US1381474A - Photo-electric cell, method of and means for making the same - Google Patents

Description

J. KUNZ.

PHOTO ELECTRIC C ELL, METHOD OF AND MEANS FOR MAKING THE SAME.

Pamnted June 14, 19211 3 SHEE TS-SHEET I.

APPLICATION HLED AUG-24' 1918.

J. KUN'Z.

-PHOTO ELECTRIC CELL, METHOD OF AND MEANS FOR MAKING THE SAME.

APPLICATION FILED Aue 24. 1918.

1,381,474, Patented June 14, 1921.

3 SHEEISSHEET 2.

J. KUNZ. PHOTO ELEC-TRIC CELL, METHOD or AND mrmsfro'a MAKING. THE SAME.-

APPLICATION FILED AUGZM I918.

1,381,474. Patented June14, 1921.

3 SHEETS-SHEET 3.

UNITED STATES PATENT OFFICE.

JAKOB KUNZ, 0F UBIBANA, ILLINOIS, ASSIGNOR T0 BOARD OF TRUSTEES OF THE UNIVERSITY OF ILLINOIS, OE URBANA, ILLINOIS, A CORPORATION OF ILLI.

NOIS.

PHOTO-ELECTRIC CELL, METHOD OF AND MEANS FOR MAKING THE SAME.

To all whom it may concern:

Be it known that-I, JAKon KUNZ, a citizen of the United States, residing at Urbana, in the county of Champaign and State of Illinois, have invented a certain new and useful Improvement in Photo-Electric Cells, Methods of and Means for Making the Same, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming Ia part of this specification.

.L y invention relates to photo-electric cells.

I employ as a sensitive element, a suitable alkali metal. The fact that alkali metals under proper conditions are sensitive to light has previously been known.

There has been an increasing demand in various arts for an accurate and sensitive photo-electriccell. Heretofore selenium has been employed but the selenium cell,at least as heretofore constructed-has not been sufiiciently sensitive, nor are its characteristics suitable for careful work.

My invention aims to provide a cell which shall meet this demand. v

I provide an evacuated glass chamber having two electrodes, one of which consists of a dense film of an alkali metal in a suitable form and condition, lying on the inner surface of the chamber. The chamber may be filled with hydrogen or an inert gas, such as nitrogen, argon, helium, or neon or the like. This film electrode is so arranged that the light to be measured will fall upon the same.

The other electrode is placed in the immediate vicinity of the film electrode and is preferably in the form of a screen lying in the path of the-enteringl light, but so constructed as to obstruct t e light as little as possible. Between these two electrodes there is formed a field subject to and sensitive to the influence of light.

A cell of this type when properly constructed is characterized by great sensitiveness, uniform sensitiveness over a wide range of light intensities or impressed voltages, not subject to change by aging, rapidity of action, and as I have found by experiment, a straight line characteristic curve.

The human eye is sensitive to light over a range of intensity of substantially from one in 10*, but the cell o y n ent on m y Specification of Letters Patent. Patented J 14 1921 Application filed August 24, 1918.

Serial No. 251,345.

The cell of my invention is more sensi-\ tive to colors than is the human eye and can be employed for distinguishing objects of dlfferent colors such as leaves, glass, silks, etc. It appears that the sensitiveness is greater for short wave lengths, as the cell is more sensitive to blue and ultra violet as well as to Roentgen rays.

I prepare the cell by first depositing a silver mirror in contact with the shorter electrode. Then I connect the cell to a system of pipes and chambers comprising a pump for evacuating the cell and containmg in one of the chambers an alkali metal and other chambers various gases re uired. The metal may be any one of the ollow- 1n group:

ithium.

Sodium.

Potassium.

Rubidium.

Ceesium.

The cell is carefully evacuated and then the metal is distilled upon the silver mirror and in contact with the short electrode, but is carefully kept off of the other electrode. Thereafter, the cell is filled with hydrogen and is subjected to a relatively high electrical potential to cause a glow discharge of electricity. The tube is then pumped out and thereafter filled with argon, nitrogen, neon or other suitable gas, to the proper degree, and is then sealed off.

