CN113838725A - Graphene field emission cathode and preparation method thereof - Google Patents
Graphene field emission cathode and preparation method thereof Download PDFInfo
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Classifications
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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
- H01J1/30—Cold cathodes, e.g. field-emissive cathode
- H01J1/304—Field-emissive cathodes
- H01J1/3042—Field-emissive cathodes microengineered, e.g. Spindt-type
- H01J1/3044—Point emitters
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
- H01J9/02—Manufacture of electrodes or electrode systems
- H01J9/022—Manufacture of electrodes or electrode systems of cold cathodes
- H01J9/025—Manufacture of electrodes or electrode systems of cold cathodes of field emission cathodes
Abstract
The invention discloses a graphene field emission cathode and a preparation method thereof. The graphene field emission cathode includes: a conductive substrate; graphene nanoplatelets grown upright on the conductive substrate; a metal nanoparticle bonded on a surface of the graphene nanoplatelet. The graphene field emission cathode provided by the invention can greatly increase the density of electron emission tips and the number of effective emission tips, and can improve the field emission current.
Description
Technical Field
The invention relates to the technical field of field emission, in particular to a graphene field emission cathode and a preparation method thereof.
Background
Vacuum electronic devices have wide application in the fields of communication, space technology, security detection, medical imaging and the like. The core component of the vacuum electronic device is a cathode which is used for generating electron beam current required by the operation of the vacuum electronic device. At present, the most widely used cathode is a metal hot cathode, however, the hot cathode has the defects of large volume, large heat radiation power consumption, long starting time, material evaporation at high temperature and the like, and the development of vacuum electronic devices towards miniaturization and integration is limited.
In recent years, field emission cold cathodes based on various one-dimensional/two-dimensional nanomaterials are widely focused and researched by researchers, under a lower electric field, the nanometer tips of the field emission cold cathodes can form a local enhancement effect, electrons can generate a tunneling effect under the action of the lower electric field, and a larger emission current is formed, and the typical examples of the field emission cold cathodes are graphene and carbon nanotubes. The graphene has rich sharp edge structures, can be used as an effective electron emission address, and is an ideal field emission nanometer material due to stable mechanochemical properties and excellent electric and heat conduction characteristics. However, the number of active emission tips in the existing graphene field emission cathode is small, and thus the corresponding field emission current is to be further improved.
Disclosure of Invention
In view of this, the present invention provides a graphene field emission cathode and a method for manufacturing the same, so as to solve the problem of how to increase the field emission current of the graphene field emission cathode.
In order to achieve the purpose, the invention adopts the following technical scheme:
a graphene field emission cathode, comprising:
a conductive substrate;
graphene nanoplatelets grown upright on the conductive substrate;
a metal nanoparticle bonded on a surface of the graphene nanoplatelet.
Preferably, the thickness of the graphene nanosheet is 0.5nm to 5 nm; and/or the growth height of the graphene nano sheet is5-20 μm; and/or the distribution density of the graphene nano sheets on the conductive substrate is 107～108Tablet/mm2。
Preferably, the conductive substrate is a titanium substrate, a tantalum substrate, a stainless steel substrate or a glassy carbon substrate.
Preferably, the metal nanoparticles have a work function of no greater than 5.7 eV; and/or the particle size of the metal nano-particles is 10 nm-100 nm; and/or the distribution density of the metal nanoparticles on the surface of the graphene nano sheet is 109～1011Per mm2。
Preferably, the metal nanoparticles are selected from at least one of palladium nanoparticles, gold nanoparticles, copper nanoparticles, platinum nanoparticles, and silver nanoparticles.
Another aspect of the present invention is to provide a method for preparing a graphene field emission cathode, which includes:
providing the conductive substrate and carrying out cleaning treatment;
preparing a mixed solution containing graphene oxide and target metal ions;
preparing the graphene field emission cathode by taking the mixed solution as an electrolyte solution and the conductive substrate as a working electrode and adopting an electrodeposition process of a three-electrode system;
wherein, during the electrodeposition process, the graphene oxide in the mixed solution is deposited on the conductive substrate and reduced to graphene, formed into graphene nanoplatelets growing in an upright state, and the target metal ions are reduced to metal nanoparticles and bonded to the surfaces of the graphene nanoplatelets.
