JP4423496B2 - Electron emission electrode - Google Patents

Description

The present invention relates to an electron emission electrodes having excellent thin carbon film to the electron emission characteristics, an electron emission electrode, particularly with a non-tubular carbon film.

  In a field emission type electron source, a portion where electrons are emitted has a strong electric field concentration that pulls out electrons in the vicinity of the tip portion thereof, so that electrons can be emitted with a low applied voltage. For this reason, since the discovery of carbon nanotubes (hereinafter referred to as CNT), many developments have been made in which carbon materials having a nanometer-sized microstructure are applied to electron-emitting electrodes.

As a development example related to these electron emission electrodes, a metal substrate to be an electron emission electrode is etched to provide convex portions with a constant interval, and a conductive layer such as Al is coated on the convex surface, and a plurality of CNTs are formed thereon. After attaching the conductive layer, the conductive layer is dissolved to make it difficult for the CNT to peel off, and since the CNT is electrically connected to the electrode substrate through the conductive layer, the conductivity between the electrode substrate and the CNT is reduced. It has been reported that uniform electron emission can be obtained from the entire region of the electron emission source (Patent Document 1).
JP 2003-59391 A

  The electron emission electrode is formed by immersing a metal substrate in a solution obtained by dispersing a plurality of linear CNTs in an organic solvent and adding an electrolyte, and attaching the CNTs by electrophoresis. Therefore, the mechanical strength against external stress is fragile, so that there is a risk of being broken by resistance in the liquid phase caused by dispersion in a solution or electrophoresis. As described above, after the CNT is generated separately from the metal substrate, it is necessary to perform electrophoresis or dissolve the conductor to fix the CNT, and the process after the CNT is generated becomes complicated, and the CNT tube There was a problem that the factors that the structure is easily destroyed increased.

  As described above, the conventional electron emission electrode is required to be improved in the manufacturing method and the electron emission capability. Naturally, various electronic devices using these electron-emitting electrodes also have technical problems such as difficulty in manufacturing and high operating voltage.

The present invention has been made in consideration of the above, and an advantage thereof is to provide an electron emission electrodes having excellent electron emission characteristics it is easy to manufacture.

In order to obtain the above advantages, the electron emission electrode according to the first aspect of the present invention is:
A substrate composed of a substrate and a plurality of granular diamonds disposed on the substrate;
An electron emission film formed on the surface of the granular diamond of the substrate and made of a petal-like carbon flake aggregate composed of a plurality of carbon flakes ;
The carbon flakes are composed of a graphene sheet having a thickness of 1 nm to 500 nm, and the interval between the flakes in the outer side opening is 3 μm or less,
The size of the carbon flake aggregate is 5 μm to 30 μm, and the distance between adjacent carbon flake aggregates is 1D to 10D, where D is the diameter of the flake aggregate.
It is characterized by that .

  The petal-like carbon flake aggregate has a function of concentrating the electric field from its shape to the central portion thereof, and electric field concentration due to the effect of the shape of the carbon flake itself is added thereto. Further, the petal-like carbon flake aggregate formed on the protrusion is located at a position protruding toward the anode with respect to the flat portion of the substrate and has a function of concentrating the electric field. Therefore, a double electric field concentration effect occurs at the tip of the petal-like carbon flake aggregate formed on the protrusion, and the threshold voltage at which electrons can be emitted can be lowered.

  The carbon flakes are composed of graphene sheets, for example. By constituting the carbon flakes from a graphene sheet, the electric field concentration is higher than that of an insulator such as diamond or an amorphous carbon film, and high electron emission efficiency can be obtained.

The substrate may, for example, composed of a granular material constituting the substrate, the collision Okoshibutsu disposed on said substrate. The granules, for example, the particle size is composed of diamond particles of 5 to 30 [mu] m. If diamond fine particles are used as the granular material, unlike the iron group element known as a catalyst in carbon film formation, the growth edge is not contaminated with the catalyst element, and the carbon film crystal (graphite on the substrate surface) ) Nucleation can be reduced, so that carbon flakes with better crystallinity can be obtained.

  Since the particulate matter has a low impurity concentration like diamond and maintains a solid phase state even at high temperatures, it does not adversely affect the growth of petal-like carbon flake aggregates by diffusing impurities even if they contain impurities. Absent.

