Deep ultraviolet photocathode for streak camera and preparation method thereof

Abstract

The invention relates to a deep ultraviolet photocathode for a streak camera, which is mainly used for solving the technical problems that the existing ultraviolet band photocathode needs to be connected with a vacuum pump to keep vacuum and cannot meet the picosecond-level fast time response requirement in an ultrafast detection experiment when being used. The invention relates to a deep ultraviolet photocathode for a streak camera. The deep ultraviolet photocathode comprises a substrate layer, a conductive layer and a photoelectric emission layer, the substrate layer is made of MgF2, the conductive layer is an Al film, and the photoelectric emission layer is made of Cs2Te. The response wave band of the photoelectric cathode is a deep ultraviolet wave band, and the photoelectric cathode is suitable for deep ultraviolet ultrafast light detection and has the advantages of being fast in time response, good in stability, high in repeatability, low in material cost and the like. The invention also provides a preparation method of the deep ultraviolet photocathode for the streak camera.

Description

Technical Field

[0001] The invention relates to a photocathode and a preparation method thereof, and in particular to a deep ultraviolet photocathode for a streak camera and a preparation method thereof. Background Art

[0002] The photocathode is a photoelectric conversion material that can convert light pulses into electron pulses. It consists of a photoelectric emission layer, a substrate and a conductive base. Streak cameras have important applications in laser inertial confinement fusion, high energy density physics research, weak signal detection, material fluorescence lifetime and bioluminescence imaging. The core component of the streak camera, the streak converter tube, requires an ultrafast photocathode at the front end to achieve ultrafast imaging.

[0003] Different types of streak cameras have different spectral response bands. For example, the spectral response band of the photocathode of a visible light streak camera is the visible light band (350-850nm). The photocathode generally uses a bi-alkali cathode or a multi-alkali cathode and needs to be potted before use. However, it cannot be applied to the ultraviolet band.

[0004] The photocathode spectral response band of the X-ray streak camera is from the soft X-ray band to the ultraviolet band; the photocathode generally uses a gold (Au) cathode or a cesium iodide (CsI) cathode, and an open system is required, and a vacuum pump needs to be connected to maintain a vacuum when in use. The open structure is very likely to cause contamination of the Au cathode and the internal electrodes of the streak image converter, and CsI is very easy to deliquesce in the atmosphere, causing its photoelectric conversion efficiency to continuously decay as the exposure time to the atmosphere increases. These all affect the stability of the streak camera and the consistency of the test results to a certain extent.

[0005] In addition, since the photocathode material in the ultraviolet band is generally a semiconductor structure, its time response is in the nanosecond level, which cannot meet the fast time response requirements of the picosecond level in ultrafast detection experiments. Therefore, for streak cameras, how to prepare a fast time response ultraviolet photocathode is a technical problem that urgently needs to be solved. Summary of the invention

[0006] The purpose of the present invention is to solve the technical problems that the existing ultraviolet photocathode needs to be connected to a vacuum pump to maintain vacuum when in use, and cannot meet the fast time response requirements of the picosecond level in ultrafast detection experiments, and proposes a deep ultraviolet photocathode for a streak camera and a preparation method thereof.

[0007] To solve the above technical problems, the technical solutions provided by the present invention are as follows:

[0008] A deep ultraviolet photocathode for a streak camera, which is special in that it comprises a substrate layer, a conductive layer and a photoelectric emission layer arranged in sequence from bottom to top;

[0009] The material of the substrate layer is MgF2; the conductive layer is an Al film; and the material of the photoelectric emission layer is Cs2Te.

[0010] Furthermore, the thickness of the Cs2Te film is 20 to 30 nm; the thickness of the Al film is 3 to 5 nm.

[0011] The present invention also provides a method for preparing a deep ultraviolet photocathode for a streak camera, which is used to prepare the above-mentioned deep ultraviolet photocathode for a streak camera, and the special feature of the method is that it comprises the following steps:

[0012] S1, cleaning the cathode window, the cathode window is composed of MgF2, which serves as a base layer;

[0013] S2, the cathode window, Te alloy source, Cs source and Al source are placed in the cathode chamber of the vacuum system, and the cathode chamber is baked and degassed for the first time, the baking temperature is 250℃-280℃, and the baking time is 45h-50h; after baking, the vacuum degree of the cathode chamber is 10 -7 Pa magnitude;

[0014] S3, using electric current heating method to pre-evaporate Te alloy source and Cs source in sequence;

[0015] S4, the cathode chamber is baked and degassed for the second time, the baking temperature is 250℃-280℃, and the baking time is 24 hours; after baking, the vacuum degree of the cathode chamber is 10 -8 Pa magnitude;

