CN111403252B - Double-alkali photocathode with high quantum efficiency and low thermal emission used for photomultiplier and preparation method thereof - Google Patents

Double-alkali photocathode with high quantum efficiency and low thermal emission used for photomultiplier and preparation method thereof Download PDF

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CN111403252B
CN111403252B CN202010246717.XA CN202010246717A CN111403252B CN 111403252 B CN111403252 B CN 111403252B CN 202010246717 A CN202010246717 A CN 202010246717A CN 111403252 B CN111403252 B CN 111403252B
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antimony
potassium
current
alkali
double
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CN111403252A (en
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金睦淳
任玲
孙建宁
司曙光
王兴超
侯巍
王亮
王从杰
纪路路
顾莹
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North Night Vision Technology Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
    • H01J9/02—Manufacture of electrodes or electrode systems
    • H01J9/12—Manufacture of electrodes or electrode systems of photo-emissive cathodes; of secondary-emission electrodes
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
    • C23C14/14—Metallic material, boron or silicon
    • C23C14/18—Metallic material, boron or silicon on other inorganic substrates
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/24—Vacuum evaporation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/34—Photo-emissive cathodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J43/00—Secondary-emission tubes; Electron-multiplier tubes
    • H01J43/04—Electron multipliers
    • H01J43/06—Electrode arrangements
    • H01J43/08—Cathode arrangements

Abstract

The invention belongs to the technical field of photomultiplier tubes, and discloses a double-alkali photocathode with high quantum efficiency and low thermal emission used for a photomultiplier tube and a preparation method thereof, wherein the obtained double-alkali photocathode structure is formed by sequentially stacking multiple layers of alkali antimonides on a substrate, and the composition of the alkali antimonides is in a rule that antimony elements are gradually reduced and alkali metal elements are gradually increased from the substrate of the double-alkali photocathode to the outer surface direction, so that the quantum efficiency of a microchannel plate type photomultiplier tube is improved; in the preparation process, the photocurrent inflection point is controlled by adjusting the rate of increasing the current of the antimony balls in the first stage of co-evaporation of potassium and antimony, and the thermionic emission of the photocathode is reduced by comprehensively regulating and controlling the change of the observed reflectivity of antimony in the second stage of co-evaporation of potassium and antimony, so that the integral sensitivity of the double-alkali cathode is reduced, the noise of the microchannel plate type photomultiplier is improved, and the process consistency is better.

Description

Double-alkali photocathode with high quantum efficiency and low thermal emission used for photomultiplier and preparation method thereof
Technical Field
The invention relates to the technical field of photomultiplier tubes, in particular to a double-alkali photocathode used for a high-quantum-efficiency low-thermal-emission photomultiplier tube and a preparation method thereof.
Background
Photomultiplier tubes (PMTs) are vacuum electronic devices that convert weak optical signals into electrical signals and multiply amplify the electrical signals. The photocathode is one of the core components of the photomultiplier, and is used for capturing incident photons to excite photoelectrons, the performance of the photocathode directly affects the performance of the whole photomultiplier, the main performance parameter is quantum efficiency (quantum efficiency refers to the number of photoelectrons emitted by the photocathode per 100 photons received), and the higher the quantum efficiency is, the higher the detection efficiency of the photomultiplier is. In addition, with the large-scale application of the large-size photomultiplier in the high-energy physical field, such as the neutron detection test, the requirement for low noise of the photomultiplier is higher and higher, and the thermionic emission of the photocathode is the main source of the whole-tube noise. Therefore, K is commonly used for such photomultiplier tubes2CsSb double-base photocathodes are required to have both high quantum efficiency and low thermionic emission.