In order to'eXplain to those skilled in the art how to construct and practice my invention, I shall now describe one embodiment thereof in connection with the accompanying drawings which form a part of the present specification.

Figure 1 is a side elevation of a cell embodying my invention;

Fig. 2 is a longitudinal axial section taken on a plane at right angles to the plane of the sheet in Fig. 1;

Fig. 3 is a diagram illustrating the use of my invention with a source current in series with t-he cell;

Fig. lis a similar diagram indicating the use of the cell of my invention as a wave detector;

Fig. 5 is a diagrammatic layout of the apparatus and method employed in forming the cell of my invention; and Fig. 6 is a diagram similar to the diagram of Fig. 4.

The cell comprises a glass bulb 1 having a laterally extending arm 2 through which the leading in wire for the screen electrode 3 is introduced. The bulb 1 has an arm 1 lying upon the opposite side and in line with the arm 2 through which the alkali metal for the film electrode 5 is introduced. This leg is also employed for exhausting the bulb 1 and for connecting the same with the various chambers and pipes to be described later. The arm t might very well be dispensed with and could be sealed oft close to the bulb 1, if desired.

A. leading in wire 6 is disposed in a thickened portion 7 of the side walls of the bulb 1. This leading in wire comprises an outer loop 8 and an inner portion which is maintained in contact with the film electrode 5. The film electrode 5 comprises a film or surface of an alkali metal which in this par-' glass bulb above the line 10 has no coating of potassium metal as this portion of the bulb is left clear for the admission light be measured. The film of alkali metal is backed in the lower portion of the bulb by a silver backing or mirror which lies below the line 11 indicated in 1. This silver mirror is first deposited on the walls of the bulb prior to the distilling of the allrali metal upon the bulb. The silver mirror insures the electrical contact between the alkali film and the leading in wire 6. The screen electrode 3 comprises a circuring or" metallic wire, in this case silver wire,which ring is provided with a plurality of cross wires 12 having their ends attached to the ring and being arranged in criss-cross fashion to form a coarse screen. The wires 12 are or" very small diameter.

The leading in wire for the screen electrode 3 comprises two sections 13 and 14, respectively. The section 13 passes through the end wall 15 of the arm 2 with a concentric metal sleeve 16 about the same. Between the wire 13 and the sleeve 16 there is a filling of glass 17 for maintaining a tight closure. lhe wire 13 and the sleeve 16 bre made of platinum as this metal has substantially the same coeliicient of expansion as glass.

The wire 14 which is joined to the wire 13 might also be of platinum as could the wire ring 18, but I prefer to employ silver as the same is equally satisfactory and more plentiful. The wire 14 is covered with a coating of glass 19, this coating serving the double purpose of insulating the wire 1 and of stiliening the same so as to support the screen electrode 3 in proper position.

In Figs. 3, at and 6 l have indicated the manner of use of the cell of my invention. As shown in Fig. 3, for the measurement of light from the source L, the photo-electric cell is so placed that light from the source L will enter the clear space or opening 20 in the bulb 1 of the cell and pass through the screen electrode 3 and tall upon the film electrode 5.

The cell is connected in series with an indicator 25 which indicator may be a very sensitive galvanometer. A suitable source of current, such as a storage battery, and a resistance 27 are connected in series with the ell and the indicator 25: The potential of the storage battery may be varied by an adjustable contact mechanism 28 so that the voltage across the terminals of the cell may be varied from about four volts to 120 volts.

have conducted numerous experiments with cells of this type made up with various alkali metals and filled with various gases or evacuated only, and l have dis covered that the cell is suitable for measuring purposes in that over a given range the photoelectric. current given oil by the cell is proportional to the intensity of illumination to which the cell is subjected. The cell is useful for photometric purposes, particularly in investigations in physics having to do with measurement of the rel'lection, transmission, radiation and absorption oi light under various conditions. The cell is also highly useful in spectroscopy and in astronomy it is particularly useful in the measurement of double star systems in order to ascertain their radius, mass, density, distance and surface brightness. Further uses of the cell of my invention are in plant physiology and photochemistry.

