Photocathode electron source, device, method for generating electrons and electron beam system

Abstract

The invention relates to the technical field of photocathodes, and particularly provides a photocathode electron source, a photocathode electron source device, an electron generation method and an electron beam system, and the photocathode electron source comprises a photocathode and an anode. Wherein the photocathode comprises: a diamond doped with color center defects; the transparent conducting layer is arranged on the first surface of the diamond, and the transmittance of the transparent conducting layer to near-infrared light and short-wavelength light is larger than a preset transmission threshold value; the negative electron affinity surface is arranged on the second surface of the diamond, and the emitting rate of the negative electron affinity surface to electrons excited by the diamond is larger than a preset emitting threshold value. In this way, the incident light modulation cost can be reduced, and meanwhile the electron excitation efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the field of photocathode technology, and in particular to a photocathode electron source, a device, a method for generating electrons and an electron beam system. Background Art

[0002] A photocathode electron source is an electron source that uses the photoelectric effect of photocathode materials to convert incident light into outgoing electrons. Photocathode electron sources have a series of advantages such as high efficiency, stability and controllability, and are widely used in scientific research, industry and medical fields. Specifically, they can be applied to electron beam systems or X-ray systems, especially in electron beam imaging or electron beam lithography of electron beam systems.

[0003] However, photocathode electron sources under different photocathode materials have different cutoff wavelengths, wherein the photocathode electron source can only excite electrons when the wavelength of the incident light is shorter than the cutoff wavelength. For common metal or semiconductor photocathode materials, the cutoff wavelength is generally in the wavelength range from ultraviolet to visible light. However, within this cutoff wavelength range, the modulation cost of the incident light is high, which greatly limits the photocathode electron source's acquisition of parallel electron beams. At present, the optical module technology in the field of communications is relatively mature. The use of optical modules in the field of communications can obtain modulated near-infrared light at a very low cost, which can solve the problem of high incident light modulation cost. However, the existing photocathode electron source solutions cannot guarantee the electron excitation efficiency when using near-infrared light as the incident light.

[0004] Therefore, how to reduce the cost of incident light modulation while ensuring the efficiency of electron excitation has become a problem that needs to be solved urgently. Summary of the invention

[0005] In view of this, the present invention provides a photocathode electron source, a device, a method for generating electrons and an electron beam system, which can reduce the incident light modulation cost and improve the electron excitation efficiency.

[0006] In order to solve the above technical problems, on the one hand, the present invention provides a photocathode electron source, comprising: a photocathode and an anode, wherein the photocathode comprises: a diamond doped with a color center defect; a transparent conductive layer disposed on the first surface of the diamond, the transmittance of the transparent conductive layer to near-infrared light and short-wavelength light being greater than a preset transmittance threshold; a negative electron affinity surface disposed on the second surface of the diamond, the emission rate of electrons excited by the negative electron affinity surface to the diamond being greater than a preset emission threshold; wherein the diamond comprises a first region, near-infrared light and short-wavelength light are overlapped and projected onto the first region, the color center defects in the first region undergo two-photon transitions to excite electrons, and thus, under the action of the voltage difference between the photocathode and the anode, the electrons are emitted through the negative electron affinity surface.

[0007] The photocathode electron source of this embodiment can reduce the cost of the photocathode electron source by selecting near-infrared light as the incident light source. At the same time, by using diamond as the photocathode material and utilizing the high thermal conductivity of the diamond matrix material, it can provide good thermal conductivity when the total emission current is large, thereby improving the stability of the photocathode electron source and improving the efficiency and stability of electron excitation. Moreover, by doping color center defects in diamond and superimposing short-wavelength light on the basis of near-infrared light, two-photon transitions can be achieved at the color center defects of diamond, and the excitation of electrons from the color center defect ground state to the conduction band can be achieved, thereby ensuring the electron excitation effect.

[0008] According to some embodiments of the present invention, the density of color center defects in the diamond is greater than a preset density threshold.

[0009] By providing a high density of color center defects in diamond, the stability of electron excitation can be further improved.

[0010] According to some embodiments of the present invention, the color center defect is a nickel vacancy defect or a silicon vacancy defect.

[0011] According to some embodiments of the present invention, the negative electron affinity surface is formed by hydrogenating or metallizing the second surface of diamond.

[0012] The negative electron affinity surface on diamond formed by hydrogenation or metal plating has more stable chemical properties than the negative electron affinity surface of the Cs-O layer used in most metal or semiconductor photocathodes. It does not need to be stored in an ultra-high vacuum environment, which greatly reduces the vacuum environment requirements for the photocathode electron source, thereby reducing the manufacturing and maintenance costs of the photocathode electron source, allowing the photocathode electron source to be used in more occasions. At the same time, it can also work stably in a lower vacuum environment, thereby ensuring the stability of electron emission.

[0013] In the second aspect, an embodiment of the present invention provides a photocathode electron source device, comprising: a near-infrared light source assembly for outputting near-infrared light; a short-wavelength light source assembly for outputting short-wavelength light; the photocathode electron source in the above technical solution is used to receive the near-infrared light output by the near-infrared light source assembly and the short-wavelength light output by the short-wavelength light source assembly, and emit electrons.

[0014] The photocathode electron source device in this embodiment can use the existing mature near-infrared light source components to obtain modulated near-infrared light at low cost, which can reduce the modulation cost of the incident light required by the photocathode electron source. At the same time, the short-wavelength light source component is set up, so that the photocathode electron source can use the received near-infrared light and short-wavelength light to achieve two-photon transition, while ensuring low cost and further improving the electron excitation efficiency.

[0015] According to some embodiments of the present invention, the near-infrared light source assembly is further used to modulate the intensity of the output near-infrared light.

[0016] By modulating the intensity of near-infrared light, the intensity of electrons generated by the photocathode electron source can be adjusted. At the same time, the near-infrared light source assembly can be used to modulate near-infrared light at a low cost and high speed, so that the photocathode electron source can generate electron beam pulses with ultra-short pulse width in the time domain. While solving the problem of high cost of modulating incident light, high repetition rate incident light modulation is achieved, so that the photocathode electron source can obtain multiple beams of parallel high-speed modulated electron sources.

