WO2018016291A1 - Electron emitting material and electron emitting element - Google Patents
Electron emitting material and electron emitting element Download PDFInfo
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- WO2018016291A1 WO2018016291A1 PCT/JP2017/023982 JP2017023982W WO2018016291A1 WO 2018016291 A1 WO2018016291 A1 WO 2018016291A1 JP 2017023982 W JP2017023982 W JP 2017023982W WO 2018016291 A1 WO2018016291 A1 WO 2018016291A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
- H01J1/02—Main electrodes
- H01J1/13—Solid thermionic cathodes
- H01J1/14—Solid thermionic cathodes characterised by the material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
- H01J1/02—Main electrodes
- H01J1/34—Photo-emissive cathodes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J45/00—Discharge tubes functioning as thermionic generators
Definitions
- the present disclosure relates to an electron emission material used when heat energy or light energy is converted into electric energy and an electron emission element using the electron emission material.
- Examples of the electron-emitting device include a field emission device and a thermionic power generation device.
- a field emission device utilizes a phenomenon in which electrons are emitted by applying a high electric field to metal and semiconductor materials, and electrons are emitted from the cathode electrode by applying a voltage to the cathode electrode and the anode electrode.
- the thermoelectric power generation element converts the thermal energy into electric energy by utilizing the phenomenon that the hot electrons are emitted from the surface of the high temperature electrode.
- the thermoelectrons are emitted by raising the temperature of the emitter electrode, and the collector Reach the electrode.
- thermoelectric power generation element various studies have been made to improve the power generation output.
- a thermionic power generation element using diamond that exhibits negative electron affinity (hereinafter referred to as “NEA”) and has an effect of lowering the work function (hereinafter referred to as “lower work function”) is provided.
- NAA negative electron affinity
- lower work function the work function
- the energy level of the conduction band of diamond exceeds the vacuum level. In this state, the electrons in the conduction band have sufficient energy to jump out into the vacuum, so that the electrons in the conduction band can be easily released into the vacuum.
- photoexcited thermionic power generation (hereinafter referred to as “PETE”) using electrons excited by light in order to perform highly efficient thermionic power generation at a low temperature.
- PETE photoexcited thermionic power generation
- electrons are emitted from an emitter electrode by irradiating the emitter electrode with light and once exciting the electrons of the electrode material with the light, followed by heating. That is, the photo-excited thermionic power generation emits electrons at a lower temperature than the thermionic power generation element, and the power generation output is further improved.
- the work function is made lower than that of the uncoated diamond film surface.
- an alkali metal such as Li
- the interaction between the diamond film and the alkali metal is weak because the alkali metal does not terminate the surface of the diamond film by a chemical bond. Therefore, when diamond whose surface is coated with an alkali metal is used as an electrode material, when the electrode temperature is increased, the alkali metal covering the diamond surface is detached from the diamond surface. That is, diamond whose surface is coated with an alkali metal cannot maintain the work function of the surface at a high temperature at a low temperature.
- the work function can be kept low while suppressing the separation of the alkali metal from the diamond surface at high temperature by terminating the diamond film surface with Li via oxygen.
- the present disclosure has been made in view of the above points, and an object thereof is to provide an electron-emitting material that can maintain a low work function during high-temperature driving and an electron-emitting device using the material.
- An electron emission material is an electron emission material including a diamond film, oxygen bonded to the surface of the diamond film, and a termination metal bonded to the diamond film via oxygen,
- the film is an N-type diamond semiconductor doped with impurities, and the termination metal contains at least one of Na, K, Rb, Cs, and Mg.
- the work function of the diamond film can be lowered by terminating the surface of the diamond film with at least one metal of Na, K, Rb, Cs, and Mg via oxygen.
- the metal that terminates the diamond film is referred to as “termination metal” for convenience.
- the terminal metal when the terminal metal is bonded to the diamond film through oxygen, a Coulomb force acts between the terminal metal and oxygen, and these are Coulomb bonded. As a result, even if the termination metal is heated to a high temperature, the termination metal is hardly separated from the diamond film by the above-described Coulomb coupling. Therefore, by adopting such a configuration, the terminal metal is stable without being detached from the surface of the diamond film even when driven at a high temperature, and the electron emission material can maintain the work function of the surface low. In the following description, for the sake of convenience, the property that the terminal metal does not separate from the surface of the diamond film even when the temperature is raised is referred to as “high temperature stability”.
- the electron emission material according to the second aspect is laminated on the diamond film, oxygen bonded to the surface of the diamond film, a first metal layer bonded to the diamond film via oxygen, and the first metal layer.
- the diamond film is an N-type diamond semiconductor doped with impurities, and the first metal layer is composed of Li, Na, K, Rb, Cs, and Mg.
- the second metal layer includes at least one of Li, Na, K, Rb, Cs, and Mg, which is different from the first metal layer.
- the above-mentioned first metal layer is provided on the surface of the diamond film, and the above-mentioned second metal layer is laminated on the first metal layer.
- high temperature stability and low work function can be achieved by combining a metal containing at least one of the alkali metal and Mg of the first metal layer with oxygen through oxygen.
- the termination metal of the second metal layer can provide an electron emission material in which the surface of the diamond film is further reduced in work function while ensuring the high temperature stability by the first metal layer.
- the electron-emitting device includes a pair of electrodes consisting of an emitter electrode and a collector electrode arranged so as to face each other.
- the emitter electrode is an electrode that emits electrons, and is formed of, for example, an electron-emitting material according to the first aspect.
- the work function can be kept low while ensuring high temperature stability.
- the electron emission material according to the first aspect as the emitter electrode, the efficiency of electron emission from the emitter electrode can be increased. Thereby, an electron-emitting device with high electron emission efficiency can be obtained.
- the electron emission material 10 of 1st Embodiment is demonstrated with reference to FIG.
- substrate 1 As the substrate 1, for example, Mo or Si can be used.
- the electron emission material 10 is a material that emits electrons from the material surface, and can be used as an emitter electrode that emits electrons in, for example, a thermionic power generation element, a photoexcitation electron emission element, a photoexcitation thermoelectron generation element, or the like.
- the electron-emitting material 10 of the present embodiment is bonded to the diamond film 11 which is a diamond semiconductor, oxygen bonded to the surface of the diamond film 11 (hereinafter referred to as “bonded oxygen 12”), and the diamond film 11 via the oxygen. It is comprised with the termination
- the diamond film 11 is composed of an N-type diamond thin film doped with impurities such as nitrogen and phosphorus at a high concentration, for example, 1 ⁇ 10 20 cm ⁇ 3 to 1 ⁇ 10 21 cm ⁇ 3 .
- impurities such as nitrogen and phosphorus at a high concentration, for example, 1 ⁇ 10 20 cm ⁇ 3 to 1 ⁇ 10 21 cm ⁇ 3 .
- this dope concentration the higher one is preferable. This is because, when the doping concentration is low, the number of excited thermal electrons is small and the efficiency of electron emission is low.
- N (nitrogen), P (phosphorus), As (arsenic), Sb (antimony), S (sulfur), etc. are used, for example.
- the bonded oxygen 12 does not exist at the time of forming the diamond film 11, it was formed on the surface of the diamond film 11 by ozone oxidation treatment, oxygen plasma surface treatment, or oxygen radical treatment in the manufacturing process described later. Is.
- the terminating metal 13 is formed by forming bonded oxygen 12 on the surface of the diamond film 11 and then performing vapor deposition in a manufacturing process described later, and terminating the diamond film 11 through the bonded oxygen 12. It is.
- the termination metal 13 is a metal containing at least one of, for example, Na (sodium), K (potassium), Rb (rubidium), Cs (cesium), and Mg (magnesium).
- the termination metal 13 may be a combination of two or more kinds of alkali metals, a combination of alkali metals and Mg, or a combination of two or more kinds of alkali metals and Mg.
- FIG. 2A shows a case where the surface of the diamond film 11 constituting the electron emission material is terminated with oxygen
- FIG. 2B shows a case where the surface of the diamond film 11 constituting the electron emission material is terminated with oxygen via Cs.
- the polarity of the electron affinity can be changed by the termination structure on the surface of the diamond film 11 constituting the electron emission material 10.
- a metal containing at least one of an alkali metal and Mg via oxygen is used as a termination structure, extremely stable NEA can be obtained, and highly efficient thermoelectrons can be obtained. Release can be realized in a long time.
- the present inventors have conducted intensive studies on the termination metal 13 from the viewpoint of achieving both a low work function on the diamond film surface and high-temperature stability.
- the termination metal 13 is an alkali metal
- the work function of the diamond film 11 tends to decrease as the atomic weight of Li, Na, K, Rb, Cs increases, and Na, K, Rb
- the efficiency of electron emission is increased by selecting Cs as compared with Li.
- the termination metal 13 is an alkali metal
- the alkali metal tends to be detached from the diamond film 11 at high temperatures as the number of Li, Na, K, Rb, Cs and their atomic numbers increases. I found out. That is, there is a trade-off relationship between lowering the work function and stability at high temperature, and the work function can be lowered by appropriately selecting the termination metal 13 according to the driving temperature, and electron emission with excellent electron emission efficiency.
- Material 10 can be used.
- the diamond film 11 is formed, for example, as an N-type diamond film doped with nitrogen by, for example, a microwave CVD (abbreviation of chemical vapor deposition) method.
- a microwave CVD abbreviation of chemical vapor deposition
- a mixed gas obtained by diluting CH 4 with H 2 is used as a reactive gas, and for example, N 2 gas is used as a dopant.
- the doping amount of nitrogen is adjusted by adjusting these gas flow rates.
- the substrate 1 when the diamond film 11 is formed on the substrate 1 such as Mo or Si, the substrate 1 is set in a vacuum chamber of microwave CVD. Then, the vacuum chamber is decompressed, and the substrate 1 is heated within a range of 600 to 1100 ° C., for example. Thereafter, a mixed gas obtained by diluting CH 4 with H 2 (CH 4 concentration: 0.05 to 5%) and N 2 gas are introduced into the vacuum chamber. At this time, the mixing ratio of the N 2 gas and the mixed gas is adjusted so that the nitrogen of N 2 becomes 1 to 200, for example, when the carbon of CH 4 in the mixed gas is 1.
- the film forming conditions at this time are adjusted, for example, within a range of a reaction pressure of 40 to 150 Torr and an input power of a microwave power source within a range of 500 to 1500 W. Then, a diamond film 11 having a thickness of, for example, 100 nm is formed while these mixed gases are reacted in the microwave. Thereby, an N-type diamond thin film doped with nitrogen at a high concentration is obtained.
- a thin film of N-type diamond doped with phosphorus at a high concentration can be obtained by replacing the N 2 gas with a PH 3 gas. .
- the diamond film 11 has no particular upper limit because the film thickness dependence on thermoelectric emission has not been confirmed.
- the diamond film 11 has a film thickness of at least 100 nm and the same thickness with no unevenness over the entire surface of the substrate. Preferably it is formed. This is because a defect site that is not formed as a film occurs in the diamond film having a film thickness of less than 100 nm, and when used as the emitter electrode 3, the efficiency of electron emission may be reduced.
- the diamond film 11 has no reason to increase the film thickness more than necessary, but rather increases the manufacturing cost.
- the surface of the diamond film 11 is oxidized using ozone generated by decomposing oxygen with ultraviolet rays, and the surface of the diamond film 11 is terminated with oxygen. Subsequently, the diamond film 11 terminated with oxygen is vacuum-deposited with an alkali metal such as Cs to obtain the electron emission material 10 terminated with Cs via oxygen.
- the termination metal 13 is composed of a plurality of metals
- a plurality of metals can be terminated on the surface of the diamond film 11 by co-evaporating alkali metal or the like from a plurality of deposition sources.
- FIG. 3 shows an example in which the electron-emitting material 10 of the present embodiment is formed as an electrode on the substrate 1 as in FIG. 1, and M1 is a first metal layer 14 to be described later, and M2 is a second metal to be described later. Layer 15 is shown.
- the electron-emitting material 10 of this embodiment includes a diamond film 11, a bonded oxygen 12 bonded to the diamond film 11, a first metal layer 14 bonded to the diamond film 11 via the bonded oxygen 12, and the first metal layer. 14 and a second metal layer 15 stacked on top of each other.
- the 1st metal layer 14 and the 2nd metal layer 15 are comprised by the metal which mentions mutually different later. That is, in the electron emission material 10 of the present embodiment, not only the first metal layer 14 is bonded via the diamond film 11 and the bonded oxygen 12, but in addition, the second metal layer 15 is replaced with the first metal layer 15. 14 is different from that of the first embodiment in that the configuration is stacked on top of 14. Further, the metals that can be the terminal metal 13 of the electron emission material 10 of the first embodiment are Na, K, Rb, Cs, and Mg, but the first metal layer 14 and the second metal layer of the present embodiment. 15 is different from the first embodiment in that it includes Li in addition to these. In the present embodiment, these differences will be mainly described.
- the metal used for the 1st metal layer 14 and the 2nd metal layer 15 metals with high high temperature stability, such as Li, Na, Mg, are used, and the 2nd metal For the layer 15, it is preferable to use a metal such as Rb or Cs that can lower the work function.
- a metal such as Rb or Cs that can lower the work function.
- Li is bonded to the diamond film 11 via the bonded oxygen 12 as the first metal layer 14, and Cs is stacked as the second metal layer 15 on the first metal layer 14.
