GB1416043A - Electron microscope aperture system - Google Patents

Abstract

1416043 Electron microscopes NATIONAL AERONAUTICS & SPACE ADMINISTRATION 15 Jan 1973 [28 Jan 1972] 1941/73 Heading H1D In an electron microscope having an objective lens 18 for focusing the electrons passing through the specimen 16 on to an image plane 24, the lens includes an aperture plate 20, Figs. 1 and 2, having an annular aperture to reduce chromatic aberation. The aperture in the condenser lens aperture plate 14, for focusing the electron stream on to the specimen, may be either annular, as shown, or circular (Fig. 9, not shown). The objective aperture may be 50 Ám. in diameter and 3 Ám. in ring width, and may be fabricated (Figs. 4 to 8, not shown) by evaporating a first metal film, e.g. 300Š silver, on to a collodion film; mounting the composite structure on the objective aperture slide of an electron microscope having an annular condenser aperture; operating the microscope to form a contamination layer, caused by the decomposition of residual gas molecules, over the annular illuminated area; removing the structure from the microscope and galvanically depositing a second metal layer, e.g. 10,000Š Cu, over the non-contaminated area of the first metal film; and finally etching away, by ion bombardment from the rear surface, the collodion layer, the first metal film, and sufficient of the second metal layer to remove the contamination layer and leave the annular aperture. A third metal layer, e.g. 1000Š gold, may finally be evaporated on the structure surface, for stability and cleanliness. The size of the objective aperture formed may be adjusted by varying the objective lens current, and the method may be employed to produce a multi-aperture plate.