[0017] In a third aspect, an embodiment of the present invention provides a method for generating electrons using a photocathode electron source device, wherein the photocathode electron source device is the photocathode electron source device in the above technical solution, wherein the photocathode electron source device includes a near-infrared light source component, a short-wavelength light source component and a photocathode electron source, the photocathode electron source includes a photocathode and an anode, and the photocathode includes: diamond doped with color center defects, a transparent conductive layer disposed on a first surface of the diamond, and a negative electron affinity surface disposed on a second surface of the diamond. The method includes:

[0018] A near-infrared light source component and a short-wavelength light source component are used to output near-infrared light and short-wavelength light respectively.

[0019] Near infrared light and short wavelength light are transmitted through the transparent conductive layer of the photocathode electron source and overlappedly incident on the first area of ​​the diamond on the photocathode electron source. The color center defect in the first area undergoes a two-photon transition to excite electrons, and the electrons are emitted through the negative electron affinity surface under the action of the voltage difference between the photocathode and the anode.

[0020] This embodiment uses a photocathode electron source to receive near-infrared light and short-wavelength light and emit electrons, thereby reducing the modulation cost of the incident light while improving the electron excitation efficiency and stability. In addition, by overlapping near-infrared light and short-wavelength light incident on the first area of ​​the diamond on the photocathode electron source, a two-photon transition occurs in the diamond, achieving the excitation of electrons from the color center defect ground state to the conduction band, thereby ensuring the electron excitation effect.

[0021] According to some embodiments of the present invention, the intensity of near-infrared light is modulated by a near-infrared light source assembly to adjust the intensity of electrons emitted by a photocathode electron source.

[0022] This embodiment utilizes the low cost and high-speed modulation characteristics of the near-infrared light source assembly, and controls the electron beam intensity by modulating the near-infrared light. This can solve the high-speed modulation problem of the photocathode electron source while controlling the cost, thereby achieving low-cost high-speed modulation of the electron source.

[0023] According to some embodiments of the present invention, the near-infrared light is a pulsed laser, the short-wavelength light is a continuous laser, and the projection range of the short-wavelength light on the transparent conductive layer covers the projection range of the near-infrared light on the transparent conductive layer.

[0024] This embodiment makes the projection range of short-wavelength light on the transparent conductive layer cover the projection range of near-infrared light on the transparent conductive layer, which can ensure the modulatable characteristics of near-infrared light while allowing near-infrared light and short-wavelength light to overlap in diamond to the greatest extent to produce two-photon transition, thereby effectively avoiding the waste of incident light energy and improving the utilization rate of incident light energy.

[0025] In a fourth aspect, an embodiment of the present invention provides an electron beam system, comprising: the photocathode electron source device in the above technical solution, used to emit electrons; a focusing assembly, placed behind the photocathode electron source device, used to focus the electrons emitted by the photocathode electron source device to obtain a first target electron beam, and project it onto a target object; and / or a deflection assembly, placed behind the photocathode electron source device, used to deflect the electrons emitted by the photocathode electron source device or the first target electron beam to obtain a second target electron beam, and project it onto the target object. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A graph showing the variation of the electron excitation efficiency of a photocathode electron source according to an embodiment with the photon energy;

[0027] Figure 2 A graph showing the variation of the electron excitation efficiency of a photocathode electron source according to an embodiment with the photon energy;

[0028] Figure 3 is a schematic diagram of a photocathode electron source according to an embodiment;

[0029] Figure 4 A schematic diagram of a photocathode electron source device according to an embodiment of the present invention;

[0030] Figure 5 A schematic diagram of a photocathode electron source device according to an embodiment of the present invention;

[0031] Figure 6 is a schematic diagram of a photocathode electron source according to an embodiment of the present invention;

[0032] Figure 7 An energy band model diagram of a photocathode electron source according to an embodiment of the present invention;

[0033] Figure 8 A flow chart of a method for generating electrons using a photocathode electron source device according to an embodiment of the present invention;

[0034] Fig. 9 FIG. 4 is a schematic diagram of an electron beam system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The specific implementation of the present invention will be further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0036] A photocathode electron source is an electron source that uses the photoelectric effect of the photocathode material to convert incident light into outgoing electrons. The basic principle of a photocathode electron source is to use the energy of the incident light to excite the electrons in the photocathode material and enable the electrons to obtain enough energy to escape from the photocathode material. Photocathode electron sources have a series of advantages such as high efficiency, stability and controllability. They are widely used in scientific research, industry and medical fields. Specifically, they can be applied to electron beam systems or X-ray systems, especially in electron beam imaging or electron beam lithography of electron beam systems.

[0037] First, the response time of the photocathode electron source to the incident light is usually less than 1ns, that is, it can respond quickly to the incident light. Secondly, the photocathode electron source has a simple structure and strong scalability. In addition, as a planar electron source, the electron beam generated by the photocathode electron source has the advantages of good uniformity, high parallelism, and small energy divergence, which can achieve a good electron excitation effect.

[0038] Photocathode electron sources with different photocathode materials have different cutoff wavelengths, where the photocathode electron source can only excite electrons when the wavelength of the incident light is shorter than the cutoff wavelength. For common metal or semiconductor photocathode materials, the cutoff wavelength is generally in the range of ultraviolet to visible light. However, within this cutoff wavelength range, the incident light is difficult to modulate. In other words, the modulation cost of the incident light is high, which greatly limits the photocathode electron source's acquisition of parallel electron beams.

