreatment with coating deposition, and the composite coating (PN4/CrAlN) possessed the superior wear resistant.

Change in Dislocation Structure and Phase Composition of 1565Ч Alloy Exposed to Ion Irradiation (Cu + Pb)

Background/Objectives: Using electron microscopy, it was revealed that exposure to ion irradiation (Cu + Pb) with an energy of 35 keV of samples sized 25 × 25 × 3 mm of 1565ч industrial aluminum alloy after cold rolling, leads to a significant narrowing of the boundaries of intragranular cellular dislocation structure and increase in the extent of its regularity. Methods/Statistical Analysis: We have studied samples of 1565ч alloy sized 25 × 25 mm 2 cut from non-clad sheets of a thickness of 3 mm, a change in the structure of cold-worked 1565ч alloy exposed to the beams of accelerated ions (Cu + Pb) with an energy of 30 keV at the densities of ion current of 100, 200 and 300 μA/cm 2 and irradiation doses of 1016 and 1017 cm -2 . Irradiation with pulsed beams of ions (Cu + Pb) was conducted at the setup for ion beam implantation equipped with ion source based on plasma arc in vacuo. Electron microscopic study by the method of thin foils was conducted at JEM-2100 transmission electron microscope. Findings: It was found that irradiation of cold-worked clad 1565ч alloy with copper and lead ions does not lead to a fundamental change in its structure compared to the structure existing in the deformed condition: cellular dislocation structure remains. With increase in ion current density and irradiation dose, the cellular structure becomes more regular - well-formed cells are observed throughout almost the entire volume of the sample. The average width of dislocation-free regions reaches 2.5 μm at the width of the boundaries not exceeding 0.6 μm. The effect of accelerated ions (Cu + Pb) (E = 30 keV, j = 100 μA/cm 2 ) on the alloy without the cladding layer even at a dose of 1016 cm -2 leads to formation of the developed subgrain structure in initially deformed alloy. The average size of subgrains with interlacements of dislocations varies in the range of 0.6 - 2.2 μm. In other words, a polygonal structure forms in the alloy similar to the structure forming at the initial stages of recrystallization annealing. Applications/Improvements: This applies to many industries associated with the development of high-tech and energy-saving technologies as well as addressing environmental problems.

Extraction characteristics of a low-energy ion beam system with a remote plasma chamber.

Low-energy argon beams were extracted from a dual-chamber ion source system. The first chamber is a quartz cylinder where dense inductively coupled plasmas were produced using 13.56 MHz radio frequency (rf) power. The discharge was driven into an adjacent chamber which acts as a reservoir for ion beam extraction using a dual-electrode extractor configuration. Extraction of ions from the second chamber with energies in the 100 eV range was achieved while minimizing fluctuations induced by the rf signal. A custom-built retarding potential analyzer was used to analyze the effectiveness of ion beam transport using the remote plasma chamber. Well-defined beams were extracted between 60 and 100 V extraction potentials at 50-100 W rf powers. An increase in rf power resulted in an increase in average ion energy, increase in ion current density while the energy spread remains constant.

Study of magnetic field enhanced plasma immersion ion implantation in Silicon

A comparison between experimental measurements and numerical calculations of the ion current distribution in plasma immersion ion implantation (PIII) with external magnetic field is presented. Later, Silicon samples were implanted with nitrogen ion to analyze the effect on them. The magnetic field considered is essentially non-uniform and is generated by two magnetic coils installed on vacuum chamber. The presence of both, electric and magnetic field in PIII create a crossed ExB field system, promoting drift velocity of the plasma around the target. The results found shows that magnetized electrons drifting in ExB field provide electron-neutral collision. The efficient ionization increases the plasma density around the target where a magnetic confinement is formed. As result, the ion current density increases, promoting significant changes in the samples surface properties, especially in the surface wettability.

Effect of External Cathode Azimuthal Position on Hall-Effect Thruster Plume and Diagnostics

The T-220HT Hall-effect thruster was tested with the external cathode at different azimuthal locations to determine the effect of an external cathode on the far-field plume. The cathode is mounted in two configurations: 1) on top of the thruster, perpendicular to the plane of plume measurements, and 2) in the plane of plume measurements. The thruster was tested at discharge voltages of 150–300 V at a constant discharge current of 9 A on krypton propellant. The vacuum facility operating pressure was below for all operating conditions. Noticeable changes in the plume ion current density were measured that indicate plume asymmetry. With the cathode in the plane of the probes, the ion current density peak increases by up to 43% and the divergence angle decreases by up to 2.6 deg. However, there is less than a 5 V shift in the ion energy distribution, and the distribution shape remains constant. The results indicate that an external cathode alters the plume symmetry and creates a region of increased ion flux. An analysis of the cathode generated species densities indicates that the increase in ion current density is caused by nonuniform ingestion of cathode neutrals and nonuniform electron density near the cathode. This phenomenon can affect thruster plume measurements as well as the orientation of thrusters for satellite integration.

