Search

An experimental study of 0.5-5.0 keV-energy H+ ion scattering on Cu(100) has been presented at a grazing scattering angle of 7°. The velocity dependent ion fractions have been measured in this work. The positive-ion fraction increases with the increase of incident velocity, which can be described by the exponential scaling. In particular, the threshold velocity for the positive-ion fraction is observed at about 0.25 a.u., and explained by the Auger ionization process. The negative-ion fraction increases monotonically with the impact velocity, which can be explained by the first type of the parallel velocity effect. Considering the formation of positive ions and the contribution of the parallel velocity effect, the negative-ion fraction is calculated by the modified theoretical model and the general trend is consistent with the experimental data. [ABSTRACT FROM AUTHOR]

Resonant electron capture negative ion mass spectrometry (REC NI MS) is a highly informative method of investigation of low-energy electron-molecule reactions, thermochemistry, and kinetics of negative ion formation and decay. The review includes consideration of the physical principles and specific features of the method, a brief historical survey, terminological issues, and an outline of instrumentation. The potential of REC NI MS for solving structural and analytical problems is analyzed and the advantages of the method over classical positive ion MS are demonstrated. The results of analytical studies of organic and organoelement compounds using various types of mass spectrometers are reviewed. The reasons for low adoption of REC NI MS are analyzed and arguments are presented in favor of introducing the method into analytical practice as an additional tool implemented on the available instruments. Prospects for the development and improvement of REC NI MS for solving unconventional problems are discussed. [ABSTRACT FROM AUTHOR]

Abstract We have developed a gating foil for the time projection chamber envisaged as a central tracker for the international linear collider experiment. It has a structure similar to the Gas Electron Multiplier (GEM) with a higher optical aperture ratio and functions as an ion gate without gas amplification. The transmission rate for electrons was measured in a counting mode for a wide range of the voltages applied across the foil using an 55Fe source and a laser in the absence of a magnetic field. The blocking power of the foil against positive ions was estimated from the electron transmissions. [ABSTRACT FROM AUTHOR]

The frequency domain dielectric response method has been one of the most effective approaches for condition assessment of an electrical insulation system. The low‐frequency part is more effective for diagnosing the moisture content and aging status of oil‐paper insulation. To facilitate the study of the low‐frequency dielectric spectrum of oil‐paper insulation, a model applicable to the low‐frequency dielectric response of insulation oil is proposed in this study, which is based on the ionic motion of insulation oil. The creation of charge carriers under field test conditions mainly derives from the dissociation of ionic pairs. During testing, ionic motion of insulation oil is jointly affected by thermal diffusion and the electric field; moreover, dissociation and recombination of negative and positive ions also occur. Therefore, the above factors were all considered in the modelling process. The applicability of the model is verified against measured results. For further interpreting the proposed model, the characteristics of the ionic concentration distribution, the relation between ionic distribution and dielectric properties, and the application of the proposed model are analysed. [ABSTRACT FROM AUTHOR]

The use of zinc oxide (ZnO) nanoparticles (NPs) for cancer is not yet clear for human clinical applications, which is primarily due to the lack of a better understanding of the action mechanisms and cellular consequences of the direct exposure of cells to these NPs. In this work, the authors have selected zinquin ethyl ester, a Zn2+ ‐specific fluorescent molecular probe, to efficiently differentiate ZnO NPs and Zn2+, and combined with confocal laser scanning microscopy (CLSM) to in situ study the Zn2+ release process of ZnO NPs in cancer cell system through detecting the change of Zn2+ level over time. During the experiments, the authors have designed the test group ZnO‐2 in addition to assess the influence of a long‐term storage on the characteristics of ZnO NPs in aqueous solution, and the Zn2+ release process of ZnO NPs in cancer cell system. After three‐month storage at room temperature, the release process became earlier and faster, which was consistent with previous results of transmission electron microscope, UV‐Vis and PL spectra. It is a good detection method that combination of Zn2+ ‐specific fluorescent molecular probe and CLSM, which will be helpful for ZnO NPs using in clinical research. [ABSTRACT FROM AUTHOR]