[0039] After research, the applicant found that the optical module technology in the field of communications is relatively mature. The optical modules in the field of communications can be used to obtain modulated near-infrared light at a very low cost, which can solve the problem of high cost of incident light modulation. However, some known photocathode electron source solutions cannot guarantee the electron excitation efficiency under the condition of using near-infrared light as the incident light; that is, the photocathode electron source cannot improve the electron excitation efficiency while controlling the cost. Among them, the "electron excitation efficiency" mentioned in this embodiment can also be understood as the photoelectric conversion efficiency. The higher the electron excitation efficiency, the higher the photoelectric conversion efficiency, and the energy of the incident light can be absorbed to a great extent, thereby exciting electrons.

[0040] In the scheme of the photocathode electron source under one embodiment, the photocathode electron source can use single crystal silicon Si with a cutoff wavelength of about 1100nm as the photocathode material. By alternately plating cesium Cs and passing oxygen O2 on the Si(100) surface, a Cs-O dipole layer is formed on the Si(100) surface, so that the Cs-O dipole layer serves as a negative electron affinity surface (Negative Electron Affinity, NEA) on the photocathode material. In this embodiment, near-infrared light with a wavelength shorter than the cutoff wavelength of 1100nm can be used to excite electrons in the single crystal silicon Si, and the electrons are emitted from the Cs-O dipole layer.

[0041] Although the photocathode electron source of the above embodiment can realize electron excitation through near-infrared light, since silicon Si used as the photocathode material is an indirect bandgap semiconductor, the absorption efficiency of the near-infrared band is not high, so it is impossible to achieve good electron excitation efficiency in the near-infrared band. Figure 1 As shown, Figure 1 FIG. 1 is a graph showing the variation of the electron excitation efficiency of the photocathode electron source of this embodiment with the photon energy. Figure 1 It can be seen that when the incident photon energy of the photocathode electron source in this embodiment is less than 1.5eV, the emission efficiency of the silicon photocathode decreases rapidly with the increase of wavelength and is less than 10%, indicating that the electron excitation efficiency of the photocathode electron source in this embodiment is still not high enough in the near-infrared band. Moreover, the chemical properties of the Cs-O dipole layer in this embodiment are active and unstable, and it needs to be in an ultra-high vacuum (pressure <10 -8 Pa) to work stably, the vacuum environment requirements are high, and the stability of electronic excitation is poor.

[0042] In another embodiment of the photocathode electron source, the photocathode electron source can use epitaxially grown III-V narrow bandgap semiconductors as photocathode materials, and simultaneously eject electrons from the negative electron affinity surface of the epitaxially grown III-V narrow bandgap semiconductors after electric field acceleration. "Epitaxial growth" refers to growing a single crystal layer with certain requirements and the same crystal orientation as the substrate on a single crystal substrate (substrate).

[0043] In the above embodiment, the III-V narrow bandgap semiconductor (such as indium gallium arsenic phosphide InGaAsP, indium arsenic phosphide InAsP, etc.) epitaxially grown on the indium phosphide InP substrate can be used as the photocathode material, and then the optical absorption characteristics of the III-V narrow bandgap semiconductor with a long cutoff wavelength and a high direct bandgap can be used to achieve efficient absorption of near-infrared light and convert it into electrons. Among them, the electron excitation efficiency of the photocathode electron source in this embodiment varies with the photon energy as shown in the figure below: Figure 2 As shown. Figure 2It can be seen that as the photon energy increases, indium gallium arsenic phosphide InGaAsP reaches the maximum photon excitation efficiency the fastest, that is, it responds to the photon energy the fastest. Second only to indium gallium arsenic phosphide InGaAsP, indium arsenic phosphide InAsP can also achieve a rapid response to photon energy. This shows that the use of III-V narrow bandgap semiconductors such as indium gallium arsenic phosphide InGaAsP or indium arsenic phosphide InAsP as photocathode materials can more efficiently absorb near-infrared light and convert it into electrons. The photocathode electron source in this embodiment can alternately implement cesium Cs plating and oxygen O2 on the surface of the III-V narrow bandgap semiconductor to form a Cs-O dipole layer on the surface, so that the Cs-O dipole layer is used as a negative electron affinity surface.

[0044] However, the photocathode electron source in the above embodiment still has the problem that the chemical properties of the Cs-O dipole layer are active and unstable, and needs to be placed in an ultra-high vacuum (pressure <10 -8 Pa) to work stably, and the stability of electronic excitation is poor.

[0045] like Figure 3 As shown, in the scheme of the photocathode electron source under one embodiment, the photocathode electron source can use cold atomic gas as the photocathode material, and use the electric field to limit the spatial range of the cold atomic gas. Then, the near-infrared light modulated by the spatial light modulator and another short-wavelength light are simultaneously incident on the cold atomic gas to realize electron emission by utilizing the two-photon transition of the cold atomic gas. Among them, the cold atomic gas can be an extremely low temperature (100μK) alkali metal atomic gas obtained by laser cooling technology.

[0046] However, the capture rate of the cold atomic gas used in the photocathode electron source of this embodiment is low, generally not exceeding 10 10 / s, the capture cost is high and high electron excitation efficiency cannot be guaranteed.

[0047] Therefore, how to reduce the cost of incident light modulation while ensuring the efficiency of electron excitation has become a problem that needs to be solved urgently.

[0048] In order to solve the above technical problems, an embodiment of the present application proposes a photocathode electron source, which includes a photocathode and an anode. The photocathode includes a diamond doped with a color center defect, a transparent conductive layer and a negative electron affinity surface respectively placed on two opposite surfaces (i.e., a first surface and a second surface) of the diamond. The transmittance of the transparent conductive layer to near-infrared light and short-wavelength light is greater than a preset transmittance threshold, and the emission rate of the electrons excited by the diamond from the negative electron affinity surface is greater than a preset emission threshold. The diamond includes a first region, and the near-infrared light and the short-wavelength light are overlapped and projected on the first region. The color center defect in the first region undergoes a two-photon transition to excite electrons, so that under the action of the voltage difference between the photocathode and the anode, the electrons are emitted through the negative electron affinity surface.

