JP2007214117A - Electron emission device and electromagnetic wave generator using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electron emission device which can achieve a high electron emission efficiency even in case of a small exciting energy. <P>SOLUTION: The electron emission device is provided with a carbon nanotube layer 12 formed on a SiC base plate 11 and composed of a plurality of carbon nanotubes oriented in a perpendicular direction to a surface of the SiC base plate 11, a MgO layer 13 formed on the carbon nanotube layer 12 and contacting with the carbon nanotube layer 12, an Ohmic electrode 17 connected with the carbon nanotube layer 12, an electrode 15 arranged to face the MgO layer 13 with a space 14 in-between, and a voltage source to impress a voltage between the Ohmic electrode 17 and the electrode 15. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electron emission device and an electromagnetic wave generation device, and more particularly to an electron emission device and an electromagnetic wave generation device using carbon nanotubes.

  In recent years, due to the increasing demand for improved performance of displays, electron microscopes, illumination devices, electromagnetic wave generators, etc., electrons using carbon nanotubes are aimed at increasing the efficiency and output of electron emission devices used in these devices. Development of discharge devices is underway. Carbon nanotubes can have very high electrical conductivity in the direction along the tube. In addition, since the tip of the tube is sharper than a metal material used in a conventional electron emission source, the electric field strength at the tip is 10 times higher than that of a flat plane. Therefore, it is expected that high electron emission efficiency can be obtained by using carbon nanotubes in the electron emission device (Non-patent Document 1). In addition, since carbon nanotubes have high mechanical strength, it is expected that advantages such as longer life and lower costs can be obtained by using carbon nanotubes in electron emission devices.

  By the way, in order to obtain the expected high electron emission efficiency, it is necessary to orient the carbon nanotubes in the direction in which the electrons are emitted and to reliably emit the electrons from the tip of the carbon nanotubes. Carbon nanotubes are oriented and grown by depositing a metal layer that acts as a catalyst on the substrate, and generating a carbon nanotube by subjecting the hydrocarbon gas to a gas phase chemical reaction while keeping the substrate on which the metal layer is deposited at a high temperature. (For example, see Patent Documents 1, 2, and 3), or a method for generating oriented carbon nanotubes by detaching Si when annealing SiC at high temperature in a vacuum (see, for example, Patent Documents 4 and 5). ) Has been reported. Further, as an electron emission device constructed using such oriented carbon nanotubes, there is one as shown in FIG.

This electron emission device includes an n ⁻ -type SiC substrate 11, a carbon nanotube layer 12 composed of oriented carbon nanotubes formed by the high-temperature annealing method in vacuum, an electrode 15, an ohmic electrode 17, and the like. The voltage source 16 applies a voltage between the electrode 15 and the ohmic electrode 17 on the SiC substrate 11. In such an electron emission device, electrons emitted from the surface of the carbon nanotube layer 12 travel through the gap 14.
JP 2001-15077 A Japanese Patent Laid-Open No. 2001-20071 Japanese Patent Laid-Open No. 2001-20072 Japanese Patent Laid-Open No. 10-265208 JP 2002-293522 A JM Bonard, et al., Solid-State Electronics Vol. 45 (2001), p.893

  However, even in an electron emission device using oriented carbon nanotubes as shown in FIG. 8, the work function, which is a parameter governing the electron emission efficiency, is as extremely high as 4 to 5 eV, realizing high electron emission efficiency. To do so, high excitation energy is still required. Therefore, this electron emission device cannot realize high electron emission efficiency.

  At this time, as a technique for increasing the electron emission efficiency, WS Kim, et al., Applied Physics Letters, Vol. .81 (2002), p.1098. However, this technique cannot achieve the expected high electron emission efficiency when the excitation energy of the electron beam is low. Therefore, even with this technique, high electron emission efficiency cannot be realized.

  Therefore, an object of the present invention is to provide an electron emission device capable of realizing high electron emission efficiency even when excitation energy is low.

