Abstract: A scanning electron microscope has means for generating a beam of electrons which is scanned over a specimen held within a holder in a chamber which contains a gaseous medium. A negative potential is applied to the holder so as to generate an electric field which accelerates secondary electrons, formed by the interaction or the primary beam with the specimen, in a direction away from the specimen surface and into a collision zone in the chamber. In that zone, the accelerated secondary electrons collide with gas molecules of the gaseous medium, thereby initiating a cascade of collisions which, in effect, amplifies the secondary electron signal. That signal (which may take the form of photons generated as a result of the collisions) is detected by detecting means, such as a photo-multiplier.

Abstract: A novel high brightness point ion source (10) that is adapted to operate with liquid ionic compounds such as mixtures of molten salts, bases or acids. The ion source is basically comprised of two parts: the needle assembly (11) and the extraction assembly (12). The former consists of a point shaped needle (13) made of a refractory ceramic material, whose sharpened extremity is referred to as the tip (13a). The needle is partially lodged in a recess of an insulating support (15). A heating coil (14) made of stainless steel is tightly wound around a portion of the needle adjacent to the tip. The needle is coated with the mixture, for instance, by dipping in a crucible containing the mixture. The extraction assembly is comprised of a metal extracting electrode (20) provided with a central aperture that is screwed on a cylindrical metallic body (19), so that the spacing between the tip and the aperture center is adjustable.