[0049] The photocathode electron source of the embodiment of the present application can reduce the operating cost of the photocathode electron source by selecting near-infrared light as the incident light source. At the same time, by using diamond as the photocathode material and utilizing the high thermal conductivity of the diamond matrix material, it can provide good thermal conductivity when the total emission current is large, thereby improving the use stability of the photocathode electron source and improving the stability of electron excitation. Moreover, by doping color center defects in diamond and superimposing short-wavelength light on the basis of near-infrared light, two-photon transitions can be achieved at the color center defects of diamond, further improving the efficiency of electron excitation.

[0050] The photocathode electron source device including the photocathode electron source proposed in the present application will be described in detail below in conjunction with the accompanying drawings and embodiments.

[0051] like Figure 4 As shown, the photocathode electron source device 10 of the embodiment of the present application includes a near-infrared light source assembly 11 , a short-wavelength light source assembly 12 and a photocathode electron source 13 .

[0052] The near-infrared light source assembly 11 is used to output near-infrared light. The near-infrared light source assembly 11 can be a communication band optical module that outputs near-infrared light, such as an 850nm optical module. The short-wavelength light source assembly 12 is used to output short-wavelength light. The short-wavelength light source assembly 12 can be a short-wavelength optical module or a short-wavelength laser, etc. The short-wavelength light output by the short-wavelength light source assembly 12 can be visible light, near-ultraviolet light, or ultraviolet light, etc., which is not limited here.

[0053] The photocathode electron source 13 is used to receive the near-infrared light output by the near-infrared light source assembly 11 and the short-wavelength light output by the short-wavelength light source assembly 12, and emit electrons. Figure 5 As shown, the photocathode electron source 13 may include a photocathode 131 and an anode 132 , wherein the photocathode 131 includes: diamond 1311 doped with color center defects, a transparent conductive layer 1312 disposed on a first surface of the diamond 1311 , and a negative electron affinity surface 1313 disposed on a second surface of the diamond 1311 .

[0054] Diamond 1311 includes an incident light overlapping region (as an example of a first region), and near-infrared light and short-wavelength light are projected onto the incident light overlapping region in an overlapping manner. A two-photon transition occurs at the color center defect in the incident light overlapping region, exciting electrons, which are then emitted through the negative electron affinity surface 1313 under the action of the voltage difference between the photocathode 131 and the anode 132.

[0055] In the spatial dimension, "near-infrared light and short-wavelength light overlap and are projected in the incident light overlap region" means that near-infrared light and short-wavelength light are projected in the same region in the diamond (i.e., the incident light overlap region), and overlap occurs in the incident light overlap region, so that two-photon transitions occur in the color center defects in the incident light overlap region, exciting electrons. The specific location of the incident light overlap region in the diamond can be customized according to actual needs and is not limited here.

[0056] In the time dimension, "near-infrared light and short-wavelength light are projected overlappingly in the incident light overlap area" can also be understood as near-infrared light and short-wavelength light are projected simultaneously in the incident light overlap area. "Near-infrared light and short-wavelength light are projected simultaneously in the incident light overlap area" means that the irradiation time of near-infrared light and short-wavelength light overlaps. In other words, it is sufficient that there is overlapping irradiation time in the irradiation period of near-infrared light and short-wavelength light, and the irradiation start time of near-infrared light and short-wavelength light can be the same or different. It can be understood that in one embodiment, the irradiation start time of near-infrared light and short-wavelength light can be set to be the same, so as to avoid invalid light source irradiation and waste of light source energy.

[0057] In one embodiment, the near-infrared light source assembly 11 can also be used to modulate the intensity of the output near-infrared light. By modulating the intensity of the near-infrared light, the intensity of the electrons generated by the photocathode electron source 13 (i.e., the current intensity of the electrons) can be adjusted. The intensity of the projection light source (i.e., the near-infrared light) is proportional to the current intensity of the electrons emitted by the photocathode electron source 13. The greater the intensity of the projection light source, the more photons the projection light source provides, and accordingly, the more electrons are excited by the photocathode electron source 13 in response to the projection light source, i.e., the greater the current intensity of the generated electrons.

[0058] The pulse repetition frequency of electrons emitted by the photocathode electron source 13 is the same as the modulation frequency of near-infrared light. The near-infrared light source assembly 11 can modulate near-infrared light at high speed and low cost, so that the photocathode electron source 13 can generate electron beam pulses with ultra-short pulse width (i.e., high pulse repetition frequency, generally greater than 1 GHz) in the time domain. While solving the problem of high cost of modulating the incident light, high-repetition-rate modulation of the incident light is achieved, so that the photocathode electron source 13 can obtain multiple beams of parallel high-speed modulated electron sources.

[0059] In one embodiment, if Figure 5 As shown, the modulated near-infrared light output by the near-infrared light source assembly 11 may be a pulsed laser, and the short-wavelength light output by the short-wavelength light source assembly 12 may be a continuous laser, wherein the projection range of the short-wavelength light on the transparent conductive layer covers the projection range of the near-infrared light on the transparent conductive layer. In this way, while ensuring the modulatable characteristics of the near-infrared light, the near-infrared light and the short-wavelength light can be overlapped in the diamond to the greatest extent to cause a two-photon transition, thereby effectively avoiding the waste of incident light energy and improving the utilization rate of the incident light energy.

[0060] It can be understood that the "modulation" of near-infrared light may include but is not limited to the modulation of the light intensity of the near-infrared light. In other embodiments, the pulse frequency or pulse width of the near-infrared light may also be modulated as required, which is not limited here.

[0061] It is worth mentioning that Figure 5 The example in which the short-wavelength light source component 12 is arranged on the right side of the near-infrared light source component 11 is used for illustration. In other embodiments, the short-wavelength light source component 12 can also be arranged on the left side of the near-infrared light source component 11. It is only necessary to ensure that the projection range of the short-wavelength light output by the short-wavelength light source component 12 on the transparent conductive layer can cover the projection range of the near-infrared light on the transparent conductive layer. No limitation is imposed on its placement position.

