US3515587A - Method for changing the optical characteristics of an article - Google Patents

Description

United States Patent 3,515,587 METHOD FOR CHANGING THE OPTICAL CHARACTERISTICS OF AN ARTICLE Eugene C. Letter, Penfield, N.Y., assignor to Bausch & Lomb Incorporated, Rochester, N.Y., a corporation of New York No Drawing. Continuation-impart of application Ser. No. 706,700, Feb. 19, 1968, which is a continuation-in-part of application Ser. No. 355,959, Mar. 30, 1964. This application Dec. 27, 1968, Ser. No. 787,547

Int. Cl. B44d J/18 US. Cl. 117-217 4 Claims ABSTRACT OF THE DISCLOSURE A substrate is coated with a thin film of an alkali halide such as sodium chloride. Predetermined portions of the alkali halide film are colored by bombardment by an electron beam or a glow discharge to produce colloidal color centers. A further feature includes an electron conductive film between the alkali halide film and the substrate to improve color contrast.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of my copending application Ser. No. 706,700, filed Feb. 19, 1968, and now abandoned, which application was a continuation-in-part of my prior application Ser. No. 355,959, filed Mar. 30, 1964, and now abandoned BACKGROUND OF THE INVENTION This invention relates to a new optical element and a method for changing the optical characteristics of the element, and in particular to a novel method for changing the color in predetermined areas on a surface of a coated article.

It has been determined that it would be desirable to be able to produce new articles comprised of a substrate such as glass coated with a thin film, the color of the film changeable by exposure to electron beams. Such a method can be used to produce, among other things optical scales, reticles, gratings, thin film circuits, filter elements, electron sensitive films, photosensitive elements, as well as devices for data storage and data recording.

Electron beams have low deflection inertia, high energy, high resolution, and are relatively flexible, i.e., they may be deflected and controlled easily and rapidly by electrical signals. In addition, their energy density is relatively high so that writing times are relatively short. Therefore, it is desirable to incorporate electron beams for recording picture elements or information bits. One approach to utilizing electron beams for recording purposes is disclosed in the article, Thermo Plastic Recording, by William E. Glenn and J. Edmund Wolfe, which appeared in International Science and Technology, June 1962, at pages 2835.

Studies of ionic crystals under electron bombardment indicate that small crystals of the alkali halides produce colors when the crystal is subjected to X-rays, cathode rays, and also by heating above 600 C. in an atmosphere of an alkali metal.

Coloration of a halide fihn is the operative mechanism in the well-known skiatron tube as typified by US. Pat. No. 2,545,200 granted Mar. 13, 1951 to G R. Fonda. However, in this type of tube the image does not last and fades shortly after projection onto the screen. Such a device cannot be used for recording or information storage as the image is not of a permanent nature. Images of this type are generally not sharp at the edges and therefore, this teaching would not be applicable to making a precision reticle or ruling.

SUMMARY OF THE INVENTION In order to produce the articles as disclosed above, I have found that when a suitable substrate such as glass is coated with a thin film of an alkali halide, the film or predetermined areas thereof, may be colored by exposing those areas to electron bombardment. The electron bombardment may be achieved by a controlled beam of electrons or by glow discharge. In the latter case the predetermined areas would be exposed through a suitable mask such as a photoresist. The preferred method of practicing the invention utilizes a beam of electrons in the order of 1 to k v. to produce the desired coloration.

Accordingly, it is the primary object of the present invention to provide a method for producing a color change in portions of a coated substrate.

It is a further object of the present invention to provide a method for producing a color change in an alkali halide film deposited on a glass substrate.

-It is another object of the present invention to provide a method of controlled coloration in an alkali halide film deposited on a substrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the practice of the invention a substrate such as glass is cleaned and placed in a vacuum chamber. An alkali halide such as sodium chloride is placed in a molybdenum or tungsten boat. The use of a small boat requires the use of a current of about 20 to 50 amps to obtain the 10-20 volts used for evaporating the sodium chloride. The pressure in the chamber is reduced to a pressure of less than 1 1O- mm. of mercury and preferably to a pressure in the range of l l0 to 1 10- mm. of mercury. An electrical current is passed through the boat to raise the temperature of the sodium chloride whereby a thin film of sodium chloride will be deposited onto the substrate. It is believed that a thin film of onequarter wavelength of light measured at approximately 5500 A. units produces satisfactory results. Other thicknesses will be desirable for different applications. At this thickness the sodium chloride film is transparent in order to provide the contrast between those areas containing reduced colloidal color centers and the rest of the layer.

