Increasing Ion Energy Research Articles

Frequency doubling and field‐aligned ion streaming in a long‐period poloidal pulsation

We reexamine a long‐period (10–18 min) poloidal pulsation observed by THEMIS‐A in the outer dawn magnetosphere from 10:00 to 12:30 UT on 7 November 2007. The interval was originally reported by Korotova et al. (2009). Although the nonlinear compressional plasma and magnetic field perturbations observed by THEMIS‐A during this interval agree well with model predictions for the linear perturbations associated with antisymmetric waves generated by the ballooning‐mirror mode instability, the phase relationships between these perturbations indicates a complex frequency rather than the purely imaginary frequency that theory predicts for the outer dawnside magnetosphere. Variations in the radial plasma velocity confirm that a phase‐locked north/south oscillation in the equatorial line of nodes associated with the ballooning‐mirror mode waves doubles the frequency of the compressional component of the magnetic field during these pulsations. The same velocity and magnetic field perturbations exclude explanations for the frequency doubling in terms of spatial gradients sweeping back and forth across the spacecraft or drift‐bounce resonances. Azimuthal electric fields associated with the pulsations generate field‐aligned anisotropies in the pitch angle distributions that become more prominent with increasing ion energy due to the presence of drift‐shell splitting and radial flux gradients that steepen with increasing energy. Although there was no evidence for drift‐bounce interactions during this event, the role of such events in ion energization in other events and at other locations remains to be evaluated.

Effect of ion-beam assisted deposition on the film stresses of TiO2 and SiO2 and stress control

Based on Hartmann-Shack sensor technique, an online thin film stress measuring system was introduced to measure the film stresses of TiO2 and SiO2, and comparison was made between the film stresses prepared respectively by the conventional process and the ion-beam assisted deposition. The effect of ion-beam assisted deposition on the film stresses of TiO2 and SiO2 was investigated in details, and the stress control methodologies using on-line adjustment and film doping were put forward. The results show that the film stress value of TiO2 prepared by ion-beam assisted deposition is 40 MPa lower than that prepared by conventional process, and the stress of TiO2 film changes gradually from tensile stress into compressive stress with increasing ion energy; while the film stress of SiO2 is a tensile stress under ion-beam assisted deposition because of the ion-beam sputtering effect, and the film refractive index decreases with increasing ion energy. A dynamic film stress control can be achieved through in-situ adjustment of the processing parameters based on the online film stress measuring technique, and the intrinsic stress of film can be effectively changed through film doping.

Dipolarization fronts and associated auroral activities: 1. Conjugate observations and perspectives from global MHD simulations

Earthward‐propagating dipolarization fronts (DFs) are often found to be associated with magnetic reconnection and bursty bulk flows (BBFs) in the magnetotail. Recent THEMIS (Time History of Events and Macroscale Interactions During Substorms) probe observations have shown a DF propagating over 10REfrom the mid‐tail region to the near‐Earth tail region, and THEMIS All‐Sky Imager data show a north‐south auroral form and intensification of westward auroral zone currents. In this study, we examine THEMIS in situ observations of DFs in the magnetotail and simultaneous observations of the proton aurora from ground‐based CANOPUS (the Canadian Auroral Network for the OPEN Program Unified Study) Meridian Scanning Photometers (MSPs). We find that earthward‐moving DFs are often associated with intensification of proton aurora when the THEMIS probes are conjugate to the meridian of the MSP. The proton auroral intensifications are transient and in some cases detached from the background proton precipitation. Just before the DFs, the ion distribution is anisotropic in the field‐aligned direction (mostly earthward) and the ion energy increases. These observations suggest that plasma sheet protons can be reflected and energized by earthward‐moving DFs as they propagate through the magnetotail. We postulate that this population of ions is the source of the proton auroral intensification observed on the ground. This conjecture is tested using our global MHD simulation results, where the proton precipitation is calculated with the field‐line curvature (FLC) model. The MHD simulation results show that proton precipitation enhancement can be caused by compression of plasma by approaching DFs/BBFs, which is consistent with ion reflection at DFs. Thus, using the conjugate observations from THEMIS spacecraft and MSP in this study, we are able to directly link the magnetotail dynamics, i.e., dipolarization fronts, with ground auroral activities. However, understanding of DF‐associated ion energization requires detailed test‐particle simulations with an analytical magnetotail model, such as those in our companion paper.

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.

