Electronic wire source

Abstract

This invention provides an electron beam source that is more stable and has superior electron emission performance compared to conventional semiconductor photocathodes that use Cs on the surface of an NEA state. [Solution] An electron beam source having a laminated structure of multiple layers, wherein the laminated structure includes a conductive layer and a layer of organic energy level control material, and the layer of organic energy level control material is the outermost layer of the laminated structure or a layer in its vicinity.

Description

[Technical Field]

[0001] This invention relates to an electron beam source. More specifically, it relates to an electron beam source that can be used in various fields that utilize electron beams, including electron microscopes and electron beam lithography. [Background technology]

[0002] Electron beams are used in a variety of fields, including electron microscopy, electron beam lithography, electron beam processing of materials, sterilization, and defect inspection processes in semiconductor manufacturing. In recent years, there has been a growing demand for higher performance electron sources to improve the capabilities of electron microscopes and to detect even finer defects in semiconductor manufacturing. Therefore, electron sources that meet these demands are being investigated. To meet the demand for higher performance, semiconductor photocathodes are being considered as electron sources. It has been disclosed that a semiconductor photocathode, in which an InGaN layer is formed on a sapphire substrate and a negative electron affinity (NEA) surface is formed on top of it using Cs, has high quantum efficiency and durability (see Non-Patent Literature 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] "Electron emission characteristics of InGaN photocathodes using different alkali metals," Proceedings of the 85th Autumn Meeting of the Japan Society of Applied Physics, 2024. [Overview of the project] [Problems that the invention aims to solve]

[0004] To emit electrons, the work function of the electron source surface must be reduced. In the semiconductor photocathode described above, the work function is reduced by forming a surface with a negative electron affinity (NEA) state using Cs. However, because Cs has low stability, an ultra-high vacuum state is required to create an NEA state surface, and this semiconductor photocathode has the problem of having a short lifespan. Furthermore, there is room for further improvement in the electron emission performance of conventional semiconductor photocathodes.

[0005] This invention has been made in view of the above-mentioned circumstances, and aims to provide an electron source that is more stable and has superior electron emission performance compared to conventional semiconductor photocathodes using Cs on the surface of an NEA state. [Means for solving the problem]

[0006] The inventors of the present invention investigated electron sources that are more stable and have superior electron emission performance compared to conventional semiconductor photocathodes, and found that a device having a laminated structure in which a conductive layer is included and an organic energy level control material layer is the outermost layer or a layer near the outermost layer becomes an electron source that is more stable and has superior electron emission performance compared to conventional semiconductor photocathodes, thus arriving at the present invention.

[0007] In other words, the present invention is as follows. [1] An electron beam source having a stacked structure of multiple layers, The electron beam source is characterized in that the laminated structure includes a conductive layer and a layer of organic energy level control material, wherein the layer of organic energy level control material is the outermost layer of the laminated structure or a layer in its vicinity.

[0008] [2] The electron source according to [1], characterized in that the work function of the surface is 3.5 eV or less.

[0009] [3] The electron source according to [1], characterized in that the organic energy level control material is a phenanthroline derivative represented by the following general formula (1). [ka] (In general formula (1), R 1 and R 2 are the same or different and each represent a dialkylamino group or an alkoxy group. m 1 and m 2 are the same or different and each represent a number of 1 or 2.)

[0010] [4] The electron beam source according to [1], wherein the organic energy level control material is a hexahydropyrimidopyrimidine compound represented by the following general formula (2).

[0011] [Chemical formula]

[0012] (In general formula (2), R 3 represents an aromatic hydrocarbon group which may have a substituent, an aromatic heterocyclic group, an arylalkylene group, a 2- to 4-valent chain or cyclic hydrocarbon group, a group formed by combining two or more of these groups, or a group formed by combining one or more of these groups with a nitrogen atom. n 1 is an integer of 1 to 4.)

[0013] [5] The electron beam source according to [1], wherein the laminated structure includes a semiconductor layer.

[0014] [6] The electron beam source according to [1], wherein the laminated structure includes a carbon material layer.