As a conventional double-alkali photocathode, for example, Na is proposed in Chinese patent No. 201510438585.X2The preparation method of the CsSb photocathode adopts the preparation flow of adding sodium by steaming cesium antimony, adding sodium by steaming cesium antimony and adding sodium by steaming antimony. 200780004067.0, the cathode structure using hafnium oxide, manganese and magnesium or titanium oxide as the substrate layer is helpful to improve the quantum efficiency; in the preparation of the cathode disclosed in the chinese patent No. 200710305894.5, a film layer of beryllium oxide and a mixed crystal of a plurality of metal oxides is used, so that the quantum efficiency is significantly improved. As an early-published technical scheme, the process regulation and control of the preparation process aim at realizing the improvement of the quantum efficiency of the photocathode, but do not relate to the evaluation and analysis of the influence of the improvement of the quantum efficiency on the whole-tube noise.
Prepared as also disclosed in Chinese patent No. 201710743036.22According to the scheme of the CsSb photocathode, the concentration of potassium is more and more, the concentration of antimony is less and less in the growth process, and a formed built-in electric field is beneficial to transporting electrons in the material to the surface, so that the quantum efficiency of the photocathode is improved.
Disclosure of Invention
The invention aims to provide a high-quantum-efficiency low-thermal-emission double-alkali photocathode used for a micro-channel plate type photomultiplier and a preparation method thereof, and the performance requirements of the micro-channel plate type photomultiplier on high quantum efficiency and low noise are met.
In order to achieve the above object, the double-alkali photocathode used in the microchannel plate type photomultiplier with high quantum efficiency and low noise provided by the present invention comprises a substrate and a plurality of layers of alkali antimonides, wherein the plurality of layers of alkali antimonides are stacked on the substrate in sequence, and the composition of the alkali antimonides tends to decrease gradually in antimony element and increase gradually in alkali metal element in the direction from the substrate to the outer surface of the double-alkali photocathode, wherein the preparation method of the double-alkali photocathode with high quantum efficiency and low thermal emission comprises the following steps:
firstly, evaporating a reflective film on a glass vacuum container in a normal temperature environment;
secondly, putting a frame on an antimony alkali seat filled with an alkali source and antimony balls in a normal temperature environment;
thirdly, mounting the glass vacuum container, the tube core assembly and the stibium base seat into a vacuum system, and performing air extraction and high-temperature baking degassing;
fourthly, baking the glass vacuum container at a temperature higher than 300 ℃ to degas;
fifthly, recording the reflectivity of the initial glass shell at the temperature of less than 200 ℃, and degassing the potassium source, the cesium source and the antimony balls;
sixthly, performing bottom potassium evaporation at the temperature of 120-190 ℃;
seventhly, performing a first stage of simultaneous evaporation of potassium and antimony at the temperature of 120-190 ℃;
eighthly, performing a second stage of simultaneous evaporation of potassium and antimony at the temperature of 120-190 ℃;
ninth, cesium evaporation is carried out at the temperature of 110-180 ℃, and after the evaporation is finished, the preparation of the high-quantum-efficiency low-thermal-emission double-alkali photocathode is realized;
during the preparation process, the method of simultaneously monitoring the photocurrent and the glass bulb reflectivity is adopted to control the film evaporation of the double-alkali photocathode in the glass vacuum container;
in the first stage of simultaneous evaporation of potassium and antimony, the time point of the inflection point of photocurrent is controlled by regulating the rate of increasing antimony ball current, and the increasing rate of antimony ball current and the rising time of the reflectivity curve are controlled by observing the reflectivity change of antimony in the second stage of simultaneous evaporation of potassium and antimony to reduce the integral sensitivity of the double-alkali cathode.
In a further embodiment, in a first stage of simultaneous evaporation of potassium and antimony, maintaining a constant potassium source current, increasing an antimony ball current to 1.8A at 0.2A/(1-3) min, and then increasing the antimony ball current at a rate of 0.05A/(6-7) min, wherein in the process, a photocurrent continuously rises until a certain antimony ball current is reached until an inflection point appears in the photocurrent, and the time for the inflection point to appear is controlled to be between 1/2-3/4 of the total time of the whole first stage; and after the inflection point, continuously increasing the antimony ball current at the rate of 0.03A/(6-7) min until the reflectivity curve drops to the lowest point and an ascending trend begins to appear, and closing the antimony ball current.