Specifically, the preparing a mixed solution containing graphene oxide and metal ions includes:
preparing a graphene oxide nanosheet dispersion liquid;
preparing a soluble metal salt solution containing target metal ions;
adding the soluble metal salt solution into the graphene oxide nanosheet dispersion liquid, stirring and mixing to obtain the mixed solution.
Specifically, in the mixed solution, the concentration of the graphene oxide nanosheet is 0.1-0.5 g/L, and the concentration of the target metal ion is 3-8 mM.
Specifically, the transverse size of the graphene oxide nanosheet is 1-10 μm, and the thickness of the graphene oxide nanosheet is 0.5-5 nm; and/or the target metal ion is at least one of palladium, gold, copper, platinum and silver ions, and the corresponding soluble metal salt is selected from Na2PdCl4、HAuCl4、CuSO4、CuCl2、H2PtCl6、K2PtCl6、Na2PtCl4And AgNO3At least one of (1).
Specifically, in the electrodeposition process of the three-electrode system, the reference electrode is a saturated calomel electrode, the counter electrode is a platinum sheet electrode, the voltage scanning rate is 20 mV/s-80 mV/s, the scanning voltage range is-1.4V-0.6V, and cyclic scanning is carried out for 3-10 times.
According to the graphene field emission cathode provided by the embodiment of the invention, a large number of graphene nano sheets grow on the conductive substrate in an upright manner, so that the density of electron emission tips of the field emission cathode and the number of effective emission tips are greatly increased, and the field emission current can be improved; furthermore, the metal nanoparticles combined on the surface of the graphene nanosheet and the graphene generate an electronic charge interaction, the electronic structure of the graphene is changed, the state density near the Fermi level of the graphene is increased, and the work function of the graphene is reduced, so that the opening electric field of the graphene cathode is reduced, the field emission current is further improved, and the emission stability can be improved.
Drawings
Fig. 1 is a schematic structural diagram of a graphene field emission cathode in an embodiment of the present invention;
fig. 2 is an SEM image of graphene nanoplatelets grown on a conductive substrate in an embodiment of the present invention;
fig. 3a and 3b are graphs of electrical tests of the graphene field emission cathode in this example 1;
fig. 4a and 4b are graphs of electrical tests of the graphene field emission cathode in this example 2.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention are described in detail below with reference to the accompanying drawings. Examples of these preferred embodiments are illustrated in the accompanying drawings. The embodiments of the invention shown in the drawings and described in accordance with the drawings are exemplary only, and the invention is not limited to these embodiments.
It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and/or processing steps closely related to the scheme according to the present invention are shown in the drawings, and other details not so relevant to the present invention are omitted.
An embodiment of the present invention first provides a graphene field emission cathode, as shown in fig. 1, the graphene field emission cathode includes: the graphene nano-sheet structure comprises a conductive substrate 10, graphene nano-sheets 20 vertically grown on the conductive substrate 10, and metal nano-particles 30 bonded on the surfaces of the graphene nano-sheets 20.
The graphene nanoplatelets grown in a vertical manner mean that an included angle between a height direction of the graphene nanoplatelets and a normal line of the conductive substrate is not more than 45 °.
Graphene field emission cathodes based on the above structure: (1) the graphene nanoplates 20 are vertically grown on the conductive substrate 10, so that the density of electron emission tips of the field emission cathode and the number of effective emission tips are greatly increased, and the field emission current can be improved; (2) the metal nanoparticles 30 combined on the surface of the graphene nanosheet 20 and graphene generate an electronic charge interaction, so that the electronic structure of the graphene is changed, the state density near the Fermi level of the graphene is increased, and the work function of the graphene can be remarkably reduced, so that the opening electric field of a graphene cathode is reduced, the field emission current is further improved, and the emission stability can be improved.
In some preferable technical schemes, the thickness of the graphene nano sheet is 0.5 nm-5 nm, and the thickness is within the rangeAnd the graphene emission tip has a higher local field enhancement effect, the growth height is 5-20 mu m, and the shielding effect of the emission tip can be better limited under the height. Wherein the distribution density of the graphene nano sheets on the conductive substrate is 107～108Tablet/mm2。
In some preferred technical solutions, the conductive substrate is a titanium substrate, a tantalum substrate, a stainless steel substrate, or a glassy carbon substrate.
