CN108987218B - Method for improving field emission performance of graphene sheet-silicon nanowire array composite material - Google Patents

Method for improving field emission performance of graphene sheet-silicon nanowire array composite material Download PDF

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CN108987218B
CN108987218B CN201810098840.4A CN201810098840A CN108987218B CN 108987218 B CN108987218 B CN 108987218B CN 201810098840 A CN201810098840 A CN 201810098840A CN 108987218 B CN108987218 B CN 108987218B
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nanowire array
silicon nanowire
graphene sheet
nitrogen
silicon
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CN108987218A (en
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邓建华
张燕
朱文祥
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Tianjin Normal University
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Abstract

The invention discloses a method for improving the field emission performance of a graphene sheet-silicon nanowire array composite material, and belongs to the field of preparation and application of nanomaterials. The preparation method comprises the following preparation processes: (1) preparing a silicon nanowire array by a metal catalytic corrosion method; (2) carrying out energy-carrying silver ion bombardment treatment on the silicon nanowire; (3) preparing thin graphene sheets on the silicon nanowire array by using a microwave plasma enhanced chemical vapor deposition method; (4) treating the obtained graphene sheet-silicon nanowire array at room temperature by using nitrogen and hydrogen plasmas; (5) and carrying out high-temperature annealing treatment on the obtained nitrogen-doped graphene sheet-silicon nanowire array. Compared with the prior art, the nitrogen-doped graphene sheet-silicon nanowire array composite material prepared by the method has the characteristics of low working electric field, high field emission current density, good stability and the like, and has high application value.

Description

Method for improving field emission performance of graphene sheet-silicon nanowire array composite material
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-silicon nanowire 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. The silicon nanowire is used as a quasi-one-dimensional nanomaterial, has the characteristics of high length-diameter ratio, excellent conductivity, good contact with a substrate and the like, is a field emission cathode material with excellent performance, 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, the field emission performance of the pure silicon nanowire is often poor, and the on-state electric field (the field emission current density reaches 10 muA/cm)2The corresponding external electric field intensity) is generally higher than 6.0V/mu m, and the maximum field emission current density is generally less than 1.0mA/cm2This greatly limits itApplication is carried out. The compounding of silicon nanowires with other low-dimensional nanomaterials is a big breakthrough for improving the field emission performance of the silicon nanowires, and the compounding of the silicon nanowires with graphene sheets which have good field emission stability and are quasi-two-dimensional nanomaterials is a key point of research. The one-dimensional/two-dimensional composite material can simultaneously have the large length-diameter ratio of the one-dimensional silicon nanowire 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-silicon nanowire composite material can reach 3.98mA/cm2The opening field is as low as 3.01V/mum, and the current density reaches 1.0mA/cm2The applied electric field intensity can be as low as 3.29V/mum, and the field emission stability is good under the low field emission current density, and the indexes are greatly improved compared with the original silicon nanowire. However, the field emission performance of the graphene sheet-silicon nanowire composite material is still not excellent, and firstly, the maximum field emission current density is still relatively small, so that the application of large current density is limited; secondly, the goal of realizing stable operation of the field electronic device under large field emission current density is still not achieved, which puts forward a new requirement for improving the performance of the field emission cathode based on the graphene sheet-silicon nanowire 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 the graphene sheet-silicon nanowire array, a transition layer is introduced through silver ion bombardment treatment to strengthen the binding force between the graphene sheet and the silicon nanowire array, and nitrogen-doped graphene sheet-silicon nanowire 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, using metal catalytic corrosion methodPreparing a silicon nanowire array, bombarding the silicon nanowire array by using energy-carrying silver ions in an inclination angle mode, preparing a thin graphene sheet on the silicon nanowire array by using a microwave plasma enhanced chemical vapor deposition method, processing the obtained graphene sheet-silicon nanowire array composite material by using microwave nitrogen and hydrogen plasmas at normal temperature, controlling the appearance of the graphene sheet by adjusting the microwave power to be 120-160W, the air pressure of a processing chamber to be 1.5kPa and the processing time to be 20-60 minutes, and finally annealing the obtained nitrogen-doped graphene sheet-silicon nanowire array for 2 hours in a hydrogen atmosphere at 1000 ℃, normal pressure and normal temperature to finally obtain the nitrogen-doped graphene sheet-silicon nanowire array composite material subjected to high-temperature heat treatment; the nitrogen-doped graphene sheet-silicon nanowire array composite material is composed of graphene sheets which are deposited on silicon nanowires bombarded by silver ions, have 2-5 layers of deposited edge layers, are rich in defects, are densely distributed and are doped with nitrogen; wherein the graphene sheets have a diameter of at most 50-100 nanometers; the average opening field of the prepared nitrogen-doped graphene sheet-silicon nanowire array composite material is only 2.53-2.77V/mum, and the average maximum field emission current density can reach 9.32-11.63mA/cm2Emitting current density up to 9.19mA/cm in average field2The current decay in 20 hours was only 0.76%.
In the technical scheme, the method further comprises a pretreatment process of sequentially and respectively ultrasonically cleaning the silicon single crystal wafer in deionized water and absolute ethyl alcohol by 50W power for 5 minutes.
In the technical scheme, the method further comprises the step of soaking the silicon single crystal wafer subjected to ultrasonic cleaning in hydrofluoric acid with the volume ratio of 4% for 5 minutes.
In the technical scheme, the obtained nitrogen-doped graphene sheet-silicon nanowire array is annealed for 2 hours at 1000 ℃ under normal pressure and in a hydrogen atmosphere.