In a further embodiment, in the second stage of simultaneous evaporation of potassium and antimony, the potassium source current is first increased by 0.5A until the photocurrent curve and the glass envelope reflectivity curve are both increased and then do not change, and each of the following operations is performed in sequence:
firstly, opening the antimony ball again by using antimony ball current which is less than 0.1A when the antimony ball is closed last time, so that a photocurrent curve and a glass bulb reflectivity curve are increased again, and then increasing the antimony ball current at a rate of 0.02A/(15-20) min; in the process, the current of the antimony ball is closed every 5-15 min, and the change condition of the reflectivity curve is checked, wherein: if the reflectivity curve stops rising, opening the antimony ball current to continue evaporation; if the reflectivity curve stops after rising for a period of time, continuing to evaporate after 0.05A potassium source current is needed to be added;
wherein, in the second stage of the simultaneous evaporation of the whole potassium and the antimony, the rising time of the reflectivity curve is controlled between 1h20min and 1h30 min.
Compared with the prior art, the invention has the following remarkable beneficial effects:
the invention provides a preparation method of a high quantum efficiency low thermal emission double-alkali photocathode for a micro-channel plate type photomultiplier, which is realized by controlling the evaporation process of potassium, cesium and antimony on the basis of a method for combining photocurrent and glass bulb reflectivity of the double-alkali photocathode to form K2A CsSb double-alkali photocathode structure; the time point of the occurrence of the photocurrent inflection point is controlled by adjusting the rate of increasing the antimony ball current in the first stage of simultaneous evaporation of potassium and antimony, and the increase of the antimony ball current and the rise time of the reflectivity curve are controlled by observing the reflectivity change of antimony in the second stage of simultaneous evaporation of potassium and antimony to reduce the integration sensitivity of the dibasic cathode, thereby reducing the cathode thermionic emission.
The photocathode and the photomultiplier finally prepared by the method have high quantum efficiency, low noise and excellent consistency.
Drawings
The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. Embodiments of various aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings,
FIG. 1 shows a variable doping K2Structure of CsSb double base photocathode.
FIG. 2 is a flow diagram of the preparation of a dibasic photocathode in accordance with the present invention.
FIG. 3 is a typical graph of the quantum efficiency curves of the dibasic photocathode prepared by different current increasing rates of the first stage antimony balls formed by simultaneous evaporation of different potassium and antimony.
Table 1 shows the performance characteristics of the photomultiplier tube for different antimony and potassium simultaneous vapor deposition first-stage antimony ball current increase rates.
Detailed Description
The present invention will be further described with reference to the accompanying drawings.
K prepared by the prior Chinese patent No. 201710743036.22In the process of controlling the CsSb photocathode process, a K-Sb layer is formed at first, and as the number ratio of K to Sb in the standard K-Sb layer is 3:1, but the Sb amount in the early stage is required to be slightly more in a variable doping structure, the evaporation ratio is K: sb is 2.82: 1; the Sb amount is gradually reduced and the K amount is gradually increased by continuous vapor deposition, a K-Sb layer with different proportions is formed in the repeated process of each vapor deposition period, and K is sequentially formed from the inside to the surface of the body2.88Sb1.0、K2.94Sb1.0、K3.0Sb1.0、K3.06Sb1.0And K3.12Sb1.0. In the Cs vapor deposition process, each Cs atom replaces one K atom, and finally an alkali metal antimonide structure with the K/Cs ratio of 2:1 is formed.
In the specific technological process of the preparation, a control mode of combining photocurrent and glass shell reflectivity is adopted simultaneously to control the evaporation process of potassium, cesium and antimony, the evaporation process sequentially forms a structure from a structure only containing potassium elements to a structure containing potassium and antimony elements and mainly accounting for antimony quantity, then to a structure containing potassium and antimony elements and gradually reducing antimony quantity and gradually increasing potassium quantity from the inside of a double-alkali photocathode body to the surface, and finally, the cesium atoms fully replace potassium atoms from the surface of the cathode to form a K2CsSb photocathode structure.
