A method for treating leakage during sodium evaporation in manufacturing of a super-second-generation multi-alkali photocathode

Abstract

The application discloses a processing method for leakage during sodium evaporation in super-second-generation multi-alkali photocathode production, and relates to the technical field of photocathode production. When leakage occurs during sodium evaporation in photocathode production and the leakage rises by more than 2000 nA in 1-4 minutes, the photocathode needs to be treated for leakage. The method comprises the following steps: when the leakage rises by more than 2000 nA, stopping sodium evaporation, opening a potassium power source to evaporate potassium for 1-2 minutes, closing the potassium power source and waiting for 1-2 minutes, opening a sodium power source to evaporate sodium for 1-2 minutes, opening an antimony power source to co-evaporate sodium and antimony, observing the rise and fall of photocurrent in 5 minutes, closing the antimony power source, waiting for 1 minute, and closing the sodium power source, and then entering the next process. Thus, the purpose of treating leakage during sodium evaporation in photocathode production is achieved, and the yield of photocathode production is effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of photocathode technology, specifically relating to a method for dealing with leakage current caused by sodium evaporation during the fabrication of a second-generation multi-alkali photocathode. Background Technology

[0002] The photocathode is a crucial component of photoelectric conversion in various low-light image intensifiers, responsible for converting weak photoelectron images into electrons. Failure in photocathode fabrication directly impacts various performance indicators of the image intensifier, even leading to dark areas and malfunction. Sensitivity is a key indicator for evaluating the quality of multi-alkali photocathodes. The general specification for super-second generation image intensifiers (GJB 7351-2011) stipulates that the photocathode sensitivity should be no less than 500 μA / lm; otherwise, the photocathode is considered unqualified. The super-second generation image intensifier specification also imposes strict requirements on the image quality: there should be no bright spots, streaks, emission points, or other forms of defects within the effective field of view; photocathode shadows are one such defect. The method for identifying photocathode shadows is to reduce the photocathode operating voltage from -200V to 0V. If the shadow color within the image intensifier's field of view deepens, the shadow is determined to originate from the multi-alkali photocathode.

[0003] like Figure 1 As shown, the fabrication of the multi-alkali photocathode is carried out in a vacuum environment. The main vapor deposition components are potassium, sodium, cesium, and antimony. The vapor deposition process is as follows: potassium vapor deposition → sodium vapor deposition → sodium-antimony co-deposition → potassium-sodium-antimony co-deposition → surface cesium activation. During the photocathode fabrication process, the photocurrent and leakage current are monitored in real time by switching process lights on and off (the process lights display the photocurrent when on and the leakage current when off). Generally, a leakage current below a certain value (e.g., below 1000nA) is considered normal, while a leakage current exceeding a certain limit is considered to have occurred.

[0004] It should be noted that if leakage occurs during the fabrication of the photocathode, and the photocathode is not treated, the photocurrent monitored by the photocathode fabrication equipment will be a false value. If the photocathode is fabricated according to this photocurrent value, it will lead to a mismatch in the amount of potassium, sodium, cesium, and antimony in the photocathode, resulting in unqualified photocathode sensitivity and the appearance of dark or bright areas during imaging, thus rendering the low-light image intensifier unusable.

[0005] If sodium leakage rises above 2000 nA during the fabrication of the second-generation multi-alkali photocathode film, subsequent photocathode deposition cannot be carried out. If the leakage photocathode is not treated, the photocathode fabrication will ultimately fail. Summary of the Invention

[0006] The technical problem to be solved by the invention is: In response to the problem of sodium leakage and rising current in the substrate layer during the fabrication of the above-mentioned multi-alkali photocathode film, the present invention effectively solves the problem of substandard photocathode and imaging quality caused by leakage during the fabrication of multi-alkali photocathode by controlling the current and time of sodium, potassium and antimony sources, effectively improving the sensitivity of the photocathode and the imaging quality of the low-light image intensifier, while also reducing the production cost of the image intensifier.