Correlation between Tribological Properties, sp²/sp³-Ratio and H-Content of Low-Wear Diamond-Like Carbon (DLC) Layers

It has been established that hardness and density of diamond-like carbon (DLC) layers can be raised by increasing ion energy during deposition, decreasing H-content and by increasing sp3-fraction. To confirm differences in hydrogen content of hydrogen containing and hydrogen free DLC films deposited at different bias voltages, layers were etched in oxygen atmosphere in a capacitively coupled plasma device. By employing real-time ellipsometry measurements, the H-content of the hydrogen containing a-C:H layers were estimated by determining the optical constants n and k (n-real part and k-imaginary part of the refractive index). In addition, DLC layers were analyzed by X-ray photoelectron spectroscopy to estimate the ratio of sp²- and sp³-hybridization. The mechanical and tribological properties of the coatings were evaluated by means of nanoindentation and ball-on-disc-tests. Finally correlations between these properties, H-content and sp3/sp2-ratio were obtained in an effort to explain different tribological behaviors of DLC-layers.

The effect of nitrogen ion bombarding energy on the bonding structure of nitrogenated tetrahedral amorphous carbon film

The tetrahedral amorphous carbon (ta-C) films with more than 80% sp3 in fraction are deposited by the filtered cathode vacuum arc technique. Then the energetic nitrogen (N) ions are used to bombard the ta-C films to fabricate nitrogenated tetrahedral amorphous carbon (ta-C:N) films. The composition and the structure of the films are analyzed by visible Raman spectrum and X-ray photoelectron spectroscopy. The result shows that the bombardment of energetic nitrogen ions can form CN bonds, convert CC bonds into C＝C bonds, and increase the size of sp2 cluster. The CN bonds are composed of C＝N bonds and CN bonds. The content of C＝N bonds increases with the N ion bombardment energy increasing, but the content of CN bonds is inversely proportional to the increase of nitrogen ion energy. In addition, CN bonds do not exist in the films.

The study on the stress and the friction coefficient of tetrahedral amorphous carbon films bombarded by energetic Ar ion

The ta-C films with sp3 bonds more than 80% in fraction are deposited by FCVA technique, and then they are bombarded by Ar ions. The composition and structures of the ta-C films before and after the bombardment of energetic Ar ions are analyzed by X-ray photoelectron spectroscopy. The surface morphology is investigated by AFM. The result shows that the bombardment of Ar ions induces the conversion of sp3 bond into sp2 bond, and the fraction of sp2 bonds increases with the energy of Ar ion increasing. The stress of the film decreases with the increase of the Ar ion energy. The RMS and etching pits on the surface of film increase with the increase of Ar ion bombarding energy.The friction test indicates that Ar ion bombardment has an important influence on initial friction coefficient, but just has little influence on steady state friction coefficient. The steady state friction coefficient of film keeps about 0.1, which shows a good antiwear property.

Ultra High Resolution Linear Ion Trap Orbitrap Mass Spectrometer (Orbitrap Elite) Facilitates Top Down LC MS/MS and Versatile Peptide Fragmentation Modes

Although only a few years old, the combination of a linear ion trap with an Orbitrap analyzer has become one of the standard mass spectrometers to characterize proteins and proteomes. Here we describe a novel version of this instrument family, the Orbitrap Elite, which is improved in three main areas. The ion transfer optics has an ion path that blocks the line of sight to achieve more robust operation. The tandem MS acquisition speed of the dual cell linear ion trap now exceeds 12 Hz. Most importantly, the resolving power of the Orbitrap analyzer has been increased twofold for the same transient length by employing a compact, high-field Orbitrap analyzer that almost doubles the observed frequencies. An enhanced Fourier Transform algorithm—incorporating phase information—further doubles the resolving power to 240,000 at m/z 400 for a 768 ms transient. For top-down experiments, we combine a survey scan with a selected ion monitoring scan of the charge state of the protein to be fragmented and with several HCD microscans. Despite the 120,000 resolving power for SIM and HCD scans, the total cycle time is within several seconds and therefore suitable for liquid chromatography tandem MS. For bottom-up proteomics, we combined survey scans at 240,000 resolving power with data-dependent collision-induced dissociation of the 20 most abundant precursors in a total cycle time of 2.5 s—increasing protein identifications in complex mixtures by about 30%. The speed of the Orbitrap Elite furthermore allows scan modes in which complementary dissociation mechanisms are routinely obtained of all fragmented peptides.

