US2990493A - Thin-film window device - Google Patents

Description

June 27, 1961 J. M. SEEHOF ETAL 2,990,493

THIN-FILM wmnow DEVICE Filed Dec. 25, 1957 24 Jase 2 INVENTORS JERROLD M.SEEHOF MELVIN S.ARMSTRONG STUART B. SMITHBERG WJJW THEIR ATTORN YS United tates Patent 2,990,493 I THIN-FILM WINDOW DEVICE I Jerrold-M. Seehof, Gardena, Melvin 8. Armstrong, Lomita, and Stuart B. Smithberg, Inglewood, Calrfl, assignors to The National Cash Register Company,

Dayton, Ohio, a corporation of Maryland Filed Dec. 23, 1957, Ser. No. 704,532

13 Claims. (Cl. 313-74) This invention relates to thin-window devices for scientific and other apparatus, and more particularly to thinwindow devices which are permeable to streams or beams of low-energy electrons and which may be of relatively large diametral dimension and which can successfully withstand a pressure differential of the order of one atdesirable has been a window of relatively large length and width, that is, of relatively large diametral dimension, with the aforestated strength and electron permeability'. For example, as indicated by US. Patents No. 2,616,961 and 2,630,484 to J. Groak, such a window device would make practicable'an ultra-high speed printer by eliminating the impracticable operation of the paperhandling structures in an evacuated chamber.

As another example of the indicated utility of a window of the stated nature, there may be cited'an apparatus for electronic photography, such as is disclosed in Scientific American magazine, March 1956,

7 pages 81, 82, 84, 86, 88, and 90. In the latter apparatus an optical image of a region of outer space is focused upon a photocathode located in a high-vacuum chamber, and the electron emission from the photocathode is focused upon a photographic plate. In that particular apparatus, practical considerations require passage of j the electron stream through a thin-film window situated between the photocathode and the photographic plate; but the thin-film window therein used must be 'well protected against any appreciable pressure diife'rential. Hence that thin film is initially sealed in the high-vacuum chamber, protected by a breakaway cap which is not broken until a chamber containing the photographic plate is evacuated to a high vacuum. In that device, the thin-film window serves mainly to prevent contamination or poisoning of the photocathode by substances evolved by the plate and its coating; and the apparatus isnot reusable.

The prior art offers considerable evidence of the longfelt need of an electron-permeable window device of the character indicated, and further portrays the results of a series of futile eflorts to solve the problems incident to production of a satisfactory device. The US. patent to Knoll, No. 2,263,733 presents a lengthy list of desired results in respect of electron-permeable windows, and is replete with suggestions as to how the results were expected to be attained. This indicates that as early as 1929 the need for a pressure-resistant window was evident. Later art, such as US. Patents 2,004,176, 2,373,- 661, and 2,617,953, shows a continuing unfilled need for a window of the type described. That none of the prior art suggestions or teachings resulted in a practical window The above cited article in the March 1956 issue of Scientific American magazine is pertinent in this respect I .of operating at relatively high temperature.

"one atmosphere being defined as 55' shown).

Patented June 27, *1961 2 It is evident, then, that a gas-tight electron permeable thin-film window capable of withstanding an atmosphere of :pressure difierential would greatly simplify theapparatus and procedures connected with theoperations of the exemplary systems mentioned, and would, permit or facilitate a wide variety of other research and scientific investigations. Accordingly, it is a principal object of the invention to provide an electron-permeable gastight thin-film window device of relatively large transverse dimensions and-capable of withstanding a pressure differential of the order of-one atmosphere. A subsidiary object of theinven'tion is to provide an electron-permeable gas-tight thin-film windowdevice capable of withstanding a pressure ditferential of the order of one atmosphere at temperatures of the order of 500 C.

Another object of the'invention'is to provide a gastight electron-permeable thin-film window device capable Other objects and advantages of the invention will become apparent or be made evident in the appended claims and ensuing description of a preferred embodiment of apparatus according to the invention as illustrated in the accompanying drawings, of which: f

FIG. 1 is a partly schematic diagram of a cathode ray tube incorporating a window device according to, the invention;

- FIG. 2 is a fragmentary sectional view showing-ya "window device according to the invention as employed in a printing apparatus;

FIG. 3 is anexploded view of principal of an exemplary assembly adapted to forman insert type of window device according to the invention;

FIG. 4 is a magnified representation of a small rectangular section of an. exemplary matrix and thin-film ac- .cording to the invention, with a portion of the thin film In the drawings there is illustrated a preferred but ex- ..emplary form of dimensionally large thin-film window device capable of withstanding a pressure diflerential of the order of at least one atmosphere and permeable to low-energy electrons. By dimensionally large it is meant that the eflective window opening may be at least two centimeters in length and width, or at least two centi meters in diameter. By a pressure differential ofthe order of one atmosphere is meant a difierence in fluid pressure on opposite faces of the thin-film of the window device of from one-half to' one and one-half atmosphere; I approximately 1033 grams per square centimeter.

