CN108987215B - Method for improving field emission performance of graphene sheet-carbon nanotube array composite material - Google Patents
Method for improving field emission performance of graphene sheet-carbon nanotube array composite material Download PDFInfo
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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
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- H01J1/30—Cold cathodes, e.g. field-emissive cathode
- H01J1/304—Field-emissive cathodes
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- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
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- 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 method for improving the field emission performance of a graphene sheet-carbon nanotube array composite material, and belongs to the field of preparation and application of nano materials. The preparation method comprises the following preparation processes: (1) pretreating the silicon single crystal wafer by using silver ion bombardment; (2) preparing a carbon nano tube array by utilizing a thermal chemical vapor deposition method and carrying out high-temperature annealing treatment on the carbon nano tube array; (3) preparing a thin graphene sheet on the carbon nanotube array by using a microwave plasma enhanced chemical vapor deposition method; (4) and performing nitrogen and hydrogen plasma treatment on the obtained graphene sheet-carbon nanotube array at room temperature. Compared with the prior art, the nitrogen-doped graphene sheet-carbon nanotube array composite material prepared by the method has extremely low working electric field, extremely high current density, good field emission stability under high current density and high application value.
Description
Technical Field
The invention belongs to the technical field of preparation and application of nano materials, and particularly relates to a method for preparing a nitrogen-doped graphene sheet-carbon nanotube array composite material by using plasma treatment and improving field emission performance.
Background
The field emission refers to the process that electrons in the cathode material escape from the surface of the material into vacuum under the action of an external enhanced electric field, and the excellent field emission performance generally requires that the cathode has a lower working electric field and a larger current density and good stability. As a quasi-one-dimensional nano material, the carbon nano tube has great length-diameter ratio and excellent conductivity, so that the carbon nano tube becomes an ideal field emission cathode material, and shows good application prospect in the preparation of vacuum field electronic devices such as a new generation of vacuum tubes, X-ray tubes and field emission flat panel displays. However, when the pure carbon nanotube is used as a field emission cathode, the maximum field emission current density is less than 10mA/cm because of the characteristics of poor contact with the substrate (small contact surface) and easy burning by Joule heat2This greatly limits its application. In addition, the threshold electric field of the carbon nanotube-based field emission cathode (the field emission current density reaches 10 mA/cm)2External electric field corresponding to timeStrength) is generally higher than 2.0V/μm, which in practical applications is equivalent to applying a high voltage of 2000V between the cathode and the anode at a spacing of 1 mm, and it is difficult to realize devices in the art considering that a high vacuum is also required between the cathode and the anode. The threshold field of the carbon nanotube-based field emission cathode is generally higher than 1.5V/mum even after ion irradiation, doping, chemical modification and other treatments, and meanwhile, the current density is difficult to be higher than 10mA/cm2And the long-time stable field electron emission is realized, so that the requirements on reducing the working electric field and improving the field emission current density are provided. Because the maximum field emission current density of the carbon nanotube-based field emission cathode is related to the tube-based bonding force and the electrostatic field intensity applied to the carbon nanotube, the field emission performance of the material can be improved by starting from two aspects of enhancing the tube-based bonding and reducing the working electric field. The compounding of carbon nanotubes with other low-dimensional nanomaterials is a big breakthrough in improving the field emission performance, and the compounding with graphene sheets, which are quasi-two-dimensional nanomaterials with good field emission stability, is the focus of research. The one-dimensional/two-dimensional composite material can simultaneously have the large length-diameter ratio of the one-dimensional carbon nano tube and the good field emission stability of the two-dimensional graphene sheet, so that the field emission performance of the obtained composite material is greatly improved. In the prior art, the maximum field emission current density of the graphene sheet-carbon nanotube composite material can reach 49.60mA/cm2The threshold field can be as low as 1.51V/mum, and has good field emission stability, and the indexes are greatly improved compared with the original carbon nano tube. But it is undeniable that the field emission performance of the graphene sheet-carbon nanotube composite material is still not excellent enough. Firstly, the maximum field emission current density still has a huge promotion space, so that the requirements of the preparation of a large-current density field electron emission device, such as the preparation of a large-current density field emission lamp, can be better met; secondly, the goal of realizing stable operation under large field emission current density is still not achieved, which puts forward a new requirement for further improving the performance of the field emission cathode based on the graphene sheet-carbon nanotube composite material.
Disclosure of Invention
The invention aims to overcome the defects of relatively high working electric field, small field emission current density and poor stability in field emission with large current density of the existing field emission cathode based on a graphene sheet-carbon nanotube array, a transition layer is introduced through silver ion bombardment treatment to strengthen the binding force between the carbon nanotube and a silicon single crystal sheet, and a nitrogen-doped graphene sheet-carbon nanotube array composite material with low work function and a large number of field emission points is obtained through microwave nitrogen and hydrogen plasma treatment, so that the field emission cathode composite material with low working electric field, large field emission current density and good field emission stability under large current density is finally obtained.
The object of the invention is achieved by the following measures:
firstly, bombarding a pretreated silicon single crystal wafer by using energy-carrying silver ions, then preparing a carbon nanotube array by using a thermal chemical vapor deposition method and carrying out high-temperature annealing treatment, then preparing a thin graphene sheet by using a microwave plasma enhanced chemical vapor deposition method, finally treating the obtained graphene sheet-carbon nanotube array by using microwave nitrogen and hydrogen plasmas at normal temperature, and controlling the morphology of the graphene sheet-carbon nanotube array by adjusting the microwave power to be 100-140W, the air pressure of a treatment chamber to be 1.5kPa and the treatment time to be 0.5-2 hours, thereby finally obtaining the nitrogen-doped graphene sheet-carbon nanotube array composite material; the nitrogen-doped graphene sheet-carbon nanotube array composite material consists of graphene sheets which are deposited on a carbon nanotube array, have 1-5 layers of edge layers, are rich in defects and are doped with nitrogen; the threshold field of the prepared nitrogen-doped graphene sheet-carbon nanotube array composite material is only 1.09-1.21V/mum on average, and the maximum field emission current density can reach 101.79-120.56mA/cm on average2The emission current density is up to 45.46mA/cm in average field2The current decay in 20 hours was only 3.86%.
