US2431923A - Photographic record and method of forming same - Google Patents

Description

G. L. DlMMlCK Dec. 2, 1947.

PHOTOGRAPHIC RECORD AND METHOD OF FORMING SAME Filed Aug. 23, 1943 Zinnentor film ml. [Mm/[k m m I 6 m M \W I 5 6 1 5 Z W fl r V Z Cittorneg Rammed Dec. 2, 1942' PHOTOGRAPmC RECORD AND METHOD OF FORMING SAME Glenn L. Dimmick, Indianapolis, Ind., assignor to Radio Corporation of America, a corporation of Delaware Application August 23, 1943, Serial No. 499,598

7 Claims.

My invention relates to the control of thermally evaporated films, and more particularly to controlling the deposition by radiant energy according to a desired pattern as, for example, an image.

In my applications Serial No. 470,583, filed December 30, 1942, now Patent No. 2,397,929, and entitled Reduction in reflection from glass, and Serial No. 348,815, filed July 31, 1940, now Patent No. 2,338,233, issued January 1, 1944, and entitled Reduction in reflection from transparent material, I have described methods of depositing by thermal evaporation certain metallic fluorides and sulfides onto the surface of lenses or other optical elements in order to decrease their surface reflection. In my application Serial No. 372,811, filed January 2, 1941, now Patent No. 2,338,234, issued January 1, 1944, and entitled Evaporation of transparent material on glass, I have described a method and apparatus for determining the thickness of the applied coating, this method having been found particularly useful in determining the thickness of each layer of a multi-layer coating disclosed in the above mentioned application Serial No. 470,583, now Patent No. 2,397,929.

One object of the invention is to provide a useful and novel method of controlling the deposition of evaporated solid material in accordance with a desired pattern.

Another object of the invention is to provide a new photographic method of making lasting images or records, using evaporated material without the use of masks.

Still another object of the invention is to provide' an improved photographic image of dense material with substantially no grain, particularly adapted for a high degree of enlargement.

Other and incidental objects will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawing, in which,

Fig. 1 is a sectional view in side elevation, reduced in size, of a thermal evaporation apparatus embodying the present invention,

Fig. 2 is a plan view of an optical element of Fig. 1, illustrating a result of the invention, and

Fig. 3 is a diagrammatic view of the invention applied to photography, as in a microscope.

For a complete description of the apparatus, reference is made to my prior application, Serial No. 372,811, filed Jan. 2, 1941, now Patent No. 2,338,234 and entitled Evaporation of transparent material on glass, of which the figure in the drawing is similar to Fig. 1 of my present application. To give adequate background for the present invention, the method and apparatus in common of the prior application is described below, with changes and additions descriptive of the present invention.

The evaporation apparatus includes a heavy base ID of appropriate material such, for example, as steel on which is mounted a bell jar H which may be sealed to the base by any appropriate sealing compound. A high vacuum pump 12 attached to a backing or fore pump 13 is connected to the interior of the bell jar through the large aperture 14. A filament or heating coil I5 is provided adjacent the .material to be evaporated. This material may be placed in the filament in the form of a paste, or a small boat of the material may be placed in the filament or below it as shown at 8. One end of the filament is connected to the base plate I0 through the terminal 16, while the lead from the other end passes through an appropriate insulating connection H in the base 10 to the source of current 18. The current applied to the fllament may be adjusted by the resistor l9 and measured by the ammeter 20 in the usual manner, the return lead from the ammeter being connected for convenience to the base Ill.

The objects to be coated, indicated at 23, are supported on the member 22. The evaporated material passes through holes in the member 22 to the surfaces of the objects 23. A test or optical wedge 24 is similarly placed over a hole in the member 22 and serves to provide the indication of the thickness of the deposited film.

Light from the source 25 which may be an incandescent lamp, preferably of the type used as an exciter lamp in film sound reproducing apparatus, is directed by the condenser lens 26 onto the wedge 24. The upper surface of the wedge 24 is located at such an angle that light reflected therefrom will not reach the filter 21. Light reflected from the lower surface of the wedge 24, however, is directed through the color filter 21 onto the photocell-electron multiplier tube 28. It will be noticed that the photocell 28 is so located that light from the filament l5 will not reach it and, if used in a lighted room, the tube 28 would be appropriately enclosed as well as being shielded from direct light from the source 25. The photocell is provided with an appropriate source of current 29 and with an appropriate meter 30 for measuring the current therethrough. If the usual alkali metal type of photocell is used, the meter 30 will be a microammeter. An R. C. A. 931 electron multiplier photo tube is normally used as a light control means. The color filter 21 is chosen so as to transmit light of the wavelength for which the um or maximum reflection is desired.