The purpose of this study was to design a targeted anti‐cancer drug delivery system for breast cancer. Therefore, doxorubicin (DOX) loaded poly(methyl vinyl ether maleic acid) nanoparticles (NPs) were prepared by ionic cross‐linking method using Zn2+ ions. To optimise the effect of DOX/polymer ratio, Zn/polymer ratio, and stirrer rate a full factorial design was used and their effects on particle size, zeta potential, loading efficiency (LE, %), and release efficiency in 72 h (RE72, %) were studied. Targeted NPs were prepared by chemical coating of tiptorelin/polyallylamin conjugate on the surface of NPs by using 1‐ethyl‐3‐(3‐dimethylaminopropyl) carboiimid HCl as cross‐linking agent. Conjugation efficiency was measured by Bradford assay. Conjugated triptorelin and targeted NPs were studied by Fourier‐transform infrared spectroscopy (FTIR). The cytotoxicity of DOX loaded in targeted NPs and non‐targeted ones were studied on MCF‐7 cells which overexpress luteinizing hormone‐releasing hormone (LHRH) receptors and SKOV3 cells as negative LHRH receptors using Thiazolyl blue tetrazolium bromide assay. The best results obtained from NPs prepared by DOX/polymer ratio of 5%, Zn/polymer ratio of 50%, and stirrer rate of 960 rpm. FTIR spectrum confirmed successful conjugation of triptorelin to NPs. The conjugation efficiency was about 70%. The targeted NPs showed significantly less IC50 for MCF‐7 cells compared to free DOX and non‐targeted NPs. [ABSTRACT FROM AUTHOR]

The purpose of this research is to create a laboratory model of comet phenomenon and perform mass spectral analysis of the dynamics and rate of formation of complex ions by bombarding the solid mixture of H 2 O and CO 2 with positive Cs ions with energy of 1.5 keV. Results of previous mass spectral studies of laboratory modeled comet phenomena and emission coefficient proportionality method were used in calculations. [ABSTRACT FROM AUTHOR]

High-power impulse magnetron sputtering with a pulsed reactive gas (oxygen) flow control was used for high-rate reactive depositions of densified, highly optically transparent, stoichiometric ZrO 2 films onto floating substrates. The depositions were performed using a strongly unbalanced magnetron with a directly water-cooled planar Zr target of 100 mm diameter in argon–oxygen gas mixtures at the argon pressure of 2 Pa. The repetition frequency was 500 Hz at the deposition-averaged target power density from 5 Wcm −2 to 53 Wcm −2 . The voltage pulse durations ranged from 50 μs to 200 μs. The target-to-substrate distance was 100 mm. An optimized location of the oxygen gas inlets in front of the target and their orientation toward the substrate made it possible to improve the quality of the films due to minimized arcing at the sputtered target and to enhance their deposition rates up to 120 nm/min at the deposition-averaged target power density of 52 Wcm −2 , a voltage pulse duration of 200 μs and a substrate temperature less than 120 °C. The films exhibited a hardness of 16 GPa, a refractive index of 2.19 and an extinction coefficient of 2 × 10 −3 (both at the wavelength of 550 nm). Under these optimized conditions, we measured the highest (Zr + + Zr 2+ ) and ( O 2 + + O + ) ion fractions in the total fluxes of positive ions, and a low population of high-energy O − ions at the substrate position. [ABSTRACT FROM AUTHOR]

Abstract: Amorphous indium–zinc-oxide films were deposited in the “transition region” by reactive sputtering using an In–Zn alloy target with a specially designed double feedback system. The cathode voltage showed a V- and circle-shaped curve as a function of O2 gas flow in the transition region, which differs from the S-shaped curve in Berg's model for reactive sputtering depositions. In-situ analyses with a quadrupole mass spectrometer combined with an energy analyzer revealed that the negative ions O−, O2 −, InO−, and InO2 −, with high kinetic energies corresponding to the cathode voltage, were generated at the partially oxidized target surface. Furthermore the positive ions O+, Ar+, In+, and Zn+ with rather low kinetic energies (around 10eV) were confirmed to be generated by the charge exchange of sputtered neutral O, Ar, In and Zn atoms, respectively. [Copyright &y& Elsevier]

