JP2019216095A - Electron emission element, manufacturing method of the same, hydrogen production apparatus, and hydrogen manufacturing method - Google Patents

Abstract

To provide an electron emission element capable of stably operating for a long time in liquid.SOLUTION: An electron emission element 100 comprises: a lower electrode substrate 101 made of a metal or a semiconductor; an insulation layer 102 formed on one main surface 101a of the lower electrode substrate; an electron penetration electrode layer 103 formed on the insulation layer 102; an upper electrode layer 104 formed on the electron penetration electrode layer 103; and a protective layer 105 made of a carbon material formed on a front surface of the upper electrode layer 104. The insulation layer 102 has a projection part 102a on an upper layer side, and an upper electrode layer 104 is formed in a region overlapped with the projection part 102a.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electron-emitting device, a method for manufacturing the same, a hydrogen production apparatus using the electron-emitting device, and a method for producing hydrogen.

  In recent years, attention has been focused on nanoscale electron-emitting devices. The transport medium for the electrons emitted by the electron-emitting device is a vacuum. Therefore, the electron-emitting device has a feature that it can operate at high speed without electron scattering in a channel, a feature that it can operate from a low temperature to a high temperature of 300 ° C. or more, and a feature that it has excellent radiation resistance. Due to these features, the electron-emitting device is expected as a device that complements CMOS (for example, see Non-Patent Document 1).

  As the electron-emitting device, a device having a needle-like metal cathode structure of a nano size, a planar device having a MIS (Metal / Insulator / Semiconductor) structure and a MIM (Metal / Insulator / Metal) structure are known. (For example, refer to Patent Documents 1 to 3 and Non-Patent Documents 2 and 3). Planar type electron-emitting devices have high stability of emitted electrons, high straightness of emitted electrons, can operate at low voltage of 10 V or less, can be manufactured by existing semiconductor processes, can operate stably even in low vacuum, It has features such as surface emission.

  Against this background, the present inventors disclose in Patent Document 4 the structure of an electron-emitting device (electron source) that enables highly efficient electron emission by using graphene for the upper electrode. . FIG. 7 is a cross-sectional view schematically showing the configuration of the electron-emitting device 300. The electron-emitting device 300 includes a lower electrode substrate 301, an insulator layer 302, and an electron transmission electrode layer 303. As the material of the electron transmission electrode layer 303, one layer of graphene or several layers of graphite is used. The insulator layer 302 is formed so that a part of the thickness is 5 nm to 20 nm, and functions as an electron emission surface 307. The insulator layer 302 other than the electron emission surface is usually designed to be thicker than the electron emission surface, and has a thickness of about several tens to several hundreds of nm. An upper electrode layer 304 for applying a voltage is formed on a portion of the electron transmission electrode layer 303 that does not overlap with the electron emission surface 305.

  When a voltage of about 5 V to 20 V is applied between the lower electrode substrate 301 and the upper electrode layer 304, the potential barrier formed on the insulator layer 302 becomes thinner, and the electrons in the lower electrode substrate 301 become quantum mechanical tunneling. As a result, tunneling occurs in the conduction band of the insulator layer 302. Electrons that have entered the conduction band of the insulator layer 302 lose part of their energy due to scattering of lattice vibration, but electrons having energy higher than the work function of the electron transmission electrode layer 303 pass through the electron transmission electrode layer 303. Released into a vacuum. It is known that emitted electrons increase exponentially with applied voltage. Conversely, even if the voltage applied to the electron transmission electrode layer 303 is slightly lowered, the number of emitted electrons decreases exponentially.

The total current to tunnel from the lower electrode substrate 301 to the insulating layer 302 and I _c, the current collected in the electron transmission electrode layer 303 of the total current I _c and I _d, the current emitted into vacuum I _e When, holds the Ic _{= I} d + I _e, the I e / _{I c} of the electron emission efficiency. When a defect exists in the insulator layer 302, there is a leak current flowing through the insulator layer 302 without depending on tunneling. Although the leakage current increases the I _c, the electrons constituting the leakage current has no energy, it does not contribute to the emission current I _e. Therefore, when a defect exists in the insulator layer 302, the electron emission efficiency decreases.

  2. Description of the Related Art A technique is known in which an electron-emitting device as described above is immersed in a liquid containing an electrolyte, and the electron-emitting device is operated to irradiate an electron beam to decompose surrounding liquid molecules. By applying this technology to, for example, irradiating an aqueous solution with an electron beam, water in the aqueous solution can be decomposed to generate hydrogen. In Patent Document 5, as an electron source operating in a liquid, an electron source including an electron drift layer and an electron tunnel layer made of nanocrystalline silicon is injected into an aqueous solution, and electrons emitted from the electron source are directly injected. Thus, a method of decomposing water-water molecules in a liquid to generate hydrogen is disclosed.