- Cs is stacked as the second metal layer 15 on the first metal layer 14.
- the electron emission material 10 of the present embodiment has higher temperature stability while lowering the work function than the electron emission material 10 of the first embodiment.
- the first metal layer 14 may be a combination of two or more alkali metals, a combination of alkali metals and Mg, or a combination of Mg and two or more alkali metals. Also good. Further, the second metal layer 15 is the same as the first metal layer 14.
- the electron emission material 10 of the present embodiment is manufactured by forming the second metal layer 15 by, for example, vapor deposition after the electron emission material 10 of the first embodiment is manufactured.
- thermoelectric generator 20 of the present embodiment is disposed between two substrates 1 and 2 that are disposed so as to face each other and between the two substrates 1 and 2 that are separated from each other. And an emitter electrode 3 and a collector electrode 4 laminated on the two substrates, respectively.
- thermoelectric power generation element 20 Next, a specific configuration example when the electron emitting material 10 is applied to the thermoelectric power generation element 20 will be described.
- the substrate 1 is a conductive substrate made of, for example, molybdenum.
- the substrate 2 is an insulating substrate made of, for example, Al 2 O 3 or the like.
- the insulating substrate refers to a substrate made of a high resistance material such as an oxide, nitride, ceramic, or a high resistance semiconductor material.
- the substrate 1 has an emitter electrode 3 laminated on the substrate 1 as shown in FIG.
- the emitter electrode 3 is a cathode electrode that emits electrons when heat is applied, and is composed of an electron emission material 10 that is a diamond semiconductor.
- the substrate 2 has a collector electrode 4 laminated on the substrate 2 as shown in FIG.
- the collector electrode 4 is an anode electrode that captures electrons emitted from the electrode emitter 3, and is made of a conductive material such as a metal or a low-resistance semiconductor material.
- the collector electrode 4 is made of molybdenum.
- the emitter electrode 3 and the collector electrode 4 are arranged to face each other with a predetermined distance therebetween so that the electrodes face each other as shown in FIG.
- the interval between these electrodes is set to an interval suitable for thermionic power generation, for example, 5 to 50 ⁇ m.
- This interval may be maintained by arranging the emitter electrode 3 and the collector electrode 4 apart from each other with a space therebetween, but may be maintained by using a spacer between these two electrodes. Good.
- an insulator (not shown) having a film thickness corresponding to this interval is provided between the emitter electrode 3 and the collector electrode 4 or the substrate 2 or between the substrate 1 and the collector electrode 4 or the substrate 2. Sandwich. By fixing through the spacer in this way, the interval can be more reliably maintained.
- the thermoelectron power generation element 20 of this embodiment should just be the structure where the emitter electrode 3 and the collector electrode 4 are electrically insulated.
- thermoelectric power generation element 20 converts thermal energy into electrical energy by utilizing a phenomenon in which thermoelectrons are emitted from the electrode surface. Specifically, when heat is applied to the emitter electrode 3 from an external heat source, electrons are excited from the impurity level of the diamond semiconductor that is the emitter electrode 3 to the conduction band. As shown in FIG. 2B, since the conduction band of the diamond semiconductor is higher in energy level than the vacuum level by NEA, the thermoelectrons excited in the conduction band jump out into the vacuum without a barrier. Thus, the thermoelectrons are emitted from the surface of the emitter electrode 3 that has become high temperature, and reach the collector electrode 4. In this way, since the thermoelectrons that have reached the collector electrode 4 generate an electromotive force when returning to the emitter electrode 3 via the load 5, the thermoelectric generator 20 can supply power to the load 5. it can.
- the electron emission material 10 that maintains a low work function even at a high temperature is used as the emitter electrode 3, a decrease in the amount of emitted thermoelectrons is suppressed even at a high temperature.
- the thermionic power generation element 20 with high power generation efficiency and output is obtained.
- Table 1 shows the result of measuring the thermoelectron current at a predetermined electrode temperature by using Mo for the substrate 1 and forming the electron emission material according to the configuration on the substrate 1 as the emitter electrode 3 of the thermoelectron emitting element.
- terminal atoms in Table 1 are atoms that terminate the surface of the diamond film 11.
- the “electrode temperature (° C.)” in Table 1 is the electrode temperature of the substrate when the thermionic current is measured.
- Thermionic current (A / cm 2 )” in Table 1 means that a pair of electrode substrates are arranged opposite to each other in a vacuum chamber of a vacuum vapor deposition machine, and one of the Mos formed with the diamond film 11 under vacuum. The measured value of the current between the electrodes at the temperature when the substrate is heated.
- Rb + Cs in the column of terminal atoms in Example 5 of Table 1 means a stacked state in which Rb is formed as the first metal layer 14 and Cs is formed as the second metal layer 15.
- O in the column of terminal atoms in Comparative Example 1 in Table 1 means that only bonded oxygen 12 is formed on the surface of the diamond film 11.
- H in the column of terminal atoms in Comparative Example 4 in Table 1 means that the surface of the diamond film 11 is terminated with hydrogen.
- “not measurable” in the column of the thermionic current in Table 1 means that the measurement limit value is less than 1.0 ⁇ 10 ⁇ 9 A / cm 2 .
- Example 1 The electron-emitting material of Example 1 was formed on the substrate 1 made of Mo, and was used as the diamond film 11, the bonded oxygen 12 bonded to the surface of the diamond film 11, and the termination metal 13 that terminates the bonded oxygen 12. And Na. Specifically, the diamond film 11 is formed, and the surface of the diamond film 11 is provided with bonded oxygen 12 by ozone oxidation treatment. Then, the substrate is heated to 500 ° C. and Na is supplied to the bonded oxygen 12. On the other hand, Na was supplied and terminated. A voltage was applied to the electrode facing the substrate on which the electron-emitting material of Example 1 was formed, and the thermoelectron current flowing between these electrodes was measured. As a result, the thermionic current at an electrode temperature of 500 ° C. was 7.1 ⁇ 10 ⁇ 8 A / cm 2 .
- thermoelectron current of the same level as that obtained by hydrogen-termination of the surface of the diamond film 11 of Comparative Example 4 to be described later flowed. From this, it was confirmed that the electron emission material of Example 1 was able to reduce the work function to the same extent as when hydrogen terminated. It was also confirmed that stable electron emission at a high temperature of 500 ° C., that is, a low work function can be maintained.
- Example 2 In the electron emission material of Example 2, the surface of the diamond film 11 was terminated with K through the bonded oxygen 12 as a result of supplying K by the same procedure as in Example 1.
- the substrate on which the electron-emitting material of Example 2 was formed was heated at 500 ° C., and the thermoelectron current flowing between the pair of electrodes at that time was measured.
- the thermoelectron current at an electrode temperature of 500 ° C. was 2.3 ⁇ 10 ⁇ 6 A / cm 2 .
- Example 2 when the electron emission material of Example 2 was used, it was confirmed that a thermionic current exceeding Example 1 flows and that the work function can be further reduced as compared with the case of Na termination. Moreover, it was confirmed that the low work function and the high temperature stability can be achieved in the same manner as in Example 1.
- Example 3 In the electron emission material of Example 3, as a result of supplying Rb by the same procedure as in Example 1, the surface of the diamond film 11 was terminated with Rb through the bonded oxygen 12. And the board
- Example 3 when the electron emission material of Example 3 was used, a thermionic current further exceeded that of Example 2 and the work function could be further reduced as compared with the case of K termination. Moreover, it was confirmed that the low work function and the high temperature stability can be achieved in the same manner as in Example 1.
- Example 4 In the electron emission material of Example 4, as a result of supplying Cs by the same procedure as in Example 1, the surface of the diamond film 11 was terminated with Cs through the bonded oxygen 12. The substrate on which the electron-emitting material of Example 4 was formed was heated at 500 ° C., Cs was always supplied, and the thermoelectron current flowing between the pair of electrodes at that time was measured. As a result, the thermoelectron current at an electrode temperature of 500 ° C. was 4.0 ⁇ 10 ⁇ 3 A / cm 2 .
- Example 4 when the electron emission material of Example 4 was used, a thermionic current further exceeded that of Example 3 and that the work function could be further reduced as compared with the case of Rb termination. Moreover, it was confirmed that the low work function and the high temperature stability can be achieved in the same manner as in Example 1.
- Example 5 In the electron emission material of Example 5, Rb is supplied by the same procedure as that of Example 3, Rb is bonded to the surface of the diamond film 11 through the bonded oxygen 12, and Cs is further supplied. Are obtained by laminating and terminating.
- the substrate on which the electron-emitting material of Example 5 was formed was heated at 500 ° C., Cs was always supplied, and the thermoelectron current flowing between the pair of electrodes at that time was measured.
- the thermionic current at an electrode temperature of 500 ° C. was 2.7 ⁇ 10 ⁇ 3 A / cm 2 .
- Example 5 when the electron emission material of Example 5 was used, a thermionic current exceeding Example 3 flowed, and the work function could be further reduced as compared with the case where it terminated with Rb. Moreover, it was confirmed that the low work function and the high temperature stability can be achieved in the same manner as in Example 1.
- Comparative Example 1 Unlike Example 1, the electron emission material of Comparative Example 1 is one in which the surface of the diamond film 11 is terminated with oxygen as a result of not performing evaporation of alkali metal or the like.
- the substrate on which the electron-emitting material of Example 1 was formed was heated at 500 ° C., and the thermoelectron current flowing between the pair of electrodes at that time was measured.
- the thermionic current at an electrode temperature of 500 ° C. was less than the measurement limit of 1.0 ⁇ 10 ⁇ 9 A / cm 2 .
- the thermoelectron current at 730 ° C. could not be measured.
- Comparative Examples 2 and 3 In the electron emission materials of Comparative Examples 2 and 3, Li was vapor-deposited by the same procedure as in Example 1, and the surface of the diamond film 11 was terminated with Li via the bonded oxygen 12.
- the difference between Comparative Example 2 and Comparative Example 3 is the electrode temperature.
- the substrate on which the electron-emitting material was formed was heated at 500 ° C., and the thermoelectron current flowing between the pair of electrodes at that time was measured.
- the thermionic current at an electrode temperature of 500 ° C. was less than the measurement limit of 1.0 ⁇ 10 ⁇ 9 A / cm 2 .
- Comparative Example 3 when the electrode temperature was further increased to 730 ° C., the thermionic current at the electrode temperature of 730 ° C. was 5.7 ⁇ 10 ⁇ 7 A / cm 2 .
- thermoelectron current did not flow at an electrode temperature of 500 ° C., and the electrode temperature was 730 ° C. in order to measure the thermoelectron current. It was necessary to raise to. From this, the electron-emitting material terminated with Li has a lower work function than that with oxygen termination, but has the same thermionic current unless the electrode temperature is higher than those in Examples 1 to 5. Does not flow, it is thought that low work function is not enough.
- Comparative Example 4 The electron-emitting material of Comparative Example 4 is produced by the same procedure as that of Comparative Example 1, and the alkali metal is not deposited and the surface of the diamond film 11 is terminated with hydrogen.
- the substrate on which the electron-emitting material of Comparative Example 4 was formed was heated at 500 ° C., and the thermoelectron current flowing between the pair of electrodes at that time was measured. As a result, the thermionic current at an electrode temperature of 500 ° C. was 2.2 ⁇ 10 ⁇ 7 A / cm 2 .
- thermoelectron current is equal to or less than that of Examples 1 to 5, and therefore, the work function can be made lower than that of the electron emission material of Comparative Example 1.
- low work function is not enough.
- the electron emission material 10 terminated with an alkali metal on the diamond film 11 through the bonded oxygen 12 has a low work function. It was confirmed that the high temperature stability was excellent.
- a thermionic power generation device As the electron-emitting device, a thermionic power generation device has been described as an example. However, other examples include a photo-excited electron-emitting device and a photo-excited thermionic power generation device, and the electron-emitting material 10 is used as the emitter electrode 3 in these devices. Can be applied. Since the electron emission material 10 can maintain a low work function even when driven at a high temperature, the electron emission material 10 can be used as an emitter electrode 3 such as a photoexcited electron emission element or a photoexcitation thermoelectron generation element, thereby improving the electron emission efficiency and the power generation efficiency. A high element can be obtained. In this case, the configuration of a photoexcited electron-emitting device can be a known device configuration.
- the diamond film 11 is not limited to the film forming method described above, and may be formed by, for example, a CVD method or a sputtering method, and may be formed by RF plasma CVD, DC plasma CVD, RF plasma sputtering, DC plasma sputtering, or the like.
- the N-type diamond constituting the thin film of the diamond film 11 may be either single crystal or polycrystal.
- a single crystal is formed when the diamond film 11 is formed thereon by, for example, the CVD method.
- the ozone treatment has been described in the first embodiment. However, it is sufficient that the surface of the diamond film 11 can be oxidized, and may be an oxygen plasma treatment, an oxygen radical treatment, a thermal mixed acid treatment, or the like. Other methods may be used.
- the surface of the diamond film 11 is terminated with oxygen by converting oxygen or an oxygen mixed gas into plasma in a container under reduced pressure and irradiating the diamond film 11 with oxygen.
- a substrate on which the diamond film 11 placed in the processing chamber is formed by introducing microwave power 300 W into the processing chamber in which the mixed gas pressure of argon and oxygen is 30 Pa is introduced into the processing chamber.