Abstract: This paper reports the measurements of dc cathode sheath thickness d together with the voltage drop U across it at different current I values in nitrogen. For the case of a narrow gap when the discharge consists only of a cathode sheath and a negative glow almost all voltage applied across the electrodes drops across the cathode sheath. We observe that at the nitrogen pressure p < 1 Torr, as well as for p > 1.5 Torr the Child–Langmuir collision law version characterized by the constant ion mobility is valid. Within the pressure range of 1 < p < 1.5 Torr none of Child–Langmuir law versions (with a constant mobility or a constant ion mean free path) are applicable for the description of the dc cathode sheath in nitrogen. The available references enable us to conclude that at p < 1 Torr the discharge is dominated by N+ ions whereas for p > 1.5 Torr ions dominate. These ions are not prone to charge exchange with N2 molecules and they move in the dc cathode sheath with constant mobility. Within the pressure range of 1 < p < 1.5 Torr the discharge contains N+, N2 +, and ions in comparable concentrations therefore none of the Child–Langmuir law versions can be valid. [Copyright &y& Elsevier]

Purpose: The activator ion (Eu2+ in KCl:Eu2+) plays an important role in the photostimulated luminescence (PSL) mechanism of storage phosphor radiation detectors. In order to design an accurate, effective, and robust detector, it is important to understand how the activator ion concentration affects the structure and, consequently, radiation detection properties of KCl:Eu2+. Methods: Potassium chloride pellets were fabricated with various amounts of europium dopant (0.01-5.0 mol.% Eu2+). Clinical radiation doses were given with a 6 MV linear accelerator. Radiation doses larger than 100 Gy were given with a 137Cs irradiator. Dose response curves, radiation hardness, and temporal signal stability were measured using a laboratory PSL readout system. The crystal structure of the material was studied using x ray diffraction and luminescence spectroscopy. Results: The most intense PSL signal was from samples with 1.0 mol.% Eu. However, samples with concentrations higher than 0.05 mol.% Eu exhibited significant degradation in PSL intensity for cumulated doses larger than 3000 Gy. Structural and luminescence spectroscopy showed clear evidence of precipitate phases within the KCl lattice, especially for high activator concentrations. Analysis of PL emission spectra showed that interactions between Eu-Vc dipoles and Eu-Vc trimers could explain trends in PSL sensitivity and radiation hardness observations. Conclusions: The concentration of the activator ion (Eu2+) significantly affects radiation detection properties of the storage phosphor KCl:Eu2+. An activator concentration between 0.01 and 0.05 mol.% Eu in KCl:Eu2+ storage phosphor detectors is recommended for linear dose response, good PSL sensitivity, predictable temporal stability, and high reusability for megavoltage radiation detection. [ABSTRACT FROM AUTHOR]

