CN108987218B - A method to improve the field emission performance of graphene sheet-silicon nanowire array composite material - Google Patents

Abstract

The invention discloses a method for improving the field emission performance of a graphene sheet-silicon nanowire array composite material, which belongs to the field of preparation and application of nanomaterials. The preparation process includes the following: (1) metal-catalyzed corrosion method to prepare silicon nanowire arrays; (2) silicon nanowires to be bombarded with energy-carrying silver ions; (3) microwave plasma enhanced chemical vapor deposition (4) Utilize nitrogen and hydrogen plasma to process the resulting graphene sheet-silicon nanowire array at room temperature; (5) process the obtained nitrogen-doped graphene sheet-silicon nanowire array at high temperature Annealing treatment. Compared with the prior art, the nitrogen-doped graphene sheet-silicon nanowire array composite material prepared by this method has the characteristics of low working electric field, high field emission current density and good stability, and has high application value.

Description

A method for improving the field emission performance of graphene sheet-silicon nanowire array composites method

technical field

The invention belongs to the technical field of preparation and application of nanomaterials, in particular to a method for preparing a nitrogen-doped graphene sheet-silicon nanowire array composite material by plasma treatment and for improving field emission performance.

Background technique

Field emission refers to the process of electrons inside the cathode material escaping from the surface of the material into the vacuum under the action of an externally enhanced electric field. Excellent field emission performance generally requires the cathode to have a low working electric field, a large current density and good stability. sex. As a quasi-one-dimensional nanomaterial, silicon nanowires have the characteristics of high aspect ratio, excellent electrical conductivity, and good contact with the substrate, making them a field emission cathode material with excellent performance. The preparation of vacuum field electronic devices such as field emission flat panel displays has shown good application prospects. However, the field emission performance of pure silicon nanowires is often poor, and its open electric field (the corresponding applied electric field strength when the field emission current density reaches 10μA/ ^cm2 ) is generally higher than 6.0V/μm, and the maximum field emission current density is generally less than 1.0mA/cm ² , which greatly limits its application. Combining silicon nanowires with other low-dimensional nanomaterials is a major breakthrough to improve their field emission performance. Among them, the combination of silicon nanowires with quasi-two-dimensional nanomaterials such as graphene sheets with good field emission stability is the focus of research. This one-dimensional/two-dimensional composite material can have both the large aspect 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/cm ² , the turn-on field is as low as 3.01V/μm, and the applied electric field when the current density reaches 1.0mA/cm ² The intensity can be as low as 3.29V/μm, and it has good field emission stability at low field emission current density. Compared with the original silicon nanowires, these indicators have been greatly improved. However, it is undeniable that the field emission performance of the graphene sheet-silicon nanowire composite is still not good enough. First, its maximum field emission current density is still relatively small, which is subject to many restrictions in the application of high current density; secondly, in large field emission The goal of achieving stable operation of field electronic devices at current densities has not yet been achieved, which puts forward new requirements for improving the performance of field emission cathodes based on graphene sheet-silicon nanowire composites.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the existing graphene sheet-silicon nanowire array-based field emission cathode with relatively high operating electric field, low field emission current density, and poor stability during high current density field emission. The transition layer was introduced by silver ion bombardment to strengthen the bonding force between graphene sheet and silicon nanowire, and nitrogen-doped graphene sheet-silicon with low work function and large number of field emission points was obtained by microwave nitrogen and hydrogen plasma treatment. Nanowire array composite material, and finally obtain a field emission cathode composite material with low working electric field, large field emission current density and good field emission stability under high current density.

The object of the present invention is achieved through the following measures:

Firstly, the silicon nanowire array is prepared by metal-catalyzed corrosion method, and then the energy-carrying silver ions are used to bombard the silicon nanowire array at an angle, and then the thin-layer graphene sheet is prepared on the silicon nanowire array by microwave plasma enhanced chemical vapor deposition. , and use microwave nitrogen and hydrogen plasma to treat the obtained graphene sheet-silicon nanowire array composite material at room temperature, by adjusting the microwave power to 120-160W, the pressure in the treatment chamber to 1.5kPa, and the treatment time to 20-60 minutes. Control the morphology of the graphene sheet, and finally anneal the obtained nitrogen-doped graphene sheet-silicon nanowire array at 1000 degrees Celsius, normal pressure, and hydrogen atmosphere for 2 hours, and finally obtain a high-temperature heat-treated nitrogen-doped graphene sheet- Silicon nanowire array composite material; the nitrogen-doped graphene sheet-silicon nanowire array composite material consists of 2-5 layers of edge layers deposited on silicon nanowires bombarded by silver ions, rich in defects, densely distributed, Composed of nitrogen-doped graphene sheets; the diameter of the graphene sheets is mostly 50-100 nanometers; the average turn-on field of the prepared nitrogen-doped graphene sheet-silicon nanowire array composite material is only 2.53-2.77V/μm , the average maximum field emission current density can reach 9.32-11.63mA/cm ² , the average field emission current density is as high as 9.19mA/cm ² , and the current decay within 20 hours is only 0.76%.

The above technical solution also includes a pretreatment process of ultrasonically cleaning the silicon single wafer in deionized water and absolute ethanol for 5 minutes each with a power of 50 W.

The above technical solution also includes the step of soaking the ultrasonically cleaned silicon single wafer in hydrofluoric acid with a volume ratio of 4% for 5 minutes.

In the above technical solution, the obtained nitrogen-doped graphene sheet-silicon nanowire array is annealed for 2 hours at 1000 degrees Celsius under normal pressure in a hydrogen atmosphere.