Propellant Thermal Management Effect on Neutral Residence Time in Low-Voltage Hall Thrusters

The effects of anode temperature on the performance of a 4.5 kW Hall-effect thruster are investigated. The approach separates the location of gas injection from discharge current collection using an anode band, which removes the main mechanism that heats the gas distributor. A thermal model predicts a 270 K reduction of the gas distributor temperature, which corresponds to a 28% increase in the propellant residence time. Collection of the discharge current on the anode band, which is upstream of the bulk Hall current region, generates a 10% increase in ion current density at the thruster centerline for discharge voltages of 100, 125, and 150 V at a xenon mass flow rate of . The initial reduction in neutral velocity with the anode band is counteracted by the influence of the channel wall temperature, which increases the neutral velocity of the particles by up to 25% greater than the velocity at the gas distributor exit plane. This reduces the potential thruster efficiency improvement from 5.5 to 2.5%. The selected downstream location of the anode band results in a 6–10% increase in discharge current compared with current collection on the gas distributor.

Study of plasma immersion ion implantation into silicon substrate using magnetic mirror geometry

The effect of magnetic field enhanced plasma immersion ion implantation (PIII) in silicon substrate has been investigated at low and high pulsed bias voltages. The magnetic field in magnetic bottle configuration was generated by two magnetic coils installed outside the vacuum chamber. The presence of both, electric and magnetic field in PIII creates a system of crossed E×B fields, promoting plasma rotation around the target. The magnetized electrons drifting in crossed E×B fields provide electron-neutral collision. Consequently, the efficient background gas ionization augments the plasma density around the target where a magnetic confinement is achieved. As a result, the ion current density increases, promoting changes in the samples surface properties, especially in the surface roughness and wettability and also an increase of implantation dose and depth.

Effect of the electron beam and ion flux parameters on the rate of plasma nitriding of an austenitic stainless steel

The method of nitriding of metals in an electron beam plasma is used to change the current density and energy of nitrogen ions by varying the electron beam parameters (5–20 A, 60–500 eV). An electron beam is generated by an electron source based on a self-heated hollow cathode discharge. Stainless steel 12Kh18N10T is saturated by nitrogen at 500°C for 1 h. The microhardness is measured on transverse polished sections to obtain the dependences of the nitrided layer thickness on the ion current density (1.6–6.2 mA/cm2), the ion energy (100–300 eV), and the nitrogen-argon mixture pressure (1–10 Pa). The layer thickness decreases by 4–5 μm when the ion energy increases by 100 V and increases from 19 to 33 μm when the ion current density increases. The pressure dependence of the layer thickness has a maximum. These results are in conflict with the conclusions of the theory of the limitation of the layer thickness by ion sputtering, and the effective diffusion coefficient significantly exceeds the well-known reported data.

Influence of Ion Current Density on the Surface Morphology of AZ31 Magnesium Alloy Irradiated by High-Intensity Pulsed Ion Beam

HIPIB irradiation into AZ31 magnesium alloy is performed at ion current density of 100-300 A/cm2 with 1 shot. The surface morphologies and surface profiles of the irradiated AZ31 magnesium alloy samples are characterized by scanning electron microscopy (SEM) and profilometer, respectively. It is found that HIPIB irradiation leads to the formation of crater in local region of irradiated samples, and crater density increases with increasing ion current density. Both the surface roughness that reflects the vertical wave of surface profile and the mean spacing of surface profile irregularities that reflects the horizontal wave of surface profile increase as ion current density increases. These results are in agreement with the SEM observation on the irradiated surface.

The influence of low-energy ion bombardment on the microstructure development and mechanical properties of TiB x coatings

The influence of the deposition parameters on the growth, structure and mechanical properties of the TiB x coatings is studied. The TiB x coatings represent a nanocomposite system, in which random or oriented TiB 2 nanocrystallites are embedded in an amorphous matrix as is revealed by cross-sectional transmission electron microscopy. We show that low-energy ion bombardment ( E i ) of growing TiB x coating, influences the preferred orientation of TiB 2 crystallites. The increase of ion current density ( i s ) by means of negative substrate bias voltage ( U s ) leads to change from random to the (0001) preferred crystal orientation whereby the electrical biasing promotes crystal growth in the coating and the (0001) texture appears gradually during the film growth. Together with the (0001) preferred orientation selection the composition B/Ti ratio was changed from 2.9 (floating potential, E i = 8 eV ) to 2.4 ( E i = 94 eV). The highest amount of oriented (0001) crystallites and highest hardness H = 53 GPa exhibit TiB x coatings deposited at E i = 94 eV and i s = 2.69 mA.cm −2.

