Feb- 6, 1940- B. A. DIGGORY ET AL ' 2,138,940 ELECTRON DISCHARGE DEVICE Filed Dec. 2, 1937

H20 mpon

. . B. A. D/GGORV INVENTORS- 61K. TEAL _

A 7' TORNE V ‘ Patented Feb._ 6, 1940 ' 2,188,940;

1 UNITED STATES PATENT Fries v

_ t I ' 2,188,940. ‘ ' . ELECTRON DISCHARGE DEVICE Benjamin A. mil-‘my, Plain?eld, N. 3., macer ; idon K. Teal, NewxYork», N. Y., assignors to f Bell‘ Telephone Laboratories, Incorporated, I . New York, N.v Y., a corporation of New York _ Application December 2,1937, Serial No. 177,660 11 Claims. (01'. 250M275), This invention relates to methods of oxidizing ' tures which is particularly‘ suitable for use in the ' ' metallic elements and to electrode vstructures, preparation‘of electrode structures and photo and ‘more speci?cally to- electrode structures in sensitive targets‘ such as, for example, those used special ‘types of electron discharge devices and in television electronic cameras and electron v to methods of oxidizing the electrodes inysuch vmultipliers. '‘ '. ' i _ ‘ '5 devices.v j _ . '1 X .' In the method according to this invention as In certain electron discharge devices such as, hereinafter described in detail by way of exam for example, photoelectric tubeselectroni'c cam; ple, ozone [(03) is generated ‘by any suitable‘ ‘ era tubes for television, an‘de'lectron multipliers, , means such as, for example, by means of a spark U electrodes having photosensitive surfaces are pro, coil and the gas allowed to flow through‘ water 0 vided. _. In the preparation 'of these surfaces a vapor to moisten it. ‘The moist ozone‘ is then metal face'of the electrode is oxidized and then, passed into theelectronic camera tube or elec in many teases, treated with a metal, such as sil tron multiplier to oxidize the-metal electrode or ver. followed by photosensitization with an alkali electrodes therein, the tube being heated to ‘a temperature of about 50° C. to prevent the water metal._ , I‘ . _ , 3 , ;_ . In the preparation ‘of some'types of standard from condensingtherein'. 'After oxidation of the photoelectric tubes, the oxidation of the cathode ~ \ metallic electrode, the vtube structure-is baked is accomplished by the passage of, an electric out and‘ evacuated at about 250° C. Photosensi m discharge throughan atmosphere of- oxygen'be tizaticn of the oxide ?lm follows this-vbake-out. 0 T" tween the cathode and anode of the tube. This Theinvention will be more‘ readily understood oxidation method is successful in this‘ instance from the following description taken‘ in connec- _ because ‘the ‘electrode being sensitized is fairly tion with the accompanying drawing" forming a ' . symmetrically'disposed relative to the-anode, part thereof in which: , " electrical contactcan be made to, it, it"is me Fig. 1v shows an ‘electronic camera such as is “5 chanically strong, and it is made of 'si1ver,:a used in television transmission in which the 25 material’ which is‘ readily oxidized‘ by electric method of thisinvention may ‘be applied; ‘ _ discharge. Such conditions, however, cannot be' . . Fig, 2 is'an; enlarged cross-sectional view of simultaneously ful?lled in all photoelectric and the mosaic screen or target of the tube shown secondary emission. devices; Asymmetries' in the ‘ in Fig.1; I _ '. 30 electrode structure of aydevice are re?ected in ~' ‘- Fig. 3 shows apparatus for preparing the ozone 30 asymmetries in the electric‘?elds and, where the ‘used in the method of this invention; and‘v ‘ , oxidation is accomplished by means of ‘charged Fig. 4 shows an electron multiplier tube in particles, ‘nonuniformity of oxidation of they which the method‘of this'inv‘entioncan be used. _ electrodes may follow._ ‘In a device in which. the Referring ‘more particularly to the drawing, 3'? electrode is insulated and to which an electrical Fig. vv1 shows an electronic camera tube used as 35' connection cannot bemade, 'it is impossible vto ' a pick-up device in t'elevisiontransmission com, pass a continuous current to it as is done‘ in the prising'an‘evacuated container l 0' enclosing an‘ . discharge method described. above. If the elec electron "gun assembly ll for producing a mov trode to be oxidized‘ is a‘ thin metal film on glass, ing beam ofelectrons and. for accelerating this» W a continuous discharge passed directly to it usu beam toward'a screen S at the end of the tube 40 ‘ ally tears-it o? the glass.‘ Also, it is sometimes‘. remote from the electron gum-and means (not desirable use metals other than silverfas' a shown) for’ causing the beam to scan the various base of a photoelectric or secondary emitting elemental- areas of the screens in turn.‘ matrix and difficulty may‘then ‘be experienced As an example of a satisfactory electron ‘gun. 1' 4-1 in oxidizing the metal by passing ‘adischarge assembly, reference may be madev to Patent ‘1&5 current to it in an oxygen‘ atmosphere. For'ex- ' 2,173,923 to. G. K. Teal, issued September 26,‘ ' ample, copper cannot be; oxidized, at least not > 1939, which/shows and describesan electron gun‘ f more than.