[0062] Figure 5 Only three near-infrared light source assemblies 11 are provided in the photocathode electron source device 10 as an example for illustration. In other embodiments, one, two, four or more near-infrared light source assemblies 11 may be provided in the photocathode electron source device 10 according to actual needs, and the number of near-infrared light source assemblies 11 is not limited here. It can be understood that as the number of near-infrared light source assemblies 11 increases, the number of near-infrared light beams projected onto the photocathode electron source 13 increases, and the number of electron beams emitted by the photocathode electron source 13 also increases.

[0063] When the photocathode electron source 13 receives a single beam of incident light, it can generate a single beam of electrons. When the photocathode electron source 13 receives multiple beams of parallel incident light, it can generate a parallel electron beam array. In one embodiment, the near-infrared light source assembly 11 can be used to independently modulate each beam of near-infrared light to achieve independent high-speed modulation of the electron beam array generated by the photocathode electron source 13, thereby facilitating the realization of large-scale parallel modulation of electron beams. This feature has important application value in the fields of electron beam imaging, electron beam lithography, etc.

[0064] The photocathode electron source device in this embodiment can use the existing mature near-infrared light source components to obtain modulated near-infrared light at low cost, which can reduce the modulation cost of the incident light required by the photocathode electron source. At the same time, the short-wavelength light source component is set up, so that the photocathode electron source can use the received near-infrared light and short-wavelength light to achieve two-photon transition, while ensuring low cost and further improving the electron excitation efficiency.

[0065] The photocathode electron source 13 in the photocathode electron source device 10 proposed in the embodiment of the present application is described in detail below in conjunction with the drawings and embodiments.

[0066] Please continue reading Figure 5 , the photocathode electron source 13 of the embodiment of the present application may include a photocathode 131 and an anode 132. The photocathode 131 includes a diamond 1311 doped with a color center defect, a transparent conductive layer 1312 disposed on the upper surface (as an example of a first surface) of the diamond 1311 as shown in the figure, and a negative electron affinity surface 1313 disposed on the lower surface (as an example of a second surface) of the diamond 1311. In one embodiment, the thickness of the diamond 1311 can be selected in the range of 50 μm to 400 μm according to actual needs to achieve a better electron excitation effect, and the specific thickness of the diamond 1311 is not limited here.

[0067] The transparent conductive layer 1312 is disposed on the upper surface of the diamond 1311, and the negative electron affinity surface 1313 is disposed on the lower surface of the diamond 1311. The first surface and the second surface are two opposite surfaces of the diamond 1311. The first surface of the diamond 1311 may also be referred to as the front surface of the diamond 1311, and correspondingly, the second surface of the diamond 1311 may be referred to as the back surface of the diamond 1311.

[0068] like Figure 5 As shown, Figure 5 The upper surface of the diamond 1311 is taken as an example of the first surface, and the lower surface of the diamond 1311 is taken as an example of the second surface. Figure 5 The diamond 1311 is rotated 90 degrees counterclockwise, and the left surface of the diamond 1311 can be used as the first surface, and the right surface of the diamond 1311 can be used as the second surface.

[0069] It can be understood that the first surface and the second surface can be determined according to the direction of electron emission. If the electron needs to be emitted from the right side of the diamond 1311, the first surface is the left surface of the diamond 1311, and the second surface is the right surface of the diamond 1311. If the electron needs to be emitted from the bottom side of the diamond 1311, the first surface is the upper surface of the diamond 1311, and the second surface is the lower surface of the diamond 1311, and so on, and no examples are given here.

[0070] Understandably, Figure 5 Taking the diamond 1311 as a rectangle as an example, the present application is not limited thereto. In other embodiments, it may also be an ellipse or a cylinder or other irregular shapes.

[0071] The transmittance of the transparent conductive layer 1312 to near-infrared light and short-wavelength light is greater than a preset transmittance threshold. In other words, the transparent conductive layer 1312 has a certain degree of transmittance to near-infrared light and short-wavelength light. By transmitting the near-infrared light and short-wavelength light, the near-infrared light and short-wavelength light can be projected into the diamond 1311, so that the diamond 1311 responds to the near-infrared light and short-wavelength light and excites electrons.

[0072] The emission rate of the electrons excited by the diamond 1311 from the negative electron affinity surface 1313 is greater than a preset emission threshold (the preset emission threshold is generally greater than 50%), that is, the negative electron affinity surface 1313 is easy for the electrons to be emitted. The negative electron affinity surface 1313 has no potential barrier on its surface, so that the electrons excited by the diamond 1311 can easily escape from the surface, thereby ensuring the emission rate of the electrons.

[0073] It can be understood that the preset transmission threshold and the preset emission threshold can be determined by the composition and thickness of the transparent conductive layer 1312 and the negative electron affinity surface 1313, respectively, and can be set according to actual application requirements, which is not limited here.

[0074] In one embodiment, the negative electron affinity surface 1313 may be formed by hydrogenating or metallizing (such as magnesium Mg, lithium Li or aluminum Al) the second surface of the diamond 1311. The negative electron affinity surface 1313 on the diamond 1311 formed by hydrogenation or metallization has a more stable chemical property than the negative electron affinity surface 1313 of the Cs-O layer used by most metal or semiconductor photocathodes 131. It does not need to be stored in an ultra-high vacuum environment, which greatly reduces the vacuum environment requirements for the photocathode electron source 13, thereby reducing the manufacturing and maintenance costs of the photocathode electron source 13, so that the photocathode electron source 13 can be used in more occasions. At the same time, it can also work stably in a relatively low vacuum environment, thereby ensuring the stability of electron emission and improving the electron emission efficiency.

[0075] In one embodiment, the transparent conductive layer 1312 may be ITO glass (tin-doped indium trioxide), AZO (aluminum-doped zinc oxide) or other electrode materials that can transmit near-infrared light and short-wavelength light. The thickness of the transparent conductive layer 1312 can be selected within the range of 100nm to 200nm according to demand. The composition and thickness of the transparent conductive layer 1312 are not limited herein.