For accurate measurement of light for all the above purposes, it is highly desirable that the cells remain constant, that is, not subject to deterioration or change, and that the response of the cell to the light action should be instantaneous and in proportion" to the intensity. This l have been able to accomplish by the cell of my invention.

When the cell is in use the platinum cylinder or sleeve 16 is connected to ground, as

shown at 30 in Fig. 3, in order to discharge any electricity which may accumulate on the glass surfaces in the stem or arm 2. 1 consider this construction of the grounded sleeve or cylinder 16 in conjunction with the terminal 21 to be an important structural feature of my invention.

It is not absolutely essential that a source of current such as 26 be employed in the circuit of the indicator 25, but I find that the operation of the system is more satisfacto when such a source is provided. The indicator 25 may be an electrometer and in that event the resistance 27 is preferably of a. high value of the order of between 10 and 10 ohms or higher.

I have found that the cell of my invention is a very sensitive wave detector for wireless telegraphy and telephony and the like. When thus employed, the cell is excited by light from the source L, as shown in Fig. 4, so that electrons pass from the film electrode 5 to the screen electrode 3 within the cell. The incoming waves entering by way of the antenna 31 are rectified by the cell and give an indication at the indicator 25 then passing to ground at 32. The source of current 26 may be omitted. The current operating on the indicator 25 may be amplified by an audion or other relay device.

In Fig. 6 I have shown the preferred manner in which I connect the cell for wave detection. The indicator 82 is a string electrometer, which is connected to the terminal 21 of the screen electrode 3. The electrometer is connected to ground through the middle point of the battery 83.

The antenna 31 is connected to the film electrode and also through suitable connections including the inductance 84 and resistance 85 to ground. Suitable capacities 86 and 87 are connected in a manner well understood by those skilled in the art.

I shall now describe one manner in which the cell of my invention may be constructed. The glass bulb 1 with the screen electrode in place and with the silver mirror deposited on the lower part of the bulb with the lead-.

ing in wires in place is connected by means of the arm 4 to the system shown in Fig. 5.

. The arm 4 is connected with the horizontal glass tube which has the bulbs or enlargements 42, 43 and 44 therein. The arm 4 is also provided with a small depression or cup the purpose of which will be described later. The horizontal tube 41 is connected to a vertical tube 45 and this vertical tube is connected through the stop cocks 46 and 47 to the pump main 53 and thence to a suitable suction pump for exhausting the air from the system.

Between the stop cocks 46 and 47 a plurality of tubes 54, 55 and 56 lead off to separate chambers. being. controlled by the stop cocks 48, 49 and 50, and respectively.

The connecting tube 54 leads oil to a chamber 57 containing palladium which has absorbed a relatively large content of hy drogen. A suitable burner 58 is provided for heating the palladium to cause the same t olve hvdro cn when desired.

The tubeis connected with a bulb or chamber 59 filled with charcoal 60 for absorbing and giving off argon, as will be described late For this purpose, a double walled receptacle 61 containing liquid air 62 is rovided.

he pipe 56 leads to a chamber 81 through a valve 50. This chamber contains phos by a stop cock 51. The chamber 66 is connected through the stop cock 52 with the receptacle 67 which contains argon. The chambers or bulbs 63 and 66 are provided with heating devices such as the burners 68 and 69.

The bulb 1 connected to the horizontal tube 41 is surrounded by a heating coil 70 for heating the entire bulb with both arms 2 and 4. A smallerheating coil, 71 shown in dotted lines in Fig. 5 is provided, this coil being adapted to surround the arm 2 for heating the same, as will be described later. The electric circuit including the source of current 26, the galvanometer 25 and resistance 27, is provided for connection to the terminal of the cell at the proper time, as will be described later. A suitable source of light 73 is also provided for testing the cell, after the same is nearing completion.

The outer end of the horizontal tube 41 being open, alkali metal, as indicated at 75, is introduced into the bulb 44. The end of the tube is then sealed at 76. The valves 46-47 are then opened and the valves 48, .49 and 50 are closed and the air pump which is preferably of the mercury type is operated to pump the air out of the system.