  In order to achieve the above object, an electron emission device of the present invention includes a carbon nanotube layer formed on a substrate and composed of a plurality of carbon nanotubes oriented in a direction perpendicular to the substrate surface, and the carbon nanotube layer A second metal oxide layer formed on the metal nanotube layer and contacting the carbon nanotube layer; a first electrode connected to the carbon nanotube layer; and a second electrode disposed opposite to the metal oxide layer. And an electrode.

  By adopting such a configuration, a metal oxide layer is formed on the surface of the carbon nanotube layer, and the barrier height when electrons in the carbon nanotube escape from the surface is lowered, as in the conventional electron emission device. Since high excitation energy is not required, high electron emission efficiency can be realized even when the excitation energy is small.

  Here, the maximum film thickness of the metal oxide layer is preferably smaller than the maximum diameter of the carbon nanotube. The plurality of carbon nanotubes are oriented in a direction perpendicular to the substrate surface, and the length of the metal oxide layer located on the tip of the carbon nanotubes in the direction perpendicular to the substrate surface is More preferably, it is smaller than the maximum diameter of the carbon nanotube.

  With this configuration, a metal oxide layer is selectively formed only on the tip of the carbon nanotube, so that the sharp tip having the strongest surface electric field strength of the carbon nanotube has the highest barrier height on the surface. Can be guaranteed to be low. Further, since each carbon nanotube is oriented in the electron emission direction, it is possible to reliably emit electrons with uniform characteristics from the tip of each carbon nanotube. As a result, the electron emission efficiency can be further increased.

  The metal oxide layer is preferably formed between the plurality of carbon nanotubes.

  By adopting such a configuration, electrons excited on the side wall of the carbon nanotube can escape to the vacuum due to the effect of the metal oxide. As a result, electrons can be emitted without reaching the tip of the carbon nanotube, and the time from excitation to emission is shortened, so that the electron emission efficiency can be further increased.

  The metal oxide layer is preferably formed inside the carbon nanotube.

  With such a configuration, electrons excited inside the carbon nanotubes away from the surface of the carbon nanotubes can escape to the vacuum due to the effect of the metal oxide. As a result, electrons can be emitted without reaching the tip of the carbon nanotube, and the time from excitation to emission is shortened, so that the electron emission efficiency can be further increased.

  Moreover, it is preferable that the said metal oxide layer contains either MgO, BaO, CaO, BeO, and SrO.

  By adopting such a configuration, a material having a high energy level in the electron conduction band can be used as the metal oxide, so that electrons excited by the carbon nanotubes and reaching the conduction band level escape from the surface to a vacuum. Therefore, the height of the barrier can be reduced. As a result, the electron emission efficiency can be further increased.

  The present invention also provides a carbon nanotube layer formed on a substrate and composed of a plurality of carbon nanotubes, a metal oxide layer formed on the carbon nanotube layer and in contact with the carbon nanotube layer, and the carbon nanotube. A light source for irradiating the layer with pulsed light, a first electrode connected to the carbon nanotube layer, and a second electrode disposed so as to face each other with the metal oxide layer interposed therebetween. It can also be set as an electromagnetic wave generator.

  By adopting such a configuration, even if electrons excited by pulsed light inside the carbon nanotube are not excited with sufficient energy to directly exceed the high work function of the carbon nanotube itself, the effect of the metal oxide causes the electron to Evacuation from the discharge surface becomes possible. Furthermore, it is possible to generate terahertz band electromagnetic waves by using ultrashort pulse laser light having a time width of 10 ps or less as pulse light irradiated to the carbon nanotube layer. As a result, a high-power terahertz wave generator can be realized.

  The present invention also provides a carbon nanotube formation step of forming a carbon nanotube layer composed of a plurality of carbon nanotubes on a substrate, and a metal oxide layer on the carbon nanotube layer so as to be in contact with the carbon nanotube layer. Forming the metal oxide layer so that a maximum film thickness of the metal oxide layer is smaller than a maximum diameter of the carbon nanotube in the metal oxide formation step. It can also be set as the manufacturing method of the electron emission apparatus characterized by this. Here, in the metal oxide formation step, the metal oxide layer is preferably formed in a state where the temperature of the substrate is kept at 300 ° C. or lower.