In the above technical solution, further disclosed is a method for improving field emission performance of a graphene sheet-carbon nanotube array composite material, comprising the following specific steps:
pretreating a silicon single crystal wafer: firstly cutting a silicon single crystal wafer into 2cm multiplied by 2cm small pieces, sequentially cleaning the silicon single crystal wafer in deionized water and absolute ethyl alcohol by ultrasonic waves (50W) for 5 minutes, then immersing the silicon single crystal wafer into hydrofluoric acid with the volume ratio of 4% for 5 minutes, taking out the silicon single crystal wafer and airing the silicon single crystal wafer, and then performing energy-carrying silver ion bombardment pretreatment on the obtained silicon single crystal wafer with a clean surface in a metal steam vacuum arc ion source (MEVVA source), wherein during bombardment, a sample table is kept to rotate at a constant speed, the bias voltage of the sample table is set to-15 kV, the beam current is 10 milliamperes, and the bombardment time is 10 minutes;
preparing a carbon nanotube array by a thermochemical vapor deposition method and carrying out high-temperature annealing treatment: putting the silicon single crystal wafer obtained in the step (1) into a magnetron sputtering device to deposit an iron catalyst film with the thickness of 5 nanometers, then putting the silicon single crystal wafer into a high-temperature quartz tube furnace to prepare a carbon nanotube array by using a conventional thermochemical vapor deposition method, when growing a carbon nanotube, firstly carrying out heat treatment on the silicon single crystal wafer deposited with the iron catalyst for 1 hour at 400sccm hydrogen and 580 ℃, then carrying out treatment for 10 minutes at 150sccm ammonia and 750 ℃, finally growing the carbon nanotube array at 87sccm acetylene, 600sccm hydrogen, 750 ℃ and normal pressure for 30 minutes, then raising the temperature to 1000 ℃, and treating the generated carbon nanotube at 400sccm hydrogen and normal pressure for 2 hours;
preparing graphene sheets by a microwave plasma enhanced chemical vapor deposition method: placing the carbon nano tube array obtained in the step (2) on a graphite sample table in a microwave plasma system, and vacuumizing a reaction chamber to 1.0 multiplied by 10-3Introducing 10sccm hydrogen after Pa, adjusting the air pressure to 1kPa, heating the sample platform by a heater until the temperature is stabilized to 800 ℃, starting a microwave source, adjusting the microwave power to 150W, introducing 3sccm acetylene gas, adjusting the air pressure to 1kPa again, starting the growth of the graphene sheet, wherein the growth time is 3 hours, and finally obtaining the graphene sheet-carbon nanotube array;
step (4), treating the graphene sheet-carbon nanotube array by nitrogen and hydrogen plasmas: and (3) cooling the sample to room temperature in a hydrogen atmosphere of 10sccm, performing nitrogen and hydrogen plasma treatment on the obtained graphene sheet-carbon nanotube array, wherein the gas for generating the plasma is a mixed gas consisting of nitrogen and hydrogen, the flow rates of the nitrogen and the hydrogen are respectively 5 and 10sccm, the air pressure is adjusted to be 1.5kPa, after the air pressure is stabilized, starting a microwave source, adjusting the microwave power to be 100-140W, and the treatment time to be 0.5-2 hours, so as to obtain the nitrogen-doped graphene sheet-carbon nanotube array.
In the technical scheme, the purity of all the used gases is 5N.
The nitrogen-doped graphene sheet-carbon nanotube array composite material prepared by adopting the scheme is composed of 1-5 deposited edge layers on a carbon nanotube array, and the number of the deposited edge layers is rich in defects and nitrogen-doped graphene sheets; the threshold field of the prepared nitrogen-doped graphene sheet-carbon nanotube array composite material is only 1.09-1.21V/mum on average, and the maximum field emission current density can reach 101.79-120.56mA/cm on average2The emission current density is up to 45.46mA/cm in average field2The current decay in 20 hours was only 3.86%.
Compared with the prior art, the method for improving the field emission performance of the graphene sheet-carbon nanotube array composite material by forming the transition layer through silver ion bombardment and processing the normal-temperature nitrogen and hydrogen plasmas has the advantages that: (1) the energy-carrying silver ions are used for bombarding the pretreated silicon substrate to form a silver-silicon transition layer on the silicon single crystal wafer, the transition layer can promote the transmission of electrons on one hand, and on the other hand, in the high-temperature annealing treatment after the carbon nano tube grows, the root of the carbon nano tube can be effectively coated in a silver precipitation mode, so that the binding force between the carbon nano tube and the silicon wafer is improved, and the maximum field emission current density of the material is improved; (2) the method has the advantages that the function of reducing the work function can be achieved by irradiating the graphene sheet-carbon nanotube array with nitrogen and hydrogen plasmas, electrons in the field emission cathode material can more easily tunnel through a potential barrier and escape into vacuum, and a large number of defects can be introduced, wherein the defects can become high-efficiency field emission points in the field emission process. In summary, the enhancement of the bonding force between the carbon nanotube and the silicon substrate, the reduction of the work function and the increase of the number of field emission points are the key points of the excellent field emission performance of the nitrogen-doped graphene sheet-carbon nanotube array, and the advantages of the invention. The introduction of silver ion bombardment and nitrogen doping ensures that the nitrogen-doped graphene sheet-carbon nanotube array composite material obtained by the invention has extremely low turn-on field (1.09V/mum) and extremely high field emission current density (120.56 mA/cm)2) And excellent high current density field emission stability (up to 45.46mA/cm in average field emission current density)2And the current attenuation in 20 hours is only 3.86 percent), and compared with the prior art, the indexes are greatly improved.