[0015] [7] The electron beam source according to [1], which is a photocathode. Effects of the Invention

[0016] The electron source of the present invention has higher stability and superior electron emission performance compared to conventional semiconductor photocathodes, making it suitable for use as an electron source in various fields that utilize electron beams, such as electron microscopes, electron beam processing of materials, sterilization, and defect inspection processes in semiconductor manufacturing. [Brief explanation of the drawing]

[0017] [Figure 1] This figure shows the method for measuring the electron emission performance of the samples prepared in Examples 1-3 and Comparative Examples 1 and 2. [Figure 2] This figure shows the results of measuring the number of photons irradiated and the number of electrons emitted for samples 1 and 5 of Example 1, by applying a sample bias of -10V and varying the incident light energy in the range of 2 to 7.8V. [Figure 3] This figure shows the results of observing the relationship between the thickness of the Cs layer and the work function while forming a Cs layer on a glass substrate by vacuum deposition in a vacuum environment of 10⁻⁵ Pa, using the rotational Kelvin probe method to observe the change in the work function. [Figure 4] This figure shows the results of observing the change in the work function over time using the rotating Kelvin probe method while forming a Cs layer on a glass substrate by vacuum deposition in a vacuum environment of 10⁻⁵ Pa. [Figure 5] This figure shows the results of observing the change in work function of samples 6-9, prepared in Examples 6-9, using the rotating Kelvin probe method under a vacuum of 10⁻⁵ Pa. [Modes for carrying out the invention]

[0018] The present invention will be described in detail below. Furthermore, combinations of two or more of the individual preferred embodiments of the present invention described below are also preferred embodiments of the present invention.

[0019] The electron beam source of the present invention has a laminated structure including at least a conductive layer and a layer of an organic energy level control material, and is characterized by comprising the layer of the organic energy level control material as an outermost surface layer of the laminated structure or a layer in the vicinity thereof. In the semiconductor photocathode using Cs described above, the work function of the photocathode surface is lowered by forming a surface in a negative electron affinity (NEA) state using Cs, thereby facilitating electron emission. The present invention has found that the work function of the surface can also be lowered and electron emission can be facilitated by forming a layer of an organic energy level control material as an outermost surface layer of the laminated structure or a layer in the vicinity thereof instead of Cs. Since the organic energy level control material is more stable than Cs, the 10 -9 order ultra-high vacuum required when forming a Cs layer is not necessary, and 10 -5 layer formation can be performed even in a vacuum state on the order of Pa, and production is easier compared to a semiconductor photocathode using Cs. In addition, the electron beam source of the present invention has dramatically improved stability and a long service life compared to conventional electron beam sources using Cs. Conventional electron beam sources can only be used under 10 -9 order ultra-high vacuum, but the electron beam source of the present invention can be used even at a vacuum degree on the order of 10 -5 Pa and even at a vacuum degree close to the atmosphere. Furthermore, the electron beam source of the present invention, in which a surface in a negative electron affinity (NEA) state is formed by an organic energy level control material, is superior to a semiconductor photocathode using Cs also in that it has higher electron emission performance than the case where Cs is used.

[0020] The electron source of the present invention is characterized by having a layer of organic energy level control material as the outermost layer or a layer in its vicinity in a laminated structure. A layer in the vicinity of the outermost layer means a layer located within two layers of the outermost layer, but when the layer of organic energy level control material is a layer in the vicinity of the outermost layer, it is preferable that it is the layer one layer from the outermost surface, i.e., a layer adjacent to the outermost surface. Even when the layer of organic energy level control material is not the outermost layer of the laminated structure, the electron source of the present invention can exhibit excellent electron emission performance by forming a layer located on the outermost side of the layer of organic energy level control material with an appropriate material.

[0021] The electron source of the present invention has a layer of organic energy level control material above the conductive layer in a laminated structure, with the electron-emitting surface facing upwards. As long as the layer of organic energy level control material is above the conductive layer, the laminated structure may consist only of these two layers, or it may include another layer. If another layer is included, the position of the other layer is not particularly limited and may be located below the conductive layer, between the conductive layer and the layer of organic energy level control material, or above the layer of organic energy level control material. Furthermore, there are no particular restrictions on the number of layers included in the laminated structure, but it is preferable to have 2 to 7 layers. More preferably, it is 2 to 5 layers.

