The exact solution of Maxwell's equations in the presence of arbitrarily shaped dielectrics is expressed in terms of surface-integral equations evaluated at the interfaces. The electromagnetic field induced by the passage of an external electron is then calculated in terms of self-consistently obtained boundary charges and currents. This procedure is shown to be suitable for the simulation of electron energy loss spectra when the materials under consideration are described by local frequency-dependent response functions. The particular cases of translationally invariant interfaces and axially symmetric interfaces are discussed in detail. The versatility of this method is emphasized by examples of energy loss spectra for electrons passing near metallic and dielectric wedges, coupled cylinders, spheres, and tori, and other complex geometries, where retardation aspects and Cherenkov losses can sometimes be significant.

No abstract

No abstract

The energetics of multiply twinned particles (MTPs) are investigated using elasticity theory. This allows the homogeneous strain models to be critically compared with the disclination model for the strains in decahedral particles and with a new model for the strains in icosahedral particles based on inhomogeneous elmticity. The overall energy balance between MTPs and single crystals is then evaluated, including the significant cost of e l~t i a l l y distorting the surface and using two extreme models of the faceting. The results of this analysis indicate that icosahedral MTPs will be more stable than single crystals for small sizes only for strong faceting conditions, decahedral MTPs being true intermediaries between the two. Experimentally observed stress-relief mechanisms provide indirect evidence for the inhomogeneous strain models. 7 Present address :

SUMMARY A survey is made of a number of the localized signal selection methods and related techniques which may be used to improve the electron microscope image contrast from small regions of material and thereby bring the specimen resolution actually achieved somewhat closer to the electron‐optical resolution of present‐day instruments. Geometrical and stereo methods are discussed, as well as weak‐beam and other coherent elastic scattering methods. Localization effects in inelastic scattering and the image contrast in energy loss electrons are examined in greater detail.