Drawings
FIG. 1 is a schematic flow chart of a method for preparing a nitrogen-doped graphene sheet-carbon nanotube array composite material by silver ion bombardment and nitrogen and hydrogen plasma treatment;
FIG. 2 is a schematic diagram of a microwave plasma enhanced chemical vapor deposition system used in the present invention;
fig. 3 is a scanning electron microscope and high-resolution transmission electron microscope image of the nitrogen-doped graphene sheet-carbon nanotube array obtained in example 1 after silver ion bombardment and nitrogen and hydrogen plasma treatment, including:
a is a scanning electron microscope side view of the nitrogen-doped graphene sheet-carbon nanotube array;
b is a high-resolution transmission electron microscope picture of the graphene sheet in the nitrogen-doped graphene sheet-carbon nanotube array;
FIG. 4 is a schematic diagram of a diode-type high vacuum field emission tester used in the present invention;
fig. 5 is a graph of field emission performance of the nitrogen-doped graphene sheet-carbon nanotube array composite obtained in example 1 and example 2 and the samples of prior art 1 and prior art 2;
FIG. 6 is a graph of the field emission stability of the N-doped graphene sheet-carbon nanotube array composite material obtained in example 1 after bombardment with silver ions within 20 hours, wherein "E" and "J" aremean"respectively represents the applied constant electric field strength and the average field emission current density;
Detailed Description
The present invention will be described in further detail with reference to the following drawings and examples, but the present invention is not limited to these examples. The silicon single crystal wafer, absolute ethyl alcohol, hydrofluoric acid, high-purity hydrogen, high-purity ammonia, high-purity nitrogen, high-purity acetylene gas, high-purity iron target, high-purity silver target and the like are all sold in the market. Devices such as ultrasonic cleaning, metal vapor vacuum arc ion sources (MEVVA sources), high temperature tube furnaces, microwave plasma systems, diode-type high vacuum field emission testers and the like are commercially available. The thermal chemical vapor deposition method for preparing the carbon nano tube, the plasma enhanced chemical vapor deposition method for preparing the graphene sheet, the MEVVA source silver ion bombardment method and the method for testing the field emission performance of the obtained material belong to conventional methods. The field emission performance test of the material adopts a diode type high vacuum field emission tester, during the test, the prepared material is taken as a cathode, the cathode is grounded, a stainless steel plate which is parallel and opposite to the cathode and has the diameter of 10 cm is taken as an anode, the distance between the anode and the cathode is 2 mm, and the cathode material is enabled to emit electrons in a mode of loading 0-10kV adjustable positive bias on the anode.
In specific implementation, the 'preparation method of a field emission cathode with a nano carbon sheet-carbon nanotube composite structure' (patent application No. 201510152592.3) is adopted as the prior art 1 for comparison, and the maximum field emission current density can reach 49.60mA/cm2Threshold field is as low as 1.51V/mum and emission current density is 13.46mA/cm2It shows better field emission stability.
In the specific implementation, the method for improving the field emission performance of the carbon nanotube by adopting microwave hydrogen plasma treatment (Chinese patent, patent number ZL201510153273.4) is adopted as the prior art 2 for comparison, and the threshold field and the maximum field emission current density are respectively 1.39V/mum and 74.74mA/cm2And the emission current density in the average field is 22.86mA/cm2It shows better field emission stability.
Fig. 1 is a schematic flow chart of a process for preparing a nitrogen-doped graphene sheet-carbon nanotube array composite material according to the present invention, which is mainly divided into four steps of pre-treating a silicon single crystal sheet, preparing a carbon nanotube array by a thermal chemical vapor deposition method, performing high temperature annealing treatment, preparing a thin graphene sheet by a microwave plasma enhanced chemical vapor deposition method, treating the graphene sheet-carbon nanotube array by microwave nitrogen and hydrogen plasma, and the like.
Example 1
(1) Pretreating a silicon single crystal wafer:
firstly cutting a silicon single crystal wafer into 2cm multiplied by 2cm small pieces, then sequentially carrying out ultrasonic (50W) cleaning for 5 minutes in deionized water and absolute ethyl alcohol, then immersing the silicon single crystal wafer into hydrofluoric acid with the volume ratio of 4% for 5 minutes, then taking out and airing, and carrying out energy-carrying silver ion bombardment pretreatment on the obtained silicon single crystal wafer with a clean surface in a metal vapor vacuum arc ion source (MEVVA source), wherein during bombardment, a sample table is kept to rotate at a constant speed, the bias voltage of the sample table is set to-15 kV, the beam current is 10 milliamperes, and the bombardment time is 10 minutes.
(2) Preparing a carbon nano tube array by a thermal chemical vapor deposition method and carrying out high-temperature annealing treatment:
and (2) placing the silicon single crystal wafer obtained in the step (1) into a magnetron sputtering device to deposit an iron catalyst film with the thickness of 5 nanometers, then placing the silicon single crystal wafer into a high-temperature quartz tube furnace to prepare a carbon nanotube array by using a conventional thermal chemical vapor deposition method, wherein when growing the carbon nanotube, the silicon single crystal wafer deposited with the iron catalyst is subjected to heat treatment for 1 hour at 400sccm hydrogen and 580 ℃, then is subjected to treatment for 10 minutes at 150sccm ammonia and 750 ℃, finally is subjected to growth of the carbon nanotube array at 87sccm acetylene, 600sccm hydrogen, 750 ℃ and normal pressure for 30 minutes, then the temperature is raised to 1000 ℃, and the generated carbon nanotube is treated at 400sccm hydrogen and normal pressure for 2 hours.
