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Abstract: This paper presents computed dependencies of signal amplification of detected electrons on the water vapor pressure in a variable pressure SEM using the EOD software equipped with a Monte Carlo plug-in. We analyze the amplification at selected energies of signal electrons going through a high-pressure water vapor and total signal amplification by including a realistic simulation of the secondary emission from sample. The results are compared with experimental measurements and the dependencies of published analytical models. [Copyright &y& Elsevier]

Abstract: The cathode lens is an electron optical element in an emission electron microscope accelerating electrons from the sample, which serves as a source for a beam of electrons. Special application consists in using the cathode lens first for retardation of an illuminating electron beam and then for acceleration of reflected as well as secondary electrons, made in the directly imaging low energy electron microscope or in its scanning version discussed here. In order to form a real image, the cathode lens has to be combined with a focusing magnetic lens or a focusing immersion-magnetic lens, as used for objective lenses of some commercial scanning electron microscopes. These two alternatives are compared with regards to their optical properties, in particular with respect to predicted aberration coefficients and the spot size, as well as the optimum angular aperture of the primary beam. The important role of the final aperture size on the image resolution is also presented. [Copyright &y& Elsevier]