Purpose: The LIonTrack (Light Ion Track) Monte Carlo (MC) code for the simulation of H+, He2+, and other light ions in liquid water is presented together with the results of a novel investigation of energy-deposition site properties from single ion tracks. Methods: The continuum distorted-wave formalism with the eikonal initial state approximation (CDW-EIS) is employed to generate the initial energy and angle of the electrons emitted in ionizing collisions of the ions with H2O molecules. The model of Dingfelder et al. ['Electron inelastic-scattering cross sections in liquid water,' Radiat. Phys. Chem. 53, 1-18 (1998); 'Comparisons of calculations with PARTRAC and NOREC: Transport of electrons in liquid water,' Radiat. Res. 169, 584-594 (2008)] is linked to the general-purpose MC code PENELOPE/penEasy to simulate the inelastic interactions of the secondary electrons in liquid water. In this way, the extended PENELOPE/penEasy code may provide an improved description of the 3D distribution of energy deposits (EDs), making it suitable for applications at the micrometer and nanometer scales. Results: Single-ionization cross sections calculated with the ab initio CDW-EIS formalism are compared to available experimental values, some of them reported very recently, and the theoretical electronic stopping powers are benchmarked against those recommended by the ICRU. The authors also analyze distinct aspects of the spatial patterns of EDs, such as the frequency of nearest-neighbor distances for various radiation qualities, and the variation of the mean specific energy imparted in nanoscopic targets located around the track. For 1 MeV/u particles, the C6+ ions generate about 15 times more clusters of six EDs within an ED distance of 3 nm than H+. Conclusions: On average clusters of two to three EDs for 1 MeV/u H+ and clusters of four to five EDs for 1 MeV/u C6+ could be expected for a modeling double strand break distance of 3.4 nm. [ABSTRACT FROM AUTHOR]

Purpose: Fricke-infused gel has been shown to be a simple and attainable method for the conformal measurement of absorbed radiation dose. Nevertheless, its accuracy is seriously hindered by the irreversible ferric ion diffusion during magnetic resonance imaging, particularly when three-dimensional (3D) dose measurement in radiosurgery is considered. In this study, the authors developed a fast three-dimensional spin-echo based Fricke gel dosimetry technique to reduce the adverse effects of ferric ion diffusion and to obtain an accurate isotropic 3D dose measurement. Methods: A skull shaped phantom containing Fricke-infused gel was irradiated using Leksell Gamma Knife. The rapid image-based dosimetry technique was applied with the use of a 3D fast spin-echo magnetic resonance imaging sequence. The authors mathematically derived and experimentally validated the correlations between dose-response characteristics and parameters of the 3D fast spin-echo MR imaging sequence. Absorbed dose profiles were assessed and compared to the calculated profiles given by the Gamma Knife treatment planning system. Coefficient of variance (CV%) and coefficient of determination (R2) were used to evaluate the precision of dose-response curve estimation. The agreement between the measured and the planned 3D dose distributions was quantified by gamma-index analysis of two acceptance criteria. Results: Proper magnetic resonance imaging parameters were explored to render an accurate three-dimensional absorbed dose mapping with a 1 mm3 isotropic image resolution. The efficacy of the dose-response estimation was approved by an R2 > 0.99 and an average CV% of 1.6%. Average gamma pass-rate between the experimentally measured and GammaPlan calculated dose distributions were 83.8% and 99.7% for 2%/2 and 3%/3 mm criteria, respectively. Conclusions: With the designed MR imaging sequence and parameters, total 3D MR acquisition time was confined to within 20 min postirradiation, during which time ferric ion diffusion effects were negligible, thus enabling an accurate 3D radiation dose measurement. [ABSTRACT FROM AUTHOR]

A bipolar high-voltage pulse with 20-ns rising time is employed to generate diffuse dielectric-barrier-discharge plasma with very low gas temperature in both nitrogen and air using a wire-plate electrode configuration at atmospheric pressure. Both the diffuse nanosecond pulsed discharge images and the optical emission spectra are recorded successfully. The gas temperatures of the nitrogen and air discharge plasmas are determined at 400 ± 5 K and 320 ± 5 K. The effects of discharge gap distance, pulse peak voltage, and pulse repetition rate on the emission intensities of NO (A2Σ→ X2Π), OH (A2Σ→ X2Π, 0 - 0) , N2 (C3Πu → B3Πg) , and N2+(B2Σu+ → X2 Σg+, 0 - 0, 391.4 nm) in both nitrogen and air are investigated, respectively. The effects of O2 and Ar on discharge images and the emission intensities in nitrogen are obtained. It is found that the emission intensities rise with increasing pulse peak voltage, pulse repetition rate, and the concentration of argon but decrease with increasing the discharge gap distance and the concentration of oxygen. The main physicochemical processes involved are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Boron produced in plasma devices continues to be the main p-type dopant in ion implantation of semiconductor devices. Yet plasma parameters of most frequently used Boron rich gas, BF3, are not well established. Time resolved measurements of ion energy distributions in the cathode boundary of a pulsed dc plasma doping system revealed possible role of the charge-transfer collisions between singly charged ions of various mass. The cross sections for scattering of B+, BF+ and ions on BF3 molecule are calculated by using Nanbu’s theory separating elastic from reactive collisions. A Monte Carlo simulation technique was applied to perform calculations of transport parameters in DC electric fields. [Copyright &y& Elsevier]

