CN113943932B - Preparation method of graphene field emission source - Google Patents
Preparation method of graphene field emission source Download PDFInfo
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- CN113943932B CN113943932B CN202111198934.7A CN202111198934A CN113943932B CN 113943932 B CN113943932 B CN 113943932B CN 202111198934 A CN202111198934 A CN 202111198934A CN 113943932 B CN113943932 B CN 113943932B
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
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- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
- C23C16/26—Deposition of carbon only
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- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
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- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
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- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
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- 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
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Abstract
The invention aims to provide a preparation method of a graphene field emission source, which is characterized in that carbon atoms in carbon-containing gas are dissolved into a metal material at high temperature, carbon is separated out to the surface of the metal to form a graphene layer through a gradual cooling process, the thickness and scale of the graphene layer can be controlled through controlling the concentration of the carbon source and the cooling process, graphene and a metal substrate of the graphene are more tightly combined, the resistance between the graphene and the metal substrate is far smaller than that of an emitter prepared through transfer, the heating value is smaller when a large current passes through a combining part, and meanwhile, the metal substrate exposed from an emission tip can effectively receive secondary electrons and the like reflected by a target, so that the damage of the graphene emission tip due to electron or ion back-bombardment is reduced. The graphene field emission source prepared by the method can effectively improve the emission current density of a cathode, and has the characteristics of low starting field and threshold field and good stability; meanwhile, the preparation method is simple, low in energy consumption and easy to realize industrial production; the power is higher after the emitting component is manufactured, the stability is better, and the service life is longer.
Description
Technical Field
The invention belongs to the field of nano field emission electronic materials, and relates to a preparation method of a graphene field emission source.
Background
In thermionic emission and photoelectronic emission, heat and light are used to transfer energy to electrons in the emitter, and when the energy is enough, electrons escape from the surface. The field emission only needs to apply an electric field outside the emitter: and pressing and reducing the potential barrier on the surface of the emitter, so that the forbidden bandwidth of the potential barrier is narrowed, and free electrons in the object are emitted through tunnel effect. The field emission cathode is a novel electronic device with ideal performance, can be started instantaneously, can reach very high current density theoretically, can realize radiation resistance, high temperature resistance, high speed, high frequency and high power, can realize small volume, high efficiency, integration and low cost, and has application potential in the fields of display devices, novel luminous light sources, X-ray tubes, negative hydrogen ion sources and the like.
Graphene (Graphene) is a kind of materialNovel carbon material, which is a material consisting entirely of sp 2 The thickness of the hybridized carbon atoms is only a monoatomic layer and a plurality of monoatomic layers, and the hybridized carbon atoms have excellent performances such as high light transmittance, high electrical conductivity, high thermal conductivity, high comparison area, high strength, flexibility and the like.
Currently, the field emission cathode is the main direction after field emission cathode invention instead of hot cathode in traditional vacuum electronic device, and the field intensity reduction and current density improvement of field emission are the main contents of field emission cathode research.
CN102021633a discloses a preparation method of a graphene film field emission material, which comprises the steps of mixing graphene with an organic solvent to prepare a charged graphene solution, and then preparing the graphene film through electrophoretic deposition. The method is simple to operate, but has high requirements on the quality of graphene raw materials, and raw materials meeting the standards cannot be easily obtained by the methods. In addition, in the mode of depositing on the substrate in an electrophoresis mode, the combination of the graphene and the substrate is poor, and larger heat can be generated under the condition of large field emission voltage and large current so that the graphene is separated from the substrate, and the performance is reduced. CN106098503B discloses a graphene ribbon electron beam field emission cold cathode, which is characterized in that a metal film electrode is further arranged on the rear side of the upper surface of a substrate, and one or more graphene films are further arranged on the upper surfaces of the substrate and the metal film electrode to serve as a field emitter. The graphene grows on the film in a tube furnace, and the graphene is required to be transferred. Although the method can increase the power by adding a plurality of graphene emitters connected in parallel, the complexity of the structure can be increased continuously, the size of the complete graphene layers can be transferred effectively, the application scene of a final device is related, and for example, when an X-ray tube is manufactured, the multi-layer structure of the method can cause the problems of overlarge X-ray focus and the like of the final formed X-ray. Meanwhile, when the transfer times of the graphene are more, the requirement on a large-area transfer process is higher, and the graphene is not suitable for large-scale production and application.
