Electron Microscope Camera with Fiber Optic OutputE. G. Burroughs and A. J. Kennedy Citation: Review of Scientific Instruments 37, 771 (1966); doi: 10.1063/1.1720319 View online: http://dx.doi.org/10.1063/1.1720319 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/37/6?ver=pdfcov Published by the AIP Publishing Articles you may be interested in A scanning force microscope with a fiberopticinterferometer displacement sensor Rev. Sci. Instrum. 62, 1280 (1991); 10.1063/1.1142485 Cathodoluminescence system for a scanning electron microscope using an optical fiber for light collection Rev. Sci. Instrum. 60, 226 (1989); 10.1063/1.1140466 Camera optics Phys. Teach. 20, 372 (1982); 10.1119/1.2341079 LEED Optics as Electron Mirror Microscope Rev. Sci. Instrum. 42, 189 (1971); 10.1063/1.1685041 The Universal Electron Microscope as a High Resolution Diffraction Camera Rev. Sci. Instrum. 17, 484 (1946); 10.1063/1.1770413

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:

130.113.111.210 On: Sat, 20 Dec 2014 15:14:25

DIGITAL AVERAGING 771

lated data (except for MCS channell, in which high pre­cision is not necessary) are transferred into the MCS register in a time much shorter than the channel period, it does not matter whether the MCS used with the DF has serial or parallel logic (i.e., whether the memory cycle is dependent on or independent of the contents of the channels).

For the same reasons (except for the use of channell), the MCS may be adequate even if it has much slower logical circuitry than the DF and has a rather modest memory capacity. If the logical circuitry of the MCS is slower, an oscillator with a frequency consistent with the MCS cir-

THE REVIEW OF SCIENTIFIC INSTRUMENTS

cuitry would be used to drive the OVER (A - K) scaler and load the MCS.

ACKNOWLEDGMENTS

It is a pleasure to mention our debt to several friends and colleagues who contributed to the design, engineering, and construction of the DF. D. Jacobsohn contributed heavily to the basic logical scheme finally adopted. C. Conley, G. Hoffman, and V. Tantillo all made valuable contribu­tions to the engineering details that bring such a device to fruition and also carried out the construction and testing of the instrument.

VOLUME 37, NUMBER 6 JUNE 1966

Electron Microscope Camera with Fiber Optic Output

E. G. BURROUGHS AND A. J. KENNEDY

Night Vision Laboratory, Fort Belvoir, Virginia 22060

(Received 17 December 1965; and in final form, 24 February 1966)

The design and performance of an electron microscope camera with fiber optic output is described. A line resolu­tion of 30-35 line pairs per millimeter was obtained on the negative of the Polaroid type 55 PIN film. The general features described may be helpful in developing an adaptation for other instruments.

THE design and performance of an electron microscope camera with fiber optic output is described. The

camera was developed for a bakeable ultrahigh vacuum (UHV) electron microscope,! where the high bakeout tem­perature (about 400°C) and the clean vacuum require­ments preclude the use of a conventional photographic chamber. Since the UHV electron microscope is still under development the performance of the camera was tested on an ion pumped JEM 6A electron microscope. This also presented an opportunity to evaluate the usefulness of this camera as an attachment for a conventional electron micro­scope with ion pump conversion.

A cutaway drawing of the complete camera is shown in Fig. 1. The high resolution fiber optic plate2 in our design has a thickness of 0.5 em and a diameter of 4.6 cm. It is sealed to a Kovar cylinder which is welded to a type 304 stainless steel Viton O-ring flange. The vacuum side of the fiber optic plate is coated by a settling method with a high resolution P-20 type phosphor layer. The average particle size of this phosphor is on the order of 1-2 J.L. An

1 A special purpose UHV electron microscope is being developed in our Laboratory for the investigation of highly reactive vacuum de­posited thin films in situ.

2 The high resolution fiber optic plate was obtained from Mosaic Fabrications, Inc., 205 Chapin Street, Southbridge, Masschusetts. Since up to 30 cm diam high resolution fiber optic plates are available from the same source, an increase in the diameter to about 8 cm would be advantageous to make better use of the Polaroid lOX 12.7 em film used in the camera.

800-1000 A thick aluminum film is vacuum deposited on the phosphor to eliminate static charges and to increase the light feedthrough. This layer acts as a mirror for the visible light emitted by the excited phosphor, but does not appreciably scatter electrons.