- An electrode for separating charged particles and neutral particles is installed between the diamond film substrate and the plasma generator, and a plurality of openings provided in the electrode with electrically neutral molecules, atoms or radicals. It can be transported through the part to the substrate surface. On the other hand, ions in the plasma hardly diffuse to the substrate side.
- the oxygen ratio was about 7%.
- the plasma processing is not limited to the above-described method and processing conditions, and may be RF plasma, DC plasma, or the like, for example.
- the gas in the dielectric tube is ionized by dielectric barrier discharge, and the diamond film 11 is irradiated with a plasma jet ejected from the dielectric tube under atmospheric pressure, and the surface of the diamond film 11 is terminated with oxygen.
- He gas is flowed through a quartz tube having an inner diameter of 4 mm, and plasma is generated by applying 5 to 10 kV to a copper electrode wound around and closely attached to the outside of the quartz tube.
- the surface of the film is terminated with oxygen by oxygen radicals generated by the reaction of He ions generated in the discharge part and He atoms in a metastable state with oxygen in the atmosphere.
- the oxygen ratio was about 25%.
- the gas to be converted into plasma is not limited to He, and an inert gas such as argon, oxygen or air, or a mixed gas thereof may be used.
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Abstract
One electron emitting material according to the present invention is provided with: a diamond film (11) which is an N-type diamond semiconductor doped with an impurity; oxygen (12) which is bonded to the surface of the diamond film; and a termination metal (13) which is bonded to the diamond film via the oxygen and contains at least one metal selected from among Na, K, Rb, Cs and Mg. Another electron emitting material according to the present invention is provided with: a diamond film (11) which is an N-type diamond semiconductor doped with an impurity; oxygen (12) which is bonded to the surface of the diamond film; a first metal layer (14) which is bonded to the diamond film via the oxygen and contains at least one metal selected from among Li, Na, K, Rb, Cs and Mg; and a second metal layer (15) which is laminated on the first metal layer and contains at least one metal selected from among Li, Na, K, Rb, Cs and Mg, said at least one metal being different from the metal contained in the first metal layer.
Description
本出願は、2016年7月18日に出願された日本特許出願番号2016-140962号に基づくもので、ここにその記載内容が参照により組み入れられる。
This application is based on Japanese Patent Application No. 2016-140962 filed on July 18, 2016, the description of which is incorporated herein by reference.
本開示は、熱エネルギーや光エネルギーを電気エネルギーに変換する際に用いられる電子放出材料および当該電子放出材料を用いた電子放出素子に関する。
The present disclosure relates to an electron emission material used when heat energy or light energy is converted into electric energy and an electron emission element using the electron emission material.
電子放出素子として、例えば、電界放出素子、熱電子発電素子が挙げられる。電界放出素子は、金属及び半導体材料に高電界を印加することにより電子が放出される現象を利用したものであり、カソード電極とアノード電極に電圧を印加することにより、カソード電極から電子が放出され、アノード電極に到達する。熱電子発電素子は、高温の電極表面から熱電子が放出される現象を利用して、熱エネルギーを電気エネルギーに変換するものであり、エミッタ電極を高温にすることで熱電子が放出され、コレクタ電極に到達する。
Examples of the electron-emitting device include a field emission device and a thermionic power generation device. A field emission device utilizes a phenomenon in which electrons are emitted by applying a high electric field to metal and semiconductor materials, and electrons are emitted from the cathode electrode by applying a voltage to the cathode electrode and the anode electrode. To the anode electrode. The thermoelectric power generation element converts the thermal energy into electric energy by utilizing the phenomenon that the hot electrons are emitted from the surface of the high temperature electrode. The thermoelectrons are emitted by raising the temperature of the emitter electrode, and the collector Reach the electrode.
このような電子放出素子の特性を向上させるためには、電子を放出させるのに要する電界や熱などのエネルギーを下げることが必要である。
In order to improve the characteristics of such an electron-emitting device, it is necessary to reduce energy such as an electric field and heat required for emitting electrons.
例えば熱電子発電素子においては、発電出力を向上するために、様々な検討がなされている。具体的には、例えば負性電子親和力(以下「NEA」という。)を示し、仕事関数を低下させる効果(以下「低仕事関数化」という。)が得られるダイヤモンドを用いた熱電子発電素子が挙げられる。これによれば、NEAの効果によって、ダイヤモンドの伝導帯のエネルギー準位が真空準位を上回る。この状態においては、伝導帯にある電子自身が真空に飛び出すのに十分なエネルギーを有していることから、伝導帯にある電子を容易に真空に放出させることができる。つまり、NEAの効果により真空準位とフェルミ準位との差、すなわち仕事関数を小さくすることで、電極表面からの極めて高効率な熱電子放出が可能となり、金属に比べて低温で高効率な発電が可能となる。
For example, in the thermoelectric power generation element, various studies have been made to improve the power generation output. Specifically, for example, a thermionic power generation element using diamond that exhibits negative electron affinity (hereinafter referred to as “NEA”) and has an effect of lowering the work function (hereinafter referred to as “lower work function”) is provided. Can be mentioned. According to this, due to the effect of NEA, the energy level of the conduction band of diamond exceeds the vacuum level. In this state, the electrons in the conduction band have sufficient energy to jump out into the vacuum, so that the electrons in the conduction band can be easily released into the vacuum. In other words, by reducing the difference between the vacuum level and the Fermi level, that is, the work function, due to the effect of NEA, extremely high-efficiency thermal electron emission from the electrode surface becomes possible, which is more efficient at lower temperatures than metal. Power generation is possible.
また、例えば低温で高効率な熱電子発電を行うために光により励起した電子を用いる光励起熱電子発電(以下「PETE」という。)なども挙げられる。光励起熱電子発電は、エミッタ電極に光を照射していったん光により電極材料の電子を励起させた後に加熱されることで、エミッタ電極から電子を放出する。つまり、光励起熱電子発電は、熱電子発電素子に比べて低温で電子を放出するため、さらに発電出力が向上する。
Also, for example, photoexcited thermionic power generation (hereinafter referred to as “PETE”) using electrons excited by light in order to perform highly efficient thermionic power generation at a low temperature. In photoexcited thermionic power generation, electrons are emitted from an emitter electrode by irradiating the emitter electrode with light and once exciting the electrons of the electrode material with the light, followed by heating. That is, the photo-excited thermionic power generation emits electrons at a lower temperature than the thermionic power generation element, and the power generation output is further improved.
加えて、近年では、シリコン基板上のダイヤモンド膜を用いたPETEの可能性も検討されており、シリコン基板中の電子が光励起され、この励起されたシリコン基板の電子がダイヤモンド膜からの熱電子放出に寄与していることが明らかにされている。さらに、特許文献1に示される電子放出材料においては、ダイヤモンド膜表面に酸素を介してリチウム(Li)により終端すると、ダイヤモンド表面が水素で終端されているものよりも仕事関数が小さくなることが知られている。このように低仕事関数化された電子放出材料は、電極材料表面から電子を放出させるために必要なエネルギーが低減されるため、さらに発電出力を向上させる効果が期待される。
In addition, in recent years, the possibility of PETE using a diamond film on a silicon substrate has also been studied. Electrons in the silicon substrate are photoexcited, and the electrons on the excited silicon substrate are emitted from the diamond film as thermal electrons. It has been clarified that it contributes to Further, in the electron emission material disclosed in Patent Document 1, it is known that when the diamond film surface is terminated with lithium (Li) via oxygen, the work function is smaller than that of the diamond surface terminated with hydrogen. It has been. The electron emission material having such a low work function is expected to have an effect of further improving the power generation output because the energy required for emitting electrons from the electrode material surface is reduced.
ここで、ダイヤモンド膜表面をLiなどのアルカリ金属で被覆することで、被覆されていないダイヤモンド膜表面よりも低仕事関数化される。しかし、その場合、アルカリ金属が化学結合によりダイヤモンド膜表面を終端していないため、ダイヤモンド膜とアルカリ金属との相互作用は弱い。そのため、アルカリ金属で表面が被覆されたダイヤモンドを電極材料として用いた場合、その電極温度が高くなると、ダイヤモンド表面を被覆しているアルカリ金属は、ダイヤモンド表面から離脱してしまう。つまり、アルカリ金属で表面が被覆されたダイヤモンドは、高温においてその表面の仕事関数を低く維持することができない。
Here, by coating the surface of the diamond film with an alkali metal such as Li, the work function is made lower than that of the uncoated diamond film surface. However, in that case, the interaction between the diamond film and the alkali metal is weak because the alkali metal does not terminate the surface of the diamond film by a chemical bond. Therefore, when diamond whose surface is coated with an alkali metal is used as an electrode material, when the electrode temperature is increased, the alkali metal covering the diamond surface is detached from the diamond surface. That is, diamond whose surface is coated with an alkali metal cannot maintain the work function of the surface at a high temperature at a low temperature.
また、特許文献1の材料については、酸素を介してLiでダイヤモンド膜表面を終端することで高温におけるアルカリ金属のダイヤモンド表面からの離脱を抑制しつつ、仕事関数を低く維持できる。しかしながら、当該材料から熱電子を放出させ、十分な熱電子電流を得るためには高温で駆動する必要がある。このことから、酸素を介してLiで終端したダイヤモンド膜では、高温駆動時における安定性が得られるものの、ダイヤモンド膜表面の低仕事関数化についてはまだ十分ではないと考えられる。
In addition, with respect to the material of Patent Document 1, the work function can be kept low while suppressing the separation of the alkali metal from the diamond surface at high temperature by terminating the diamond film surface with Li via oxygen. However, it is necessary to drive at a high temperature in order to emit thermoelectrons from the material and obtain a sufficient thermoelectron current. From this, it is considered that a diamond film terminated with Li via oxygen can provide stability at high temperature driving but is still not sufficient for lowering the work function of the diamond film surface.
本開示は、上記の点に鑑みてなされたものであり、高温駆動時における仕事関数を低く維持できる電子放出材料および当該材料を使用した電子放出素子を提供することを目的とする。
The present disclosure has been made in view of the above points, and an object thereof is to provide an electron-emitting material that can maintain a low work function during high-temperature driving and an electron-emitting device using the material.
本開示の第1の観点による電子放出材料は、ダイヤモンド膜と、ダイヤモンド膜の表面に結合する酸素と、酸素を介してダイヤモンド膜に結合する終端金属と、を含む電子放出材料であって、ダイヤモンド膜は、不純物をドープしたN型ダイヤモンド半導体であり、終端金属は、Na、K、Rb、Cs、Mgのうち少なくとも1つを含む。
An electron emission material according to a first aspect of the present disclosure is an electron emission material including a diamond film, oxygen bonded to the surface of the diamond film, and a termination metal bonded to the diamond film via oxygen, The film is an N-type diamond semiconductor doped with impurities, and the termination metal contains at least one of Na, K, Rb, Cs, and Mg.
ダイヤモンド膜の表面に酸素を介してNa、K、Rb、Cs、Mgのうち少なくとも1つの金属で終端することにより、ダイヤモンド膜の仕事関数を低くすることができる。以降の説明において、ダイヤモンド膜を終端する金属を、便宜的に「終端金属」という。
The work function of the diamond film can be lowered by terminating the surface of the diamond film with at least one metal of Na, K, Rb, Cs, and Mg via oxygen. In the following description, the metal that terminates the diamond film is referred to as “termination metal” for convenience.
また、終端金属が酸素を介してダイヤモンド膜と結合することにより、終端金属と酸素との間にクーロン力が働き、これらがクーロン結合する。その結果、終端金属が高温に加熱されても前述のクーロン結合により終端金属がダイヤモンド膜から離脱しにくくなる。よって、このような構成とされることにより、高温駆動時においても終端金属がダイヤモンド膜の表面から離脱せずに安定であり、表面の仕事関数を低く維持できる電子放出材料となる。なお、以降の説明において便宜的に、高温にされても終端金属がダイヤモンド膜の表面から離脱せずに安定な性質を「高温安定性」という。
In addition, when the terminal metal is bonded to the diamond film through oxygen, a Coulomb force acts between the terminal metal and oxygen, and these are Coulomb bonded. As a result, even if the termination metal is heated to a high temperature, the termination metal is hardly separated from the diamond film by the above-described Coulomb coupling. Therefore, by adopting such a configuration, the terminal metal is stable without being detached from the surface of the diamond film even when driven at a high temperature, and the electron emission material can maintain the work function of the surface low. In the following description, for the sake of convenience, the property that the terminal metal does not separate from the surface of the diamond film even when the temperature is raised is referred to as “high temperature stability”.
第2の観点による電子放出材料は、ダイヤモンド膜と、ダイヤモンド膜の表面に結合する酸素と、酸素を介してダイヤモンド膜に結合する結合する第1金属層と、第1金属層の上に積層された第2金属層と、を含む電子放出材料であって、ダイヤモンド膜は、不純物をドープしたN型ダイヤモンド半導体であり、第1金属層は、Li、Na、K、Rb、Cs、Mgのうち少なくとも1つを含み、第2金属層は、Li、Na、K、Rb、Cs、Mgのうち第1金属層とは異なる金属を少なくとも1つを含む。
The electron emission material according to the second aspect is laminated on the diamond film, oxygen bonded to the surface of the diamond film, a first metal layer bonded to the diamond film via oxygen, and the first metal layer. The diamond film is an N-type diamond semiconductor doped with impurities, and the first metal layer is composed of Li, Na, K, Rb, Cs, and Mg. The second metal layer includes at least one of Li, Na, K, Rb, Cs, and Mg, which is different from the first metal layer.