Disclosure of Invention
The invention aims to provide a preparation method of a graphene field emission source, which is characterized in that carbon atoms in carbon-containing gas are dissociated at high temperature and then dissolved into a metal material, and carbon is separated out to the surface of the metal to form a graphene layer through a step cooling process; and the control of the carbon source concentration and the cooling process can realize the control of the thickness and the scale of the graphene layer. The cold cathode materials used at present are mainly made of alloy, and the efficiency is lower, so that the treatment of the emission tip has more emission edges compared with other types of edge emitters. Meanwhile, the thickness of the graphene is less than 1nm, and the graphene is thinner than cathodes of other structures, and the transverse dimension of the graphene can reach tens of micrometers, so that the graphene has a higher length-diameter ratio and is more beneficial to field emission.
The graphene layer prepared by the method is tightly combined with the metal substrate, the resistance between the graphene layer and the metal substrate is far smaller than that of an emitter prepared after transfer, the heating value is smaller when a large current passes through the combination part, and the metal substrate exposed from the emission tip can effectively receive secondary electrons and the like reflected by a target, so that the damage of the emission tip of the graphene caused by electron or ion bombardment is reduced. The graphene field emission source prepared by the method has the characteristics of effectively improving the emission current density of a cathode, along with low starting field, low threshold field and good stability; meanwhile, the preparation method is simple, low in energy consumption and easy to realize industrial production. The power is higher after the emitting component is manufactured, the stability is better, and the service life is longer.
To achieve the object of the present invention, the following embodiments are provided.
In one embodiment, the preparation method of the graphene field emission source comprises the following steps:
(1) Putting the metal substrate into a metal lotion and acetone for cleaning, and then washing with deionized water;
(2) Soaking the washed metal substrate in hydrochloric acid solution, and washing with deionized water after soaking;
(3) Polishing the metal substrate washed in the previous step with a metal polishing solution to remove an oxide layer, washing with deionized water, dehydrating with ethanol, and preserving in vacuum;
(4) Placing a metal substrate on a corundum carrier and placing the metal substrate in a CVD cavity;
(5) Vacuumizing the cavity, and introducing gaseous hydrogen and carbon-containing gas;
(6) Electrifying to heat the base material, heating to 1100-1250 ℃, preferably 1200 ℃, and keeping the temperature for 120-360 min to dissolve carbon atoms in the carbon gas into the metal material;
(7) Then slowly cooling, precipitating carbon atoms dissolved into the metal material on the surface of the metal material through stepwise cooling to form a graphene layer, and taking out the metal material after the power supply is turned off and the temperature is reduced to room temperature;
(8) And polishing the emission end of the metal material until the metal luster is exposed, and then cleaning with ethanol and drying to obtain the graphene field emission source product.
Preferably, the method of the present invention described in the above is the method of the present invention described in the item 1, wherein in the step (1), the metal substrate is selected from nickel, titanium, molybdenum, and stainless steel, and the diameter of the metal substrate is 100 μm to 500. Mu.m, more preferably 300. Mu.m; in the step (2), the concentration of the hydrochloric acid solution is 5% -20%, preferably 10%; in the step (3), the metal polishing solution is a mixture of glacial acetic acid, nitric acid and sodium chloride, wherein the glacial acetic acid is as follows: nitric acid: the mass ratio of the sodium chloride is 100:30:1, a step of; in the step (4), when the metal material is placed, the emission end of the metal material is vertically upwards, and the cavity is made of stainless steel; in the step (5), the vacuum is a vacuum degree of 1.0X10 -2 Torr～3.0×10 - 3 Torr; the carbon-containing gas is CH 4 Wherein H is 2 :CH 4 =10: 1 to 10:3, more preferably H 2 :CH 4 =10: 1, a step of; in the step (7), the temperature is reduced from the constant temperature to 300 ℃, the temperature reduction rate is 10 ℃/min-30 ℃/min, more preferably 10 ℃/min, and the thickness of the graphene layer is less than 1 nm.