The initial depositing of the silver mirror upon the bottom of the bulb may be performed in any of the well known ways, as is understood by those skilled in the art.

After the air has been pumped out of the system the alkali metal 75 is distilled from the bulb 44 into the bulb 43 by heating the bulb 44 with a Bunsen burner as shown at 77 and at the same time cooling the bulb 43. It isapparent that any source of heat other than the Bunsen burner may be employed.

After the air has been pumped out, the heating coil 70 is slipped over the cell and the entire cell is heated to about 177 centigrade and is subjected to the heat for two or three hours to take out all gases which may have been occluded or absorbed in the glass or in any of the parts of the cell. During all this time the air pump 18 in operation to carry away such gases or vaors.

p The metal which has been distilled in the bulb 43 is now evaporated therefrom and distilled in the bulb 4L2. Thereafter, while the pump is still operating and the beaten, the alkali metal is distilled or poured into the enlargement 4.0 in the arm 4 of the cell. The heating coil is then removed and a smaller heating coil, as shown in dotted lines at 71 is placed about the arm 2 which contains the leading in Wire for the screen electrode 3 and the lower portion of the bulb l which contains the silver mirror is cooled with water or with ice. A small burner flame is then put below the alkali metalat the point 40 in the stem or arm 4' while the pump is active and while the coil 71 maintains the heat of substantially 150 centigrade upon the arm 2, the interior of the bulb becomes substantially uniformlycoated with the alkali metal. When: such a coating has been established, the application of heat at the point QO-isstopped and the top of the bulb 1 is heated, as indicated by the burner 78 shown in dotted lines, to drive the alkali metal away from the top of the bulb to form a window for the admission of light. This is to main tain a clear transparent portion 20 through which the light may enter the cell. The heating coil 71 prevents the distillation of any metal in the leg 2 or on the electrode 3. The metal of the electrode conducts heat from the stem or arm 2 time remaining hot and tending to keep the alkali metal from. distilling or condensing thereupon.

After the first layer has been distilled upon the interior of the bulb, another layer is deposited in the same manner, and thereafter the clear space 78 is again heated to drive away the metal vapor. The coating of alkali metal is applied in about three steps in order to secure a uniform layer of the same. The silver mirror tends to maintain a conducting relation between all the particles of the alkali metal which is in fact deposited in minute droplets but which, when the process of distilling is finished, form a continuous layer upon the inside of the cell. It is quite important that the alkali metal be kept out of the stem 2 and off of the positive electrode, otherwise the action of the cell may be interfered with.

Thereafter the valve 47 is closed and with the valvest) and-'50 remaining closed and the valve d6 remaining open, the valve- 4:8

is opened. This connects the bulb or chamber 57 to the system. Hydrogen at a pres sure of two or three millimeters is then admitted through the cell, this hydrogen being preferably secured from palladium byheating the same. With the hydrogen remaining in the-bulb 1, the source of current 26 is connected through the terminals of the cell and an. electro-motive force of'about 300 volts is impressed upon the terminals of-the cell.' A beautiful golden glow which assume is an electrical discharge, then. occurs in the tube. This potential is employed for only probably other gases may be employed.

When the sensitive film is thus formed I test the cell to ascertain its condition. For this purpose- I decrease the voltage across the terminals to about 120 volts and energize the source of light 73. The current through the galvanometer 7 5 is then measured and if the right sensitiveness has been secured, the operation is then finished.

If the sensitiveness is not high enough the potential is increased to about 300 volts and the formation of thelayer with hydrogen is continued. It is very easy to pass the most sensitive point and if this occurs the hydrogen is pumped out and a little more of the alkali metal is distilled, as be fore, and the formation of the film with hydrogen and the electrical discharge is repeated. been secured, the hydrogen is pumped out of the system, the valve 48 being at this time closed and the valves 46 and 47 open. The valves 47 and 46 are thereafter closed.