In the technical scheme, the method for improving the field emission performance of the graphene sheet-silicon nanowire array composite material comprises the following specific steps:
step (1), preparing a silicon nanowire array by a metal catalytic corrosion method: firstly, cutting a silicon single crystal wafer into 2cm multiplied by 2cm small pieces, and then sequentially and respectively ultrasonically cleaning the silicon single crystal wafer in deionized water and absolute ethyl alcohol (50W) for 5 minutesThen immersing the silicon single crystal wafer into hydrofluoric acid with the volume ratio of 4% for 5 minutes, and then sequentially placing the obtained silicon single crystal wafers with clean surfaces into AgNO with the volume ratio3:HF:H2Soaking in solution with O2: 10:38 ratio of H for 1 minute2O2:HF:H2Soaking the silicon nanowire array in a solution with the ratio of O to O being 1:10:39 for 45 minutes to obtain a silicon nanowire array; AgNO used as described above3The concentrations of HF acid and hydrogen peroxide are respectively 0.01, 4 and 0.176 mol/L;
step (2), pretreating the silicon nanowire array by silver ion bombardment: carrying out energy-carrying silver ion bombardment pretreatment on the silicon nanowire array obtained in the step (1) in a metal vapor vacuum arc ion source (MEVVA source), wherein during bombardment, the incident direction of silver ions and the axial direction of the silicon nanowires form an included angle of about 10 degrees, 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 graphene sheets by a microwave plasma enhanced chemical vapor deposition method: placing the silicon nanowire array bombarded by the silver ions obtained in the step (2) on a graphite sample table in a microwave plasma system, and vacuumizing a reaction chamber to 1.0 x 10-3Introducing 10sccm hydrogen after Pa, adjusting the pressure to 1kPa, heating the sample platform by using a self-made graphite heater until the temperature is stabilized to 800 ℃, starting a microwave source, adjusting the microwave power to 180W, introducing 5sccm 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 sheet-silicon nanowire array;
step (4), treating the graphene sheet-silicon nanowire array by nitrogen and hydrogen plasmas: on the basis of the step (3), cooling the sample to room temperature in a hydrogen atmosphere of 10sccm, performing nitrogen and hydrogen plasma treatment on the obtained graphene sheet-silicon nanowire array, wherein the gas for generating the plasma is a mixed gas composed of nitrogen and hydrogen, the flow rates of the nitrogen and the hydrogen are respectively 5 and 10sccm, the gas pressure is adjusted to be 1.5kPa, after the gas pressure is stable, starting a microwave source, adjusting the microwave power to be 120-160W, and the treatment time to be 20-60 minutes, so as to obtain the nitrogen-doped graphene sheet-silicon nanowire array;
and (5) high-temperature annealing: and (3) carrying out high-temperature annealing treatment on the nitrogen-doped graphene sheet-silicon nanowire array obtained in the step (4) in a quartz tube furnace, wherein the treatment temperature is 1000 ℃, the used protective gas is 400sccm hydrogen, the pressure in the quartz tube is normal pressure, and the treatment time is 2 hours.
In the technical scheme, the purity of all the used gases is 5N.
The nitrogen-doped graphene sheet-silicon nanowire array composite material prepared according to the technical scheme; the nitrogen-doped graphene sheet-silicon nanowire array composite material is composed of graphene sheets which are deposited on silicon nanowires bombarded by silver ions, have 2-5 layers of deposited edge layers, are rich in defects, are densely distributed and are doped with nitrogen; wherein the graphene sheets have a diameter of at most 50-100 nanometers; the average opening field of the prepared nitrogen-doped graphene sheet-silicon nanowire array composite material is only 2.53-2.77V/mum, and the average maximum field emission current density can reach 9.32-11.63mA/cm2Emitting current density up to 9.19mA/cm in average field2The current decay in 20 hours was only 0.76%.
Compared with the prior art, the method for improving the field emission performance of the graphene sheet-silicon nanowire 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) before growing the graphene sheet, energy-carrying silver ions are injected into the silicon nanowire array to form a silver-silicon transition layer on the surface of the silicon nanowire, the transition layer can promote the transmission of electrons on one hand, and on the other hand, in the later-stage high-temperature annealing treatment, the root of the graphene sheet can be effectively coated at the contact part of the graphene sheet and the silicon nanowire in a silver precipitation mode, so that the binding force between the graphene sheet and the silicon nanowire is improved, and the maximum field emission current density of the material is improved; (2) by irradiating the graphene sheet-silicon nanowire array with nitrogen and hydrogen plasmas, firstly, the graphene sheet can be subjected to nitrogen doping, so that the escape work function of the graphene sheet is reduced, electrons in the graphene sheet can more easily tunnel through a potential barrier and escape into vacuum, namely, the field electron emission capability of the graphene sheet is enhanced, secondly, a large number of defects can be introduced into the graphene sheet, and the defects can become high in the field emission processThe efficient field emission point, which is the normal temperature plasma treatment rather than the high temperature treatment, is also used in the present invention to better preserve these defects. In conclusion, the further enhancement of the combination of the graphene sheet and the silicon nanowire, 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-silicon nanowire array, and the superiority of the invention is also the main point. The introduction of silver ion bombardment and nitrogen doping ensures that the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained by the invention has low turn-on field (2.53V/mum) and high field emission current density (11.63 mA/cm)2) And excellent high current density field emission stability (up to 9.19mA/cm in average field emission current density)2And the current attenuation in 20 hours is only 0.76 percent), and compared with the prior art, the indexes are greatly improved.