[0076] like Figure 6 As shown, the diamond 1311 includes an incident light overlap region 1314 (as an example of a first region), and the incident light overlap region 1314 is an overlap region of near-infrared light and short-wavelength light on the diamond 1311, and the near-infrared light and short-wavelength light are overlapped and projected on the incident light overlap region 1314. It is worth noting that Figure 6 Taking the projection of three beams of near-infrared light, the diamond 1311 includes three incident light overlapping areas 1314 as an illustration. The positions and number of the incident light overlapping areas 1314 can be set according to actual conditions. By adjusting the incident angle and range of the near-infrared light and the short-wavelength light, incident light overlapping areas 1314 of different numbers and positions can be obtained, which is not limited here.

[0077] Near infrared light and short wavelength light overlap and project onto the incident light overlap region 1314. The color center defects in the incident light overlap region 1314 can undergo two-photon transitions, thereby exciting electrons. Then, under the action of the voltage difference between the photocathode 131 and the anode 132, the electrons are emitted through the negative electron affinity surface 1313. Figure 5 and Figure 6 As shown, the transparent conductive layer 1312 in the photocathode 131 can be connected to the anode 132, forming a voltage difference between the transparent conductive layer 1312 and the anode 132, so that the voltage difference is used to form an accelerating electric field to provide acceleration for the electrons excited by the diamond 1311, so that the electrons excited by the diamond 1311 are emitted through the negative electron affinity surface 1313.

[0078] In the photocathode electron source 13, the electrons in the photocathode material can be excited by absorbing the energy of the projected light source to achieve energy level transition. Among them, the state with the lowest electron energy is the ground state. After absorbing a certain amount of energy, the electron enters the excited state. With the continuous absorption of energy, the electron can transition from the excited state to the conduction band, achieve energy level transition, and become electrons that can move freely in the conduction band of the photocathode material, that is, free electrons, and thus be excited.

[0079] Combine the following Figure 7 , the process of two-photon transition generated at the color center defect is introduced, among which, Figure 7 FIG. 4 is an energy band model diagram of the photocathode electron source 13 in this embodiment.

[0080] like Figure 7As shown, the "two-photon transition" process occurring in the color center defect in the incident light overlap region 1314 includes: the electron first enters the excited state from the ground state by absorbing the energy of the near-infrared light. Through the energy superposition of short-wavelength light, the electron realizes energy level transition, transitions from the excited state to the conduction band, and thus becomes a free electron in the conduction band of diamond 1311. The above-mentioned "two-photon transition" process can be completed within 0.1ns to 10ns. After the "two-photon transition" is completed, under the action of the voltage difference between the transparent conductive layer 1312 and the anode 132, the electron excited into the conduction band gains acceleration and is ejected from the negative electron affinity surface 1313.

[0081] It can be understood that the energy required for the energy level transition of the color center defect in the diamond 1311 corresponds to the wavelength band where the near-infrared light is located, wherein the energy required for the energy level transition is the energy required for the electron to transition from the ground state to the excited state. In other words, the color center defect in the diamond 1311 can enter the excited state from the ground state by absorbing the energy of the near-infrared light. In one embodiment, the color center defect can be a nickel vacancy defect (NiV - ) or silicon vacancies (SiV 0 ) defect, in other embodiments, it can also be a nickel vacancy defect (NiV - ) or silicon vacancies (SiV 0 ) defects, it is sufficient for defects other than the above defects to satisfy the condition that the wavelength band corresponding to the energy required for energy level transition is the wavelength band where near-infrared light is located, and no limitation is made here.

[0082] In one embodiment, the density of the color center defects in the diamond 1311 is greater than a preset density threshold, wherein the preset density threshold can generally be set to 10 16 cm -3 The stability of electron excitation can be further improved by providing a high density of color center defects in the diamond 1311. The color center defects can be formed by ion implantation, doping during the growth process, or other methods, and the injection process of the color center defects will not be described in detail or limited herein.

[0083] The photocathode electron source of this embodiment can reduce the cost of the photocathode electron source by selecting near-infrared light as the incident light source. At the same time, diamond is used as the photocathode material, and the high thermal conductivity of the diamond matrix material is utilized to provide good thermal conductivity when the total emission current is large, thereby improving the use stability of the photocathode electron source and improving the electron excitation efficiency and stability. Moreover, color center defects are doped in diamond, and short-wavelength light is superimposed on the basis of near-infrared light, which can realize two-photon transition at the color center defect of diamond, realize the excitation of electrons from the color center defect ground state to the conduction band, and ensure the electron excitation effect. Moreover, the negative electron affinity surface of the diamond surface has a more stable chemical property compared to the negative electron affinity surface of the Cs-O layer used in most metal or semiconductor photocathodes, and does not need to be stored in an ultra-high vacuum environment, which greatly reduces the vacuum environment requirements for the photocathode electron source, thereby reducing the manufacturing and maintenance costs of the photocathode electron source, so that the photocathode electron source can be applied in more occasions. At the same time, it can also work stably in a relatively low vacuum environment, thereby ensuring the stability of electron emission. In addition, near-infrared light has the characteristics of low cost and high-speed modulation. By selecting near-infrared light as the incident light, the high-speed modulation problem of the photocathode electron source can be solved while controlling the cost, thereby realizing low-cost high-speed modulation of the electron source.

[0084] like Figure 8 As shown, a method for generating electrons using a photocathode electron source device according to an embodiment of the present invention, wherein the photocathode electron source device is the photocathode electron source device 10 in the above embodiment, which includes a near-infrared light source assembly 11, a short-wavelength light source assembly 12, and a photocathode electron source 13. The specific structure of the photocathode electron source device 10 can refer to the above embodiment and will not be described in detail here. The method specifically includes:

[0085] Step 110: Utilize a near-infrared light source assembly and a short-wavelength light source assembly to output near-infrared light and short-wavelength light respectively.