Abstract: Using a quadrupole mass spectrometer combined with an energy analyser, we have investigated the in-situ energy distribution of highly energetic ions generated during reactive sputtering of In–Sn alloy (IT) targets and non-reactive sputtering of Sn-doped In2O3 (ITO) ceramic targets. Ar+, In+, O+, O−, O2 −, InO− and InO2 − ions with kinetic energies greater than 40eV were clearly observed. Upon increasing the O2 flow ratio for reactive sputtering, the surface of the IT target changes from metal (metal mode) to oxide (oxide mode) via a state of mixed metal and oxide (transition region). O− ions with the kinetic energy corresponding to cathode voltage are generated at the oxide layer, which expands upon the target surface with increasing O2 flow ratio in the metal mode and the transition region. In contrast, the flux of 60-eV Ar+ ions decreases with increasing O2 flow ratio. The presence of 125- and 200-eV In+ ions is attributed to the dissociation of InSnO2 − and InO2 − with the kinetic energy corresponding to cathode voltage, respectively, while the presence of 40- and 150-eV O+ ions is attributed to the dissociation of InO2 − and O2 − with the kinetic energy corresponding to cathode voltage, respectively. [Copyright &y& Elsevier]

Abstract: Ionic desorption from polypyrrole films doped with dodecylsulfate as counter anion (PPyDS) deposited onto fluorine tin oxide glass (FTO) was studied through electron (ESID) and photon (PSID) stimulated ion desorption techniques, employing time-of-flight mass spectrometry (TOF-MS) for ion analysis. ESID results suggested strong contribution from DS fragments to the mass spectra. In the 650–1500eV energy range the relative desorption ion yield curves show maxima at about 700, 1200 and 1400eV, which may be related to carbon, nitrogen and oxygen containing fragments, respectively, and interpreted in terms of the Auger stimulated ion desorption (ASID) mechanism. For energies greater than 1500eV, the secondary electrons play an important role in the ion formation. PSID studies were performed at the Brazilian Synchrotron Light Source (LNLS) covering the sulphur K-shell photoexcitation during a single-bunch operation mode of the storage ring. Ionic desorption of atomic and molecular fragments were also observed. Relative desorption ion yield curves have been determined as a function of the photon energy, indicating that at the photon energy region covered by the PSID studies the indirect XESD (X-ray induced electron stimulated desorption) process plays an important role in the ionic desorption of PPyDS irradiated by soft X-rays. [Copyright &y& Elsevier]

Abstract: Positive photoresists are widely used in lithographic process for the fabrication of relief components. When exposed to UV radiation they suffer chemical reactions modifying their chemical and physical properties. Aiming to follow molecular modifications among two different photoresists unexposed and previously exposed to ultraviolet light we have employed spectroscopic techniques coupled with mass spectrometry in the study of the AZ-1518 and AZ-4620 photoresists. The photon stimulated ion desorption (PSID) technique following the S K-edge NEXAFS spectrum was employed at the brazilian synchrotron light source (LNLS), during single-bunch operation and using time-of-flight mass spectrometry (TOF-MS) for ion analysis. NEXAFS and PSID mass spectra on both AZ-1518 and AZ-4620 photoresists (unexposed and exposed) were obtained and relative desorption ion yield curves determined for the main fragments as a function of the photon energy. They present marked different PSID spectra. Fragments related to the photochemical decomposition of the AZ-1518 photoresist could be clearly identified differently from the AZ-4620. Studies on the hardness of both photoresists were performed using plasma reactive ion etching (RIE) technique, analyzed by scanning electron microscopy (SEM) and used to explain different desorption yields in the PSID spectra. These results show that the PSID technique is adequate to investigate structural changes in molecular level in different unexposed and exposed photoresists, which is crucial for improving our knowledge about the breakup process. [Copyright &y& Elsevier]