Drawings
FIG. 1 is a schematic flow diagram of a method for preparing a nitrogen-doped graphene sheet-silicon nanowire array composite 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 picture of the nitrogen-doped graphene sheet-silicon nanowire array obtained by silver ion bombardment in example 1, including:
FIG. 3a is a scanning electron microscope side view of an array of nitrogen-doped graphene sheet-silicon nanowires;
FIG. 3b is a high resolution transmission electron microscope picture of graphene sheets in a nitrogen-doped graphene sheet-silicon nanowire 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 a graphene sheet-silicon nanowire array obtained after silver ion bombardment treatment in the prior art and of a nitrogen-doped graphene sheet-silicon nanowire array composite material obtained after silver ion bombardment, nitrogen and hydrogen plasma treatment in example 1 and example 2;
FIG. 6 shows the silver ion in example 1The field emission stability chart of the obtained nitrogen-doped graphene sheet-silicon nanowire array composite material after the bombardment of the seeds within 20 hours is shown, wherein ' E ' and ' Jmean"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, hydrogen peroxide, silver nitrate, high-purity hydrogen, high-purity nitrogen, high-purity acetylene gas, 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 metal catalytic corrosion method for preparing the silicon nanowire array, 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 1 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 the field emission cathode with the nano carbon sheet-silicon nanowire composite structure (Chinese patent, patent number ZL201510152591.9) is adopted as the prior art for comparison, and the maximum field emission current density can reach 3.98mA/cm2The opening field is as low as 3.01V/mum, and the current density reaches 1.0mA/cm2The applied electric field intensity can be as low as 3.29V/mu m, and the emission current density in the average field is 1.34mA/cm2It shows better field emission stability.
Fig. 1 is a schematic flow chart of the preparation of the nitrogen-doped graphene sheet-silicon nanowire array composite material in the present invention, which is mainly divided into five steps of preparation of a silicon nanowire array by a metal catalytic corrosion method, bombardment of the silicon nanowire array by silver ions, preparation of a thin graphene sheet by a microwave plasma enhanced chemical vapor deposition method, microwave nitrogen treatment, hydrogen plasma treatment of the graphene sheet-silicon nanowire array, high-temperature annealing, and the like.
Example 1
(1) Preparing a silicon nanowire array by a metal catalytic corrosion method:
firstly, cutting a silicon single crystal wafer into 2cm multiplied by 2cm small pieces, then sequentially and respectively ultrasonically cleaning (50W) in deionized water and absolute ethyl alcohol for 5 minutes, then immersing the silicon single crystal wafer into hydrofluoric acid with the volume ratio of 4 percent for 5 minutes, and then sequentially placing the obtained silicon single crystal wafer with clean surface into AgNO with the volume ratio3:HF:H2Soaking in solution with O2: 10:38 ratio of H for 1 minute2O2:HF:H2Soaking the silicon nanowire array in a solution with the ratio of O to O being 1:10:39 for 45 minutes to obtain a silicon nanowire array; AgNO used as described above3And the concentrations of the HF acid and the hydrogen peroxide are respectively 0.01, 4 and 0.176 mol/L.
(2) Pretreating the silicon nanowire array by silver ion bombardment:
and (2) performing energy-carrying silver ion bombardment pretreatment on the silicon nanowire array obtained in the step (1) in a metal vapor vacuum arc ion source (MEVVA source), wherein during bombardment, the incident direction of silver ions forms an included angle of about 10 degrees with the axial direction of the silicon nanowires, 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.
(3) Preparing a graphene sheet by a microwave plasma enhanced chemical vapor deposition method:
placing the silicon nanowire array bombarded by the silver ions obtained in the step (2) on a graphite sample stage in a microwave plasma system (figure 2 is a structural schematic diagram of the device), and vacuumizing a reaction chamber to 1.0 x 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 180W, introducing 5sccm 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 sheet-silicon nanowire array.
(4) Treating the graphene sheet-silicon nanowire array by using 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-silicon nanowire 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, adjusting the gas pressure to be 1.5kPa, starting a microwave source after the gas pressure is stable, setting the microwave power to be 140W, and setting the treatment time to be 40 minutes. The X-ray photoelectron spectroscopy analysis shows that a certain amount of nitrogen atoms are doped in the graphene sheet-silicon nanowire array composite material, and the nitrogen-doped graphene sheet-silicon nanowire array is obtained.
(5) And (3) carrying out high-temperature annealing treatment on the obtained nitrogen-doped graphene sheet-silicon nanowire array:
and (3) carrying out high-temperature annealing treatment on the nitrogen-doped graphene sheet-silicon nanowire array obtained in the step (4) in a quartz tube furnace, wherein the treatment temperature is 1000 ℃, the used protective gas is 400sccm hydrogen, the pressure in the quartz tube is normal pressure, and the treatment time is 2 hours, so as to finally obtain the annealed nitrogen-doped graphene sheet-silicon nanowire array composite material, and the scanning electron microscope side view of the composite material is shown in fig. 3 a. Fig. 3b shows a high-resolution transmission electron microscope picture of the nitrogen-doped graphene sheet-silicon nanowire array, which shows the structures of the edge and the surface of the graphene sheet, and it can be seen that the edge of the graphene has only 2 layers and the surface has many defects, 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 2 to 5.
