Nanoparticle structure photocathode with resonance enhanced light absorption and preparation method thereof

Abstract

The present invention discloses a photocathode with a nanoparticle structure for resonance-enhanced light absorption and a preparation method thereof, which are used to solve the technical problem that the prior art can only reduce the incident light reflectivity of the photocathode but cannot enhance its incident light absorption rate. The photocathode of the present invention comprises a substrate layer, a metal nanoparticle layer and a photoelectric emission layer. By introducing the metal nanoparticle layer into the photocathode, the surface plasmon characteristics are utilized to improve the capture of photons by the material and reduce the reflectivity of photons. At the same time, through the local surface plasmon resonance effect, local light field enhancement and far-field scattering enhancement are formed, the absorption efficiency of the photocathode to the incident light is improved, and then the photoelectric conversion efficiency and the comprehensive characteristics of the photocathode are improved.

Description

Technical Field

[0001] The present invention relates to a photoelectric emission material and a preparation method thereof, and in particular to a photoelectric cathode with a nano-particle structure for resonance-enhanced light absorption and a preparation method thereof. Background Art

[0002] Photocathodes achieve photoelectric conversion by absorbing incident photon energy and stimulating photoelectrons. Currently, there are many types of photocathodes, including antimony-alkali photocathodes, semiconductor photocathodes, and cesium iodide. Among them, antimony-alkali photocathodes are widely used in low-light-level image intensifiers, photomultiplier tubes, electron microscopes, and electron accelerators due to their high quantum efficiency, high operating stability, low dark emission, and simple manufacturing process.

[0003] The emissive layer (light-absorbing layer) in an antimony-alkali photocathode is typically tens of nanometers thick and primarily functions to absorb photons and generate photoelectrons. However, this thickness also limits the light's propagation distance within it to just a few tens of nanometers. Over such a short transmission distance, incident photons pass directly through the emissive layer without being fully absorbed. Only a portion of the light is effectively absorbed and converted into photoelectron signals, resulting in low parameters such as the quantum efficiency of the antimony-alkali photocathode. Therefore, the photon absorption capacity directly affects the performance of the antimony-alkali photocathode and also restricts the overall performance of devices fabricated using the photocathode.

[0004] In order to increase the absorption of incident photons by the photocathode, Hamamatsu Corporation of Japan reported SBA and UBA antimony-alkali photocathodes coated with dielectric films. By reducing the reflectivity of the incident light, the number of photons entering the photocathode is increased. This method greatly improves the light response characteristics of the photocathode. In addition, China North Night Vision Technology Co., Ltd. has disclosed a method for preparing an antimony-alkali photocathode coated with a SiO2 or Al2O3 dielectric film, which improves the performance of the photocathode by reducing the reflectivity of the incident light. However, the method of introducing a dielectric film into the photocathode structure mainly increases the number of incident photons by reducing the reflectivity of the incident light, and fails to directly enhance the light absorption performance of the photoelectric material. The degree to which it improves the performance of the photocathode is limited. Summary of the Invention

[0005] In order to solve the technical problem that the prior art can only reduce the incident light reflectivity of the photocathode but cannot enhance its incident light absorptivity, the present invention provides a nanoparticle structure photocathode with resonance enhanced light absorption and a preparation method thereof.

[0006] To achieve the above object, the technical solution of the present invention is:

[0007] A photocathode with a nanoparticle structure for resonance-enhanced light absorption, which is special in that it comprises a substrate layer, a metal nanoparticle layer and a photoemission layer;

[0008] The metal nanoparticle layer is located on the upper surface of the substrate layer and includes a plurality of uniformly distributed metal nanoparticles;

[0009] The photoelectric emission layer is a photoelectric thin film, which covers the upper surface of the metal nanoparticle layer and the substrate layer and is compatible with the structure of the metal nanoparticle layer.

