CN113205987A - Planar photoinduced electron emission source based on multilayer two-dimensional material - Google Patents
Planar photoinduced electron emission source based on multilayer two-dimensional material Download PDFInfo
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/02—Details
- H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
- H01J37/06—Electron sources; Electron guns
- H01J37/065—Construction of guns or parts thereof
Abstract
The invention provides a planar photoinduced electron emission source based on a multilayer two-dimensional material, which comprises a pumping source, a cathode power supply, a grid power supply, an electron collector and a van der Waals heterojunction, wherein the van der Waals heterojunction comprises a graphene material, an insulating two-dimensional material and a transition metal sulfide material which are sequentially arranged, and the planar photoinduced electron emission source comprises a plurality of layers of two-dimensional materials, wherein: the pump source interacts with the transition metal sulfide material and is used for valence electron generation transition in the transition metal sulfide material; the cathode power supply is connected with the transition metal sulfide material and is used for providing electrons; the grid power supply is connected with the graphene material and used for providing bias voltage for the grid and reducing the material potential barrier; the electron collector is used for collecting the electron beams emitted by the Van der Waals heterojunction. The embodiment of the invention can generate the electron beam with extremely low energy dispersion; the planar electron source is realized by utilizing multiple layers of two-dimensional materials, so that the scattering phenomenon of electrons in the materials is effectively reduced, and the cost of the electron source is reduced.
Description
Technical Field
The invention relates to the technical field of electron emission sources, in particular to a planar photoinduced electron emission source based on a multilayer two-dimensional material.
Background
In recent years, the development of Electron microscopy instruments has made tremendous progress, and one of the key advances is Scanning Electron Microscopy (SEM). The scanning electron microscope bombards the sample by point scanning with electron beams, and signal electrons are collected to represent the appearance of the sample. Scanning electron microscopes have found widespread use in the fields of materials science, life science, and semiconductor manufacturing. The characteristics of scanning electron microscopy systems are closely related to the electron source. Low cost, high resolution scanning electron microscope systems require electron sources that produce low energy dissipation, high brightness electron beams, and low vacuum, low voltage operating conditions. Wherein, energy dissipation refers to the consistent degree of electron energy. The electrons with consistent energy deflect at the same angle when being focused by the electromagnetic lens, so that the electron beams with low energy dispersion can be converged into a small-sized probe, and the imaging resolution is ensured. Brightness refers to the total electron beam current per unit area and per unit solid angle. Electrons emitted by the high-brightness electron source can be more easily converged into a small probe, and the small probe is provided with a larger electron beam current so as to ensure the resolution and the imaging quality. The electron source operates in a vacuum environment. The realization of a high vacuum degree working environment requires a high-tightness vacuum chamber and expensive molecular pumps and ion pumps. The development of an electron source working in a low vacuum environment will significantly reduce the cost of SEM. Advantages of scanning electron microscopes operating at low voltages include detection of finer surface sensitive information, realization of scanning images with good contrast, and reduction of radiation damage and charge effects on specimens. Reducing the electron beam energy can significantly enhance SEM performance.
SEM in the market is mainly based on thermal emission (energy spread 1.5-3eV, brightness 10)4A/m2Per/V, vacuum degree 10- 4Pa), Schottky field emission (energy spread 0.6-0.8eV, brightness 107A/m2Per/V, vacuum degree 10-7Pa), cold field emission (energy spread 0.3eV, brightness 109A/m2Per/V, vacuum degree 10-9Pa) and the working voltage of the electron source is 5-30 kV. It is very difficult to improve the electron beam energy dispersion and brightness or optimize the working conditions based on the electron source.
Metal-Oxide-Semiconductor (MOS) planar electron emission source satisfying low voltage (< 5kV) and low vacuum degree (10)-6Pa) and has a small divergence angle to ensure the brightness of the electron beam. At present, MOS electron sources have been applied to field emission displays, highly sensitive image sensors, electron beam lithography systems, and the like. Due to its excellent characteristics, the MOS electron source has potential application in a new generation of low-cost, high-performance electron microscope system. Nevertheless, the emission efficiency of the MOS electron source is very low (0.002%), and the electron beam energy dispersion is high (10eV), mainly due to elastic scattering and inelastic scattering of electrons in semiconductor materials, oxide materials, and metal materials, thereby losing energy. Therefore, most of the electrons reaching the surface have a lower work function than the metal gate and cannot escape from the material, and the emission efficiency is reduced; the free electron energy distribution of the escaping material is broadened, and the electron beam energy dispersion is increased.