  In Patent Document 6, by irradiating a hydrocarbon-based fuel with at least one of electrons and ultraviolet rays to excite hydrocarbons into highly active hydrocarbons, and to cause a dehydrogenation reaction using a catalyst, hydrogen gas is produced. A method of occurrence is disclosed. Further, in Patent Document 7, in addition to a method of directly irradiating radiation to water molecules in a liquid, a metal member is distributed in the liquid, the metal member is irradiated with radiation, and the secondary There is also a method of irradiating water molecules with electrons. Also disclosed is a method of irradiating a water molecule in a liquid with a high-energy electron beam generated in a vacuum through a titanium thin film to decompose the water molecule.

JP 2010-244735 A JP 2003-162956 A JP 2001-23511 A JP 2017-45639A Japanese Patent No. 5200240 JP 2004-315305 A JP 2002-338201 A

H. H. Busta, J .; Micromech. Microeng. 2, (1992) 43-74. K. Yokoo et al. , J. et al. Vac. Sci. Technol. B 11, (1993) 429-432. T.A. Kusunoki et al. , Jpn. J. Appl. Phys. 32, (1993) L1695-L1697. Hiroyasu Kubota “Silicon material technology in the 65 nano age”

  It has been found that a metal upper electrode constituting an electron-emitting device does not corrode unless accompanied by electron emission, but may corrode when accompanied by electron emission. Therefore, it is considered difficult to operate the electron-emitting device stably in the liquid for a long time and keep emitting electrons efficiently.

  When an electron-emitting device that is not immersed in a liquid is used as disclosed in Patent Document 6, it is necessary to heat the catalyst, which causes a problem that energy consumption increases. Further, as disclosed in Patent Document 7, when radiation is used, it is difficult to manage the radiation, so that it cannot be performed at an arbitrary place. When irradiating water molecules in a liquid with an electron beam through a titanium thin film, the electron beam requires energy of about 10 V or more in order to transmit through the titanium thin film. The problem is that the energy consumption increases.

  The present invention has been made in view of the above circumstances, and can be used in any place, is stable for a long time in liquid, and can be operated at low energy, an electron-emitting device, and a method for manufacturing the same. Another object of the present invention is to provide a hydrogen production apparatus using an electron-emitting device and a hydrogen production method.

  In order to solve the above problems, the present invention employs the following means.

(1) An electron-emitting device according to one embodiment of the present invention includes a lower electrode substrate made of a metal or a semiconductor, an insulator layer formed on one main surface of the lower electrode substrate, and formed on the insulator layer. An electron transmission electrode layer, an upper electrode layer formed on the electron transmission electrode layer, and a protective layer made of a carbon material formed on the surface of the upper electrode layer, wherein the insulator layer is an upper layer. A projection on the side, and the upper electrode is formed in a region overlapping with the projection.

(2) In the electron-emitting device according to (1), the carbon material may be graphene.

(3) In the electron-emitting device according to (1), the carbon material may be graphite.

(4) In the electron-emitting device according to any one of (1) to (3), at least an outer portion of the upper electrode layer that is in contact with the protective layer may be made of nickel.

(5) In the electron-emitting device according to any one of (1) to (4), a region of the electron-transmitting electrode layer that does not overlap with the protrusion of the insulator layer is the same as the protective layer. A layer made of a material having a thickness of 1 μm or less may be formed.

(6) In the electron-emitting device according to any one of (1) to (4), a region of the electron-transmissive electrode layer that does not overlap with the protrusion of the insulator layer is exposed. preferable.

(7) In the electron-emitting device according to any one of (1) to (6), an outer peripheral portion of the upper electrode layer is formed as a protrusion of the insulator layer in a plan view from a stacking direction of each layer. It is preferable to be inside the outer peripheral portion on the tip side.

(8) The method for manufacturing an electron-emitting device according to one embodiment of the present invention is a method for manufacturing an electron-emitting device according to any one of the above (1) to (7), wherein A step of forming the protective layer using a CVD method in a range of minutes or less.

(9) An apparatus for producing hydrogen according to one embodiment of the present invention, comprising: the electron-emitting device according to any one of (1) to (7); a container that stores the electron-emitting device and a non-electrolyte solution; Gas collecting means for collecting gas in the container, wherein an electron emission surface of the electron emission element located on one main surface of the lower electrode substrate is in contact with the non-electrolyte solution.

(10) In the hydrogen production device according to (9), the container includes a first storage unit that stores the non-electrolyte solution, and a second storage unit that stores the electron-emitting device. It is preferable that an opening for communicating the one housing part and the second housing part with each other is provided, and the electron emission surface is in contact with the non-electrolyte solution at the communication part.

(11) A hydrogen production method according to one embodiment of the present invention is a hydrogen production method using the hydrogen production apparatus according to any one of (9) and (10), wherein the electron-emitting device comprises A step of applying a voltage between the upper electrode layer and the lower electrode substrate so that the upper electrode layer side has a high potential, and a step of collecting hydrogen gas generated in the container with the application of the voltage, Having.