[0010] Furthermore, the uniformly distributed metal nanoparticles refer to metal nanoparticles uniformly distributed in a rectangular grid, and each metal nanoparticle is distributed at an intersection of the rectangular grid;

[0011] Alternatively, the uniformly distributed metal nanoparticles refer to metal nanoparticles uniformly distributed in a hexagonal grid, and each metal nanoparticle is distributed at the intersection of the hexagonal grid structure or at the intersection of the hexagonal grid structure and the center of the hexagon.

[0012] Furthermore, the metal nanoparticles are spherical structures, and the surface of the spherical structure is connected to the upper surface of the substrate layer 1;

[0013] Alternatively, the metal nanoparticles are in a hemispherical structure, and the center plane of the hemispherical structure is connected to the upper surface of the substrate layer 1 .

[0014] Furthermore, the diameter of the metal nanoparticles is 20 nm-100 nm, and the distance between the centers of two adjacent metal nanoparticles is 100 nm-300 nm.

[0015] Furthermore, the metal nanoparticles are cylindrical in structure, and one end surface of the cylindrical structure is connected to the upper surface of the substrate layer 1 .

[0016] Furthermore, the bottom diameter of the metal nanoparticles is 20nm-100nm, the height is 20nm-100nm, and the vertical distance between the central axes of two adjacent metal nanoparticles is 100nm-300nm.

[0017] Furthermore, the material of the metal nanoparticles is one of silver, gold, aluminum, and copper; the material of the substrate layer is one of quartz glass, 7056 glass, and silicon; and the material of the photoelectric emission layer is one of CsTe, SbKCs, and SbKNaCs.

[0018] In addition, the present invention also provides a method for preparing a nanoparticle structure photocathode with resonance-enhanced light absorption, comprising the following steps:

[0019] Step 1: Prepare the substrate layer of the photocathode, ultrasonically clean its surface using acetone, anhydrous ethanol and deionized water, and blow dry;

[0020] Step 2: growing metal nanoparticles on the surface of the substrate layer that has been cleaned and dried in Step 1, to obtain a substrate layer having metal nanoparticles on the surface;

[0021] Step 3: Place the substrate layer with metal nanoparticles on the surface into a photocathode manufacturing device, and deposit a photocathode film on the surface of the metal nanoparticles to obtain a nanoparticle structure photocathode with resonance enhanced light absorption; the photocathode film is the photoemission layer.

[0022] Furthermore, in step 2, metal nanoparticles are grown on the upper surface of the substrate layer by adopting physical deposition coating and metal nanoparticle self-assembly.

[0023] Furthermore, step 3 is specifically as follows: placing the obtained substrate layer with metal nanoparticles on the surface in a photocathode manufacturing device, and after thermal cleaning, using Cs source, Na source, Sb source and K source to alternately or jointly evaporate to deposit a layer of photocathode film on the surface of the metal nanoparticles, thereby obtaining a nanoparticle structure photocathode with resonance enhanced light absorption.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The photocathode of the present invention comprises a substrate layer, a metal nanoparticle layer, and a photoemission layer. By introducing the metal nanoparticle layer into the photocathode, the surface plasmon properties are utilized to enhance the material's photon capture and reduce photon reflectivity. Furthermore, through localized surface plasmon resonance, localized light field enhancement and far-field scattering are achieved, increasing the photocathode's absorption efficiency for incident light, thereby improving both photoelectric conversion efficiency and the overall photocathode properties.

[0026] 2. The metal nanoparticles in the photocathode of the present invention can be spherical, hemispherical, or cylindrical. The structure, size, and period of the nanoparticles can be flexibly adjusted according to actual conditions to achieve regulation of the resonant absorption peak from the visible to the near-infrared, meet the peak response requirements of the photocathode in different application scenarios, and have a wider range of applications.