However, in the process of actual mass production, we find that the above scheme can achieve stable operation in the test process, but in the process of mass production, it is difficult to stably control the gradual change process of the doping concentration of potassium and antimony, great uncertainty exists in the increase and decrease control of the specific doping concentration and the evaporation current, and the performance of the cathode also has a promotion space.
Meanwhile, in the existing preparation method for the photocathode, attention is focused on quantum efficiency performance, and for the photocathode and the whole tube (vacuum device), the noise of the whole tube increases along with the increase of the quantum efficiency of the cathode, and two opposite directions are pursued for high quantum efficiency and low noise. Taking the cathode thickness as an example, because the double-alkali cathode is of a non-single-crystal structure, the thinner the cathode film layer is, the fewer the impurity defects in the unit volume are, and the fewer the generated hot electrons are; however, the thin cathode thickness greatly affects the absorption of incident light, and thus, quantum efficiency.
Through continuous research on the double-alkali photocathode, the lower the integral sensitivity of the double-alkali cathode is, the less the thermionic emission is. Therefore, in the implementation process of the invention, the integral sensitivity is taken as a zero-one key index for evaluating the performance of the photocathode, and is defined as: under the condition that a standard light source with the color temperature of 2856K irradiates and a collecting anode is under the saturated working voltage (generally equal to or more than 100V), a photocathode receives the photocurrent generated by unit luminous flux, and the specific formula is as follows:
Figure GDA0002487887840000041
in the formula SiIs the integral sensitivity (in. mu.A/lm) of the cathode, I is the photocurrent emitted by the cathode, phiνV (λ) represents the spectral luminous efficiency (also called the visual function) of the human eye, W (λ) represents the spectral distribution of the radiant flux of the standard light source, and S (λ) is the radiation sensitivity of the photocathode.
Since W (λ) is a function that increases with λ, S (λ) in the long wavelength band contributes more to the integral sensitivity. For a double-alkali broadcast cathode with a non-single crystal structure, the long-wave response of the double-alkali broadcast cathode is mainly contributed by an impurity energy level, so that when the double-alkali broadcast cathode with high quantum efficiency is prepared, the influence of the double-alkali broadcast cathode on noise of a photomultiplier is considered at the same time, and the long-wave response is reduced through process control, so that the integral sensitivity of the double-alkali cathode is reduced, the thermionic emission is reduced, and finally, the noise performance of the photomultiplier is optimized while high quantum efficiency is provided.
In a specific embodiment, the contribution of the long-wave band S (λ) to the integral sensitivity is controlled by controlling the rate of the evaporation current and the process time of the different evaporation stages during the implementation of the present invention.
FIG. 1 is a schematic diagram schematically illustrating an ideal structure of a double-alkali photocathode for use in a high quantum efficiency, low noise microchannel plate type photomultiplier according to the present invention. The double-alkali photoelectric cathode used by the micro-channel plate type photomultiplier with high quantum efficiency and low noise comprises a substrate and multiple layers of alkali antimonides, wherein the multiple layers of alkali antimonides are sequentially stacked on the substrate, and the composition of the alkali antimonides in the direction from the substrate of the double-alkali photoelectric cathode to the outer surface tends to decrease antimony elements and increase alkali metal elements gradually.
In a particularly preferred embodiment, the substrate is a low background borosilicate glass. Namely, the borosilicate glass with low background on the inner surface of the glass vacuum container, which is a borosilicate glass containing very small proportion of radioactive elements, has the characteristics of good chemical stability and good thermal stability.