(6) The field emission performance of the obtained material is characterized in that:
the obtained nitrogen-doped graphene sheet-silicon nanowire 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 the field emission performance of the graphene sheet-silicon nanowire array after the silver ion bombardment treatment and the field emission performance of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained after the silver ion bombardment, nitrogen and hydrogen plasma treatment in this embodiment, and it is characterized in thatThe variation relationship of the field emission current density of the cathode material along with the increase of the external electric field intensity is shown in the table 1. It can be seen that after the silver ion bombardment treatment is introduced, the opening field of the graphene sheet-silicon nanowire array is 3.08V/mum, and the field emission current density reaches 1.0mA/cm2The applied electric field intensity is 3.25V/mum, and the maximum field emission current density is 7.93mA/cm2Compared with the prior art (the corresponding numerical values are respectively 3.01V/mum, 3.29V/mum and 3.98 mA/cm)2) Although the change of the working electric field is small, the maximum field emission current density is 1.99 times that of the prior art, which shows that the silver ion bombardment treatment greatly improves the binding force between the graphene sheet and the silicon nano-wire, and further improves the maximum field emission current density. In addition, after silver ion bombardment and nitrogen and hydrogen plasmas are introduced, the opening field of the obtained nitrogen-doped graphene sheet-silicon nanowire is only 2.53V/mum, and the field emission current density reaches 1.0mA/cm2The external electric field intensity is only 2.71V/mum, and the maximum field emission current density is up to 11.63mA/cm2Compared with the prior art, the change conditions of the three indexes are respectively as follows: the voltage is reduced by 0.48V/mum and 0.58V/mum, and the field emission performance of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained by the invention is greatly improved compared with the field emission performance of the prior art by 2.92 times (shown in table 1). Fig. 6 shows the time-dependent change of the field emission current density of the nitrogen-doped graphene sheet-silicon nanowire 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 2.88V/mum, and the average field emission current density is as high as 9.19mA/cm2(far better than the prior art of 1.34mA/cm2And the corresponding external constant electric field intensity is 3.45V/mum), the attenuation of the field emission current density within 20 hours is only 0.76 percent, and the application prospect is excellent.
Example 2
(1) Preparing a silicon nanowire array by a metal catalytic corrosion method:
firstly, cutting a silicon single crystal wafer into 2cm multiplied by 2cm small pieces, then sequentially and respectively ultrasonically cleaning the silicon single crystal wafer (50W) in deionized water and absolute ethyl alcohol for 5 minutes, and then immersing the silicon single crystal wafer into the silicon single crystal waferAdding 4% hydrofluoric acid for 5 min, and sequentially placing the silicon single crystal wafers with clean surfaces into AgNO3:HF:H2Soaking in solution with O2: 10:38 ratio of H for 1 minute2O2:HF:H2Soaking the silicon nanowire array in a solution with the ratio of O to O being 1:10:39 for 45 minutes to obtain a silicon nanowire array; AgNO used as described above3And the concentrations of the HF acid and the hydrogen peroxide are respectively 0.01, 4 and 0.176 mol/L.
(2) Pretreating the silicon nanowire array by silver ion bombardment:
and (2) performing energy-carrying silver ion bombardment pretreatment on the silicon nanowire array obtained in the step (1) in a metal vapor vacuum arc ion source (MEVVA source), wherein during bombardment, the incident direction of silver ions forms an included angle of about 10 degrees with the axial direction of the silicon nanowires, 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.
(3) Preparing a graphene sheet by a microwave plasma enhanced chemical vapor deposition method:
placing the silicon nanowire array bombarded by the silver ions obtained in the step (2) on a graphite sample table in a microwave plasma system, and vacuumizing a reaction chamber to 1.0 x 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 180W, introducing 5sccm 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 sheet-silicon nanowire array.
(4) Treating the graphene sheet-silicon nanowire array by using 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-silicon nanowire 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, adjusting the gas pressure to be 1.5kPa, starting a microwave source after the gas pressure is stable, setting the microwave power to be 140W, and setting the treatment time to be 60 minutes, thereby obtaining the nitrogen-doped graphene sheet-silicon nanowire array.
(5) And (3) carrying out high-temperature annealing treatment on the obtained nitrogen-doped graphene sheet-silicon nanowire array:
and (3) carrying out high-temperature annealing treatment on the nitrogen-doped graphene sheet-silicon nanowire array obtained in the step (4) in a quartz tube furnace, wherein the treatment temperature is 1000 ℃, the used protective gas is 400sccm hydrogen, the pressure in the quartz tube is normal pressure, and the treatment time is 2 hours, so as to finally obtain the annealed nitrogen-doped graphene sheet-silicon nanowire array composite material.
(6) The field emission performance of the obtained material is characterized in that:
the field emission test shows (FIG. 5) that the opening field of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained in the embodiment is only 2.57V/μm, and the field emission current density reaches 1.0mA/cm2The applied electric field intensity is 2.75V/mum, and the maximum field emission current density is 10.44mA/cm2Compared with the prior art, the change conditions of the three indexes are respectively as follows: the voltage is reduced by 0.44V/mum and 0.54V/mum, and the field emission performance of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained by the invention is greatly improved compared with the field emission performance of the prior art by 2.62 times (shown in table 1).
Example 3
(1) Preparing a silicon nanowire array by a metal catalytic corrosion method:
firstly, cutting a silicon single crystal wafer into 2cm multiplied by 2cm small pieces, then sequentially and respectively ultrasonically cleaning (50W) in deionized water and absolute ethyl alcohol for 5 minutes, then immersing the silicon single crystal wafer into hydrofluoric acid with the volume ratio of 4 percent for 5 minutes, and then sequentially placing the obtained silicon single crystal wafer with clean surface into AgNO with the volume ratio3:HF:H2Soaking in solution with O2: 10:38 ratio of H for 1 minute2O2:HF:H2Soaking the silicon nanowire array in a solution with the ratio of O to O being 1:10:39 for 45 minutes to obtain a silicon nanowire array; AgNO used as described above3And the concentrations of the HF acid and the hydrogen peroxide are respectively 0.01, 4 and 0.176 mol/L.
