Single Channel Electron Multiplier Research Articles

Induction spectrometry using an ultrafast hollow-cored toroidal-coil (HTC) detector.

Ultrafast photoelectron and photoion spectroscopy (as well as their combination known as "coincidence spectroscopy") utilizes detectors based on different electron multipliers such as microchannel plates or single-channel electron multipliers. These detectors have a few important limitations such as fast-signal distortion (low pass operation), mutually exclusive positive or negative mode, dead time, and requirement of trigger. A high-pass induction detector, based on a hollow-cored toroidal coil, was developed that overcomes the above-mentioned limitations. The frequency-dispersive response and linearity of different configurations were analyzed. It is shown that the response is enhanced for ultrafast electron signals, dependent on construction parameters, thus offering response flexibility by design. Kinetic energy distributions of pseudospark-induced electron pulses are characterized in order to validate the capabilities in real applications.

Laser wavelength effects on the charge state resolved ion energy distributions from laser-produced Sn plasma

The effects of laser wavelength on the charge state resolved ion energy distributions from laser-produced Sn plasma freely expanding into vacuum are investigated. Planar Sn targets are irradiated at laser wavelengths of 10.6 and 1.064 μm and intensities of 1.8×1010 and 3.4×1011 W/cm2, respectively. These parameters are relevant to the extreme ultraviolet x-ray source application. An electrostatic deflection probe and single channel electron multiplier are used to record the charge state resolved ion energy distributions 100 cm from the laser plasma source. At the longer laser wavelength, higher charge state ions are observed. At both laser wavelengths, the peak ion energies increase approximately linearly as a function of charge state, and all ion energies greatly exceed the initial thermal electron temperature. The differences in the ion energy distributions are attributed to the laser wavelength dependence of the laser energy absorption, the resulting plasma density in the corona, and the subsequent recombination after the laser pulse. Numerical simulations of the plasma expansion from a collisional-radiative steady state model support the experimental results.

Static SIMS: ion detection efficiencies in a channel electron multiplier

The energy and spatial counting efficiencies of single channel electron multipliers (CEMs) have been analysed for axially incident argon and xenon ions with energies in the range 0.1 to 9 keV. Theoretical predictions have been compared with data for a Philips X919BL CEM. It is recommended that, to minimise the variation in detection efficiencies between ion species, the ions should impact the detector surface at grazing incidence and at as high an energy as possible, typically 10 to 20 keV. Furthermore, the CEM should be operated in the plateau part of the curve of efficiency as a function of detector voltage determined using ions of high mass.

Energy and spatial dependence of the electron detection efficiencies of single channel electron multipliers used in electron spectroscopy

Measurements for axially incident electrons are reported for the energy and spatial dependencies of the detection efficiency of a Philips X919BL single channel electron multiplier (CEM) in both the pulse counting and analog amplification modes. The behavior may be understood in terms of the general theory reported earlier.1 Essentially there are three regions to consider: the horn, the channel and the edge of the channel. In the pulse counting mode the difference in efficiencies between the channel and horn may reach a factor of two whereas in the analog mode the difference between the channel edge and the horn may reach a factor of five. The same behavior occurs when the CEM is used as the output stage of an electron spectrometer. The above variations may lead to (i) loss of efficiency in spectrometers, (ii) spectral distortion arising from the associated presence of stray magnetic fields, and (iii) irreproducibility of spectra from different regions of the sample surface, unless specific measures, such as larger horns, off-axis channels or lens defocusing, are used to eliminate them.

Channel electron multiplier efficiencies: the effect of the pulse height distribution on spectrum shape in auger electron spectroscopy

Measurements are reported of one factor causing changes in the spectrum shape which occur in AES systems with single channel electron multipliers used in the pulse counting mode. This factor, the voltage across the electron multiplier, is usually set so that the counting rate just reaches its maximum value. The lowest possible voltage is usually chosen to prolong the multiplier life. However, it is shown that the setting chosen in this way depends on the incident electron energy in such a way that a higher voltage is required for lower energy electrons. If too low voltage is chosen, not only is the counting efficiency less than it should be, but the intensity in the low energy part of the spectrum is progressively lost. This arises since the mean output pulse height is a function of both the applied voltage and the incident electron energy. It is concluded that the problem is best avoided by adopting a reference procedure to set the multiplier voltage to just maximise the lowest energy electrons in the spectrum being studied.