In the above technical solution, the specific steps of the method for improving the field emission performance of the graphene sheet-silicon nanowire array composite material are further disclosed as follows:

Step (1) Preparation of silicon nanowire arrays by metal-catalyzed corrosion method: first cut the silicon single wafer into small pieces of 2cm×2cm, and then clean them with ultrasonic (50W) in deionized water and absolute ethanol for 5 minutes respectively, and then the The silicon single wafer is immersed in hydrofluoric acid with a volume ratio of 4% for 5 minutes, and then the obtained silicon single wafer with a clean surface is successively placed in a solution with a volume ratio of AgNO ₃ :HF:H ₂ O=2:10:38 Soak for 1 minute in a solution with a volume ratio of H ₂ O ₂ :HF:H ₂ O=1:10:39 for 45 minutes to obtain a silicon nanowire array; the concentrations of AgNO ₃ , HF acid and hydrogen peroxide used above are respectively 0.01, 4 and 0.176mol/L;

Step (2) silver ion bombardment pretreatment of silicon nanowire array: the silicon nanowire array obtained in step (1) is subjected to energy-carrying silver ion bombardment pretreatment in a metal vapor vacuum arc ion source (MEVVA source), during bombardment, The angle between the incident direction of silver ions and the axial direction of silicon nanowires is about 10 degrees, and the sample stage is kept rotating at a constant speed. The bias voltage of the sample stage is set to -15kV, the beam current is 10 mA, and the bombardment time is 10 minutes;

Step (3) Preparation of graphene sheet by microwave plasma enhanced chemical vapor deposition method: place the silicon nanowire array bombarded by silver ions obtained in step (2) on the graphite sample stage in the microwave plasma system, and vacuum the reaction chamber After pumping to 1.0×10 ^-3 Pa, inject 10 sccm of hydrogen, adjust the pressure to 1 kPa, heat the sample stage with a self-made graphite heater until the temperature is stable at 800 degrees Celsius, start the microwave source, adjust the microwave power to 180W, and inject 5 sccm Acetylene gas, adjust the air pressure again to 1kPa, that is, start the growth of graphene sheets, the growth time is 3 hours, and the final result is graphene sheets-silicon nanowire arrays;

Step (4) Nitrogen and hydrogen plasma treatment of graphene sheet-silicon nanowire array: on the basis of step (3), cool the sample to room temperature in a 10sccm hydrogen atmosphere, and perform nitrogen treatment on the obtained graphene sheet-silicon nanowire array. , hydrogen plasma treatment, the gas that is used to produce plasma is the mixed gas that is made up of nitrogen and hydrogen, and the flow rate of nitrogen, hydrogen is respectively 5, 10sccm, and the adjustment air pressure is 1.5kPa, and after the air pressure stabilizes, start the microwave source, adjust The microwave power is 120-160W, and the processing time is 20-60 minutes, and the nitrogen-doped graphene sheet-silicon nanowire array is obtained;

Step (5) high-temperature annealing: the nitrogen-doped graphene sheet-silicon nanowire array obtained in step (4) is subjected to high-temperature annealing treatment in a quartz tube furnace, the treatment temperature is 1000 degrees Celsius, and the protective gas used is 400 sccm hydrogen, and the quartz tube The medium pressure is normal pressure, and the treatment time is 2 hours.

In the above-mentioned technical scheme, the purity of various gases used is 5N.

The nitrogen-doped graphene sheet-silicon nanowire array composite material prepared according to the above-mentioned technical scheme; The number is 2-5 layers, rich in defects, densely distributed, and nitrogen-doped graphene sheets; the diameter of the graphene sheets is mostly 50-100 nanometers; the prepared nitrogen-doped graphene sheets-silicon nanowire array composite The average open field of the material is only 2.53-2.77V/μm, the average maximum field emission current density can reach 9.32-11.63mA/cm ² , and the current decay within ²⁰ hours is only There is 0.76%.

Compared with the prior art, the method disclosed by the present invention to form a transition layer by bombardment of silver ions and treat with nitrogen and hydrogen plasma at normal temperature for improving the field emission performance of graphene sheets-silicon nanowire array composites is that: (1 ) before the growth of graphene sheets, the energy-carrying silver ions are used to implant silicon nanowire arrays to form a silver-silicon transition layer on the surface of silicon nanowires. On the one hand, this transition layer can promote electron transmission. During the treatment, the root of the graphene sheet can be effectively coated at the contact part of the graphene sheet and the silicon nanowire through the precipitation of silver, and the bonding force between the graphene sheet and the silicon nanowire can be improved, thereby increasing the maximum field emission current of the material Density; (2) By irradiating the graphene sheet-silicon nanowire array with nitrogen and hydrogen plasma, the graphene sheet can be doped with nitrogen first, thereby reducing its work function and making the electrons in the graphene sheet It is easier to tunnel through the potential barrier and escape into the vacuum, that is, the field electron emission capability of the graphene sheet is enhanced, and secondly, a large number of defects can be introduced into the graphene sheet, and these defects can become high-efficiency field emission during the field emission process. The reason why the present invention adopts normal temperature plasma treatment instead of high temperature treatment is also to better preserve these defects. In a word, the further enhancement of the combination of graphene sheets and silicon nanowires, the reduction of work function and the increase of the number of field emission points are the key to the excellent field emission performance of nitrogen-doped graphene sheet-silicon nanowire arrays, and it is also the key of the present invention. The superiority lies. The introduction of silver ion bombardment and nitrogen doping makes the nitrogen-doped graphene sheet-silicon nanowire array composite material of the present invention have low turn-on field (2.53V/μm), high field emission current density (11.63mA/cm ² ) and excellent high current density field emission stability (the average field emission current density is as high as 9.19mA/cm ² , and the current decay within 20 hours is only 0.76%). Compared with the existing technology, these indicators have a large improvement.