[0022] The electron source of the present invention preferably has a surface work function of 3.5 eV or less. When the surface work function is 3.5 eV or less, the electron source exhibits superior electron emission performance. More preferably, the surface work function is 3.0 eV or less, and even more preferably 2.6 eV or less, which is below the wavelength energy of a general-purpose blue LED. The work function of the electron source surface can be determined by the Kelvin probe method or photoelectron spectroscopy.

[0023] The organic energy level control material included in the electron source of the present invention is not particularly limited as long as it is an organic material with electron injection properties that can form layers by vapor deposition. However, using a phenanthroline derivative represented by the following general formula (1) as the organic energy level control material is one of the preferred embodiments of the present invention. An electron beam source using this phenanthroline derivative as an organic energy level control material will have excellent electron emission performance.

[0024] [ka]

[0025] (In general formula (1), R 1 , R 2 These are identical or distinct, representing a dialkylamino group or an alkoxy group. 1 , m 2 (These represent the number 1 or 2, which may be the same or different.)

[0026] R in the above general (1) 1 , R 2 These represent a dialkylamino group or an alkoxy group, either identical or distinct. The dialkylamino group is preferably one having an alkyl group with 1 to 20 carbon atoms, such as a methyl group or an ethyl group. More preferably, it is a dialkylamino group having an alkyl group with 1 to 10 carbon atoms. The two alkyl groups of the dialkylamino group may have the same number of carbon atoms or different numbers of carbon atoms. Also preferred are amino groups formed by linking two alkyl groups, such as cyclic amino groups like a piperidino group, a pyrrolidino group, or a morpholino group. Examples of alkoxy groups include linear or branched alkoxy groups having 1 to 20 carbon atoms, such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, tert-butoxy, pentyloxy, hexyloxy, heptyloxy, and octyloxy groups. More preferably, linear or branched alkoxy groups having 1 to 10 carbon atoms are used.

[0027] Furthermore, using a hexahydropyrimidopyrimidine compound represented by the following general formula (2) as an organic energy level control material is also one of the preferred embodiments of the present invention. The hexahydropyrimidopyrimidine compound represented by the general formula (2) below interacts with inorganic compounds contained in adjacent layers, thereby reducing the work function of the inorganic compounds. For this reason, when this hexahydropyrimidopyrimidine compound is used as an organic energy level control material, it also becomes an electron source with excellent electron emission performance.

[0028] [ka]

[0029] (In general formula (2), R 3 n represents an aromatic hydrocarbon group which may have substituents, an aromatic heterocyclic group, an arylalkylene group, a 2- to 4-valent linear or cyclic hydrocarbon group, or a group formed by combining two or more of these groups, or a group formed by combining one or more of these groups with a nitrogen atom. 1 (This is an integer between 1 and 4.)

[0030] In the above general formula (2), R 3 This represents an aromatic hydrocarbon group which may have substituents, an aromatic heterocyclic group, an arylalkylene group, a 2- to 4-valent linear or cyclic hydrocarbon group, or a group formed by combining two or more of these groups, or a group formed by combining one or more of these groups with a nitrogen atom. The aromatic hydrocarbon group and aromatic heterocyclic group are preferably those having 3 to 30 carbon atoms, more preferably those having 4 to 24 carbon atoms, and even more preferably those having 5 to 20 carbon atoms. Aromatic hydrocarbon groups include compounds consisting of only one aromatic ring, such as benzene; compounds in which multiple aromatic rings are directly bonded to one carbon atom, such as biphenyl and diphenylbenzene; and groups formed by removing one to four hydrogen atoms from any of the aromatic rings of fused ring aromatic hydrocarbon compounds, such as naphthalene, anthracene, phenanthrene, and pyrene. Aromatic heterocyclic groups include compounds consisting of only one aromatic heterocyclic ring, such as thiophene, furan, pyrrole, oxazole, oxadiazole, thiazole, thiadiazole, imidazole, pyridine, pyrimidine, pyrazine, and triazine; compounds in which multiple of these compounds consisting of only one aromatic heterocyclic ring are directly bonded to each other by a single carbon atom (such as bipyridine); and groups formed by removing 1 to 4 hydrogen atoms from any aromatic heterocyclic ring of fused cyclic heteroaromatic hydrocarbon compounds such as quinoline, quinoxaline, benzothiophene, benzothiazole, benzimidazole, benzoxazole, indole, carbazole, dibenzofuran, dibenzothiophene, acridine, and phenanthroline. Examples of arylalkylene groups include groups that combine the above-mentioned aromatic hydrocarbon group with an alkylene group having 1 to 3 carbon atoms. The 2-4 valent linear or cyclic hydrocarbon group is preferably one with 1 to 12 carbon atoms, more preferably one with 1 to 6 carbon atoms, and even more preferably one with 1 to 4 carbon atoms. The linear hydrocarbon group may be linear or branched. Also, R 3 This may also be a group formed by combining two or more of the above-mentioned aromatic hydrocarbon groups, aromatic heterocyclic groups, arylalkylene groups, or divalent to tetravalent chain hydrocarbon groups. Furthermore, R 3 The group may be formed by combining one or more of the above-mentioned aromatic hydrocarbon groups, aromatic heterocyclic groups, arylalkylene groups, or 2- to 4-valent linear hydrocarbon groups with a nitrogen atom. Examples of such groups include trialkylamines such as trimethylamine and groups formed by removing 1 to 4 hydrogen atoms from triphenylamine.