Effect of mid-frequency discharge assistance on dual-high power impulse magnetron sputtering

The present paper is focused on time-resolved diagnostics of the simultaneous combination of dual mid-frequency and dual-high power impulse magnetron sputtering discharges (so-called hybrid-dual-HiPIMS systems). Combined systems are operated with the following parameters – dual-high power impulse magnetron sputtering (fH=100Hz, duty cycle 1%) and dual mid-frequency discharge (fM=94kHz, duty cycle 30%) – running simultaneously with two magnetron guns. The magnetrons in dual configuration are electrically confined, i.e. electrodes are alternately operated as an anode–cathode (and vice versa) during the sputtering. The dual MF discharge causes a pre-ionization effect which is an important feature because of: (i) a significant reduction of the working pressure by more than one order of magnitude, (ii) an increase of electron and ion energy, and (iii) an increase of the deposition rate. It was found that the ion velocity distribution function (IVDF) during HiPIMS pulses reaches a maximum of about 15–20eV whereby the dual MF discharge reaches about 0.5–1.5eV. The time-resolved IVDF measurements revealed that ions with high energy generated at the cathode arrive at the substrate position about 25–30μs after the HiPIMS pulse ignition. The effect of the hybrid system is illustrated on the deposition of Ti–Cu films. The crystallographic phase and properties of the deposited films are strongly influenced by the energy of incoming particles and by reduced pressure in the chamber.

Erosion of tungsten-doped amorphous carbon films in oxygen plasma

Tungsten-doped amorphous carbon films with 0–9 at.% W concentration were produced by magnetron sputtering and eroded in oxygen plasmas applying different bias voltages and substrate temperatures. The partial C and W erosion rates were determined from the C and W areal density changes measured by Rutherford backscattering spectrometry (RBS). The initial C removal rate increases with increasing ion energy and temperature and decreases with increasing W concentration. For W-doped films the erosion rate decreases with increasing plasma exposure duration. At low bias voltages the erosion process stops after W accumulation at the surface, which protects the carbon underneath from further erosion. RBS and X-ray photoelectron spectroscopy suggest that the W-rich layer at the surface is carbon free and consists of porous WO 3. Biasing to 200 V leads to removal of W by physical sputtering and, therefore, inhibits the formation of the protecting W oxide layer and the C erosion proceeds.

Modeling of implantation and mixing damage during etching of SiO2 over Si in fluorocarbon plasmas

Energetic ion bombardment during plasma etching of microelectronics devices is necessary to activate chemical process and define features through the ions’ anisotropic trajectories. These energetic fluxes can also cause damage and mixing of the constituents of crystalline lattices. These properties are likely best modeled using molecular dynamics (MD) simulations. The computational expense of these techniques makes feature scale simulations difficult, and so motivates development of approximate methods that can be used to model full features. In this regard, an implantation and mixing model has been developed and implemented into a Monte Carlo feature profile model to simulate the mixing and damage to the underlying Si during high aspect ratio (HAR) etching of SiO2 trenches. Fluxes to the surface were provided by a reactor scale model. The feature scale model was validated by comparison to the mixing produced by Ar+ bombardment of Si with and without F and CF fluxes as predicted by MD simulations. Scaling of mixing damage of underlying Si during HAR of SiO2 etching in Ar/C4F8/O2 plasmas for rf bias powers of 1–4 kW was investigated. The authors found that mixing damage at the bottom of HAR features, though increasing in magnitude with increasing ion energy, does not scale as dramatically as on flat surfaces. This is due to the reflection of ions off of sidewalls which moderate the ion energies.

Controlled Nanostructuring of Ag Films by Ion Beam Sputter Deposition for Surface Plasmon Resonance Applications

The growth of Ag nanostrucutres on borosilicate glass substrates by ion beam sputter deposition in the Ar ion energy range from 150 to 600 eV is demonstrated. Rates of deposition as low as 0.01 nm/s are achieved at an Ar ion energy of 150 eV. This leads to the formation of a random array of nearly spherical Ag particles with a mean size of approximately 100 nm, separated by distances of similar order of magnitude. The particles organize themselves into arrays over lengths of at least 10 microm. As the thickness is increased from 3 to 18 nm there is a transition in morphology from an array to linear chains and finally a dense continuous film. There is a similar microstructural evolution as a function of increasing ion energy. The plasmon resonances can be tuned depending on shape, size and interparticle distances. As the thickness of the films increase, the main plasmon peaks can be tuned from 380 to 680 nm. The spheroidal shape of the particles induces additional peaks (localized surface plasmons) centered around 430 +/- 10 nm. Detailed simulations have been carried out based on Maxwell Garnett theory to distinguish the effects of shape and size on plasmon resonances. It is demonstrated that shape rather than the size of the particles has a stronger influence on the shift in plasmon resonances.