- very super?cially, by an electric dis‘ comprising a cathode and two accelerating an ~ charge. ' v ' " . odes for iocussing. a beam of electrons upon ‘a so It is an object of this invention to ‘provide target, one ‘of these anodes being'a conducting cu, ' , novellelectron'discharge structures utilizing elec coating on the inside wall of the tube A simi-' trodes which behave differently in. the presence lar. coating is shown in Fig. l of this application of an oxidizing atmosphere. ' ' . and is designated by‘ the reference numeral l2. vIt is aiurther object of this invention to pro Either electrostatic or, electromagneticv means. ' “ vide anovel method ofuoxidizing metal vstruc ,(not shown) can .be. used for deflecting) the 55 2,188,940 . beam so that it scans ‘every elemental area in ing the latter to about 50° '0. Failure ‘to do this , turn of the screen S. Both of these means are 1 results in a 'non-uniform?lm of silver oxide; * well known to the art. The excess ozone delivered from the‘,electronic._fv"l. vReference will. now be made to Fig. '2 for a camera‘tube through tube M is preventedfront,v more detailed description of the mosaic screen entering the outside atmosphere by decomp'osi- , structure S. This screen structure has as a tio-n brought about by passage of the excess gases ' base a glass member 20 in the form of a very through a glass tube heated to about 550‘? C. ' (not thin center portion 2| and ya thicker edge por shown).‘ ' . " ’, :1 l r tion 22. On the face of the glass member remote The degree of oxidation of the silver ?lm mayv 10 from the electron beam is evaporated a thin be followed by determining its resistance as a ’ _ coating 23 of a suitable electrical conducting function of time. When the‘resistance reaches a j . . - ' material, such as aluminum. On the surface of limiting value it is assumed that oxidation of the, ' the center portion 21 nearer the electron beam silver is approximately complete. Measurements . . is coated a discontinuous layer 24 of photosen made on the approximate ratio of silver to oxygen 15 sitized metallic globules which isfprepared by in silver ?lms oxidized with moist ozone, in-Y sputtering the center portionwith a layer of dicated approximate agreement with the formula I metallic material such as silver, which is heated AgzOL‘ This indicates thatthe chief reaction I, to make it discontinuous. The discontinuous occurring‘ maybe represented by the equation J" globules are oxidized and caesium is'introduced 20 and the tube is‘ baked to make the surface 24 20v. -" photo-emissive. ' p Moisture :is necessary to catalyze the reaction; The preparation. of the glass member'ZEl for without it, the oxidation proceeds with extreme, use in the screen S will now be described. A slowness. ' piece of glass, preferably about .005 inch thick . vAfter oxidation of the silver ?lm, the electronic \ ‘ 25 is etched by total immersion in a suitable etching camera‘ tube is then baked out and'evacuate'd at vsolution, such as hydro?uoric acid, the edges of about 250° C. This vtemperature is su?icicnt to - the glass being ‘protected by a coating of a suit decompose the silver oxide‘ completely if ‘main able substance which is not affected by‘ the hy 'tained for a sufficient length, of time to fully l . i dro?uoric acid, such as, for example, beeswax, establish equilibrium. conditions. I However, the 30 so that the ?lmlof glass produced by the etching approach to these conditions is rather slow and : process has a. border of glass of the thickness of the amount of decomposition, is made negligible - I the original‘ glass plate by which it may be sup by limiting the time‘ of baking. If thaozone ported. For amore complete description of the method of oxidation asv described abov'ejis used, method of preparing these glass screen members, the metal portions of the tube ‘should be made of 35 reference maybe made to the above-mentioned materials not attacked readily by ozone. Alumi- ' ‘Teal patent wherein the process is described in num metal, platinum, and chromium-plated _ nickel ~have been found, to be‘ fairly satisfactory‘ detail. ‘ . - , ‘ v a After the glass blank has been prepared so in-this respect. 1 I ' ‘ > that the center portion is as thin as desired and ,At the conclusion" of the: ‘oxidation process, there is approximately a quarter of an inch of excess gas is removed by evacuation and a known raised border alljaround the center portion, silver amount of caesium is emitted in the bulb by is sputtered on the center portion of one face of ?ashing a “caesium” pill.‘ The‘ pill is ?ashedin , " the blank for about 20 to 30 minutes. The silver a side tube or in the ‘bulb so that caesium .vapor layer is then heated to a temperature from 400 passesinto the bulb to photosensitize the globules.