  The electron-emitting device of the present invention has high corrosion resistance to a liquid such as ethanol because the surface of the upper electrode layer is covered with a protective layer made of a carbon material having low reactivity. Therefore, the electron-emitting device of the present invention can suppress the corrosion of the upper electrode layer even in a liquid, operate for a long time, operate with low energy, and continue to emit electrons efficiently. Further, since the electron-emitting device of the present embodiment does not need to use radiation and has no difficulty in management, hydrogen can be produced using the electron-emitting device at an arbitrary place.

  ADVANTAGE OF THE INVENTION According to the hydrogen production apparatus of this invention, the electron produced | generated by the electron-emitting device can be continuously made to collide with the molecule in a liquid directly. Therefore, regardless of whether the liquid is an electrolyte solution or a non-electrolyte solution, the molecule can be decomposed at a low voltage, and a useful element such as hydrogen can be obtained.

FIG. 2A is a cross-sectional view of the electron-emitting device according to the first embodiment of the present invention. FIG. 3B is an enlarged view of one end of the cross section of the electron-emitting device in FIG. FIGS. 4A to 4E are cross-sectional views in a manufacturing process of the electron-emitting device according to the first embodiment. FIGS. 2A and 2B are cross-sectional views in a manufacturing process of the electron-emitting device according to the first embodiment. FIG. 2 is a sectional view of a hydrogen production apparatus including the electron-emitting device of FIG. 1. FIG. 1A is a diagram illustrating a circuit configuration when operating an electron-emitting device as Example 1 of the present invention. (B) It is a graph which shows the measurement result about the electron current emitted by the electron emission element of (a). 6 is a graph showing a result of analyzing a gas collected using a hydrogen production apparatus as Example 2 of the present invention. FIG. 9 is a cross-sectional view of a conventional electron-emitting device.

  Hereinafter, an electron-emitting device according to an embodiment to which the present invention is applied, a method for manufacturing the same, a hydrogen production apparatus, and a hydrogen production method will be described in detail with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent. In addition, the materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be appropriately changed and implemented without changing the gist thereof.

<First embodiment>
(Emission device)
FIG. 1 is a sectional view of an electron-emitting device 100 according to the first embodiment of the present invention. The electron-emitting device 100 includes a lower electrode substrate 101, an insulator layer 102 formed on one main surface 101 a of the lower electrode substrate, an electron transmission electrode layer 103 formed on the insulator layer 102, and an electron transmission electrode 103. An upper electrode layer 104 formed on the layer 103 and a protective layer 105 formed on the surface of the upper electrode layer 104 are provided.

  The lower electrode substrate 101 is made of a metal or semiconductor material. Examples of the metal material include gold, silver, aluminum, and titanium. Examples of the semiconductor material include silicon and the like. When a semiconductor material is used, it is desirable to select highly doped n-type silicon or the like from the viewpoint of easily emitting electrons. Here, the lower electrode substrate 101 has a plate shape, but may have another shape such as a cylindrical shape. Each layer formed on one main surface 101a of the lower electrode substrate has a shape that follows the shape of the lower electrode substrate 101. For example, when the lower electrode substrate 101 has a plate shape, the insulating layer 102 and the electron transmission electrode layer 103 formed on one main surface 101a are flat layers. Further, for example, when the lower electrode substrate 101 has a cylindrical shape, the insulating layer 102 and the electron transmission electrode layer 103 formed on the outer wall surface or the inner wall surface are layers having a curved surface that follows the shape of the lower electrode substrate 101. Become.

The insulator layer 102 is formed so as to cover substantially the entire one main surface 101a of the lower electrode substrate. Examples of the material of the insulator layer 102 include SiO ₂ , Al ₂ O ₃ , and TiO ₂ .

  The insulator layer 102 has a thin film portion in the electron emission region 106 when the electron emission element 100 is operated, and has a protrusion 102 a on an upper layer side (the electron transmission electrode layer 103 side) in a region excluding the electron emission region. Having. The insulator layer 102 is formed thicker in the region having the protruding portion 102a than in the electron emission region.

  The thickness of the thin film portion of the insulator layer 102 is preferably 5 nm to 30 nm, more preferably 5 nm to 15 nm. Further, the thickness of the insulator layer 102 in the thick film portion having the protruding portion 102a is preferably from 100 nm to 1000 nm, and more preferably from 100 nm to 500 nm.

  By forming the thin film portion thin, scattering of electrons emitted from the lower electrode substrate 101 in the insulator layer 102 can be suppressed. Furthermore, since the energy barrier is small for the electrons to be tunneled through the thin film portion, the voltage required for the tunneling can be reduced.

  The electron transmission electrode layer 103 is formed so as to cover at least the surface of the thin film portion of the insulator layer 102, preferably, the entire surface of the insulator layer 102. The electron transmission electrode layer 103 is desirably formed thin so as to have high electron transmission performance, more preferably has a thickness of 7 nm or less, and further preferably has a thickness of about one atom.