Disclosure of Invention
The invention provides a planar photoinduced electron emission source based on a multilayer two-dimensional material, which is used for solving the technical defects in the prior art.
The invention provides a planar photoinduced electron emission source based on a multilayer two-dimensional material, which comprises a pumping source, a cathode power supply, a grid power supply, an electron collector and a van der Waals heterojunction, wherein the van der Waals heterojunction comprises a graphene material, an insulating two-dimensional material and a transition metal sulfide material which are sequentially arranged, and the planar photoinduced electron emission source comprises a plurality of layers of two-dimensional materials, wherein:
the pump source interacts with the transition metal sulfide material and is used for valence electron generation transition in the transition metal sulfide material;
the cathode power supply is connected with the transition metal sulfide material and is used for providing electrons;
the grid power supply is connected with the graphene material and used for providing bias voltage for the grid and reducing the material potential barrier;
the electron collector is used for collecting the electron beams emitted by the Van der Waals heterojunction.
According to the planar photoinduced electron emission source based on the multilayer two-dimensional material, the working waveband of the pumping source can be selected in a visible light range, and is matched with the band gap width of the electron energy band of the transition metal sulfide material.
According to the planar photoelectron emission source based on the multilayer two-dimensional material, the planar photoelectron emission source also comprises a transparent insulating medium as a substrate, and the transparent insulating medium is positioned at the lower layer of the Van der Waals heterojunction.
According to the planar photoinduced electron emission source based on the multilayer two-dimensional material, the cathode power supply and the grid power supply are respectively prepared by sputtering on the transparent dielectric material substrate.
According to the plane photoinduced electron emission source based on the multilayer two-dimensional material, the Van der Waals heterojunction is prepared by utilizing a bulk material mechanical stripping-transferring method, and the area of the Van der Waals heterojunction is 10 mu m2-100μm2The thickness is 1nm-10 nm.
According to the planar photoinduced electron emission source based on the multilayer two-dimensional material, the cathode electrode and the gate electrode are prepared by performing electron beam lithography and sputtering on a transition metal sulfide material and a graphene material.
According to the plane photoinduced electron emission source based on the multilayer two-dimensional material, the Van der Waals heterojunction is prepared by a chemical vapor deposition method and has an area of 0.01cm2-2cm2The thickness is 1nm-10 nm.
According to the planar photoelectron-emitting source based on the multilayer two-dimensional material provided by the present invention, the transition metal sulfide material is a semiconductor of a type having MX2, wherein M represents a transition metal, the transition metal comprises Mo, W, X represents a chalcogen element, and the chalcogen element comprises S, Se, Te.
According to the planar photoinduced electron emission source based on the multilayer two-dimensional material, the cathode power supply and the grid power supply respectively apply voltage to the transition metal sulfide material and the graphene material, and when the grid voltage is higher than the cathode voltage, the Fermi level of the graphene material is relatively lower than that of the transition metal sulfide; when the bias voltage between the grid and the cathode is larger than the work function of the graphene material, the Fermi level of the transition metal sulfide exceeds the vacuum level of the graphene material.
According to the planar photoinduced electron emission source based on the multilayer two-dimensional material, photogenerated carriers exist in a conduction band after interaction of transition metal sulfide and light, the photogenerated carriers generate quantum tunneling effect, penetrate through a potential barrier, enter an insulating layer material, and enter a graphene material through the insulating layer material under the action of an electric field generated by the insulating layer material; and the average energy of the current carriers entering the graphene material is higher than the vacuum level of the graphene material.
The invention provides a planar photoinduced electron emission source based on a multilayer two-dimensional material, which utilizes the photoinduced electron emission principle, utilizes the interaction of light and the two-dimensional material, and generates an electron beam with extremely low energy dispersion by electron absorption photon transition and escape from the material; the embodiment of the invention introduces a Van der Waals heterojunction structure, realizes a planar electron source by utilizing a plurality of layers of two-dimensional materials, effectively reduces the scattering phenomenon of electrons in the materials, and meets the working conditions of low voltage and low vacuum degree, so the scheme optimizes the quality of electron beams and reduces the cost of the electron source. The electron source emission area of the embodiment of the invention has flexible design and simple and durable emission structure, and has wider application prospect compared with the electron source in the traditional SEM, such as application to integration, array design and the like.