(3) Preparing a graphene sheet by a microwave plasma enhanced chemical vapor deposition method:
placing the carbon nanotube array obtained in step (2) on a graphite sample stage in a microwave plasma system shown in FIG. 2, and vacuumizing the reaction chamber to 1.0 × 10-3Introducing 10sccm hydrogen after Pa, adjusting the pressure to 1kPa, heating the sample platform by a heater until the temperature is stabilized to 800 ℃, starting a microwave source, adjusting the microwave power to 150W, introducing 3sccm acetylene gas, adjusting the pressure to 1kPa again, starting the growth of the graphene sheet, wherein the growth time is 3 hours, and finally obtaining the graphene sheetIs a graphene sheet-carbon nanotube array.
(4) Treating the graphene sheet-carbon nanotube array by nitrogen and hydrogen plasmas:
and (3) cooling the sample to room temperature in a hydrogen atmosphere of 10sccm, performing nitrogen and hydrogen plasma treatment on the obtained graphene sheet-carbon nanotube array, wherein the gas for generating the plasma is a mixed gas consisting of nitrogen and hydrogen, the flow rates of the nitrogen and the hydrogen are respectively 5 and 10sccm, the air pressure is adjusted to be 1.5kPa, after the air pressure is stabilized, starting a microwave source, and adjusting the microwave power to be 120W and the treatment time to be 1 hour. The X-ray photoelectron spectroscopy analysis shows that a certain amount of nitrogen atoms are doped in the graphene sheet-carbon nanotube array composite material, and the nitrogen-doped graphene sheet-carbon nanotube array is obtained. Fig. 3 a and fig. 3B are a scanning electron microscope side view and a high-resolution transmission electron microscope picture of the obtained nitrogen-doped graphene sheet-carbon nanotube array, respectively. It can be seen that the number of layers of the graphene edge is small, the defects are enriched on the surface, and the structural characteristics can promote the field electron emission of the material. It is emphasized that the number of graphene sheets obtained by the present invention is usually 1 to 5.
(5) The field emission performance of the obtained material is characterized in that:
the obtained nitrogen-doped graphene sheet-carbon nanotube array composite material is used as a cathode, and the field emission performance of the material is tested by using a diode type high vacuum field emission tester shown in fig. 4. Fig. 5 is a graph showing a comparison of field emission performance between the nitrogen-doped graphene sheet-carbon nanotube array composite material obtained in this example and samples in prior art 1 and prior art 2, which shows a relationship between field emission current density of the cathode material and increase of applied electric field strength, and corresponding test results are shown in table 1. It can be seen that after introducing silver ion bombardment and nitrogen and hydrogen plasma treatment, the threshold field of the obtained nitrogen-doped graphene sheet-carbon nanotube is only 1.14V/mum, and the maximum field emission current density is as high as 120.56mA/cm2Compared with the prior art 1, the change conditions of the two indexes are respectively as follows: a reduction of 0.37V/. mu.m, 2.43 times of the prior art (Table 1); compared with the prior art 2, the change conditions of the two indexes are respectively as follows: reduced by 0.25V/mum, prior art1.61 times (table 1), which shows that the field emission performance of the nitrogen-doped graphene sheet-carbon nanotube array composite material obtained by the invention is greatly improved compared with the prior art. Fig. 6 shows the time-dependent change of the field emission current density of the nitrogen-doped graphene sheet-carbon nanotube array obtained in this example after aging treatment for 1 hour under the condition of a constant electric field. It can be seen that the external constant electric field intensity is only 1.42V/mum, and the average field emission current density is as high as 45.46mA/cm2In the case of (1), the attenuation of the field emission current density within 20 hours is only 3.86%, which is far better than that of the 13.86mA/cm in the prior art 12(which corresponds to an applied constant electric field strength of 1.57V/. mu.m) and 22.86mA/cm of the prior art 22(the corresponding external constant electric field intensity is 1.54V/mum) shows excellent application prospect.
Example 2
(1) Pretreating a silicon single crystal wafer:
firstly cutting a silicon single crystal wafer into 2cm multiplied by 2cm small pieces, then sequentially carrying out ultrasonic (50W) cleaning for 5 minutes in deionized water and absolute ethyl alcohol, then immersing the silicon single crystal wafer into hydrofluoric acid with the volume ratio of 4% for 5 minutes, then taking out and airing, and carrying out energy-carrying silver ion bombardment pretreatment on the obtained silicon single crystal wafer with a clean surface in a metal vapor vacuum arc ion source (MEVVA source), wherein during bombardment, a sample table is kept to rotate at a constant speed, the bias voltage of the sample table is set to-15 kV, the beam current is 10 milliamperes, and the bombardment time is 10 minutes.
(2) Preparing a carbon nano tube array by a thermal chemical vapor deposition method and carrying out high-temperature annealing treatment:
and (2) placing the silicon single crystal wafer obtained in the step (1) into a magnetron sputtering device to deposit an iron catalyst film with the thickness of 5 nanometers, then placing the silicon single crystal wafer into a high-temperature quartz tube furnace to prepare a carbon nanotube array by using a conventional thermal chemical vapor deposition method, wherein when growing the carbon nanotube, the silicon single crystal wafer deposited with the iron catalyst is subjected to heat treatment for 1 hour at 400sccm hydrogen and 580 ℃, then is subjected to treatment for 10 minutes at 150sccm ammonia and 750 ℃, finally is subjected to growth of the carbon nanotube array at 87sccm acetylene, 600sccm hydrogen, 750 ℃ and normal pressure for 30 minutes, then the temperature is raised to 1000 ℃, and the generated carbon nanotube is treated at 400sccm hydrogen and normal pressure for 2 hours.
(3) Preparing a graphene sheet by a microwave plasma enhanced chemical vapor deposition method:
placing the carbon nano tube array obtained in the step (2) on a graphite sample table in a microwave plasma system, and vacuumizing a reaction chamber to 1.0 multiplied by 10-3Introducing 10sccm hydrogen after Pa, adjusting the air pressure to 1kPa, heating the sample platform by a heater until the temperature is stabilized to 800 ℃, starting a microwave source, adjusting the microwave power to 150W, introducing 3sccm acetylene gas, adjusting the air pressure to 1kPa again, starting the growth of the graphene sheet, wherein the growth time is 3 hours, and finally obtaining the graphene sheet-carbon nanotube array.