[0007] The technical solution of this invention is as follows:

[0008] A method for handling leakage current during sodium evaporation in the fabrication of a second-generation multi-alkali photocathode involves detecting photocurrent and leakage current by intermittently switching process lamps during the photocathode fabrication process. When leakage current occurs during sodium evaporation, the following steps are followed:

[0009] Step 1: Disconnect the sodium power supply to prevent the leakage current from continuing to rise;

[0010] Step 2: After the photocurrent stabilizes, turn on the potassium power supply, adjust the current to the initial value, allow the potassium to evaporate for 1-2 minutes, and then turn off the potassium power supply.

[0011] Step 3: Turn on the sodium power supply. After adjusting the sodium current to the initial value, increase it at a rate of 100mA per minute for 4 minutes.

[0012] Step 4: When the photocurrent begins to rise, turn on the antimony power supply to allow the sodium and antimony to evaporate simultaneously.

[0013] Step 5: Adjust the antimony current to the initial value, and increase the antimony current at a rate of 500mA per minute. When the photocurrent rises or falls by 5 divisions, cut off the antimony power supply.

[0014] Step 6: After one minute, disconnect the sodium power supply to complete the process of handling the leakage caused by sodium evaporation during the fabrication of the second-generation multi-alkali photocathode.

[0015] Preferably, the leakage phenomenon in the sodium evaporation refers to the fact that both the photocurrent and the leakage current show an upward trend.

[0016] Preferably, leakage is determined to have occurred when the leakage current rises to above 2000nA within 1-4 minutes.

[0017] Preferably, the initial value of the potassium current in step 2 is 2000-2500mA; the initial value of the sodium current in step 3 is 2000-2500mA; and the initial value of the antimony current in step 5 is 1000-1300mA.

[0018] The mechanism of this invention is as follows: the elemental metal atoms of evaporated Na are adsorbed on the antimony alkali base shield and the insulating parts of the terminal. The elemental alkali metal atoms are conductive. The outermost electron of the alkali metal atom is only one electron, which is easily lost to form a free electron. Therefore, the elemental alkali metal is easy to conduct electricity and generate leakage current. When the evaporated antimony reacts with sodium to form antimony compound, the conductivity of the antimony compound becomes weak, and the leakage current no longer increases, thus achieving the purpose of preventing the leakage current from increasing.

[0019] The beneficial effects of this invention include:

[0020] First, during the preparation of multi-alkali photocathodes, leakage phenomena generated during sodium evaporation are easily identified; second, the leakage treatment method for multi-alkali photocathodes is simple and easy to operate, and can be widely promoted and used. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a multi-alkali photocathode implemented in this invention.

[0022] Figure 2 A schematic diagram of the process flow for handling leakage current during sodium evaporation in the fabrication of the second-generation multi-alkali photocathode.

[0023] Figure 3 The image shows the imaging effect of a normal photocathode low-light image intensifier. The left and right images are from two different image intensifiers, and the brightness uniformity of the imaging field is good.

[0024] Figure 4 The images show the imaging effect of the low-light image intensifier after leakage current photocathode treatment. The left and right images show the imaging field brightness uniformity of two different image intensifiers after leakage current treatment, which can meet the general specifications of the second-generation image intensifier.

[0025] Figure 5 The image shows the imaging effect of a low-light image intensifier without processing of a leakage photocathode. The left image shows a large dark area in the field of view, while the right image shows a bright spot, which does not meet the general specifications of the super second generation image intensifier.

[0026] Figure 1 In the middle: 1-Process lamp; 2-Substrate; 3-Positive electrode collecting plate; 4-Alkali source evaporation source; 5-Antimony evaporation source; 6-Antimony evaporation source heating wire; 7-Positive electrode collecting terminal; 8-Alkali source heating power cord; 9-Reaction chamber; 10-Vacuum pump pipeline; 11-Heating cover. Detailed Implementation

[0027] This invention aims to find a method for handling leakage in multi-alkali photocathodes, thereby improving the success rate and yield of multi-alkali photocathode fabrication. On a dedicated photocathode fabrication apparatus, multi-alkali photocathodes that failed to fabricate due to leakage are treated. A control group consists of photocathodes with leakage that were fabricated using normal processes. The steps for handling leakage in multi-alkali photocathodes are as follows:

[0028] Step 1: During the fabrication of the photocathode, if leakage current rises to over 2000nA within 4 minutes during sodium deposition, it is considered abnormal and the photocathode needs to be repaired to address the leakage. At this point, the sodium current is cut off to prevent the photocurrent from continuing to rise.