Drawings
In order to more clearly illustrate the technical solutions of the present invention or the prior art, the drawings needed for the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.
FIG. 1 is a schematic view of one of the planar photoelectron-emitting sources based on multiple layers of two-dimensional materials in an embodiment of the present invention;
FIG. 2 is a schematic three-dimensional view of a second planar photoelectron-emitting source based on multiple layers of two-dimensional materials according to an embodiment of the present invention;
FIG. 3 is a three-dimensional schematic view of a second planar photoelectronic emission source based on an enlarged central portion of a multi-layer two-dimensional material in accordance with an embodiment of the present invention;
FIG. 4 is a three-dimensional schematic view of a third embodiment of a planar photo-generated electron-emitting source of Van der Waals heterojunction in accordance with the present invention;
FIG. 5 is a diagram of the structure of the Van der Waals heterojunction energy band without bias applied in an embodiment of the invention;
FIG. 6 is a diagram of the structure of the Van der Waals heterojunction energy band under the bias applied in the embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, an embodiment of the present invention provides a planar photoemission source based on a multilayer two-dimensional material, including a pump source 1, a cathode power source 2, a gate power source 3, an electron collector 4, and a van der waals heterojunction, where the van der waals heterojunction includes a graphene material 5, an insulating two-dimensional material 6, and a transition metal sulfide material 7, which are sequentially disposed, where:
the pump source 1 interacts with the transition metal sulfide material 7 and is used for valence electron generation transition in the transition metal sulfide material 7;
the working wave band of the pump source 1 can be selected in the visible light range and is matched with the band gap width of the electronic energy band of the transition metal sulfide material 7, and valence electrons in the transition metal sulfide material 7 can be stimulated to generate transition by the interaction of the pump source and the transition metal sulfide material 7;
the cathode power supply 2 is connected with a transition metal sulfide material 7, and the cathode power supply 2 is used for providing electrons;
the grid power supply 3 is connected with the graphene material 5 and used for providing bias voltage for the grid and reducing the material potential barrier;
the graphene material 5 is a two-dimensional material with metal characteristics, is stacked on the insulating two-dimensional material 6 and can be used as an electron source grid to greatly reduce electron scattering;
the insulating two-dimensional material 6 is a non-conductive two-dimensional material, typically a hexagonal boron nitride material, stacked below the graphene material 5 and above the transition metal sulfide material 7, and serves as a dielectric layer to greatly reduce electron scattering; the transition metal sulfide material 7 is a two-dimensional material with semiconductor characteristics, typically a single-layer molybdenum disulfide material, stacked under the insulating two-dimensional material 6, and used as an electron source cathode to greatly reduce electron scattering;
the electron collector 4 is used for collecting the electron beam emitted by the van der waals heterojunction.
The embodiment of the invention utilizes the photoinduced electron emission principle, utilizes the interaction of light and a two-dimensional material, and electrons absorb photons to jump and escape from the material to generate an electron beam with extremely low energy dispersion; the embodiment of the invention introduces a Van der Waals heterojunction structure, realizes a planar electron source by utilizing a plurality of layers of two-dimensional materials, effectively reduces the scattering phenomenon of electrons in the materials, and meets the working conditions of low voltage and low vacuum degree, so the scheme optimizes the quality of electron beams and reduces the cost of the electron source. The electron source emission area of the embodiment of the invention has flexible design and simple and durable emission structure, and has wider application prospect compared with the electron source in the traditional SEM, such as application to integration, array design and the like.
According to the planar photoinduced electron emission source based on the multilayer two-dimensional material, the working waveband of the pump source 1 can be selected in a visible light range, and is matched with the band gap width of an electron energy band of the transition metal sulfide material 7.
According to the planar photoelectron emission source based on the multilayer two-dimensional material, the planar photoelectron emission source also comprises a transparent insulating medium 8 as a substrate, and the transparent insulating medium 8 is positioned at the lower layer of the Van der Waals heterojunction.