Description of drawings

Fig. 1 is the schematic flow chart of the method for preparing nitrogen-doped graphene sheet-silicon nanowire array composite material by silver ion bombardment and nitrogen and hydrogen plasma treatment;

Fig. 2 is the structural representation of the microwave plasma enhanced chemical vapor deposition system used in the present invention;

Fig. 3 is the scanning electron microscope and the high-resolution transmission electron microscope pictures of the nitrogen-doped graphene sheet-silicon nanowire array obtained through silver ion bombardment in embodiment 1, including:

Figure 3a is a side view of the scanning electron microscope of the nitrogen-doped graphene sheet-silicon nanowire array;

Figure 3b is a high-resolution transmission electron microscope image of graphene sheets in a nitrogen-doped graphene sheet-silicon nanowire array;

Fig. 4 is the structural representation of diode type high vacuum field emission tester used in the present invention;

Fig. 5 shows the field emission properties of the prior art, the obtained graphene sheet-silicon nanowire array after silver ion bombardment treatment, and the nitrogen-doped silicon nanowire array obtained after silver ion bombardment, nitrogen, and hydrogen plasma treatment in Example 1 and Example 2. Field emission performance map of heterographene sheet-silicon nanowire array composite;

Fig. 6 is the field emission stability diagram of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained after silver ion bombardment in Example 1 within 20 hours, wherein "E" and "J _mean "represent the external constant Electric field strength and average field emission current density;

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments, but the present invention is not limited to these embodiments. The silicon single wafer, absolute ethanol, hydrofluoric acid, hydrogen peroxide, silver nitrate, high-purity hydrogen, high-purity nitrogen, high-purity acetylene, and high-purity silver targets used are all commercially available. Ultrasonic cleaning, metal vapor vacuum arc ion source (MEVVA source), high temperature tube furnace, microwave plasma system, diode type high vacuum field emission tester and other devices are commercially available. The metal catalyzed corrosion method used in the preparation of silicon nanowire arrays, the plasma enhanced chemical vapor deposition method used in the preparation of graphene sheets, the MEVVA source silver ion bombardment method and the method of field emission performance testing of the obtained materials are all 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 used as the cathode, and the cathode is grounded, and the parallel and facing stainless steel plate with a diameter of 10 cm is used as the anode, and the distance between the cathode and the anode is 1 mm, the cathode material emits electrons by loading the anode with an adjustable positive bias voltage of 0-10kV.

In the specific implementation, "a preparation method of field emission cathode with nanocarbon sheet-silicon nanowire composite structure" (Chinese patent, patent number ZL201510152591.9) is used as the prior art for comparison, and its maximum field emission current density can reach 3.98mA/cm ² , the open field is as low as 3.01V/μm, the applied electric field strength can be as low as 3.29V/μm when the current density reaches 1.0mA/cm ² , and when the average field emission current density is 1.34mA/cm ² It shows good field emission stability.

Fig. 1 is a schematic flow chart of the preparation of nitrogen-doped graphene sheet-silicon nanowire array composite material in the present invention, mainly divided into metal-catalyzed corrosion method to prepare silicon nanowire array, silver ion bombardment of silicon nanowire array, microwave plasma enhanced chemical Preparation of thin-layer graphene sheets by vapor deposition method, microwave nitrogen, hydrogen plasma treatment of graphene sheets-silicon nanowire arrays, and high-temperature annealing. Materials were prepared according to this procedure.

Example 1

(1) Preparation of silicon nanowire arrays by metal-catalyzed corrosion method:

First cut the silicon single wafer into small pieces of 2cm×2cm, then ultrasonically (50W) clean them in deionized water and absolute ethanol for 5 minutes, and then immerse the silicon single wafer in 4% hydrofluoric acid by volume 5 minutes, and then put the obtained silicon single wafers with a clean surface into the solution with the volume ratio of AgNO ₃ :HF:H ₂ O=2:10:38 and soak for 1 minute, and the volume ratio is H ₂ O ₂ :HF :H ₂ O=1:10:39 solution for 45 minutes to obtain the silicon nanowire array; the concentration of AgNO ₃ , HF acid and hydrogen peroxide used above are 0.01, 4 and 0.176 mol/L respectively.

(2) Silver ion bombardment pretreatment silicon nanowire array:

The silicon nanowire array obtained in step (1) is subjected to energy-carrying silver ion bombardment pretreatment in a metal vapor vacuum arc ion source (MEVVA source). During the bombardment, the incident direction of the silver ion is about 10 degrees from the axial direction of the silicon nanowire The included angle is , and the sample stage is kept rotating at a constant speed. The bias voltage of the sample stage is set to -15kV, the beam current is 10 mA, and the bombardment time is 10 minutes.

(3) Preparation of graphene sheet by microwave plasma enhanced chemical vapor deposition method:

Place the silicon nanowire array bombarded by silver ions obtained in step (2) on the graphite sample stage in the microwave plasma system (Fig. 2 is a schematic structural diagram of the device), and vacuumize the reaction chamber to 1.0×10 ^-3 Pass into 10sccm hydrogen after Pa, adjust the air pressure to 1kPa, heat the sample stage with a heater until the temperature is stable at 800 degrees Celsius, start the microwave source, adjust the microwave power to 180W, and feed 5 sccm of acetylene gas, adjust the air pressure to 1kPa again, That is, the growth of the graphene sheet starts, and the growth time is 3 hours, and the final result is a graphene sheet-silicon nanowire array.