In a specific embodiment, the preparation method of the graphene field emission source comprises the following steps:
(1) Putting the metal substrate into a metal lotion and acetone for ultrasonic cleaning, and repeatedly flushing the metal substrate with deionized water after the cleaning is finished;
(2) Soaking the washed metal substrate in hydrochloric acid solution for 30min, and repeatedly washing and soaking with deionized water;
(3) Polishing the washed metal substrate in a metal polishing solution to remove an oxide layer, repeatedly washing with deionized water, dehydrating with ethanol, and preserving the dehydrated metal substrate in vacuum;
(4) Placing a metal substrate on a corundum carrier and placing the metal substrate in a CVD cavity;
(5) Vacuumizing the cavity, and introducing gaseous hydrogen and carbon-containing gas into the cavity;
(6) The power supply is turned on, the base material is heated, the temperature is raised to 1100-1250 ℃, the constant temperature is kept for 120-360 min, preferably 180min, and carbon atoms in the carbon gas are dissolved into the metal material;
(7) Adjusting a power supply to reduce power, slowly cooling, precipitating carbon atoms dissolved into the metal material to the surface of the metal material through stepwise cooling to form a graphene layer, and taking out a metal material sample after the power supply is turned off and cooled to room temperature;
(8) And fixing the sample on a clamp, polishing the emission end of the metal material sample by using sand paper until the metal luster is exposed, putting the metal material sample into ethanol for cleaning, taking out and drying to obtain the graphene field emission source product.
Preferably, the method of the present invention described in the above is the method of claim 1, wherein in the step (1), the metal substrate is selected from nickel, titanium, molybdenum, and stainless steel, preferably nickel. The diameter of the metal base material is 100-500 mu m; in the step (2), the concentration of the hydrochloric acid solution is 5% -20%; in the step (3), the metal polishing solution is a mixture of glacial acetic acid, nitric acid and sodium chloride, wherein the glacial acetic acid is as follows: nitric acid: the mass ratio of the sodium chloride is 100:30:1, a step of; in the step (4), when the metal material is placed, the emission end of the metal material is vertically upwards, and the cavity is made of stainless steel; in the step (5), the vacuum is a vacuum degree of 1.0X10 -2 Torr～3.0×10 -3 Torr; the carbon-containing gas is CH 4 Wherein H is 2 :CH 4 =10: 1 to 10:3, a step of; in the step (7), the temperature is reduced from constant temperature to 300 ℃, the temperature reduction rate is 10 ℃/min-30 ℃/min, and the temperature reduction rate is 10 ℃/minThe thickness of the graphene layer is below 1 nm.
Compared with the prior art, the invention has the following remarkable advantages:
1) According to the method, a metal substrate and carbon source-containing gas are used as raw materials, carbon atoms are firstly dissolved in the metal substrate by adopting a chemical vapor deposition method, and then the dissolved carbon atoms are separated out to the surface of the metal material by stage cooling to form a graphene layer. The graphene layer prepared by the method disclosed by the invention is more tightly combined with the metal substrate, the resistance between the graphene layer and the metal substrate is far smaller than that of an emitter prepared by transferring, the heating value is smaller when a large current passes through a combining part, and the service life is longer when the graphene layer is applied to a high-power emitting device.
2) The method has the characteristics of high emission current density, small volume, low starting field and threshold field and good stability; meanwhile, the preparation method is simple, low in energy consumption and easy to realize industrial production. Can be used as the cathode of vacuum electronic devices, and the cathode of projection tubes and related electronic devices.
In a word, the invention solves the problem that graphene is used as a field emission material and has low power. And a graphene layer is directly precipitated on the surface of the metal material to be used as an emission source, so that a plurality of problems in the transfer process of the graphene layer are avoided.
Drawings
FIG. 1 is a schematic illustration of a graphene-metal substrate composite prepared by the method of the present invention;
fig. 2 is a graph of field emission effect test data of a graphene field emission source prepared by the method of the present invention.
Detailed Description
The following examples are merely representative for further understanding and explanation of the essence of the present invention. But do not limit the scope of the invention in any way.