It is desirable for some purposes to deposit an opaque, semitransparent or transparent film of a metal or conductor such as aluminum, copper, silver, gold, tin oxide, etc., onto the substrate prior to depositing the sodium chloride. The aluminum film has been found to improve the color contrast for various operations. I have found that by grounding (relative to the negative electron beam) the thin conducting film the rate of coloration increases and the contrast is improved. The aluminum may be deposited under similar conditions to those used for forming the sodium chloride film. Accordingly, the use of multiple sources allows for multiple depositions to be made without breaking the vacuum.

It is known in the prior art to use a conducting film such as I use in a skiatron type tube for decreasing the erasure time. This is typified by US. Pat. 2,836,754 granted to F. Holborn et al. on May 27, 1958. However, I find the film does not only not cause the image to fade, but rather deepens the contrast and improves the image quality.

The conducting film must be placed between the halide film and the substrate in order to ground the electrons. The electrons must strike the sodium chloride film in order to produce the reduced colloidal color centers. If the conducting film was placed between the sodium chloride and the electron source and made conductive to the electron beam the grounding would not take place. Conversely, if the conducting film was opaque to the electron beam and on top of the sodium chloride film the colloidal color centers would not be formed. -It is therefore imperative that the conducting layer be placed between the substrate and the sodium chloride film.

The color of the alkali halide film may be changed by irradiating the film. Irradiation can be accomplished by a glow discharge at a pressure of about 1-20 microns of mercury. The glow discharge for a non-directed beam was a D-C glow from i to 5 kv. and -180 milliamps. Using a controlled beam of electrons it is necessary to have a beam of electron in the order of l-lOO kv. to produce the desired color change.

The color centers are produced by a method of reduction using low energy electron beams. Using this method the color produced in the sodium chloride film is in the blue region of the visible spectrum. A discussion of the theory underlying the formation of colloidal color centers is contained in Color Centers in Solids, by Schuman and Compton, 1962, pages 256 to 273.

I have found that a device a described above can be used to measure the degree and uniformity of a glow discharge in a vacuum coating chamber. Heretofore there has been no reliable method for measuring the intensity of discharge across a substrate to be vacuum coated. Placing a glass substrate coated with a sodium chloride film, similar in size to the article to be coated, in a vacuum chamber in the position where the piece to be coated is normally placed and exposing this piece to the conditions (e.g., pressure, temperature, time and intensity of irradiation) to be used for vacuum coating will cause coloration of the film.

The test sample can then be removed and examined for variations in color intensity across the film. The variations in color intensity will denote variations in the intensity of discharge, other conditions remaining constant, to be expected when an actual coating run is taking place. Based upon this information corrections in the vacuum coating cycle can be made.

Having thus described my invention by reference to a preferred embodiment I wish it understood that it may be modified or embodied in other forms without departing from the spirit and scope of the appended claims.

I claim: 1. An optical element comprising a substrate and a thin film of alkali halide supported by said substrate, a

4 thin electrically conductive film separating said substrate and said alkali'halide film,

said substrate being glass,

said alkali halide film being sodium chloride, and

said thin conducting film selected from the group consisting of tin oxide, copper, aluminum, gold, and silver.

2. An optical element according to claim 1 in which the sodium chloride film has a thickness of about onequarter of a wavelength of light measured at about 5500 A. units.

3. An optical element according to claim 1, wherein the alkali halide film contains reduced colloidal color centers.

4. A method for changing the optical characteristics of an article comprising the steps of providing a glass substrate,

coating said substrate with a conducting film selected from the group consisting of tin oxide, aluminum, copper, gold, and silver,

grounding said conducting film,

depositing a sodium chloride film onto the conducting film, and

exposing the sodium chloride film to a controlled beam of electrons at 1-100 kv. to thereby produce colloidal color centers in the sodium chloride film.

References Cited UNITED STATES PATENTS 2,532,971 12/1950 Van Leer et al. 2,533,381 12/1950 Levy et al. 2,545,200 3/1951 Fonda. 2,836,754 5/1958 Holborn et al. 2,903,378 9/ 1959 Rychlewski.

OTHER REFERENCES Wikkenhauser, G.: The Skiatron or Dark Trace Tube, in Electronic Engineering, 20 (239), pp. 20-22, January 1948.

Honig, I. M.: Imperfections in Crystals, in Journal of Chemical Education, 34, No. 7 (1967), pp. 343-347.

ALFRED L. LEAVITT, Primary Examiner C. K. WEIFFENBACH, Assistant Examiner US. Cl. X.R.