  From the viewpoint of efficient electron emission, a region of the electron transmission electrode layer 103 that does not overlap with the protrusion 102a of the insulator layer, that is, the electron emission region 106 is preferably not covered and exposed. However, a layer made of an unavoidable residue or the like generated when the protective layer 105 is formed, that is, a layer made of the same material as the protective layer 105 may be formed in the electron emission region 106 in some cases. However, the thickness of the electron transmission electrode layer 103 is desirably suppressed to 10 nm or less so that the effective thickness of the electron transmission electrode layer 103 does not increase excessively and does not hinder the electron emission function.

  Further, the electron transmission electrode layer 103 preferably has a high electric resistance, and more preferably has a sheet resistance of about 10 kΩ / □. In order to satisfy such electric resistance, in order to cover the stepped region of the insulator layer 102 without causing distortion or wrinkles, the electron transmission electrode layer 103 is formed of a polycrystal rather than a single crystal. More preferably, the size (grain size) of one crystal is about 200 to 500 nm.

  As a material of the electron transmission electrode layer 103, for example, polycrystalline graphene, graphite, or the like, which has a high electron transmission probability and a high electric resistance, may be used.

  The upper electrode (contact electrode) layer 104 is formed outside the electron emission region, that is, on the region having the protrusion 102a of the insulator layer so as not to hinder the transmission of the emitted electrons. The electron transmission electrode layer 103 may be interposed between the protrusion 102a of the insulator layer and the upper electrode layer 104 in some cases. The upper electrode layer 104 supports energization of the electron transmission electrode 103, and suppresses a decrease in potential due to the influence of defects, as described later.

  The material of the upper electrode layer 104 may be a material having high conductivity, and examples thereof include gold, silver, aluminum, chromium, titanium, nickel, and a laminate thereof. Among them, nickel is particularly preferable from the viewpoint of forming a protective layer made of a carbon material because nickel is a material that easily grows a carbon material on the surface.

  Although the entire upper electrode layer 104 may be made of only nickel, in order to facilitate formation of the protective layer, the outer portion of the upper electrode layer 104 is made of nickel and the inner portion is made of another conductive material. May be. The outer portion here is a portion having a thickness of about 30 nm or more from the surface of the upper electrode layer 104.

  The protective layer 105 is made of a carbon material such as graphene, graphite, and diamond. The thickness of the protective layer 105 is preferably 10 nm or more and 1 μm or less. If the protective layer 105 is thinner than 10 nm, the corrosion of the upper electrode layer 104 cannot be sufficiently suppressed. If the protective layer 105 is thicker than 1 μm, the protection layer 105 protrudes from the protrusion 102 a of the insulator layer, and the protruding portion covers the outer peripheral portion of the electron emission surface, thereby hindering electron emission.

  FIG. 1B is an enlarged view of one end S in the cross section of the electron-emitting device 100 in FIG. In a plan view from the stacking direction L of each layer, the outer peripheral portion 104b of the upper electrode layer 104 may overlap the outer peripheral portion 102b on the tip side (the upper side in FIG. 1B) of the protrusion 102a of the insulator layer. However, it is preferably inside (outside the right side in FIG. 1B) the outer peripheral portion 102b. That is, in a plan view from the lamination direction L, it is preferable that the outer peripheral portion 104b of the upper electrode layer has an offset on the inner side with respect to the outer peripheral portion 102b of the insulator layer. When there is an offset, a portion of the protective layer 105 that covers the side of the upper electrode layer 104 can be formed on the offset, so that the protective layer 105 does not protrude onto the electron emission surface 106 and the electron emission surface A large effective area of 106 can be secured.

(Method of manufacturing electron-emitting device)
A method for manufacturing the electron-emitting device 100 will be described with reference to FIGS. 2 (a) to 2 (e), 3 (a) and 3 (b). The electron-emitting device 100 can be manufactured mainly through the following steps A1 to A6.

(Process A1)
First, as shown in FIG. 2A, on one main surface 101a of the lower electrode substrate 101, an insulating layer (insulating film) 102 having a sufficient insulating performance and a thickness (about 300 nm) is formed. A method for forming the insulator layer 102 is not particularly limited, and examples thereof include a thermal oxidation method, a chemical vapor deposition (CVD) method, and an anodic oxidation method.

For example, when highly doped n-type silicon is used for the lower electrode substrate 101, the surface of the n-type silicon substrate is thermally oxidized at a high temperature of about 800 ° C. to 1100 ° C., thereby forming a dense insulator layer 102. An SiO ₂ film can be formed. Alternatively, for example, when an aluminum substrate is used for the lower electrode substrate 101, an alumina layer can be formed as the insulator layer 102 by anodizing the surface of the aluminum substrate. Alternatively, the insulator layer 102 may be formed by a known method such as sputtering.

(Process A2)
Next, a portion 102B of the insulator layer 102 overlapping with the electron emission surface 101A of the lower electrode substrate 101 is etched to expose the electron emission surface 101A as shown in FIG. As a method for etching, a method that does not damage the lower electrode substrate 101 serving as a base is desirable, and for example, etching with buffered hydrofluoric acid can be mentioned.