[0086] In one embodiment, the near-infrared light source assembly 11 can be used to modulate the intensity of the near-infrared light to adjust the intensity of the electrons emitted by the photocathode electron source 13. By utilizing the low cost and high-speed modulation characteristics of the near-infrared light source assembly 11, the near-infrared light can be modulated to control the intensity of the electron beam, and the high-speed modulation problem of the photocathode electron source 13 can be solved while controlling the cost, so as to achieve a low-cost high-speed modulation of the electron source. It can be understood that in other embodiments, the near-infrared light source assembly 11 can also be used to modulate the pulse frequency or pulse width of the near-infrared light, which is not limited here.

[0087] Step 120: Near infrared light and short wavelength light are transmitted through the transparent conductive layer of the photocathode electron source, and overlap and incident on the first area of ​​diamond on the photocathode electron source.

[0088] In one embodiment, the near-infrared light source assembly 11 and the short-wavelength light source assembly 12 can be used to simultaneously irradiate the photocathode electron source 13 with near-infrared light and short-wavelength light, so that the near-infrared light and the short-wavelength light overlap in the first area of ​​the diamond. By irradiating the near-infrared light and the short-wavelength light simultaneously, it is possible to avoid the situation of ineffective irradiation of the light source, avoid the waste of light source energy, and thus improve the conversion rate of light source energy. It can be understood that in other embodiments, the irradiation start time of the near-infrared light and the short-wavelength light can also be different, as long as it is ensured that there is an overlapping irradiation time in the irradiation period of the near-infrared light and the short-wavelength light.

[0089] In one embodiment, the near-infrared light may be a pulsed laser, the short-wavelength light may be a continuous laser, and the projection range of the short-wavelength light on the transparent conductive layer 1312 may cover the projection range of the near-infrared light on the transparent conductive layer 1312. In this way, while ensuring the modulatable characteristics of the near-infrared light, the near-infrared light and the short-wavelength light can be overlapped in the diamond 1311 to the greatest extent to cause a two-photon transition, thereby effectively avoiding the waste of incident light energy and improving the utilization rate of incident light energy.

[0090] Step 130: A two-photon transition occurs in the color center defect in the first region to excite electrons.

[0091] Step 140: Electrons are emitted through the negative electron affinity surface under the action of the voltage difference between the photocathode and the anode.

[0092] The above steps 120 to 140 are the same as the process of the photocathode electron source 13 emitting electrons described in the above embodiment, and are not described in detail here.

[0093] This embodiment uses a photocathode electron source to receive near-infrared light and short-wavelength light and emit electrons, which can reduce the modulation cost of the incident light while improving the electron excitation efficiency and stability. By overlapping the near-infrared light and the short-wavelength light and incident on the first area of ​​the diamond on the photocathode electron source, a two-photon transition occurs in the diamond, further improving the electron excitation efficiency. Moreover, by irradiating the near-infrared light and the short-wavelength light at the same time, the near-infrared light and the short-wavelength light can be overlapped in the diamond to the greatest extent to cause a two-photon transition, thereby effectively avoiding the waste of incident light energy and improving the utilization rate of the incident light energy. In addition, by utilizing the low cost and high-speed modulation characteristics of the near-infrared light source assembly, the near-infrared light can be modulated, and the electron beam intensity can be controlled by modulating the near-infrared light. The high-speed modulation problem of the photocathode electron source can be solved while controlling the cost, and a low-cost high-speed modulation electron source can be achieved.

[0094] like Fig. 9As shown, the electron beam system 100 of the embodiment of the present invention comprises: the photocathode electron source device 10, focusing assembly and / or deflection assembly as in the above embodiment. In practical application scenarios, the electron beam system 100 can be an electron microscope or an electron beam lithography machine.

[0095] The photocathode electron source device 10 is used to emit electrons. The structure of the photocathode electron source device 10 and the process of emitting electrons have been described in detail in the above embodiments and will not be repeated here. The focusing assembly is placed behind the photocathode electron source device 10, and is used to focus the electrons emitted by the photocathode electron source device 10 to obtain a first target electron beam and project it onto a target object. The deflection assembly is placed behind the photocathode electron source device 10, and is used to deflect the electrons or the first target electron beam emitted by the photocathode electron source device 10 to obtain a second target electron beam and project it onto a target object.

[0096] The focusing assembly can change the trajectory of the electrons by applying an electric field or a magnetic field to the electrons, thereby forming a focus. Taking an electron microscope as an example, the focusing assembly used can be an electron lens. The electron lens can use a spatial electric field or a magnetic field symmetrical to the axis of the lens barrel to bend the electron trajectory toward the axis, thereby forming a focus. The deflection assembly can also be called an electromagnetic deflection assembly, which can use magnetic deflection or electric deflection technology to generate a magnetic field or an electric field to exert an effect on the electron beam to achieve electron deflection.

[0097] In general, if Fig. 9 As shown, a vacuum chamber 20 may be provided in the electron beam system 100, and the photocathode electron source 13, the focusing assembly and the deflection assembly may be placed in the vacuum chamber 20. The vacuum chamber 20 provides a stable vacuum environment, thereby improving the electron beam transmission, the focusing assembly focusing the electron beam, and the deflection assembly deflecting the electron beam, thereby ensuring the stability of the electron beam system 100.

[0098] In one embodiment, the electron beam system 100 may only include the photocathode electron source device 10 and the focusing assembly. In other words, the deflection assembly may not be provided in the electron beam system 100. The focusing assembly is disposed behind the photocathode electron source device 10, and is used to focus the electrons emitted by the photocathode electron source device 10 to obtain a first target electron beam, and project it onto a target object to detect or process the target object.

[0099] In one embodiment, the electron beam system 100 may only include the photocathode electron source device 10 and the deflection assembly. In other words, the electron beam system 100 may not be provided with a focusing assembly. The deflection assembly is disposed behind the photocathode electron source device 10, and is used to deflect the electrons emitted by the photocathode electron source device 10 to obtain a second target electron beam, and project the second target electron beam onto a target object to detect or process the target object.