(2) Pretreating the silicon nanowire array by silver ion bombardment:
and (2) performing energy-carrying silver ion bombardment pretreatment on the silicon nanowire array obtained in the step (1) in a metal vapor vacuum arc ion source (MEVVA source), wherein during bombardment, the incident direction of silver ions forms an included angle of about 10 degrees with the axial direction of the silicon nanowires, 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.
(3) Preparing a graphene sheet by a microwave plasma enhanced chemical vapor deposition method:
placing the silicon nanowire array bombarded by the silver ions obtained in the step (2) on a graphite sample table in a microwave plasma system, and vacuumizing a reaction chamber to 1.0 x 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 180W, introducing 5sccm 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 sheet-silicon nanowire array.
(4) Treating the graphene sheet-silicon nanowire array by using 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-silicon nanowire 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, adjusting the gas pressure to be 1.5kPa, starting a microwave source after the gas pressure is stable, setting the microwave power to be 140W, and setting the treatment time to be 20 minutes, thereby obtaining the nitrogen-doped graphene sheet-silicon nanowire array.
(5) And (3) carrying out high-temperature annealing treatment on the obtained nitrogen-doped graphene sheet-silicon nanowire array:
and (3) carrying out high-temperature annealing treatment on the nitrogen-doped graphene sheet-silicon nanowire array obtained in the step (4) in a quartz tube furnace, wherein the treatment temperature is 1000 ℃, the used protective gas is 400sccm hydrogen, the pressure in the quartz tube is normal pressure, and the treatment time is 2 hours, so as to finally obtain the annealed nitrogen-doped graphene sheet-silicon nanowire array composite material.
(6) The field emission performance of the obtained material is characterized in that:
the field emission test shows that the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained in the embodimentThe turn-on field is only 2.77V/mum, and the field emission current density reaches 1.0mA/cm2The applied electric field intensity is 2.96V/mum, and the maximum field emission current density is 9.32mA/cm2Compared with the prior art, the change conditions of the three indexes are respectively as follows: the voltage is reduced by 0.24V/mum and 0.33V/mum, and the field emission performance of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained by the invention is greatly improved compared with the field emission performance of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained by the prior art (Table 1).
Example 4
(1) Preparing a silicon nanowire array by a metal catalytic corrosion method:
firstly, cutting a silicon single crystal wafer into 2cm multiplied by 2cm small pieces, then sequentially and respectively ultrasonically cleaning (50W) in deionized water and absolute ethyl alcohol for 5 minutes, then immersing the silicon single crystal wafer into hydrofluoric acid with the volume ratio of 4 percent for 5 minutes, and then sequentially placing the obtained silicon single crystal wafer with clean surface into AgNO with the volume ratio3:HF:H2Soaking in solution with O2: 10:38 ratio of H for 1 minute2O2:HF:H2Soaking the silicon nanowire array in a solution with the ratio of O to O being 1:10:39 for 45 minutes to obtain a silicon nanowire array; AgNO used as described above3And the concentrations of the HF acid and the hydrogen peroxide are respectively 0.01, 4 and 0.176 mol/L.
(2) Pretreating the silicon nanowire array by silver ion bombardment:
and (2) performing energy-carrying silver ion bombardment pretreatment on the silicon nanowire array obtained in the step (1) in a metal vapor vacuum arc ion source (MEVVA source), wherein during bombardment, the incident direction of silver ions forms an included angle of about 10 degrees with the axial direction of the silicon nanowires, 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.
(3) Preparing a graphene sheet by a microwave plasma enhanced chemical vapor deposition method:
placing the silicon nanowire array bombarded by the silver ions obtained in the step (2) on a graphite sample table in a microwave plasma system, and vacuumizing a reaction chamber to 1.0 x 10-3Introducing 10sccm hydrogen after Pa, adjusting the pressure to 1kPa, heating the sample stage with a heater until the temperature is stabilized at 800 ℃, starting the microwave source, adjusting the microwave power to 180W, and introducing 5sAnd regulating the pressure of acetylene gas of ccm to 1kPa again, namely starting the growth of the graphene sheet, wherein the growth time is 3 hours, and finally obtaining the graphene sheet-silicon nanowire array.
(4) Treating the graphene sheet-silicon nanowire array by using 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-silicon nanowire 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, adjusting the gas pressure to be 1.5kPa, starting a microwave source after the gas pressure is stable, setting the microwave power to be 120W, and setting the treatment time to be 40 minutes, thereby obtaining the nitrogen-doped graphene sheet-silicon nanowire array.
(5) And (3) carrying out high-temperature annealing treatment on the obtained nitrogen-doped graphene sheet-silicon nanowire array:
and (3) carrying out high-temperature annealing treatment on the nitrogen-doped graphene sheet-silicon nanowire array obtained in the step (4) in a quartz tube furnace, wherein the treatment temperature is 1000 ℃, the used protective gas is 400sccm hydrogen, the pressure in the quartz tube is normal pressure, and the treatment time is 2 hours, so as to finally obtain the annealed nitrogen-doped graphene sheet-silicon nanowire array composite material.
