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

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Abstract
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.