In some preferred embodiments, the work function of the metal nanoparticles is not greater than 5.7eV, and examples of the metal nanoparticles include palladium (Pd), gold (Au), copper (Cu), platinum (Pt), silver (Ag), hafnium (Hf), molybdenum (Mo), niobium (Nb), ruthenium (Ru), tantalum (Ta), vanadium (V), and yttrium (Y).
In a further preferable scheme, the particle size of the metal nanoparticles is 10nm to 100 nm; the distribution density of the metal nanoparticles on the surface of the graphene nanoplatelets is 109～1011Per mm2。
The metal nanoparticles are more preferably at least one of palladium (Pd) nanoparticles, gold (Au) nanoparticles, copper (Cu) nanoparticles, platinum (Pt) nanoparticles, or silver (Ag) nanoparticles.
The embodiment of the invention also provides a preparation method of the graphene field emission cathode, which comprises the following steps:
and S10, providing the conductive substrate and carrying out cleaning treatment.
In a specific technical scheme, the cleaning treatment specifically may be: and sequentially placing the conductive substrate in deionized water and absolute ethyl alcohol for ultrasonic cleaning, and then blowing the conductive substrate to dry by using nitrogen for later use.
And S20, preparing a mixed solution containing graphene oxide and target metal ions.
In a preferred embodiment, the step S20 includes:
and S21, preparing a graphene oxide nanosheet dispersion liquid.
Specifically, the prepared graphene oxide nanosheet is added into deionized water, and is dispersed by an ultrasonic dispersion method, wherein the ultrasonic power is 100-200W, and the time is 1-3 h. After the ultrasonic treatment is finished, removing the agglomerates in the solution by adopting a centrifugal separation method to obtain a stably dispersed graphene oxide solution with a certain concentration.
The graphene oxide nanosheet can be prepared by a graphite oxidation-reduction method (Hummer method), the graphene oxide nanosheet can be a single layer, a few layers or multiple layers, and in a preferred scheme, the graphene oxide nanosheet has a transverse size of 1-10 microns and a thickness of 0.5-5 nm.
S22, preparing a soluble metal salt solution containing the target metal ions.
Specifically, the target metal ion refers to a metal ion corresponding to a metal nanoparticle bound to the surface of the graphene nanoplate. Dissolving soluble metal salt containing target metal ions in water to prepare an aqueous solution of the soluble metal salt.
Wherein the target metal ion is at least one of palladium, gold, copper, platinum and silver ion, and the corresponding soluble metal salt is selected from Na2PdCl4、HAuCl4、CuSO4、CuCl2、H2PtCl6、K2PtCl6、Na2PtCl4And AgNO3At least one of (1). The soluble metal salt is selected primarily based on the metal nanoparticles that are ultimately to be produced.
S23, adding the soluble metal salt solution into the graphene oxide nanosheet dispersion liquid, stirring and mixing to obtain the mixed solution.
Among them, stirring and mixing are preferably performed by using a magnetic stirring system.
In a preferable scheme, in the mixed solution, the concentration of the graphene oxide nanosheets is 0.1-0.5 g/L, and the concentration of the soluble metal salt is 3-8 mM.
And S30, taking the mixed solution as an electrolyte solution, taking the conductive substrate as a working electrode, and preparing the graphene field emission cathode by adopting an electrodeposition process of a three-electrode system.
Specifically, in the electrodeposition process of the three-electrode system, the reference electrode is a saturated calomel electrode, the counter electrode is a platinum sheet electrode, the voltage scanning rate is 20 mV/s-80 mV/s, the scanning voltage range is-1.4V-0.6V, and cyclic scanning is carried out for 3-10 times.
Wherein, during the electrodeposition process, the graphene oxide in the mixed solution is deposited on the conductive substrate and reduced to graphene, formed into graphene nanoplatelets growing in an upright state, and the metal ions are reduced to metal nanoparticles and bonded to the surfaces of the graphene nanoplatelets.
Further, after the electrodeposition process is finished, the conductive substrate on which the graphene nanosheets are grown is cleaned by deionized water, and vacuum drying is carried out at 50-80 ℃ to finally obtain the graphene field emission cathode.
Example 1
The embodiment provides a graphene field emission cathode, wherein a conductive substrate of the graphene field emission cathode is selected as a titanium substrate, an upright graphene nanosheet grows on the titanium substrate, and metal nanoparticles combined on the surface of the graphene nanosheet are palladium nanoparticles. The preparation process of the graphene field emission cathode of the embodiment is as follows:
1) and (3) placing the titanium conductive substrate in deionized water and absolute ethyl alcohol in sequence, ultrasonically cleaning for 10min, and then drying by using nitrogen.