The valve 52 is next opened to admit argon from the chamber 67 to the chamber 66. The chamber 66 contains calcium in broken up form and as the argon is admitted to the chamber 66, the calcium is heated with a Bunsen flame or other source of heat, such as electric current. The calcium absorbs any oxygen and nitrogen which may be contained with the argon.

The valve 51 is next opened and the purifled argon is then passed to the chamber 63 which contains copper oxid. The copper oxid is heated to substantially red heat and serves to absorb any hydrogen which may be contained in the stream of argon. The pipe 56 has a chamber 81 in which is lodged some phosphorous pentoxi'd for absorbing any moisture that might be contained in the argon or that mi ht be evolved by heating of the copper-0x161. The valve 50 is then opened to admit argon into the system between the valves 46 and 47, and after the system is substantially filled with argon the valve 50 is again closed. The body of charcoal 60in the chamber 59is surrounded with a bath of liquid air at 62 and the valve 49 is opened. The argon which is contained in the system is then absorbed by the charcoal 60.

When the last trace of argon has been absorbed by the charcoal, the source of our- When the right sensitiveness has i ar on gas.

rent 26 is connected across the terminals of the cell to impress substantially 120 volts across the same through the galvanometer or electroineter 25. If the body of charcoal 60 does not absorb all of the argon, the same ma be removed by means of the air pump. he valve 46 is thereafter opened and the valve 49 being open, the chamber 61 containing the liquid air 62 is removed from the bulb 59 and the charcoal 60 begins to evolve The indicator 25 is then carely watched as the argon is admitted until the point of maximum deflection is attained. The valve 46 is then closed and the cell is ready to be sealed off at the point 8Q.

If neon or helium were employed instead of argon, a suitable container for the same would be connected to the system, as indicated by the container 67 which contains argon.

It is not essential that the cell be filled with an inert gas, but I find that greater sensitiveness is secured by doing so.

I do not intend to be limited to the precise details of construction or operation above indicated.

I claim:

1. In combination, a transparent bulb of insulating material, a wire passing through and sealed in the walls of the bulb, a metallic cylinder concentric with the wire and extending through and sealed in the walls of the bulb.

2. In combination, a glass bulb, a wire passing through the walls of the bulb, a metallic cylinder concentric with the wire and extending through the wall of the bulb, said wire being connected to a suitable source of current, and saidmetallic cylinder being connected to round.

3. In combination, a glass vessel having a tube integral with and extending therefrom, a wire passing through the wall of said tube, a metallic cylinder concentric with the wire and extending through the wall of the tube, said wire extending through said tube into the glass vessel and a coating of glass on said wire and forming a tight closure between the wire and the cylinder.

4. The method of forming a light sensitive surface in a photo-electric cell which comprises evacuating a glass bulb forming the cell, cooling a portion of the cell externally, introducing the vapor of an alkaline metal into the bulb to deposit a film of metal upon the inner walls of the same and then heating a portion of the cell while another portion is being cooled to drive away the alkaline metal from said heated portion to form a transparent portion.

5. In the formation of a photo-electric cell comprising a bulb havin an extendin arm with an electrode in the bulb supporte on a leading-in wire, said wire extending through the arm, the process which comprises evacuating the bulb and arm, introducing the vapor of an alkaline metal into the bulb, cooling a portion of the bulb, and

heating the arm to cause heat to be conductprevent deposit of the alkaline metal thereupon, and simultaneously heating a portion of the bulb to form a transparent portion in line with said electrode and the portion which is cooled.

7. The method of depositing a film of alkali metal in a photoelectric cell which comprises cooling a portion of the cell introducing a vapor of the metal to be deposited and heating the portions of the cell upon which no film is to be deposited.

8. The method of forming a photo-electric cell which comprises evacuating the cell, distilling a thin coating of alkali metal upon one electrode only, subjecting said coating to an electric discharge in the presence of hydrogen and then filling the cell with argon and then sealing off the cell.

9. The method of forming a light sensitive film of an alkali metal upon one of the electrodes of a photo-electric cell which comprises filling the cell with vapor of the metal, cooling the one electrode to deposit a film of metal thereupon, and heating the other electrode to prevent the deposit of the metal thereupon.