  By passing through such a process, a metal oxide layer can be selectively formed only at the tip of the carbon nanotube.

  Here, in the metal oxide formation step, the metal oxide layer is preferably formed in a state where the temperature of the substrate is maintained at 100 ° C. or higher.

  By passing through such a process, the metal oxide is sufficiently diffused into the gaps and defects between the carbon nanotubes when forming the metal oxide, so that the metal oxide is reliably formed in the gaps between the carbon nanotubes, And a metal oxide can be reliably formed inside a carbon nanotube.

  Here, in the carbon nanotube formation step, a carbon nanotube layer composed of a plurality of carbon nanotubes oriented in a direction perpendicular to the substrate surface is formed, and the method for manufacturing the electron emission device further includes the carbon nanotube A metal oxide layer is formed on the carbon nanotube layer composed of the carbon nanotubes from which the tip portion has been removed in the metal oxide forming step. It is preferable.

  By having such a process, it becomes possible to introduce the metal oxide into the inside of the carbon nanotube from the removed portion of the carbon nanotube at the time of forming the metal oxide, and it is formed inside the carbon nanotube. The amount of metal oxide produced can be increased.

  According to the electron emission device of the present invention, high electron emission efficiency can be realized even when the excitation energy is low.

(First embodiment)
An electron emission apparatus according to a first embodiment of the present invention will be described with reference to the drawings.

FIG. 1A is a cross-sectional view schematically showing the structure of the electron emission device according to the present embodiment.
As shown in FIG. 1A, on the n ⁻ -type SiC substrate 11, there is a high orientation in which the tip is oriented perpendicular to the surface of the SiC substrate 11, that is, the tip is oriented perpendicular to the surface of the SiC substrate 11. A carbon nanotube layer 12 composed of a plurality of carbon nanotubes having a thickness of 200 nm is formed. This carbon nanotube layer 12 is obtained by subjecting the SiC substrate 11 to an annealing process at a temperature of 1000 ° C. for 60 minutes in a vacuum of 1 × 10 ⁻⁵ Torr to desorb Si and leave carbon. It is formed.

  On the carbon nanotube layer 12, a magnesium oxide (MgO) layer 13 having a thickness of 100 nm or less, for example, a thickness of 10 nm, which is in contact with the carbon nanotube layer 12 is formed. The MgO layer 13 is formed by depositing MgO on the carbon nanotube layer 12 by an electron beam evaporation method. The electron emission surface is constituted by the MgO layer 13 and the carbon nanotube layer 12.

  Further, above the MgO layer 13, an electrode 15 is disposed so as to face the MgO layer 13 with a gap 14 having a gap of 10 μm between the MgO layer 13 and the MgO layer 13. The electrode 15 is an electrode that can apply a relatively positive bias voltage to the SiC substrate 11 and functions as an anode electrode that focuses emitted electrons. An ohmic electrode 17 electrically connected to the carbon nanotube layer 12 is formed on the back surface of the SiC substrate 11. The voltage source 16 is connected to the electrode 15 and the ohmic electrode 17, and applies a voltage between the electrode 15 and the ohmic electrode 17. Although the ohmic electrode 17 is formed on the back surface of the SiC substrate 11, the MgO layer 13 and the carbon nanotube layer 12 may be partially removed and formed on the surface of the SiC substrate 11.

  FIG. 1B and FIG. 1C are a cross-sectional view and a top view showing the detailed structure of the outermost surface of the electron emission surface, respectively.