[0027] 3. In the preparation method of the photocathode of the present invention, the metal nanoparticle layer can be prepared by physical deposition coating and metal nanoparticle self-assembly technology. The processes of the two technologies are relatively mature, have good repeatability, can meet the needs of mass production, and have low cost; in addition, the preparation method can adjust and control the size, shape and period of the metal nanoparticles, and has good compatibility with the existing related preparation processes that use photocathode as raw materials, which is conducive to the promotion and application of this method. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic structural diagram of Embodiment 1 of the present invention;

[0029] Figure 2 This is a diagram of the local light field intensity distribution under resonance conditions in Example 1 of the present invention;

[0030] Figure 3 This is a comparison of the reflectivity of the photocathode according to Example 1 of the present invention and that without the addition of the nanoparticle array layer;

[0031] Figure 4 This is a comparison of the photocathode absorption rates of Example 1 of the present invention and that without the addition of the nanoparticle array layer;

[0032] Figure 5 This is a structural diagram of embodiment 2 of the present invention;

[0033] Figure 6 This is a diagram of the local light field intensity distribution under resonance conditions in Example 2 of the present invention;

[0034] Figure 7 This is a comparison chart of the reflectivity of the photocathode according to Example 2 of the present invention and that without the addition of the nanoparticle array layer;

[0035] Figure 8 This is a comparison of the absorption rates of the photocathode according to Example 2 of the present invention and that without the addition of the nanoparticle array layer.

[0036] The reference numerals are as follows:

[0037] 1-substrate layer, 2-metal nanoparticle layer, 3-photoelectric emission layer. DETAILED DESCRIPTION

[0038] The design principle of the present invention is: in order to improve the limited utilization rate of photons by the antimony alkali photocathode, the present invention adopts surface plasmon technology to change the photocathode structure, and uses surface plasmon technology to prepare a metal nanoparticle layer on the photocathode substrate and the photocathode. Under the strong local confinement of plasmons, the energy of the incident light is concentrated in the deep subwavelength or even nanoscale space range, and the energy density of light and the local electric field intensity are greatly enhanced, thereby significantly enhancing the interaction between photons and the photocathode material. Therefore, under the action of the incident light electric field, plasmon oscillations occur on the surface of the metal nanoparticles, and under the action of plasmon scattering and local field enhancement, the incident light increases the effective propagation path of light in the cathode, improves the light absorption efficiency of the emission layer in the photocathode, and achieves the purpose of improving the performance of the photocathode.

[0039] The present invention will be described in further detail below with reference to the accompanying drawings. It should be noted that the embodiments described here are only for illustration and do not limit the present invention.

[0040] Combine Figures 1 to 8As shown, the present invention provides a nanoparticle structure photocathode with resonance enhanced light absorption, comprising a substrate layer 1, a metal nanoparticle layer 2, and a photoemission layer 3. The material of the substrate layer 1 can be selected from quartz glass, 7056 glass, silicon, or other materials for preparing photocathodes.

[0041] The metal nanoparticle layer 2 is located on the upper surface of the substrate layer 1 and includes a plurality of uniformly distributed metal nanoparticles. The uniformly distributed metal nanoparticles refer to metal nanoparticles uniformly distributed in a rectangular grid pattern, with each metal nanoparticle distributed at the intersection of the rectangular grid pattern; alternatively, the uniformly distributed metal nanoparticles refer to metal nanoparticles uniformly distributed in a hexagonal grid pattern, with each metal nanoparticle distributed at the intersection of the hexagonal grid structure, or at the intersection of the hexagonal grid structure and the center of the hexagon.

[0042] The metal nanoparticles are spherical or hemispherical in structure, or, depending on actual needs, can be designed as a multi-hemispherical structure or a less-hemispherical structure. The diameter of the metal nanoparticles is generally 20nm-100nm, and the distance between the centers of two adjacent metal nanoparticles is 100nm-300nm. When the metal nanoparticles are spherical, they are in point contact with the upper surface of the photocathode substrate layer 1; when the metal nanoparticles are hemispherical, multi-hemispherical, or less-hemispherical in structure, they are in surface contact with the upper surface of the photocathode substrate layer 1, and the plane end of the hemispherical, multi-hemispherical, or less-hemispherical shape is connected to the upper surface of the substrate layer 1.