‘ to 500° C. (usually between 425 to 450° C.) and of the screen S. Fora description of ‘a process , then cooled. The heating causes the silver to ' of vphotos'ensitizing with a “caesium” pill' and the‘ break up into discrete globules. This process may composition of , ‘such a' pill, ‘reference . ‘may . be > be repeated one or more times in order to obtain made to British Patent381§606 ‘to George R. I, a ?lm of silver of the desired. thickness. A ,Stilwell and Charles H.‘ Prescott, Jr.,> complete 50 platinum ?lm'is then formed on the entire backv accepted-October 10; 1932. ‘.The tube may then be J surface of ‘the blank by sputtering. The blank baked‘at a temperature- of about 200 to 225"v .C.v ’ is then mounted in the tube and the tube baked for varying degrees of time to remove all gases. out and evacuated so that all the elements in the For a further description ofa tubehaving .a tube are thoroughly degassed. Thetube isthen ’ mosaic photosensitive targetv of the type de- f ready for the oxidation process. scribed‘ herein together with a method‘of opera- j Referring now to Fig. 3 which shows a preferred ‘ tion of a tube of this type, reference may be'made form of apparatus for preparing moist ozone used to‘ they above-menti'oned'Teal patent.‘ " in the oxidizing process, oxygen is introduced Fig. 4 shows an electron multiplier tube similar - ‘ , through the inlet ‘38 and passesv between the to ‘that described byP. T.;Farnsworth in the, 1' . ‘I’ ‘to electrodes 3i and 32 which are connected to a . Journal .of the‘ Franklin Institute, volume 218,. spark coil (not shown). The inside electrode 32 page-411 .(1934). This electron multiplier com-f vis an aluminum cylinder sealed into the pyrex prises anenVe-lope vt?enclosing an anode .51 and a glass tube 33 while the outside electrode is of " cathode structure 52,.both' of vwhich are supported copper foil attached to the external surface of the from a- press 53 by support members 5d and 55.-? 65 glass tube 33. The ozone formed in the silent The photo-cathode 52 is made by sputtering a discharge in the condenser chamber 36 is swept ' very thin ?lm of nickel on the inside of the glass ' ‘through the glass. tube 35 and the‘sintered glass cylinder 56 and then‘ asemitransparent‘?lm of ' I‘ ' ?lter 3t and is saturated with water vapor by silver on the nickel ?lm. Heavy rings 51 and 58 passing through the water in the reservoir 37. of platinum are sputtered on the inside at the ' ‘ 170 The‘ moist gas isfcollected in the tube 33 and‘ ends of the cylinder to make contact with the 70 spray is removed from it by passage through‘ the. silver ?lm. The silver ?lm‘ is oxidized and" then ' trap 39. The electronic camera tube is sealed photosensitized. Several attempts using various to the ozone'generator at the‘ point 80. The other methods of oxidizing the silver vwere made water vapor in the ozone is prevented from con prior to ‘the use of theimeth'od according to this densing in the electronic camera tube by heat invention. An attempt. was made to‘ox'i'di’ze " the 3 I ' silveri-by passage of a ‘direct electric current The combination with a'gas-tight container,‘v between the wire anode 5| and the cylinder 56" ofelectrode elements therein, one of said ele _ .' by ‘the-production of an oxygen-gas discharge. ’ ments :being of material which oxidizes in the '."In this'attempt the silver film was made about presencefof moist ozone ‘and another of material‘ 750 volts‘ negative with respect to the anode 5|. which .d'oes‘not so oxidize when subjected to ' An attempt was .alsomade to accomplish the ' ‘moist ozone at the same temperature, means for oxidation by‘ the passage of a high frequency“!v producing a mixture of ozone and water vapor, gas discharge between the ‘film on theqglass and means‘ for conducting said mixture to the cylinder 56 and theanode 5|.‘ In‘ both cases interior of said container to produce an oxide 10 di?iculties were encountered because of the silver coating on said element which oxidizes in the‘ 10 ?lm being torn away from the‘glass. The oxida-‘ I _4 presence oi‘ moist ozone. . tion was satisfactorily accomplished, however, by, 6. The‘ combination with a gas-tight container, using’ the method ‘of this invention. of‘ an electrode of silver and a cooperating elec The ozone vapor isladmitted to the tube at trode of a material which does not readily oxi 15 the inlet cc and passes from the tube through dize in the vpresence of water vapor and ozone, is. outlet 6|‘; ‘Tube'lil is sealed, on‘ at .the conclu means for producing a mixture of ozone and sion? of the oxidation but tube 60 is used to seal - water, vapor, and means for conducting said mix . the envelope to the vacuum station. The proc ture to the interior of said container to produce ‘ess is similar to that described above in connec an oxide coating on said silver electrode. 