  As shown in FIG. 1B, the carbon nanotube layer 12 formed on the surface of the SiC substrate 11 has an average diameter consisting of five carbon surfaces on average (carbon nanotubes 12a in the X direction of FIG. 1B). (Average length) of a plurality of carbon nanotubes 12a of 110 nm multi-wall type. Each carbon nanotube 12a has a structure in which each carbon surface is closed at the outermost surface while maintaining a predetermined inter-surface distance, and the tip of each carbon nanotube 12a (A in FIG. 1B) has a sharp shape. ing. An MgO layer 13 deposited by electron beam evaporation is formed on the carbon nanotube 12a having such a structure. The MgO layer 13 is selectively migrated to the tip of the carbon nanotube 12a so that the length in the vertical direction is smaller than the maximum diameter of the carbon nanotube 12a. It is comprised from MgO13b formed in the part. In this way, the migrated MgO 13a is formed at the tip of the carbon nanotube 12a because the atomic arrangement of graphite-type carbon on the ideal carbon surface collapses at the tip of the carbon nanotube 12a, and the atoms rearrange. This is because a defective structure is formed and extremely high reactivity with respect to different atoms and molecules is exhibited. At this time, the maximum film thickness B (the maximum value of the length of the MgO layer 13 in the Y direction in FIG. 1B) is the maximum diameter C of the carbon nanotubes 12a (the carbon nanotubes 12a in the X direction in FIG. 1B). The MgO layer is controlled so that the temperature of the SiC substrate 11 is maintained at 300 ° C. or less so that the temperature is less than one-tenth of the maximum diameter of the carbon nanotubes 12a. 13 is formed. Thereby, it becomes possible to form the MgO layer 13 in which the coating amount is selectively increased at the tip of the carbon nanotube 12a. As a result, the thickness of the portion of the MgO layer 13 located on the tip of the carbon nanotube 12a is thicker than the thickness of the portion other than the portion of the MgO layer 13 located on the tip of the carbon nanotube 12a.

  In the electron emission device having the structure as described above, by applying a relatively positive bias voltage to the SiC substrate 11 from the voltage source 16, the electrons in the carbon nanotube layer 12 are emitted from the surface and emitted. The emitted electrons travel through the gap 14.

  FIG. 2 is an energy diagram of the electron emission surface. 2A is an energy diagram when a positive voltage is applied from the surface vacuum side 31 to the carbon nanotube layer 12 whose surface is not covered with the MgO layer 13, and FIG. 2B is an MgO layer. 4 is an energy diagram when a positive voltage is applied from the surface vacuum side 31 to the carbon nanotube layer 12 whose surface is covered with the layer 13.

From FIG. 2A, in the carbon nanotube layer 12 whose surface is not covered with the MgO layer 13, the electrons excited in the carbon nanotube layer 12 directly overcome the barrier corresponding to the work function φ _M of the carbon nanotube itself. It can be seen that it is emitted to the surface vacuum side 31 by the path 32 or by the path 33 passing through the barrier by the tunnel. On the other hand, from FIG. 2B, in the carbon nanotube layer 12 whose surface is covered with the MgO layer 13, the electrons excited in the carbon nanotube layer 12 pass through the energy level Ec near the conduction band of MgO. It can be seen that it is emitted to the surface vacuum side 31 by the conducting path 32 ′ or the path 33 ′. Accordingly, in the carbon nanotube layer 12 whose surface is covered with the MgO layer 13, the barrier height when electrons escape from the surface is reduced to about the electron affinity χ of MgO (usually 2 eV or less), and from the surface. The excitation energy required for electron emission is reduced.

  Next, electrical characteristics of the electron emission device having the above structure will be described with reference to FIG. FIG. 3 is a diagram showing a current-voltage characteristic curve of the electron-emitting device. In FIG. 3, a solid line (curve I) indicates a current-voltage characteristic curve of the electron emission device having the above structure, and a dotted line (curve II) indicates a current-voltage characteristic curve of the electron emission device having the above structure not using MgO. The alternate long and short dash line (curve III) shows the current-voltage characteristic curve of the electron emission device having the above structure in which MgO is not used and each carbon nanotube is not oriented in the carbon nanotube layer.