10. In combination, a leading-in wire, a glass coating on said wire, a cylinder fitting upon and sealed to said glass coating, a glass bulb, said cylinder passlng through and being sealed in the walls of said bulb, said cylinder being electrically independent of said leading-in wire.

11. In a device of the class described, a closed tube having a pair of electrodes within the same. a thin film of a suitable light sensitive metal in contact with the walls of the tube and forming one electrode, sald thin film lining substantially the entire inner walls of the tube with the exception of an opening-in line with the other electrode, whereby substantially all extraneous li ht other than that to be measured is exclu ed.

12. In a cell of the class described, a closed chamber of substantially s herical form having an interior coating 0 a light sensitive alkali metal except for a small portion forming a window, and a flat screen electrode lying at the center of the chamber and at substantially right angles to the light rays admitted through the window whereby a substantially uniform field is formed be tween the coating and the screen.

13. In a cell of the class described, a bulb having a hollow substantially cylindrical arm extending laterally therefrom, an electrode comprising a metallic ring lying within the bulb with its axis in the direction of the rays of light which act upon the cell, a wire extending from said ring through said arm and terminating outside the Wall of the end of the arm, said ring having a plurality of fine wires connected thereto to form a screen within the ring, a silver mirror coating one side of the bulb, a leading in wire passing through the wall of the bulb and connecting with the silver mirror, and a coating of sensitized alkali metal deposited upon the silver mirror and upon the walls of the bulb except a relatively small portion of the bulb in line with the axis of the ring for the admission of light, said coating of alkali metal forming a light sensitive electrode and preventing the accumulation of a static charge upon the walls of the bulb.

14:. In a photo-electric cell, a spherical bulb havinga substantially cylindrical hollow arm extending laterally therefrom, an-

electrode comprising a metallic ring lying centrally within the bulb with its axis in'the direction of the rays of light which act upon the cell, a wire extending from said ring through said arm and terminating outside the end Wall of the arm, a glass coating upon said wire, a metallic sleeve covering said glass coating where the wire passes through the end wall of the arm said sleeve extending beyond the sides of the end wall of the arm both internally and externally to prevent any creepage of electricity over either the external or internal walls of the bulb between electrodes, a metallic mirror coating one side of the bulb, a leading in wire passing through the side wall of the bulb at substantially right angles to the axis of said ring and being in electrical connection with said mirror, and a plural coating of sensitized alkali metal deposited upon the silver mirror and the inner walls of the bulb excepting a small portion of the bulb in line with the axis of the ring for the admission of light, said coating of alkali metal forming a light sensitive electrode and preventing the accumulation of a static charge upon the walls of the bulb.

15. In a device of the class described, a bulb, an electrode in the bulb, a glass stem for the electrode having a wire running therethrough and connected to the electrode, and a metallic coating for the outer end of the stem said bulb forming a seal with the stem on said metallic coating, a second electrode projecting through a wall of the bulb, said metallic coating being interposed between the electrodes to prevent surface creepage of electricity along either the external surface or the internal surface of the bulb.

16. The method of depositing an alkali metal in a photoelectric cell from a vessel which comprises connecting the vessel containing the alkali metal through a plurality of chambers with the -cell, evacuating the cell and progressively distilling the alkali metal from the vessel through the chambers successively while the cell is being evacuated and finally into the cell.

17. The method of depositing an alkali metal in a photo-electric cell from a vessel, which comprises distilling the metal in a plurality of successive steps toward and nally into the cell and repeating the distillation to form a plurality of coatings upon the interior of the cell, said distillation being carried on while the cell is evacuated.

18. In a cell of the class described, a closed. glass bulb having a photo sensitive interior coating of alkaline metal over the major portion thereof forming one electrode, and a flat screen electrode placed substantially at the center of the bulb and at right angles to the light admitted to the electrode whereby a substantially uniform field is formed between the electrodes.

In witness whereof I hereunto subscribe my name this 17 day of Au st 1918.

' JA OB KUNZ.

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