Image intensification in the field-ion microscope

Abstract

The ion current available in a field-ion image varies from 10^-12 to 10^-9 A, while the ion current per image point is of the order of 10^-14 A. The very low phosphor response for neon and argon ions as compared with electrons or helium ions makes image recording for the heavier gases extremely difficult. Post-acceleration of the ion image through a fine mesh grid gives an appreciable improvement in intensity but conversion of the ion image to an electron image, using a fine mesh, aluminium coated grid as an image converter, is far more promising and the secondary electron image obtained is of greater intensity than the normal helium image, even with neon or argon as the image gas. Commercial image intensifiers reduce the photographic exposure times to a few seconds or less, but with optical coupling to the field-ion microscope there may be a severe loss of information. This can be avoided by using an image converter inside the microscope and then intensifying the secondary electron image.