GB708434A - Improvements in or relating to electron microscopes - Google Patents

Abstract

708,434. Electron microscopes. PYE. Ltd. May 30, 1952 [March 2, 1951], No. 5129/51. Class 39(1) [Also in Group XL(b)] In electron microscope apparatus the electron image of the specimen is used to lay down a charge image on a storage target and the target is scanned by a separate electron beam to produce an output signal which is fed to a picture reconstituting cathode ray tube. In the form shown the composite stream emerging from the object falls on charge storage electrode 4 and builds up a charge image thereon and the electrode 4 is then scanned by electrons from gun 7 to produce an output signal from signal plate 5 across resistor 10. The scanning beam at the same time partially or wholly erases the charge image. The output voltage variations are fed to an amplifier 11 and the amplified output modulates the beam of a cathode ray reproducing tube 12 which is scanned synchronously with the beam from gun 7 to give a picture on the screen. Preferably an A.C. amplifier is used, which enables the A.C. signal to be separated from the D.C. component. The final image may be remote from the microscope and the output from 4, 5 transmitted over a radio or wire link to the reproducing tube. The scanning of 4, 5 can be sequential or with intervals between scans, and the stored charge may be reduced by only a small amount at each scan. The scanning can be relatively slow, the reproducing tube screen having a suitably long afterglow period. The storage period may be preceded by a period in which screen 4, 5 is flooded with electrons to bias it negatively while pulsing collector 6 negatively, either as described in Specification 687,270 or by increasing the current in the scanning, beam which is kept on. During the storage period, which is preferably longer than the biasing period, the scanning beam may be cut off. In a modification the scanning is effected with low velocity electrons and the screen 4, 5 operated with cathode potential stabilization; the returning electrons may pass to a multiplier from which the output is derived. In another modification the screen may be of semi-conducting or insulating material exhibiting bombardment induced conductivity. The resistance picture' is converted to a charge storage pattern by continuously or intermittently applying a diffuse electron shower to the target, which is then scanned as before. The reproducing tube may alternatively produce a photographic record. Magnetic lenses 2, 3 focus the electrons before and after passing through the object.