Referring to FIG. 1, a window device according-to the invention is shown as applied to the target end of an exemplary type of cathode ray tube 20. The evacuable vessel or envelope 21 of the tube may enclose a source of electrons such as an electrically heated filament 22,

conventional electron-accelerating and electron-beatnshaping means such as is indicated at 23, electron-beam deflection means such as vertical and horizontal electrode pairs 24 and 25. The pairs of deflecting plates may be provided with sealed leads such as 24a, 25a, respectively, for application of beam-deflecting potentials; and the tube may be provided with other conventional control means such as a magnetic focusing and deflection means-(not Envelope 21 includes an end wall 21a which may be of conductive metal or of conductively coated glass as in conventional cathode ray tubes. The end wall is'provided with a suitable aperturein which a win- 'ductive material such as metal, to which is secured an -ext-remely thin-film of an electron-permeable material.

The matrix of film-supporting element may be of any of a variety of forms, but preferably is of very finemetal -m'esh, electroformed or woven. An exemplary suitable -mesh is 80 count nickel-copper Lektromesh marketed iby t C., 0.. Jellif Corporation, Southport, Connecticut. The electron-permeable thin-filmwhich is supported by thewmatrix andwhich'may, for example, beof the order of eighty micro-inches thick, is substantially impermeable to atmospheric gases, and with its supporting matrix is capable of withstanding a pressuredifferential of the order of one atmosphere. The preferred mode of producing a window device as exemplified. in FIG. 1 comprises :the' following steps:

(1) The matrix or, mesh 30, in the form of a discCFIG. 3'), is pressed into a flanged electrically conductive mount 27 by an internal metallic ring 31 which forms a close fit with the mesh in .the mount, as indicated in FIG. 2. Themounting is analogous to mounting a piece of cloth in an embroidery hoop, and the result is that the mesh is '-;firmly.snpported about its periphery and is taut. (2) The mounted mesh is thoroughly and carefully cleaned, as by using trichloroethylene followed by detergent'z'andihot water. and distilled water baths, in an ultrai-sonic-cleanerdevice; and the assembled components dried.

(3) ,A commercial 3% aqueous dispersion (by weight) :of: sodium bentonite gel is diluted to a .4% dispersion distilled .water, and the dispersion very carefully spread over the exposed portion of the mesh. .Care is exercised to make certain that all openings in the mesh contain: a;-fihn of: the dispersion.

(A) The mountedand coated matrix is placed under cover and carefully dried. A drying period of considerable duration, as forty hours, may be necessary for pgoper drying.

(5.)..'Ihe mount, matrix and coating or film are. carefully baked; for example, eight hours at 315 C. a L (.61) After. cooling,.the peripheral areastof the device warefsealedg astwith .Pyseald or apiezon wax, to insure .gasatightness between, ring 31 and mount 27.

:Thewindow device is. most conveniently applied to :1 thertubeend wall 21a bypartial insertion in the aperture ;..fonmed..in the wall, a hardening. sealant beingemployed was-indicated at32 (FIG-2) andthe fiangeof the'mount slicing pressed against the. exterior face of the end wall tsosthata firmand. gas.-tight.support is secured. There- ,afterl'the: vesselimaylbeevacuated, as byway of the tube 129n(:EIG.. 1).. As indicated imFIG. 4, .in which a small :section. of .a: completed device is .shown considerably magnified and with a portion of the thinefiim removed, =2thezex emplaryi matrix; 30tis a foraminous sheetlike structure produced by 'electro-formin-g and having clear openings or apertures 30a therethrough. The openings as depicted are of generally square configuration, and form massages-through which low-energy electrons pass .prior "to passagethrough the thin-film which extends across the openings in the matrix. The matrix may be of other eenfigurations'tha-n the exemplary form shown, but pref- 'erably provides a substantially. planar support for the "thin-film.- The latter, as; depicted at 33 in FIG.-4, is of the order of eighty micro-inches thick and is composed of th'eceramic remainder left upon baking of the dried lav's I "lfiis evident that some electrons of a beam directed at the -thimfilmwindow device installedin an envelope such I as'tu'be 20 impinge-upon the matrix rather than passiii'g through anopening, and for this reason the matrix preferably is made electrically conductive either by being formedof conductive material or by being given a conductive coating, whereby the charge of the intercepted electrons may drain away. As hereinafter explained in connection with FIG. 2, an electron-attracting device may be employedto enhancepassage of electrons through the openings in the matrix; The end portionof the tube,