“Magnetically enhanced hollow cathode—a new plasma source for high‐rate deposition processes”

AbstractHollow cathode arc discharges have been studied for some decades in basic research and different fields of practical application. Especially in the field of physical vapor deposition (PVD) they are often used for metal evaporation and the generation of plasma. Problematical aspects were found in the high throughput of working gas necessary for stable operation and in the inhomogeneous, locally concentrated ionization efficiency. A promising way out of this dilemma was found in a special arrangement of hollow cathode and annular anode in an axial magnetic field. This configuration allows a drastic reduction of working gas flow without loss of discharge stability. Moreover, with reduction of gas flow a strong increase in ion current density was observed together with a highly expanded volume of plasma plume.

Nanostructuring of silicate glass under low-energy Ag-ion implantation

Silicate glasses implanted by 30 keV Ag + ions with a dose of 5 × 10 16 ion/cm 2 at ion current densities from 4 to 15 μA/cm 2 were investigated using optical spectroscopy and atomic force microscopy (AFM). Optical spectroscopy measurements show a characteristic absorption band of surface plasmon resonance that is associated with nanosize Ag particles formed in the implanted glasses. Observed both the shift of transmittance band minimum to long wavelengths and the intensity change with rise of ion current density are caused by increase of the nanoparticle sizes. AFM images of the implanted glass surfaces show a formation of semispherical hills. These hills are tops of the spherical nanoparticles towering above the surface due to sputtering of the glass surface layer under the implantation. The increase of ion current density leads to enlarge of the hill size, i.e. nanoparticles. The nanoparticle enlargement is explained in terms of enhanced thermal diffusion of the implanted Ag atoms. Increase of the ion current density leads to temperature rise in the glass matrix that elevates atoms mobility and causes effective collection of the silver atoms into nucleated particles and their growth.

Charge carrier transport in polyimide with Co nanoparticles formed by ion implantation

Temperature dependence of resistance is studied for polyimide (PI) samples implanted by Co + ions with fluences of 2.5 × 10 16–1.25 × 10 17 cm −2 at ion current densities of 4, 8 and 12 μA cm −2. It is found that electron transport in the implanted samples originates from radiation-induced changes of the PI and Co nanoparticle formation and it depends dramatically on the ion current density. A variable range hopping mechanism dominates for all fluences at a low ion current density of 4 μA cm −2 while a transition to a semimetallic type of conductance is observed with an increase in ion current density due to agglomeration of the Co nanoparticles forming a percolation way for the charge carriers. It is shown that both quantum effects of weak localisation and electron–electron interaction give a significant contribution to the transport mechanism.

Effects of bias frequency on reactive ion etching lag in an electron cyclotron resonance plasma etching system

We examined the etch characteristics of SiO2 contact holes which have the sizes of 0.3–1.2 μm in a C4F8+H2 electron cyclotron resonance plasma etching system. We varied the chamber pressure (3–7.5 mTorr), microwave power (300–800 W), gas mixing ratio, bias voltage (100–300 V) and bias frequency (100 –800 kHz) as the experimental parameters to investigate the reactive ion etching (RIE) lag. The RIE lag improved, as the bias voltage increased and this RIE lag improvement was thought to be due to the increase of ion energy incident on the substrate. The RIE lag also improved as the chamber pressure decreased and this improvement is due to the increase of ion current density as the chamber pressure decreases. When we increased the bias frequency from 100 to 800 kHz maintaining the same bias voltage, the RIE lag improved considerably. We calculated energy distribution of ions striking the rf biased substrate using Monte Carlo particle-in-cell method to understand this phenomenon. The ion energy distributions are bimodal when the bias frequencies are below 1 MHz, but as the bias frequency increases from 100 kHz to 1 MHz, the low energy part decreases and the high energy part increases, and it is suggested that this change of ion energy distribution is responsible for the RIE lag improvement with the bias frequency increase.

Ion Assisted Deposition of TiO2 Thin Films by Kaufman and Gridless Ion Sources.

TiO2 thin films were deposited by Ar ion beam assistance of Kaufman and gridless ion sources. Optical and structural properties of IAD TiO2 thin films and comparison between two types of sources are described. The result shows that Ar IAD by both ion sources improves the packing density and refractive index of TiO2 thin films. The high energy Ar ion beam of the Kaufman ion source induces an increase in extinction coefficient as the ion current density increases, while the gridless ion source results in a decrease in extinction coefficient. The crystal-line structure of conventional and Kaufman-IAD TiO2 films is amorphous whereas some gridless-IAD TiO2 films show anatase phases as the ion current density increases.