The air side of the fiber optic plate is polished to an optical flat to ensure distortion free contact with the nega­tive. The spring loaded stainless steel pressure plate, which incorporates a conventional Polaroid No. 500 film holder, provides adjustable pressure contact between the fiber optic plate and the negative of the Polaroid type 52, 55, and 57 films. To ensure maximum sharpness, the compres­sion in the springs is adjustable by four knurled nuts to provide adequate uniform con tact pressure withou t damage to the fiber optics. A simple mechanism retracts the pres­sure plate for loading and unloading the film cassette.

The line resolution of the Polaroid type 52, 55, and 57 films was investigated with a standard Air Force resolution pattern illuminated with collimated white light. The limit of resolution of the positives was about 15-18 line pairs per millimeter (lp/mm), and about 80 Ip/mm on the negative of the type 55 film. The P-20 phosphor used has a resolution in excess of 100 lp/mm. The vacuum tight fiber optic plate, which has a numerical aperture of approximately 1 and an opaque second cladding for extramural absorption to eliminate cross talk, has a resolution limit of 90 Ip/mm. The aluminized phosphor coated fiber optics has demon-

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:

130.113.111.210 On: Sat, 20 Dec 2014 15:14:25

772 E. G. BURROUGHS AND A. ]. KENNEDY

strated a resolution of about 60 Ip/mm. However, when contact prints were made only 3S Ip/mm could be resolved on the negative of the type SS film. This loss of resolution is probably due to the following three factors in the contact photography process, the zero working distance of the fiber optic plate, the finite thickness of the photographic emul­sion, and the very thin protective layer covering the emulsion. The zero working distance of the fiber optics means that an image is in focus only on the surface, be­cause light is emitted from the individual fibers with a cosine law distribution. The separation between the output of the fibers and the photographic emulsion, as well as the thickness of the emulsion itself, permits the light emitted from an individual fiber to expose an area greater than the approximately 30 f.L2 cross section of the fiber itself. This reduction in resolution can be alleviated by photo­graphing at higher electronic magnification with very satis­factory results.

High contrast contact photographs of pre- and self­shadowed carbon replicas of various glass surfaces and of thin films vacuum deposited on carbon film substrates were obtained through the fiber optic window. A typical example is shown in Fig. 2. The photographs can be developed in ordinary room light which completely eliminates darkroom preparation and processing. The immediate availability of the results is very convenient and economical, particularly when only a few photographs are taken at a time. Also, direct coupling of a single or multiple stage photocathode image intensifier tube is possible.

CYLINDER

VITON O-RING

POLAROID NO. 500 FILM HOLDER

FIG. 1. Electron microscope camera with fiber optic output.

FIG. 2. A typical contact electron micrograph showing a recrys­tallized Ag film deposited to 50% light transmission on carbon sub­strate (X 100 000).

The cleaner vacuum system has made the reduction of polymerized organic material apparent.3 After days of con­tinuous pumping the contamination rate, as measured on Kodak contrast plates by the decrease in the radius of a hole in a holey carbon film, was reduced by a factor of X30 to about 0.03 A/sec. This effect was probably the result of the ion pump conversion and that all gaskets in the microscope column and vacuum manifold were replaced by ones made of Viton. Although no further appreciable decrease in the contamination rate was measurable with the use of the fiber optic camera, it eliminated the film charge-up and the long pumpdown time4 required to obtain the base pressure in the electron microscope due to the outgassing of the conventional photographic plates.

Since commerical flber optic cameras are not available for electron microscopes the general features described in this paper may be helpful in developing an adaptation for other instruments. On the JEM-6 electron microscopes, for example, a fiber optic window could easily be in­corporated on the regular photographic chamber, which would make it possible to take either conventional or con­tact photographs. The only modiflcation that would be required is to replace the isolating valve on the photo­graphic chamber with a thin gate valve5 and to install a high resolution fiber optic window in place of the vertical motion mechansim of the isolating valve.

3 R. E. Hartman, Symposium On Quantitative Electron Microscopy, Washington, D. C. (1964).

4 Approximately 3 days were required to reach the base pressure of about 10-7 Torr, because at the best obtainable roughing pressure of approximately 10-3 Torr the pumping speed of our Ultek ion pump is only about 30% of its rated 200 liter/sec speed. Moreover, ion pump outgassing, which occurs when operated in 10-L 10-4 Torr, further reduces the effective pumping speed.

5 J. C. Sheffield, Rev. Sci. 1nstr. 36, 1269 (1965).

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:

130.113.111.210 On: Sat, 20 Dec 2014 15:14:25