ダイヤモンド膜の表面に上記の第1金属層を備え、第1金属層の上に上記の第2金属層を積層する。これに加えて、第1金属層のアルカリ金属、Mgのうち少なくとも1つを含む金属が酸素を介してダイヤモンド膜と結合することにより、高温安定性と低仕事関数化を両立できる。また、さらに第2金属層の終端金属により、第1金属層により高温安定性を確保しつつ、さらにダイヤモンド膜の表面を低仕事関数化した電子放出材料とできる。
The above-mentioned first metal layer is provided on the surface of the diamond film, and the above-mentioned second metal layer is laminated on the first metal layer. In addition, high temperature stability and low work function can be achieved by combining a metal containing at least one of the alkali metal and Mg of the first metal layer with oxygen through oxygen. Further, the termination metal of the second metal layer can provide an electron emission material in which the surface of the diamond film is further reduced in work function while ensuring the high temperature stability by the first metal layer.
第3の観点による電子放出素子は、互いに対向するように配置されたエミッタ電極とコレクタ電極からなる一対の電極を備える。このような構成において、エミッタ電極は、電子放出を行う電極であって、例えば第1の観点による電子放出材料で構成される。
The electron-emitting device according to the third aspect includes a pair of electrodes consisting of an emitter electrode and a collector electrode arranged so as to face each other. In such a configuration, the emitter electrode is an electrode that emits electrons, and is formed of, for example, an electron-emitting material according to the first aspect.
高温安定性を確保しつつ、仕事関数を低く維持でき、例えば第1の観点による電子放出材料をエミッタ電極として適用することにより、エミッタ電極からの電子放出の効率を高くすることができる。これにより、電子放出効率の高い電子放出素子とすることができる。
The work function can be kept low while ensuring high temperature stability. For example, by applying the electron emission material according to the first aspect as the emitter electrode, the efficiency of electron emission from the emitter electrode can be increased. Thereby, an electron-emitting device with high electron emission efficiency can be obtained.
以下、本開示の実施形態について図に基づいて説明する。なお、以下の各実施形態相互において、互いに同一もしくは均等である部分には、同一符号を付して説明を行う。
Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other will be described with the same reference numerals.
(第1実施形態)
第1実施形態の電子放出材料10について、図1を参照して説明する。図1では、基板1に本実施形態の電子放出材料10を電極に対して適用した例を示している。基板1としては、例えばMoやSiなどを使用することができる。電子放出材料10は、材料表面から電子放出を行う材料であり、例えば熱電子発電素子、光励起電子放出素子、光励起熱電子発電素子などにおいて電子放出を行うエミッタ電極として用いることができる。 (First embodiment)
Theelectron emission material 10 of 1st Embodiment is demonstrated with reference to FIG. In FIG. 1, the example which applied the electron emission material 10 of this embodiment with respect to the electrode to the board | substrate 1 is shown. As the substrate 1, for example, Mo or Si can be used. The electron emission material 10 is a material that emits electrons from the material surface, and can be used as an emitter electrode that emits electrons in, for example, a thermionic power generation element, a photoexcitation electron emission element, a photoexcitation thermoelectron generation element, or the like.
第1実施形態の電子放出材料10について、図1を参照して説明する。図1では、基板1に本実施形態の電子放出材料10を電極に対して適用した例を示している。基板1としては、例えばMoやSiなどを使用することができる。電子放出材料10は、材料表面から電子放出を行う材料であり、例えば熱電子発電素子、光励起電子放出素子、光励起熱電子発電素子などにおいて電子放出を行うエミッタ電極として用いることができる。 (First embodiment)
The
本実施形態の電子放出材料10は、ダイヤモンド半導体であるダイヤモンド膜11と、ダイヤモンド膜11の表面に結合する酸素(以下「結合酸素12」という。)と、該酸素を介してダイヤモンド膜11と結合する終端金属13とにより構成されている。また、図1のMは、終端金属13を示している。
The electron-emitting material 10 of the present embodiment is bonded to the diamond film 11 which is a diamond semiconductor, oxygen bonded to the surface of the diamond film 11 (hereinafter referred to as “bonded oxygen 12”), and the diamond film 11 via the oxygen. It is comprised with the termination | terminus metal 13 to perform. Further, M in FIG. 1 indicates a termination metal 13.
ダイヤモンド膜11は、例えば窒素や燐などの不純物を高濃度、例えば1×1020cm-3~1×1021cm-3でドープしたN型のダイヤモンドの薄膜で構成されている。このドープ濃度については、高いほうが好ましい。ドープ濃度が低いと、励起される熱電子が少なく、電子放出の効率が低くなるためである。また、ダイヤモンド膜11に添加する半導体不純物としては、例えば、N(窒素)、P(燐)、As(ヒ素)、Sb(アンチモン)、S(硫黄)等が用いられる。
The diamond film 11 is composed of an N-type diamond thin film doped with impurities such as nitrogen and phosphorus at a high concentration, for example, 1 × 10 20 cm −3 to 1 × 10 21 cm −3 . About this dope concentration, the higher one is preferable. This is because, when the doping concentration is low, the number of excited thermal electrons is small and the efficiency of electron emission is low. Moreover, as a semiconductor impurity added to the diamond film 11, N (nitrogen), P (phosphorus), As (arsenic), Sb (antimony), S (sulfur), etc. are used, for example.
次に、結合酸素12については、ダイヤモンド膜11を形成した時点では存在していないが、後述する製造工程のオゾン酸化処理または酸素プラズマ表面処理、酸素ラジカル処理によりダイヤモンド膜11の表面に形成されたものである。
Next, although the bonded oxygen 12 does not exist at the time of forming the diamond film 11, it was formed on the surface of the diamond film 11 by ozone oxidation treatment, oxygen plasma surface treatment, or oxygen radical treatment in the manufacturing process described later. Is.
次に、終端金属13については、ダイヤモンド膜11の表面に結合酸素12を形成した後、後述する製造工程の蒸着等を行うことで形成され、結合酸素12を介してダイヤモンド膜11を終端したものである。終端金属13は、例えばNa(ナトリウム)、K(カリウム)、Rb(ルビジウム)、Cs(セシウム)、Mg(マグネシウム)のうち少なくとも1つを含む金属である。なお、終端金属13は、2種以上のアルカリ金属の組み合わせであってもよく、アルカリ金属とMgの組み合わせであってもよく、2種以上のアルカリ金属とMgの組み合わせであってもよい。
Next, the terminating metal 13 is formed by forming bonded oxygen 12 on the surface of the diamond film 11 and then performing vapor deposition in a manufacturing process described later, and terminating the diamond film 11 through the bonded oxygen 12. It is. The termination metal 13 is a metal containing at least one of, for example, Na (sodium), K (potassium), Rb (rubidium), Cs (cesium), and Mg (magnesium). The termination metal 13 may be a combination of two or more kinds of alkali metals, a combination of alkali metals and Mg, or a combination of two or more kinds of alkali metals and Mg.
ここで、ダイヤモンド膜11の表面に酸素を介してアルカリ金属およびMgのうち少なくとも1つの金属で終端することについての効果を、酸素で終端した場合と、アルカリ金属、例えばCsで終端した場合とを比較して図2を参照して説明する。
Here, the effect of terminating at the surface of the diamond film 11 with at least one of an alkali metal and Mg via oxygen is the case where it is terminated with oxygen and the case where it is terminated with an alkali metal such as Cs. A comparison will be described with reference to FIG.
図2(a)は電子放出材料を構成するダイヤモンド膜11の表面を酸素終端した場合、図2(b)は電子放出材料を構成するダイヤモンド膜11の表面に酸素を介してCsで終端した場合のエネルギーバンド図である。
2A shows a case where the surface of the diamond film 11 constituting the electron emission material is terminated with oxygen, and FIG. 2B shows a case where the surface of the diamond film 11 constituting the electron emission material is terminated with oxygen via Cs. FIG.
まず、電子放出材料を構成するダイヤモンド膜11の表面を酸素で終端した場合、図2(a)に示されるように、正の電子親和力により真空準位が伝導帯よりも高くなる(ΔE>0)。このため、伝導帯にある電子を真空に放出するにはエネルギーが必要となり、この状態では、真空準位とフェルミ準位との差である仕事関数が高くなる。すなわち、この状態の電子放出材料は、電子を放出させるために要するエネルギーが高く、電子放出の効率が悪い。一方、図2(b)に示されるように、電子放出材料を構成するダイヤモンド膜11の表面に酸素を介して例えばCsで終端した場合、NEAにより、真空準位が伝導帯よりも低くなる(ΔE<0)。このため、伝導帯にある電子をエネルギー=0で真空に放出させることができ、この状態の電子放出材料は、その仕事関数が低い。言い換えれば、仕事関数が低くなるように調整することで、高効率な電子放出が実現できる。
First, when the surface of the diamond film 11 constituting the electron emission material is terminated with oxygen, as shown in FIG. 2A, the vacuum level becomes higher than the conduction band due to positive electron affinity (ΔE> 0). ). For this reason, energy is required to discharge electrons in the conduction band to the vacuum, and in this state, the work function, which is the difference between the vacuum level and the Fermi level, becomes high. That is, the electron emission material in this state has high energy required for emitting electrons, and the efficiency of electron emission is poor. On the other hand, as shown in FIG. 2B, when the surface of the diamond film 11 constituting the electron emitting material is terminated with, for example, Cs via oxygen, the vacuum level is lower than the conduction band by NEA ( ΔE <0). For this reason, electrons in the conduction band can be emitted to vacuum with energy = 0, and the electron emission material in this state has a low work function. In other words, highly efficient electron emission can be realized by adjusting the work function to be low.
このように、電子放出材料10を構成するダイヤモンド膜11の表面の終端構造によって、電子親和力の極性を変えることができる。そして、ダイヤモンド膜11の表面に酸素を介してアルカリ金属およびMgのうち少なくとも1つを含む金属で終端したものを、終端構造とすると、極めて安定なNEAを得ることができ、高効率な熱電子放出を長時間において実現することが可能となる。
Thus, the polarity of the electron affinity can be changed by the termination structure on the surface of the diamond film 11 constituting the electron emission material 10. When the surface of the diamond film 11 terminated with a metal containing at least one of an alkali metal and Mg via oxygen is used as a termination structure, extremely stable NEA can be obtained, and highly efficient thermoelectrons can be obtained. Release can be realized in a long time.
ここで、本発明者らは、ダイヤモンド膜表面の低仕事関数化と高温安定性との両立の観点から終端金属13についての鋭意検討を行った。その結果、終端金属13をアルカリ金属とした場合においては、Li、Na、K、Rb、Csとその原子量が多くなるにつれて、ダイヤモンド膜11の仕事関数が低くなる傾向があり、Na、K、Rb、Csを選択することでLiに比べて電子放出の効率が上がることを見出した。その一方で、終端金属13をアルカリ金属とした場合においては、Li、Na、K、Rb、Csとその原子番号が多くなるにつれて、高温時においてアルカリ金属がダイヤモンド膜11から離脱しやすくなる傾向があることを見出した。つまり、低仕事関数化と高温安定性とがトレードオフの関係となっており、駆動温度に合わせて終端金属13を適宜選択することで低仕事関数化でき、電子放出の効率に優れた電子放出材料10とすることができる。
Here, the present inventors have conducted intensive studies on the termination metal 13 from the viewpoint of achieving both a low work function on the diamond film surface and high-temperature stability. As a result, when the termination metal 13 is an alkali metal, the work function of the diamond film 11 tends to decrease as the atomic weight of Li, Na, K, Rb, Cs increases, and Na, K, Rb It has been found that the efficiency of electron emission is increased by selecting Cs as compared with Li. On the other hand, when the termination metal 13 is an alkali metal, the alkali metal tends to be detached from the diamond film 11 at high temperatures as the number of Li, Na, K, Rb, Cs and their atomic numbers increases. I found out. That is, there is a trade-off relationship between lowering the work function and stability at high temperature, and the work function can be lowered by appropriately selecting the termination metal 13 according to the driving temperature, and electron emission with excellent electron emission efficiency. Material 10 can be used.
次に、本開示の電子放出材料の製造方法の一例について説明する。
Next, an example of a method for manufacturing the electron emission material according to the present disclosure will be described.
ダイヤモンド膜11については、例えばマイクロ波CVD(chemical vapor depositionの略)法により、例えば窒素をドープしたN型ダイヤモンド膜として形成される。この際、反応ガスとして例えばCH4をH2で希釈した混合ガスを用い、ドーパントとしては例えばN2ガスを用いる。そして、これらのガス流量を調整することで窒素のドーピング量を調整する。
The diamond film 11 is formed, for example, as an N-type diamond film doped with nitrogen by, for example, a microwave CVD (abbreviation of chemical vapor deposition) method. At this time, for example, a mixed gas obtained by diluting CH 4 with H 2 is used as a reactive gas, and for example, N 2 gas is used as a dopant. And the doping amount of nitrogen is adjusted by adjusting these gas flow rates.