such as end .walllla, is insulated from the anodevoltage ,of the; tube. That portion of the electron beam. which passes through the thin-film may be made intense enough to produce desired effects. To that end, an intense beam may be produced. Such a' beam may produce considerable heating effect in the thin-film and matrix, and in fact may heat those elements to a dull red glow. However, the thin-film, being of ceramic nature, is capable of-enduring suchtreatment without being harmed; and the filmsupport or matrix, when made of nickel-clad copper,

is eapable'of carrying away the heat to the end wall of the-tube (which maybe metallic) and of radiating acousiderable fraction of the heat. Thus the matrix mayperform the triple role of supporting the thin ceramic film, draining away intercepted electrons, and acting as a heat conductor; while the thin-film not only permits passage of electrons, but excludes gas under a pressure difierential while operating at a fairly high temperature.

As'illustrated in FIG. 2, the window device is adapted such-as 24-, 25 of the tube 20 (FIG. 1), directly onto a surface placed in close proximity to the window device.

'Forexample, as indicated, the beam may be directed to pass through the Window device and onto a moving sensitized film or recordmedium 35. Also, passage of electrons through the window and onto the target may be enhancedby applying an attracting potential to the target ifit be conductive, or by providing a positively charged plateinback of the target if the latter is not conductive.

For example, as indicated in FIG. 2, a conductive plate 34' may be placed in close proximity to the target opposite the window, and connected to a source of potential as indicated, whereby electrons are attracted through the window and drawn to the film or target. The film is, for clarity of illustration, shown somewhat displaced from the thin-window device surface; however, in practice the film or other target may be disposed substantially in contact-with the window device. Under some circumstances; it may be desirable to delimit the areal cross-section of the beam passed through the window, and this may be done,-in-in stances, by so focusing the beam that substantially all of it passes through a single opening of the matrix, usingknown beam-focusing means and techniques.

' In other instances, as where a predetermined pattern or trace-configuration is to be produced-on the target by the beam- (as, for example, in printing a specific predetermined character onabeamsensitive film), the beammay rapidly be deflected to-and-fro across the window, and intermittently suppressed, while the target or film is traversed past-the window in a direction transverse to that of the beam deflection; and in such instances the beam may be. of a selected density and cross-section to suit the circumstances. In the particular usage illustrated in FIG, 2,

the beauty-sensitive record medium 35, in the nature of a strip'film; is drawn from a supply 355' over a guide36 and past the window device by a driven draw roll 37, from which it passes to suitable means such as a receiverroll 38. The record mediumis exposed by the electrons passed through the window device; and it is understood that it may be developed if necessary, by conventional procedure and means (not shown) on its way to roll 38.

Any suitable evacnable vessel may be fitted with a windowdevice of the character described, and any suitable sourceof electrons may be utilized. As indicated in FIG. 5, a window device 40, similar to that previously described and explained, is shown installed in a thickwalled vessel 41 which is evacuable as by way of a tube 42. Within the vessel is situated a source of radiation in the form of a radioactive mass 43 which is depicted as being adhesively secured to the inner wall or surface of the vessel. The vessel may be of suitable radiation-absorbing material, such as lead, and of a thickness to prevent undesired radiation to exit from the vessel through other than the window device. Similarly, the mount and ring of device 40 may be made of a like material to thus substantially restrict exiting radiation to the area of the thin-film and matrix.

From the preceding description and explanation it is evident that the invention comprehends and provides a gas-tight window device comprising essentially a supporting matrix having opposed faces of large dimensions relative to its thickness, and a thin electron-permeable ceramic film supported by the matrix and adapted to withstand at least one atmosphere of pressure differential. While the matrix is shown as one having large transverse dimensions, that is, of large diametral dimensions, it is clear that the window device may equally well be in the form of a long narrow structure. Also, in view of the preceding explanation and description of a preferred exemplary embodiment of the invention, other changes and modifications within the spirit and scope of the invention will occur to those skilled in the art; and accordingly it is not desired to be limited to the specific details of the described structure.