(4) Nitrogen and hydrogen plasma treatment of graphene sheets-silicon nanowire arrays:

On the basis of step (3), the sample is cooled to room temperature in a 10 sccm hydrogen atmosphere, and the obtained graphene sheet-silicon nanowire array is subjected to nitrogen and hydrogen plasma treatment, and the gas used to generate the plasma is composed of nitrogen and hydrogen The flow rates of nitrogen and hydrogen were 5 and 10 sccm respectively, and the air pressure was adjusted to 1.5 kPa. After the air pressure was stabilized, the microwave source was started, and the microwave power was set to 140W, and the processing time was 40 minutes. X-ray photoelectron spectroscopy analysis shows that a certain amount of nitrogen atoms are doped in the graphene sheet-silicon nanowire array composite material, that is, a nitrogen-doped graphene sheet-silicon nanowire array is obtained.

(5) Nitrogen-doped graphene sheet-silicon nanowire array obtained by high temperature annealing treatment:

The nitrogen-doped graphene sheet-silicon nanowire array obtained in step (4) is subjected to high-temperature annealing treatment in a quartz tube furnace, the treatment temperature is 1000 degrees Celsius, the protective gas used is 400 sccm hydrogen, and the pressure in the quartz tube is normal pressure. The time is 2 hours, and the annealed nitrogen-doped graphene sheet-silicon nanowire array composite material is finally obtained, and the side view of the scanning electron microscope is shown in Figure 3a. Figure 3b shows the high-resolution transmission electron microscope image of the nitrogen-doped graphene sheet-silicon nanowire array, which shows the structure of the edge and surface of the graphene sheet. It can be seen that the graphene edge has only 2 layers and the surface has These structural features can promote the field electron emission of materials. It should be emphasized that the number of layers of graphene sheets obtained in the present invention is mostly 2-5 layers.

(6) Field emission performance characterization of the gained material:

The obtained nitrogen-doped graphene sheet-silicon nanowire array composite material was used as a cathode, and the field emission performance of the material was tested with a diode-type high vacuum field emission tester shown in FIG. 4 . Figure 5 shows the field emission performance of the obtained graphene sheet-silicon nanowire array after silver ion bombardment treatment and the nitrogen-doped graphene sheet-silicon nanowire array obtained after silver ion bombardment, nitrogen, and hydrogen plasma treatment in this embodiment. The field emission performance diagram of the nanowire array composite material represents the change relationship of the field emission current density of the cathode material with the increase of the applied electric field intensity. The corresponding test results are shown in Table 1. It can be seen that after the introduction of silver ion bombardment treatment, the open field of the graphene sheet-silicon nanowire array is 3.08V/μm, and the applied electric field strength when the field emission current density reaches 1.0mA/ ^cm2 is 3.25V/μm, The maximum field emission current density is 7.93mA/cm ² . Compared with the existing technology (the corresponding values are: 3.01V/μm, 3.29V/μm, 3.98mA/cm ² ), although the change of the working electric field is small, the maximum The field emission current density is 1.99 times that of the prior art, indicating that the silver ion bombardment treatment greatly improves the binding force between the graphene sheet and the silicon nanowire, thereby increasing the maximum field emission current density. In addition, after the introduction of silver ion bombardment and nitrogen and hydrogen plasma, the turn-on field of the obtained nitrogen-doped graphene sheet-silicon nanowire is only 2.53V/μm, and the field emission current density reaches 1.0mA/cm ² . The electric field intensity is only 2.71V/μm, and the maximum field emission current density is as high as 11.63mA/cm ² . Compared with the existing technology, the changes of these three indicators are: 0.48V/μm, 0.58V/ μm, 2.92 times that of the prior art (Table 1), indicating that the field emission performance of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained in the present invention is greatly improved compared with the prior art. FIG. 6 shows the relationship of the field emission current density with time after the nitrogen-doped graphene sheet-silicon nanowire array obtained in this embodiment is subjected to an aging treatment for 1 hour under a constant electric field. It can be seen that the applied constant electric field strength is only 2.88V/μm, and the average field emission current density is as high as 9.19mA/cm ² (far better than 1.34mA/cm ² in the prior art, and the corresponding applied constant electric field strength is 3.45V/μm), the attenuation of the field emission current density within 20 hours is only 0.76%, showing an excellent application prospect.

Example 2

(1) Preparation of silicon nanowire arrays by metal-catalyzed corrosion method:

First cut the silicon single wafer into small pieces of 2cm×2cm, then ultrasonically (50W) clean them in deionized water and absolute ethanol for 5 minutes, and then immerse the silicon single wafer in 4% hydrofluoric acid by volume 5 minutes, and then put the obtained silicon single wafers with a clean surface into the solution with the volume ratio of AgNO ₃ :HF:H ₂ O=2:10:38 and soak for 1 minute, and the volume ratio is H ₂ O ₂ :HF :H ₂ O=1:10:39 solution for 45 minutes to obtain the silicon nanowire array; the concentration of AgNO ₃ , HF acid and hydrogen peroxide used above are 0.01, 4 and 0.176 mol/L respectively.