According to the above configuration, the electric field concentration due to the petal-type structure formed by the carbon flakes and the electric field concentration due to the shape effect of the carbon flakes themselves are added, so the electric field concentration at the tip of the assembly is enhanced and the electron emission characteristics are improved. To do.
In addition, the method may further include a step of forming the plurality of protrusions by crystal growth on the substrate, and diamond is particularly preferable as such a protrusion.

  Hereinafter, electron emission electrodes according to embodiments of the present invention will be described with reference to the drawings.

  As shown in a cross section in FIG. 1, an electron emission electrode 10 according to this embodiment includes a substrate 11 composed of a conductive substrate 12 and a plurality of granular materials 13 fixed on the conductive substrate 12, It consists of a petal-like carbon flake aggregate 14 having a petal-like structure formed on the granular material 13 and a planar carbon flake aggregate film 16 formed on the conductive substrate 12.

  The conductive substrate 12 constituting the substrate 11 is made of a conductive material that can withstand a temperature of about 950 ° C. or higher, such as nickel or silicon crystal, and is connected with an electrode for applying a negative voltage.

The granular material 13 constituting the substrate 11 is composed of fine particles of a material such as diamond, molybdenum, SiC, SiN or the like that can grow graphite and can withstand a temperature of about 950 ° C. or higher (a heat treatment temperature during manufacturing). The protruding portion is formed. The granular material 13 has a particle size (about 5 μm to 30 μm) larger than the size of an abnormally grown carbon mass (usually a carbon flake mass) 15 generated due to defects on the substrate 11, and the desired particle size. Is about 5 μm to 30 μm. Further, in order to increase the surface area of the petal-like carbon flake aggregate 14 per unit area of the conductive substrate 12 to improve the electron emission characteristics, the granular material 13 preferably has a polygonal shape having a large surface area. It is preferable that there are tips (corners, sharp corners, etc.) in some places so as to easily release. The arrangement density of the particulate matter on the conductive substrate 12 is, for example, about 10 ⁴ pieces / cm ² to 10 ⁷ pieces / cm ² , depending on the discharge current or the like.

  As schematically shown in a plan view in FIG. 2 and a cross-sectional view taken along the line BB in FIG. 2, a typical petal-like carbon flake aggregate 14 grows from the surface of the granular material 13 and has a curved surface. A plurality of petal-like carbon flakes 14 a are formed so as to be connected to each other in a random direction while standing on the surface of the granular material 13. Each carbon flake 14a is composed of several layers of graphene sheets, and the distance between the flakes in the outer side opening is 3 μm or less.

  One petal-like carbon flake aggregate 14 has a height of 5 μm to 30 μm corresponding to the height of the granular material 13 with respect to the surface of the base 12 or the planar carbon flake aggregate film 16 formed on the base 12. is doing. For this reason, it is closer to the anode than the surface of the base 12 and the abnormally grown lump 15, and the electric field concentration occurs due to the petal-like structure containing the particulate matter.

  By adopting the above structure, a synergistic effect of the electric field concentration due to the shape of each carbon flake 14a and the electric field concentration due to the shape of the petal-like carbon flake aggregate 14 occurs. On the other hand, in the case of the substrate 11 on which the particulate matter 13 is not formed, the petal-like carbon flake aggregate 14 is not formed at a position corresponding to the surface of the particulate matter 13, and the flat planar carbon flake is flat on the smooth surface of the substrate 12. Only the aggregate film 16 is formed. The electron emission electrode 10 provided with the granular material 13 and the petal-like carbon flake aggregate 14 in the present invention emits electrons with the planar carbon flake aggregate film 16 without the granular material 13 and the petal-like carbon flake aggregate 14. Compared with the electrode, the surface is rich in unevenness, and electrons can be easily emitted, and the threshold voltage until a predetermined field emission current is reached can be lowered.

  FIG. 4 shows an SEM (high resolution scanning electron microscope) image of one petal-like carbon flake aggregate 14, and FIG. 5 shows an enlarged image of the central portion thereof. As shown in the figure, curved walls (carbon thin pieces 14a) are connected together at random to substantially surround the opening (gap) and form a circular aggregate as a whole in a petal shape.

  Such petal-like carbon flake assemblies 14 are distributed and formed so as to be arranged at intervals of 1D to 10D when the diameter of the petal-like carbon flake assemblies 14 is D, as shown in FIG. Has been.