(4) Treating the graphene sheet-carbon nanotube array by nitrogen and hydrogen plasmas:
and (3) cooling the sample to room temperature in a hydrogen atmosphere of 10sccm, performing nitrogen and hydrogen plasma treatment on the obtained graphene sheet-carbon nanotube array, wherein the gas for generating the plasma is a mixed gas consisting of nitrogen and hydrogen, the flow rates of the nitrogen and the hydrogen are respectively 5 and 10sccm, the air pressure is adjusted to be 1.5kPa, after the air pressure is stabilized, starting a microwave source, adjusting the microwave power to be 140W, and the treatment time to be 0.5 hour, so as to obtain the nitrogen-doped graphene sheet-carbon nanotube array.
(5) The field emission performance of the obtained material is characterized in that:
the field emission test shows (FIG. 5) that the threshold field of the nitrogen-doped graphene sheet-carbon nanotube obtained in the embodiment is only 1.09V/mum, and the maximum field emission current density is as high as 112.56mA/cm2Compared with the prior art 1, the change conditions of the two indexes are respectively as follows: a reduction of 0.42V/. mu.m, 2.27 times of the prior art (Table 1); compared with the prior art 2, the change conditions of the two indexes are respectively as follows: the voltage is reduced by 0.20V/mu m and is reduced by 1.51 times in the prior art (Table 1), which shows that the field emission performance of the nitrogen-doped graphene sheet-carbon nanotube array composite material obtained by the invention is greatly improved compared with the prior art.
Example 3
(1) Pretreating a silicon single crystal wafer:
firstly cutting a silicon single crystal wafer into 2cm multiplied by 2cm small pieces, then sequentially carrying out ultrasonic (50W) cleaning for 5 minutes in deionized water and absolute ethyl alcohol, then immersing the silicon single crystal wafer into hydrofluoric acid with the volume ratio of 4% for 5 minutes, then taking out and airing, and carrying out energy-carrying silver ion bombardment pretreatment on the obtained silicon single crystal wafer with a clean surface in a metal vapor vacuum arc ion source (MEVVA source), wherein during bombardment, a sample table is kept to rotate at a constant speed, the bias voltage of the sample table is set to-15 kV, the beam current is 10 milliamperes, and the bombardment time is 10 minutes.
(2) Preparing a carbon nano tube array by a thermal chemical vapor deposition method and carrying out high-temperature annealing treatment:
and (2) placing the silicon single crystal wafer obtained in the step (1) into a magnetron sputtering device to deposit an iron catalyst film with the thickness of 5 nanometers, then placing the silicon single crystal wafer into a high-temperature quartz tube furnace to prepare a carbon nanotube array by using a conventional thermal chemical vapor deposition method, wherein when growing the carbon nanotube, the silicon single crystal wafer deposited with the iron catalyst is subjected to heat treatment for 1 hour at 400sccm hydrogen and 580 ℃, then is subjected to treatment for 10 minutes at 150sccm ammonia and 750 ℃, finally is subjected to growth of the carbon nanotube array at 87sccm acetylene, 600sccm hydrogen, 750 ℃ and normal pressure for 30 minutes, then the temperature is raised to 1000 ℃, and the generated carbon nanotube is treated at 400sccm hydrogen and normal pressure for 2 hours.
(3) Preparing a graphene sheet by a microwave plasma enhanced chemical vapor deposition method:
placing the carbon nano tube array obtained in the step (2) on a graphite sample table in a microwave plasma system, and vacuumizing a reaction chamber to 1.0 multiplied by 10-3Introducing 10sccm hydrogen after Pa, adjusting the air pressure to 1kPa, heating the sample platform by a heater until the temperature is stabilized to 800 ℃, starting a microwave source, adjusting the microwave power to 150W, introducing 3sccm acetylene gas, adjusting the air pressure to 1kPa again, starting the growth of the graphene sheet, wherein the growth time is 3 hours, and finally obtaining the graphene sheet-carbon nanotube array.
(4) Treating the graphene sheet-carbon nanotube array by nitrogen and hydrogen plasmas:
and (3) cooling the sample to room temperature in a hydrogen atmosphere of 10sccm, performing nitrogen and hydrogen plasma treatment on the obtained graphene sheet-carbon nanotube array, wherein the gas for generating the plasma is a mixed gas consisting of nitrogen and hydrogen, the flow rates of the nitrogen and the hydrogen are respectively 5 and 10sccm, the air pressure is adjusted to be 1.5kPa, after the air pressure is stabilized, starting a microwave source, adjusting the microwave power to be 100W, and the treatment time to be 1 hour, so as to obtain the nitrogen-doped graphene sheet-carbon nanotube array.
(5) The field emission performance of the obtained material is characterized in that:
the field emission test shows that the threshold field of the nitrogen-doped graphene sheet-carbon nanotube obtained in the embodiment is only 1.17V/mum, and the maximum field emission current density is up to 105.25mA/cm2Compared with the prior art 1, the change conditions of the two indexes are respectively as follows: a reduction of 0.34V/. mu.m, 2.12 times of the prior art (Table 1); compared with the prior art 2, the change conditions of the two indexes are respectively as follows: the voltage is reduced by 0.22V/mu m and is reduced by 1.41 times in the prior art (Table 1), which shows that the field emission performance of the nitrogen-doped graphene sheet-carbon nanotube array composite material obtained by the invention is greatly improved compared with the prior art.