As shown in fig. 2-3, in the planar photoemission source according to an embodiment of the present invention, the cathode power supply 2 and the gate power supply 3 are respectively prepared by sputtering on the transparent dielectric substrate. Common materials of the metal electrode structures 2 and 3 include gold, silver, aluminum, and the like. The Van der Waals heterojunction structure comprises a graphene material 5, an insulating two-dimensional material 6 and a transition metal sulfide material 7 from top to bottom. Wherein the graphene material 5 is in contact with the grid power supply 3 and the transition metal sulfide 7 is in contact with the cathode power supply 2. The insulating two-dimensional material 6 ensures that the graphene material 5 is not conducted with the transition metal sulfide material 7. The Van der Waals heterojunction is prepared by a bulk material mechanical stripping-transferring method, and has an area of 10 μm2-100μm2The thickness is 1nm-10 nm.
As shown in fig. 4, in a planar photoemission source based on a multilayer two-dimensional material according to another embodiment of the present invention, a cathode power supply 2 (i.e., a cathode electrode 2) and a gate power supply 3 (i.e., a gate electrode 3) are prepared by performing e-beam lithography and sputtering on a transition metal sulfide material 7 and a graphene material 5. Common materials of the metal electrode structures 2 and 3 include gold, silver, aluminum, and the like. The Van der Waals heterojunction structure comprises a graphene material 5, an insulating two-dimensional material 6 and a transition metal sulfide material 7 from top to bottom. Wherein the graphene material 5 is in contact with the gate electrode 3 and the transition metal sulphide 7 is in contact with the cathode electrode 2. The insulating two-dimensional material 6 ensures that the graphene material 5 is not conducted with the transition metal sulfide material 7. The Van der Waals heterojunction is prepared by chemical vapor deposition, and has an area of 0.01-2cm2The thickness is 1-10 nm.
With respect to the above chip structure, the working principle and the specific working flow of the chip are explained below. The invention aims to combine the multilayer two-dimensional material and the photoinduced electron emission principle, optimize the quality of electron beams and reduce the cost of an electron source. The content is mainly divided into three parts, wherein the first part is a transition metal sulfide material which is incident by pump light and has electron absorption photon transition; the second part is that the potential barrier of an insulating layer and the vacuum level of the graphene material are reduced by applying voltage to the grid cathode; the third portion is that the photogenerated carriers tunnel through and out of the material. The operation of the chip will be described in detail in three sections.
First, pump light is incident on the transition metal sulfide material and the electrons absorb photon transition.
The content of the first part of the chip operation is that the pump light is incident on the transition metal sulfide material and the electrons absorb photon transitions. Electrons are emitted into vacuum from the surface or inside of a material according to the principle of photoemission. The electron beam emitted from the photo-induced electron emission source has extremely low energy dispersion, which is helpful for improving the quality of the electron beam.
Under the irradiation of electromagnetic waves with a frequency higher than a specific frequency, electrons in a substance escape after absorbing energy to form a free space electron beam, i.e., a phenomenon of generating electricity by light is called photo-induced electron emission or photoelectric effect. Light is composed of photons of quantized energy, explained in quantum mechanics by the theory of the particle nature of light. When a beam of light strikes a particular material, the entire energy of the photon can be fully absorbed by an electron in the particular material. The kinetic energy increases immediately after the electron absorbs the energy of the photon, and if the kinetic energy increases enough to overcome the attraction of the atomic nucleus to it, it can escape the surface of the material and become a free electron. Because the frequency of the pumping light is fixed and the energy absorbed by the electrons is consistent, the electrons emitted by the photoelectron emitting source have the same energy theoretically, and therefore the energy dispersion can reach a lower value.
Transition metal chalcogenide materials are a class of semiconductors having the MX2 type, where M represents a transition metal (e.g., Mo, W, etc.) and X represents a chalcogen (e.g., S, Se, Te, etc.). The chemical composition and structural phase of the transition metal sulfide material have diversity, and the energy band structural characteristics of the transition metal sulfide material show abundant electrical characteristics. For example, MoS2, MoSe2, WS2, and WSe2 all have semiconductor characteristics and are applicable to electronic devices. It is worth mentioning that the band structure evolution of such materials depends on the number of layers. As the number of layers decreases, the edge positions of the valence and conduction bands change, and the indirect bandgap of the bulk semiconductor material will change to the direct bandgap of the single layer semiconductor material. The momentum of valence band electrons and conduction band electrons of the direct band gap semiconductor material is naturally matched, so that valence electrons can absorb energy to directly generate transition, and a large number of photon-generated carriers with higher energy and consistent energy can be generated by utilizing the principle.