2) Ultrasonically dispersing multilayer graphene oxide with the transverse size of 1-10 mu m and the thickness of 1-3 nm in deionized water to form graphene oxide dispersion liquid with the concentration of 0.1g/L, and adding Na2PdCl4Dissolving in deionized water to obtain Na2PdCl4An aqueous solution. Then, adding Na2PdCl4And adding the aqueous solution into the graphene oxide dispersion liquid, and magnetically stirring and mixing to form a mixed solution, wherein the concentration of palladium metal ions in the mixed solution is 4 mM.
3) And preparing the graphene field emission cathode by taking the mixed solution as an electrolyte solution and the titanium conductive substrate as a working electrode and adopting an electrodeposition process of a three-electrode system. Wherein, the reference electrode is a saturated calomel electrode, the counter electrode is a platinum sheet electrode, the voltage scanning rate is 50mV/s, the scanning voltage range is-1.4V-0.6V, and the cyclic scanning is carried out for 10 times.
4) And after the electrodeposition process is finished, washing the titanium conductive substrate on which the graphene nanosheets grow by using deionized water, and drying in vacuum at 60 ℃ to obtain the graphene field emission cathode with the surface combined with the palladium metal nanoparticles.
Fig. 2 is an SEM image of the graphene nanoplatelets grown on the conductive substrate in the present embodiment, and it can be seen that the graphene nanoplatelets are grown in a vertical shape.
Fig. 3a and 3b are graphs of electrical tests of the graphene field emission cathode in this embodiment, in which fig. 3a is a graph of the relationship between the electric field intensity and the current density, and fig. 3b is a graph of the relationship between time and the current density. As can be known from fig. 3a, the graphene field emission cathode provided in this embodiment can obtain a larger emission current density at a lower electric field strength, and has a good field emission I-V characteristic. As can be known from fig. 3b, after the graphene field emission cathode provided by the embodiment of the invention continuously emits for 150min, the current is not substantially attenuated, and the graphene field emission cathode has excellent current emission stability.
Example 2
The embodiment provides a graphene field emission cathode, wherein a conductive substrate of the graphene field emission cathode is selected as a titanium substrate, an upright graphene nanosheet grows on the titanium substrate, and metal nanoparticles bonded on the surface of the graphene nanosheet are platinum nanoparticles. The preparation process of the graphene field emission cathode of the embodiment is as follows:
1) and (3) placing the titanium conductive substrate in deionized water and absolute ethyl alcohol in sequence, ultrasonically cleaning for 10min, and then drying by using nitrogen.
2) Ultrasonically dispersing multilayer graphene oxide with the transverse size of 1-10 mu m and the thickness of 1-3 nm in deionized water to form graphene oxide dispersion liquid with the concentration of 0.2g/L, and adding H2PtCl6Dissolving in deionized water to obtain H2PtCl6An aqueous solution. Then, H is reacted with2PtCl6An aqueous solution is added to the oxygenAnd magnetically stirring and mixing the graphene oxide dispersion liquid to form a mixed solution, wherein the concentration of platinum metal ions in the mixed solution is 6 mM.
3) And preparing the graphene field emission cathode by taking the mixed solution as an electrolyte solution and the titanium conductive substrate as a working electrode and adopting an electrodeposition process of a three-electrode system. Wherein, the reference electrode is a saturated calomel electrode, the counter electrode is a platinum sheet electrode, the voltage scanning rate is 50mV/s, the scanning voltage range is-1.4V-0.6V, and the cyclic scanning is carried out for 5 times.
4) And after the electrodeposition process is finished, washing the titanium conductive substrate for growing the graphene nanosheets by using deionized water, and drying in vacuum at 60 ℃ to obtain the graphene field emission cathode with the surface combined with the platinum metal nanoparticles.
Fig. 4a and 4b are graphs of electrical tests of the graphene field emission cathode in this embodiment, in which fig. 4a is a graph of electric field strength versus current density, and fig. 4b is a graph of time versus current density. As can be known from fig. 4a, the graphene field emission cathode provided in this embodiment can obtain a larger emission current density at a lower electric field strength, and has a good field emission I-V characteristic. As can be known from fig. 4b, after the graphene field emission cathode provided by the embodiment of the present invention continuously emits for 150min, the current is not substantially attenuated, and the graphene field emission cathode has excellent current emission stability.
