CN109755081B - An automatic control method of antimony current for the fabrication of high-performance alkali metal antimonide photocathode - Google Patents

Abstract

The present invention provides an antimony current automatic regulation method for the production of high-performance alkali metal antimonide photocathode, including: alkali metal evaporation, antimony evaporation, photocurrent curve fitting and prediction, photocurrent curve slope judgment and antimony evaporation current adjustment. It is suitable for the simultaneous evaporation of alkali metal and antimony. First, the photocurrent curve is fitted, and then it is predicted whether the slope of the photocurrent curve in a fixed time range in the future reaches the expected value, and then it is judged whether the slope of the actual photocurrent curve reaches the expected value. If both If any one reaches the expected value, then judge whether the slope of the actual photocurrent curve reaches the specified value, and finally adjust the antimony evaporation current according to the judgment conditions. Repeat the above process until the slope of the photocurrent curve reaches the specified angle. The invention can solve the problem that the ratio of alkali metal and antimony is unbalanced due to the uncontrollable amount of antimony in the production process of the alkali metal antimonide photocathode, and improve the photoelectric emission performance of the alkali metal antimonide photocathode.

Description

Automatic regulation of antimony current for fabrication of high-performance alkali metal antimonide photocathodes method

technical field

The invention relates to the technical field of vacuum photoelectric detection devices, in particular to the preparation of cathodes, and in particular to an antimony current automatic regulation method for the preparation of high-performance alkali metal antimonide photocathodes.

Background technique

Vacuum photodetectors are electronic devices that convert optical signals into electrical signals, which can effectively detect weak light, and are widely used in extremely weak light detection, photon detection, chemiluminescence, bioluminescence and other research fields. Including low-light image intensifiers, photomultiplier tubes, streak tubes, etc. The core part of the above vacuum photodetection device is the photocathode, and its performance directly affects the performance of the entire device. Its main performance parameter is quantum efficiency, that is, the number of electrons that the photocathode can emit per 100 photons received. At present, the commonly used alkali metal antimonides include various mono-, di- and poly-alkali antimonides with potassium, sodium, lithium and cesium as alkali metal materials, including: K ₃ Sb, Cs ₃ Sb, K ₂ CsSb, K ₂ NaSb, _K2LiSb and KNaCsSb etc.

The preparation method of alkali metal antimonide photocathode is mainly distinguished according to whether alkali metal and antimony are evaporated at the same time. Preparation Process. A method for preparing a K ₂ CsSb photocathode combining photocurrent monitoring and reflectivity monitoring proposed in the patent application with application number 201610856127.2 adopts the preparation process of bottom potassium, potassium and antimony co-evaporating and finally cesium; application number 201510438585.X A preparation method for Na ₂ CsSb photocathode is proposed in the patent of . The built-in electric field diffusion theory of semiconductor carriers is applied to the preparation of double-alkali cathodes, that is, there is a built-in electric field in the energy band bending region, which is conducive to the transport of electrons in the material to the surface.

It can be seen from the above-mentioned patents that at present, alkali metal antimonide photocathodes all adopt co-evaporation of alkali metal and antimony, rather than separate evaporation. This is because co-evaporation can control the coating composition by adjusting the ratio of alkali metal and antimony, thereby effectively improving the quantum efficiency of the photocathode. There are two schemes for co-evaporation. The first is to find out a fixed time and a fixed evaporation through a large number of experiments; the second is to adjust the evaporation in real time according to the change of the photocurrent curve. The premise of the application of the first scheme is that the vacuum atmosphere, alkali metal evaporation source and antimony evaporation source are highly consistent, otherwise the second scheme is more universal, and it is easier to produce photocathodes with high performance. Therefore, when the alkali metal evaporation is solidified during co-evaporation, how to effectively control the antimony evaporation according to the change trend of the photocurrent curve becomes the key factor affecting the performance of the cathode.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for automatic regulation of antimony current for the fabrication of high-performance alkali metal antimonide photocathode.

