Electron Monochromator Research Articles

Observation of vibrationally excited nitrogen with a simplified electron transmission apparatus

A simple electron transmission apparatus is used to observe vibrationally excited N2 in the first two vibrational levels. The method is based on the pronounced peaks appearing in the total electron scattering cross section in the range of energy 2–4 eV. Because of the wide spacing between these peaks, good energy resolution is not required and measurements can be performed without an electron monochromator.

Imaging properties of electrostatic energy analyzers with toroidal fields

Numerical values of the second-order aberration coefficients are given for two classes of toroidal fields, namely (1) the “quasi-spherical” field with c = 1, c′ ≠ − 1, and (2) fields with c in the region 1.6–1.8. For the “quasi-spherical” fields, the second-order coefficients are given as functions of the deflection angles ω for 90° ≤ ω ≤ 180°. The third-order coefficients for the spherical field are given in the same region. For the devices in the second class, which have one intermediary axial image, the second-order coefficients are studied as functions of c and ω, subject to the condition that double-focussing should be obtained. The conditions under which the radial and axial image planes coincide are considered. The influence of axially curved entrance and exit surfaces is investigated. One special case (ω = 180°, c = 1.691, c′= − 1.11), which may be favourable for an electron monochromator is discussed.

Characteristics of the 180 degrees backscattering trochoidal spectrometer

The characteristics are investigated by calculation of the energy distribution of the electrons whose trajectories pass through the spectrometer. This work is an extension of previous calculations on the trochoidal electron monochromator on which the backscattering spectrometer is based. A comparison between certain of the predicted characteristics and those determined by experiment is made.

Resonances near threshold in the electron impact excitation and polarization of the 61S0-63P1line of mercury

Data are presented for the positions and plarizations of resonances occurring within a few volts of threshold of the 2537 AA line of mercury, excited by electron impact. A 127 degrees electron monochromator was used in a standard crossed-beam apparatus, the results being obtained by measuring separately the I/sub /// and Iperpendicular to contributions to the excitation function. The normalization procedure and the checks made on the data are described. Several resonances are clearly observed; a comparison of the measured polarization of one of them with a theoretical value leads to a possible J value for the negative ion state being formed.

Quenching of spin-spin relaxation in Fe(NO 3) 3·9H 2O single crystals by application of a magnetic field

Dissociative electron attachment (DEA) experiments to Cl2 are reported for the extended energy range between about 0 and 9 eV using a high-resolution crossed beam apparatus. A hemispherical electron monochromator is used to produce an electron beam with a small energy distribution. Electron currents of 20 nA at an electron energy of 20 eV with an energy resolution in the incident electron beam of about 80–150 meV full-width half-maximum (FWHM) were achieved. Three dissociative attachment processes peaking at slightly above 0, 2.53 and 5.64 eV were observed.

Structure in near-threshold excitation of krypton

The excitation of the first excited levels of krypton with the configuration (4p55s) by electron impact has been observed near threshold. The experiment was carried out in a crossed-beam arrangement, using an electron monochromator of the 127 degrees type with an energy width of less than 100 meV. The ultraviolet photons were observed at 90 degrees with respect to the beams. The excitation function near threshold is dominated by a strong resonance and comparison is made with experiments on the inelastic scattering of electrons from krypton.

Electron energy loss spectrum of ozone

Electron energy loss spectra for ozone are presented over the energy loss range 1–30 eV with an incident electron energy of 300 eV. The data are obtained using an electron monochromator—analyzer combination and a static gas cell, and have a resolution of 0.035 eV fwhm.

Resonance Structure in the Excitation Cross Section by Electron Impact of the2sState in Atomic Hydrogen

The cross section for excitation of atomic hydrogen to the $2s$ state by electron impact has been remeasured in a crossed-beam experiment in the energy range from threshold to 12.3 eV. An electron monochromator of the cylindrical type with a full width at half-maximum of 110 meV has been used. The $2s$ atoms were detected by quenching in an electrostatic field and observing the emitted Lyman-$\ensuremath{\alpha}$ photons. Absolute values for the cross section were obtained by normalizing to the close-coupling calculations of Burke et al. at 10.8 eV. Resonance structure at 11.7 eV, which is a superposition of the $^{1}S$ and $^{3}P$ resonances predicted by theory, has been detected. There is good agreement between the present experiment and the experiment by Oed.