The inelastic collisions of positrons with calcium and strontium positive ions are treated for the first time as a three-channel problem within the framework of the improved coupled-static and frozen-core approximations with the assumption that the elastic, ground positronium and excited-positronium formation channels are open. The calculations of the partial and total cross sections are carried out for eight values of the total angular momentum ℓ (0 ≤ ℓ ≤7), at 20 values of the incident energy lying above the excited positronium formation threshold and extending to a wide region above the ionization threshold of the target ion. The total collisional positronium formation cross sections of e+–Sr+ scattering show a peak around the ionization threshold of Sr+ but display a peak at 30 eV for e+–Ca+ scattering. In both scattering problems the total excited Ps formation cross sections have considerable values in the energy range $15\, {\rm eV}\le k_1^2 \le 100\, {\rm eV}$. [ABSTRACT FROM AUTHOR]

Abstract: A critical review of the available experimental data on Stark widths and shifts for spectral lines of non-hydrogenic neutral atoms and positive ions has been carried out. The review covers the period from 2001 through the end of 2007 and represents a continuation of earlier critical reviews up to 2000. Data tables containing the selected experimental Stark broadening parameters are presented with estimated accuracy. Guidelines for the accuracy estimates, developed during the previous reviews, are summarized again. The data are arranged according to elements and spectra, and these are presented in alphabetical and numerical order, respectively. A total of 41 spectra are covered. Comparisons with comprehensive calculations based on semi-classical theory or on semi-empirical method are made whenever possible, since the comparison with theory has often been a principal motivation for the experiments. [Copyright &y& Elsevier]

