Parallel Plate Electrostatic Analyzer Research Articles

Energy and angular distributions of electrons ejected from CH4 and C3H8 under 16.0 keV electron impact

Relative cross sections, differential in energy and angle, for electrons ejected from CH4 and C3H8 molecules under 16.0 keV electron impact have been measured. Electrons were analyzed by a 45° parallel plate electrostatic analyzer at emission angles varying from 60° to 135° with energies from 50 eV to 1000 eV. The angular distributions of electrons exhibit structures which are found to arise from Coulomb and non-Coulomb interactions. Furthermore, the double differential cross sections of electrons ejected from C3H8 molecule are found to be higher in magnitude than those from CH4. This result supports the fact that the number of ejected electrons participating in collisions with C3H8 molecules is more than that in CH4. Also, the angular distributions of C-K-shell Auger electrons emitted from the target molecules have been studied and shown to be isotropic within the experimental uncertainty

Development of a new experimental setup for studying collisions of keV-electrons with thick and thin targets

Development of a new lectron-recoil ion/photon coincidence setup for investigating some of the electron induced collision processes, such as electron bremsstrahlung, electron backscattering, innershell excitation and multiple ionization of target atoms/molecules in bombardment of electrons having energies from 2.0 keV to 30.0 keV with solid and gaseous targets is described. The new features include the use of a compact multipurpose scattering chamber, a time-of-flight spectrometer for detection of multiply charged target ions, a 45°-parallel plate electrostatic analyzer for measuring energy and angle of the ejected electrons, a room temperature high resolution Si-PIN photo diode X-ray detector for counting the collisionally induced photons, a coincidence data acquisition system consisting of a 200 MHz Pentium based 8K-multichannel analyzer and a standard network of a fast/slow coincidence electronics. In particular, the details of design, fabrication and assembly of indigenous components employed in the setup are presented. Selected experiments planned with the setup are mentioned and briefly discussed. A report on performance, optimization, efficiency, time resolution etc. of the time-of-flight (TOF) spectrometer and that of the 45°-parallel plate electrostatic analyzer (PPEA) is presented. Test spectra of electron-recoil ion coincidences, energy distribution of ejected electrons and characteristic plus non-characteristic X-ray spectrum are illustrated to exhibit the satisfactory performance of the developed setup.

Mesh effect in a parallel-plate analyzer

The effect of field irregularity due to the use of conducting meshes to cover holes of a lower electrode in a parallel-plate electrostatic analyzer, is experimentally and numerically investigated. Displacement of a focal point and degradation of analyzer characteristics are found in the experiment. Dependence of analyzer characteristics on wire spacing is obtained. Primary results are also confirmed by numerical analysis. Criteria for error estimation are theoretically derived and found to be consistent with the experiment.

Dissociative photoionisation of H 2 AT 27–40 eV

A new apparatus has been developed to study the dissociative photoionisation of H 2 molecules using synchrotron radiation. A parallel-plate electrostatic analyser equipped with a micro-channel plate/position-sensitive detector system was used to improve the detection efficiency in this measurement. The H + kinetic energy distribution was measured in the photon energy region 27–40 eV. Below the threshold energy of the H 2 + 2pσ u state, the production of slow protons with ≈ 3 eV through the Q 1 states, converging to the H 2 + 2pπ u state, was seen at 34–36 eV. We detected the fast protons produced from the direct ionisation to the well known 2pσ u, 2pπ u and 2sσ g repulsive H 2 + states.

Molecular effects in carbon K-shell Auger-electron production by 0.6–2.0 MeV protons and extraction of an atomic cross section

Carbon K-shell Auger-electron production cross sections are reported for 0.6–2.0 MeV protons incident on CH 4 (methane), C 2H 2 (acetylene), C 2H 4 (ethylene), C 2H 6 (ethane), nC 4H 10 (normal butane), i-C 4H 10 (isobutane), C 6H 6 (b monoxide), and CO 2 (carbon dioxide). A constant-energy mode 45° parallel-plate electrostatic analyzer was used for detection of Auger electrons. The carbon KLL Auger-electron cross sections for all molecules were found to be lower than that found for CH 4 by 9–23%. All carbon KLL Auger-electron data could be brought into agreement when corrected for the chemical shift of the carbon K-shell binding energy in molecules and for intramolecular scattering. KLL Auger-electron production cross sections are compared to first Born and ECPSSR theories and show good agreement with both after the chemical shift of the carbon K-shell binding energy in molecules and the effects of intramolecular scattering are considered.

Carbon K-shell x-ray and Auger-electron production in hydrocarbons and carbon oxides by 0.6-2.0-MeV protons.