(Process A3)
Next, the object to be processed after the process A2 is subjected to a cleaning process such as RCA cleaning in order to reduce defects as much as possible, and then thermally oxidized, and as shown in FIG. An insulator layer 102C (102) is formed on the surface 101A. The thermal oxidation here can be performed using, for example, an electric furnace or the like. Regarding the processing temperature and the processing time, the thickness of the insulator layer 102C formed on the electron emission surface 101A is about 4 nm to 20 nm. It is desirable to adjust as follows.

  If the insulator layer 102C is thinner than 4 nm, a tunnel current flows between the lower electrode substrate 101 and the subsequently formed electron transmission electrode layer 103 before a sufficient voltage is applied. Even if a tunnel current flows with the potential of the electron transmission electrode layer 103 being lower than the work function, the electrons in the tunnel current have low energy and cannot pass through the electron transmission electrode layer 103, so that the corresponding amount of electrons is emitted. Can not be obtained. Therefore, the insulator layer 102C needs to be thicker than 4 nm.

  If the thickness of the insulating layer 102C is greater than 20 nm, the traveling distance of the tunneled electrons in the insulating layer 102C becomes longer, and energy is lost due to scattering of lattice vibration during the movement. Therefore, also in this case, the number of electrons having energy equal to or higher than the work function decreases, and the electron emission efficiency deteriorates. According to the results of repeated studies by the present inventors, the thickness of the insulator layer 102C is preferably 20 nm or less, and more preferably 10 nm or less.

  At the point of time after the step A3, the insulator layer 102 includes a thin film portion 102C overlapping the electron emission surface 101A and a thick film portion 102A overlapping the upper electrode formed later, and a step is formed between the two. State. The thick film portion 102A corresponds to the protrusion 102a shown in FIG.

(Step A4)
Next, as shown in FIG. 2D, an electron transmission electrode layer 103 is formed on the insulator layer 102 formed through the step (A3) by exposing to a mixed atmosphere of gallium vapor and methane gas. . The processing temperature and the processing time are desirably adjusted so that the thickness of the formed electron transmission electrode layer 103 is about 0.3 nm to 10 nm.

(Process A5)
Next, by forming the upper electrode 104 only on the surface of the electron transmission electrode layer 103 at a position overlapping the thick film portion 102A of the insulator layer 102, the electron-emitting device 100 of the present embodiment can be obtained. .

  There are two methods for forming the upper electrode 104. One is a method of forming a metal film constituting an upper electrode on the entire surface and then patterning / etching only a portion overlapping with the electron emission surface 101A using photolithography. The other is to apply a photoresist on the electron emission surface 101 by photolithography, form a metal film constituting the upper electrode 104, and finally dissolve the photoresist with a solution, This is a method of lifting off the metal film.

  Either method may be used, but since the portion of the electron transmission electrode layer 103 that overlaps with the electron emission surface 101A is very thin, this portion is not damaged during etching. For example, when the electron transmission electrode layer 103 is made of graphene or graphite, a method using an acid, an alkali, or the like that does not etch the graphene may be used. It is desirable not to perform dry etching by plasma or the like.

  On the other hand, in the lift-off method, it is desirable to completely remove the photoresist applied to the portion overlapping the electron emission surface 101A. If the organic component of the photoresist remains as a residue on the electron emission surface, the electron emission efficiency decreases. In an experiment conducted by the present inventors, a normal electron emission surface free of organic components was obtained by removing the photoresist with an organic solvent and then heating it at about 300 ° C. in a vacuum.

  The material of the upper electrode 104 is not particularly limited. However, when the electron transmission electrode layer 103 is made of graphene or graphite, it is preferable that the material has a strong adhesive force to the electron transmission electrode layer 103, for example, when the graphene film is formed. Catalyst metals, specifically, iron, cobalt, nickel and the like can be mentioned. In addition, a material having a generally strong adhesive force, for example, chromium, titanium, or the like can also be used. The upper electrode 104 may have a two-layer structure in which a thin film of these metals is formed only on a portion in contact with graphene and a film of another metal is formed thereon.

(Process A6)
Finally, by forming a protective layer 105 made of a carbon material such as graphene or graphite on the surface (exposed surface) of the upper electrode layer 104, the electron-emitting device 100 of the present embodiment can be obtained. As a method for forming the protective layer 105, it is necessary to select a method in which the protective layer 105 is not formed in the electron emission region 106, or a method of removing the protective layer 105 once formed in the electron emission region 106. is there. This is because if the protective layer 105 is formed in the electron emission region 106, the electron transmission electrode layer 103 becomes thicker, and the electron emission efficiency decreases.