具体的には、例えばMoやSiなどの基板1にダイヤモンド膜11を形成する場合、マイクロ波CVDの真空チャンバー内に基板1をセットする。そして、真空チャンバーを減圧して、基板1を例えば600~1100℃の範囲内で加熱する。その後、真空チャンバー内に、CH4をH2で希釈した混合ガス(CH4濃度:0.05~5%)とN2ガスを導入する。この際、N2ガスと混合ガスとの混合の割合を、混合ガス中のCH4の炭素を1とした場合においてN2の窒素が例えば1~200となるように調整する。また、この際の成膜条件は、例えば、反応圧力が40~150Torrの範囲内で調整され、マイクロ波電源の投入電力が500~1500Wの範囲内で調整される。そして、これらの混合ガスをマイクロ波で反応させながら例えば100nmの厚みのダイヤモンド膜11を成膜する。これにより、窒素が高濃度でドープされたN型ダイヤモンドの薄膜が得られる。なお、燐をドープしたN型ダイヤモンドの薄膜でダイヤモンド膜11を形成する場合、上記のN2ガスをPH3ガスに置き換えることで燐を高濃度でドープしたN型ダイヤモンドの薄膜とすることができる。
Specifically, for example, when the diamond film 11 is formed on the substrate 1 such as Mo or Si, the substrate 1 is set in a vacuum chamber of microwave CVD. Then, the vacuum chamber is decompressed, and the substrate 1 is heated within a range of 600 to 1100 ° C., for example. Thereafter, a mixed gas obtained by diluting CH 4 with H 2 (CH 4 concentration: 0.05 to 5%) and N 2 gas are introduced into the vacuum chamber. At this time, the mixing ratio of the N 2 gas and the mixed gas is adjusted so that the nitrogen of N 2 becomes 1 to 200, for example, when the carbon of CH 4 in the mixed gas is 1. Further, the film forming conditions at this time are adjusted, for example, within a range of a reaction pressure of 40 to 150 Torr and an input power of a microwave power source within a range of 500 to 1500 W. Then, a diamond film 11 having a thickness of, for example, 100 nm is formed while these mixed gases are reacted in the microwave. Thereby, an N-type diamond thin film doped with nitrogen at a high concentration is obtained. In the case where the diamond film 11 is formed from a thin film of N-type diamond doped with phosphorus, a thin film of N-type diamond doped with phosphorus at a high concentration can be obtained by replacing the N 2 gas with a PH 3 gas. .
なお、ダイヤモンド膜11は、熱電放出に対する膜厚依存性が確認されなかったことから特にその膜厚の上限はないが、少なくとも100nm以上の膜厚であって基板の表面全面に偏り無く同じ厚みで形成されているのが好ましい。この理由は、100nm未満の膜厚とされたダイヤモンド膜に膜として形成されない欠陥部位が生じ、エミッタ電極3として使用する場合に電子放出の効率が低下するおそれがあるためである。一方で、ダイヤモンド膜11は、その膜厚を必要以上に増加させる理由はなく、むしろ製造コストの増加につながるため、欠陥部位が生じない程度の膜厚であれば十分である。
The diamond film 11 has no particular upper limit because the film thickness dependence on thermoelectric emission has not been confirmed. However, the diamond film 11 has a film thickness of at least 100 nm and the same thickness with no unevenness over the entire surface of the substrate. Preferably it is formed. This is because a defect site that is not formed as a film occurs in the diamond film having a film thickness of less than 100 nm, and when used as the emitter electrode 3, the efficiency of electron emission may be reduced. On the other hand, the diamond film 11 has no reason to increase the film thickness more than necessary, but rather increases the manufacturing cost.
次に、例えば紫外線で酸素を分解して発生させたオゾンを用いてダイヤモンド膜11の表面の酸化処理を行い、ダイヤモンド膜11の表面を酸素で終端する。続けて、酸素で終端されたダイヤモンド膜11に、アルカリ金属、例えばCsの真空蒸着を行い、酸素を介してCsで終端された電子放出材料10を得る。
Next, for example, the surface of the diamond film 11 is oxidized using ozone generated by decomposing oxygen with ultraviolet rays, and the surface of the diamond film 11 is terminated with oxygen. Subsequently, the diamond film 11 terminated with oxygen is vacuum-deposited with an alkali metal such as Cs to obtain the electron emission material 10 terminated with Cs via oxygen.
なお、終端金属13を複数の金属で構成する場合には、複数の蒸着源からアルカリ金属等を共蒸着することで、ダイヤモンド膜11の表面に複数の金属を終端させることができる。
When the termination metal 13 is composed of a plurality of metals, a plurality of metals can be terminated on the surface of the diamond film 11 by co-evaporating alkali metal or the like from a plurality of deposition sources.
このような製造方法により、低仕事関数化をしつつ、高温安定性に優れた電子放出材料10を製造できる。
By such a manufacturing method, it is possible to manufacture the electron emission material 10 excellent in high-temperature stability while reducing the work function.
(第2実施形態)
次に、第2実施形態の電子放出材料10について、図3を参照して説明する。図3では、図1と同様に基板1に本実施形態の電子放出材料10を電極として形成した例を示しており、M1については後述する第1金属層14、M2については後述する第2金属層15を示している。本実施形態の電子放出材料10は、ダイヤモンド膜11と、ダイヤモンド膜11に結合する結合酸素12と、結合酸素12を介してダイヤモンド膜11と結合する第1金属層14と、該第1金属層14の上に積層された第2金属層15とにより構成されている。また、第1金属層14と第2金属層15は、互いに異なる後述する金属により構成されている。つまり、本実施形態の電子放出材料10は、ダイヤモンド膜11と結合酸素12を介して第1金属層14が結合しているだけでなく、それに加えて、第2金属層15を第1金属層14の上に積層した構成である点が上記第1実施形態と相違する。また、上記第1実施形態の電子放出材料10の終端金属13となりうる金属については、Na、K、Rb、Cs、Mgであったが、本実施形態の第1金属層14および第2金属層15については、これらに加えてLiを含む点も上記第1実施形態と相違する。本実施形態については、これらの相違点について主に説明する。 (Second Embodiment)
Next, theelectron emission material 10 of 2nd Embodiment is demonstrated with reference to FIG. FIG. 3 shows an example in which the electron-emitting material 10 of the present embodiment is formed as an electrode on the substrate 1 as in FIG. 1, and M1 is a first metal layer 14 to be described later, and M2 is a second metal to be described later. Layer 15 is shown. The electron-emitting material 10 of this embodiment includes a diamond film 11, a bonded oxygen 12 bonded to the diamond film 11, a first metal layer 14 bonded to the diamond film 11 via the bonded oxygen 12, and the first metal layer. 14 and a second metal layer 15 stacked on top of each other. Moreover, the 1st metal layer 14 and the 2nd metal layer 15 are comprised by the metal which mentions mutually different later. That is, in the electron emission material 10 of the present embodiment, not only the first metal layer 14 is bonded via the diamond film 11 and the bonded oxygen 12, but in addition, the second metal layer 15 is replaced with the first metal layer 15. 14 is different from that of the first embodiment in that the configuration is stacked on top of 14. Further, the metals that can be the terminal metal 13 of the electron emission material 10 of the first embodiment are Na, K, Rb, Cs, and Mg, but the first metal layer 14 and the second metal layer of the present embodiment. 15 is different from the first embodiment in that it includes Li in addition to these. In the present embodiment, these differences will be mainly described.
次に、第2実施形態の電子放出材料10について、図3を参照して説明する。図3では、図1と同様に基板1に本実施形態の電子放出材料10を電極として形成した例を示しており、M1については後述する第1金属層14、M2については後述する第2金属層15を示している。本実施形態の電子放出材料10は、ダイヤモンド膜11と、ダイヤモンド膜11に結合する結合酸素12と、結合酸素12を介してダイヤモンド膜11と結合する第1金属層14と、該第1金属層14の上に積層された第2金属層15とにより構成されている。また、第1金属層14と第2金属層15は、互いに異なる後述する金属により構成されている。つまり、本実施形態の電子放出材料10は、ダイヤモンド膜11と結合酸素12を介して第1金属層14が結合しているだけでなく、それに加えて、第2金属層15を第1金属層14の上に積層した構成である点が上記第1実施形態と相違する。また、上記第1実施形態の電子放出材料10の終端金属13となりうる金属については、Na、K、Rb、Cs、Mgであったが、本実施形態の第1金属層14および第2金属層15については、これらに加えてLiを含む点も上記第1実施形態と相違する。本実施形態については、これらの相違点について主に説明する。 (Second Embodiment)
Next, the
ここで、第1金属層14と第2金属層15に用いる金属についての制限はないが、第1金属層14についてはLi、Na、Mgなどの高温安定性が高い金属を用い、第2金属層15についてはRb、Csなどのより低仕事関数化できる金属を用いることが好ましい。本発明者らが鋭意検討した結果、より低仕事関数化できるRbやCsを終端金属とした第1実施形態の電子放出材料10に比べ、低仕事関数化しつつも高温安定性を向上できることを見出したからである。
Here, although there is no restriction | limiting about the metal used for the 1st metal layer 14 and the 2nd metal layer 15, For the 1st metal layer 14, metals with high high temperature stability, such as Li, Na, Mg, are used, and the 2nd metal For the layer 15, it is preferable to use a metal such as Rb or Cs that can lower the work function. As a result of intensive studies by the present inventors, it has been found that high temperature stability can be improved while lowering the work function as compared with the electron emission material 10 of the first embodiment in which Rb and Cs capable of lowering the work function are used as termination metals. This is because the.
具体的には、例えばダイヤモンド膜11に結合酸素12を介して第1金属層14としてLiが結合され、この第1金属層14の上に第2金属層15としてCsが積層された構造とされた場合を例に説明する。第1金属層14にLiを用いる場合には、低仕事関数化についてはまだ十分ではないが、高温安定性に優れる。さらに第1金属層14であるLiの上にCsを第2金属層15として積層して終端することにより、表面をさらに低仕事関数化することができる。また、アルカリ金属のLiの上に、同じアルカリ金属のCsを積層することで、安定した仕事関数が得られる。つまり、同じCsであっても、第1実施形態のように終端金属13とした場合よりも、本実施形態の第2金属層15とした場合のほうが、高温駆動時におけるダイヤモンド膜11の表面からの離脱が起きにくくなる。このようにして、本実施形態の電子放出材料10は、第1実施形態の電子放出材料10に比べて、低仕事関数化しつつ、より高温安定性を備える。
Specifically, for example, Li is bonded to the diamond film 11 via the bonded oxygen 12 as the first metal layer 14, and Cs is stacked as the second metal layer 15 on the first metal layer 14. An example will be described. When Li is used for the first metal layer 14, the work function is not sufficiently lowered, but the high temperature stability is excellent. Further, by stacking Cs as the second metal layer 15 on the first metal layer 14 and terminating it, the work surface can be further reduced in work function. Moreover, a stable work function can be obtained by laminating the same alkali metal Cs on the alkali metal Li. That is, even when the Cs is the same, the case of the second metal layer 15 of the present embodiment from the surface of the diamond film 11 at the time of high temperature driving is more than the case of the termination metal 13 as in the first embodiment. The withdrawal becomes difficult. In this way, the electron emission material 10 of the present embodiment has higher temperature stability while lowering the work function than the electron emission material 10 of the first embodiment.
また、第1金属層14については、2種以上のアルカリ金属の組み合わせであってもよく、アルカリ金属とMgの組み合わせであってもよく、Mgと2種以上のアルカリ金属との組み合わせであってもよい。さらに、第2金属層15についても、第1金属層14と同様である。
The first metal layer 14 may be a combination of two or more alkali metals, a combination of alkali metals and Mg, or a combination of Mg and two or more alkali metals. Also good. Further, the second metal layer 15 is the same as the first metal layer 14.
なお、本実施形態の電子放出材料10については、第1実施形態の電子放出材料10を製造後に続けて第2金属層15を例えば蒸着などにより成膜することで製造される。
The electron emission material 10 of the present embodiment is manufactured by forming the second metal layer 15 by, for example, vapor deposition after the electron emission material 10 of the first embodiment is manufactured.
このような製造方法により、低仕事関数化をしつつ、高温安定性に優れた電子放出材料10を製造できる。
By such a manufacturing method, it is possible to manufacture the electron emission material 10 excellent in high-temperature stability while reducing the work function.
(第3実施形態)
次に、電子放出材料10を用いた第3実施形態の素子について、例えば熱電子発電素子とされた例について図4を参照して説明する。図4に示すように、本実施形態の熱電子発電素子20は、互いに対向するように配置された2つの基板1、2と、互いに離された状態で2つの基板1、2の間に配置され、該2つの基板にそれぞれ積層されたエミッタ電極3およびコレクタ電極4と、を備えている。 (Third embodiment)
Next, the element of the third embodiment using theelectron emission material 10 will be described with reference to FIG. As shown in FIG. 4, the thermoelectric generator 20 of the present embodiment is disposed between two substrates 1 and 2 that are disposed so as to face each other and between the two substrates 1 and 2 that are separated from each other. And an emitter electrode 3 and a collector electrode 4 laminated on the two substrates, respectively.
次に、電子放出材料10を用いた第3実施形態の素子について、例えば熱電子発電素子とされた例について図4を参照して説明する。図4に示すように、本実施形態の熱電子発電素子20は、互いに対向するように配置された2つの基板1、2と、互いに離された状態で2つの基板1、2の間に配置され、該2つの基板にそれぞれ積層されたエミッタ電極3およびコレクタ電極4と、を備えている。 (Third embodiment)
Next, the element of the third embodiment using the
次に、電子放出材料10を熱電子発電素子20に適用する場合の具体的な構成例について説明する。
Next, a specific configuration example when the electron emitting material 10 is applied to the thermoelectric power generation element 20 will be described.