[0043] The metal nanoparticles can also be cylindrical or semi-cylindrical structures. The central axis of the cylindrical or semi-cylindrical structure can be perpendicular to the upper surface of the substrate layer 1 or can be placed parallel to the upper surface of the substrate layer 1. However, regardless of whether they are placed perpendicularly or parallel, all metal nanoparticles must maintain the same placement and together constitute a metal nanoparticle layer. When the metal nanoparticles are cylindrical, one end face of the cylindrical structure or the side face of the cylinder is connected to the upper surface of the substrate layer 1; when the metal nanoparticles are semi-cylindrical, one end face of the semi-cylindrical structure or the center face of the cylinder is connected to the upper surface of the substrate layer 1. Each metal nanoparticle has a diameter of 20nm-100nm and a height of 20nm-100nm. The vertical distance between the central axes of two adjacent metal nanoparticles is 100nm-300nm. The material of the metal nanoparticles can be selected from one of silver, gold, aluminum, and copper materials, or other metal materials suitable for plasmon preparation.

[0044] The photoelectric emission layer 3 is a photoelectric thin film, which covers the upper surface of the metal nanoparticle layer 2 and the substrate layer 1 and is compatible with the structure of the metal nanoparticle layer 2. The material of the photoelectric thin film can be selected from CsTe, SbKCs, SbKNaCs, or other materials that can achieve similar effects.

[0045] In addition, the present invention also provides a method for preparing a nanoparticle structure photocathode with resonance-enhanced light absorption, comprising the following steps:

[0046] Step 1: Prepare a photocathode substrate layer 1 made of glass or silicon, ultrasonically clean the surface with acetone, anhydrous ethanol, and deionized water to remove surface grease and contaminants, and then use a nitrogen gun to blow dry the surface of the photocathode substrate layer 1 for later use;

[0047] Step 2: growing metal nanoparticles on the surface of the photocathode substrate layer 1 cleaned and dried in step 1 by physical deposition coating, metal nanoparticle self-assembly, or other techniques to obtain a substrate layer having metal nanoparticles on the surface;

[0048] Step 3: Place the substrate layer with metal nanoparticles on the surface obtained in step 2 in an ultra-high vacuum photocathode manufacturing device. After thermal cleaning, alternately evaporate or co-evaporate Cs source, Na source, Sb source and K source to deposit a layer of photocathode film on the surface of the metal nanoparticles. The photocathode film is the photoemission layer 3, thereby obtaining a nanoparticle structure photocathode with resonance enhanced light absorption.

[0049] The technical solution of the present invention is described in more detail below with reference to specific embodiments.

[0050] Example 1

[0051] like Figure 1 As shown, this embodiment provides a silver nanoparticle structure antimony-alkali photocathode with surface optical resonance enhancement, comprising a substrate layer 1, a metal nanoparticle layer 2 disposed on the substrate layer 1, and a photoemission layer 3 disposed on the metal nanoparticle layer 2. The substrate layer 1 is made of quartz glass; the metal nanoparticle layer 2 is composed of spherical Ag nanoparticles, each with a diameter of 50 nm, and the distance between the centers of two adjacent Ag nanoparticles is 240 nm; and the photoemission layer 3 is made of a SbKCs dual-alkali photoelectric thin film with a thickness of 40 nm.

[0052] Figure 2 3 is a local light field intensity distribution diagram of this embodiment under resonance conditions. It can be seen from the figure that under the action of plasmon resonance, a light field enhancement effect occurs in the range near the nanoparticles in the Ag nanoparticle array.

[0053] Figure 3This is a comparison of the photocathode reflectivity of this embodiment with that without the nanoparticle array layer. Theoretical simulation results of this embodiment before and after the addition of the Ag nanoparticle array show that the Ag nanoparticle array significantly reduces the reflectivity of light in the 400nm-650nm band, with a particularly significant reduction at 550nm, from 41% to 27%.

[0054] Figure 4 The comparison of the photocathode absorption rate of this embodiment and that without the addition of the nanoparticle array layer is shown in the figure. The theoretical simulation results of the present invention before and after the addition of the Ag nanoparticle array show that the Ag nanoparticle array significantly improves the light absorption rate of the photocathode in the 400nm-650nm band.