In the invention, in the process of forming the gradually-changed internal structure of the double-alkali photocathode, the alkali antimonide positioned in a certain layer in the middle is a standard layer, the ratio of the number of alkali metal elements to the number of antimony elements in the standard layer is 3:1, the ratio of the number of alkali metal elements to the number of antimony elements in the alkali antimonide close to the substrate of the double-alkali photocathode relative to the standard layer is less than 3:1, and the ratio of the number of alkali metal elements to the number of antimony elements in the alkali antimonide close to the outer surface of the double-alkali photocathode relative to the standard layer is more than 3: 1. And the layers form an integral structure and are in gradual transition, wherein the ratio of the number of alkali metal elements to the number of antimony elements in the alkali antimonide attached to the base of the photocathode is 2.75: 1-2.85: 1, the semiconductor is an obvious strong P-type semiconductor, and then the semiconductor is gradually transited to the position of the outer surface of the photocathode, wherein the ratio of the number of alkali metal elements to the number of antimony elements in the alkali antimonide is 3.05: 1-3.25: 1, and the semiconductor is a weak P-type semiconductor.
In the invention, except that the alkali metal elements in one layer of alkali antimonide attached to the inner surface of the photocathode only comprise potassium elements, the alkali metal elements in the other layers of alkali antimonides comprise two types of potassium and cesium, and the number ratio of the potassium elements to the cesium elements in each layer of alkali antimonide is 2: 1.
In the following detailed description of the invention, the preparation is carried out specifically using the double base cathode of the above example (shown in FIG. 1). With reference to fig. 2, the specific preparation process includes:
firstly, evaporating a reflective film on a glass vacuum container in a normal temperature environment;
secondly, putting a frame on an antimony alkali seat filled with an alkali source and antimony balls in a normal temperature environment;
thirdly, mounting the glass vacuum container, the tube core assembly and the stibium base seat into a vacuum system, and performing air extraction and high-temperature baking degassing;
fourthly, baking the glass vacuum container at a temperature higher than 300 ℃ to degas;
fifthly, recording the reflectivity of the initial glass shell at the temperature of less than 200 ℃, and degassing the potassium source, the cesium source and the antimony balls;
sixthly, performing bottom potassium evaporation at the temperature of 120-190 ℃;
seventhly, performing a first stage of simultaneous evaporation of potassium and antimony at the temperature of 120-190 ℃;
eighthly, performing a second stage of simultaneous evaporation of potassium and antimony at the temperature of 120-190 ℃;
ninth, cesium evaporation is carried out at the temperature of 110-180 ℃, and after the evaporation is finished, the preparation of the high-quantum-efficiency low-thermal-emission double-alkali photocathode is realized;
wherein, in the preparation process, the photocurrent and the glass bulb reflectivity are simultaneously monitored to control the film evaporation of the double-alkali photocathode in the glass vacuum container;
in the first stage of simultaneous evaporation of potassium and antimony, the time point of the inflection point of photocurrent is controlled by regulating the rate of increasing antimony ball current, and the increasing rate of antimony ball current and the rising time of the reflectivity curve are controlled by observing the reflectivity change of antimony in the second stage of simultaneous evaporation of potassium and antimony to reduce the integral sensitivity of the double-alkali cathode.
During the operation from the first step to the sixth step, corresponding processes in the prior art can be adopted.
In an alternative embodiment, for example, in the second step, the focusing electrode, the microchannel plate type multiplier and the power supply electrode are mounted as a die assembly in a normal temperature environment, and the stibine base containing the alkali source and the stibine balls is mounted.
In the fourth step, the temperature of the high-temperature baking is 350 +/-5 ℃. In a fifth step, the lamp current was adjusted to 5.5A, the voltage was adjusted to 106V, and the potassium source, cesium source, and antimony sphere were degassed with degassing currents of 3.5A, 2.0A, and 0.5A, respectively.
In the sixth step, on the basis of the potassium source current of 3.5A, the potassium source current is adjusted according to a certain increase speed until the photocurrent curve rises and reaches a peak value and keeps constant, wherein the increase speed of the potassium source current is adjusted to be 0.05A/5 min.
In a further embodiment, in the first stage of simultaneous evaporation of potassium and antimony, the current of a potassium source is kept unchanged, the current of an antimony ball is increased to 1.8A at a speed increasing rate of 0.2A/(1-3) min, then the current of the antimony ball is increased at a speed increasing rate of 0.05A/(6-7) min, in the process, the photocurrent continuously rises until a certain antimony ball current is lower until an inflection point appears in the photocurrent, and the time of the inflection point is controlled to be 1/2-3/4 of the total time of the whole first stage. The stage is the first key link of the whole preparation process, and the control of the long wave band of the low-thermal emission double-alkali photocathode is realized.