20 The method of oxidizing a plurality of elec- ' tion\ Itwill with‘ be the, understood electronic thatcamera." this method, is not trode elements in a gas-tight container, oneof "limited to the preparation or electronic camera I said elements being of material which oxidizes I tubes or electron multipliers, but is of‘IapplIica -in the presence of moist ozone to producev an - , tion in photoelectric tubes or in any other cases‘ - oxide which is ‘unstable when subjected to tem 25' where it is desired to produceuniiornroxidation peratures ordinarily employed in baking elec and it is impossible-‘to make electric contact to. trodes, in electronic current discharge devices] electrodes in the tube or other containing vese I and another-‘of said elements being of material sel. While the method has been described in‘ which 'does, not so oxidize when subjected to _ connection with oxidizing silver it is to be under~ moist ozone at the same temperature, which stood that it is suitable also in connection with comprises the steps of mixing water vapor with the oxidation of certain, other metals, suchv as, ozone, conducting said mixture to the interior for example, copper. The heating temperatures I. of, said container and simultaneously therewith in the process where copper is used are likely. maintaining said electrodes at a temperature at - ' to be higher than when silver is used due to‘ ‘*which one of said elements will oxidize while the tact that copper oxide ismore stable than , the other of said electrode elements willnot oxi silver oxide but otherwise the processesare simi ' dize to produce an oxide coating on one of said lar. Other modi?cations and applications of - electrodes. _ - the invention may obviouslyv be made without I 8. The method of oxidizing an electrode ele departing from the spirit of the invention, the meritv in a gas-tight container which electrode scope or which is de?ned ‘by the appended claims. . element is of a material which oxidizes in the presence of moist ozone, comprising the steps of What is claimed is: I ‘ I _ ' » > mixing ozone with. water vapor, conducting the I 1. The method of o'xidizing‘an electrode struc ture to produce "on. said structure a uniform vmixtureto the interior of the containerto form oxide layer of a thickness within predetermined an oxide coating on said element, and applying heat to said element while said mixture is being ' limits, :which comprises the steps of subjecting. conducted into the tubesuf?cient to prevent con- ‘I the electrode structure to moist ozone, and simul taneously heating the electrode structure to ,a Idensation of water vapor thereon. I I I temperature-Isuf?cient to prevent condensation of ‘ _ 9. The ‘method of oxidizing a metallic electrode structure’ to produce thereon a uniform oxide ' water vapor thereon; layer‘ ‘ comprising‘ the steps of passing ozone ' 2. The method of; oxidizing ‘an electrode struc through water to add water vapor to said ozone, ture to, produce on said. structure a uniform removing the spray fromsaid mixture by passage oxide'layer, of a thickness within predetermined through a trap, ‘ and directing the remaining limits, which comprises the steps of subjecting, mixture to the electrode structure. the electrode structureto moist ozone, and there-' 10. The method of oxidizing .a metallic elec after baking the structure. , I I ~ 7 trode structure of a material which readily oxi 3. The method ‘of oxidizingtansilver electrode dizes in the presence of moist ozone to produce. structure to‘v produce on Isaidstructure a uni-v on said. structure a uniform oxide layer of a form ‘oxide layer of a'thickness within predeter- I thickness within‘ predetermined limits, compris mined limits, .which-comprisesthe steps of sub: ing the steps ,of producing ozone, mixing the jectinig the‘. silver electrode structure to moist ozone with water vapor,Iand passing the resultantv ozone atIa temperature of about '50“ C., and mixture in controlled amounts to the electrode thereafter ba " "g the structure toIa temperature structure. . I of approximately 250° C. I 11. The method of oxidizing a‘metallic elec 4. The" method of *oxidizing a metallic elec-, . trode structure of a material which readily oxi trode structure to produce on'said structure a dizes "in the .presence of ozone to'produce on ‘uniform oxide layer of a thickness within pre- ' said structure a uniform oxide layer of a thick determined limits comprising the steps [of in-I - ness within predetermined limits, comprising the troducing oxygen into, a chamber wherein an steps of introducing oxygen vinto a I chamber wherein an electric discharge is produced to form electric Jdischargeisproduced to form therein 70 I ozone, passing the ozone through a reservoir therein ozone, passing the ozone through a reser having water therein to add water vapor to said voir having water therein to add water vapor to ozone, removing 'thejsprayfrom said‘m'ixture , saidozon'e, and passing the resultant mixture to by passage through-atrap, and passing the re- . the _I electrode structure, . sultant mlxturefwhich comprises oxygen, --ozone_'. » ' ' BENJAMINIA. DIGGORY. I, a ‘and water vapor to theelectrode structure. ' GORDON I