熱電子発電素子20の場合、基板1は、例えばモリブデン等で構成された導電性基板とされる。基板2は、例えばAl2O3等で構成された絶縁基板とされる。ここで、絶縁基板とは、酸化物、窒化物、セラミック、高抵抗の半導体材料等の高抵抗材料で構成された基板をいう。
In the case of the thermoelectric generator 20, the substrate 1 is a conductive substrate made of, for example, molybdenum. The substrate 2 is an insulating substrate made of, for example, Al 2 O 3 or the like. Here, the insulating substrate refers to a substrate made of a high resistance material such as an oxide, nitride, ceramic, or a high resistance semiconductor material.
基板1は、図4に示すように、基板1にはエミッタ電極3が積層されている。エミッタ電極3は、熱をかけることにより電子を放出するカソード電極であり、ダイヤモンド半導体である電子放出材料10で構成されている。
The substrate 1 has an emitter electrode 3 laminated on the substrate 1 as shown in FIG. The emitter electrode 3 is a cathode electrode that emits electrons when heat is applied, and is composed of an electron emission material 10 that is a diamond semiconductor.
基板2は、図4に示すように、基板2にはコレクタ電極4が積層されている。コレクタ電極4は、電極エミッタ3から放出された電子を捕獲するアノード電極であり、金属や低抵抗の半導体材料等の導電材料で構成されている。本実施形態では、コレクタ電極4は、モリブデンで構成されている。
The substrate 2 has a collector electrode 4 laminated on the substrate 2 as shown in FIG. The collector electrode 4 is an anode electrode that captures electrons emitted from the electrode emitter 3, and is made of a conductive material such as a metal or a low-resistance semiconductor material. In the present embodiment, the collector electrode 4 is made of molybdenum.
エミッタ電極3およびコレクタ電極4については、真空環境下において、図4に示されるように、互いに電極が向かい合うように一定間隔離間して対向配置されている。これらの電極間の間隔は、熱電子発電に適した間隔、例えば5~50μmとされている。この間隔は、エミッタ電極3とコレクタ電極4とを空間を空けて離れた配置にすることによって保たれるようにしてもよいが、これらの両電極間にスペーサーを介することにより保たれていてもよい。スペーサーを介する場合には、例えばこの間隔と対応する膜厚の図示しない絶縁体などをエミッタ電極3とコレクタ電極4もしく基板2との間または基板1とコレクタ電極4もしくは基板2との間に挟み込む。このようにスペーサーを介して固定することで、より確実に間隔が保たれるようにすることができる。なお、スペーサーを用いる場合には、本実施形態の熱電子発電素子20は、エミッタ電極3とコレクタ電極4とが電気的に絶縁される構造となっていればよい。
As shown in FIG. 4, the emitter electrode 3 and the collector electrode 4 are arranged to face each other with a predetermined distance therebetween so that the electrodes face each other as shown in FIG. The interval between these electrodes is set to an interval suitable for thermionic power generation, for example, 5 to 50 μm. This interval may be maintained by arranging the emitter electrode 3 and the collector electrode 4 apart from each other with a space therebetween, but may be maintained by using a spacer between these two electrodes. Good. In the case of using a spacer, for example, an insulator (not shown) having a film thickness corresponding to this interval is provided between the emitter electrode 3 and the collector electrode 4 or the substrate 2 or between the substrate 1 and the collector electrode 4 or the substrate 2. Sandwich. By fixing through the spacer in this way, the interval can be more reliably maintained. In addition, when using a spacer, the thermoelectron power generation element 20 of this embodiment should just be the structure where the emitter electrode 3 and the collector electrode 4 are electrically insulated.
ここで、熱電子発電素子20の作動原理について説明する。図2(b)で説明したように、熱電子発電素子20は、電極表面から熱電子が放出される現象を利用して、熱エネルギーを電気エネルギーに変換する。具体的には、外部の熱源から熱がエミッタ電極3に加わると、電子がエミッタ電極3であるダイヤモンド半導体の不純物準位から伝導帯に励起される。図2(b)に示されるように、ダイヤモンド半導体の伝導帯がNEAによって真空準位よりエネルギー準位が高くなっているため、伝導帯に励起された熱電子は、障壁なく真空中へ飛び出す。このように、高温になったエミッタ電極3の表面から熱電子が放出され、コレクタ電極4に到達する。このようにして、コレクタ電極4に到達した熱電子が負荷5を介してエミッタ電極3に戻る際に起電力を生じるため、熱電子発電素子20は、負荷5に対して電力を供給することができる。
Here, the operating principle of the thermoelectric generator 20 will be described. As described in FIG. 2B, the thermoelectric power generation element 20 converts thermal energy into electrical energy by utilizing a phenomenon in which thermoelectrons are emitted from the electrode surface. Specifically, when heat is applied to the emitter electrode 3 from an external heat source, electrons are excited from the impurity level of the diamond semiconductor that is the emitter electrode 3 to the conduction band. As shown in FIG. 2B, since the conduction band of the diamond semiconductor is higher in energy level than the vacuum level by NEA, the thermoelectrons excited in the conduction band jump out into the vacuum without a barrier. Thus, the thermoelectrons are emitted from the surface of the emitter electrode 3 that has become high temperature, and reach the collector electrode 4. In this way, since the thermoelectrons that have reached the collector electrode 4 generate an electromotive force when returning to the emitter electrode 3 via the load 5, the thermoelectric generator 20 can supply power to the load 5. it can.
このように、本実施形態では、高温であっても仕事関数を低く維持する電子放出材料10をエミッタ電極3として用いていることから、高温であっても熱電子の放出量の低下が抑制され、発電の効率や出力の高い熱電子発電素子20となる。
Thus, in this embodiment, since the electron emission material 10 that maintains a low work function even at a high temperature is used as the emitter electrode 3, a decrease in the amount of emitted thermoelectrons is suppressed even at a high temperature. Thus, the thermionic power generation element 20 with high power generation efficiency and output is obtained.
次に、第1、第2、第3実施形態にて示した電子放出材料10を用いた場合の効果を、次の各実施例1~5、比較例1~4および表1を参照して、より具体的に述べることとする。表1では、基板1にMoを用い、基板1に構成別の電子放出材料を熱電子放出素子のエミッタ電極3として形成し、所定の電極温度における熱電子電流を測定した結果を示している。
Next, the effects of using the electron emission material 10 shown in the first, second, and third embodiments will be described with reference to the following Examples 1 to 5, Comparative Examples 1 to 4 and Table 1. I will say more specifically. Table 1 shows the result of measuring the thermoelectron current at a predetermined electrode temperature by using Mo for the substrate 1 and forming the electron emission material according to the configuration on the substrate 1 as the emitter electrode 3 of the thermoelectron emitting element.
なお、表1における「終端原子」とは、ダイヤモンド膜11の表面を終端する原子である。また、表1の「電極温度(℃)」とは、熱電子電流を測定した際の基板の電極温度である。さらに、表1の「熱電子電流(A/cm2)」とは、真空蒸着機の真空チャンバー内に一対の電極基板を対向して配置し、真空下においてダイヤモンド膜11を形成した一方のMo基板を加熱し、当該温度における当該電極間の電流の測定値である。加えて、表1の実施例5における終端原子の欄における「Rb+Cs」とは、第1金属層14としてRb、第2金属層15としてCsを成膜した積層状態を意味する。また、表1の比較例1の終端原子の欄における「O」とは、ダイヤモンド膜11の表面に結合酸素12を形成しただけの状態であることを意味する。さらに、表1の比較例4の終端原子の欄における「H」とは、ダイヤモンド膜11の表面を水素終端した状態であることを意味する。また、表1の熱電子電流の欄における「測定不可」とは、測定限界値である1.0×10-9A/cm2未満であることを意味する。
Note that “terminal atoms” in Table 1 are atoms that terminate the surface of the diamond film 11. The “electrode temperature (° C.)” in Table 1 is the electrode temperature of the substrate when the thermionic current is measured. Furthermore, “Thermionic current (A / cm 2 )” in Table 1 means that a pair of electrode substrates are arranged opposite to each other in a vacuum chamber of a vacuum vapor deposition machine, and one of the Mos formed with the diamond film 11 under vacuum. The measured value of the current between the electrodes at the temperature when the substrate is heated. In addition, “Rb + Cs” in the column of terminal atoms in Example 5 of Table 1 means a stacked state in which Rb is formed as the first metal layer 14 and Cs is formed as the second metal layer 15. In addition, “O” in the column of terminal atoms in Comparative Example 1 in Table 1 means that only bonded oxygen 12 is formed on the surface of the diamond film 11. Further, “H” in the column of terminal atoms in Comparative Example 4 in Table 1 means that the surface of the diamond film 11 is terminated with hydrogen. Further, “not measurable” in the column of the thermionic current in Table 1 means that the measurement limit value is less than 1.0 × 10 −9 A / cm 2 .
(実施例1)
実施例1の電子放出材料は、Moからなる基板1上に形成され、ダイヤモンド膜11と、ダイヤモンド膜11の表面に結合した結合酸素12と、結合酸素12を終端する終端金属13として用いられたNaとにより構成されている。具体的には、ダイヤモンド膜11を形成して、ダイヤモンド膜11の表面にオゾン酸化処理により結合酸素12を設けた上で、基板を500℃に加熱しNaを供給することにより該結合酸素12に対してNaを供給して終端することで作製した。そして、実施例1の電子放出材料を形成した基板と対向する電極に電圧を印加し、これらの電極間に流れる熱電子電流を測定した。その結果、電極温度500℃における熱電子電流は、7.1×10-8A/cm2であった。 Example 1
The electron-emitting material of Example 1 was formed on thesubstrate 1 made of Mo, and was used as the diamond film 11, the bonded oxygen 12 bonded to the surface of the diamond film 11, and the termination metal 13 that terminates the bonded oxygen 12. And Na. Specifically, the diamond film 11 is formed, and the surface of the diamond film 11 is provided with bonded oxygen 12 by ozone oxidation treatment. Then, the substrate is heated to 500 ° C. and Na is supplied to the bonded oxygen 12. On the other hand, Na was supplied and terminated. A voltage was applied to the electrode facing the substrate on which the electron-emitting material of Example 1 was formed, and the thermoelectron current flowing between these electrodes was measured. As a result, the thermionic current at an electrode temperature of 500 ° C. was 7.1 × 10 −8 A / cm 2 .
実施例1の電子放出材料は、Moからなる基板1上に形成され、ダイヤモンド膜11と、ダイヤモンド膜11の表面に結合した結合酸素12と、結合酸素12を終端する終端金属13として用いられたNaとにより構成されている。具体的には、ダイヤモンド膜11を形成して、ダイヤモンド膜11の表面にオゾン酸化処理により結合酸素12を設けた上で、基板を500℃に加熱しNaを供給することにより該結合酸素12に対してNaを供給して終端することで作製した。そして、実施例1の電子放出材料を形成した基板と対向する電極に電圧を印加し、これらの電極間に流れる熱電子電流を測定した。その結果、電極温度500℃における熱電子電流は、7.1×10-8A/cm2であった。 Example 1
The electron-emitting material of Example 1 was formed on the
また、実施例1の電子放出材料を用いた場合、後述する比較例4のダイヤモンド膜11の表面を水素終端したものと同程度の熱電子電流が流れた。このことから、実施例1の電子放出材料は、水素終端した場合と同程度に低仕事関数化できていることが確認された。また、500℃の高温においても安定して電子放出すること、すなわち低仕事関数化を維持できることが確認された。
Further, when the electron emission material of Example 1 was used, a thermoelectron current of the same level as that obtained by hydrogen-termination of the surface of the diamond film 11 of Comparative Example 4 to be described later flowed. From this, it was confirmed that the electron emission material of Example 1 was able to reduce the work function to the same extent as when hydrogen terminated. It was also confirmed that stable electron emission at a high temperature of 500 ° C., that is, a low work function can be maintained.
なお、ダイヤモンド膜11の表面をマイクロ波プラズマによる酸化処理によって作製したものであっても、同等の測定結果を得られた。
Even when the surface of the diamond film 11 was produced by oxidation treatment using microwave plasma, an equivalent measurement result was obtained.
(実施例2)
実施例2の電子放出材料は、実施例1と同様の手順によりKを供給した結果、結合酸素12を介してダイヤモンド膜11の表面がKで終端されたものである。そして、実施例2の電子放出材料を形成した基板を500℃で加熱し、その際に前述の一対の電極間に流れる熱電子電流を測定した。その結果、電極温度500℃における熱電子電流は、2.3×10-6A/cm2であった。 (Example 2)
In the electron emission material of Example 2, the surface of thediamond film 11 was terminated with K through the bonded oxygen 12 as a result of supplying K by the same procedure as in Example 1. The substrate on which the electron-emitting material of Example 2 was formed was heated at 500 ° C., and the thermoelectron current flowing between the pair of electrodes at that time was measured. As a result, the thermoelectron current at an electrode temperature of 500 ° C. was 2.3 × 10 −6 A / cm 2 .
