Energy Filter for High Resolution Low-Loss Scanning Electron Microscopy

Abstract

Images are formed in low-loss scanning electron microscopy with electrons scattered from the sample surface with little energy loss. These Electrons have not penetrated deeply into the sample and only provide information about the region immediately surrounding the incident beam. High resolution can therefore be obtained. The low energy loss electrons can be selected in two ways; by the use of an energy filter, or by arranging the detector so that only those electrons emerging almost parallel to the sample surface are collected. For optimum operation both approaches can be used simultaneously. With the high resolution low-loss method the sample is placed at the center of the pole-piece gap of a condenser-objective final lens. The action of the second half of the lens is such that for most samples only electrons emerging almost parallel to the specimen surface reach the detector. An energy filter is therefore not necessary to form a high resolution image and 20 Å point-to-point resolution (7 Å resolution using the width of the dark space criterion) has already been demonstrated without one.