  The formation of the protective layer 105 only on the surface of the upper electrode layer 104 can be performed by various methods. For example, as shown in FIG. 3A, a film (protective layer 105) made of a carbon material such as graphene or graphite is formed on the entire surface of the object by thermal CVD or plasma CVD, and FIG. As shown in b), there is a method in which a portion of the film overlapping with the electron emission region 106 is removed by etching using photolithography.

  In the case of using a thermal CVD method or a plasma CVD method, the processing temperature is preferably set to 600 ° C. or higher and 800 ° C. or lower, and the processing time is preferably set to 5 minutes to 60 minutes.

  When the upper electrode layer 104 is formed of a metal material such as graphene or graphite on which a carbon material is easily grown, it can be selectively grown only on the surface of the upper electrode layer 104. In this case, it is possible to save time and effort such as shielding the carbon material film from being formed in the electron emission region and removing the carbon material film formed in the electron emission region later. Nickel, titanium, iron, cobalt, copper, and the like are given as examples of the metal material on which the carbon material easily grows.

  For example, when the upper electrode layer 104 is made of nickel and the thermal CVD method is used, graphene does not grow on the electron emission surface, grows only on the surface of the upper electrode layer 104, and covers the surface without gaps. . As an example, by flowing 2 sccm of methane gas and 100 sccm of argon gas in a furnace maintained at about 750 ° C. and performing a thermal CVD process for 30 minutes, a graphene film is not formed on the electron emission surface. A state in which only the surface of the upper electrode layer made of nickel is completely covered has been confirmed in experiments by the present inventors.

(Hydrogen production equipment)
FIG. 4 is a sectional view of the hydrogen production apparatus 10 according to the present embodiment. The hydrogen production apparatus 10 mainly includes the electron-emitting device 100 of the present embodiment, a container 11 for storing the electron-emitting device 100 and a liquid, and gas collecting means 12 for collecting gas in the container 11. . As the liquid, any of an electrolyte solution and a non-electrolyte solution may be used. In the present embodiment, a case where a non-electrolyte solution is used will be described as an example. The non-electrolyte contained in the non-electrolyte solution is not particularly limited, but includes a useful element such as hydrogen, for example, ethanol, methanol, 1-propanol, 2-propanol, kerosene (kerosene), light oil, and the like. Is mentioned.

  The container 11 has high airtightness, and includes a first storage portion 11A for storing the non-electrolyte solution M and a second storage portion 11B for storing the electron-emitting device 100. The container 11 has an opening 11C that connects (connects) the first housing 11A and the second housing 11B to each other. Although the shape of the container 11 is not limited, in the present embodiment, an opening 11C is provided in a part of the side wall of the cylindrical first housing 11A, and the second housing protrudes outside the container 11. 11B illustrates a case where the opening 11C is provided so as to cover the opening 11C.

  The electron emission surface 100a of the electron emission element 100, which is located on one main surface 101a of the lower electrode substrate, is exposed to the space inside the first accommodation portion 11A at the opening 11C and is accommodated in the first accommodation portion 11A. In contact with (exposed to) the non-electrolyte solution M. When the electron transmission electrode layer 103 is the outermost layer (when it is exposed), the surface of the electron transmission electrode layer 103 corresponds to the electron emission surface 100a. When the electron transmission electrode layer 103 is covered with a layer (not shown) made of the same material as the protective layer 105, the surface of the layer corresponds to the electron emission surface 100a.

  The gas collecting means 12 is a device such as a pump, and is disposed outside the container 11. The top 11D in which a cavity is formed inside the container 11, more specifically, inside the container 11 via a pipe 12A. That is, it is connected to the upper part in the vertical direction. Thereby, gas such as hydrogen generated by decomposing the non-electrolyte solution M can be collected outside the container 11.

  The upper electrode layer 104 is connected to the positive electrode terminal 13 provided around the opening 11C in the second housing portion 11B, and the wiring drawn therefrom is connected to the positive electrode power source 14 arranged outside the container 11. It is connected. Further, the lower electrode substrate 101 is connected to the negative electrode terminal 15 provided on the side wall facing the opening 11C in the second housing portion 11B, and the wiring drawn out therefrom is connected to the negative electrode power supply 16. . The wiring structure shown here is an example, and another wiring structure may be applied.

(Hydrogen production method)
The hydrogen production method using the hydrogen production apparatus 10 of the present embodiment mainly includes the following steps B1 and B2.

(Process B1)
First, a predetermined voltage is applied between the upper electrode layer 104 and the lower electrode substrate 101 constituting the electron-emitting device 100 using the positive electrode power supply 14 and the negative electrode power supply 15 so that the upper electrode layer 104 side has a high potential. Apply. At this time, it is preferable to adjust so that the voltage applied between the electron transmission electrode layer 103 and the lower electrode substrate 101 is about 5 to 20 V.

