JPS59114745A - Photoelectric screen and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve sensibility in the red range by forming a photoelectric screen with a silver layer prepared on a transparent substrate, a silver oxide layer prepared on the surface thereof, a natrium layer, cesium layer and the silver layer further prepared on the surface thereof. CONSTITUTION:After heating and cooling a photoelectric tube 1, silver is vacuum evaporated on the inside wall of a face plate 3 to become a photoelectric screen 4 from silver grains 7 prepared on anode 5, oxygen gas introduced into the tube 1 is discharged in order to oxidize a silver thin film. Next, after exhausting and heating, natrium is emitted from a natrium container 9 in order to be adsorbed on a silver layer, further cesium is emitted from a cesium container 10 to be adsorbed on a natrium layer. A photoelectric screen 4 is formed by further vacuum evaporating silver again. Accordingly, by making silver, natrium and cesium to be major constituents, the long-waved and big photosensibility can be obtained while minimizing deterioration of photosensibility.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photocathode that has high sensitivity in the red and infrared regions and little deterioration in sensitivity, and a method for manufacturing the photocathode.

Conventionally, a photocathode having the highest photosensitivity in the infrared region has been formed of silver, oxygen, and cesium. Such photocathode is summarized in "Photoemissive Materials" written by Alfreund Schimmer (John Wiley and Kens Inc. 1968). According to pages 134 to 140 of the aforementioned book, the optimal thickness of the silver thin film is 100 angstroms to 200 angstroms. These can be obtained reproducibly using an experimentally calibrated relationship between thickness and optical transmittance. The silver layer is oxidized in 0.1 Torr oxygen by applying a high frequency electric field. When the transmittance approaches the level before depositing silver, stop applying the electric field.

Further, silver is deposited until the transmittance reaches 50%. Treatment with cesium was developed empirically; for example, the photocathode was heated to 150 to 200 degrees Celsius, cesium was introduced, the photocurrent and thermionic current were observed, and the photocurrent and thermionic current were observed until the thermionic current passed its peak. Continue until it reaches zero. Heating continues until the photocurrent becomes constant. Furthermore, silver is deposited on the photocathode at room temperature.

The photocathode formed by this method has photosensitivity up to a wavelength of 1.2 microns, as shown by curve A in FIG.

, this graph shows the horizontal axis of log-log graph paper as the wavelength and the vertical axis as the photocurrent output per unit incident energy.

However, as the photocathode described above is used, its photoelectric sensitivity deteriorates as shown in FIG. 3C. Therefore, when a phototube or photomultiplier tube having such a photocathode is used in a measuring device such as a spectrometer, the gain must be calibrated every time a measurement is made.

An object of the present invention is to provide a photocathode that is sensitive to wavelengths as long as 1.2 microns and exhibits little deterioration in sensitivity, and a method for manufacturing the same.

In order to achieve the above object, the inventors of the present invention developed a photocathode whose main components are silver, sodium, and cesium, and confirmed that the photocathode met the above object.

This photocathode consists of a silver layer formed on a glass-like transparent substrate, the surface of the silver layer being oxidized to silver oxide, a sodium layer on top of that, a cesium layer on top of that, and a cesium layer on top of that. A silver layer is formed. The photocathode thus formed has a photosensitivity down to 1.2 microns, and the photocathode has high stability.

The present invention will be described in more detail below with reference to the drawings and the like.

Next, specific examples will be shown to provide a more detailed explanation.

FIG. 1 is a cross-sectional view of a phototube in the process of manufacturing a phototube to which a photocathode according to the present invention is applied.

The phototube 1 has a cylindrical airtight container 2 with a bottom. The airtight container 2 is formed from a glass wall.

A photocathode 4 is formed on the inner wall of the first bottom surface 3 of the airtight container 2, and a plate-shaped anode 5 is provided opposite to the photocathode 4. A thin layer 6 made of chromium is formed on the inner wall of the side wall of the airtight container 2 from the first bottom surface (hereinafter referred to as face plate) 3 to the anode 5, and this chromium layer 6 supplies current to the photocathode 4. It serves as a conductive wire for the purpose of the present invention, and also blocks light other than the light that enters through the face plate 3. A silver layer 7 fixed to a nichrome wire is attached to the anode 5 flush with the photocathode 4 . One end of the nichrome wire to which this silver layer 7 is attached is connected to the lead-in wire 12, and the other end is connected to the anode 5. A sodium container 9 and a cesium container 10 are installed between the second bottom surface (hereinafter referred to as stem) 8 and the anode 5. stem 8
Conductive wires 11, 12, 13, 14, 15, 16 and 17 are installed in a ring shape, and an exhaust pipe 18 is provided in the center. The photocathode 4 is electrically connected to the lead-in line 11 via the chromium layer 6. The anode 5 is electrically connected to the lead-in line 17. The sodium container 9, a cylinder of tantalum foil, contains sodium chromate, zirconium, and tungsten. A cesium container 10 is connected to an inlet line 13 at one end of the sodium container 9 and to an inlet line 14 at the other end.