In order to achieve the above object, the present invention proposes a method for automatic regulation of antimony current used in the manufacture of high-performance alkali metal antimonide photocathode, characterized in that the method comprises:

Alkali metal evaporation, by adjusting the alkali metal evaporation current, the alkali metal can be stably precipitated with a fixed evaporation amount;

Antimony vapor deposition, after degassing the antimony, adjust the antimony current to the precipitation value;

Fitting and predicting the photocurrent curve, fitting the trend of the collected photocurrent curve, and predicting the slope α of the subsequent photocurrent curve;

Judging the slope of the photocurrent curve, first determine whether the predicted photocurrent curve slope α reaches the expected value, if so, wait and continue to judge whether the actual photocurrent curve slope β reaches the expected value, otherwise increase the antimony current immediately;

If the slope β of the actual photocurrent curve reaches the expected value, wait and continue to judge whether the slope β of the actual photocurrent curve reaches the specified value, otherwise immediately judge whether the slope β of the actual photocurrent curve is a positive value:

If the slope β of the actual photocurrent curve is a positive value, wait and continue to judge whether the slope β of the actual photocurrent curve reaches the expected value, otherwise increase the antimony current immediately;

If the continuous judgment of the actual photocurrent curve slope β reaches the desired value, then wait and then judge whether the actual photocurrent curve slope β reaches the specified value, otherwise immediately increase the antimony current;

If it is judged that the slope β of the actual photocurrent curve reaches the specified value, the antimony adjustment phase ends; otherwise, the antimony current is immediately increased;

Antimony current vapor deposition adjustment, according to whether the predicted photocurrent curve slope α reaches the expected value, and the deviation of the actual photocurrent curve slope β from the expected value and the specified value to adjust the antimony current.

Further, the alkali metal evaporation refers to forming an alkali metal atmosphere in a vacuum environment before evaporating antimony, and the sign of the end of the alkali metal evaporation is that the photocurrent rises to a maximum value and then starts to fall.

Further, the photocurrent curve is fitted by using a polynomial fitting or a least squares curve fitting algorithm.

Further, the trend of the fitted photocurrent curve is within the range of the predetermined time ΔT ₁ , and its value is between 0 and 5 min.

Further, the predicted slope of the photocurrent curve is within the range of the predetermined time ΔT ₂ , and its value is between 0 and 2 min.

Further, for the set photocurrent regulation gear, the expected value and the specified value should be a fixed value or a fixed range value, and the specified value is faster than the photocurrent rising rate corresponding to the expected value.

Further, the photocurrent regulation gears include 1 mA, 500 μA, 200 μA, 100 μA, 50 μA, 20 μA, 10 μA, 5 μA, 2 μA, 1 μA, 500 nA, 200 nA, 100 nA, 50 There are 16 levels of nA, 20 nA and 10 nA.

Further, for the predicted slope α of the photocurrent curve and the actual slope β of the photocurrent curve, the smallest photocurrent regulation gear that can be located is selected.

Further, for the predicted slope α of the photocurrent curve and the actual slope β of the photocurrent curve, the antimony current that needs to be adjusted and increased without reaching the expected value is greater than the antimony current increased without reaching the specified value.

Further, in the case that the actual photocurrent curve slope β does not reach the expected value or the specified value, the adjustment of the increased antimony current is proportional to the angle deviation.

From the above technical solutions, the significant advantages of the aforementioned implementation method of the present invention are:

1) Due to the method of adjusting the evaporation amount in real time according to the change of the photocurrent curve in the co-evaporation of alkali metal and antimony, the composition ratio control can be realized;

2) Not only refer to the actual photocurrent curve changes, but also refer to the predicted photocurrent theoretical curve changes. The added judgment content during the antimony adjustment process makes the judgment of the completed antimony current evaporation more accurate;

3) Compare the deviation of the actual photocurrent curve with the expected value and the theoretical value. The added judgment conditions in the process of antimony adjustment make the antimony current adjustment to be carried out more accurate;

4) The antimony current regulation method of high-performance alkali metal antimonide photocathode is based on the automatic regulation system. Compared with manual antimony regulation, the error rate is low and the repeatability is high. The prepared photocathode is used in large-scale photomultiplier tubes for neutrino detection. The K ₂ CsSb photocathode in the photocathode has a quantum efficiency of over 35% at 410 nm, which is significantly better than the existing artificial regulation.