実施例2の電子放出材料は、実施例1と同様の手順によりKを供給した結果、結合酸素12を介してダイヤモンド膜11の表面がKで終端されたものである。そして、実施例2の電子放出材料を形成した基板を500℃で加熱し、その際に前述の一対の電極間に流れる熱電子電流を測定した。その結果、電極温度500℃における熱電子電流は、2.3×10-6A/cm2であった。 (Example 2)
In the electron emission material of Example 2, the surface of the
これにより、実施例2の電子放出材料を用いた場合、実施例1を超える熱電子電流が流れ、Na終端の場合に比べてさらに低仕事関数化できることが確認された。また、実施例1と同様に低仕事関数化と高温安定性を両立できることが確認された。
Thus, when the electron emission material of Example 2 was used, it was confirmed that a thermionic current exceeding Example 1 flows and that the work function can be further reduced as compared with the case of Na termination. Moreover, it was confirmed that the low work function and the high temperature stability can be achieved in the same manner as in Example 1.
(実施例3)
実施例3の電子放出材料は、実施例1と同様の手順によりRbを供給した結果、ダイヤモンド膜11の表面が結合酸素12を介してRbで終端されたものである。そして、実施例3の電子放出材料を形成した基板を500℃で加熱し、その際に前述の一対の電極間に流れる熱電子電流を測定した。その結果、電極温度500℃における熱電子電流は、3.6×10-4A/cm2であった。 (Example 3)
In the electron emission material of Example 3, as a result of supplying Rb by the same procedure as in Example 1, the surface of thediamond film 11 was terminated with Rb through the bonded oxygen 12. And the board | substrate with which the electron emission material of Example 3 was formed was heated at 500 degreeC, and the thermoelectron current which flows between the above-mentioned pair of electrodes in that case was measured. As a result, the thermionic current at an electrode temperature of 500 ° C. was 3.6 × 10 −4 A / cm 2 .
実施例3の電子放出材料は、実施例1と同様の手順によりRbを供給した結果、ダイヤモンド膜11の表面が結合酸素12を介してRbで終端されたものである。そして、実施例3の電子放出材料を形成した基板を500℃で加熱し、その際に前述の一対の電極間に流れる熱電子電流を測定した。その結果、電極温度500℃における熱電子電流は、3.6×10-4A/cm2であった。 (Example 3)
In the electron emission material of Example 3, as a result of supplying Rb by the same procedure as in Example 1, the surface of the
これにより、実施例3の電子放出材料を用いた場合、実施例2をさらに超える熱電子電流が流れ、K終端の場合に比べてさらに低仕事関数化できることが確認された。また、実施例1と同様に低仕事関数化と高温安定性を両立できることが確認された。
Thus, it was confirmed that when the electron emission material of Example 3 was used, a thermionic current further exceeded that of Example 2 and the work function could be further reduced as compared with the case of K termination. Moreover, it was confirmed that the low work function and the high temperature stability can be achieved in the same manner as in Example 1.
(実施例4)
実施例4の電子放出材料は、実施例1と同様の手順によりCsを供給した結果、ダイヤモンド膜11の表面が結合酸素12を介してCsで終端されたものである。そして、実施例4の電子放出材料を形成した基板を500℃で加熱し、常にCsを供給してその際に前述の一対の電極間に流れる熱電子電流を測定した。その結果、電極温度500℃における熱電子電流は、4.0×10-3A/cm2であった。 (Example 4)
In the electron emission material of Example 4, as a result of supplying Cs by the same procedure as in Example 1, the surface of thediamond film 11 was terminated with Cs through the bonded oxygen 12. The substrate on which the electron-emitting material of Example 4 was formed was heated at 500 ° C., Cs was always supplied, and the thermoelectron current flowing between the pair of electrodes at that time was measured. As a result, the thermoelectron current at an electrode temperature of 500 ° C. was 4.0 × 10 −3 A / cm 2 .
実施例4の電子放出材料は、実施例1と同様の手順によりCsを供給した結果、ダイヤモンド膜11の表面が結合酸素12を介してCsで終端されたものである。そして、実施例4の電子放出材料を形成した基板を500℃で加熱し、常にCsを供給してその際に前述の一対の電極間に流れる熱電子電流を測定した。その結果、電極温度500℃における熱電子電流は、4.0×10-3A/cm2であった。 (Example 4)
In the electron emission material of Example 4, as a result of supplying Cs by the same procedure as in Example 1, the surface of the
これにより、実施例4の電子放出材料を用いた場合、実施例3をさらに超える熱電子電流が流れ、Rb終端の場合に比べてさらに低仕事関数化できることが確認された。また、実施例1と同様に低仕事関数化と高温安定性を両立できることが確認された。
Thus, it was confirmed that when the electron emission material of Example 4 was used, a thermionic current further exceeded that of Example 3 and that the work function could be further reduced as compared with the case of Rb termination. Moreover, it was confirmed that the low work function and the high temperature stability can be achieved in the same manner as in Example 1.
(実施例5)
実施例5の電子放出材料は、実施例3と同様の手順によりRbを供給してダイヤモンド膜11の表面に結合酸素12を介してRbを結合させ、さらにCsを供給し当該Rbの上にCsを積層して終端して得られたものである。そして、実施例5の電子放出材料を形成した基板を500℃で加熱し、常にCsを供給しその際に前述の一対の電極間に流れる熱電子電流を測定した。その結果、電極温度500℃における熱電子電流は、2.7×10-3A/cm2であった。 (Example 5)
In the electron emission material of Example 5, Rb is supplied by the same procedure as that of Example 3, Rb is bonded to the surface of thediamond film 11 through the bonded oxygen 12, and Cs is further supplied. Are obtained by laminating and terminating. The substrate on which the electron-emitting material of Example 5 was formed was heated at 500 ° C., Cs was always supplied, and the thermoelectron current flowing between the pair of electrodes at that time was measured. As a result, the thermionic current at an electrode temperature of 500 ° C. was 2.7 × 10 −3 A / cm 2 .
実施例5の電子放出材料は、実施例3と同様の手順によりRbを供給してダイヤモンド膜11の表面に結合酸素12を介してRbを結合させ、さらにCsを供給し当該Rbの上にCsを積層して終端して得られたものである。そして、実施例5の電子放出材料を形成した基板を500℃で加熱し、常にCsを供給しその際に前述の一対の電極間に流れる熱電子電流を測定した。その結果、電極温度500℃における熱電子電流は、2.7×10-3A/cm2であった。 (Example 5)
In the electron emission material of Example 5, Rb is supplied by the same procedure as that of Example 3, Rb is bonded to the surface of the
これにより、実施例5の電子放出材料を用いた場合、実施例3を超える熱電子電流が流れ、Rbで終端した場合に比べてさらに低仕事関数化できることが確認された。また、実施例1と同様に低仕事関数化と高温安定性を両立できることが確認された。
Thus, it was confirmed that when the electron emission material of Example 5 was used, a thermionic current exceeding Example 3 flowed, and the work function could be further reduced as compared with the case where it terminated with Rb. Moreover, it was confirmed that the low work function and the high temperature stability can be achieved in the same manner as in Example 1.
(比較例1)
比較例1の電子放出材料は、実施例1とは異なり、アルカリ金属等の蒸着を行わなかった結果、ダイヤモンド膜11の表面が酸素で終端されたものである。そして、実施例1の電子放出材料を形成した基板を500℃で加熱し、その際に前述の一対の電極間に流れる熱電子電流を測定した。その結果、電極温度500℃における熱電子電流は、測定限界の1.0×10-9A/cm2未満であった。さらに電極温度を730℃にまで上げた場合であっても、730℃における熱電子電流を測定することができなかった。 (Comparative Example 1)
Unlike Example 1, the electron emission material of Comparative Example 1 is one in which the surface of thediamond film 11 is terminated with oxygen as a result of not performing evaporation of alkali metal or the like. The substrate on which the electron-emitting material of Example 1 was formed was heated at 500 ° C., and the thermoelectron current flowing between the pair of electrodes at that time was measured. As a result, the thermionic current at an electrode temperature of 500 ° C. was less than the measurement limit of 1.0 × 10 −9 A / cm 2 . Furthermore, even when the electrode temperature was increased to 730 ° C., the thermoelectron current at 730 ° C. could not be measured.
比較例1の電子放出材料は、実施例1とは異なり、アルカリ金属等の蒸着を行わなかった結果、ダイヤモンド膜11の表面が酸素で終端されたものである。そして、実施例1の電子放出材料を形成した基板を500℃で加熱し、その際に前述の一対の電極間に流れる熱電子電流を測定した。その結果、電極温度500℃における熱電子電流は、測定限界の1.0×10-9A/cm2未満であった。さらに電極温度を730℃にまで上げた場合であっても、730℃における熱電子電流を測定することができなかった。 (Comparative Example 1)
Unlike Example 1, the electron emission material of Comparative Example 1 is one in which the surface of the
このことから、ダイヤモンド膜11の表面を酸素で終端した電子放出材料を用いた場合、図2(a)での説明のように当該電子放出材料ではNEAが起きておらず、仕事関数が大きいために、熱電子電流が流れなかったと考えられる。
For this reason, when an electron emitting material in which the surface of the diamond film 11 is terminated with oxygen is used, NEA does not occur in the electron emitting material and the work function is large as described with reference to FIG. In addition, it is considered that the thermionic current did not flow.
(比較例2、3)
比較例2、3の電子放出材料は、実施例1と同様の手順によりLiを蒸着してダイヤモンド膜11の表面に結合酸素12を介してLiで終端されたものである。比較例2と比較例3との違いは、電極温度である。まず、比較例2については、電子放出材料を形成した基板を500℃で加熱し、その際に前述の一対の電極間に流れる熱電子電流を測定した。その結果、電極温度500℃における熱電子電流は、測定限界の1.0×10-9A/cm2未満であった。比較例3ではさらに電極温度を上げて730℃にしたところ、電極温度730℃における熱電子電流は、5.7×10-7A/cm2であった。 (Comparative Examples 2 and 3)
In the electron emission materials of Comparative Examples 2 and 3, Li was vapor-deposited by the same procedure as in Example 1, and the surface of thediamond film 11 was terminated with Li via the bonded oxygen 12. The difference between Comparative Example 2 and Comparative Example 3 is the electrode temperature. First, for Comparative Example 2, the substrate on which the electron-emitting material was formed was heated at 500 ° C., and the thermoelectron current flowing between the pair of electrodes at that time was measured. As a result, the thermionic current at an electrode temperature of 500 ° C. was less than the measurement limit of 1.0 × 10 −9 A / cm 2 . In Comparative Example 3, when the electrode temperature was further increased to 730 ° C., the thermionic current at the electrode temperature of 730 ° C. was 5.7 × 10 −7 A / cm 2 .
比較例2、3の電子放出材料は、実施例1と同様の手順によりLiを蒸着してダイヤモンド膜11の表面に結合酸素12を介してLiで終端されたものである。比較例2と比較例3との違いは、電極温度である。まず、比較例2については、電子放出材料を形成した基板を500℃で加熱し、その際に前述の一対の電極間に流れる熱電子電流を測定した。その結果、電極温度500℃における熱電子電流は、測定限界の1.0×10-9A/cm2未満であった。比較例3ではさらに電極温度を上げて730℃にしたところ、電極温度730℃における熱電子電流は、5.7×10-7A/cm2であった。 (Comparative Examples 2 and 3)
In the electron emission materials of Comparative Examples 2 and 3, Li was vapor-deposited by the same procedure as in Example 1, and the surface of the
比較例2および比較例3の構成の電子放出材料を用いた場合、電極温度が500℃においては測定できるほどの熱電子電流が流れず、熱電子電流を測定するためには電極温度を730℃にまで上げる必要があった。このことから、Liで終端した電子放出材料については、酸素終端した場合に比べると低仕事関数化できているものの、電極温度を実施例1~5に比べて高温にしなければ同等の熱電子電流が流れないため、低仕事関数化が十分でないと考えられる。
When the electron emission materials having the configurations of Comparative Example 2 and Comparative Example 3 were used, a measurable thermoelectron current did not flow at an electrode temperature of 500 ° C., and the electrode temperature was 730 ° C. in order to measure the thermoelectron current. It was necessary to raise to. From this, the electron-emitting material terminated with Li has a lower work function than that with oxygen termination, but has the same thermionic current unless the electrode temperature is higher than those in Examples 1 to 5. Does not flow, it is thought that low work function is not enough.
(比較例4)
比較例4の電子放出材料は、比較例1と同様の手順により作製され、アルカリ金属を蒸着せず、ダイヤモンド膜11の表面が水素で終端されたものである。比較例4の電子放出材料を形成した基板を500℃で加熱し、その際に前述の一対の電極間に流れる熱電子電流を測定した。その結果、電極温度500℃における熱電子電流は、2.2×10-7A/cm2であった。 (Comparative Example 4)
The electron-emitting material of Comparative Example 4 is produced by the same procedure as that of Comparative Example 1, and the alkali metal is not deposited and the surface of thediamond film 11 is terminated with hydrogen. The substrate on which the electron-emitting material of Comparative Example 4 was formed was heated at 500 ° C., and the thermoelectron current flowing between the pair of electrodes at that time was measured. As a result, the thermionic current at an electrode temperature of 500 ° C. was 2.2 × 10 −7 A / cm 2 .