The lamp 25 and the photocell 28, together with its attendant filter, are made movable in a vertical are about the bell Jar so that the angle of incidence of the light may be varied and the reflected beam may be picked up. If the surfaces to be coated are of such a nature that the average angle of incidence of the light is to be 45, then the lamp and photocell would be arranged approximately as shown at angles of 45 to the normal to the bottom surface of the wedge 24. If a lens of relatively small angular aperture is to be coated or, similarly, if an optical element which is to be used at a small angle to the average angle of incidence of the light is to be coated, the lamp and photocell are moved upwardly until the angle of incidence and reflection correspond.

The manner of operation of the apparatus is as follows: The elements to be coated 23 and the wedge 2 are placed in position after the filament 15 has been charged with the coating material and the bell jar I l is evacuated to an appropriate degree, approximately 0.1 micron. The filament I5 is then heated with the exciter lamp 25 in operation, and the current through the microammeter is observed. This current will fall at first rather slowly as the filament I5 approaches the proper temperature and then more rapidly as the material evaporates at a substantially continuous rate. The rate of rise or fall of the current through the microammeter will gradually decrease until the current momentarily reaches a practically stationary value, after which it will reverse direction. If the current to the filament I5 is cut off just as the microammeter reaches its first maximum or minimum depending on the index of refraction of the evaporated material and that of the glass, a coating will be produced on the element having a, thickness of a quarter of a wavelength of the average light transmitted by the filter 21. A slight allowance must be made for the fact that the filament l5 and its charge do not cool instantaneously, and the evaporation proceeds at a decreasing rate for a few seconds after the current is turned off through the filament.

In accordance with the present invention, mercuric sulfide, HgS, was evaporated in vacuo from a lava boat 8 heated by a molybdenum coil I! located across the top of the boat 8. The coating was applied to the optical wedge 24 in the usual manner, as above outlined, using the light beam and photocell-amplifier to determine the coating thickness.

The needle on the meter started going up when the current through the coil I5 was about 12.5 amperes. On the first test the reflectivity went up to 280% and on the second 340%. In both cases, an image of the light filament was formed, on both surfaces of the test wedge, and a spot was formed where the light beam passed through the jar (on the inside of the jar). The evaporated mercuric sulfide did not deposit on the uniliuminated areas of the top side of the wedge (as ZnS does) because there was no pattern showing where the glass was covered by the holder on top. The only coating on th top surface of the wedge was the image of the lament, but the underneath surface had a coating which looked like the other sulfide coatings, as well as a heavier deposit forming an image 01 the light filament.

The image darkened when the coating was sub- Jected to the usual baking process for several hours at C. When the baking was continued several hours longer at C. (overnight) the image disappeared. From this I learned that the coating should not be baked at a temperature above 120 C. if the image is to be retained.

It was found that the ultra-violet content of the light was responsible for the formation of the image in the deposited film. While I do not wish to be limited to any theory of operation, it is believed that HgS is negatively charged when it is evaporated. It is also believed to have photoelectric properties by which ultra-violet light al lows the negative charge to escape. Thus where there is light, the particles are neutral and deposit normally. In the absence of light, a negative charge accumulates on the glass and repels charged HgS molecules.

In order to make the image and the coating durable in regards to water, certain chemicals, abrasion, etc., a superficial layer of thorium oxy fluoride the material disclosed in my said application Serial No. 470,583, Patent No. 2,397,929, issued April 9, 1946, may be finally applied over the mercuric sulfide coating. Fig. 2 ShOWs the image of the lamp filament 25 that was formed on the bottom surface ofthe glass wedge 24 in the deposited HgS coating. An image or print can be formed also from a photographic negative. The .image is negative by transmission and positive by reflection.

Fig. 3 shows the application of the invention to a species of photography, e. g., as applied to microscopy. An object, such as a biological specimen on a plate 6, illuminated by alight source 25, is placed in proper spaced relation to the lens system 2 for projecting an image upon a glass plate 4. The lenses of the projection system may be outside the vacuum if desired. A grainless lasting image or record is formed by evaporation from the source of heated mercuric sulfide, as in the case of Fig. 1. Such an image is capable of a substantial amount of magnification subsequently without substantial loss in detail, in view of the grainless nature of the recorded image.