By utilizing the direct band gap semiconductor characteristic of the single-layer transition metal sulfide material and adding pump light with the incident wavelength matched with the band gap of the material, a large number of photon-generated carriers with higher energy and consistent energy can be excited and generated in the material.
And secondly, applying voltage to the gate cathode to reduce the potential barrier of the insulating layer and the vacuum level of the graphene material.
The second part of the chip operation is that the gate cathode applied voltage lowers the insulating layer barrier and graphene material vacuum level. Lowering the barrier and vacuum levels facilitates the process of electron escape from the material.
As shown in fig. 5, the energy band diagram of the van der waals heterojunction structure composed of three layers of two-dimensional materials is shown, from left to right, as transition metal sulfide (semiconductor characteristic), insulating layer material (insulator characteristic), graphene material (metal characteristic), and free space. The band gap of the semiconductor is narrow, and valence band electrons are likely to enter a conduction band through band-to-band transition; the band gap of the insulator is too large, and electrons do not exist in a conduction band; the conduction band in metal has more electrons. The fermi levels of the three materials remained consistent, indicating that the carrier concentrations remained consistent. The rightmost curve is the vacuum level. The electrons can escape the material as free electrons beyond the vacuum level.
The cathode and the grid will apply a voltage to the transition metal sulfide material and the graphene material, respectively. The fermi levels of the two materials will no longer be equal due to the bias between the two materials. When the gate voltage is higher than the cathode voltage, the fermi level of the graphene material will be relatively lower than that of the transition metal sulfide. When the bias voltage between the gate and the cathode is greater than the work function of the graphene material, the fermi level of the transition metal sulfide will exceed the vacuum level of the graphene material.
When voltages are applied to the cathode and the gate, respectively, an electric field is generated in the insulating layer material. The electric field strength is the ratio of the potential difference to the distance, and because the thickness of the insulating layer material is relatively thin and is in a nanometer scale, even a low gate cathode bias voltage can generate a very strong electric field in the insulating layer. When the strong electric field acts on the insulating layer material, the potential barrier of the insulating layer material is greatly inclined. At this time, the potential barrier between the transition metal chalcogenide material and the insulating layer material will be significantly reduced.
A bias voltage is also present between the electron extraction device and the grid for extracting and directing the exiting free electrons. The presence of this bias also causes the vacuum level to tilt to some extent and the surface barrier to be reduced. The above process is shown in fig. 6.
Third, the photogenerated carriers tunnel through and out of the material.
The content of the third part of the chip operation is that photogenerated carriers tunnel through and out of the material. The energy distribution of photon-generated carriers is concentrated, meanwhile, the two-dimensional material ensures that the scattering phenomenon of electrons in the material is obviously reduced, and free electrons escaping from the material have extremely low energy dispersion, thereby being beneficial to improving the quality of electron beams.
In quantum mechanics, the quantum tunneling effect refers to a quantum behavior in which a microscopic particle can cross a potential barrier. In classical mechanics theory, the particle energy must be higher than the potential barrier to be able to pass through; in quantum mechanics, the tunneling effect is utilized, and even when the energy of a particle is lower than a potential barrier, the particle can pass through the potential barrier.
Photogenerated carriers exist in a conduction band after the interaction of the transition metal sulfide and light. In the face of the reduced potential barrier between the transition metal sulfide and the insulating layer material under the action of a strong electric field, photon-generated carriers have probability to generate quantum tunneling effect and penetrate through the potential barrier to enter the insulating layer material. And then, the current carriers enter the graphene material through the insulating layer material under the action of a strong electric field. Since the insulating layer material has a single-layer structure, electrons are subjected to very little scattering. Because the insulating layer material is of a single-layer structure, electrons are subjected to extremely small scattering, and energy is not lost too much, so that the average energy of carriers entering the graphene material is higher than the vacuum level of the graphene material.