[0016] S5, evaporating an Al film on the surface of the cathode window as a conductive layer;

[0017] S6, preparing Cs2Te;

[0018] S6.1. Control the cathode chamber temperature to 150°C, turn on the Te source current, and the Te alloy source begins to evaporate Te molecules under the action of the Te source current. Control the Te source current value to increase, so that the Te molecules are deposited on the Al film surface on the cathode window;

[0019] S6.2, monitoring the transmittance of Te atoms, and when the transmittance drops to 85% of the initial value, turning off the Te source current;

[0020] S6.3, controlling the cathode chamber temperature to 140°C, turning on the Cs source current, and the Cs source begins to evaporate Cs molecules under the action of the Cs source current;

[0021] S6.4. Allow Te molecules and Cs molecules to fully react to generate a Cs2Te layer as a photoelectric emission layer, thereby completing the preparation of a deep ultraviolet photocathode.

[0022] Furthermore, the step S6.4 is specifically as follows:

[0023] S6.4.1, causing Te molecules and Cs molecules to start reacting to form a Cs2Te layer;

[0024] S6.4.2, irradiating the Cs2Te layer with a light source, and detecting a photocurrent formed in the Cs2Te layer during the irradiation process;

[0025] S6.4.3. Gradually increase the current value of the Cs source current. When the photocurrent begins to change suddenly, keep the current value of the Cs source current unchanged.

[0026] S6.4.4. When the photocurrent increases to the preset maximum value, turn off the Cs source current and stop evaporating the Cs molecules; the Te molecules and Cs molecules react fully, and the generated Cs2Te layer is used as the photoelectric emission layer to complete the preparation of the deep ultraviolet photocathode.

[0027] Furthermore, the step S3 is specifically as follows:

[0028] S3.1, turning on the Te source current to pre-evaporate the Te alloy source for 5-10 minutes, and then turning off the Te source current to complete the pre-evaporation of the Te alloy source;

[0029] S3.2, turning on the Cs source current to pre-evaporate the Cs source, the evaporation time is 10-20 minutes, and turning off the Cs source current to complete the pre-evaporation of the Cs source.

[0030] Furthermore, the step S5 is specifically as follows:

[0031] The temperature of the cathode chamber is lowered to room temperature, the Al source current is turned on, and Al is evaporated on the surface of the cathode window for 8 to 10 seconds to form an Al film as a conductive layer.

[0032] Furthermore, the step S6.1 is specifically as follows:

[0033] The cathode chamber temperature was controlled at 150°C, and the Te source current was turned on. The Te alloy source began to evaporate Te molecules under the action of the Te source current. The Te source current value was controlled to increase at a rate of 0.2 A / min, so that the Te molecules were uniformly deposited on the Al film surface on the cathode window.

[0034] Furthermore, in step S2, the baking temperature is 280° C. and the baking time is 48 hours.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The present invention discloses a deep ultraviolet photocathode for a streak camera, comprising a substrate layer, a conductive layer and a photoemission layer. The substrate layer is made of MgF2, the conductive layer is an Al film, and the photoemission layer is made of Cs2Te. The photocathode of the present invention has a response band of the deep ultraviolet band and is suitable for deep ultraviolet ultrafast light detection. It has the characteristics of fast time response, good stability, high repeatability, and low material cost.

[0037] 2. The present invention provides a method for preparing a deep ultraviolet photocathode for a streak camera, firstly evaporating a layer of transparent conductive Al film on the surface of a MgF2 cathode window as a conductive layer of the photocathode, and then preparing Cs2Te at a suitable temperature as a photoemission layer of the photocathode to complete the preparation of the photocathode.

[0038] 3. The present invention provides a method for preparing a deep ultraviolet photocathode for a streak camera, which solves the problem of long response time of ultraviolet photocathode. MgF2 has high chemical stability and good light transmittance, and can effectively transmit photons. The Al film can make Cs2Te better attached to the substrate layer, and the electrons in the Cs2Te material can be quickly excited to generate photoelectrons, and the photoelectrons can quickly leave the photoemission layer under the synergistic effect of the conductive layer and the substrate layer, thereby achieving a fast response of picosecond response time. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a structural schematic diagram of an embodiment of a deep ultraviolet photocathode for a streak camera of the present invention;

[0040] Figure 2 It is a flow chart of an embodiment of a method for preparing a deep ultraviolet photocathode for a streak camera of the present invention;

[0041] Figure 3 The figure is a spectral response curve diagram of a deep ultraviolet photocathode embodiment for a streak camera according to the present invention.