And after the inflection point, continuously increasing the antimony ball current at the rate of 0.03A/(6-7) min until the reflectivity curve drops to the lowest point and an ascending trend begins to appear, and closing the antimony ball current.
In a further embodiment, in the second stage of simultaneous evaporation of potassium and antimony, the potassium source current is first increased by 0.5A until the photocurrent curve and the glass envelope reflectivity curve are both increased and then do not change, and each of the following operations is performed in sequence:
firstly, opening the antimony ball again by using antimony ball current which is less than 0.1A when the antimony ball is closed last time, so that a photocurrent curve and a glass bulb reflectivity curve are increased again, and then increasing the antimony ball current at a rate of 0.02A/(15-20) min; in the process, the current of the antimony ball is closed every 5-15 min, and the change condition of the reflectivity curve is checked, wherein: if the reflectivity curve stops rising, opening the antimony ball current to continue evaporation; if the reflectivity curve stops after rising for a period of time, continuing to evaporate after 0.05A potassium source current is needed to be added;
wherein, in the second stage of the simultaneous evaporation of the whole potassium and the antimony, the rising time of the reflectivity curve is controlled between 1h20min and 1h30 min. The method is the second key link of preparation, realizes process control, and controls the adjustment of long-wave band to integral sensitivity.
And finally, in the ninth step, reducing the temperature by 10 ℃, then starting cesium evaporation, wherein the initial cesium source current is 4.5A, increasing the cesium source current to 6A according to the increasing speed of 0.5A/30min, continuously increasing the photocurrent curve in the process, increasing the glass shell reflectivity to 1.4-2.4 times of the initial glass shell reflectivity after 1 hour, and stopping evaporation to obtain the low-heat-emission double-alkali cathode.
The performance characteristics of the photomultiplier tube under different cathode preparation processes are shown in combination with fig. 3 and table 1. In the first stage of simultaneous evaporation of potassium and antimony, the current increase rate of an antimony ball in 0.05A/(6-7) min adopted by the method is taken as a standard, when the increase rate is too high, the potassium-antimony proportion is seriously unbalanced, the quantum efficiency is low, the integral sensitivity is high, and the noise is high; when the increasing rate is slower, the gradually-changed proportion degree of potassium and antimony is weaker, the transport assistance of the built-in electric field to electrons is weakened, the quantum efficiency is slightly lower, the corresponding integral sensitivity is slightly lower, and the noise is slightly lower; when the antimony balls in the first stage of the whole co-evaporation are not increased completely, namely under the condition of the traditional double-alkali cathode preparation process, the cathode body is uniformly doped, and the quantum efficiency, the integral sensitivity and the noise are low.
TABLE 1
Figure GDA0002487887840000071
The above is only a preferred embodiment of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.