Continuously sampling a flame, burning at 1 atm., for mass spectrometry at ≈ 10–8 atm. seriously disturbs the flame. Not only are a flame's temperature and velocity altered, often the composition of a sample is falsified. Thus, "fake" ions appear, even when sampling as quickly as possible, i.e. supersonically, to quench chemical reactions. However, studying these spurious ions is fruitful. They arise, because a sample is unavoidably cooled; the drop in temperature causes a rapid chemical equilibrium to shift position and change the sample's composition. That ions react faster than neutrals (to perturb a sample) magnifies the problem for ions. When continuously sampling a flame, burning at 1 atm., through an inlet at the tip of a hollow, metallic nozzle, cooling can occur in three ways during the formation of a beam for mass spectrometry. Firstly, before a sample passes through the inlet hole to enter the supersonic expansion into the first vacuum chamber of the mass spectrometer, it loses heat to the cooler, sampling nozzle, usually conical in shape. By detecting spurious ions from a flame, this drop in temperature has been measured to be greatest (≈ 400 K) for the smallest orifices. This cooling becomes smaller for larger holes and is trivial for diameters above 150 µm. Secondly, a sample cools (by maybe ≈ 300 K), whatever the orifice's size, on being accelerated to the local speed of sound in the narrowest part, i.e. the throat of the inlet orifice. Thirdly, the drop in temperature in the subsequent, near-adiabatic expansion inside the nozzle is greatest (≈ 1000 K) and most prolonged for the largest inlet holes (diam. > 150 µm). The upshot is that with a small hole (diam. < 100 µm), a sample is cooled by both the sampling nozzle and the acceleration to sonic velocity in the throat of the inlet. However, with a large orifice (diam. > 150 µm), cooling happens in the acceleration to a Mach number of unity and the following supersonic expansion. Analysis shows that, if a positive ion reacts exothermally in a reversible reaction with a time constant briefer than ≈ 0.5 µs, that reaction will be equilibrated early in the flame. In addition, if the orifice is small, the equilibrium will be just fast enough to shift position to that for a temperature reduced in both the thermal boundary layer around the inlet, and in accelerating to the speed of sound. Consequently, the sample begins the expansion with new species. When using a big orifice, the reaction's time constant (in the flame) must be less than ≈ 0.05 µs (depending on the flame) to generate new ions in the supersonic expansion. It follows that, if there is not an exothermic chemical reaction with a time constant less than ≈ 0.5 µs, sampling is most probably genuine. A similar criterion usually means that no fake neutral species are observed in a low-pressure flame. Negative ions are complicated by their reactions often involving free electrons. Being mobile, they often leave a sample to attach to the metallic sampling nozzle. This loss of free electrons changes the ionic composition, because rapid, steady-state relationships for individual negative ions are thereby shifted, with the change in composition depending on the orifice's size. A theme of this review is that these problems can be identified and resolved by repeating observations using sampling orifices with a range of different diameters. The resulting measurements are then extrapolated to a hole size of either zero or infinity, when there is no effect of a perturbation in either the expansion or the boundary layer; this yields a measurement, e.g. of an equilibrium constant, for the known conditions in the neck of the orifice. In addition, applying a voltage between the burner and the sampling nozzle considerably improves the accuracy, with which ionic concentrations are measured. Consequently, many rapid reactions have had their equilibrium constants measured, yielding the proton affinities of e.g. H 2 O, CO, CO 2 and NH 3 , the hydration energies of many ions, the stability of ions like MnOH+ (resulting from seeding a flame with Mn) and also the standard changes of enthalpy and entropy for e.g. OH– + CO 2 + M = HCO 3 – + M and HCO 3 – + OH = CO 3 – + H 2 O. In addition, rate constants have been deduced for reactions like the mono-hydration of H 3 O+, for LiOH + H 3 O+ → Li+ + H 2 O and Li+ + CO + M → Li+.CO + M, as well as those for the forward and reverse steps in: e– + O 2 + M ⇄ O 2 – + M, Cl– + H ⇄ HCl + e–, O 2 – + H ← → HO 2 + e– and O 2 – + OH ← → OH– + O 2. The design of mass spectrometers was discussed, as well as the sampling of neutral species. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: With the aim of identifying molecular modifications among photoresists unexposed and previously exposed to the ultraviolet light the photon stimulated ion desorption (PSID) technique was employed in the study of the AZ-1518 photoresist. Data acquisition was performed at the Brazilian Synchrotron Light Source (LNLS), during a single-bunch operation mode of the storage ring and using high-resolution time-of-flight mass spectrometry (TOF-MS) for ion analysis. PSID mass spectra on both photoresists (unexposed and exposed) were obtained following the S K-shell photoexcitation and desorption ion yield curves have been determined for the main fragments as a function of the photon energy. The AZ-1518 photoresists presented different PSID spectra, showing characteristic fragments. Most of the analyzed ions showed larger relative yields for the exposed photoresist. Fragments related to the photochemical decomposition of the photoresist could be clearly identified. These results showed that the PSID technique is adequate to investigate structural changes in molecular level in unexposed and exposed photoresists. [Copyright &y& Elsevier]

The collision of positrons with beryllium and magnesium positive ions is treated for the first time as a three-channel problem with the assumption that the elastic, ground-positronium and excited-positronium formation channels are open. A one-valence-electron model for the targets, based on the Clementi–Roetti Slater basis functions, as well as an improved coupled-static approach allowing for the polarization of the excited positronium, are used for calculating the partial cross-sections of eight partial waves (corresponding to 0≤ℓ≤7, where ℓ is the total angular momentum of the scattering problem considered). The calculations are carried out, in each case, at 19 values of the incident energy lying above the excited positronium formation threshold (i.e. above 16.42 eV in e+–Be+ scattering and above 13.02 eV in e+–Mg+ scattering). The total elastic cross-sections of e+–Mg+ scattering show a peak around the ionization threshold of Mg+ (at 14.723 eV) but for e+–Be+ scattering, display a peak at 90 eV (remember that the ionization threshold of Be+ is 18.2 eV). Although the resulting total collisional positronium formation cross-sections are smaller than the elastic ones, their relatively large values should draw the attention of experimental and theoretical physicists to the field of positron–ion collisions. [ABSTRACT FROM AUTHOR]