What is claimed is:

1. A substantially gas-tight window device adapted for use as an electron-permeable element of an evacuable vessel, comprising, in combination: a support presenting a transverse opening therethrough from face to face there of; and thin non-vitreous ceramic means permeable to low-energy electrons and substantially impermeable to gas under a pressure difierential of the order of one atmosphere, closing said opening.

2. A gas-tight window device adapted for use as an element of an evacuable vessel, comprising, in combination: a foraminous support of large face dimensions relative to its thickness and presenting a plurality of generally transverse openings therethrough from face to face thereof; and thin non-vitreous ceramic film means permeable to low-energy electrons and substantially impermeable to gas under a pressure differential of the order of one atmosphere, closing said openings in said support.

3. Apparatus for providing a beam of electrons outside an evacuable vessel, comprising: an evacuable vessel having a wall with an aperture therein; a source of lowenergy electrons in said vessel; a window device forming a substantially gas-tight closure for said aperture and consisting essentially of a thin gas-tight electron-permeable non-vitreous ceramic film and a support matrix hav ing a plurality of openings therethrough from face to face and all of the openings of which are closed to passage of gas therethrough by the thin ceramic film; and electrode means outside said vessel and positioned closely adjacent said window device, for attracting electrons through the openings of said matrix.

4. Apparatus according to claim 3, said matrix comprising electrically conductive material.

5. Apparatus according to claim 4, said film comprising essentially a substance capable of withstanding an operating pressure difierential of the order of one atmosphere applied across the faces of the window device.

6. Apparatus according to claim 5, the substance of said film being of baked ceramic material capable of operating at a temperature of the order of 500 C.

7. Apparatus according to claim 6, said vessel having at least said wall made of metal.

8. An evacuable vessel having a wall and comprising: a gas-tight window device sealed in an aperture in the wall of said vessel and comprising as essential parts a support and thin-film means, said support presenting opposite faces of large dimensions relative to its thickness and having a plurality of openings therethrough from face to face, and said thin-film consisting essentially of a thin non-vitreous ceramic film permeable to lowenergy electrons and impermeable to gas under a pressure diiferential of the order of one atmosphere and closing said openings, whereby low-energy electrons may pass through the aperture in the wall of said vessel and gases prohibited entry thereinto, while the vessel is evacuated.

9. A device according to claim 8, said support comprising metallic material adapted to readily conduct heat and electric charges produced by intercepted electrons.

10. A device according to claim 9, said ceramic material being capable of operating to pass electrons and exclude gas while at a temperature of the order of 500 C.

11. A device according to claim 9, said device including a rigid metallic mount in which said support is fixed.

12. An apparatus for supplying a stream of electrons including low-energy electrons to a readily accessible target outside an evacuable vessel, comprising, in combination: an evacuable vessel comprising a wall having an aperture of large transverse dimensions therein; means for supplying a stream of electrons including low-energy electrons for passage through said aperture from the interior to the exterior of said vessel while the latter is evacuated; a gas-tight window device sealing said aperture against entry of gas but permitting exit of electrons including low-energy electrons through the device, said device comprising a foraminous support of large transverse face dimensions sealed in said aperture and presenting a multiplicity of unobstructed openings extending directly therethrough from face to face, and said device also comprising non-vitreous ceramic thin-film means permeable to low-energy electrons and effectively closing said openings against passage of gas under a pressure differential of the order of one atmosphere; electrode means outside said vessel and closely adjacent said window device for attracting electrons through the openings of said support; and said apparatus also including means by way of which said vessel may be evacuated; whereby a stream of electrons directed toward said window device from the interior of said vessel is at least in part passed through said thin-film means for collision with a target placed between said window device and said electrode means.

13. Apparatus according to claim 12 said support being in the form of a heat-conductive matrix of electrically conductive metal.

References Cited in the file of this patent UNITED STATES PATENTS 1,679,894 Bucky Aug. 7, 1928 2,015,570 Sabbah Sept. 24, 1935 2,273,793 Ekstrand Feb. 17, 1942 2,291,476 Kernkamp July 28, 1942 2,617,953 Brasch Nov. 11, 1952 2,657,377 Gray Oct. 27, -3 2,657,378 Gray Oct. 27, 1953 2,820,168 Stiff Jan. 14, 1958 2,887,599 Trump May 19, 1959 FOREIGN PATENTS 560,370 Germany Oct. 1, 1932 592,015 Great Britain Sept. 4, 1947 618,811 Great Britain Feb. 28, 1949 OTHER REFERENCES R.C.A. Technical Note 159, Aug. 18, 1958.

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