Laser fluence effects on ion emission from a laser-generated Cu plasma

We present details of an experimental facility developed for the diagnostics of highly charged ions produced during pulsed laser ablation of solid targets. A range of laser fluences (2–10 J cm−2) from a Q-switched Nd : YAG laser (wavelength = 1064 nm, pulse duration ∼10 ns) was used to generate a copper plasma. The ion diagnostics were based on the time-of-flight (TOF) methods; an ion collector and a 45° parallel plate electrostatic ion energy analyser were used. A channel electron multiplier located 1.31 m away from the Cu target was used to record the energy-resolved TOF ion spectrum. The effect of laser fluence on the total ion charge, average ion energy and charge state distribution was investigated. The estimated threshold fluence for the onset of the plasma was 2.5 J cm−2. About four times increase in both average ion energy and total ion charge was observed in the investigated laser fluence range. The maximum attainable charge state of the Cu ions increased from 1+ to 7+ with the increase in laser fluence. The correlation between relative abundance of the various ion charge states indicated that the formation of Cun+ occurred through ionization from Cu(n−1)+ by the impact of fast electrons or by multiphoton interactions.

Effect of impinging ion energy on the substrates during deposition of SiO x films by radiofrequency plasma enhanced chemical vapor deposition process

Radiofrequency (13.56 MHz) plasma enhanced chemical vapor deposition process is used for deposition of SiO x films on bell metal substrates using Ar/hexamethyldisiloxane/O 2 glow discharge. The DC self-bias voltage developed on the substrates is observed to be varied from − 35 V to − 115 V depending on the RF power applied to the plasma. Plasma potential measurements during film deposition process are carried out by self-compensated emissive probe. The deposited films are characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation, nano-scratch test and thermogravimetric analysis. The characterization results show strong dependency of the SiO x films properties on the energy of the ions impinging on the substrates during deposition. Analysis of Raman spectra indicates an increase in vitreous silica content and reduction in defective Si–O–Si chemical structure in the deposited SiO x films with increasing ion energy impinging on the substrates. The increase in inorganic (Si and O) content in the SiO x films is further confirmed from XPS analysis. The growth of SiO x films with more inorganic content and defect free chemical structure apparently contribute to the increase in their hardness and scratch resistance behavior. The films show higher thermal stability as the energy of the ions arriving at substrates increases with DC self-bias voltage. The possibility of using SiO x films for surface protection of bell metal is also explored.

Ion-assisted vapor deposition of acryl polymer thin films

Polymer thin films were prepared by an ion-assisted vapor deposition polymerization method that involves physical vapor deposition of monomer combined with low-energy ion irradiation. In a high vacuum environment, zinc diacrylate monomer was evaporated at a rate of 0.8 nm/min on gold-coated glass substrates under simultaneous irradiation by nitrogen ions of 20 nA/cm 2 at ion energy ranging from 500 to 2000 eV. The ion irradiation remarkably reduced the surface roughness of the deposited films. Infrared spectroscopy showed that the absorption bands of the vinyl group diminish with increasing ion energy. Formation of polymer molecules was confirmed by gel permeation chromatograph. Moreover, the film became insoluble to organic solvents when the ion energy was increased. These results indicate that polymer thin films can be prepared by vapor deposition of monomers under ion irradiation. The ion-assisted vapor deposition polymerization was also possible on insulating substrates.

Violation of the additivity rule for the ion energy loss in hydrocarbons

Based on the experimental data, the rule of additivity of energy losses in hydrocarbon compounds is shown to be violated at low ion energies. This indicates the necessity of taking into account the chemical bonds in molecular targets. Deviation from the additivity rule increases with increasing nuclear charge of incident ions and decreases with increasing ion energy. The additivity rule is most strongly violated in the molecular targets with double and triple carbon-carbon bonds.

A study of the critical factor determining the size of etched latent tracks formed on SiO 2 glass by swift-Cl-ion irradiation

When a Cl ion with energy of the order of megaelectronvolts collides with SiO 2 glass, it penetrates the glass along a straight line. The region through which the ion passes and its vicinity, called the latent track, can be easily etched by hydrofluoric acid, resulting in the formation of a nanopore. With increasing ion energy, the nanopore radius first increases, reaches a maximum, and then decreases. In order to analyze this strange phenomenon, we investigated the radius of the region that melted upon ion irradiation, as one of the possible approaches. We calculated its radius using heat diffusion equations and compared it with the radius of nanopores. We found that both the radii depend on the ion energy in a similar manner.