In summary, in the graphene field emission cathode provided in the embodiment of the present invention, a large number of graphene nanosheets grow vertically on the conductive substrate, so that the density of electron emission tips and the number of effective emission tips of the field emission cathode are greatly increased, and the field emission current can be increased; furthermore, the metal nanoparticles combined on the surface of the graphene nanosheet and the graphene generate an electronic charge interaction, the electronic structure of the graphene is changed, the state density near the Fermi level of the graphene is increased, and the work function of the graphene is reduced, so that the opening electric field of the graphene cathode is reduced, the field emission current is further improved, and the emission stability can be improved.
The foregoing is directed to embodiments of the present application and it is noted that numerous modifications and adaptations may be made by those skilled in the art without departing from the principles of the present application and are intended to be within the scope of the present application.
Claims (10)
1. A graphene field emission cathode, comprising:
a conductive substrate;
graphene nanoplatelets grown upright on the conductive substrate;
a metal nanoparticle bonded on a surface of the graphene nanoplatelet.
2. The graphene field emission cathode according to claim 1, wherein the graphene nanoplatelets have a thickness of 0.5nm to 5 nm; and/or the presence of a gas in the gas,
the growth height of the graphene nanosheet is 5-20 microns; and/or the presence of a gas in the gas,
the distribution density of the graphene nanosheets on the conductive substrate is 107～108Tablet/mm2。
3. The graphene field emission cathode of claim 1, wherein the conductive substrate is a titanium substrate, a tantalum substrate, a stainless steel substrate, or a glassy carbon substrate.
4. The graphene field emission cathode according to any one of claims 1-3, wherein the metal nanoparticles have a work function of no greater than 5.7 eV; and/or the particle size of the metal nano-particles is 10 nm-100 nm; and/or the distribution density of the metal nanoparticles on the surface of the graphene nano sheet is 109～1011Per mm2。
5. The graphene field emission cathode according to claim 4, wherein the metal nanoparticles are selected from at least one of palladium nanoparticles, gold nanoparticles, copper nanoparticles, platinum nanoparticles, and silver nanoparticles.
6. A method for preparing a graphene field emission cathode according to any one of claims 1 to 5, comprising:
providing the conductive substrate and carrying out cleaning treatment;
preparing a mixed solution containing graphene oxide and target metal ions;
preparing the graphene field emission cathode by taking the mixed solution as an electrolyte solution and the conductive substrate as a working electrode and adopting an electrodeposition process of a three-electrode system;
wherein, during the electrodeposition process, the graphene oxide in the mixed solution is deposited on the conductive substrate and reduced to graphene, formed into graphene nanoplatelets growing in an upright state, and the target metal ions are reduced to metal nanoparticles and bonded to the surfaces of the graphene nanoplatelets.
7. The method of claim 6, wherein the preparing a mixed solution containing graphene oxide and target metal ions comprises:
preparing a graphene oxide nanosheet dispersion liquid;
preparing a soluble metal salt solution containing target metal ions;
adding the soluble metal salt solution into the graphene oxide nanosheet dispersion liquid, stirring and mixing to obtain the mixed solution.
8. The method for preparing the graphene field emission cathode according to claim 7, wherein the concentration of the graphene oxide nanosheets in the mixed solution is 0.1-0.5 g/L, and the concentration of the target metal ions is 3-8 mM.
9. The method for preparing a graphene field emission cathode according to claim 7, wherein the graphene oxide nanosheets have a lateral dimension of 1-10 μm and a thickness of 0.5-5 nm;
and/or the presence of a gas in the gas,
the target metal ion is at least one of palladium, gold, copper, platinum and silver ions, and the corresponding soluble metal salt is selected from Na2PdCl4、HAuCl4、CuSO4、CuCl2、H2PtCl6、K2PtCl6、Na2PtCl4And AgNO3At least one of (1).
10. The preparation method of the graphene field emission cathode according to any one of claims 6 to 9, wherein in the electrodeposition process of the three-electrode system, the reference electrode is a saturated calomel electrode, the counter electrode is a platinum sheet electrode, the voltage scanning rate is 20mV/s to 80mV/s, the scanning voltage range is-1.4V to 0.6V, and the cyclic scanning is performed for 3 to 10 times.
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