Example 4
(1) Pretreating a silicon single crystal wafer:
firstly cutting a silicon single crystal wafer into 2cm multiplied by 2cm small pieces, then sequentially carrying out ultrasonic (50W) cleaning for 5 minutes in deionized water and absolute ethyl alcohol, then immersing the silicon single crystal wafer into hydrofluoric acid with the volume ratio of 4% for 5 minutes, then taking out and airing, and carrying out energy-carrying silver ion bombardment pretreatment on the obtained silicon single crystal wafer with a clean surface in a metal vapor vacuum arc ion source (MEVVA source), wherein during bombardment, a sample table is kept to rotate at a constant speed, the bias voltage of the sample table is set to-15 kV, the beam current is 10 milliamperes, and the bombardment time is 10 minutes.
(2) Preparing a carbon nano tube array by a thermal chemical vapor deposition method and carrying out high-temperature annealing treatment:
and (2) placing the silicon single crystal wafer obtained in the step (1) into a magnetron sputtering device to deposit an iron catalyst film with the thickness of 5 nanometers, then placing the silicon single crystal wafer into a high-temperature quartz tube furnace to prepare a carbon nanotube array by using a conventional thermal chemical vapor deposition method, wherein when growing the carbon nanotube, the silicon single crystal wafer deposited with the iron catalyst is subjected to heat treatment for 1 hour at 400sccm hydrogen and 580 ℃, then is subjected to treatment for 10 minutes at 150sccm ammonia and 750 ℃, finally is subjected to growth of the carbon nanotube array at 87sccm acetylene, 600sccm hydrogen, 750 ℃ and normal pressure for 30 minutes, then the temperature is raised to 1000 ℃, and the generated carbon nanotube is treated at 400sccm hydrogen and normal pressure for 2 hours.
(3) Preparing a graphene sheet by a microwave plasma enhanced chemical vapor deposition method:
placing the carbon nano tube array obtained in the step (2) on a graphite sample table in a microwave plasma system, and vacuumizing a reaction chamber to 1.0 multiplied by 10-3Introducing 10sccm hydrogen after Pa, adjusting the air pressure to 1kPa, heating the sample platform by a heater until the temperature is stabilized to 800 ℃, starting a microwave source, adjusting the microwave power to 150W, introducing 3sccm acetylene gas, adjusting the air pressure to 1kPa again, starting the growth of the graphene sheet, wherein the growth time is 3 hours, and finally obtaining the graphene sheet-carbon nanotube array.
(4) Treating the graphene sheet-carbon nanotube array by nitrogen and hydrogen plasmas:
and (3) cooling the sample to room temperature in a hydrogen atmosphere of 10sccm, performing nitrogen and hydrogen plasma treatment on the obtained graphene sheet-carbon nanotube array, wherein the gas for generating the plasma is a mixed gas consisting of nitrogen and hydrogen, the flow rates of the nitrogen and the hydrogen are respectively 5 and 10sccm, the air pressure is adjusted to be 1.5kPa, after the air pressure is stabilized, starting a microwave source, adjusting the microwave power to be 100W, and the treatment time to be 2 hours, so as to obtain the nitrogen-doped graphene sheet-carbon nanotube array.
(5) The field emission performance of the obtained material is characterized in that:
the field emission test shows that the threshold field of the nitrogen-doped graphene sheet-carbon nanotube obtained in the embodiment is only 1.11V/mum, and the maximum field emission current density is up to 114.73mA/cm2Compared with the prior art 1, the change conditions of the two indexes are respectively as follows: 0.40V/mum reduction, 2.31 times of the prior art (Table 1); compared with the prior art 2, the change conditions of the two indexes are respectively as follows: a reduction of 0.28V/. mu.m, 1.54 times that of the prior art (Table 1), sayCompared with the prior art, the field emission performance of the nitrogen-doped graphene sheet-carbon nanotube array composite material is greatly improved.
Example 5
(1) Pretreating a silicon single crystal wafer:
firstly cutting a silicon single crystal wafer into 2cm multiplied by 2cm small pieces, then sequentially carrying out ultrasonic (50W) cleaning for 5 minutes in deionized water and absolute ethyl alcohol, then immersing the silicon single crystal wafer into hydrofluoric acid with the volume ratio of 4% for 5 minutes, then taking out and airing, and carrying out energy-carrying silver ion bombardment pretreatment on the obtained silicon single crystal wafer with a clean surface in a metal vapor vacuum arc ion source (MEVVA source), wherein during bombardment, a sample table is kept to rotate at a constant speed, the bias voltage of the sample table is set to-15 kV, the beam current is 10 milliamperes, and the bombardment time is 10 minutes.
(2) Preparing a carbon nano tube array by a thermal chemical vapor deposition method and carrying out high-temperature annealing treatment:
and (2) placing the silicon single crystal wafer obtained in the step (1) into a magnetron sputtering device to deposit an iron catalyst film with the thickness of 5 nanometers, then placing the silicon single crystal wafer into a high-temperature quartz tube furnace to prepare a carbon nanotube array by using a conventional thermal chemical vapor deposition method, wherein when growing the carbon nanotube, the silicon single crystal wafer deposited with the iron catalyst is subjected to heat treatment for 1 hour at 400sccm hydrogen and 580 ℃, then is subjected to treatment for 10 minutes at 150sccm ammonia and 750 ℃, finally is subjected to growth of the carbon nanotube array at 87sccm acetylene, 600sccm hydrogen, 750 ℃ and normal pressure for 30 minutes, then the temperature is raised to 1000 ℃, and the generated carbon nanotube is treated at 400sccm hydrogen and normal pressure for 2 hours.
(3) Preparing a graphene sheet by a microwave plasma enhanced chemical vapor deposition method:
placing the carbon nano tube array obtained in the step (2) on a graphite sample table in a microwave plasma system, and vacuumizing a reaction chamber to 1.0 multiplied by 10-3Introducing 10sccm hydrogen after Pa, adjusting the pressure to 1kPa, heating the sample platform by a heater until the temperature is stabilized at 800 ℃, starting a microwave source, adjusting the microwave power to 150W, introducing 3sccm acetylene gas, adjusting the pressure to 1kPa again, namely, starting the growth of the graphene sheet, wherein the growth time is longerAnd 3 hours, and finally obtaining the graphene sheet-carbon nanotube array.
