Abstract
Experience with the scanning electron microscope has shown that there are fields of application where this instrument has distinct advantages over the conventional transmission microscope (with or without replicas) and the reflexion electron microscope. For example, there are specimens which are too thick to be viewed by direct transmission and which nevertheless do not lend themselves readily to the construction of replicas, either because they are too fragile, because their surfaces are undercut so that the replica would be keyed to them or because observation of the specimen at high temperatures is desired. The paper gives examples of the use of the scanning microscope in such cases and shows that the images produced are very similar in character to those obtained with optical microscopes. In particular, a pronounced three-dimensional effect is observed.
In the work described the specimens have been mounted so that the mean surface under observation is at a glancing angle of about 25° to the incident electron beam. Contrast is provided by the variation of the local angle of incidence as the scanning electron beam moves over the surface, and does not depend on secondary emission. With the present apparatus a resolution of about 200 Å has been attained, but there appears to be no reason why this performance should not be substantially improved.
It is shown that, with the scanning microscope, bombardment of the specimen is much less severe than with other electron microscopes.