Abstract
With the addition of an imaging energy analyzer to a low energy emission microscope (LEKM) (1), it becomes possible to use inelastic scattering (secondaries, Auger and x-ray emissions) to form high resolution images. One can then obtain complimentary diffraction, structural, topological (2) and chemical information in the same instrumental environment. The favorable noise/bandwidth associated with the parallel imaging of many pixels may allow dynamic surface processes to be observed. The goal of this paper is to compare hypothetical scanning (SEM/SAM) with direct imaging (SPEC-LEEM) instruments in terms of resolution and signal/noise ratio vs integration time (visibility). By comparison, one may extrapolate experience with the more common scanning instrument (3), in order to predict the advantages and disadvantages of the newer analytic imaging technology.The complete analysis will be published in “Ultramicroscopy”.Briefly, the signal to noise ratio within an image element is expressed in terms of incident flux density, net collection efficiency, integration time and quantum yields for spectral lines upon a diffuse background. While ultimate resolution is determined by lens aberrations, practical resolution is defined by a minimum tolerable signal/noise criteria. Aperture angles, energy window, lens field strength, and electron gun configuration are considered (within technical limits) to be free variables that can be optimized for a given resolution requirement, emission spectrum, and surface standoff field strength. The optimization techniques are developed in a form applicable to both instruments, and comparative predictions are made for a specific numerical example.
Published Version
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