August 1967 Brief 67-10312 • AEC—NASA TECH BRIEF AEC-NASA Tech Briefs describe innovations resulting from the research and development program of the U.S. AEC Or from AEC-NASA interagency efforts. They are issued to encourage commercial application. Tech Briefs are published by NASA and may be purchased, at 15 cents each, from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. New Electron Microscope Employs New Video Display Technique —50KV D.C. Supply 1 Field Control i Emission 5KV D.C. Electrode '- - Point Supply Anode Aperture Sweep Slits 3 Octupole I Generator I Current I - I I - 11 Supplies 1= ___ StorageDisplay - Quadrupoll Tubes Magnification Current I Selector Supplies Specimen - Deflection I Plates Positive' Voltage MN Supply Photomultiplier -- / And Amplifier Scintillators Electrostatic Photomultiplier g ' Analyzer And - - Plate Amplifier i Analyzer Slits Vacuum The problem: and require visual control of specimen positioning, To design, for a scanning electron microscope, a adjustment of the magnification range, and image video display system which will provide advantages in refocusing when magnification is changed. Conven- visual observation over conventional display systems. tional electron microscopes generally do not permit The desired features include: (I) a color gradient tech- leisurely viewing over extended periods. Visual nique generated within the display system, (2) the display with a standard oscilloscope requires either ability to change the apparent specimen position with- high electron microscope beam strength or the use of out necessitating fine adjustment of the specimen photographic techniques to avoid image flicker. location, (3) good resolution for viewing portions of The solution: the specimen where selected energy regions contribute Direct-view storage display tubes in an integral relatively few electrons, (4) the ability to change the system which combines features found in scanning magnification range without refocusing, and (5) the electron microscopes, electrostatic energy analyzers, ability to permit leisurely viewing over extended and CRT display methods. This microscope display observation periods without using photographic tech- system provides (I) slow-scanning rates, used with the niques, and without continuous and excessive bom- two direct-view storage display tubes, , allowing the bardment of the specimen. microscope electron beam to be continually focused Electron microscopes employing high-magnification sharply on' the specimen while the image is slowly electron imaging depend upon "fast-scan" techniques "written" on the display tubes; (2) a superimposed (continued overleaf) This document was prepared under the sponsorship of the Atomic liability resulting from the use of the information contained in this Energy Commission and/or the National Aeronautics and Space document, or warrants that the use of any information, apparatus, Administration. Neither the United States Government nor any per- method, or process disclosed in this document may not infringe pri- son acting on behalf of the United States Government assumes any vately owned rights. imaging and color gradient technique using precisely- specimen, varying slightly in the relative number of adjusted mirrors for use with the dual (side-by-side) electrons being contributed to the two energy images, storage tube output; (3) change of apparent specimen appear substantially different in hue. At the design location by applying dc biases to the microscope strength of the microscope electron beam of 1 x 10 beam deflection plates; (4) a microscope beam amperes, with slow scan, a photomultiplier output strength of lx 10- 9 amperes which, when used with amplifier of moderate gain and bandwidth is adequate slow scan, provides a sufficient number of events per even for observations in energy rgions where there picture element, including observations in energy are relatively few electrons, allowing good resolution regions containing few electrons; (5) a change in mag- for very faint specimens. nification by changing the amplitude of the sweep The extended storage time of the direct-view storage voltages applied to the microscope deflection plates; display tubes, as compared with phosphor decay times and (6) storage tubes which permit viewing periods of of standard oscilloscope tubes, permits visual observa- several hours, with the image persisting through shut- tion of a single slowly scanned raster. Specimen downs and power failures. examination may begin before a single scan is com- How it's done: pleted, with the presentation persisting for many The integrated microscope system employs three seconds, even at high display intensities. In addition, basic functional units which are used for electron successive "writes" may be partially added, permit- beam emission and control, specimen bombardment ting averaging and integration over long observation with subsequent electron beam focusing, and a photo- times without extremely slow initial scanning. Suc- multiplier output display system. cessive scans may be piled up until visual observation Electrons emitted from the beam control and field indicates that a good statistical integration has been emission point pass through the specimen and enter achieved. A recording camera and/or the optical the electrostatic energy analyzer (see Figure). The superposition device may be interposed leisurely while electrostatic energy analyzer plates refocus the elec- the displays are retained in storage. trons at the analyzer slits. Electrons that have tra- Notes: versed the specimen with little loss of energy are I. Magnification may be chosen by simple switching, focused at the lower slit, while the upper slit is used and specimen position is also obtained electroni- to observe electrons that have suffered appreciable cally. The color optical system provides contrast energy loss. Behind the slits are cesium iodide scintil- without specimen "staining", and identification of lators with quartz light pipes leading to the photo- specimen constituents is possible. multiplier tubes; the outputs of the photo multipliers 2. The factor causing the greatest degree of difficulty and amplifiers are then applied to the storage tubes. in the practical use of the system has been the The two display patterns produced on the storage relatively poor quality and characteristics of the tubes simultaneously produce images of the speci- available storage tubes. The lack of illumination men using two different electron energies. uniformity over the 6x6 inch tube area, for elec- An optical device permits the observation of the tron beam intensities below saturation illumina- two displays by superimposing and viewing the images tion, and the slight dynamic range of the tubes through separate color filters. A pair of mirrors, such have contributed to a very high contrast display as used in a periscope, produces an image of one image. display tube which appears to be located midway 3. Additional details are contained in IEEE Transac- between the tubes. A second set of semisilvered tions on Nuclear Science, April 1965, p. 104-110. mirrors, similarly arranged, is placed in the viewing 4. Inquiries concerning this innovation may be di- path of the first set of mirrors. With the four mirrors rected to: adjusted exactly, the images are congruent, and Office of Industrial Cooperation exhibit no parallax problems or differences of mag- Argonne National Laboratory nification. 9700 South Cass Avenue Since the eye has difficulty judging the relative Argonne, Illinois 60439 illumination of nonadjacent areas in a nonuniform Reference: B67-10312 field, but may quite easily distinguish slight color Source: W. K. Brookshier and J. Gilroy changes in nearby areas, a set of color filters is used Electronics Division to observe contrast effects of the displays being pre- (ARG- 158) sented at different electron energies. Although the illumination of the storage tubes normally appears Patent status: yellow-green (P20 phosphor), illuminated areas of the Inquiries about obtaining rights for commercial first display tube, when used with a red filter, will use of this innovation may be made to: appear bright pink, and areas of the second tube, Mr. George H. Lee, Chief viewed through a blue filter, appear bright green. In Chicago Patent Group a display region where both images are contributing U.S. Atomic Energy Commission an appreciable portion of the light, a slight change in Chicago Operations Office illumination from either display will produce substan- 9800 South Cass Avenue tial color variation. Thus neighboring areas of a Chicago, Illinois 60439 Brief 67-10312 Category 03.