[0031] The above-mentioned aromatic hydrocarbon group, aromatic heterocyclic group, or arylalkylene group may have one or more monovalent substituents. Monovalent substituents include: fluorine atom; haloalkyl groups such as fluoromethyl, difluoromethyl, and trifluoromethyl groups; linear or branched alkyl groups having 1 to 20 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, and tert-butyl groups; cyclic alkyl groups having 5 to 7 carbon atoms such as cyclopentyl, cyclohexyl, and cycloheptyl groups; linear or branched alkoxy groups having 1 to 20 carbon atoms such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, tert-butoxy, pentyloxy, hexyloxy, heptyloxy, and octyloxy groups; nitro groups; cyano groups; alkylamino groups having 1 to 10 carbon atoms such as methylamino, ethylamino, dimethylamino, and diethylamino groups; cyclic amino groups such as pyrrolidino, piperidino, and morpholino groups; and diphenylamino Examples include: diarylamino groups such as carbazolyl groups; acyl groups such as acetyl groups, propionyl groups, and butyryl groups; C2-C30 alkenyl groups such as styryl groups; C5-C20 aryl groups (specific examples of aryl groups are the same as those for aromatic hydrocarbon groups above) which may be substituted with halogen atoms such as fluorine atoms, or C1-C20 alkyl groups, alkoxy groups, amino groups, etc.; heterocyclic groups containing one or more C4-C20 nitrogen atoms, sulfur atoms, or oxygen atoms (heterocyclic groups may consist of only one ring, or may be compounds in which multiple compounds consisting of only one aromatic heterocyclic ring are directly bonded to one carbon atom each, or may be fused heterocyclic groups. Specific examples of heterocyclic groups include the specific examples of aromatic heterocyclic groups above); ester groups, thioether groups, etc. These groups may be substituted with halogen atoms, heteroatoms, alkyl groups, aromatic rings, etc.

[0032] n in the general formula (2) above 1 This is an integer from 1 to 4, but is preferably 2 or 3. Specific examples of hexahydropyrimidopyrimidine compounds having the structure represented by the general formula (2) above include, for example, the compounds represented by the following formulas (2-1) to (2-34).

[0033] [ka] [ka] [ka] [ka] [ka]

[0034] The hexahydropyrimidopyrimidine compounds represented by the above general formula (2) can be synthesized using a halogen compound containing iodine, bromine, chlorine, and fluorine and hexahydropyrimidopyrimidine as starting materials, as shown in formula (3) below, by Ullmann coupling reaction, Buchwald-Hartwig amination reaction, or nucleophilic substitution reaction.

[0035] [ka]

[0036] The average thickness of the organic energy level control material layer is preferably 0.1 to 10 nm, and more preferably 1 to 5 nm. The average thickness of layers in organic energy level-controlled materials can be measured, for example, by a stylus step meter or spectroscopic ellipsometry.