(2) Silver ion bombardment pretreatment silicon nanowire array:

The silicon nanowire array obtained in step (1) is subjected to energy-carrying silver ion bombardment pretreatment in a metal vapor vacuum arc ion source (MEVVA source). During the bombardment, the incident direction of the silver ion is about 10 degrees from the axial direction of the silicon nanowire The included angle is , and the sample stage is kept rotating at a constant speed. The bias voltage of the sample stage is set to -15kV, the beam current is 10 mA, and the bombardment time is 10 minutes.

(3) Preparation of graphene sheet by microwave plasma enhanced chemical vapor deposition method:

Place the silicon nanowire array bombarded by silver ions obtained in step (2) on the graphite sample stage in the microwave plasma system, vacuumize the reaction chamber to 1.0 × 10 ^-3 Pa, and then feed 10 sccm of hydrogen gas to adjust the pressure. 1kPa, heat the sample stage with a heater until the temperature is stable at 800 degrees Celsius, start the microwave source, adjust the microwave power to 180W, and feed 5 sccm of acetylene gas, and adjust the air pressure to 1kPa again to start the growth of graphene sheets. 3 hours, and the final result is a graphene sheet-silicon nanowire array.

(4) Nitrogen and hydrogen plasma treatment of graphene sheets-silicon nanowire arrays:

On the basis of step (3), the sample is cooled to room temperature in a 10 sccm hydrogen atmosphere, and the obtained graphene sheet-silicon nanowire array is subjected to nitrogen and hydrogen plasma treatment, and the gas used to generate the plasma is composed of nitrogen and hydrogen The flow rate of nitrogen and hydrogen is 5 and 10 sccm respectively, and the air pressure is adjusted to 1.5kPa. After the air pressure is stabilized, start the microwave source, set the microwave power to 140W, and the processing time to 60 minutes, and the nitrogen-doped graphite is obtained. Alkene sheets - arrays of silicon nanowires.

(5) Nitrogen-doped graphene sheet-silicon nanowire array obtained by high temperature annealing treatment:

The nitrogen-doped graphene sheet-silicon nanowire array obtained in step (4) is subjected to high-temperature annealing treatment in a quartz tube furnace, the treatment temperature is 1000 degrees Celsius, the protective gas used is 400 sccm hydrogen, and the pressure in the quartz tube is normal pressure. The time is 2 hours, and the annealed nitrogen-doped graphene sheet-silicon nanowire array composite material is finally obtained.

(6) Field emission performance characterization of the gained material:

The field emission test shows (Fig. 5), the open field of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained in this embodiment is only ^2.57V /μm, and the applied electric field when the field emission current density reaches 1.0mA/cm The intensity is 2.75V/μm, and the maximum field emission current density is 10.44mA/cm ² . Compared with the existing technology, the changes of these three indicators are: 0.44V/μm, 0.54V/μm, 2.62 times that of the prior art (Table 1), indicating that the field emission performance of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained in the present invention is greatly improved compared with the prior art.

Example 3

(1) Preparation of silicon nanowire arrays by metal-catalyzed corrosion method:

First cut the silicon single wafer into small pieces of 2cm×2cm, then ultrasonically (50W) clean them in deionized water and absolute ethanol for 5 minutes, and then immerse the silicon single wafer in 4% hydrofluoric acid by volume 5 minutes, and then put the obtained silicon single wafers with a clean surface into the solution with the volume ratio of AgNO ₃ :HF:H ₂ O=2:10:38 and soak for 1 minute, and the volume ratio is H ₂ O ₂ :HF :H ₂ O=1:10:39 solution for 45 minutes to obtain the silicon nanowire array; the concentration of AgNO ₃ , HF acid and hydrogen peroxide used above are 0.01, 4 and 0.176 mol/L respectively.

(2) Silver ion bombardment pretreatment silicon nanowire array:

The silicon nanowire array obtained in step (1) is subjected to energy-carrying silver ion bombardment pretreatment in a metal vapor vacuum arc ion source (MEVVA source). During the bombardment, the incident direction of the silver ion is about 10 degrees from the axial direction of the silicon nanowire The included angle is , and the sample stage is kept rotating at a constant speed. The bias voltage of the sample stage is set to -15kV, the beam current is 10 mA, and the bombardment time is 10 minutes.

(3) Preparation of graphene sheet by microwave plasma enhanced chemical vapor deposition method:

Place the silicon nanowire array bombarded by silver ions obtained in step (2) on the graphite sample stage in the microwave plasma system, vacuumize the reaction chamber to 1.0 × 10 ^-3 Pa, and then feed 10 sccm of hydrogen gas to adjust the pressure. 1kPa, heat the sample stage with a heater until the temperature is stable at 800 degrees Celsius, start the microwave source, adjust the microwave power to 180W, and feed 5 sccm of acetylene gas, and adjust the air pressure to 1kPa again to start the growth of graphene sheets. 3 hours, and the final result is a graphene sheet-silicon nanowire array.

(4) Nitrogen and hydrogen plasma treatment of graphene sheets-silicon nanowire arrays:

On the basis of step (3), the sample is cooled to room temperature in a 10 sccm hydrogen atmosphere, and the obtained graphene sheet-silicon nanowire array is subjected to nitrogen and hydrogen plasma treatment, and the gas used to generate the plasma is composed of nitrogen and hydrogen The flow rate of nitrogen and hydrogen is 5 and 10 sccm respectively, and the air pressure is adjusted to 1.5kPa. After the air pressure is stabilized, start the microwave source, set the microwave power to 140W, and the processing time to 20 minutes, and the nitrogen-doped graphite is obtained. Alkene sheets - arrays of silicon nanowires.