  In the electron emission electrode having such a configuration, each carbon flake 14a has a curved base part in contact with the substrate 11, and has a large area in contact with the substrate 11 compared to the point-like contact in the vertically aligned carbon nanotube. Therefore, the adhesion strength with the substrate is much higher than the point-contact carbon nanotube.

  If diamond fine particles are used as the granular material 13, unlike the iron group element known as a catalyst in the graphene sheet formation, the growth edge is not contaminated with the catalyst element, and the carbon crystal ( The energy required for nucleation of (graphite) can be reduced. Therefore, the petal-like carbon flake aggregate 14 with good crystallinity is obtained.

Next, a method for manufacturing the electron emission electrode 10 having the above configuration will be described.
First, the substrate 12 is ultrasonically cleaned with ethanol and acetone for 10 minutes each.
Subsequently, a suspension is prepared by adding 1 g of fine particles (abrasive grains) containing ceramic particles such as silicon nitride having a particle size of 10 μm to 30 μm, diamond, or silicon carbide to 25 ml of an organic solvent (ethanol). To stir.

  Subsequently, the cleaned substrate 12 is immersed in this turbid liquid, and a 43 kHz ultrasonic wave is applied for 10 minutes.

  Thereafter, the substrate 12 is taken out and subjected to ultrasonic cleaning with ethanol and acetone for 10 minutes. Through the above steps, the substrate 11 is formed with the diamond particles 13 fixed on the surface of the base 12. An SEM image of the substrate 11 at this stage is shown in FIG. Comparison of FIG. 7 and FIG. 6 shows that the petal-like carbon flake aggregate 14 is formed with the diamond granular material 13 as a nucleus.

  Next, the substrate 11 is placed on a susceptor 202 in a DC (direct current) plasma CVD apparatus 200 having the configuration illustrated in FIG.

  The DC plasma CVD apparatus 200 is a general-purpose processing apparatus, and includes a processing container (chamber) 201, a susceptor (lower electrode) 202, an upper electrode 203, a processing gas shower head 204, and gas supply pipes 205 and 206. A purge gas supply pipe 207, an exhaust pipe 208, and a DC power source 209.

  The susceptor 202 also serves as a lower electrode and places an object to be processed. A voltage lower than that of the lower electrode 202 is applied to the upper electrode 203.

  The processing gas supply pipe 205 includes an MFC (mass flow controller) and a valve and guides hydrogen gas to the shower head 204. The processing gas supply pipe 206 includes an MFC (mass flow controller) and a valve, and includes carbon-containing gases (for example, hydrocarbon compounds such as methane, ethane, and acetylene, oxygen-containing hydrocarbon compounds such as methanol and ethanol, benzene, toluene, and the like. Aromatic hydrocarbons, carbon dioxide and mixtures thereof) are directed to the showerhead 204.

  The purge gas supply pipe 207 guides nitrogen gas as the purge gas into the processing container 201. The exhaust pipe 208 is connected to the exhaust system 210 and exhausts the inside of the processing container 201. The DC power source 209 applies a DC voltage between the susceptor 202 and the upper electrode 203.

  When the placement of the substrate 11 on the susceptor 202 is completed, the inside of the processing container 11 is then decompressed to about 1 Pa. Subsequently, hydrogen gas and a carbon-containing gas such as methane are led from the gas supply source to the shower head 204 through the gas supply pipes 205 and 206, and the DC power supply 209 is connected between the susceptor (lower electrode) 202 and the upper electrode 203. A plasma state and the temperature of the substrate 11 are controlled by applying a voltage of about 500 V (when the distance between the upper electrode 203 and the susceptor 202 is about 4 cm) and controlling the flowing current. It is desirable to control the temperature of the substrate 11 to 950 ° C. or more and 1200 ° C. or less. The reason why the growth temperature is set to 950 ° C. or higher is that if the temperature is set to 950 ° C. or lower, the quality of the crystals of the formed carbon flakes is lowered and a part thereof may become amorphous. On the other hand, the reason why the temperature is set to 1200 ° C. or lower is that if the temperature is too high, the growth rate of the carbon flakes slows or stops growing, or warps or breaks the substrate due to thermal expansion. The film forming process is continued for about 40 to 180 minutes.

  When the film forming process is executed for a certain period of time, the application of voltage between the susceptor 202 and the upper electrode 203 is stopped, the supply of the processing gas is subsequently stopped, and the nitrogen gas is introduced into the processing container 201 via the purge gas supply pipe 207. Is returned to normal pressure, and the formed electron emission electrode 10 is taken out.