Claims (5)

1. A preparation method of a high-quantum-efficiency low-thermal-emission double-alkali photocathode used for a photomultiplier is characterized by comprising the following steps of:
firstly, evaporating a reflective film on a glass vacuum container in a normal temperature environment;
secondly, putting a frame on an antimony alkali seat filled with an alkali source and antimony balls in a normal temperature environment;
thirdly, mounting the glass vacuum container, the tube core assembly and the stibium base seat into a vacuum system, and performing air extraction and high-temperature baking degassing;
fourthly, baking the glass vacuum container at a temperature higher than 300 ℃ to degas;
fifthly, recording the reflectivity of the initial glass shell at the temperature of less than 200 ℃, and degassing the potassium source, the cesium source and the antimony balls;
sixthly, performing bottom potassium evaporation at the temperature of 120-190 ℃;
seventhly, performing a first stage of simultaneous evaporation of potassium and antimony at the temperature of 120-190 ℃;
eighthly, performing a second stage of simultaneous evaporation of potassium and antimony at the temperature of 120-190 ℃;
ninth, cesium evaporation is carried out at the temperature of 110-180 ℃, and after evaporation, the preparation of the high-quantum-efficiency low-thermal-emission double-alkali photocathode is realized;
wherein, in the preparation process, the photocurrent and the glass bulb reflectivity are simultaneously monitored to control the film evaporation of the double-alkali photocathode in the glass vacuum container;
in the first stage of simultaneous evaporation of potassium and antimony, the rate of increasing antimony ball current is adjusted to control the time point of the occurrence of photocurrent inflection point, and in the second stage of simultaneous evaporation of potassium and antimony, the change of reflectivity is observed to control the increase of antimony ball current and the rising time of reflectivity curve, so as to reduce the integral sensitivity of the double-alkali cathode;
in the seventh step, in the first stage of simultaneous evaporation of potassium and antimony, keeping the current of a potassium source unchanged, increasing the current of an antimony ball to 1.8A at a speed increasing rate of 0.2A/(1-3) min, and then increasing the current of the antimony ball at a speed increasing rate of 0.05A/(6-7) min, wherein in the process, the photocurrent continuously rises until the current of the antimony ball falls below a certain photocurrent until an inflection point appears in the photocurrent, and the time of the inflection point is controlled to be 1/2-3/4 of the total time of the whole first stage; after the inflection point, continuously increasing the current of the antimony balls at the rate of 0.03A/(6-7) min until the reflectivity curve drops to the lowest point and an ascending trend begins to appear, and closing the current of the antimony balls;
in the eighth step, in the second stage of simultaneous evaporation of potassium and antimony, the potassium source current is increased by 0.5A first until the photocurrent curve and the glass bulb reflectivity curve are raised and then do not change, and each of the following operations is performed in sequence:
firstly, opening the antimony ball again by using antimony ball current which is less than 0.1A when the antimony ball is closed last time, so that a photocurrent curve and a glass bulb reflectivity curve are increased again, and then increasing the antimony ball current at a rate of 0.02A/(15-20) min; in the process, the current of the antimony ball is closed every 5-15 min, and the change condition of the reflectivity curve is checked, wherein: if the reflectivity curve stops rising, opening the antimony ball current to continue evaporation; if the reflectivity curve stops after rising for a period of time, continuing to evaporate after 0.05A potassium source current is needed to be added;
in the second stage of the simultaneous evaporation of the potassium and the antimony, the rising time of the reflectivity curve is controlled to be 1h20 min-1 h30 min.
2. The method for preparing a double-alkali photocathode with high quantum efficiency and low thermal emission for use in a photomultiplier according to claim 1, wherein in the fourth step, the high-temperature baking temperature is 350 ± 5 ℃; in a fifth step, the lamp current was adjusted to 5.5A, the voltage was adjusted to 106V, and the potassium source, cesium source, and antimony ball were degassed with degassing currents of 3.5A, 2.0A, and 0.5A, respectively.
3. The method for producing a double alkali photocathode with high quantum efficiency and low thermal emission for use in a photomultiplier according to claim 2, wherein in the sixth step, the potassium source current is adjusted at a certain rate of increase based on the potassium source current of 3.5A until the photocurrent curve rises and reaches a peak value and is kept constant, wherein the rate of increase of the potassium source current is adjusted to 0.05A/5 min.
4. The method for preparing a high quantum efficiency low thermal emission dibasic photocathode for a photomultiplier according to claim 1, wherein in the ninth step, the temperature is lowered by 10 ℃, then cesium evaporation is started, the initial cesium source current is 4.5A, the cesium source current is increased to 6A at a rate of 0.5A/30min, the photocurrent curve continues to rise during the cesium source current, and after 1 hour, the glass shell reflectance value rises to 1.4 to 2.4 times the initial glass shell reflectance value, and the evaporation is stopped to obtain a low thermal emission dibasic cathode.
5. A double-alkali photocathode with high quantum efficiency and low thermal emission, which is used for a photomultiplier tube prepared by the method of any one of claims 1 to 4.
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