I am aware of the fact that an image has been formed prior to my invention in a thermal y deposited metal film, but as a result of a different process which is not adapted to the photographic uses given above. In Strongs textbook Proceedings in Experimental Physics," page 174, published 1942 by Prentice Hall, a crude image of the evaporating filament was formed by the passage of the evaporated material through a pin hole in a plate onto the depositing surface. This was an interesting experiment but lacks the utility and advantages of the present invention.

Strong also shows a rotating cam-like mask for controlling the distribution of evaporated material specifically to control the relative thickness of different portions. According to the present invention, however, a novel way has been found to control the deposit by intangible means such as rays of radiant energy characterized by greater flexibility of control and many practical possibilities.

The efiect of radiant energy, particularly ultraviolet, in influencing the deposit of evaporated material as above described is something heretofore unknown. It will be understood that other uses and modifications, particularly as to other materials, are possible without departing from the spirit and scope of my invention. The invention, therefore, should not be restricted except in so far as is necessitated by the spirit of the appended claims.

What .I claim as new is:

1. The method of forming-a lasting image on an untreated surface which comprises thermally evaporating mercuric sulfide material in vacuo and controlling the deposit of said material upon said surface by means of a beam of ultra-violet light waves focused on said surface during said deposit.

2. The method of controlling the deposit of mercuric sulfide material from a source onto a surface of a support which comprises causing the passage of particles of said material from said source to form a film of said material on said surface, and varying the nature of said deposit by the action of ultra-violet light wave energy upon said particles adjacent said surface.

3. The method of depositing a thin film of mercuric sulfide material on a surface which comprises thermally evaporating said material from a source to form a vapor, depositing from said vapor a film of said material upon said surface and subjecting said vapor adjacent said surface to ultra-violet light to control the deposit.

4. The method of forming a photographic image or print on a surface which comprises thermally evaporating mercuric sulfide in an inertatmosphere and causing the deposit of said material upon said surface while controlling the deposit upon selected portions of said surface by means of a beam of ultra-violet light directed upon said surface.

5. The method of controlling a vaporous deposit upon the surface of a transparent support body which comprises thermally evaporating mercuric sulfide in an inert atmosphere and causing the deposit of the vapor upon said surface while controlling the deposit upon selected portions of said surface by means of ultra-violet light selectively directed upon said surface.

6. The method of depositing a thin film of mercuric sulfide material upon a surface which comprises thermally evaporating said material from a source to form a vapor, and depositing from said vapor a film upon said surface while subjecting said vapor adjacent said surface to ultraviolet light to control the deposit and subsequently heat treating said surface.

7. A photographic record comprising a support surface, a thin film of mercuric sulfide deposited on said surface as a substantially grainless permanent image and a thin layer of thorium oxyfluoride superposed on said film.

GLENN L. DIMMICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 125,726 Davis Apr, 16, 1872 689,525 Wagner Dec. 24, 1901 1,529,643 Fenderl Mar. 10, 1925 1,647,857 Colbert Nov. 1, 1927 1,802,168 Colbert Apr. 21, 1931 1,818,760 Selenyi Aug. 11, 1931 1,902,213 Brockway May 21, 1933 1,994,483 Ott Mar. 19, 1935 2,042,049 Heidenhain May 26, 1936 2,060,977 Boer et al. Nov. 17, 1936 2,103,623 Kott Dec. 28, 1937 2,153,628 Knoll Apr. 11, 1939 2,221,776 Carlson Nov. 19, 1940 2,239,452 Williams et el Apr. 22, 1941 2,252,770 Janes Aug. 19, 1941 2,263,008 McRae Nov. 18, 1941 2,281,638 Sukumlyn May 5, 1942 2,297,691 Carlson Oct. 6, 1942 2,338,234 Dlmmick Jan. 4, 1944 2,338,497 Dimmick Jan. 4, 1944 2,351,537 Osterberg June 13, 1944 OTHER REFERENCES Clerc, Photography Theory and Practice, pub. by Sir Isaac Pitman 8: Sons, Ltd., New York 1930, P e 293.

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