  Through the above steps, an electron emission electrode excellent in electron emission and output is manufactured by a relatively simple process using a processing apparatus having a simple structure as compared with an ECR plasma apparatus such as a DC (direct current) plasma CVD method. be able to.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation and application are possible.

For example, the size and density of the petal-like carbon flake aggregate 14 can be changed as appropriate.
In addition, the process for manufacturing the substrate 11 and the process for manufacturing the petal-like carbon flake aggregate 14 can be appropriately changed.

  For example, the process of forming the substrate 11 having protrusions on the surface is not limited to the above-described process. For example, the surface of the film forming portion of the substrate 12 is rubbed with diamond having a particle diameter of 5 to 30 μm or silicon carbide abrasive grains. A streak of particles is formed on the surface of the substrate 12. By this treatment, abrasive grains (granular materials) are embedded in the surface of the base 12. In this friction step, the normal stress and the number of frictions are adjusted to the base 12 so that the average interparticle distance is 1D to 10D, preferably 3 to 5D, when the average particle diameter is D. Subsequently, in order to remove excess abrasive grains and clean the substrate 12, cleaning is performed for several minutes using an ultrasonic cleaner using an organic solvent. Also by this method, the granular material 13 is firmly fixed to the base body 12, and the substrate 11 having the protrusions is obtained.

Further, diamond or the like may be selectively grown by a CVD method (selective nucleation growth method). In this case, first, etching is performed on the substrate 12 made of a silicon substrate by a photolithography method, and convex portions of ² × ² μm ^{2 in} height and 0.1 μm to 0.2 μm in height are formed on the surface, and an interval (pitch) of about 5 to 100 μm is provided. A plurality of them are formed. The protrusions may be island-like and patterned in a matrix, or may be stripes that are continuous in the vertical or horizontal direction.

  Next, the substrate 12 is washed with an organic solvent such as ethanol or acetone, and then a suspension in which minute diamond nuclei are dispersed is applied onto the substrate 12. The number of times of application is set according to the concentration of fine diamond nuclei in the suspension, and if thin, the application and drying of the suspension may be repeated a plurality of times. In this way, fine diamond nuclei are arranged around the convex portion. Thereafter, an argon beam is irradiated for several minutes to 30 minutes from an oblique direction of 60 ° to 80 ° with respect to the normal direction of the surface of the substrate 12. Then, the exposed diamond micronuclei are destroyed, and the diamond micronuclei that have escaped the exposure due to the steric hindrance of the convex portion remain.

  Subsequently, the diamond micronuclei remaining by the microwave plasma CVD method are crystal-grown to form the granular material 13, and the petal-like carbon flake aggregate 14 is formed on the surface of the granular material 13 and the exposed surface of the substrate 12 by the DC plasma CVD method. Is deposited.

  In such a manufacturing method, since the granular material 13 having an arbitrary diameter can be formed at an arbitrary position by setting the position and interval of the convex portions in advance, the arrangement and density of the granular material 13 can be precisely controlled.

  Etching of the surface of the substrate 12 may be dry etching or wet etching, but leaving a residue adversely affects the growth of the diamond crystal, so that sufficient cleaning is required. Further, if the convex portions are formed with a sufficient interval, a conductor or a semiconductor may be formed on the smooth surface of the base 12 using a metal mask.

  Next, the process of forming the petal-like carbon flake aggregate 14 is also optional. For example, the structure of the processing apparatus can be arbitrarily changed.

An example of the above embodiment will be described below.
A nickel substrate having a diameter of 40 mm was prepared. The nickel substrate was subjected to ultrasonic cleaning with ethanol and acetone for 10 minutes each.
Next, the cleaned nickel substrate is immersed in a solution of 1 g of diamond fine particle powder having a particle size of 20 μm / 25 ml of ethanol, the diamond fine particles are adsorbed on the surface, and ultrasonic waves of 43 kHz are applied for 10 minutes. A substrate having protrusions was formed by biting into and fixing. Such an SEM image of the substrate surface is the image shown in FIG.

  The substrate was taken out and subjected to ultrasonic cleaning with ethanol and acetone for 10 minutes each.