Example 1 preparation method of graphene field emission source:
(1) Putting a pure nickel substrate with the diameter of 300 mu m and the length of 20mm into a metal lotion and acetone, ultrasonically cleaning for 30min, and repeatedly flushing the substrate with deionized water after the cleaning is finished;
(2) Soaking the washed pure nickel substrate in 10% hydrochloric acid solution for 30min;
(3) Repeatedly washing the soaked pure nickel base material by using deionized water, putting the washed pure nickel base material into a mixture solution of glacial acetic acid, nitric acid and sodium chloride (the mass ratio is 100:30:1), polishing for 10s, removing an oxide layer, repeatedly washing the polished pure nickel base material by using deionized water, and dehydrating by using ethanol after washing;
(4) Placing the pure nickel substrate with its emission end upward on corundum carrier, placing into CVD stainless steel cavity, vacuum-pumping the cavity to 1.0X10 -2 Torr；
(5) Introducing H into the cavity 2 And CH (CH) 4 Is a mixed gas (H) 2 :CH 4 =10: 2 molar ratio), the pressure in the chamber is maintained at 100Torr;
(6) Turning on CVD power, heating the substrate to 1200deg.C, maintaining the temperature for 180min, and collecting CH 4 The dissociated carbon atoms are dissolved in the metal substrate;
(7) After the constant temperature time is up, adjusting the power supply to reduce the power, setting the temperature reduction rate to be 30 ℃/min, reducing the temperature to 300 ℃, precipitating the carbon atoms of the dissolved carbon atoms on the surface of the metal material to form a graphene layer through stepwise cooling, and taking out a graphene pure nickel substrate sample after the power supply is turned off and the temperature is reduced to the room temperature;
(8) Fixing a graphene pure nickel substrate sample on a clamp, polishing a sample emission end by using 2500-mesh sand paper until silver metallic luster is exposed, soaking and cleaning the polished sample in absolute ethyl alcohol, taking out and drying to obtain a graphene field emission source product (named sample 1).
And (3) effect test:
the graphene field emission source sample 1 obtained in example 1 was tested, as shown in FIG. 1, to have an on-electric field of 0.72V/μm in field emission, and a current density of 12.85mA/cm was reached when the electric field was 1.89V/μm 2 。
Example 2 preparation of graphene field emission sources
The preparation referring to the preparation process of example 1 is different from example 1 in that the temperature decrease rate of step (7) of the preparation process section of the graphene field emission source is set to 10 deg.c/min. The rest steps and the technological parameters are the same, and the graphene field emission source product (named sample 2) is prepared.
And (3) effect test:
the graphene field emission source sample 2 obtained in example 2 was tested, as shown in FIG. 1, to obtain an open electric field of 0.69V/μm in field emission, and a current density of 14.57mA/cm was reached when the electric field was 1.89V/μm 2 。
Example 3 preparation of vertical graphene carbon fiber composite
The process of preparation reference example 1 differs from example 1 in step (5) H of the upright graphene reinforced carbon fiber preparation process section 2 And CH (CH) 4 The ratio of the mixed gas of (C) is H 2 :CH 4 =10: 1 molar ratio, the temperature drop rate in the step (7) is set to 10 ℃/min. The rest steps and process parameters are the same as those of the embodiment 1, and the graphene field emission source sample 3 is prepared.
And (3) effect test:
the graphene field emission source sample 2 obtained in example 2 was tested, as shown in FIG. 1, to have an on-electric field of 0.67V/μm in field emission, and a current density of 17.03mA/cm was reached when the electric field was 1.89V/μm 2 。
To analyze the field emission performance of the graphene field emission source obtained in examples 1, 2, and 3, the present inventors mounted three groups of sample samples into field emission test benches, respectively, for testing.
The field emission performance test results of the graphene field emission source samples of examples 1, 2 and 3 are shown in fig. 2. As can be seen from the test results, the sample prepared in example 3 has the best field emission effect, which not only has smaller turn-on electric field and only needs 0.67. 0.67V/μm, but also has better stability in the test, the growth rate is the highest, and the current density is as high as 17.03mA/cm when the electric field strength is 1.89V/μm 2 Far above the other two groups of samples. It is expected that the current density increase rate and stability will also perform well as the electric field strength increases.
Example 2 during the test, the front section had a larger current density increase and then began to flatten out, with both the middle and back sections having significantly less current densities than sample 3. There was little fluctuation in current density throughout the test. The growth of the front stage is mainly due to the fact that the carbon concentration is large when the sample is prepared, carbon atoms dissolved in metal are large, graphene sheets precipitated during cooling are thick, but with the increase of voltage, too thick atomic layers consume excessive energy inside, and emission current is inferior to sample 3.