[0100] In one embodiment, the electron beam system 100 may include a photocathode electron source device 10, a focusing assembly, and a deflection assembly placed in sequence. The focusing assembly is placed after the photocathode electron source device 10, and is used to focus the electrons emitted by the photocathode electron source device 10 to obtain a first target electron beam. The deflection assembly is placed after the focusing assembly, and is used to deflect the first target electron beam to obtain a second target electron beam, and project it onto a target object to detect or process the target object.

[0101] Specifically, the near-infrared light source assembly 11 and the short-wavelength light source assembly 12 in the photocathode electron source device 10 can be used to output near-infrared light and short-wavelength light respectively, and the near-infrared light and the short-wavelength light are transmitted through the transparent conductive layer 1312 of the photocathode electron source 13, and overlapped and incident on the first area of ​​the diamond 1311 on the photocathode electron source 13. The color center defect in the first area undergoes a two-photon transition, excites electrons, and under the action of the voltage difference between the photocathode 131 and the anode 132, the electrons are emitted through the negative electron affinity surface 1313. The emitted electrons are transmitted to the focusing assembly, and the focusing assembly is used to apply an electric field or a magnetic field to the electrons to form a focus, so as to obtain a first target electron beam. Then the first target electron beam is transmitted to the deflection assembly, and the deflection assembly is used to apply an electric field or a magnetic field to the electrons to change the running trajectory of the first target electron beam, so that the first target electron beam is deflected, thereby obtaining a second target electron beam. Finally, the second target electron beam is projected onto the target object to detect or process the target object.

[0102] The electron beam system in the above embodiment can utilize the photocathode electron source device to reduce the cost while improving the electron excitation efficiency and stability. At the same time, with the subsequent setting of the focusing component and / or the deflection component, the effect of detecting or processing the target object can be further improved.

[0103] It can be understood that in other embodiments, the electron beam system 100 may also include a photocathode electron source device 10, a deflection assembly, and a focusing assembly placed in sequence. The deflection assembly is placed after the photocathode electron source device 10, and is used to deflect the electrons emitted by the photocathode electron source device 10 to obtain a second target electron beam. The deflection assembly is placed after the deflection assembly, and is used to focus the second target electron beam to obtain a first target electron beam, and project it onto a target object to detect or process the target object.

[0104] It is worth noting that the components in the electron beam system 100 can be increased or decreased according to actual needs, which is not limited here.

[0105] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A photocathode electron source, characterized in that: include: A photocathode and an anode, wherein the photocathode comprises: Diamond doped with color center defects; A transparent conductive layer disposed on the first surface of the diamond, wherein the transmittance of the transparent conductive layer to near-infrared light and short-wavelength light is greater than a preset transmittance threshold; A negative electron affinity surface disposed on the second surface of the diamond, wherein the negative electron affinity surface has an emission rate of electrons excited by the diamond greater than a preset emission threshold; The diamond includes a first region, the near-infrared light and the short-wavelength light are projected onto the first region in an overlapping manner, a two-photon transition occurs in the color center defect in the first region, electrons are excited, and then under the action of the voltage difference between the photocathode and the anode, the electrons are emitted through the negative electron affinity surface.

2. The photocathode electron source according to claim 1, characterized in that: The density of color center defects in the diamond is greater than a preset density threshold.

3. The photocathode electron source according to claim 1, characterized in that: The color center defect is a nickel vacancy defect or a silicon vacancy defect.

4. The photocathode electron source according to claim 1, characterized in that: The negative electron affinity surface is formed by hydrogenating or metallizing the second surface of the diamond.

5. A photocathode electron source device, characterized in that: include: A near-infrared light source assembly, used for outputting near-infrared light; A short-wavelength light source assembly, used for outputting short-wavelength light; The photocathode electron source according to any one of claims 1 to 4 is used to receive the near-infrared light output by the near-infrared light source assembly and the short-wavelength light output by the short-wavelength light source assembly, and emit electrons.

6. The photocathode electron source device according to claim 5, characterized in that: The near-infrared light source assembly is also used to modulate the intensity of the output near-infrared light.

7. A method for generating electrons using a photocathode electron source device, characterized in that: The photocathode electron source device is a photocathode electron source device as described in any one of claims 5 to 6, wherein the photocathode electron source device comprises a near-infrared light source assembly, a short-wavelength light source assembly and a photocathode electron source, the photocathode electron source comprises a photocathode and an anode, the photocathode comprises: a diamond doped with a color center defect, a transparent conductive layer disposed on a first surface of the diamond, and a negative electron affinity surface disposed on a second surface of the diamond; the method comprises the following steps: Utilizing the near-infrared light source assembly and the short-wavelength light source assembly to output near-infrared light and short-wavelength light respectively; The near-infrared light and the short-wavelength light pass through the transparent conductive layer of the photocathode electron source, and overlap and incident on the first area of ​​the diamond on the photocathode electron source; A color center defect in the first region undergoes a two-photon transition to excite an electron, and The electrons are emitted through the negative electron affinity surface under the action of the voltage difference between the photocathode and the anode.

8. The method for generating electrons using a photocathode electron source device according to claim 7, characterized in that: The method further comprises: The near-infrared light source assembly is used to modulate the light intensity of the near-infrared light to adjust the intensity of electrons emitted by the photocathode electron source.

9. The method for generating electrons using a photocathode electron source device according to claim 8, characterized in that: The near-infrared light is a pulsed laser, the short-wavelength light is a continuous laser, and the projection range of the short-wavelength light on the transparent conductive layer covers the projection range of the near-infrared light on the transparent conductive layer.

10. An electron beam system, characterized in that include: The photocathode electron source device according to any one of claims 5 to 6, used for emitting electrons; A focusing assembly, disposed behind the photocathode electron source device, for focusing the electrons emitted by the photocathode electron source device to obtain a first target electron beam and projecting it onto a target object; and / or The deflection assembly is disposed behind the photocathode electron source device and is used to deflect the electrons emitted by the photocathode electron source device or the first target electron beam to obtain a second target electron beam and project it onto a target object.

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