The graphene material is a two-dimensional material with carbon atoms closely packed in a monolayer two-dimensional honeycomb lattice structure. Researches show that the graphene has excellent optical and electrical properties and has important application prospects in the aspects of materials, energy, biology and the like. The graphene has excellent conductivity and high mobility, so electrons are transmitted in the graphene and are not easy to scatter. Meanwhile, graphene is a typical semimetal, and a small part of conduction band and valence band are overlapped. Without excitation, electrons at the top of the valence band flow into the bottom of the conduction band where energy is lower, and thus graphene can be considered to have metallic properties.
The graphene material is of a single-layer structure, the electron mobility of the material is extremely high, and electrons are still subjected to extremely small scattering, so that carriers can directly escape from the material to become free electrons. The electron source has high emission efficiency and extremely low energy dispersion, and the quality of the electron beam is ensured.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. The planar photoinduced electron emission source based on the multilayer two-dimensional material is characterized by comprising a pumping source, a cathode power supply, a grid power supply, an electron collector and a van der Waals heterojunction, wherein the van der Waals heterojunction comprises a graphene material, an insulating two-dimensional material and a transition metal sulfide material which are sequentially arranged, and the planar photoinduced electron emission source comprises a plurality of layers of two-dimensional materials, wherein:
the pump source interacts with the transition metal sulfide material and is used for valence electron generation transition in the transition metal sulfide material;
the cathode power supply is connected with the transition metal sulfide material and is used for providing electrons;
the grid power supply is connected with the graphene material and used for providing bias voltage for the grid and reducing the material potential barrier;
the electron collector is used for collecting the electron beams emitted by the Van der Waals heterojunction.
2. The planar photoemitter based on multilayer two-dimensional material according to claim 1, characterized in that:
the working waveband of the pump source can be selected in a visible light range and is matched with the band gap width of the electronic energy band of the transition metal sulfide material.
3. The planar photoemitter based on multilayer two-dimensional material as claimed in claim 1, further comprising a transparent insulating medium as a substrate, said transparent insulating medium underlying said van der waals heterojunction.
4. The planar photoelectron emission source based on multilayer two-dimensional material of claim 3, wherein the cathode power supply and the gate power supply are respectively prepared by sputtering on the transparent dielectric material substrate.
5. The planar photoemitter electron emitter based on multilayer two-dimensional material as claimed in claim 4, wherein said van der Waals heterojunction is prepared by mechanical peeling-transferring method of bulk material, and has an area of 10 μm2-100μm2The thickness is 1nm-10 nm.
6. The planar photoelectron emission source based on multilayer two-dimensional material of claim 1, wherein the cathode and gate electrodes are prepared by electron beam lithography and sputtering on transition metal sulfide material and graphene material.
7. The planar photoemitter based on multilayer two-dimensional material according to claim 6, which comprisesCharacterized in that the Van der Waals heterojunction is prepared by a chemical vapor deposition method, and the area of the Van der Waals heterojunction is 0.01cm2-2cm2The thickness is 1nm-10 nm.
8. The planar photoemitter electron emitter based on multilayer two-dimensional material as claimed in claim 1, characterized in that said transition metal sulfide material is a semiconductor of the type MX2, wherein M represents a transition metal comprising Mo, W, X represents a chalcogen element, S, Se, Te.
9. The planar photoelectron emission source based on multilayer two-dimensional material of claim 1, wherein the cathode power supply and the gate power supply apply voltages to the transition metal sulfide material and the graphene material, respectively, and when the gate voltage is higher than the cathode voltage, the fermi level of the graphene material is relatively lower than that of the transition metal sulfide; when the bias voltage between the grid and the cathode is larger than the work function of the graphene material, the Fermi level of the transition metal sulfide exceeds the vacuum level of the graphene material.
10. The planar photoelectron emission source based on multilayer two-dimensional material of claim 9, wherein the transition metal sulfide and light interact to generate photon-generated carriers in a conduction band, and the photon-generated carriers generate quantum tunneling effect, penetrate through a potential barrier, enter an insulating layer material, and pass through the insulating layer material under the action of an electric field generated by the insulating layer material, and enter a graphene material; and the average energy of the current carriers entering the graphene material is higher than the vacuum level of the graphene material.
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