Description of drawings

1 is a flowchart of automatic regulation of antimony current for alkali metal antimonide photocathodes according to some embodiments of the present invention.

FIG. 2 is an automatic antimony current control system for alkali metal antimonide photocathodes according to some embodiments of the present invention, and is a diagram showing cathode fabrication parameters and photocurrent levels displayed on a control software interface.

3 is a photocurrent curve for automatic regulation of antimony current of an alkali metal antimonide photocathode according to some embodiments of the present invention, and is a graph showing the photocurrent and the theoretical curve when judging whether β reaches a desired value.

FIG. 4 is a photocurrent curve for automatic regulation of antimony current of an alkali metal antimonide photocathode according to some embodiments of the present invention, and is a graph showing the photocurrent and the theoretical curve when judging whether β reaches a specified value.

5 is a photocurrent curve of antimony current automatic regulation for alkali metal antimonide photocathode according to some embodiments of the present invention, and the photocurrent and the theoretical curve after the antimony regulation is finished are shown.

6 is a comparison of the quantum efficiency distribution of the sample tube prepared by the automatic antimony amount adjustment method for alkali metal antimonide photocathode according to some embodiments of the present invention and the quantum efficiency distribution prepared by artificial antimony adjustment.

Detailed ways

1 is a flowchart of automatic regulation of antimony current for alkali metal antimonide photocathodes according to some embodiments of the present invention. Including: adding antimony 101, predicting whether α reaches the expected value 102, judging whether β reaches the expected value 103, judging whether β is a positive value 104, judging whether β reaches the expected value 105, judging whether β reaches the specified value 106 and ending antimony adjustment 107.

In general, the method for automatic regulation of antimony current for alkali metal antimonide photocathode proposed by the present invention includes: alkali metal evaporation, antimony evaporation, photocurrent curve fitting and prediction, photocurrent curve slope judgment, and photocurrent Antimony current vapor deposition adjustment based on the result of the judgment of the slope of the curve.

Alkali metal evaporation refers to the stable precipitation of alkali metal with a fixed evaporation amount by adjusting the alkali metal evaporation current.

After antimony vapor deposition and degassing of antimony, the antimony current was adjusted to the precipitation value.

Photocurrent curve fitting and prediction: Fit the trend of the collected photocurrent curve and predict the slope α of the subsequent photocurrent curve.

Judging the slope of the photocurrent curve, including:

First, judge whether the predicted photocurrent curve slope α reaches the expected value, if so, wait and continue to judge whether the actual photocurrent curve slope β reaches the expected value, otherwise increase the antimony current immediately;

If the slope β of the actual photocurrent curve reaches the expected value, wait and continue to judge whether the slope β of the actual photocurrent curve reaches the specified value, otherwise immediately judge whether the slope β of the actual photocurrent curve is a positive value:

If the slope β of the actual photocurrent curve is a positive value, wait and continue to judge whether the slope β of the actual photocurrent curve reaches the expected value, otherwise increase the antimony current immediately;

If the continuous judgment of the actual photocurrent curve slope β reaches the desired value, then wait and then judge whether the actual photocurrent curve slope β reaches the specified value, otherwise immediately increase the antimony current;

If it is judged that the slope β of the actual photocurrent curve reaches a specified value, the antimony adjustment phase ends; otherwise, the antimony current is immediately increased.

Antimony current vapor deposition adjustment, according to whether the predicted photocurrent curve slope α reaches the expected value, and the deviation of the actual photocurrent curve slope β from the expected value and the specified value to adjust the antimony current.

