The local field effects on voltage contrast in the scanning electron microscope (SEM) mean that local fields generated by a non-uniform potential distribution on specimen surface cause a variation in the secondary electron (SE) detector current. It causes some errors in the voltage measurement. The authors present a theory to calculate the SE detector current in the presence of the local fields. In the calculation, they assume that the field distribution above the specimen surface (metal electrodes with 8 mu m width and 12 mu m separation) is two-dimensional. Analysed models are a conventional SEM detector system (model A), a retarding-field energy analyser with an extraction field (model B) and a high-resolution energy analyser with an extraction field (model C). The results show that the local field effects could not be neglected even in models B and C with strong extraction fields. The calculated values of local field effects in models A and B agree well with the experimental ones. The dependence of local field effects on the electrode geometry is equivalent to that on the extraction field, though this dependency is not so strong.

The polymorphs that appear in the low-temperature phase of silver selenide have been studied by highresolution electron microscopy. The specimen films are intentionally prepared with excess silver or selenium over stoichiometric composition by flash evaporation, asdepositing carbon films on both sides of the specimen films to protect them from selenium sublimation and to maintain the composition throughout the heat treatment. It is shown that four different types of low-temperature phase exist: tetragonal (a = 6.98, c = 4.96A) for a metastable phase only formed with a small grain size of less than 50 nm; face-centred cubic (a = 10.9 ~) for a non-stoichiometric phase with excess silver; monoclinic (a = 7.05, b = 8.17, c = 4.34~, o~ = 101.0 °) for a non-stoichiometric phase with excess selenium; and orthorhombic (a = 7.05, b = 7.82, c = 4.34A) for the stoichiometric stable phase. The topotactic relations between the orthorhombic and monoclinic types are found to be fully coherent, having the same a and c lattice parameters.

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The charging effect of an insulating specimen from electron beam (e-beam) irradiation may be utilized to facilitate imaging in the scanning electron microscope (SEM). This has been confirmed by a great deal of experimental work during the last three decades. Particularly, recent investigations indicate that even located underneath insulating thin films that a low energy e-beam cannot penetrate, conductors not biased and overlay marks, are observable through a novel imaging pattern, charging contrast. Unlike conventional SEM contrasts, which usually reflect surface characteristics, the dynamic charging contrast can reveal information of underlying structures without any external exciting signal. The authors consider that this kind of charging contrast arises from the different redistribution rates of secondary electrons returning to the surface under the surface local field of the charged specimen. The charging contrast has the prospect of extending the SEM application and forming new testing methods matched with the fast development of integrated circuits.