  From the difference between curve II and curve III in FIG. 3, when the applied voltage when the field emission current exceeds 0.01 μA is defined as the threshold voltage by orienting the carbon nanotubes, the threshold voltage is about 350 V ( It can be seen that the current value is increased by about 10 times as compared with the applied voltage of 325 V, and is decreased by about 50 V from the curve III) to about 300 V (curve II). This is because the electric field strength at the tip of each carbon nanotube is enhanced by orienting each carbon nanotube. On the other hand, from the difference between curve I and curve II, it can be seen that by coating each carbon nanotube with MgO, the threshold voltage is further reduced by about 50 V and the current is further increased by about 10 times. This is because by depositing MgO on the carbon nanotubes, the barrier height when electrons escape from the surface is lowered, and the electron emission efficiency is increased.

  As described above, according to the electron emission device of the present embodiment, the carbon nanotube is coated with MgO. Therefore, the barrier height when electrons escape from the surface is lowered, and electrons are emitted to the outside even when the voltage applied by the voltage source is small. That is, since high excitation energy is not required as in the conventional electron emission device, high electron emission efficiency can be realized even when the excitation energy is small.

  In addition, according to the electron emission device of the present embodiment, the carbon nanotubes are aligned in the electron emission direction, and the tips of the aligned carbon nanotubes are covered with MgO. Therefore, the electrons emitted from the carbon nanotubes are easily emitted from the tip part into the vacuum, so that the electron emission efficiency can be increased. At this time, MgO corresponding to the thickness of the MgO deposited during the formation of the MgO layer is also formed in the gaps between the carbon nanotubes. Therefore, electrons are emitted also from the carbon nanotube side wall through MgO deposited on the side wall.

  Further, according to the electron emission device of the present embodiment, the carbon nanotubes are aligned, so that the electron emission directions are aligned. Therefore, electron emission with uniform characteristics can be surely performed from the tip of the carbon nanotube, and the electron emission efficiency can be increased.

In the electron emission device of the present embodiment, as shown in FIG. 4, the MgO layer 13 has MgO 13c formed in the gaps between the carbon nanotubes 12a and MgO 13d formed inside the carbon nanotubes 12a. May be. By adopting such a configuration, it is possible to cause electron emission to the vacuum via MgO also from the side wall and the inner wall of the part away from the tip of the carbon nanotube, and it is possible to increase the electron emission probability. . This configuration is realized by the manufacturing method shown in the flowchart of FIG. That is, first, the substrate is annealed under the conditions of temperature: 1700 ° C., time: 20 minutes, pressure: 10 ⁻² Pa, and oxygen partial pressure of 1% to grow carbon nanotubes (step S11). Thereafter, the tip of the carbon nanotube is thermally oxidized under the conditions of temperature: 700 ° C., time: 20 minutes, pressure: atmospheric pressure, and oxygen partial pressure 20%, and the thermally oxidized portion is removed to remove the tip of the carbon nanotube. A part is released (step S12). And this structure is formed by depositing MgO with a film thickness of 10 nm by evaporating MgO on the opened tip portion under the conditions of the substrate temperature: 300 ° C. and the pressure of 10 ⁻³ Pa using the electron beam evaporation method. Is realized (step S13). The SiC substrate on which the carbon nanotube layer is formed is kept at a high temperature of 100 ° C. or higher during vacuum deposition of MgO by utilizing the fact that MgO is selectively diffused into voids and defects of the carbon nanotube during MgO deposition. This is because MgO can sufficiently diffuse into the gaps and defects of each carbon nanotube during deposition in this temperature range, and the carbon nanotube itself can maintain a mechanical shape. Thereby, the amount of MgO formed inside the carbon nanotube can be increased. The opening of the tip of the carbon nanotube may be performed by removing the tip by irradiating the tip of the carbon nanotube with an electron beam.

  In the electron emission device of the present embodiment, MgO is exemplified as the metal oxide deposited on the carbon nanotube layer. However, the oxide is not limited to this as long as it is a Group 2 oxide, and alternatively, SrO, BaO, BeO, Even if CaO or these alloys are used, an equivalent effect can be obtained.