The field emission of the sample prepared in example 1 has a current density greatly increased when the electric field strength is 1.0V/μm, and the field emission current density is even larger than that of the sample prepared in example 3 under partial field intensity, but the increase rate of the field emission current density starts to be flat after the voltage field intensity reaches 1.24V/μm, the subsequent field intensity increases, the current density also has larger fluctuation, and the fluctuation current density starts to increase after the voltage field intensity reaches 1.5V/μm. The above phenomenon occurs as long as the carbon concentration is large at the time of preparing the sample, and the carbon atoms of the metal dissolved are also large. In the subsequent cooling process, the precipitated graphene layers are more, so that the current of the graphene layers can be greatly increased under a certain field intensity. In addition, when the temperature is reduced, the temperature reduction rate is higher, and the quantity of carbon atoms precipitated by metal can form graphene sheets with uneven thickness due to larger temperature change, which is also the reason that the emission performance of the graphene sheets is more fluctuating.
In addition, a graphene field emission source sample of the graphene nickel base material is prepared by adopting a traditional transfer method, and a test sample is used for starting an electric field of 0.98V/mu m in field emission, and when the electric field is 1.89V/mu m, the current density reaches 8.56mA/cm 2 . The method of the invention is obviously superior to the traditional transfer method.
The foregoing is merely representative of embodiments of the present invention, and it will be understood that the spirit of the present invention, although not listed, and that any variations and modifications which come within the spirit of the invention fall within the scope of the invention.
Claims (8)
1. A method for preparing a graphene field emission source, comprising the steps of:
(1) Putting the metal substrate into a metal lotion and acetone for cleaning, and then washing with deionized water;
(2) Soaking the washed metal substrate in hydrochloric acid solution, and washing with deionized water after soaking;
(3) Polishing the metal substrate washed in the previous step with a metal polishing solution to remove an oxide layer, washing with deionized water, dehydrating with ethanol, and preserving in vacuum;
(4) Placing a metal substrate on a corundum carrier and placing the metal substrate in a CVD cavity;
(5) Vacuumizing the cavity, and introducing gaseous hydrogen and carbon-containing gas;
(6) Electrifying to heat the base material, heating to 1100-1250 ℃, and keeping the temperature for 120-360 min to dissolve carbon atoms in the carbon gas into the metal material;
(7) Then slowly cooling, precipitating carbon atoms dissolved into the metal material on the surface of the metal material through stepwise cooling to form a graphene layer, and taking out the metal material after the power supply is turned off and the temperature is reduced to room temperature;
(8) Polishing the emission end of the metal material until the metal luster is exposed, then cleaning with ethanol and drying to obtain a graphene field emission source product,
wherein in the step (5), the carbon-containing gas is CH 4 Wherein H is 2 :CH 4 Molar ratio = 10:1, a step of; and (3) the temperature is reduced in the step (7) in a stepwise manner from constant temperature to 300 ℃, and the temperature reduction rate of the slow temperature reduction is 10 ℃/min.
2. The production method according to claim 1, wherein in the step (1), the metal substrate is selected from the group consisting of nickel, titanium, molybdenum, and stainless steel, and the diameter of the metal substrate is 100 μm to 500 μm.
3. The process according to claim 1, wherein the concentration of the hydrochloric acid solution in the step (2) is 5% to 20%.
4. The method according to claim 1, wherein in the step (3), the metal polishing liquid is a mixture of glacial acetic acid, nitric acid and sodium chloride.
5. The method of claim 4, wherein the metal polishing solution comprises glacial acetic acid: nitric acid: the mass ratio of the sodium chloride is 100:30:1.
6. the preparation method of claim 1, wherein in the step (4), when the metal material is placed, the emission end of the metal material is vertically upward, and the cavity is made of stainless steel.
7. The process according to claim 1, wherein in the step (5), the vacuum is a vacuum degree of 1.0X10 -2 Torr～3.0×10 -3 Torr。
8. The method according to claim 1, wherein the thickness of the graphene layer in the step (7) is 1nm or less.
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