[0042] Description of reference numerals:

[0043] 1. Base layer; 2. Conductive layer; 3. Photoelectric emission layer. DETAILED DESCRIPTION

[0044] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0045] The present invention provides a deep ultraviolet photocathode for a streak camera, such as Figure 1 As shown, it includes a substrate layer 1, a conductive layer 2 and a photoelectric emission layer 3. The substrate layer 1 is made of MgF2, the conductive layer 2 is an Al film, and the photoelectric emission layer 3 is made of Cs2Te.

[0046] The present invention also provides a method for preparing a deep ultraviolet photocathode for a streak camera, such as Figure 2 As shown, the specific steps include:

[0047] S1. Clean the cathode window to remove impurities, oil stains, dust and other pollutants that may exist on the surface of the cathode window. The cathode window is a channel for light or particles to enter the cathode chamber, and its surface cleanliness must be ensured to avoid interference with subsequent processes; the cathode window is a MgF2 cathode window;

[0048] S2. Place the cathode window, Te alloy source, Cs source and Al source into the cathode chamber of the vacuum system, and perform the first baking and degassing of the cathode chamber to make the vacuum degree reach 10 -7 Pa level, specifically 1×10 -7 ~9.99×10 -7 Pa, the baking temperature is 250℃-280℃, and the baking time is 45h-50h; if it is higher than this range, it is easy to damage the performance and structure of the component, and if it is lower than this range, it is easy to make it difficult for gas molecules to escape from the surface of the material. In this embodiment, the baking temperature is 280℃ and the baking time is 48h.

[0049] The purpose of baking and degassing is to remove residual gases in the cathode chamber, such as water vapor, oxygen, etc., to prevent the gas from affecting the vacuum degree of the vacuum system.

[0050] S3, using electric current heating method to pre-evaporate Te alloy source and Cs source in sequence;

[0051] S3.1, turn on the Te source current to pre-evaporate the Te alloy source, the evaporation time is 5-10 minutes, and turn off the Te source current;

[0052] S3.2, turn on the Cs source current to pre-evaporate the Cs source, the evaporation time is 10-20 minutes, and turn off the Cs source current;

[0053] S4, bake and degas the cathode chamber for the second time to make the vacuum degree reach 10 -8 Pa level, the baking temperature is 280℃, and the baking time is 24 hours;

[0054] S5, evaporating Al on the cathode window surface; lowering the temperature of the cathode chamber to room temperature, turning on the Al source current, and evaporating on the cathode window surface for 8 to 10 seconds to form an Al film as the conductive layer 2;

[0055] S6, preparing Cs2Te, specifically comprising the following steps

[0056] S6.1. Control the cathode chamber temperature to 150°C, turn on the Te source current, and the Te alloy source begins to evaporate Te molecules under the action of the Te source current. Control the Te source to increase at a rate of 0.2 A / min, so that the Te molecules are uniformly deposited on the Al film surface on the cathode window;

[0057] S6.2, the surface reflectivity of the cathode window is tested by the light control component on the top of the cathode chamber, so as to monitor the transmittance of Te atoms. As the Te molecules evaporate, the transmittance of Te atoms on the cathode window gradually decreases. When the transmittance drops to 85% of the initial value, the Te source current is turned off;

[0058] S6.3, controlling the cathode chamber temperature to 140°C, turning on the Cs source current, and the Cs source begins to evaporate Cs molecules under the action of the Cs source current;

[0059] S6.4, allowing Te molecules and Cs molecules to fully react to generate a Cs2Te layer as the photoelectric emission layer 3, completing the preparation of the deep ultraviolet photocathode, specifically including:

[0060] S6.4.1, causing Te molecules and Cs molecules to start reacting to form a Cs2Te layer;

[0061] S6.4.2, irradiating the Cs2Te layer with a light source, and detecting a photocurrent formed in the Cs2Te layer during the irradiation process;

[0062] S6.4.3. Gradually increase the current value of the Cs source current. When the photocurrent begins to change suddenly, keep the current value of the Cs source current unchanged.

[0063] S6.4.4. When the photocurrent increases to the preset maximum value, turn off the Cs source current and stop evaporating the Cs molecules; the Te molecules and Cs molecules react fully, and the generated Cs2Te layer is used as the photoelectric emission layer 3, completing the preparation of the deep ultraviolet photocathode.

[0064] After the photocathode is prepared, it needs to be plated on the streak tube. The streak tube is placed in the cathode chamber, the temperature of the cathode chamber is controlled at 110°C, the cathode window is transferred to the streak tube using a magnetic rotating rod, and the streak tube and the photocathode are thermally sealed with indium.

[0065] like Figure 3 Shown are the spectral response and quantum efficiency curves of the deep ultraviolet photocathode, where the peak quantum efficiency is at 254nm, reaching a peak of 12%, and the lowest response wavelength is 180nm.

