Abstract

The recent developments of the in-lens field emission scanning electron microscopes (FESEM) make it possible to image specimen surfaces with subnanometer resolution by collecting type I secondary electrons, with an incident electron probe size of about 0.5 nm in diameter. A resolution of the same order of magnitude has also been obtained in a STEM instrument with secondary electron signals. Both in-lens FESEM and STEM utilize field emission gun as electron beam source (high intensity and small probe size) and high excitation objective lenses to reduce abberations. The examined samples have to be positioned inside the objective pole-pieces. Thus the emitted secondary electrons will experience a strong magnetic field and spiral around the magnetic field lines (cyclotron orbit) before they are collected by the secondary electron detector. The radius and the pitch height of the cyclotron orbit depend on the secondary electron energy and the emission angle with respect to the magnetic field axis.

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