[0037] The material for the conductive layer of the electron source of the present invention can be any material capable of supplying electrons, and examples include oxides such as ITO (indium tin oxide), IZO (indium zinc oxide), FTO (fluorine tin oxide), In3O3, SnO2, Sb-containing SnO2, Al-containing ZnO, as well as Al, Au, Pt, Ag, Cu, or alloys containing these materials.

[0038] The average thickness of the conductive layer is not particularly limited, but is preferably 5 to 10,000 nm, and more preferably 10 to 1,000 nm. The average thickness of the conductive layer can be measured using a stylus-type step meter or spectroscopic ellipsometry.

[0039] The electron source of the present invention preferably includes a semiconductor layer in its stacked structure. Including a semiconductor layer between the conductive layer and the organic energy level control material layer reduces the binding of electrons from the conductive layer, improving the electron extraction efficiency, and thus the electron source exhibits superior electron emission performance. The semiconductor layer can be an inorganic semiconductor such as InGaN or GaAs (Ga-based or InP-based), an organic semiconductor, or a perovskite semiconductor, which is an organic-inorganic composite material such as CH3NH3PbI3. Although the fabrication process for inorganic semiconductors is somewhat complex, electron sources using inorganic semiconductors can be expected to have high photoelectron emission intensity. Organic semiconductors are relatively easy to fabricate and have excellent stability in air. Perovskite semiconductors are easy to fabricate, and electron sources using perovskite semiconductors can be expected to have high photoelectron emission intensity, but there are challenges in terms of stability in air. When using organic semiconductors, it is easy to make electron sources flexible, whereas when using inorganic semiconductors or perovskite semiconductors, it is difficult to make electron sources flexible. As such, each semiconductor has its own characteristics, so when using semiconductors, it is best to select a semiconductor that suits the application of the electron source and the performance required. In addition to vacuum deposition, semiconductor layers can also be formed by coating when using organic semiconductors or perovskite semiconductors, and by sputtering when using inorganic semiconductors.

[0040] The average thickness of the semiconductor layer is not particularly limited, but is preferably 1 to 1000 nm, and more preferably 10 to 500 nm. The average thickness of the semiconductor layer can be measured using a stylus-type step meter or spectroscopic ellipsometry.

[0041] The electron source of the present invention preferably includes a layer of carbon material in its laminated structure. Including a layer of carbon material between the conductive layer and the organic energy level control material is expected to increase the electron emission intensity. This is because carbon material is used as a material for field emission and is therefore considered suitable for electron emission. As carbon materials, carbon black, carbon nanotubes, etc., can be used, but carbon nanotubes are preferred among these.

[0042] The average thickness of the carbon material layer is not particularly limited, but is preferably 1 to 1000 nm, and more preferably 10 to 300 nm. The average thickness of the carbon material layer can be measured using a stylus step meter or spectroscopic ellipsometry.

[0043] When the electron source of the present invention has a layer of organic energy level control material as a layer near the outermost layer of the laminated structure, examples of materials for the layer above (closer to the outermost surface of) the organic energy level control material layer include metals with excellent coordination ability such as Al.

[0044] The average thickness of the upper layer of the above-mentioned organic energy level control material is not particularly limited, but is preferably 0.1 to 100 nm, and more preferably 1 to 10 nm. The average thickness of the upper layer of an organic energy level-controlled material can be measured using a stylus step meter or spectroscopic ellipsometry.

[0045] Specific examples of the layered structure of the electron source of the present invention include a structure consisting of two layers: a conductive layer and a layer of organic energy level control material; a structure having three layers in this order: a conductive layer, a semiconductor layer, and a layer of organic energy level control material; a structure having three layers in this order: a conductive layer, a layer of carbon material, and a layer of organic energy level control material; a structure having three layers in this order: a conductive layer, a layer of carbon material, a semiconductor layer, and a layer of organic energy level control material; and structures in which a layer of a metal with excellent coordination ability, such as Al, is further formed above or below the layer of organic energy level control material in these structures. This metal may form clusters and have a plasmon resonance effect.