[0055] Example 2

[0056] like Figure 5 As shown, this embodiment provides a surface optical resonance-enhanced silver nanoparticle structure antimony-alkali photocathode, comprising a substrate layer 1, a metal nanoparticle layer 2 disposed on substrate layer 1, and a photoemission layer 3 disposed on metal nanoparticle layer 2. Substrate layer 1 is made of quartz glass; metal nanoparticle layer 2 is composed of hemispherical Ag nanoparticles with a diameter of 50 nm, and the distance between the centers of adjacent Ag nanoparticle arrays is 240 nm; and photoemission layer 3 is a SbKNaCs multi-alkali photoelectric thin film with a thickness of 80 nm.

[0057] Figure 6 3 is a local light field intensity distribution diagram of this embodiment under resonance conditions. It can be seen from the figure that under the action of plasmon resonance, a light field enhancement effect occurs in the range near the nanoparticles in the Ag nanoparticle array.

[0058] Figure 7 The following chart compares the reflectivity of the photocathode in this embodiment with that in the absence of the nanoparticle array layer. Theoretical simulation results of this embodiment before and after the addition of the Ag nanoparticle array show that the reflectivity in the 600nm-850nm band is significantly reduced, with a particularly significant decrease at 720nm, from 37% to 15%.

[0059] Figure 8 The following is a comparison of the photocathode absorptivity of this embodiment with that of a cathode without the addition of the nanoparticle array layer. Theoretical simulation results of this embodiment before and after the addition of the Ag nanoparticle array show a significant improvement in light absorptivity in the 600nm-850nm band, particularly at the resonance peak at 700nm, where the absorptivity increases from 18% to 58%, a significant improvement in absorptivity.

[0060] In addition, as can be seen from Table 1 and Table 2, the present invention also provides information on changes in the absorption rates of photocathodes formed based on different nanoparticle sizes and corresponding nanoparticle sizes.

[0061] Table 1: Photocathode absorptivity of Ag hemispherical particles with a metal nanoparticle size of 40 nm and different array periods

[0062]

[0063] Table 2: Cathodic absorption rate of Ag hemispherical particles with different nanoparticle sizes at the same array period

[0064]

[0065] In summary, it can be seen that, unlike the traditional photocathode with an anti-reflection film that reduces reflectivity, the present invention introduces a metal nanoparticle layer in the photocathode, and utilizes the surface plasmon characteristics of the metal nanoparticles to improve the capture of photons by the material. Under the action of the incident light electric field, plasmon oscillations occur on the surface of the metal nanoparticles. In the emission layer at a distance greater than the range of action of the local field formed by the surface plasmons, the incident light is scattered by the surface plasmons and the propagation direction is distributed at a certain angle, which effectively increases the propagation distance of the light in the emission layer and improves the light absorption efficiency; in the emission layer at a distance less than the range of action of the local field formed by the surface plasmons, the local field enhancement caused by resonance increases the effective propagation distance of the light in the emission layer and improves the light absorption efficiency. Under the combined action of the above factors, the absorption efficiency of the incident light by the emission layer in the photocathode is significantly improved, thereby improving the photoelectric conversion efficiency. Nanophotonic materials based on plasmon resonance properties have excellent light control properties. By changing the material, morphology, structure and other properties, the modulated resonance wavelength can cover the ultraviolet, visible, near-infrared and even far-infrared bands, thereby improving the overall performance of the photocathode. It can be applied to low-light image intensifiers, photomultiplier tubes, electron microscopes and electron accelerators.

[0066] Although a number of embodiments of the present invention have been shown and described above, it will be apparent to those skilled in the art that any changes or modifications to the above embodiments should fall within the scope of protection of the present invention as long as they fall within the spirit of the present invention.