High resolution studies of electron excitation - I. The 4S states of helium and the energy scale

We describe an electron monochromator using hemispherical deflecting electrodes and its application to the measurement of electron excitation functions. We present excitation functions of the 4 1 S and 4 3 S states of helium for energies within about 1 V of threshold. We find a prominent peak in each function and determine its energy as 4 1 S 23.937 ± 0.007 ± 0.011 eV, 4 3 S 23.939 ± 0.007 ± 0.009 eV, where the first limits represent a systematic error and the second are standard deviations of several determinations.

Simple Electron Monochromator of Three-Diaphragm Einzel Lens

A three-diaphragm einzel lens is utilized as an electron monochromator of a usual electron microscope. An energy dispersion of the monochromator of 1.5 mm/Volt is obtained in an appropriate operating condition at the accelerating voltage of 50 kV. Thus the estimated energy resolution becomes 10 mV by using an energy selecting aperture of 15 µmφ. The beam current passed through the energy selecting aperture of 90 µmφ (an energy spread is 60 mV) is one-twentieth of a total beam current of a non-monochromatic beam. The construction and performance of the monochromator are described, and it is suggested that some advantages are obtained in the high resolution electron loss spectroscopy when the monochromator is used in common with the 2nd condenser lens.

Excitation of optically forbidden transitions in argon and neon by electron impact

A radial electron monochromator and analyser system employing several new features has been used to study low energy differential inelastic electron scattering by ground state argon and neon atoms. Angular distributions for a number of optically inaccessible states are reported at energies between 30 and 100 eV and over a range of scattering angles from 0–90°. In particular, results are shown for the metastable states ( 3 P 2 , 3 P 0 ) of argon as well as for various J levels in the parity forbidden bands ( ns 2 np 6 → ns 2 np 5 ( n + 1) p ) for argon and neon.

Numerical Solution to Laplace's Equation in Spherical Coordinates with Axial Symmetry

A numerical method for solving Laplace's equation in spherical coordinates for an axially symmetric geometry has been developed. Dirichlet boundary conditions on a closed surface yield a set of difference equations. The method of successive overrelaxation has been employed to find solutions to those equations. Application of the method is illustrated by finding the field configuration in a new type of electron gun used in a spherical electron monochromator.

Characteristics of the Trochoidal Electron Monochromator

An electron monochromator for use in an axial magnetic field is described. Electrons are injected parallel to the magnetic field and an electric field is applied in a perpendicular direction. The electrons thus describe trochoids and drift in a direction perpendicular to both the electric and magnetic fields and disperse according to their initial velocities. An electron energy width at half-maximum of 0.020 eV can be obtained, with a transmitted current of about 10−9 A.

Nanosecond Time-of-Flight Studies of Electrons

Low-energy electron guns have been constructed in planar and coaxial geometry. When pulsed with nanosecond pulses from an avalanche transistor pulser, they emit bursts of electrons of a few nanoseconds duration having energies adjustable between 1 and 15 eV. Electrons are focused along a drift tube by a magnetic field of the order of 1 G and are collected and then amplified by a 3-stage transistorized pulse amplifier for display on a sampling oscilloscope. For microsecond drift times an energy resolution of about 0.01 eV is calculated. The depletion of 2.5-eV electrons in the time-of-arrival distribution when the pumping system was cut off from the drift tube was attributed to vibrational excitation of N2, and a cross section of 1.34×10−15 cm2 was determined. When the drift tube was re-evacuated and a jet of nitrogen gas was directed across the electron beam at right angles to it and close to the gun, the time-of-arrival distribution revealed energy losses of 0.6 or 1.0 eV which were attributed to vibrational excitation of the v=0 to v=2 or v=3 levels in nitrogen. These experiments, plus work done in other laboratories on gating grid arrangements, seem to indicate that a time-of-flight electron monochromator having energy resolution comparable to the best systems in operation at this time may be possible in the future.

High-resolution measurement of electron excitation to the 4S states of helium

We have made a hemispherical electron monochromator and measured the optical excitation functions of the 4 1S and 4 3S states of helium close to threshold. Both excitation functions reach a significant value within 30 mV of threshold and show two narrow maxima. The second maxima coincide in energy (between 23.77 and 23.80 eV) and are identified with a resonance having the configuration (1s5s2)2S1/2.

High Resolution, Low Energy Electron Spectrometer

An electron spectrograph consisting of an electron source, an electron monochromator, a gas cell, and an electron energy analyzer is described. The electron energy spread from the monochromator as seen by the analyzer is 0.005 eV at 3.35 eV primary energy. It is shown that space charge within the beam requires operation of the energy selectors at the lowest possible energy if high current, together with high resolution, is required.