(4) Treating the graphene sheet-carbon nanotube array by nitrogen and hydrogen plasmas:
and (3) cooling the sample to room temperature in a hydrogen atmosphere of 10sccm, performing nitrogen and hydrogen plasma treatment on the obtained graphene sheet-carbon nanotube array, wherein the gas for generating the plasma is a mixed gas consisting of nitrogen and hydrogen, the flow rates of the nitrogen and the hydrogen are respectively 5 and 10sccm, the air pressure is adjusted to be 1.5kPa, after the air pressure is stabilized, starting a microwave source, adjusting the microwave power to be 140W, and the treatment time to be 1 hour, so as to obtain the nitrogen-doped graphene sheet-carbon nanotube array.
(5) The field emission performance of the obtained material is characterized in that:
the field emission test shows that the threshold field of the nitrogen-doped graphene sheet-carbon nanotube obtained in the embodiment is only 1.21V/mum, and the maximum field emission current density is as high as 101.79mA/cm2Compared with the prior art 1, the change conditions of the two indexes are respectively as follows: 0.30V/. mu.m, 2.05 times lower than the prior art (Table 1); compared with the prior art 2, the change conditions of the two indexes are respectively as follows: the voltage is reduced by 0.17V/mu m and is reduced by 1.36 times in the prior art (Table 1), which shows that the field emission performance of the nitrogen-doped graphene sheet-carbon nanotube array composite material obtained by the invention is greatly improved compared with the prior art.
Example 6
(1) Pretreating a silicon single crystal wafer:
firstly cutting a silicon single crystal wafer into 2cm multiplied by 2cm small pieces, then sequentially carrying out ultrasonic (50W) cleaning for 5 minutes in deionized water and absolute ethyl alcohol, then immersing the silicon single crystal wafer into hydrofluoric acid with the volume ratio of 4% for 5 minutes, then taking out and airing, and carrying out energy-carrying silver ion bombardment pretreatment on the obtained silicon single crystal wafer with a clean surface in a metal vapor vacuum arc ion source (MEVVA source), wherein during bombardment, a sample table is kept to rotate at a constant speed, the bias voltage of the sample table is set to-15 kV, the beam current is 10 milliamperes, and the bombardment time is 10 minutes.
(2) Preparing a carbon nano tube array by a thermal chemical vapor deposition method and carrying out high-temperature annealing treatment:
and (2) placing the silicon single crystal wafer obtained in the step (1) into a magnetron sputtering device to deposit an iron catalyst film with the thickness of 5 nanometers, then placing the silicon single crystal wafer into a high-temperature quartz tube furnace to prepare a carbon nanotube array by using a conventional thermal chemical vapor deposition method, wherein when growing the carbon nanotube, the silicon single crystal wafer deposited with the iron catalyst is subjected to heat treatment for 1 hour at 400sccm hydrogen and 580 ℃, then is subjected to treatment for 10 minutes at 150sccm ammonia and 750 ℃, finally is subjected to growth of the carbon nanotube array at 87sccm acetylene, 600sccm hydrogen, 750 ℃ and normal pressure for 30 minutes, then the temperature is raised to 1000 ℃, and the generated carbon nanotube is treated at 400sccm hydrogen and normal pressure for 2 hours.
(3) Preparing a graphene sheet by a microwave plasma enhanced chemical vapor deposition method:
placing the carbon nano tube array obtained in the step (2) on a graphite sample table in a microwave plasma system, and vacuumizing a reaction chamber to 1.0 multiplied by 10-3Introducing 10sccm hydrogen after Pa, adjusting the air pressure to 1kPa, heating the sample platform by a heater until the temperature is stabilized to 800 ℃, starting a microwave source, adjusting the microwave power to 150W, introducing 3sccm acetylene gas, adjusting the air pressure to 1kPa again, starting the growth of the graphene sheet, wherein the growth time is 3 hours, and finally obtaining the graphene sheet-carbon nanotube array.
(4) Treating the graphene sheet-carbon nanotube array by nitrogen and hydrogen plasmas:
and (3) cooling the sample to room temperature in a hydrogen atmosphere of 10sccm, performing nitrogen and hydrogen plasma treatment on the obtained graphene sheet-carbon nanotube array, wherein the gas for generating the plasma is a mixed gas consisting of nitrogen and hydrogen, the flow rates of the nitrogen and the hydrogen are respectively 5 and 10sccm, the air pressure is adjusted to be 1.5kPa, after the air pressure is stabilized, starting a microwave source, adjusting the microwave power to be 120W, and the treatment time to be 2 hours, so as to obtain the nitrogen-doped graphene sheet-carbon nanotube array.
(5) The field emission performance of the obtained material is characterized in that:
the field emission test shows that the threshold field of the nitrogen-doped graphene sheet-carbon nanotube obtained in the embodiment is only 1.15V/mum, and the maximum field emission currentThe density is as high as 109.75mA/cm2Compared with the prior art 1, the change conditions of the two indexes are respectively as follows: 0.36V/. mu.m, 2.21 times lower than the prior art (Table 1); compared with the prior art 2, the change conditions of the two indexes are respectively as follows: the voltage is reduced by 0.24V/mu m and is reduced by 1.47 times in the prior art (Table 1), which shows that the field emission performance of the nitrogen-doped graphene sheet-carbon nanotube array composite material obtained by the invention is greatly improved compared with the prior art.