  As a result, electrons in the lower electrode substrate 101 are tunneled and injected into the conduction band of the insulator layer 102, and accelerated toward the electron transmission electrode layer 103 by an electric field generated in the insulator layer 102. . The accelerated electrons have energy of about 8 to 13 eV, preferably about 10 eV, pass through the electron transmission electrode layer 103, and are emitted to the outside of the electron emission element 100 on the electron emission surface 100a. Here, since the electron emission surface 100a is in contact (covered) with the non-electrolyte solution M at the opening 11C, the emitted electrons are immediately injected into the non-electrolyte solution M. Molecules contained in the non-electrolyte solution M are decomposed by collision of the injected electrons to generate a gas such as hydrogen.

  It is known that the collision cross section of an electron with respect to a hydrogen molecule becomes remarkably large when the energy of the electron is 10 to 20 eV, and at this time, it is most efficiently decomposed into a hydrogen atom. It is considered that the same tendency is generally observed even when the molecule that collides with the electron has a C—H bond. Therefore, by setting the voltage conditions as described above, electrons in the energy band of 10 to 20 eV can be efficiently injected, and hydrogen can be efficiently generated.

(Process B2)
Next, the generated gas is drawn out of the container 11 and collected using the gas collecting means 12. By separating the collected gas using a known method (cryogenic separation method, adsorption separation method, membrane separation method, or the like), a gas of a desired element can be produced. According to the production method of the present embodiment, as will be described later as an example, hydrogen gas can be produced particularly efficiently, but carbon is deposited as a solid, and at the same time, other gas components such as oxygen and nitrogen Can also be manufactured at the same time.

  As described above, in the electron-emitting device 100 according to the present embodiment, since the surface of the upper electrode layer 104 is covered with the protective layer 105 made of a carbon material having low reactivity, a liquid such as ethanol, water, or the like is formed. Has high corrosion resistance. Therefore, in the electron-emitting device 100 of the present embodiment, even in a liquid, corrosion of the upper electrode layer 104 is suppressed, and the electron-emitting device 100 is operated for a long time, operates at low energy, and continuously emits electrons efficiently. it can. In addition, since the electron-emitting device 100 of the present embodiment does not need to use radiation and has no management difficulty, hydrogen can be produced using the electron-emitting device at an arbitrary place.

  According to the hydrogen production apparatus 10 of the present embodiment, the electrons generated by the electron-emitting device 100 can be continuously caused to directly collide with the molecules in the liquid. Therefore, regardless of whether the liquid is an electrolyte solution or a non-electrolyte solution, the molecule can be decomposed at a low voltage, and a useful element such as hydrogen can be obtained.

  Hereinafter, the effects of the present invention will be made clearer by examples. In addition, this invention is not limited to a following example, In the range which does not change the summary, it can change suitably and can implement.

(Example 1)
The electron current generated in the electron-emitting device 100 according to the embodiment was measured. FIG. 5A is a diagram schematically illustrating a cross-sectional configuration of the electron-emitting device 100 and a circuit configuration for operating the electron-emitting device 100 according to the first embodiment.

  The lower electrode substrate 101 was grounded, and a voltage of 0 to 15 V was applied between the lower electrode substrate 101 and the upper electrode layer 104 so that the upper electrode layer 104 side had a high potential. Further, a substantially flat counter electrode substrate 107 is disposed at a position about 5 mm away from the electron emission surface 106, and between the upper electrode 104 and the counter electrode substrate 107, the counter electrode substrate 107 side has a high potential. A voltage of 1000 V was applied.

FIG. 5B is a graph showing the measurement results of the electron emission characteristics of the electron-emitting device 100 under the above voltage conditions. The horizontal axis of the graph indicates the voltage (V) applied between the lower electrode substrate 101 and the upper electrode layer 104. The vertical axis on the left side of the graph indicates the areal density (A / cm ² ) of the electron current emitted from the electron emission surface 106 in a vacuum. The right vertical axis of the graph of the current (cathode current) I _c to tunnel from the lower electrode substrate 101 on the insulating layer 102, the current (anode current) to be recovered to the electron transmissive electrode layer 103 ratio of I _e (I _e / I _c ), indicating the electron emission efficiency (%). The cathode current is indicated by a blue line, the anode current is indicated by a red line, and the electron emission efficiency is indicated by a green line.

  From the measurement results, it is possible to confirm electron emission at an efficiency of about 10% in a voltage range of about 8 to 13 V. From this result, when the electron-emitting device 100 incorporated in the hydrogen production apparatus 10 of the above embodiment is operated in the range of 8 to 13 V, electrons having an energy of about 8 to 13 eV are transferred to the non-electrolyte solution M. It is thought to be injected.

(Example 2)
The gas generated from the non-electrolyte solution M was analyzed using the hydrogen production apparatus 10 according to the above embodiment. FIG. 6 is a graph showing the result of analyzing the gas collected by the gas collecting means 12 using a gas chromatograph. The horizontal axis of the graph indicates the time (retention time) (minutes) until each gas component reaches a predetermined detector. The vertical axis of the graph indicates the signal intensity of each gas component.