(5) Nitrogen-doped graphene sheet-silicon nanowire array obtained by high temperature annealing treatment:

The nitrogen-doped graphene sheet-silicon nanowire array obtained in step (4) is subjected to high-temperature annealing treatment in a quartz tube furnace, the treatment temperature is 1000 degrees Celsius, the protective gas used is 400 sccm hydrogen, and the pressure in the quartz tube is normal pressure. The time is 2 hours, and the annealed nitrogen-doped graphene sheet-silicon nanowire array composite material is finally obtained.

(6) Field emission performance characterization of the gained material:

The field emission test shows that the opening field of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained in this embodiment is only 2.77V/μm, and the applied electric field strength when the field emission current density reaches 1.0mA/cm is ^2.96V /μm, the maximum field emission current density is 9.32mA/cm ² , compared with the existing technology, the changes of these three indicators are: 0.24V/μm, 0.33V/μm, and the existing technology 2.34 times (table 1), illustrate that the field emission performance of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained by the present invention is greatly improved compared with the prior art.

Example 4

(1) Preparation of silicon nanowire arrays by metal-catalyzed corrosion method:

First cut the silicon single wafer into small pieces of 2cm×2cm, then ultrasonically (50W) clean them in deionized water and absolute ethanol for 5 minutes, and then immerse the silicon single wafer in 4% hydrofluoric acid by volume 5 minutes, and then put the obtained silicon single wafers with a clean surface into the solution with the volume ratio of AgNO ₃ :HF:H ₂ O=2:10:38 and soak for 1 minute, and the volume ratio is H ₂ O ₂ :HF :H ₂ O=1:10:39 solution for 45 minutes to obtain the silicon nanowire array; the concentration of AgNO ₃ , HF acid and hydrogen peroxide used above are 0.01, 4 and 0.176 mol/L respectively.

(2) Silver ion bombardment pretreatment silicon nanowire array:

The silicon nanowire array obtained in step (1) is subjected to energy-carrying silver ion bombardment pretreatment in a metal vapor vacuum arc ion source (MEVVA source). During the bombardment, the incident direction of the silver ion is about 10 degrees from the axial direction of the silicon nanowire The included angle is , and the sample stage is kept rotating at a constant speed. The bias voltage of the sample stage is set to -15kV, the beam current is 10 mA, and the bombardment time is 10 minutes.

(3) Preparation of graphene sheet by microwave plasma enhanced chemical vapor deposition method:

Place the silicon nanowire array bombarded by silver ions obtained in step (2) on the graphite sample stage in the microwave plasma system, vacuumize the reaction chamber to 1.0 × 10 ^-3 Pa, and then feed 10 sccm of hydrogen gas to adjust the pressure. 1kPa, heat the sample stage with a heater until the temperature is stable at 800 degrees Celsius, start the microwave source, adjust the microwave power to 180W, and feed 5 sccm of acetylene gas, and adjust the air pressure to 1kPa again to start the growth of graphene sheets. 3 hours, and the final result is a graphene sheet-silicon nanowire array.

(4) Nitrogen and hydrogen plasma treatment of graphene sheets-silicon nanowire arrays:

On the basis of step (3), the sample is cooled to room temperature in a 10 sccm hydrogen atmosphere, and the obtained graphene sheet-silicon nanowire array is subjected to nitrogen and hydrogen plasma treatment, and the gas used to generate the plasma is composed of nitrogen and hydrogen The flow rates of nitrogen and hydrogen are 5 and 10 sccm respectively, and the air pressure is adjusted to 1.5kPa. After the air pressure is stabilized, start the microwave source, set the microwave power to 120W, and the processing time to 40 minutes, and the nitrogen-doped graphite is obtained. Alkene sheets - arrays of silicon nanowires.

(5) Nitrogen-doped graphene sheet-silicon nanowire array obtained by high temperature annealing treatment:

The nitrogen-doped graphene sheet-silicon nanowire array obtained in step (4) is subjected to high-temperature annealing treatment in a quartz tube furnace, the treatment temperature is 1000 degrees Celsius, the protective gas used is 400 sccm hydrogen, and the pressure in the quartz tube is normal pressure. The time is 2 hours, and the annealed nitrogen-doped graphene sheet-silicon nanowire array composite material is finally obtained.

(6) Field emission performance characterization of the gained material:

The field emission test shows that the opening field of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained in this embodiment is only 2.67V/μm, and the applied electric field strength when the field emission current density reaches 1.0mA/cm is ^2.86V /μm, the maximum field emission current density is 10.05mA/cm ² , compared with the existing technology, the changes of these three indicators are: reduced by 0.34V/μm, reduced by 0.43V/μm, the existing technology 2.53 times (table 1), illustrate that the field emission performance of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained by the present invention is greatly improved compared with the prior art.

Example 5

(1) Preparation of silicon nanowire arrays by metal-catalyzed corrosion method:

First cut the silicon single wafer into small pieces of 2cm×2cm, then ultrasonically (50W) clean them in deionized water and absolute ethanol for 5 minutes, and then immerse the silicon single wafer in 4% hydrofluoric acid by volume 5 minutes, and then put the obtained silicon single wafers with a clean surface into the solution with the volume ratio of AgNO ₃ :HF:H ₂ O=2:10:38 and soak for 1 minute, and the volume ratio is H ₂ O ₂ :HF :H ₂ O=1:10:39 solution for 45 minutes to obtain the silicon nanowire array; the concentration of AgNO ₃ , HF acid and hydrogen peroxide used above are 0.01, 4 and 0.176 mol/L respectively.