  Next, a voltage of 700 V is applied between the susceptor (lower electrode) and the shower head (upper electrode) with a spacing of 40 mm, the current flowing between the electrodes is controlled to 4 A, and hydrogen gas and methane gas are used as source gases. A carbon flake that is a continuous layer over the substrate 12 and the granular material 13 is formed for 60 minutes, using an overall pressure of 8000 Pa (60 Torr), a methane gas ratio of 8% (volume ratio), and a substrate temperature of 1000 ° C. did.

  As can be seen from FIG. 6, petal-like carbon flake aggregates 14 are formed in a substantially dispersed manner on the substrate. The average diameter of each petal-like carbon flake aggregate is about 10 μm.

FIG. 9 shows the electron emission characteristics of the electron emission electrodes of this example and the comparative example.
Comparative Example 1 is an electron emission electrode in which a petal-like carbon flake aggregate 14 is grown without providing a granular material 13 on a smooth substrate 12, and Comparative Example 2 is a petal after providing a granular material 13 on a substrate 12. An amorphous carbon film is coated instead of the carbon flake aggregate 14.

The electric field strength until reaching the threshold electric field (the electric field between the electrodes for obtaining a radiation current density of 10 μA / cm ² is defined as the threshold electric field) is about 1 V in the electron emission electrode of the example, as is apparent from the figure. / Μm, which is about 3.5 V / μm in Comparative Example 1 and about 12 V / μm in Comparative Example 2, indicating that the electron-emitting electrode of this example exhibits very excellent electron-emitting characteristics. confirmed. From this, even if the petal-like carbon flake aggregate 14 is simply provided, if the granular material 13 is not provided therebelow, sufficient electron emission characteristics cannot be obtained as in Comparative Example 1, and the granular material is simply granular. Even when the object 13 is provided, it can be understood that sufficient electron emission characteristics cannot be obtained as in Comparative Example 2 unless the petal-like carbon flake aggregate 14 is provided as in the example.

In addition, FIG. 10 shows the result of structural analysis of the petal-like carbon flake aggregate 14 formed under the conditions of the above-described example by Raman spectroscopy. As illustrated, the carbon flakes embodiment, the carbon graphite near 1580 cm ^-1 - peak intensity of G-band and 1350 cm ^-1 vicinity of D band caused by vibration of the carbon atoms in the hexagonal lattice of carbon coupling ratio It is clear that the petal-like carbon flake aggregate 14 composed of dense and high-purity graphite is produced from the fact that no other peaks are observed.

  In the electron emission electrode 10 shown in the above embodiment, the abnormally grown lump 15 and the planar carbon flake aggregate film 16 are formed on the conductive substrate 12 between the granular materials 13. Since it occurs mainly in the petal-like carbon flake aggregate 14, it can operate as an electrode without the abnormally growing lump 15 or the planar carbon flake aggregate film 16.

It is sectional drawing which shows the structure of the electron emission electrode concerning embodiment of this invention. It is a top view which shows the structure of the typical petal-like carbon thin piece aggregate | assembly concerning embodiment. It is sectional drawing which shows the structure of the typical petal-like carbon thin piece aggregate | assembly concerning embodiment. It is a SEM image of a petal-like carbon flake aggregate. It is a SEM enlarged image of a petal-like carbon flake aggregate. It is a SEM image which shows distribution of a petal-like carbon flake aggregate on a substrate. It is a SEM image of the board | substrate of the state which coated the diamond particle in the manufacture process. It is a figure which shows the structural example of a DC plasma processing apparatus. It is a figure for demonstrating the electron emission performance of the petal-like carbon flake aggregate manufactured by the present Example. It is a graph which shows the Raman spectrum of the carbon flake of an Example.

Explanation of symbols

11 Substrate 12 Base 13 Protrusion (diamond grain)
14 Petal-like carbon flake aggregate 15 Abnormally growing lump 16 Planar carbon flake aggregate

Claims (1)

A substrate composed of a substrate and a plurality of granular diamonds disposed on the substrate;
An electron emission film formed on the surface of the granular diamond of the substrate and made of a petal-like carbon flake aggregate composed of a plurality of carbon flakes ;
The carbon flakes are composed of a graphene sheet having a thickness of 1 nm to 500 nm, and the interval between the flakes in the outer side opening is 3 μm or less,
The size of the carbon flake aggregate is 5 μm to 30 μm, and the distance between adjacent carbon flake aggregates is 1D to 10D, where D is the diameter of the flake aggregate.
An electron emission electrode.

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