Claims

1. A photocathode with a nanoparticle structure for resonance-enhanced light absorption, characterized in that: It comprises a substrate layer (1), a metal nanoparticle layer (2) and a photoelectric emission layer (3); The metal nanoparticle layer (2) is located on the upper surface of the substrate layer (1), and comprises a plurality of uniformly distributed metal nanoparticles; the uniformly distributed metal nanoparticles refer to metal nanoparticles uniformly distributed in a rectangular grid shape, and each metal nanoparticle is distributed at an intersection of the rectangular grid structure; Alternatively, the uniformly distributed metal nanoparticles refer to metal nanoparticles uniformly distributed in a hexagonal grid, and each metal nanoparticle is distributed at the intersection of the hexagonal grid structure or at the intersection of the hexagonal grid structure and the center of the hexagonal grid structure; The metal nanoparticles are spherical structures, the surface of the spherical structure is connected to the upper surface of the substrate layer (1); or, the metal nanoparticles are hemispherical structures, the center plane of the hemispherical structure is connected to the upper surface of the substrate layer (1); or, the metal nanoparticles are cylindrical structures, one end surface of the cylindrical structure or the side surface of the cylinder is connected to the upper surface of the substrate layer (1); or, the metal nanoparticles are semi-cylindrical structures, one end surface of the semi-cylindrical structure or the center plane of the cylinder is connected to the upper surface of the substrate layer (1); the material of the metal nanoparticles is one of silver, gold, aluminum and copper; The photoelectric emission layer (3) is a photoelectric thin film, which covers the upper surfaces of the metal nanoparticle layer (2) and the substrate layer (1), and is compatible with the structure of the metal nanoparticle layer (2).

2. The photocathode with a nanoparticle structure for resonance-enhanced light absorption according to claim 1, characterized in that: When the metal nanoparticles are spherical or hemispherical, the diameter of each metal nanoparticle is 20nm-100nm, and the distance between the spherical centers of two adjacent metal nanoparticles is 100nm-300nm.

3. The photocathode with a nanoparticle structure for resonance-enhanced light absorption according to claim 1, characterized in that: When the metal nanoparticles are cylindrical or semi-cylindrical, the diameter of each metal nanoparticle is 20nm-100nm, the height is 20nm-100nm, and the vertical distance between the central axes of two adjacent metal nanoparticles is 100nm-300nm.

4. The photocathode with a nanoparticle structure having a resonance enhanced light absorption according to any one of claims 1 to 3, characterized in that: The material of the substrate layer (1) is one of quartz glass, 7056 glass and silicon; The material of the photoelectric emission layer (3) is one of CsTe, SbKCs and SbKNaCs.

5. A method for preparing a photocathode with a nanoparticle structure for resonance-enhanced light absorption, characterized in that: The following steps are involved: Step 1, preparing a substrate layer of the photocathode, ultrasonically cleaning the surface of the substrate layer using acetone, anhydrous ethanol and deionized water, and then drying the substrate layer; Step 2, growing metal nanoparticles on the upper surface of the substrate layer after being cleaned and dried in step 1, to obtain a substrate layer having metal nanoparticles on the surface; Step 3, placing the obtained substrate layer with metal nanoparticles on the surface into a photocathode manufacturing device, and depositing a photocathode film on the surface of the metal nanoparticles to obtain a nanoparticle structure photocathode with resonance enhanced light absorption; the photocathode film is the photoemission layer.

6. The method for preparing the resonance enhanced light absorption nanoparticle structure photocathode according to claim 5, characterized in that: In step 2, metal nanoparticles are grown on the upper surface of the substrate layer by means of physical deposition coating and metal nanoparticle self-assembly.

7. The method for preparing the resonance enhanced light absorption nanoparticle structure photocathode according to claim 6, characterized in that: Specifically, step 3 is to place the obtained substrate layer with metal nanoparticles on the surface in a photocathode manufacturing device, and after thermal cleaning, alternately or jointly evaporate Cs source, Na source, Sb source and K source to deposit a layer of photocathode film on the surface of the metal nanoparticles, thereby obtaining a nanoparticle structure photocathode with resonance enhanced light absorption.

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