(2) Silver ion bombardment pretreatment silicon nanowire array:

The silicon nanowire array obtained in step (1) is subjected to energy-carrying silver ion bombardment pretreatment in a metal vapor vacuum arc ion source (MEVVA source). During the bombardment, the incident direction of the silver ion is about 10 degrees from the axial direction of the silicon nanowire The included angle is , and the sample stage is kept rotating at a constant speed. The bias voltage of the sample stage is set to -15kV, the beam current is 10 mA, and the bombardment time is 10 minutes.

(3) Preparation of graphene sheet by microwave plasma enhanced chemical vapor deposition method:

Place the silicon nanowire array bombarded by silver ions obtained in step (2) on the graphite sample stage in the microwave plasma system, vacuumize the reaction chamber to 1.0 × 10 ^-3 Pa, and then feed 10 sccm of hydrogen gas to adjust the pressure. 1kPa, heat the sample stage with a heater until the temperature is stable at 800 degrees Celsius, start the microwave source, adjust the microwave power to 180W, and feed 5 sccm of acetylene gas, and adjust the air pressure to 1kPa again to start the growth of graphene sheets. 3 hours, and the final result is a graphene sheet-silicon nanowire array.

(4) Nitrogen and hydrogen plasma treatment of graphene sheets-silicon nanowire arrays:

On the basis of step (3), the sample is cooled to room temperature in a 10 sccm hydrogen atmosphere, and the obtained graphene sheet-silicon nanowire array is subjected to nitrogen and hydrogen plasma treatment, and the gas used to generate the plasma is composed of nitrogen and hydrogen The flow rate of nitrogen and hydrogen is 5 and 10 sccm respectively, and the air pressure is adjusted to 1.5kPa. After the air pressure is stabilized, start the microwave source, set the microwave power to 120W, and the processing time to 60 minutes, and the nitrogen-doped graphite is obtained. Alkene sheets - arrays of silicon nanowires.

(5) Nitrogen-doped graphene sheet-silicon nanowire array obtained by high temperature annealing treatment:

The nitrogen-doped graphene sheet-silicon nanowire array obtained in step (4) is subjected to high-temperature annealing treatment in a quartz tube furnace, the treatment temperature is 1000 degrees Celsius, the protective gas used is 400 sccm hydrogen, and the pressure in the quartz tube is normal pressure. The time is 2 hours, and the annealed nitrogen-doped graphene sheet-silicon nanowire array composite material is finally obtained.

(6) Field emission performance characterization of the gained material:

The field emission test shows that the opening field of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained in this embodiment is only 2.60V/μm, and the applied electric field strength when the field emission current density reaches 1.0mA/cm is ^2.79V /μm, the maximum field emission current density is 10.90mA/cm ² , compared with the existing technology, the changes of these three indicators are: 0.41V/μm, 0.50V/μm, and the existing technology 2.74 times (table 1), illustrate that the field emission performance of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained by the present invention is greatly improved compared with the prior art.

Example 6

(1) Preparation of silicon nanowire arrays by metal-catalyzed corrosion method:

First cut the silicon single wafer into small pieces of 2cm×2cm, then ultrasonically (50W) clean them in deionized water and absolute ethanol for 5 minutes, and then immerse the silicon single wafer in 4% hydrofluoric acid by volume 5 minutes, and then put the obtained silicon single wafers with a clean surface into the solution with the volume ratio of AgNO ₃ :HF:H ₂ O=2:10:38 and soak for 1 minute, and the volume ratio is H ₂ O ₂ :HF :H ₂ O=1:10:39 solution for 45 minutes to obtain the silicon nanowire array; the concentration of AgNO ₃ , HF acid and hydrogen peroxide used above are 0.01, 4 and 0.176 mol/L respectively.

(2) Silver ion bombardment pretreatment silicon nanowire array:

The silicon nanowire array obtained in step (1) is subjected to energy-carrying silver ion bombardment pretreatment in a metal vapor vacuum arc ion source (MEVVA source). During the bombardment, the incident direction of the silver ion is about 10 degrees from the axial direction of the silicon nanowire The included angle is , and the sample stage is kept rotating at a constant speed. The bias voltage of the sample stage is set to -15kV, the beam current is 10 mA, and the bombardment time is 10 minutes.

(3) Preparation of graphene sheet by microwave plasma enhanced chemical vapor deposition method:

Place the silicon nanowire array bombarded by silver ions obtained in step (2) on the graphite sample stage in the microwave plasma system, vacuumize the reaction chamber to 1.0 × 10 ^-3 Pa, and then feed 10 sccm of hydrogen gas to adjust the pressure. 1kPa, heat the sample stage with a heater until the temperature is stable at 800 degrees Celsius, start the microwave source, adjust the microwave power to 180W, and feed 5 sccm of acetylene gas, and adjust the air pressure to 1kPa again to start the growth of graphene sheets. 3 hours, and the final result is a graphene sheet-silicon nanowire array.

(4) Nitrogen and hydrogen plasma treatment of graphene sheets-silicon nanowire arrays:

On the basis of step (3), the sample is cooled to room temperature in a 10 sccm hydrogen atmosphere, and the obtained graphene sheet-silicon nanowire array is subjected to nitrogen and hydrogen plasma treatment, and the gas used to generate the plasma is composed of nitrogen and hydrogen The flow rates of nitrogen and hydrogen are 5 and 10 sccm respectively, and the air pressure is adjusted to 1.5kPa. After the air pressure is stabilized, start the microwave source, set the microwave power to 160W, and the processing time to 20 minutes, and the nitrogen-doped graphite is obtained. Alkene sheets - arrays of silicon nanowires.