(6) The field emission performance of the obtained material is characterized in that:
the field emission test shows that the opening field of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained in the embodiment is only 2.67V/mum, and the field emission current density reaches 1.0mA/cm2The applied electric field intensity is 2.86V/mum, and the maximum field emission current density is 10.05mA/cm2Compared with the prior art, the change conditions of the three indexes are respectively as follows: the voltage is reduced by 0.34V/mum and 0.43V/mum, and the field emission performance of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained by the invention is greatly improved compared with the field emission performance of the prior art by 2.53 times (shown in table 1).
Example 5
(1) Preparing a silicon nanowire array by a metal catalytic corrosion method:
firstly, cutting the silicon single crystal wafer into 2cm multiplied by 2cm small pieces, and thenSequentially and respectively ultrasonically (50W) cleaning in deionized water and absolute ethyl alcohol for 5 minutes, then immersing the silicon single crystal wafer into hydrofluoric acid with the volume ratio of 4% for 5 minutes, and sequentially placing the obtained silicon single crystal wafer with clean surface into AgNO with the volume ratio3:HF:H2Soaking in solution with O2: 10:38 ratio of H for 1 minute2O2:HF:H2Soaking the silicon nanowire array in a solution with the ratio of O to O being 1:10:39 for 45 minutes to obtain a silicon nanowire array; AgNO used as described above3And the concentrations of the HF acid and the hydrogen peroxide are respectively 0.01, 4 and 0.176 mol/L.
(2) Pretreating the silicon nanowire array by silver ion bombardment:
and (2) performing energy-carrying silver ion bombardment pretreatment on the silicon nanowire array obtained in the step (1) in a metal vapor vacuum arc ion source (MEVVA source), wherein during bombardment, the incident direction of silver ions forms an included angle of about 10 degrees with the axial direction of the silicon nanowires, 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.
(3) Preparing a graphene sheet by a microwave plasma enhanced chemical vapor deposition method:
placing the silicon nanowire array bombarded by the silver ions obtained in the step (2) on a graphite sample table in a microwave plasma system, and vacuumizing a reaction chamber to 1.0 x 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 180W, introducing 5sccm 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 sheet-silicon nanowire array.
(4) Treating the graphene sheet-silicon nanowire array by using 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-silicon nanowire 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, adjusting the gas pressure to be 1.5kPa, starting a microwave source after the gas pressure is stable, setting the microwave power to be 120W, and setting the treatment time to be 60 minutes, thereby obtaining the nitrogen-doped graphene sheet-silicon nanowire array.
(5) And (3) carrying out high-temperature annealing treatment on the obtained nitrogen-doped graphene sheet-silicon nanowire array:
and (3) carrying out high-temperature annealing treatment on the nitrogen-doped graphene sheet-silicon nanowire array obtained in the step (4) in a quartz tube furnace, wherein the treatment temperature is 1000 ℃, the used protective gas is 400sccm hydrogen, the pressure in the quartz tube is normal pressure, and the treatment time is 2 hours, so as to finally obtain the annealed nitrogen-doped graphene sheet-silicon nanowire array composite material.
(6) The field emission performance of the obtained material is characterized in that:
the field emission test shows that the opening field of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained in the embodiment is only 2.60V/mum, and the field emission current density reaches 1.0mA/cm2The applied electric field intensity is 2.79V/mu m, and the maximum field emission current density is 10.90mA/cm2Compared with the prior art, the change conditions of the three indexes are respectively as follows: the voltage is reduced by 0.41V/mum and 0.50V/mum, and the field emission performance of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained by the invention is greatly improved compared with the field emission performance of the prior art by 2.74 times (Table 1).
Example 6
(1) Preparing a silicon nanowire array by a metal catalytic corrosion method:
firstly, cutting a silicon single crystal wafer into 2cm multiplied by 2cm small pieces, then sequentially and respectively ultrasonically cleaning (50W) in deionized water and absolute ethyl alcohol for 5 minutes, then immersing the silicon single crystal wafer into hydrofluoric acid with the volume ratio of 4 percent for 5 minutes, and then sequentially placing the obtained silicon single crystal wafer with clean surface into AgNO with the volume ratio3:HF:H2Soaking in solution with O2: 10:38 ratio of H for 1 minute2O2:HF:H2Soaking the silicon nanowire array in a solution with the ratio of O to O being 1:10:39 for 45 minutes to obtain a silicon nanowire array; AgNO used as described above3And the concentrations of the HF acid and the hydrogen peroxide are respectively 0.01, 4 and 0.176 mol/L.
(2) Pretreating the silicon nanowire array by silver ion bombardment:
and (2) performing energy-carrying silver ion bombardment pretreatment on the silicon nanowire array obtained in the step (1) in a metal vapor vacuum arc ion source (MEVVA source), wherein during bombardment, the incident direction of silver ions forms an included angle of about 10 degrees with the axial direction of the silicon nanowires, 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.
(3) Preparing a graphene sheet by a microwave plasma enhanced chemical vapor deposition method:
placing the silicon nanowire array bombarded by the silver ions obtained in the step (2) on a graphite sample table in a microwave plasma system, and vacuumizing a reaction chamber to 1.0 x 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 180W, introducing 5sccm 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 sheet-silicon nanowire array.
(4) Treating the graphene sheet-silicon nanowire array by using 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-silicon nanowire 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, adjusting the gas pressure to be 1.5kPa, starting a microwave source after the gas pressure is stable, setting the microwave power to be 160W, and setting the treatment time to be 20 minutes, thereby obtaining the nitrogen-doped graphene sheet-silicon nanowire array.