[0046] The electron source of the present invention may have a laminated structure formed on a substrate, including a conductive layer and a layer of organic energy level control material. Examples of substrate materials include resin materials and glass materials. Examples of resin materials used for substrates include polyethylene terephthalate, polyethylene naphthalate, polypropylene, cycloolefin polymer, polyamide, polyethersulfone, polymethyl methacrylate, polycarbonate, and polyarylate. Examples of glass materials used for substrates include quartz glass and soda glass.

[0047] When the electron source of the present invention includes a substrate, the average thickness of the substrate is preferably 0.1 to 3 mm, and more preferably 0.1 to 1 mm. The average thickness of the circuit board can be measured using a digital multimeter or calipers.

[0048] The electron source of the present invention can be any device capable of extracting electrons from a conductive layer, but it is preferably a photocathode that extracts electrons photoexcited in a semiconductor layer. A photocathode can be suitably used in applications such as scanning electron microscopes, electron guns, free electron laser accelerators, electron beam holography devices, electron beam lithography devices, electron beam curing devices, electron beam sterilization devices, electron beam germicidal devices, plasma generators, atomic element generators, spin-polarized electron beam generators, cathode doluminescence devices, inverse photoelectron spectroscopy devices, semiconductor inspection devices, and photocatalysts that promote chemical reactions.

[0049] The electron source of the present invention can be fabricated by sequentially forming each layer constituting the stacked structure using a vacuum deposition method. The manufacturing of the electron source of the present invention involves 10 such that are necessary when forming the Cs layer. -9 Ultra-high vacuum on the order of Pa is not required, 10 -5 Manufacturing is possible even under vacuum conditions of around Pa. [Examples]

[0050] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means "parts by weight" and "%" means "mass%".

[0051] Example 1 A glass substrate with aluminum-Phen-pyrrd and 100nm ITO film deposited on it is placed in a vacuum chamber, and 5 × 10 -5 The surface was vacuumed to Pa. Then, 1 nm aluminum and 3 nm Phen-pyrrd were deposited in a stepwise vacuum deposition process. During deposition, the surface work function was measured using a rotary Kelvin probe system. The thickness of each layer was measured using a palpation-type step meter. The same procedure was followed in the following examples and comparative examples.

[0052] Examples 2 and 3, Comparative Examples 1 and 2 In the same manner as in Example 1, a sample having the laminated structure shown in Table 1 was placed on a glass substrate on which an ITO film had been deposited, under a vacuum of 5 × 10⁻¹⁰. -5 The samples were fabricated by vacuum deposition under a Pa environment, and the work function of the surface was measured. The thickness of each layer is shown in Table 1. The compounds constituting the layered structure are as follows: v-DABNA / F16CuPc and HN-D2 / B4PyMPM are semiconductor layers, while Phen-pyrrd and Py-hpp2 are organic energy level control materials.

[0053] For the samples prepared in Examples 1-3 and Comparative Examples 1 and 2, a rotating Kelvin probe apparatus was used to position the sample and probe as shown in Figure 1. A UV light, Photocure200, was used as the light source without a focusing lens. The light intensity was set to maximum, the sample side was grounded, and a voltage of +200V was applied to the probe side. The current value during light irradiation was measured. The atmospheric pressure during measurement was 5 × 10⁻⁶ -5 The level was approximately Pa. The results are shown in Table 1.

[0054] [Table 1]

[0055] [ka]

[0056] Examples 4 and 5 After washing the ITO substrate with purified water, acetone, and isopropanol, a single-walled carbon nanotube aqueous solution (EC-DL, Meijo Nanocarbon Co., Ltd., concentration 0.05 wt%) was spray-coated onto the ITO substrate to form a carbon nanotube layer. Anest Iwata's TOF-5RB-05 was used for spray coating, and the substrate was heated to 120°C on a hot plate while spraying at a pressure of 0.3 MPa for 1 second each time for a predetermined number of times. The spray-coated substrate was then immersed in 60°C hot water for 2 minutes to remove the dispersant, and then dried with a nitrogen gun. The thickness of the carbon nanotube layer was approximately 100 nm. Afterward, a vacuum of 10°C was applied.-6 Sample 5 was prepared by forming an Al layer (thickness 1 nm) and a Phen-pyrrd layer (thickness 3 nm) in that order under a Pa environment. For samples 1 and 5 of Example 1, a sample bias of -10V was applied, and the energy of the incident light was varied in the range of 2 to 7.8V. The number of photons irradiated and the number of electrons emitted were measured, respectively, and the quantum efficiency was calculated. The number of photons irradiated and the number of electrons emitted were measured using a photomultisupplier and a subfemtoampere source meter, respectively. The results are shown in Figure 2. The measurement results showed that sample 1 achieved quantum efficiencies of 0.1-5% at 3.7-7.7 eV. This was higher than the quantum efficiency of elemental Cs deposited on molybdenum reported in a previous study (Journal of Materials Chemistry C9, 13013 (2021)). Furthermore, sample 5, which had a carbon nanotube layer, showed even greater quantum efficiency, achieving a high quantum efficiency of over 10% particularly with light irradiation at around 7.4 eV.