3–10 keV Xe + ion beam machining of ultra low thermal expansion glasses for EUVL projection optics: Evaluation of surface roughness

In order to obtain surface figure error of 0.15 nm rms and surface roughness ( R rms ) of 0.12 nm rms for aspherical substrates in EUVL tools, ion beam figuring may be adopted to final surface figure error correction of aspherical substrates. During figure error correction, machined surface of the substrate becomes rougher than the pre-finished one. Therefore, we investigated the machined depth and ion energy dependences of R rms (measured by an AFM) of substrates machined by 3–10 keV Xe + ion beam, and compared them with the results obtained for Ar + ion beam. Result shows that the R rms s of CLEARCERAM®-Z, Zerodur® and ULE® substrates machined to the depth of 50 nm by 3–10 keV Xe + ion beam at the normal ion incidence angle become approximately 0.25, 0.28 and 0.15 nm rms, respectively. Those values are larger than the pre-finished substrates (0.07–0.09 nm rms), but smaller than that (0.60 nm rms for CLEARCERAM®-Z, 0.61 nm rms for Zerodur® and 0.18 nm rms for ULE®) of the substrates machined by Ar + ion beam. Moreover, the R rms s merely increase with increasing ion energy. The R rms s of the ULE® substrate machined by 3–10 keV Xe + ion beam rapidly increase with increasing machined depth, then saturate at machined depth of 10–50 nm. The saturated values of the R rms s are 0.12 and 0.15 nm rms for 3 and 10 keV Xe + ion beam respectively. We suggest that the 3 keV Xe + ion beam machining can be applicable for final shape correction of ULE® substrates for EUVL projection optics in association with considering further ultra smoothing process such as Si deposition or low energy ion beam smoothing.

Surface Roughening of Polystyrene and Poly(methyl methacrylate) in Ar/O2 Plasma Etching

Selectively plasma-etched polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer masks present a promising alternative for subsequent nanoscale patterning of underlying films. Because mask roughness can be detrimental to pattern transfer, this study examines roughness formation, with a focus on the role of cross-linking, during plasma etching of PS and PMMA. Variables include ion bombardment energy, polymer molecular weight and etch gas mixture. Roughness data support a proposed model in which surface roughness is attributed to polymer aggregation associated with cross-linking induced by energetic ion bombardment. In this model, RMS roughness peaks when cross-linking rates are comparable to chain scissioning rates, and drop to negligible levels for either very low or very high rates of cross-linking. Aggregation is minimal for very low rates of cross-linking, while very high rates produce a continuous cross-linked surface layer with low roughness. Molecular weight shows a negligible effect on roughness, while the introduction of H and F atoms suppresses roughness, apparently by terminating dangling bonds. For PS etched in Ar/O2 plasmas, roughness decreases with increasing ion energy are tentatively attributed to the formation of a continuous cross-linked layer, while roughness increases with ion energy for PMMA are attributed to increases in cross-linking from negligible to moderate levels.

Conductive and optical properties of PPV modified by N+ ion implantation

In this article, a soluble poly[2-methoxy-5-(3′-methyl)butoxy]-p-phenylene vinylene (MMB-PPV) was synthesized by dehydrochlorination reaction and the MMB-PPV film was implanted by nitrogen ions (N+) with the ion dose and energy in the range of 3.8 × 1015 to 9.6 × 1016 ions/cm2 and 15–35 keV, respectively. The surface conductivity, optical absorption, optical band gap (Eg) of modified MMB-PPV film were studied, and the third-order nonlinear optical susceptibility (χ(3)) as well as its environmental stability of modified MMB-PPV film were also measured by degenerate four-wave mixing system. The results showed that the surface conductivity of MMB-PPV film was up to 3.2 × 10−2 S when ion implantation was performed with the energy of 35 keV at an ion dose of 9.6 × 1016 ions/cm2, which was seven order of magnitude higher than that of the pristine film. UV-Vis absorption spectra demonstrated that the optical absorption of MMB-PPV film was enhanced gradually in the visible region followed by a red shift of optical absorption threshold and the Eg value was reduced from 2.12 eV to 1.59 eV with the increase of ion dose and energy. The maximum χ(3) value of 2.45 × 10−8 esu for modified MMB-PPV film was obtained with the ion energy of 20 keV at an ion dose of 3.8 × 1016 ions/cm2, which was almost 33 times larger than that for pristine film. In comparison to the reduction of 17% in the χ(3) value of pristine MMB-PPV film, the maximum χ(3) value of 2.45 × 10−8 esu for modified MMB-PPV film decreased by over 5.3% when they had been exposed under the same ambient conditions for 90 days. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2072–2077, 2010