(5) And (3) carrying out high-temperature annealing treatment on the obtained nitrogen-doped graphene sheet-silicon nanowire array:
and (3) carrying out high-temperature annealing treatment on the nitrogen-doped graphene sheet-silicon nanowire array obtained in the step (4) in a quartz tube furnace, wherein the treatment temperature is 1000 ℃, the used protective gas is 400sccm hydrogen, the pressure in the quartz tube is normal pressure, and the treatment time is 2 hours, so as to finally obtain the annealed nitrogen-doped graphene sheet-silicon nanowire array composite material.
(6) The field emission performance of the obtained material is characterized in that:
the field emission test shows that the opening field of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained in the embodiment is only 2.58V/mum, and the field emission current density reaches 1.0mA/cm2The applied electric field intensity is 2.77V/mum, and the maximum field emission current density is 11.15mA/cm2Compared with the prior art, the change conditions of the three indexes are respectively as follows: the voltage is reduced by 0.43V/mum and 0.52V/mum, and the field emission performance of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained by the invention is greatly improved compared with the field emission performance of the prior art by 2.80 times (shown in table 1).
Example 7
(1) Preparing a silicon nanowire array by a metal catalytic corrosion method:
firstly, cutting a silicon single crystal wafer into 2cm multiplied by 2cm small pieces, then sequentially and respectively ultrasonically cleaning (50W) in deionized water and absolute ethyl alcohol for 5 minutes, then immersing the silicon single crystal wafer into hydrofluoric acid with the volume ratio of 4 percent for 5 minutes, and then sequentially placing the obtained silicon single crystal wafer with clean surface into AgNO with the volume ratio3:HF:H2Soaking in solution with O2: 10:38 ratio of H for 1 minute2O2:HF:H2Soaking the silicon nanowire array in a solution with the ratio of O to O being 1:10:39 for 45 minutes to obtain a silicon nanowire array; AgNO used as described above3And the concentrations of the HF acid and the hydrogen peroxide are respectively 0.01, 4 and 0.176 mol/L.
(2) Pretreating the silicon nanowire array by silver ion bombardment:
and (2) performing energy-carrying silver ion bombardment pretreatment on the silicon nanowire array obtained in the step (1) in a metal vapor vacuum arc ion source (MEVVA source), wherein during bombardment, the incident direction of silver ions forms an included angle of about 10 degrees with the axial direction of the silicon nanowires, 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.
(3) Preparing a graphene sheet by a microwave plasma enhanced chemical vapor deposition method:
placing the silicon nanowire array bombarded by the silver ions obtained in the step (2) on a graphite sample table in a microwave plasma system, and vacuumizing a reaction chamber to 1.0 x 10-3Introducing 10sccm hydrogen after Pa, adjusting the pressure to 1kPa, and heatingHeating the sample platform by the device until the temperature is stabilized at 800 ℃, starting the microwave source, adjusting the microwave power to 180W, introducing acetylene gas of 5sccm, adjusting the gas pressure to 1kPa again, starting the growth of the graphene sheet, wherein the growth time is 3 hours, and finally obtaining the graphene sheet-silicon nanowire array.
(4) Treating the graphene sheet-silicon nanowire array by using 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-silicon nanowire 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, adjusting the gas pressure to be 1.5kPa, starting a microwave source after the gas pressure is stable, setting the microwave power to be 160W, and setting the treatment time to be 40 minutes, thereby obtaining the nitrogen-doped graphene sheet-silicon nanowire array.
(5) And (3) carrying out high-temperature annealing treatment on the obtained nitrogen-doped graphene sheet-silicon nanowire array:
and (3) carrying out high-temperature annealing treatment on the nitrogen-doped graphene sheet-silicon nanowire array obtained in the step (4) in a quartz tube furnace, wherein the treatment temperature is 1000 ℃, the used protective gas is 400sccm hydrogen, the pressure in the quartz tube is normal pressure, and the treatment time is 2 hours, so as to finally obtain the annealed nitrogen-doped graphene sheet-silicon nanowire array composite material.
(6) The field emission performance of the obtained material is characterized in that:
the field emission test shows that the opening field of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained in the embodiment is only 2.68V/mum, and the field emission current density reaches 1.0mA/cm2The applied electric field intensity is 2.86V/mum, and the maximum field emission current density is 10.35mA/cm2Compared with the prior art, the change conditions of the three indexes are respectively as follows: the voltage is reduced by 0.33V/mum and 0.43V/mum, and the field emission performance of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained by the invention is greatly improved compared with the field emission performance of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained by the prior art (Table 1).
Finally, it is to be understood that the foregoing is only illustrative of the exemplary embodiments of this invention(ii) a The preparation of the nitrogen-doped graphene sheet-silicon nanowire array composite material and the improvement of field emission performance can be realized by adjusting the process parameters of the invention, the average starting field can reach 2.53-2.77V/mum, and the average maximum field emission current density can reach 9.32-11.63mA/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 the prior art and various examples of the present invention, where "Eon"denotes the opening field," E1.0"indicates that the field emission current density reached 1.0mA/cm2The intensity of the applied electric field "J" corresponding to timemax"denotes the maximum field emission current density and" ↓ "denotes a decline.
