US2168259A - Photoelectrically responsive layer - Google Patents

Description

Aug. 1, 1939. P. GRLICH 2,168,259

II'IO'I'OEI.|ECTRICLLYl RESPONSIVE LAYER Original Filed May 3, 1957 Inde/taf PML 'rLc/L ha dzggs.

Patented Aug. l, 1939 UNITEDZS'TATES PATENT Aol-Ficla PHOTOELECTRICALLY R-.ESPONSIYE l Paul (inirliclx, Dresden, Germany, assignor to Zeiss Ikon Aktiengesellschaft, Dresden, Germany Original application May 3, 1937, Serial No. 140,449. Divided and thisapplication August 29, 1938, Serial No. 227,292. In Germany February 22, 1936 3 Claims. (Cl. 25o-27.5)

The present invention is a division of my application for Letters Patent led in the United States Patent Oce on the 3rd day of May 1937, Serial No. 140,449, nowpatent numbered @40,994

5 relating to improvements' in photoelectrically responsive layers and in particular to a method of producing Aminutely subdivided photoelectrically responsive layers upon carriers of any desired kind. Photoelectrically responsive. layers ofl l this type are employed particularly in television transmitting (dissectors) tubes'.

Owing to the resemblance which this minute subdivision has with the surface of screen as used in printing processes they 4are referred to as l5 screen areas in the following--specicati'on Television tubes frequently are provided with extensive photoelectrically responsive areas, and

it has been found that the eiiciency of these areas is enhanced if the same are minutely subdivided, 2g to resemble in appearance that of an extremely ne mesh screen. Whenever a point of light strikes a dot of this photoelectrically'responsive screen area electrical charges are instantly set up with the magnitude of the electric charge dependg5` ent upon the intensity of the light. These charges are utilized for modulating the television transmitter.

'I'he production of screen layers-of photoelec trically responsive vmaterial heretofore was very diilicult, because it is necessary to make the inf.

dividual layer sections extremely small. One method used heretofore consists inA this, that an extremely thin silver coating is deposited by vaporization upon a carrier of insulating material in such manner, that the silver particles -do not form a closely coherent area. Such incoherent layer, however, can be produced only under conditions that the silver coating is extremely thin so as to be almost transparent. Obviously,

the photoelectric eciency of such layers 'is very poor, because the greatest amount of lightpasses unrestricted through the layer.

-It is now an object'of the invention toeliminate the disadvantages vof the known methods of this type. Y

^ Fig. 1 illustrates diagrammatically and highly magnied a plan view of a carrier base provided with nely distributed selenium dots in accord-` ance with the irst method step of the present invention.

Fig. 2 is a cross sectional view substantially along the line of 2-2 of Fig. 1, and the Figs. 3, 4 and 5 are crosssectional -views'similar to Fig. 2 and illustrate additional steps of the method of the invention.

`immediately flow into each other.

The present invention makes use of the fact that selenium, particularly when in an `extremely pure state, has a very high surface tension. It is possible to liquefy nely distributed selenium Without the line selenium droplets thus produced `5 being of such low surface tension that they 'would 'I'his property. of selenium is made use of by the present invention, for producing upon a carriet-base innumerable point-like dots in extreme-v l0 ly fine distribution. The base may be of conductive material, as for instance silver,l or of nonconductive material. These dots are then rendered photoelectrically responsive by some subsequent treatment. y

The selenium screens may be produced in various manners. It is for instance possible to mix the selenium with a oating agent, which may consist of any desired liquid, and to deposit the selenium from this mixture upon the carrier base. .0 Another method, which may be used, consists in mixing finely divided selenium' with a material which forms a paste with the selenium, and

' spreading this selenium containing paste upon the carrier base. 'I'he foreign material may then be 25.

removed from the selenium paste by steaming, dissolution, evaporation or the like.