Finally, it is noted that the above only illustrates typical embodiments of the invention; the preparation of the nitrogen-doped graphene sheet-carbon nanotube array composite material and the improvement of field emission performance can be realized by adjusting the process parameters of the invention, the average threshold field is only 1.09-1.21V/mum, and the average maximum field emission current density can reach 101.79-120.56A/cm2Stable field electron emission can be realized at high field emission current density. It is obvious that the present invention is not limited to the above embodiments, and many other experimental parameter combinations are possible, and those skilled in the art can directly derive or associate the relevant cases from the disclosure of the present invention and should be considered as the protection scope of the present invention.
Table 1 compares the field emission results of samples of Prior Art 1, Prior Art 2, and various examples of the present invention, wherein
“Eth"represents a threshold field," Jmax"denotes the maximum field emission current density and" ↓ "denotes a decline.
Claims (4)
1. A method for improving the field emission performance of a graphene sheet-carbon nanotube array composite material is characterized by comprising the following steps: firstly, bombarding and pretreating a silicon single crystal wafer by using energy-carrying silver ions, then preparing a carbon nano tube array by using a thermal chemical vapor deposition method, carrying out high-temperature annealing treatment, preparing a thin graphene sheet by using a microwave plasma enhanced chemical vapor deposition method, and finally treating the obtained graphene sheet-carbon nano tube by using microwave nitrogen and hydrogen plasmas at normal temperatureThe morphology of the rice tube array is controlled by adjusting the microwave power to be 100-140W, the air pressure of a treatment chamber to be 1.5kPa and the treatment time to be 0.5-2 hours, and finally the nitrogen-doped graphene sheet-carbon nano tube array composite material is obtained; the nitrogen-doped graphene sheet-carbon nanotube array composite material consists of graphene sheets which are deposited on a carbon nanotube array, have 1-5 layers of edge layers, are rich in defects and are doped with nitrogen; the threshold field of the prepared nitrogen-doped graphene sheet-carbon nanotube array composite material is only 1.09-1.21V/mum on average, and the maximum field emission current density can reach 101.79-120.56mA/cm on average2The emission current density is up to 45.46mA/cm in average field2The current decay in 20 hours was only 3.86%.
2. The method for improving the field emission performance of the graphene sheet-carbon nanotube array composite material according to claim 1, comprising the following steps:
pretreating a silicon single crystal wafer: firstly cutting a silicon single crystal wafer into 2cm multiplied by 2cm small pieces, sequentially and respectively adopting 50W power ultrasonic cleaning for 5 minutes in deionized water and absolute ethyl alcohol, then immersing the silicon single crystal wafer into hydrofluoric acid with the volume ratio of 4% for 5 minutes, taking out and drying, and then carrying out energy-carrying silver ion bombardment pretreatment on the obtained silicon single crystal wafer with a clean surface in a metal vapor vacuum arc ion source (MEVVA source), wherein during bombardment, the sample table is kept to rotate at a constant speed, the bias voltage of the sample table is set to-15 kV, the beam current is 10 milliamperes, and the bombardment time is 10 minutes;
preparing a carbon nanotube array by a thermochemical vapor deposition method and carrying out high-temperature annealing treatment: putting the silicon single crystal wafer obtained in the step (1) into a magnetron sputtering device to deposit an iron catalyst film with the thickness of 5 nanometers, then putting the silicon single crystal wafer into a high-temperature quartz tube furnace to prepare a carbon nanotube array by using a conventional thermochemical vapor deposition method, when growing a carbon nanotube, firstly carrying out heat treatment on the silicon single crystal wafer deposited with the iron catalyst for 1 hour at 400sccm hydrogen and 580 ℃, then carrying out treatment for 10 minutes at 150sccm ammonia and 750 ℃, finally growing the carbon nanotube array at 87sccm acetylene, 600sccm hydrogen, 750 ℃ and normal pressure for 30 minutes, then raising the temperature to 1000 ℃, and treating the generated carbon nanotube at 400sccm hydrogen and normal pressure for 2 hours;
preparing graphene sheets by a microwave plasma enhanced chemical vapor deposition method: placing the carbon nano tube array obtained in the step (2) on a graphite sample table in a microwave plasma system, and vacuumizing a reaction chamber to 1.0 multiplied by 10-3Introducing 10sccm hydrogen after Pa, adjusting the air pressure to 1kPa, heating the sample platform by a heater until the temperature is stabilized to 800 ℃, starting a microwave source, adjusting the microwave power to 150W, introducing 3sccm acetylene gas, adjusting the air pressure to 1kPa again, starting the growth of the graphene sheet, wherein the growth time is 3 hours, and finally obtaining the graphene sheet-carbon nanotube array;
step (4), treating the graphene sheet-carbon nanotube array by nitrogen and hydrogen plasmas: and (3) cooling the sample to room temperature in a hydrogen atmosphere of 10sccm, performing nitrogen and hydrogen plasma treatment on the obtained graphene sheet-carbon nanotube array, wherein the gas for generating the plasma is a mixed gas consisting of nitrogen and hydrogen, the flow rates of the nitrogen and the hydrogen are respectively 5 and 10sccm, the air pressure is adjusted to be 1.5kPa, after the air pressure is stabilized, starting a microwave source, adjusting the microwave power to be 100-140W, and the treatment time to be 0.5-2 hours, so as to obtain the nitrogen-doped graphene sheet-carbon nanotube array.
3. The method of claim 2, wherein the purity of each gas used is 5N.
4. The graphene sheet-carbon nanotube array composite material prepared by the method of claim 1, wherein the nitrogen-doped graphene sheet-carbon nanotube array composite material is composed of 1-5 layers of defect-rich and nitrogen-doped graphene sheets deposited on a carbon nanotube array; the threshold field of the prepared nitrogen-doped graphene sheet-carbon nanotube array composite material is only 1.09-1.21V/mum on average, and the maximum field emission current density can reach 101.79-120.56mA/cm on average2In the mean fieldThe emission current density is as high as 45.46mA/cm2The current decay in 20 hours was only 3.86%.
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