Combined with the process shown in Figure 1, after adjusting the antimony current to the precipitation value, there are four antimony adding operations in the step of adding antimony 101. They are adding antimony after α does not reach the expected value of 102, and adding antimony after judging that β is not a positive value of 104. , add antimony after judging that β does not reach the expected value 105 and add antimony after judging that β does not reach the specified value 106 .

According to the embodiment of the present invention, for a 20-inch photomultiplier tube K ₂ CsSb photocathode, the antimony current increases of the above four antimony adding operations are 0.4 A, 0.2 A, 0.5 A, and 0.3 A, respectively, and the corresponding waiting times for 2.0 min. The antimony currents 0.5 A and 0.3 A added after judging that β does not reach the expected value 105 and the antimony current 0.5 A and 0.3 A that are added after judging that β does not reach the specified value 106 are only basic amounts, which are also affected by the difference between β and the expected value and the specified value.

In step 102 of predicting whether α reaches the expected value, the curve automatically adjusts the gear position to ensure that the displayed photocurrent is greater than 4.5 grids in the coordinates, otherwise the display is reduced by 1 gear. Combined with the cathode fabrication parameters and photocurrent gear display diagrams on the control software interface given in Figure 2, it can be seen that the gears include 1 mA, 500 μA, 200 μA, 100 μA, 50 μA, 20 μA, 10 μA, 5 μA , 2 μA, 1 μA, 500 nA, 200 nA, 100 nA, 50 nA, 20 nA and 10 nA, a total of 16 levels. And each gear only displays 10 grids in the photocurrent coordinate system. For example, when the photocurrent level is 5 μA, 1 division represents 0.5 μA; when the photocurrent level is 100 nA, 1 division represents 10 nA. With this display method, whenever the photocurrent is at the 10th grid, the gear will automatically increase by 1, and the photocurrent will automatically fall back to the 5th grid; when the photocurrent is less than 4.5 grids, the gear will automatically decrease by 1 level, the photocurrent will automatically increase to twice the number of grids. In addition, other cathode fabrication parameters are also displayed on the control software interface, including: photocurrent, leakage current, current slope, reflectivity and reflectivity slope and other information.

Based on the above gear change principle, the photocurrent corresponding to the desired value should stay at the minimum gear it can be in. The expected value is defined as the angle between the slope of the photocurrent in the first quadrant of the coordinate system and the vertical direction, with a fixed range angle of 30°. When α reaches the expected value, wait for 1 min to determine whether β reaches the expected value 103; otherwise, when α does not reach the value, immediately increase the antimony current by 0.4 A, that is, repeat the steps to add antimony 101.

In the step of judging whether β reaches the expected value 103 , the expected value is also the included angle of 30° between the slope of the photocurrent in the first quadrant and the vertical direction. When β reaches the expected value, wait for 5 minutes to judge whether β reaches the specified value 106 ; otherwise, when β does not reach the expected value, immediately judge whether β is a positive value 104 .

In the step 104 of determining whether β is a positive value, the positive value means that the photocurrent is in the first quadrant of the coordinate system, responsible for the decrease of the photocurrent, and its slope enters the second quadrant of the coordinate system. The positive value is set to -5°, the purpose is to eliminate the interference caused by signal jitter to judge whether β is a positive value. When β is a positive value, wait for 1 min to judge whether β reaches the expected value of 105; when β is not a positive value, immediately increase the antimony current by 0.2 A, that is, repeat the steps to add antimony 101.

In the step of judging whether β reaches the expected value 105 , the expected value is also the included angle of 30° between the slope of the photocurrent in the first quadrant and the vertical direction. When β reaches the expected value, wait for 5 minutes to determine whether β reaches the specified value 106; otherwise, when β does not reach the expected value, for every 5° decrease in β , the antimony current increases by 0.05 A, and the waiting time increases by 0.5 min. As shown in Table 1.