Claims

1. A deep ultraviolet photocathode for a streak camera, characterized in that: It comprises a substrate layer (1), a conductive layer (2) and a photoelectric emission layer (3) which are arranged in sequence from bottom to top; The material of the base layer (1) is MgF2; the material of the conductive layer (2) is an Al film; and the material of the photoelectric emission layer (3) is Cs2Te.

2. A deep ultraviolet photocathode for a streak camera according to claim 1, characterized in that: The thickness of the Cs2Te film is 20-30 nm; the thickness of the Al film is 3-5 nm.

3. A method for preparing a deep ultraviolet photocathode for a streak camera, used to prepare a deep ultraviolet photocathode for a streak camera according to claim 1 or 2, characterized in that: The following steps are involved: S1, cleaning the cathode window, the cathode window is composed of MgF2, which serves as a base layer (1); S2, the cathode window, Te alloy source, Cs source and Al source are placed in the cathode chamber of the vacuum system, and the cathode chamber is baked and degassed for the first time, the baking temperature is 250℃-280℃, and the baking time is 45h-50h; after baking, the vacuum degree of the cathode chamber is 10 - 7 Pa magnitude; S3, using electric current heating method to pre-evaporate Te alloy source and Cs source in sequence; S4, the cathode chamber is baked and degassed for the second time, the baking temperature is 250℃-280℃, and the baking time is 24 hours; after baking, the vacuum degree of the cathode chamber is 10 -8 Pa magnitude; S5, evaporating an Al film on the surface of the cathode window as a conductive layer (2); S6, preparing Cs2Te; S6.

1. Control the cathode chamber temperature to 150°C, turn on the Te source current, and the Te alloy source begins to evaporate Te molecules under the action of the Te source current. Control the Te source current value to increase, so that the Te molecules are deposited on the Al film surface on the cathode window; S6.2, monitoring the transmittance of Te atoms, and when the transmittance drops to 85% of the initial value, turning off the Te source current; S6.3, controlling the cathode chamber temperature to 140°C, turning on the Cs source current, and the Cs source begins to evaporate Cs molecules under the action of the Cs source current; S6.

4. Allow Te molecules and Cs molecules to fully react to generate a Cs2Te layer as a photoelectric emission layer (3), thereby completing the preparation of a deep ultraviolet photocathode.

4. The method for preparing a deep ultraviolet photocathode for a streak camera according to claim 3, characterized in that: The step S6.4 is specifically as follows: S6.4.1, causing Te molecules and Cs molecules to start reacting to form a Cs2Te layer; S6.4.2, irradiating the Cs2Te layer with a light source, and detecting a photocurrent formed in the Cs2Te layer during the irradiation process; S6.4.

3. Gradually increase the current value of the Cs source current. When the photocurrent begins to change suddenly, keep the current value of the Cs source current unchanged. S6.4.

4. When the photocurrent increases to the preset maximum value, the Cs source current is turned off to stop evaporating the Cs molecules; the Te molecules and Cs molecules react fully, and the generated Cs2Te layer is used as the photoelectric emission layer (3), completing the preparation of the deep ultraviolet photocathode.

5. The method for preparing a deep ultraviolet photocathode for a streak camera according to claim 4, characterized in that: The step S3 is specifically as follows: S3.1, turning on the Te source current to pre-evaporate the Te alloy source for 5-10 minutes, and then turning off the Te source current to complete the pre-evaporation of the Te alloy source; S3.2, turning on the Cs source current to pre-evaporate the Cs source, the evaporation time is 10-20 minutes, and turning off the Cs source current to complete the pre-evaporation of the Cs source.

6. The method for preparing a deep ultraviolet photocathode for a streak camera according to claim 5, characterized in that: The step S5 is specifically as follows: The temperature of the cathode chamber is lowered to room temperature, the Al source current is turned on, and Al is evaporated on the surface of the cathode window for 8 to 10 seconds to form an Al film as a conductive layer (2).

7. The method for preparing a deep ultraviolet photocathode for a streak camera according to claim 6, characterized in that: The step S6.1 is specifically as follows: The cathode chamber temperature was controlled at 150°C, and the Te source current was turned on. The Te alloy source began to evaporate Te molecules under the action of the Te source current. The Te source current value was controlled to increase at a rate of 0.2 A / min, so that the Te molecules were uniformly deposited on the Al film surface on the cathode window.

8. The method for preparing a deep ultraviolet photocathode for a streak camera according to claim 7, characterized in that: In step S2, the baking temperature is 280° C. and the baking time is 48 hours.

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