(Second Embodiment)
An electromagnetic wave generator according to a second embodiment of the present invention will be described with reference to the drawings.

FIG. 6 is a cross-sectional view schematically showing the structure of the electromagnetic wave generator according to the present embodiment.
As shown in FIG. 6, the n ⁻ type SiC substrate 11 is formed with a carbon nanotube layer 12 composed of a plurality of carbon nanotubes having a height of 200 nm oriented in a direction perpendicular to the surface of the SiC substrate 11. . The carbon nanotube layer 12 is formed by subjecting the SiC substrate 11 to a temperature of 1000 ° C. for 60 minutes in a vacuum of 1 × 10 ⁻⁵ Torr to desorb Si to leave carbon. It is formed.

  On the carbon nanotube layer 12, an MgO layer 13 having a thickness of 100 nm or less, for example, 10 nm, which is in contact with the carbon nanotube layer 12 is formed. The MgO layer 13 is formed by depositing MgO on the carbon nanotube layer 12 by an electron beam evaporation method. The electron emission surface is constituted by the MgO layer 13 and the carbon nanotube layer 12.

  Here, the electron emission surface constituted by the MgO layer 13 and the carbon nanotube layer 12 is irradiated with an ultrashort pulse light train 28 that passes through the electrode 25 and the substrate 26. The ultrashort pulse light train 28 is light having energy smaller than the electron affinity χ of MgO that becomes a barrier height when electrons escape from the electron emission surface, for example, pulse light having a wavelength of 780 nm, a pulse width of 100 fs, and a repetition frequency of 50 MHz. Yes, generated by a femtosecond laser light source 27.

  An electrode 25 is disposed above the MgO layer 13 so as to face the MgO layer 13 with a gap 14 of 10 μm between the MgO layer 13 and the MgO layer 13. The electrode 25 is an electrode made of ITO having a film thickness of 200 nm to which a positive bias voltage can be applied relative to the SiC substrate 11, and functions as an anode electrode that focuses emitted electrons. The electrode 25 is formed on a substrate 26 made of cycloolefin glass. An ohmic electrode 17 electrically connected to the carbon nanotube layer 12 is formed on the back surface of the SiC substrate 11. The voltage source 16 is connected to the electrode 25 and the ohmic electrode 17, and applies a voltage between the electrode 25 and the ohmic electrode 17. Although the ohmic electrode 17 is formed on the back surface of the SiC substrate 11, a part of the MgO layer 13 and the carbon nanotube layer 12 may be removed and formed on the surface of the SiC substrate 11.

  The electron emission surface has the same configuration as the electron emission surface shown in FIGS. That is, the carbon nanotube layer 12 formed on the surface of the SiC substrate 11 is composed of a plurality of multiwall-type carbon nanotubes 12a having an average diameter of 110 nm and comprising five carbon surfaces on average. Each carbon nanotube 12a has a structure in which each carbon surface is closed at the outermost surface while maintaining a predetermined inter-surface distance, and the tip of each carbon nanotube 12a has a sharp shape. On the carbon nanotube 12a, an MgO layer 13 deposited by electron beam evaporation is formed. The MgO layer 13 is selectively migrated to the tip of the carbon nanotube 12a so that the length in the vertical direction is smaller than the maximum diameter of the carbon nanotube 12a. It is comprised from MgO13b formed in the part. In this way, the migrated MgO 13a is formed at the tip of the carbon nanotube 12a because the atomic arrangement of graphite-type carbon on the ideal carbon surface collapses at the tip of the carbon nanotube 12a, and the atoms rearrange. This is because a defective structure is formed and extremely high reactivity with respect to different atoms and molecules is exhibited. At this time, the temperature of the SiC substrate 11 is kept at 300 ° C. or less so that the maximum film thickness is thinner than the maximum diameter of the carbon nanotubes 12a, preferably 1/10 or less of the maximum diameter of the carbon nanotubes 12a. The MgO layer 13 is formed under the control. Thereby, it becomes possible to form the MgO layer 13 in which the coating amount is selectively increased at the tip of the carbon nanotube 12a.