TABLE 1

Claims (7)

1. A method for improving the field emission performance of a graphene sheet-silicon nanowire array composite material is characterized by comprising the following steps: preparing a silicon nanowire array by using a metal catalytic corrosion method, bombarding the silicon nanowire array by using energy-carrying silver ions in an inclination angle mode, preparing a thin-layer graphene sheet on the silicon nanowire array by using a microwave plasma enhanced chemical vapor deposition method, processing the obtained graphene sheet-silicon nanowire array at normal temperature by using microwave nitrogen and hydrogen plasmas, controlling the appearance of the graphene sheet by adjusting the microwave power to be 120-160W, the air pressure of a processing chamber to be 1.5kPa and the processing time to be 20-60 minutes, annealing the obtained nitrogen-doped graphene sheet-silicon nanowire array for 2 hours, and finally obtaining the nitrogen-doped graphene sheet-silicon nanowire array composite material subjected to high-temperature heat treatment; the nitrogen-doped graphene sheet-silicon nanowire array composite material is prepared from silicon nanowires bombarded by silver ionsThe upper deposition edge layer number is 2-5, and the upper deposition edge layer number is rich in defects, densely distributed and nitrogen-doped graphene sheets; wherein the graphene sheets have a diameter of at most 50-100 nanometers; the average opening field of the prepared nitrogen-doped graphene sheet-silicon nanowire array composite material is only 2.53-2.77V/mum, and the average maximum field emission current density can reach 9.32-11.63mA/cm2Emitting current density up to 9.19mA/cm in average field2The current decay in 20 hours was only 0.76%.
2. The method of claim 1, further comprising a pretreatment process of sequentially subjecting the silicon single crystal wafer to ultrasonic cleaning with 50W power for 5 minutes in each of deionized water and absolute ethanol.
3. The method according to claim 1, further comprising the step of immersing the ultrasonically cleaned silicon single crystal wafer in hydrofluoric acid of 4% by volume for 5 minutes.
4. The method of claim 1, wherein the resulting nitrogen-doped graphene sheet-silicon nanowire array is annealed at 1000 degrees Celsius for 2 hours in a hydrogen atmosphere at atmospheric pressure.
5. The method for improving the field emission performance of the graphene sheet-silicon nanowire array composite material according to claim 1, which is characterized by comprising the following steps:
step (1), preparing a silicon nanowire array by a metal catalytic corrosion method: firstly cutting a silicon single crystal wafer into 2cm multiplied by 2cm small pieces, then 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 percent for 5 minutes, and then successively placing the obtained silicon single crystal wafer with clean surface into AgNO with the volume ratio3:HF:H2Soaking in solution with O2: 10:38 ratio of H for 1 minute2O2:HF:H2Soaking the silicon nanowire array in a solution with the ratio of O to O being 1:10:39 for 45 minutes to obtain a silicon nanowire array; AgNO used as described above3HF acid and hydrogen peroxide concentrations were 0.01, 4 and 0, respectively.176mol/L；
Step (2), pretreating the silicon nanowire array by silver ion bombardment: carrying out energy-carrying silver ion bombardment pretreatment on the silicon nanowire array obtained in the step (1) in a metal vapor vacuum arc ion source (MEVVA source), wherein during bombardment, the incident direction of silver ions forms an included angle of 10 degrees with the axial direction of the silicon nanowires, 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 graphene sheets by a microwave plasma enhanced chemical vapor deposition method: placing the silicon nanowire array bombarded by the silver ions obtained in the step (2) on a graphite sample table in a microwave plasma system, and vacuumizing a reaction chamber to 1.0 x 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 180W, introducing 5sccm acetylene gas, adjusting the pressure to 1kPa again, namely starting the growth of the graphene sheet, wherein the growth time is 3 hours, and finally obtaining the graphene sheet-silicon nanowire array;
step (4), treating the graphene sheet-silicon nanowire array by nitrogen and hydrogen plasmas: on the basis of the step (3), cooling the sample to room temperature in a hydrogen atmosphere of 10sccm, performing nitrogen and hydrogen plasma treatment on the obtained graphene sheet-silicon nanowire 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 120-160W, and the treatment time to be 20-60 minutes, so as to obtain the nitrogen-doped graphene sheet-silicon nanowire array;
and (5) high-temperature annealing: and (3) carrying out high-temperature annealing treatment on the nitrogen-doped graphene sheet-silicon nanowire array obtained in the step (4) in a quartz tube furnace, wherein the treatment temperature is 1000 ℃, the used protective gas is 400sccm hydrogen, the pressure in the quartz tube is normal pressure, and the treatment time is 2 hours.
6. The method of claim 5, wherein the purity of each gas used is 5N.
7. The nitrogen-doped graphene sheet-silicon nanowire array composite material prepared by the method of claim 1, which is characterized by consisting of graphene sheets with 2-5 layers of deposited edge layers, rich defects, dense distribution and nitrogen doping on silicon nanowires bombarded by silver ions; wherein the graphene sheets have a diameter of at most 50-100 nanometers; the opening field of the prepared nitrogen-doped graphene sheet-silicon nanowire array composite material is only 2.53-2.77V/mum on average, the maximum field emission current density can be 9.32-11.63mA/cm2 on average, the average field emission current density is up to 9.19mA/cm2, and the current attenuation in 20 hours is only 0.76%.
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CN103803486A (en) * 2014-01-20 2014-05-21 北京师范大学 Preparation method of superfine silicon nanowire array
CN105336560A (en) * 2014-06-25 2016-02-17 清华大学 Reflecting klystron and electronic emission device
CN104882347A (en) * 2015-04-02 2015-09-02 天津师范大学 Method for preparing field emission cathode of nano carbon sheet-silicon nanowire composite structure
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