A very practical method consists in depositing the selenium by condensation from vapor upon the carrier base. VContrary to expectation, it has 30 been discovered that when employing the last named method, the selenium will not be deposited on the base in form of a coherent layer, but up' to a substantial thickness of the layer it will be deposited inthe form of small drops` which are 35 spaced from each other. Only when the seleniumv llayer assumes a very great thicknessthe drops merge and form a` coherent layer. In this re spect selenium has similar properties as for instance mercury. 40

The Figs. 1 and-"2 illustrate diagrammatically in a' greatly magnified scale a carrier base consisting of a plate I of insulating material havingr Aa conductive surface coating 3, for instance silver,

provided with nnely distributed selenium dots 2 45 produced in any one of the just described manners. v

In accordance. with the present invention, the

lnext step consists in the removal of,-the silver` from those portions of the base which are n ot 50 occupied by selenium droplets 2. 'Ihis can be done, for instance, by etching.` Fig. 3 illustrates asection of the carrier after the portions 3a (Fig. 2) of the silver layer 3 have been removed.-

'Ihe agent for etchingmay be, e. g., sodium .55

tmosulphate, ammonia sulpno cyanide, nitric acid etc.

After the partion I" of the metallic coating 3 between the selenium( dots 2 have been removed any suitable means of e. g. carbon-disulphide.

The metallic dots I lare now exposed as shown in Fig. 4 and can now be made photoelectric sensitive by employing any known method. The minutely lsubdivided silver coating, for instance may be oxidised and then'be subjected to the action of light sensitive material, as caesium, whereby the dots of oxidised silver are covered with caesium. The resulting minutely subdivided light sensitive layer composed of caesium dots 4 on oxidised silver dots 3b is illustrated in Figs. 5.

The oxidation is effected in known manner by a glow discharge in an atmosphere of oxygen, and the light sensitive metal, e. g., caesium is deposited by evaporisation, thus forming the well known bodies of Cs-O-Ag. The particles .of caesium. deposited between the silver dots, are finally removed in known manner, e. g., by heating. This is possible owing to thefact, that the adsorptive forces of silver oxide against caesium is greater than the adsorptive forces of thelayer itself.

The insulating carrier of the light sensitive layer may consist of glass, mica or other transparent material or if desired, of materials, which are not transparent.

What I claim'as my invention is:

1. .A method of producing a minutely subdivided photoelectrically responsivey layer upon a carrier of insulating material provided with-a metallic coating, including the steps of depositing on the metallic coating of said carrier unfused selenium particles in .sufdcient quantity to produce from said selenium particles owing to their surface tension a screen-like layer composed of selenium dots, removing those portions of the metallic coating from said carrier which are not covered -by selenium dots, removing the selenium dots,

thereby exposing those portions of the metallic coating formerly covered by selenium, and then applying a photoelectrically responsive metal to the exposed dot-like portions of the screen-like metallic coating.

2. A method for producing a minutely subdivided photoelectricaily responsive layer upon a carrier of insulating material provided with a metallic coating, including the steps of depositing on Athe metallic coating of said carrier by condensation from vapor unfused selenium particles in suillcient. quantity to produce from said selenium particles owingl to their surface tension a screen-likelayer composed of selenium dots. removing those portions of the metallic coating from said carrier which are not covered by selenium dots, removing the selenium dots, thereby exposing those portions of the metallic coating formerly covered by selenium, and then applying a photoelectrically responsive metal to the exposed dot-like portions of the screen-like metallic coating. A

3. A method of producing a minutely subdivided photoelectrically responsive layer upon a carrier of insulating material provided with a metallic coating, including the steps of depositing on the metallic coating of said carrier by condensation from vapor unfused selenium particles in suiiicient quantityvto produce from said selenium particles owing to their surface tension a screenlike layer composed of selenium dots, removing fthose portions of the metallic coating from said carrier which are not covered by selenium dots, removing .the selenium dots, thereby exposing those portions lof the metallic coating formerly covered by selenium, oxidizing the screen-like metallic coating, and then applying a photoelectrically responsive metal to the-exposed dot-like portions of the screen-like metallic coating.

PAUL- GRLICH.

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