  The oxygen and nitrogen signals are due to air originally remaining in the container 11. The peak of hydrogen can be confirmed, and it can be confirmed that the non-electrolyte solution M is decomposed to generate hydrogen. It can be seen that the concentration of hydrogen is 0.011% by using the calibration curve. Since the volume of this container 11 was 175 mL, the volume of generated hydrogen can be calculated to be 0.0192 mL, that is, 0.86 μmol. The conditions required to generate this hydrogen were an emission current of 1 nA, an applied voltage of 15 V, and a decomposition time of 28 minutes, so that the amount of power supplied to the liquid at this time was determined to be 6.9 nWh. Therefore, in this embodiment, the electric energy required to generate 1 mol of hydrogen is 8.02 mWh / mol, and the energy efficiency (theoretical value) in the case of electrolyzing water is 80.6 Wh / mol, which is 10,000 times higher. It can be seen that decomposition is possible.

  Although the loss in the electron-emitting device 100 is not taken into account in the calculation here, even if this loss is estimated to be 90% from the result that the efficiency shown in FIG. Can be decomposed at 1000 times the efficiency of electrolysis.

From the graph of FIG. 6, it can be seen that CO ₂ is not generated. The signal intensity of CO ₂ should originally have a peak at a retention time of 8 minutes and 30 seconds, but this has not been detected. On the other hand, when the electron-emitting device 100 was operated without being incorporated in the hydrogen production apparatus 10, it was confirmed that carbon was deposited on the upper electrode layer 104 and the like. From these results, it is possible to obtain the elements contained in the non-electrolyte solution M in desired states. For example, when the non-electrolyte solution M is decomposed using the hydrogen production apparatus 100, hydrogen It can be seen that carbon is deposited as a solid as it is while generating carbon.

100 electron-emitting device 100a electron-emitting surface 101 lower electrode substrate 102 insulator layer
102a ··· Projecting portion 102A ··· Thick film portion 102B ··· Etched portion of insulator layer 102C ··· Thin film portion 103 ··· Electron transmitting electrode layer 104 ··· Upper electrode layer 105 ··· Protective layer 106 electron emission region 107 counter electrode substrate 10 hydrogen production device 11 container 11A first storage portion 11B second storage portion 11C opening 11D ··· Top section 12 ··· Gas collecting means 12A ··· Pipe 13 ··· Positive electrode terminal 14 ··· Positive power supply 15 ··· Negative terminal 16 ··· Negative power supply L ··· Stack direction M ··· Electrolyte solution S: end of electron-emitting device

Claims (11)

A lower electrode substrate made of metal or semiconductor,
An insulator layer formed on one main surface of the lower electrode substrate,
An electron transmission electrode layer formed on the insulator layer,
An upper electrode layer formed on the electron transmission electrode layer,
A protective layer made of a carbon material formed on the surface of the upper electrode layer,
An electron-emitting device, wherein the insulator layer has a protrusion on an upper layer side, and the upper electrode is formed in a region overlapping the protrusion.   2. The electron-emitting device according to claim 1, wherein the carbon material is graphene.   2. The electron-emitting device according to claim 1, wherein the carbon material is graphite.   4. The electron-emitting device according to claim 1, wherein at least an outer portion of the upper electrode layer that is in contact with the protective layer is made of nickel. 5.   5. A layer having a thickness of 1 [mu] m or less and made of the same material as the protective layer is formed in a region of the electron transmission electrode layer that does not overlap with the protrusion of the insulator layer. The electron-emitting device according to any one of the above.   5. The electron-emitting device according to claim 1, wherein a region of the electron transmission electrode layer that does not overlap with the protrusion of the insulator layer is exposed.   The planar electrode according to claim 1, wherein an outer peripheral portion of the upper electrode layer is located inside an outer peripheral portion on a tip end side of the protruding portion of the insulator layer in a plan view from a lamination direction of each layer. Item 14. The electron-emitting device according to Item 1. It is a manufacturing method of the electron-emitting device of Claims 1-7,
A method for manufacturing an electron-emitting device, comprising a step of forming the protective layer by a CVD method at a temperature of 600 ° C. to 800 ° C. and 5 minutes to 60 minutes. An electron-emitting device according to any one of claims 1 to 7,
A container containing the electron-emitting device and the non-electrolyte solution,
Gas collecting means for collecting gas in the container,
A hydrogen production apparatus, wherein an electron emission surface of the electron emission element located on one main surface of the lower electrode substrate is in contact with the non-electrolyte solution. The container has a first storage portion that stores the non-electrolyte solution, and a second storage portion that stores the electron-emitting device, and an opening that communicates the first storage portion and the second storage portion with each other. Part
The hydrogen production apparatus according to claim 9, wherein the electron emission surface is in contact with the non-electrolyte solution at the communication portion. A hydrogen production method using the hydrogen production apparatus according to claim 9,
Applying a voltage between the upper electrode layer and the lower electrode substrate constituting the electron-emitting device so that the upper electrode layer side has a high potential;
Collecting a hydrogen gas generated in the container with the application of a voltage.

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