Table 1 Sb current increase when β does not reach the expected value

<i>β</i> 0°~5° 5°~10° 10°~15° 15°~20° 20°~25° 25°~30° Sb evaporation current 0.75A 0.7A 0.65A 0.6A 0.55A 0.5A waiting time 4.5 min 4 min 3.5 min 3 min 2.5 min 2 min

In the step of judging whether β reaches a specified value 106 , the specified value is defined as an included angle of 45° between the slope of the photocurrent in the first quadrant of the coordinate system and the vertical direction. When β reaches the specified value, the antimony 107 is adjusted after waiting for 2 minutes; otherwise, when β does not reach this value, the antimony current increases by 0.05 A for every 5° decrease in β , and the waiting time increases by 0.5 min. The specific conditions are as follows: shown in Table 2.

Table 2 Sb current increase when β does not reach the specified value

<i>β</i> 25°~30° 30°~35° 35°~40° 40°~45° Sb evaporation current 0.45A 0.4A 0.35A 0.3A waiting time 3.5 min 3 min 2.5 min 2 min

3 is a photocurrent curve for automatic regulation of antimony current of an alkali metal antimonide photocathode according to some embodiments of the present invention, and is a graph showing the photocurrent and the theoretical curve when judging whether β reaches a desired value. Among them, curve 1 is the actual photocurrent curve, and curve 2 is the theoretical curve. Antimony was added at 6.5 min, and then the curve after adding antimony was theoretically fitted. The fitting time ΔT ₁ was 2 min, and the prediction time ΔT ₂ was 1 min. Finally, α is 37° and has reached the expected value (30°), β is 13° and has not reached the expected value (30°), therefore, the photocurrent curve should continue to add antimony, the antimony current is 0.65 A, and the waiting time is 3.5 min.

FIG. 4 is a photocurrent curve for automatic regulation of antimony current of an alkali metal antimonide photocathode according to some embodiments of the present invention, and is a graph showing the photocurrent and the theoretical curve when judging whether β reaches a specified value. Among them, curve 1 is the actual photocurrent curve, and curve 2 is the theoretical curve. Antimony was added at 8.3 min, and then the curve after adding antimony was theoretically fitted. The fitting time ΔT ₁ was 2 min, and the prediction time ΔT ₂ was 1 min. Finally, α is 56° has reached the desired value (30°), β is 58° has reached the specified value (45°), therefore, the photocurrent curve can end antimony tuning.

5 is a photocurrent curve for automatic regulation of antimony current for an alkali metal antimonide photocathode according to some embodiments of the present invention, and is a graph showing the actual photocurrent and theoretical curve after the antimony regulation is completed. Among them, curve 1 is the actual photocurrent curve, and curve 2 is the theoretical curve. Antimony was added at the 5th minute, and then the curve after antimony addition was theoretically fitted. The fitting time ΔT 1 was 3 min, and the prediction time ΔT ₂ was ₁ min. Finally, α is 66° and has reached the desired value (30°), β is 74° and has reached the specified value (45°), the antimony adjustment is ended, and the photocurrent begins to rise steadily. When the photocurrent rises to the 10th grid, the gear automatically Add 1 gear, and change gears 3 times in Figure 5.

6 is a comparison of the quantum efficiency distribution of the sample tube prepared by the automatic antimony amount adjustment method for alkali metal antimonide photocathode according to some embodiments of the present invention and the quantum efficiency distribution prepared by artificial antimony adjustment. The amount of sampled data for both methods is greater than 200. It can be seen that the sample tubes prepared by the method of automatic adjustment of antimony content are superior to the sample tubes prepared by the manual antimony adjustment method in the proportion of quantum efficiency greater than 27%, indicating that according to some embodiments of the present invention, the sample tubes for alkali metal antimony are used. The method of automatic regulation of antimony content in the photocathode has obvious effect on improving the quantum efficiency of the cathode.