  In the electromagnetic wave generator having the structure as described above, a relatively positive bias voltage is applied to the SiC substrate 11 by the voltage source 16, and the ultrashort pulse light train 28 generated by the femtosecond laser light source 27 is further provided. By irradiating the electron emission surface, electrons in the carbon nanotube layer 12 are emitted from the electron emission surface. The electron group 29 emitted from the MgO layer 13 and focused on the electrode 25 becomes a pulse train of about the time width of the irradiation laser pulse, and a pulse current of about 100 fs to 1 ps flows between the electrode 25 and the electron emission surface. Accordingly, an electromagnetic wave 30 having an electric field strength proportional to the temporal change rate of the instantaneous current is generated. At this time, the frequency of the generated electromagnetic wave 30 is approximately equal to the reciprocal of the pulse width of the instantaneous current and is in the region of 1 to 10 THz, that is, the terahertz band. Therefore, the distance between the electrode 25 and the electron emission surface is the terahertz band electromagnetic wave. The wavelength and the order are 10 μm.

  Next, the characteristics of the electromagnetic wave generator having the above structure will be described with reference to FIG. FIG. 7 is a diagram showing power spectrum characteristics of electromagnetic waves generated by the electromagnetic wave generator. In FIG. 7, the solid line (curve I) indicates the power spectrum characteristic (curve I) of the electromagnetic wave generated by the electromagnetic wave generator having the above structure, and the broken line (curve II) indicates the above structure in which MgO is not used on the photocathode. The power spectrum characteristic of the electromagnetic waves generated by the electromagnetic wave generator is shown.

  From FIG. 7, it can be seen that the electromagnetic wave generator of this embodiment has improved the peak power of the electromagnetic wave nearly 100 times as compared with the electromagnetic wave generator that does not use MgO. This is due to the fact that as a result of using MgO for the photocathode, the radiation current was improved 10 times as shown in FIG.

  As described above, according to the electromagnetic wave generator of the present embodiment, high electron emission efficiency can be realized even when the excitation energy is small for the same reason as in the first embodiment. A terahertz wave is generated by the emission of electrons. Therefore, a high-output terahertz wave generator can be realized.

  In the electromagnetic wave generator of the present embodiment, MgO is exemplified as the metal oxide deposited on the carbon nanotube layer. However, the oxide is not limited to this as long as it is a Group 2 oxide, and alternatively, SrO, BaO, BeO, Even if CaO or these alloys are used, an equivalent effect can be obtained.

  Moreover, in the electromagnetic wave generator of the present embodiment, the SiC substrate is exemplified as the substrate on which the metal oxide is formed. However, the substrate is not limited to this as long as it is a substrate containing carbon. The effect of can be obtained.

  The present invention can be used for an electron emission device, and in particular, can be used for a display, an electron microscope, an illumination device, an electromagnetic wave generation device, and the like.

(A) It is sectional drawing which shows typically the structure of the electron emission apparatus which concerns on the 1st Embodiment of this invention. (B) It is sectional drawing which shows the detailed structure of the outermost surface of an electron emission surface. (C) It is a top view which shows the detailed structure of the outermost surface of an electron emission surface. (A) It is the energy diagram of the electron emission surface at the time of applying a positive voltage from the surface vacuum side to the carbon nanotube layer by which the surface is not coat | covered with MgO layer. (B) It is an energy diagram of the electron emission surface at the time of applying a positive voltage from the surface vacuum side to the carbon nanotube layer by which the surface is coat | covered with the MgO layer. It is a figure which shows the electric current-voltage characteristic curve of an electron emission apparatus. It is sectional drawing which shows the detailed structure of the outermost surface of an electron emission surface. It is a flowchart which shows the manufacturing method of an electron emission apparatus. It is sectional drawing which shows typically the structure of the electromagnetic wave generator which concerns on the 2nd Embodiment of this invention. It is a figure which shows the power spectrum characteristic of the electromagnetic waves which generate | occur | produce with an electromagnetic wave generator. It is sectional drawing which shows the structure of the conventional electron emission apparatus typically.