Abstract: With the aim of performing time-of-flight studies of electron stimulated ion desorption (ESID) from polymers bombarded with a variable energy electron beam source, an experimental set-up including a homemade time-of-flight mass spectrometer has been developed for positive and negative ion analysis. This system uses as a trigger for the experiments either the pulsed electron beam or the pulsed (positive/negative) extraction high voltage applied to the sample. Results for both positive and negative ion desorption from poly(vinyl chloride) (PVC) obtained in ESID measurements with these two different modes of operation will be presented and discussed. [Copyright &y& Elsevier]

Elastic collision cross-sections for Xe+ ions with neutral Xe atoms are calculated using a modified Tang-Toennies ion-atom potential and a semi-classical approximation with phase shifts calculated by the Jeffreys-Wentzel-Kramers-Brillouin approximation. Results are presented for integral and differential cross sections at center-of-mass energies in the 1 meV to 10 eV energy range. The cross sections were then used to calculate the drift velocities and diffusion coefficients of Xe+ ions in gaseous xenon at atmospheric pressures and reduced electric fields, E/N, in the 3 to 300 Td range (N is the neutral gas number density and 1 Td=10-17 Vcm2 ) using Monte Carlo technique. The results obtained are compared and discussed with limited experimental data available from previous studies [ABSTRACT FROM PUBLISHER]

The role of positive gaseous ions in the formation of secondary electron images in low vacuum scanning electron microscopes is discussed. This paper describes the charging processes and related effects that occur during high vacuum imaging of insulators and then discusses the influence of ions on those processes. The ions are responsible for a number of phenomena, including distortion of the electric field above and below the specimen surface due to space charge, removal of excess negative charge from the specimen, alteration of the specimen surface barrier, and scavenging/filtering of the secondary electron emission. The resulting electron-specimen-ion interactions can give rise to interesting contrast effects that are unique to this class of instruments. [ABSTRACT FROM AUTHOR]

This paper presents a discussion of the discharge formation mechanism for a pseudospark switch at the conditions when the discharge is initiated by an ion beam ejected from the anode side. Experimental data show that the switch is triggered only in case when the cathode has a cavity. Then, the major factor effecting in the discharge initiation is the space charge of positive ions, which forms in the cavity. Due to this charge, the electric field is distorted in such a manner that a potential trap for secondary cathode electrons appears and the oscillatory motion of electrons provides for intense generation of plasma inside the cavity. The hollow cathode plasma serves as a source of an electron beam for the main gap, so that the switch is finally triggered under the effect of this beam [ABSTRACT FROM PUBLISHER]

Abstract: Using our collection of experimental data for ions from 18Ar to 92U, the reliability of various stopping tables is estimated by comparing them statistically to these data. For solid elements beyond 100MeV/nucleon, Lindhard–Sørensen is found best; between 30 and 100MeV/n, SRIM and Hubert are slightly better. Below 30MeV/n, on the average, SRIM is 6% high in heavy targets and 5% low in light targets. In that range, Hubert is better, and sometimes also CasP 4.0. CasP describes the “positive” solid–gas effect. SRIM does not; it is therefore too high for gases near the maximum. For solid compounds, there are larger deviations from SRIM than for elements. For gaseous compounds, SRIM is too high, as for gaseous elements. But SRIM describes all ions at all energies in all targets, and is best in most cases. [Copyright &y& Elsevier]