The tantalum foil cylinder contains cesium chromate, zirconium, and tungsten. Cesium container 1
0 is connected to the lead-in line 15 and the other end to the lead-in line 16.

The inside of the container is evacuated through the exhaust pipe 18 and maintained at a vacuum level of 10 −6 Torr. The photosensitivity of the photocathode during the process of forming the photocathode 4 is 50% for the anode 5 with respect to the photocathode 4.
Apply a voltage of 150 to 150 port, and connect the lead-in wire 17.
Determine by detecting the current sent out from the

Next, the steps for forming the photocathode will be explained with reference to FIG.

(1) Heat the tube 1 to a high temperature to purify the inside of the tube 1. For example, the temperature is 300 degrees and the time is about 1 hour.

(2) After cooling the tube 1 to room temperature, silver is deposited from the silver layer 7 onto the inner wall of the face plate 3. This vapor deposition continues until the thin silver film takes on a reddish-purple color.

(3) Pure oxygen is introduced into the tube l and the oxygen gas is discharged in a high frequency electric field to oxidize the silver thin film.

The oxygen gas pressure is approximately 1 Torr. The high frequency electric field is generated by connecting one output end of a high frequency voltage generator (not shown) to the anode 5 and the other output end to an electrode close to the outer wall of the face plate 3-.

(4) Exhaust oxygen.

(5) Heat tube 1 to 200 degrees Celsius. This temperature is 1
It may be within the range of 50 degrees to 250 degrees.

(6) By applying a voltage between the lead-in wire 13 and the lead-in wire 14, the sodium container 9 is heated and sodium is released from the sodium container 9.

Sodium is adsorbed to the silver layer. The supply of sodium continues until the silver layer turns red. At this time, a photocathode 4 is formed and a slight photocurrent can be observed (7) Next, the tube 1 is heated to 100 degrees Celsius. This temperature may be between 70 degrees and 150 degrees.

(8) Next, release cesium from the cesium container 10. Cesium is adsorbed to the photocathode 4. Cesium supply continues until the photocathode 4 turns gray.

(9) Heat tube 1 to 190 degrees Celsius. This temperature is 1
It may be between 70 degrees and 200 degrees. The heating time at this temperature is 15 minutes.

(10) Cool tube 1 to room temperature.

(11) Deposit silver on the photocathode again. This silver deposition is performed while observing the photoelectric sensitivity, and is stopped immediately after the maximum value is reached.

(12) After that, the phototube 1 is sealed from the exhaust device and cut out.

The silver layer formed on the transparent substrate as described above, the sodium layer formed on the silver oxide layer formed on the surface of the silver layer, the cesium layer formed on the sodium layer, and the cesium layer formed on the surface of the silver layer. A photocathode is formed from the silver layer formed on the photocathode.

The photocathode manufactured by the manufacturing method described above exhibits a change in sensitivity over time as shown in FIG. 3B. This is a comparison under the same conditions as a conventional photocathode.

That is, 250 volts is applied between the photocathode 4 and the anode 5, light emitted from a 0.1 lumen white light bulb is incident, and the output current from the anode 5 is plotted over time. Note that the initial value of the output current is normalized and shown as 1.

As described above, according to the method of the present invention, by oxidizing the silver layer and adding sodium and cesium, it is possible to provide a novel photocathode that has photosensitivity at long wavelengths and exhibits extremely little deterioration in photosensitivity.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a phototube in the photocathode manufacturing process for explaining an embodiment of the method for manufacturing a photocathode of a phototube to which the photocathode of the present invention is applied, and FIG. FIG. 3, a diagram showing the spectral sensitivity characteristics of the surface, is a graph comparing the sensitivity change over time of a conventional photocathode (C) and the sensitivity change over time (B) of the photocathode according to the present invention. 1... Phototube 2... Container 3... First bottom surface (face plate) 4... Photocathode
5...Anode 6...Chromium thin layer 7.
...Silver layer 8...Second bottom surface (stem) 9...Sodium container 10...Cesium container 11.12.13,14,15,16.17...Introduction line 18...Exhaust Administrative patent applicant Hamamatsu Television Co., Ltd. Agent Patent attorney Hisashi Inoro

Claims (1)

[Claims] (A photocathode made of 11 silver, silver oxide, sodium, and cesium. (2) A silver layer formed on a transparent substrate, and a silver oxide layer and an oxide m layer formed on the surface of the silver layer. A photocathode consisting of a sodium layer formed on the substrate, a cesium layer formed on the sodium layer, and a silver layer formed on the cesium layer. (3) Silver is deposited on the surface of the substrate, and oxygen The silver layer is oxidized by discharging in an atmosphere, the substrate and the silver layer are heated to 150 to 250 degrees Celsius, sodium is evaporated onto the silver layer until the highest photosensitivity is achieved, and then cesium is oxidized by photo-coating. The substrate and the photosensitive layer formed thereon are heated to 170 to 200 degrees Celsius, cooled to room temperature, and then silver is deposited on the photosensitive device until the sensitivity is maximized. A method for producing a photocathode made of silver, silver oxide, sodium, and cesium, characterized by vapor deposition.