Carbon K-shell x-ray and Auger-electron-production cross sections are reported for 0.6--2.0-MeV protons incident on ${\mathrm{CH}}_{4}$ (methane), ${\mathrm{C}}_{2}$${\mathrm{H}}_{2}$ (acetylene), n-${\mathrm{C}}_{4}$${\mathrm{H}}_{10}$ (normal butane), i-${\mathrm{C}}_{4}$${\mathrm{H}}_{10}$ (isobutane), ${\mathrm{C}}_{6}$${\mathrm{H}}_{6}$ (benzene), CO, and ${\mathrm{CO}}_{2}$. A variable-geometry end-window proportional counter with an alternate procedure for the determination of its transmission was used in collection of the x-ray data. A constant-energy-mode \ensuremath{\pi}/4 parallel-plate electrostatic analyzer served in the detection of Auger electrons. K-shell Auger-electron-production cross sections are compared with the predictions of the first Born theory and the perturbed-stationary-state theory which accounts for energy-loss, Coulomb deflection, and relativistic effects (ECPSSR). These data show fair agreement with the ECPSSR theory when the chemical shifts, of the carbon K-shell binding energy in molecules, are included in the calculations. This agreement is even better after effects of intramolecular scattering are considered. Validity of the geometrical model by Matthews and Hopkins [Phys. Rev. Lett. 40, 1326 (1978)] is established after a scrutiny of the inelastic cross sections for scattering of Auger-electrons within the molecule and their effective dislocation out of the detector's window. The x-ray cross sections show particularly strong variations with the target molecular species because of additional changes due to modifications in the fluorescence yields for molecular carbon. The correlation of these changes with the molecular character of carbon and a scaling procedure for the fluorescence yields in molecules will be discussed elsewhere.

Double parallel-plate electrostatic analyzer for Tara end-loss studies

An endloss spectrograph has been designed and is being fabricated for the Tara tandem mirror. This spectrograph is a double parallel-plate electrostatic analyzer about 60 cm in length with a 30° entrance angle; the high-voltage plate is a transparent wire cloth grid which allows higher energy particles to pass through for detection on a symmetric ground plane. The analyzer has three detection planes: first, the normal focal plane for low-energy detection at high resolution (0.1–4 keV); second, the entrance grounded plate for mid energies (4–6 keV); and third, the symmetric ground plane for coarse resolution at higher energies (8–20 keV). The analyzer is defocusing on the symmetric plane. This spectrograph will be able to measure simultaneously the endloss potential cutoff and ions from the neutral beams; in conjunction with a loss cone neutral beam source the resolution is sufficient (60 eV) to measure the plasma potential.

Electron loss to the continuum for H2+and He+ions colliding with H2, He, Ne and Ar. I. Electron cusp widths and shapes

Differential spectra for electron production in the forward direction have been obtained by collision of H2+ and He+ ions with H2, He, Ne and Ar gases. The measurements where made with ions of energy 0.8-2.8 MeV. The target consisted of a jet of gas from a multicapillary array, thereby providing a well localised and directed gas beam. A 30 degrees parallel-plate electrostatic analyser having a FWHM resolution (dE/E)=10-3 was used to study the energy of the ejected electrons. A cusp-shaped peak centred on ve=vi was observed for all the electron spectra, suggesting that these electrons were ejected with only a small energy relative to the parent ions. This process has been called electron loss to the continuum (ELC) since in some ways it mimics the now well established phenomenon of charge exchange to the continuum (CEC). In contrast to data for ELC from heavy ions the cusps observed here were generally asymmetric. They did, however, show a width approximately independent of projectile velocity, a feature which seems to distinguish ELC from CEC. Both the cusp shapes and widths are compared with theoretical predictions and other experimental measurements.

Angular and energy dependence of cross sections for ejection of electrons from water vapor. I. 50-2000-eV electron impact.

We have measured the angular and energy distribution of the absolute cross sections for ejection of electrons from water vapor by electrons incident at 50--2000 eV. The angular range was 15\ifmmode^\circ\else\textdegree\fi{} to 150\ifmmode^\circ\else\textdegree\fi{} and the range of secondary electron energies was from 2 eV to an energy equal to the primary energy minus the first ionization potential. Electron energies were analyzed with a parallel-plate electrostatic analyzer with a resolution of 1.1%. Generally good agreement is obtained with the data of Opal et al. [J. Chem. Phys. 55, 4100 (1971)] at 500 eV except at the extremes of their angular range. Our energy distributions are compared to various binary-encounter-model calculations.

An electrostatic spectrometer for a simultaneous analysis of energy and scattering angle

A simple device is described, allowing the simultaneous analysis of the energy and the scattering angle of low-energy (eV-keV) particles. This spectrometer uses a two-dimensional position-sensitive detector associated with a parallel-plate electrostatic analyser. A high resolution is obtained, both in the angle (d theta <0.1 degrees ) and energy(dE/E=2*10-4) providing an accurate tool to probe small-angle scattering processes.

Reduction of Doppler broadening in the Auger electron spectra of fast ion beams: on the refocusing properties of a parallel-plate electrostatic analyser

For a parallel-plate electrostatic analyser, the authors obtain an analytical expression for the optimum exit-slit position that reduces the Doppler line broadening by refocusing and we present a series of computer experiments which simulate our results. The refocusing technique enhances the recorded intensity of Auger lines from projectile states substantially without increasing their energy widths. The method should be extremely useful for the study of high-resolution observations of Auger decays from fast moving ion beams.

A Parallel Plate Electrostatic Spectrograph

A description is given of a new parallel plate electrostatic spectrograph. A parallel plate electrostatic analyzer has been discussed previously, in which particles issuing from a point source on the earthed plate are deflected by the electric field and brought to a focus on that plate, provided the angle of entrance to the field is 45°. This is a simple example of the more general focusing properties of a parallel plate analyzer. From consideration of these properties, it has been found possible to select a given angle of entry into the field for which second order focusing can be attained giving rise to an angular aberration term proportional to (Δθ)3. Uslng an acceptance of ±6° a resolving power of 200 is predicted and has been obtained with a prototype.