High-resolution duo-multichannel soft x-ray spectrometer for tokamak plasma diagnostics

A high-resolution, time-resolving soft x-ray multichannel spectrometer (SOXMOS) that permits the simultaneous measurement of emission in two different spectral ranges has been developed and tested extensively for tokamak plasma diagnostics. The basic instrument is a high-resolution, interferometrically adjusted, extreme grazing incidence Schwob–Fraenkel duochromator. The instrument is equipped with two multichannel detectors that are adjusted interferometrically and scan along the Rowland circle. Each consists of an MgF2 coated, funneled microchannel plate, associated with a phosphor screen image intensifier that is coupled to a 1024-element photodiode array by a flexible fiber-optic conduit. The total wavelength coverage of the instrument is 5–340 Å with a measured resolution (FWHM) of about 0.2 Å when equipped with a 600-g/mm grating, and 5–85 Å with a resolution of about 0.06 Å using a 2400-g/mm grating. The simultaneous spectral coverage of each detector varies from 15 Å at the short wavelength limit to 70 Å at the long wavelength limit with the lower dispersion grating. The minimum readout time for a full spectral portion is 16 ms, but several individual lines can be measured with 1-ms time resolution by selected pixel readout. Higher time resolution can be achieved by replacing one multichannel detector with a single channel electron multiplier detector. Examples of data from the PLT and TFTR tokamaks are presented to illustrate the instrument’s versatility, high spectral resolution, and high signal-to-noise ratio even in the 10-Å region.

Determination of the valence state of Eu atoms in implanted Eu [formula omitted] microalloy by low-temperature conversion electron Mössbauer spectroscopy

We improved the sensitivity of conversion electron Mössbauer spectroscopy to an extent sufficient for measurements on materials implanted with the stable 151 Eu isotope at doses above 10 16 atoms/cm 2 . The measurements can be performed down to liquid-helium temperature using a single-channel electron multiplier in a close to sample geometry. It is shown that europium implanted at high dose in silicon enters mostly in a divalent state Eu 2+ , the trivalent Eu 3+ contribution being smaller than 5%.

Narrow energy distribution of output electrons from a modified single channel electron multiplier

New methods which reduce the unfavorable energy spread of output electrons from a single channel electron multiplier are presented. A modified output electrode produces a pronounced narrowing effect on the energy distribution without much affect on the gain. A simplified analysis of the field inside the channel shows that the fixed channel wall potential near the output end is responsible for the narrow energy distributions obtainable.

Energy distribution of output electrons from a single channel electron multiplier

Energy distribution of output electrons from a single channel electron multiplier

Energy distribution of output electrons from a single channel electron multiplier

The fundamental characteristics of the energy distribution of output electrons from a single channel electron multiplier were studied experimentally in detail for a few types of straight channels. The width of the energy distribution curve, ranging from about 50 to 15 eV FWHM, is found to depend on the applied voltage V(A) and the length-to-diameter ratio alpha of the channel, and to vary with output current. The results can be explained in terms of the normalized field strength near the output end of the channel and generalized by a set of universal curves presenting the energy width as a function of output current level for different values of VA/alpha.

High-gain imaging electron multiplier

The chevron-shaped channel electron multiplier is a device which combines the high-gain pulse-counting operation of single channel electron multipliers with the imaging capabilities of microchannel arrays. It produces charge pulses averaging more than 107 electrons and these gain magnitudes fall into a quasi-Gaussian distribution with a full width at half-maximum FWHM of approximately 130%. Suppression of ion feedback makes possible both imaging and low noise counting applications over large areas. Dark count rates are typically 1 count/sec cm2, and the dynamic range of operation covers 5–6 decades. Active areas over 45 mm diam have been fabricated, with uniform characteristics. Limiting resolution has been measured at 5 line pairs per millimeter. Because of the short length of each channel electron multiplier, the rise time and width of the output charge pulses are extremely short; large signal pulses have been detected with rise times as short as 400 psec.