[0029] Step 2: After the photocurrent has stabilized for 5 minutes, turn on the potassium power supply, adjust the current to 2200mA, let the potassium evaporate for 2 minutes, and then turn off the potassium power supply.

[0030] Step 3: Turn on the sodium power supply, adjust the sodium current to 2200mA, and increase it at a rate of 100mA per minute for 4 minutes.

[0031] Step 4: After 2 minutes, when the photocurrent begins to rise, turn on the antimony power supply to allow the sodium and antimony to evaporate simultaneously.

[0032] Step 5: Adjust the antimony current to 1200mA, and increase the antimony current at a rate of 500mA per minute. When the photocurrent rises or falls by 5 divisions, cut off the antimony power supply.

[0033] Step 6: After one minute, disconnect the sodium power supply to complete the photocathode leakage treatment.

[0034] The sensitivity of the two photocathodes—untreated and treated using the method of this invention—was tested using a photocathode sensitivity testing device. The results showed that the sensitivity of the treated photocathode was 850 μA / lm, meeting the general specifications for Super 2 image intensifiers; the sensitivity of the untreated photocathode was 236 μA / lm, failing to meet the general specifications for Super 2 image intensifiers.

[0035] The low-light image intensifier was operated at a working voltage. The working voltage of the photocathode was then reduced from -200V to 0V. The imaging quality of the two intensifiers—one with an untreated photocathode and the other with the method of this invention—was observed. The results showed that the imaging effect of the normal photocathode image intensifier was as follows: Figure 3 As shown, the image intensifier imaging effect after leakage current photocathode processing is shown in the figure. Figure 4 As shown, the imaging effect of the unprocessed image intensifier of the leakage photocathode is shown in the figure. Figure 5 As shown. The results show that the leakage photocathode, after processing, forms an image ( Figure 4 The image intensifier has uniform brightness in its field of view, meeting the general specifications for Super 2 image intensifiers; the untreated image intensifier shows large dark areas in its field of view. Figure 5 The brightness uniformity does not meet the general specifications for super second generation image intensifiers.

Claims

1. A method for handling leakage current during sodium evaporation in the fabrication of a second-generation multi-alkali photocathode, characterized in that the photocurrent and leakage current are detected by intermittently switching process lamps during the photocathode fabrication process. When leakage occurs during sodium vapor deposition, follow these steps to handle it: Step 1: Disconnect the sodium power supply to prevent the leakage current from continuing to rise; Step 2: After the photocurrent stabilizes, turn on the potassium power supply and adjust the current to the initial value of 2000-2500mA. Let the potassium evaporate for 1-2 minutes and then turn off the potassium power supply. Step 3: Turn on the sodium power supply. After adjusting the sodium current to the initial value of 2000-2500mA, increase it at a rate of 100mA per minute for 4 minutes. Step 4: When the photocurrent begins to rise, turn on the antimony power supply to allow the sodium and antimony to evaporate simultaneously. Step 5: Adjust the antimony current to the initial value of 1000-1300mA, and increase the antimony current at a rate of 500mA per minute. When the photocurrent rises or falls by 5 divisions, cut off the antimony power supply. Step 6: After one minute, disconnect the sodium power supply to complete the process of handling the leakage caused by sodium evaporation during the fabrication of the second-generation multi-alkali photocathode.

2. The method for handling leakage current during sodium evaporation in the fabrication of the second-generation multi-alkali photocathode according to claim 1, characterized in that: The leakage phenomenon in sodium evaporation refers to the fact that both photocurrent and leakage current show an upward trend.

3. The method for handling leakage current during sodium evaporation in the fabrication of the second-generation multi-alkali photocathode according to claim 2, characterized in that: The leakage current is considered to have occurred when it rises to above 2000nA within 1-4 minutes.

4. The method for handling leakage current during sodium evaporation in the fabrication of the second-generation multi-alkali photocathode according to claim 1, characterized in that: In step 2, the potassium power supply is turned on after the photocurrent has stabilized for 5-10 minutes.

5. The method for handling leakage current during sodium evaporation in the fabrication of the second-generation multi-alkali photocathode according to any one of claims 1-4, characterized in that: Turn on the process light to detect photocurrent, and turn off the process light to detect leakage current.

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