比較例4の電子放出材料は、比較例1と同様の手順により作製され、アルカリ金属を蒸着せず、ダイヤモンド膜11の表面が水素で終端されたものである。比較例4の電子放出材料を形成した基板を500℃で加熱し、その際に前述の一対の電極間に流れる熱電子電流を測定した。その結果、電極温度500℃における熱電子電流は、2.2×10-7A/cm2であった。 (Comparative Example 4)
The electron-emitting material of Comparative Example 4 is produced by the same procedure as that of Comparative Example 1, and the alkali metal is not deposited and the surface of the
このことから、水素終端した電子放出材料を用いた場合、実施例1~5の場合に比べると熱電子電流が同等以下であるため、比較例1の電子放出材料よりも低仕事関数化できているものの、低仕事関数化が十分でないと考えられる。
From this, when a hydrogen-terminated electron emission material is used, the thermoelectron current is equal to or less than that of Examples 1 to 5, and therefore, the work function can be made lower than that of the electron emission material of Comparative Example 1. However, it seems that low work function is not enough.
これにより、第1実施形態、第2実施形態および第3実施形態で説明したように、ダイヤモンド膜11に結合酸素12を介してアルカリ金属で終端した電子放出材料10は、低仕事関数化しつつ、高温安定性に優れることが確認された。
As a result, as described in the first embodiment, the second embodiment, and the third embodiment, the electron emission material 10 terminated with an alkali metal on the diamond film 11 through the bonded oxygen 12 has a low work function. It was confirmed that the high temperature stability was excellent.
なお、表1には表していないが、実施例1ないし5の電子放出材料10において、アルカリ金属の蒸着量をさらに上げたところ、熱電子電流が増加する現象が確認された。この結果は、ダイヤモンド膜11の表面積に対して終端金属13が覆う面積の割合、すなわち被覆率が十分に最適な状態ではないことを示していると考えられる。つまり、表1における終端金属13については、ダイヤモンド膜11の表面の被覆率を上げることで電子放出を行う部位が増え、熱電子電流の増加に繋がったと考えられる。このことは、ダイヤモンド膜11の表面を終端金属13で100%被覆しなくても高温安定性を確保しつつ、低仕事関数化した電子放出材料10となり、被覆率を適正化することにより電子放出材料10の電子放出特性をさらに向上できることを示唆している。
Although not shown in Table 1, in the electron-emitting materials 10 of Examples 1 to 5, when the alkali metal deposition amount was further increased, a phenomenon in which the thermionic current increased was confirmed. This result is considered to indicate that the ratio of the area covered by the terminal metal 13 to the surface area of the diamond film 11, that is, the coverage is not sufficiently optimal. That is, for the termination metal 13 in Table 1, it is considered that increasing the coverage of the surface of the diamond film 11 increased the number of sites that emit electrons, leading to an increase in thermionic current. This means that the electron emission material 10 has a low work function while ensuring high temperature stability even if the surface of the diamond film 11 is not 100% coated with the termination metal 13, and electron emission is achieved by optimizing the coverage. This suggests that the electron emission characteristics of the material 10 can be further improved.
(他の実施形態)
なお、本開示は、上記した実施形態に限定されるものではなく、適宜変更が可能である。 (Other embodiments)
Note that the present disclosure is not limited to the above-described embodiment, and can be modified as appropriate.
なお、本開示は、上記した実施形態に限定されるものではなく、適宜変更が可能である。 (Other embodiments)
Note that the present disclosure is not limited to the above-described embodiment, and can be modified as appropriate.
例えば、電子放出素子については、熱電子発電素子を例として挙げたが、他にも光励起電子放出素子、光励起熱電子発電素子などが挙げられ、電子放出材料10をこれらの素子におけるエミッタ電極3として適用することができる。電子放出材料10は、高温駆動時においても仕事関数を低く維持することができるため、光励起電子放出素子や光励起熱電子発電素子などのエミッタ電極3として適用することにより、電子放出効率や発電効率の高い素子とすることができる。この場合の光励起電子放出素子などの構成については、公知の素子の構成をとることができる。
For example, as the electron-emitting device, a thermionic power generation device has been described as an example. However, other examples include a photo-excited electron-emitting device and a photo-excited thermionic power generation device, and the electron-emitting material 10 is used as the emitter electrode 3 in these devices. Can be applied. Since the electron emission material 10 can maintain a low work function even when driven at a high temperature, the electron emission material 10 can be used as an emitter electrode 3 such as a photoexcited electron emission element or a photoexcitation thermoelectron generation element, thereby improving the electron emission efficiency and the power generation efficiency. A high element can be obtained. In this case, the configuration of a photoexcited electron-emitting device can be a known device configuration.
また、ダイヤモンド膜11は、上記の成膜方法に限られず、例えばCVD法やスパッタ法にて行われ、RFプラズマCVD、DCプラズマCVD、RFプラズマスパッタ、DCプラズマスパッタ等により形成されてもよい。また、ダイヤモンド膜11の薄膜を構成するN型ダイヤモンドは、単結晶と多結晶のいずれであっても構わない。例えば、高圧合成によって生成したダイヤモンド基板を用いる場合、その上にダイヤモンド膜11を例えばCVD法にて形成すると単結晶となる。
Further, the diamond film 11 is not limited to the film forming method described above, and may be formed by, for example, a CVD method or a sputtering method, and may be formed by RF plasma CVD, DC plasma CVD, RF plasma sputtering, DC plasma sputtering, or the like. The N-type diamond constituting the thin film of the diamond film 11 may be either single crystal or polycrystal. For example, when a diamond substrate produced by high-pressure synthesis is used, a single crystal is formed when the diamond film 11 is formed thereon by, for example, the CVD method.
ダイヤモンド膜11の酸化処理方法として、上記第1実施形態では、オゾン処理を挙げたが、ダイヤモンド膜11の表面を酸化できればよく、酸素プラズマ処理、酸素ラジカル処理、熱混酸処理などであってもよく、他の方法であってもよい。
As the oxidation treatment method for the diamond film 11, the ozone treatment has been described in the first embodiment. However, it is sufficient that the surface of the diamond film 11 can be oxidized, and may be an oxygen plasma treatment, an oxygen radical treatment, a thermal mixed acid treatment, or the like. Other methods may be used.
酸素プラズマ処理として、例えば真空プラズマによる方法について説明する。減圧下の容器中において酸素または酸素混合ガスをプラズマ化し、ダイヤモンド膜11に照射することで、ダイヤモンド膜11の表面を酸素で終端する。具体的には、アルゴンと酸素の混合ガス圧を30Paとした処理室内に、マイクロ波電力300Wを導入することでこれらのガスをプラズマ化し、処理室内に置いたダイヤモンド膜11を成膜した基板を処理する。ダイヤモンド膜基板とプラズマ生成部の間には、荷電粒子と中性粒子を分離するための電極が設置されており、電気的に中性な分子、原子あるいはラジカルを電極に設けられた複数の開口部を通して基板表面へ輸送できる。これに対し、プラズマ中のイオンは基板側にはほとんど拡散しない。
As the oxygen plasma treatment, for example, a method using vacuum plasma will be described. The surface of the diamond film 11 is terminated with oxygen by converting oxygen or an oxygen mixed gas into plasma in a container under reduced pressure and irradiating the diamond film 11 with oxygen. Specifically, a substrate on which the diamond film 11 placed in the processing chamber is formed by introducing microwave power 300 W into the processing chamber in which the mixed gas pressure of argon and oxygen is 30 Pa is introduced into the processing chamber. To process. An electrode for separating charged particles and neutral particles is installed between the diamond film substrate and the plasma generator, and a plurality of openings provided in the electrode with electrically neutral molecules, atoms or radicals. It can be transported through the part to the substrate surface. On the other hand, ions in the plasma hardly diffuse to the substrate side.
酸素プラズマ処理後のダイヤモンド膜表面の原子組成をXPSにより測定した結果、酸素比率は約7%であった。なお、プラズマ処理は、上記の方法および処理条件に限られず、例えば、RFプラズマ、DCプラズマ等であってもよい。
As a result of measuring the atomic composition of the diamond film surface after the oxygen plasma treatment by XPS, the oxygen ratio was about 7%. Note that the plasma processing is not limited to the above-described method and processing conditions, and may be RF plasma, DC plasma, or the like, for example.
また、酸素ラジカル処理として、例えば大気圧プラズマによる方法について説明する。誘電体管内のガスを誘電体バリア放電により電離し、大気圧下において誘電体管から噴出するプラズマジェットをダイヤモンド膜11に照射し、ダイヤモンド膜11の表面を酸素で終端する。具体的には、内径4mmの石英管にHeガスを流し、石英管の外側に巻き付け密着させた銅電極に5~10kVを印加しプラズマを生成する。放電部で生成されたHeイオンおよび準安定状態のHe原子が大気中の酸素と反応することで生成される酸素ラジカルにより、膜表面が酸素で終端される。
Also, for example, a method using atmospheric pressure plasma as oxygen radical treatment will be described. The gas in the dielectric tube is ionized by dielectric barrier discharge, and the diamond film 11 is irradiated with a plasma jet ejected from the dielectric tube under atmospheric pressure, and the surface of the diamond film 11 is terminated with oxygen. Specifically, He gas is flowed through a quartz tube having an inner diameter of 4 mm, and plasma is generated by applying 5 to 10 kV to a copper electrode wound around and closely attached to the outside of the quartz tube. The surface of the film is terminated with oxygen by oxygen radicals generated by the reaction of He ions generated in the discharge part and He atoms in a metastable state with oxygen in the atmosphere.
石英管先端から下流20mmの位置で処理したダイヤモンド膜表面の原子組成をXPSにより測定した結果、酸素比率は約25%であった。なお、プラズマ化するガスについては、Heに限られず、アルゴンなどの不活性ガスや、酸素または大気、それらの混合ガスを用いてもよい。
As a result of measuring the atomic composition of the diamond film surface treated at a position 20 mm downstream from the tip of the quartz tube by XPS, the oxygen ratio was about 25%. Note that the gas to be converted into plasma is not limited to He, and an inert gas such as argon, oxygen or air, or a mixed gas thereof may be used.
Claims (7)
- ダイヤモンド膜(11)と、
前記ダイヤモンド膜の表面に結合する酸素(12)と、
前記酸素を介して前記ダイヤモンド膜に結合する終端金属(13)と、を含む電子放出材料であって、
前記ダイヤモンド膜は、不純物をドープしたN型ダイヤモンド半導体であり、
前記終端金属は、Na、K、Rb、Cs、Mgのうち少なくとも1つを含む電子放出材料。 A diamond film (11);
Oxygen (12) bound to the surface of the diamond film;
An electron-emitting material comprising a termination metal (13) bonded to the diamond film via the oxygen,
The diamond film is an N-type diamond semiconductor doped with impurities,
The termination metal is an electron emission material containing at least one of Na, K, Rb, Cs, and Mg. - 前記終端金属は、Na、K、Rb、Cs、Mgのうち少なくとも2つを含む請求項1に記載の電子放出材料。 The electron-emitting material according to claim 1, wherein the termination metal includes at least two of Na, K, Rb, Cs, and Mg.
- ダイヤモンド膜(11)と、
前記ダイヤモンド膜の表面に結合する酸素(12)と、
前記酸素を介して前記ダイヤモンド膜に結合する結合する第1金属層(14)と、
前記第1金属層の上に積層された第2金属層(15)と、を含む電子放出材料であって、
前記ダイヤモンド膜は、不純物をドープしたN型ダイヤモンド半導体であり、
前記第1金属層は、Li、Na、K、Rb、Cs、Mgのうち少なくとも1つを含み、
前記第2金属層は、Li、Na、K、Rb、Cs、Mgのうち前記第1金属層とは異なる金属を少なくとも1つを含む電子放出材料。 A diamond film (11);
Oxygen (12) bound to the surface of the diamond film;
A first metal layer (14) for bonding to the diamond film via the oxygen;
An electron emission material comprising: a second metal layer (15) laminated on the first metal layer,
The diamond film is an N-type diamond semiconductor doped with impurities,
The first metal layer includes at least one of Li, Na, K, Rb, Cs, and Mg;
The second metal layer is an electron emission material including at least one metal different from the first metal layer among Li, Na, K, Rb, Cs, and Mg. - 互いに対向するように配置されたエミッタ電極(3)とコレクタ電極(4)からなる一対の電極を備え、
前記エミッタ電極は、電子放出を行う電極であって、請求項1ないし3のいずれか1つに記載の電子放出材料で構成される電子放出素子。 A pair of electrodes consisting of an emitter electrode (3) and a collector electrode (4) arranged to face each other,
The electron emitter according to any one of claims 1 to 3, wherein the emitter electrode is an electrode that emits electrons. - 前記電子放出素子は、前記一対の電極間を移動する熱電子を利用する熱電子発電素子である請求項4に記載の電子放出素子。 The electron-emitting device according to claim 4, wherein the electron-emitting device is a thermoelectron generating device that uses thermoelectrons moving between the pair of electrodes.
- 前記電子放出素子は、前記エミッタ電極から光励起により放出される電子を利用する光励起電子放出素子である請求項4に記載の電子放出素子。 The electron-emitting device according to claim 4, wherein the electron-emitting device is a photo-excited electron-emitting device that utilizes electrons emitted from the emitter electrode by photo-excitation.
- 前記電子放出素子は、前記一対の電極間を移動する熱電子を利用する光励起熱電子発電素子である請求項4に記載の電子放出素子。 The electron-emitting device according to claim 4, wherein the electron-emitting device is a photoexcited thermoelectron generating device that uses thermal electrons moving between the pair of electrodes.
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