[0057] Comparative Example 3 Vacuum degree 10 -5 We observed the change in work function using the rotating Kelvin probe method while forming a Cs layer on a glass substrate by vacuum deposition in a Pa environment. Figure 3 shows the relationship between the thickness of the Cs layer and the work function, and Figure 4 shows the change in the work function over time. As can be seen in Figure 3, it was confirmed that the work function decreased to about 2.3 eV as the film thickness increased due to Cs deposition. However, as can be seen in Figure 4, at a vacuum of 10 -5 Under Pa conditions, the work function rapidly increased due to the degradation of Cs, reaching approximately 2.5 eV, and then gradually increased again over time.

[0058] Examples 6-9 Vacuum degree 10 -5 Sample 6 was prepared by vacuum deposition in a Pa environment, in which an ITO layer (thickness 100 nm), a Cs layer (thickness 6 nm), and a Phen-pyrrd layer (thickness 3 nm) were formed in that order on a glass substrate. Furthermore, samples 7-9 were prepared in the same manner as sample 6, except that the Cs layer of sample 6 was replaced with an Al layer, an Au layer, and an Ag layer, respectively. The thickness of the Al, Au, and Ag layers was 1 nm in all cases. Vacuum degree 10 -5 For samples 6-9 under a Pa environment, the change in work function was observed using the rotating Kelvin probe method. The results are shown in Figure 5. From a comparison with Comparative Example 3, it was found that by using Phen-pyrrd, a vacuum level of 10 is achieved even when using Cs. -5 It was confirmed that the stability of the work function of the samples under a Pa environment improved dramatically. Despite the work function of sample 6 being smaller than that of the sample in comparative example 3, its stability was confirmed to be extremely high. Furthermore, using Al as the metal further improves stability, and it was confirmed that using precious metals such as Ag or Au can further improve stability, although the work function is relatively large.

Claims

1. An electron beam source having a multilayered structure, The electron beam source is characterized in that the laminated structure includes a conductive layer and a layer of organic energy level control material, wherein the layer of organic energy level control material is the outermost layer of the laminated structure or a layer in its vicinity.

2. The electron source according to claim 1, characterized in that the work function of the surface is 3.5 eV or less.

3. The electron source according to claim 1, characterized in that the organic energy level control material is a phenanthroline derivative represented by the following general formula (1). 【Chemistry 1】 (In general formula (1), R １ , R ２ These are identical or distinct, representing a dialkylamino group or an alkoxy group. １ , m ２ (These represent the number 1 or 2, which may be the same or different.)

4. The electron source according to claim 1, characterized in that the organic energy level control material is a hexahydropyrimidopyrimidine compound represented by the following general formula (2). 【Chemistry 2】 (In general formula (2), R ３ n represents an aromatic hydrocarbon group which may have substituents, an aromatic heterocyclic group, an arylalkylene group, a 2- to 4-valent linear or cyclic hydrocarbon group, or a group formed by combining two or more of these groups, or a group formed by combining one or more of these groups with a nitrogen atom. １ (This is an integer between 1 and 4.)

5. The electron beam source according to claim 1, characterized in that the stacked structure includes a semiconductor layer.

6. The electron beam source according to claim 1, characterized in that the laminated structure includes a layer of carbon material.

7. The electron source according to claim 1, characterized in that it is a photocathode.

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