Studies of the optical and structural properties of ion-assisted deposited Al2O3 thin films

The optical and structural properties of Al 2 O 3 films produced by oxygen-ion assisted deposition (IAD) have been investigated as a function of ion energy (300–1000 eV), ion current density (50–220 μA cm −2), and substrate temperature (ambient-300°C). It is observed that films prepared by IAD with the substrates maintained at elevated temperatures show the best properties. The maximum refractive index obtained was 1.73 for films deposited at 1000 eV, 50 μA cm −2 and 300°C. Teh refractive index decreased with the increase in ion current density for ion energies exceeding 300 eV with absorption still being negligible. As-deposited films prepared, with or without ion bombardment, were amorphous. Films deposited without ions and annealed at 800°C in air for 12 h were σ- alumina, whereas those deposited at 1000 eV ion energy, 220 μA cm −2 ion current density and annealed at the same temperature for the same period were found to be α- alumina.

CF incorporated overlayer growth on silicon exposed to a d.c.-excited CF 4 plasma

The effects of d.c. biasing on the etching characteristics of silicon exposed to a d.c.-excited CF 4 plasma have been analysed to provide further insight into the energy dependence of surface ion-assisted chemistry in fluorocarbon plasmas. Time dependence variations of the desorbed SiF 4 partial pressure are reported and discussed in relation to the surface characterization with Auger sputter profiling. It is shown that, beyond a threshold ion energy W T, a CF blocking overlayer develops of which the steady state thickness increases with increasing ion energy, therefore involving an increasing attenuation of the silicon removal. Auger depth profiles demonstrate the difference between this “CF incorporated overlayer” and the “C-F mixed layer” which is set up at ion energies lower than W T. The threshold ion energy decreases as the neutral pressure decreases, ion current density increases, surface temperature increases, and F:C ratio of the active species decreases. These results are discussed on the basis of an “incorporation-combination-sputtering model” accounting for the carbon surface and volume mass balance.

Metal oxides deposited using ion assisted deposition at low temperature

We have investigated the use of ion assisted deposition (IAD) to deposit thin films of Al2O3, Ta2O5, and TiO2 at a low substrate temperature (Tsub≂100 °C). Refractive indices of films deposited using IAD initially increase for a corresponding increase in ion current density until the current density reaches a so-called ‘‘critical value.’’ Films deposited at bombardment levels greater than the critical value exhibit refractive indices that are less than those obtained at current densities below the critical value. The critical value is reduced by an increase in ion energy. We have compared the effects of using IAD at low temperature to our previous results from depositing thin films using IAD at an elevated substrate temperature (Tsub≂300 °C). This comparison shows that reducing the substrate temperature increases the critical value. The effects of IAD on optical scatter were also investigated. IAD increases the optical scatter characteristics of TiO2 thin films. Raman spectroscopy was used to correlate optical scatter in TiO2 thin films to the presence of anatase crystallites in the coatings.

イオンアシスト蒸着Ｆｅ‐Ｎ膜の構造と磁気異方性

Change of the structure and magnetic properties of Fe-N films prepared by ion assisted vapor deposition was examined with varying ion current density and substrate temperature. The structure was characterized by X-ray diffraction techniques and the magnetic anisotropy was evaluated by torque curve measurement. When both the ion current density and the substrate temperature are low, uniaxial anisotropy is induced by ion bombardment. Origin of the uniaxial anisotropy is not known. With an increase in ion current density and substrate temperature, cube textures develop and a four-fold symmetrical anisotropy appears. As the directions of closest packed atoms in the textures are coincident with the direction of ion incidence, it is thought that the dependence of sputtering yield on grain orientation causes the texture development. Results of experiments using other ion species (Ar, Ne) are also shown.

Primary Ar+ ion bombardment effect on Ni–Fe film composition formed by ion beam sputtering

This paper reports results of experimental and analytic investigations concerning the Ni–Fe film composition formed by ion beam sputtering under various forming conditions. From experiments involving the substrate angle and temperature that had dramatic influence on the Ni–Fe film composition, it is found that the primary Ar+ ion bombardment dominates the composition variation. Also, the Ni fraction in Ni–Fe film and its deposition rate decrease as the ion current density increases. As a result of simple analysis, this composition variation is found to be caused by preferential resputtering. Conversely, the Ni fraction increases as the substrate temperature increases without a deposition rate change under primary ion bombardment. This phenomenon cannot be explained only by preferential resputtering. It also includes the formation of an Fe-rich layer on the film surface.