Claims (10)

1. An antimony current automatic regulation and control method for manufacturing a high-performance alkali metal antimonide photocathode is characterized by comprising the following steps:

alkali metal evaporation, namely stably separating out alkali metal with fixed evaporation capacity by adjusting alkali metal evaporation current;

antimony evaporation, namely degassing antimony, and adjusting antimony current to a precipitation value;

fitting and predicting the photocurrent curve, fitting the trend of the collected photocurrent curve, and obtaining the slope of the predicted photocurrent curveα；

The slope of the photocurrent curve is judged by first judging the slope of the predicted photocurrent curveαWhether the slope reaches the expected value or not, if so, continuing to judge the actual photocurrent curve slope after waitingβIf the expected value is reached, otherwise, immediately increasing the antimony current;

if the actual photocurrent curve slopeβWhen the expected value is reached, the slope of the actual photocurrent curve is continuously judged after waitingβIf not, the slope of the actual photocurrent curve is immediately judgedβWhether it is a positive value:

if the actual photocurrent curve slopeβIf the actual photocurrent curve slope is positive, continuously judging whether the actual photocurrent curve slope is present after waitingβIf the expected value is reached, otherwise, immediately increasing the antimony current;

if the actual photocurrent curve slope is continuously judgedβWhen the expected value is reached, the slope of the actual photocurrent curve is judged after waitingβIf the value reaches the specified value, otherwise, the antimony current is increased immediately;

if the slope of the actual photocurrent curve is judgedβIf the value reaches the specified value, the antimony adjusting stage is ended, otherwise, the antimony current is increased immediately;

adjusting antimony current by evaporation according to the slope of predicted photocurrent curveαWhether the desired value is reached, and the actual photocurrent curve slopeβThe antimony current is adjusted for deviations from the desired and specified values.

2. The method as claimed in claim 1, wherein the alkali metal evaporation is performed by forming an alkali metal atmosphere in a vacuum environment before evaporating antimony, and the mark of the completion of the alkali metal evaporation is that a photocurrent starts to fall back after rising to a maximum value.

3. The method of claim 1, wherein the photocurrent curve is fitted using a polynomial fitting or least squares curve fitting algorithm.

4. The method as claimed in claim 1, wherein the fitted photocurrent curve trend is △ T at a predetermined time₁The range is 0-5 min.

5. The method as claimed in claim 1, wherein the slope of the predicted photocurrent curve is △ T at a predetermined time₂The range is 0-2 min.

6. The method as claimed in claim 1, wherein the expected value and the specified value are fixed values or fixed range values for the photocurrent control gear, and the increase rate of the photocurrent is faster than the expected value.

7. The method for automatically regulating and controlling the antimony current for manufacturing the high-performance alkali metal antimonide photocathode as claimed in claim 6, wherein the photocurrent regulation gear comprises 16 gears of 1mA, 500 μ A, 200 μ A, 100 μ A, 50 μ A, 20 μ A, 10 μ A, 5 μ A, 2 μ A, 1 μ A, 500 nA, 200 nA, 100 nA, 50 nA, 20 nA and 10 nA.

8. According to claim6 or 7, the antimony current automatic regulation and control method for the high-performance alkali metal antimonide photocathode is characterized in that the slope of the predicted photocurrent curveαAnd actual photocurrent curve slopeβAnd selecting the minimum photocurrent regulation gear where the light current regulation gear can be positioned.

9. The method of claim 1, wherein the method comprises predicting the slope of the photocurrent curveαAnd actual photocurrent curve slopeβThe increased antimony current that does not reach the desired value needs to be adjusted more than the increased antimony current that does not reach the specified value.

10. The method as claimed in claim 1, wherein the slope of the actual photocurrent curve is determined by the method of automatic control of the antimony current for the fabrication of high performance alkali antimonide photocathodesβIn the case where the desired or specified value is not reached, the adjustment increases the antimony current in proportion to the angular deviation.

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