Explanation of symbols

11 SiC substrate 12 Carbon nanotube layer 12a Carbon nanotube 13 Magnesium oxide (MgO) layer 13a, 13b, 13c, 13d MgO
14 Air gap 15, 25 Electrode 16 Voltage source 17 Ohmic electrode 26 Substrate 27 Femtosecond laser light source 28 Ultrashort pulse light train 29 Electron group 30 Electromagnetic wave

Claims (13)

A carbon nanotube layer formed of a plurality of carbon nanotubes formed on a substrate and oriented in a direction perpendicular to the substrate surface;
A metal oxide layer formed on the carbon nanotube layer and in contact with the carbon nanotube layer;
A first electrode connected to the carbon nanotube layer;
An electron-emitting device, comprising: a second electrode disposed to face the metal oxide layer with a space therebetween. The electron emission device according to claim 1, wherein the maximum film thickness of the metal oxide layer is smaller than the maximum diameter of the carbon nanotube. 2. The electron emission according to claim 1, wherein a length of the metal oxide layer located on a tip portion of the carbon nanotube in a direction perpendicular to the substrate surface is smaller than a maximum diameter of the carbon nanotube. apparatus. The electron emission device according to claim 1, wherein the metal oxide layer is formed between the plurality of carbon nanotubes. The electron emission device according to claim 1, wherein the metal oxide layer is formed inside the carbon nanotube. The electron emission device according to claim 1, wherein the metal oxide layer includes any one of MgO, BaO, CaO, BeO, and SrO. The thickness of the portion of the metal oxide layer located on the tip of the carbon nanotube is thicker than the thickness of the portion of the metal oxide layer other than the portion located on the tip of the carbon nanotube. The electron-emitting device according to claim 1. A carbon nanotube layer formed on the substrate and composed of a plurality of carbon nanotubes;
A metal oxide layer formed on the carbon nanotube layer and in contact with the carbon nanotube layer;
A light source for irradiating the carbon nanotube layer with pulsed light;
A first electrode connected to the carbon nanotube layer;
An electromagnetic wave generation device comprising: a second electrode disposed to face the metal oxide layer with a space therebetween. A carbon nanotube formation step of forming a carbon nanotube layer composed of a plurality of carbon nanotubes on the substrate;
Forming a metal oxide layer on the carbon nanotube layer so as to be in contact with the carbon nanotube layer; and
In the metal oxide formation step, the metal oxide layer is formed so that the maximum film thickness of the metal oxide layer is smaller than the maximum diameter of the carbon nanotube. The method for manufacturing an electron-emitting device according to claim 9, wherein, in the metal oxide formation step, the metal oxide layer is formed in a state where the temperature of the substrate is kept at 300 ° C. or lower. 11. The method for manufacturing an electron-emitting device according to claim 10, wherein in the metal oxide formation step, the metal oxide layer is formed in a state where the temperature of the substrate is maintained at 100 ° C. or higher. In the carbon nanotube formation step, a carbon nanotube layer composed of a plurality of carbon nanotubes oriented in a direction perpendicular to the substrate surface is formed,
The manufacturing method of the electron emission device further includes a removal step of removing a part of the tip of the carbon nanotube,
10. The electron emission device according to claim 9, wherein, in the metal oxide formation step, a metal oxide layer is formed on a carbon nanotube layer composed of carbon nanotubes from which a part of the tip portion has been removed. Manufacturing method. The method of manufacturing an electron-emitting device according to claim 9, wherein, in the carbon nanotube formation step, the carbon nanotube layer is formed by heat-treating the substrate containing carbon to desorb the carbon.

Images