Video display system for a scanning electron microscope provides slow scanning rates, a self-generated color gradient technique, and allows leisurely viewing of several hours. It also enables the viewing of areas where selected energy regions contribute relatively few electrons, and the changing of specimen position and magnification without adjustments

Brookshier, W. K.

Gilroy, J.

English

NASA Technical Reports Server

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 
Sweep 
Generator
Aperture 
Slits 3 Octupole	 I I	 Current	 I I 
1=
I 
-	
- 11	 Supplies 
StorageDisplay
___ 
-	 Quadrupoll 
Tubes Magnification Current	 I 
Selector Supplies  
Specimen -	 Deflection 
I	 Plates 
Positive' 
Voltage  
Supply
MN 
Photomultiplier
- / 
And  
-
Amplifier 
Scintillators g Electrostatic Photomultiplier '	 Analyzer 
And - -	 Plate 
Amplifier i 
Analyzer Slits	 Vacuum
The problem: 
To design, for a scanning electron microscope, a 
video display system which will provide advantages in 
visual observation over conventional display systems. 
The desired features include: (I) a color gradient tech-
nique generated within the display system, (2) the 
ability to change the apparent specimen position with-
out necessitating fine adjustment of the specimen 
location, (3) good resolution for viewing portions of 
the specimen where selected energy regions contribute 
relatively few electrons, (4) the ability to change the 
magnification range without refocusing, and (5) the 
ability to permit leisurely viewing over extended 
observation periods without using photographic tech-
niques, and without continuous and excessive bom-
bardment of the specimen. 
Electron microscopes employing high-magnification 
electron imaging depend upon "fast-scan" techniques
and require visual control of specimen positioning, 
adjustment of the magnification range, and image 
refocusing when magnification is changed. Conven-
tional electron microscopes generally do not permit 
leisurely viewing over extended periods. Visual 
display with a standard oscilloscope requires either 
high electron microscope beam strength or the use of 
photographic techniques to avoid image flicker. 
The solution: 
Direct-view storage display tubes in an integral 
system which combines features found in scanning 
electron microscopes, electrostatic energy analyzers, 
and CRT display methods. This microscope display 
system provides (I) slow-scanning rates, used with the 
two direct-view storage display tubes, , allowing the 
microscope electron beam to be continually focused 
sharply on' the specimen while the image is slowly 
"written" on the display tubes; (2) a superimposed 
(continued overleaf) 
This document was prepared under the sponsorship of the Atomic 
Energy Commission and/or the National Aeronautics and Space 
Administration. Neither the United States Government nor any per-
son acting on behalf of the United States Government assumes any
liability resulting from the use of the information contained in this 
document, or warrants that the use of any information, apparatus, 
method, or process disclosed in this document may not infringe pri-
vately owned rights. 
https://ntrs.nasa.gov/search.jsp?R=19670000312 2020-03-11T20:41:18+00:00Z
imaging and color gradient technique using precisely-
adjusted mirrors for use with the dual (side-by-side) 
storage tube output; (3) change of apparent specimen 
location by applying dc biases to the microscope 
beam deflection plates; (4) a microscope beam 
strength of lx 10- 9
 amperes which, when used with 
slow scan, provides a sufficient number of events per 
picture element, including observations in energy 
regions containing few electrons; (5) a change in mag-
nification by changing the amplitude of the sweep 
voltages applied to the microscope deflection plates; 
and (6) storage tubes which permit viewing periods of 
several hours, with the image persisting through shut-
downs and power failures. 
How it's done: 
The integrated microscope system employs three 
basic functional units which are used for electron 
beam emission and control, specimen bombardment 
with subsequent electron beam focusing, and a photo-
multiplier output display system. 
Electrons emitted from the beam control and field 
emission point pass through the specimen and enter 
the electrostatic energy analyzer (see Figure). The 
electrostatic energy analyzer plates refocus the elec-
trons at the analyzer slits. Electrons that have tra-
versed the specimen with little loss of energy are 
focused at the lower slit, while the upper slit is used 
to observe electrons that have suffered appreciable 
energy loss. Behind the slits are cesium iodide scintil-
lators with quartz light pipes leading to the photo-
multiplier tubes; the outputs of the photo multipliers 
and amplifiers are then applied to the storage tubes. 
The two display patterns produced on the storage 
tubes simultaneously produce images of the speci-
men using two different electron energies. 
An optical device permits the observation of the 
two displays by superimposing and viewing the images 
through separate color filters. A pair of mirrors, such 
as used in a periscope, produces an image of one 
display tube which appears to be located midway 
between the tubes. A second set of semisilvered 
mirrors, similarly arranged, is placed in the viewing 
path of the first set of mirrors. With the four mirrors 
adjusted exactly, the images are congruent, and 
exhibit no parallax problems or differences of mag-
nification. 
Since the eye has difficulty judging the relative 
illumination of nonadjacent areas in a nonuniform 
field, but may quite easily distinguish slight color 
changes in nearby areas, a set of color filters is used 
to observe contrast effects of the displays being pre-
sented at different electron energies. Although the 
illumination of the storage tubes normally appears 
yellow-green (P20 phosphor), illuminated areas of the 
first display tube, when used with a red filter, will 
appear bright pink, and areas of the second tube, 
viewed through a blue filter, appear bright green. In 
a display region where both images are contributing 
an appreciable portion of the light, a slight change in 
illumination from either display will produce substan-
tial color variation. Thus neighboring areas of a 
Brief 67-10312
specimen, varying slightly in the relative number of 
electrons being contributed to the two energy images, 
appear substantially different in hue. At the design 
strength of the microscope electron beam of 1 x 10 
amperes, with slow scan, a photomultiplier output 
amplifier of moderate gain and bandwidth is adequate 
even for observations in energy rgions where there 
are relatively few electrons, allowing good resolution 
for very faint specimens. 
The extended storage time of the direct-view storage 
display tubes, as compared with phosphor decay times 
of standard oscilloscope tubes, permits visual observa-
tion of a single slowly scanned raster. Specimen 
examination may begin before a single scan is com-
pleted, with the presentation persisting for many 
seconds, even at high display intensities. In addition, 
successive "writes" may be partially added, permit-
ting averaging and integration over long observation 
times without extremely slow initial scanning. Suc-
cessive scans may be piled up until visual observation 
indicates that a good statistical integration has been 
achieved. A recording camera and/or the optical 
superposition device may be interposed leisurely while 
the displays are retained in storage. 
Notes: 
I. Magnification may be chosen by simple switching, 
and specimen position is also obtained electroni-
cally. The color optical system provides contrast 
without specimen "staining", and identification of 
specimen constituents is possible. 
2. The factor causing the greatest degree of difficulty 
in the practical use of the system has been the 
relatively poor quality and characteristics of the 
available storage tubes. The lack of illumination 
uniformity over the 6x6 inch tube area, for elec-
tron beam intensities below saturation illumina-
tion, and the slight dynamic range of the tubes 
have contributed to a very high contrast display 
image. 
3. Additional details are contained in IEEE Transac-
tions on Nuclear Science, April 1965, p. 104-110. 
4. Inquiries concerning this innovation may be di-
rected to:
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B67-10312 
Source:	 W. K. Brookshier and J. Gilroy 
Electronics Division 
(ARG- 158) 
Patent status: 
Inquiries about obtaining rights for commercial 
use of this innovation may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Chicago, Illinois 60439
Category 03


New electron microscope employs new video display technique

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server