(5) Nitrogen-doped graphene sheet-silicon nanowire array obtained by high temperature annealing treatment:

The nitrogen-doped graphene sheet-silicon nanowire array obtained in step (4) is subjected to high-temperature annealing treatment in a quartz tube furnace, the treatment temperature is 1000 degrees Celsius, the protective gas used is 400 sccm hydrogen, and the pressure in the quartz tube is normal pressure. The time is 2 hours, and the annealed nitrogen-doped graphene sheet-silicon nanowire array composite material is finally obtained.

(6) Field emission performance characterization of the gained material:

The field emission test shows that the opening field of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained in this embodiment is only 2.58V/μm, and the applied electric field strength when the field emission current density reaches 1.0mA/cm is ^2.77V /μm, the maximum field emission current density is 11.15mA/cm ² , compared with the existing technology, the changes of these three indicators are: 0.43V/μm, 0.52V/μm, and the existing technology 2.80 times (Table 1), it shows that the field emission performance of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained in the present invention is greatly improved compared with the prior art.

Example 7

(1) Preparation of silicon nanowire arrays by metal-catalyzed corrosion method:

First cut the silicon single wafer into small pieces of 2cm×2cm, then ultrasonically (50W) clean them in deionized water and absolute ethanol for 5 minutes, and then immerse the silicon single wafer in 4% hydrofluoric acid by volume 5 minutes, and then put the obtained silicon single wafers with a clean surface into the solution with the volume ratio of AgNO ₃ :HF:H ₂ O=2:10:38 and soak for 1 minute, and the volume ratio is H ₂ O ₂ :HF :H ₂ O=1:10:39 solution for 45 minutes to obtain the silicon nanowire array; the concentration of AgNO ₃ , HF acid and hydrogen peroxide used above are 0.01, 4 and 0.176 mol/L respectively.

(2) Silver ion bombardment pretreatment silicon nanowire array:

The silicon nanowire array obtained in step (1) is subjected to energy-carrying silver ion bombardment pretreatment in a metal vapor vacuum arc ion source (MEVVA source). During the bombardment, the incident direction of the silver ion is about 10 degrees from the axial direction of the silicon nanowire The included angle is , and the sample stage is kept rotating at a constant speed. The bias voltage of the sample stage is set to -15kV, the beam current is 10 mA, and the bombardment time is 10 minutes.

(3) Preparation of graphene sheet by microwave plasma enhanced chemical vapor deposition method:

Place the silicon nanowire array bombarded by silver ions obtained in step (2) on the graphite sample stage in the microwave plasma system, vacuumize the reaction chamber to 1.0 × 10 ^-3 Pa, and then feed 10 sccm of hydrogen gas to adjust the pressure. 1kPa, heat the sample stage with a heater until the temperature is stable at 800 degrees Celsius, start the microwave source, adjust the microwave power to 180W, and feed 5 sccm of acetylene gas, and adjust the air pressure to 1kPa again to start the growth of graphene sheets. 3 hours, and the final result is a graphene sheet-silicon nanowire array.

(4) Nitrogen and hydrogen plasma treatment of graphene sheets-silicon nanowire arrays:

On the basis of step (3), the sample is cooled to room temperature in a 10 sccm hydrogen atmosphere, and the obtained graphene sheet-silicon nanowire array is subjected to nitrogen and hydrogen plasma treatment, and the gas used to generate the plasma is composed of nitrogen and hydrogen The flow rates of nitrogen and hydrogen are 5 and 10 sccm respectively, and the air pressure is adjusted to 1.5kPa. After the air pressure is stabilized, start the microwave source, set the microwave power to 160W, and the processing time to 40 minutes, and the nitrogen-doped graphite is obtained. Alkene sheets - arrays of silicon nanowires.

(5) Nitrogen-doped graphene sheet-silicon nanowire array obtained by high temperature annealing treatment:

The nitrogen-doped graphene sheet-silicon nanowire array obtained in step (4) is subjected to high-temperature annealing treatment in a quartz tube furnace, the treatment temperature is 1000 degrees Celsius, the protective gas used is 400 sccm hydrogen, and the pressure in the quartz tube is normal pressure. The time is 2 hours, and the annealed nitrogen-doped graphene sheet-silicon nanowire array composite material is finally obtained.

(6) Field emission performance characterization of the gained material:

The field emission test shows that the opening field of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained in this embodiment is only 2.68V/μm, and the applied electric field strength when the field emission current density reaches 1.0mA/cm is ^2.86V /μm, the maximum field emission current density is 10.35mA/cm ² , compared with the existing technology, the changes of these three indicators are: reduced by 0.33V/μm, reduced by 0.43V/μm, the existing technology 2.60 times (Table 1), it shows that the field emission performance of the nitrogen-doped graphene sheet-silicon nanowire array composite material obtained in the present invention is greatly improved compared with the prior art.

Finally, it should be noted that the above only lists typical embodiments of the present invention; by adjusting the process parameters of the present invention, the preparation of nitrogen-doped graphene sheet-silicon nanowire array composite material and the improvement of field emission performance can be realized, and the field The average can reach 2.53-2.77V/μm, and the average maximum field emission current density can reach 9.32-11.63mA/cm ² , which can realize stable field electron emission under high field emission current density. But obviously the present invention is not limited to above-mentioned embodiment, also has many other experimental parameter combination methods, the related situation that those of ordinary skill in this research field can directly derive or associate from the disclosed content of the present invention, all should be considered as protection scope of the present invention.

Table 1 is a comparison of the field emission results of the samples in the prior art and various embodiments of the present invention, wherein "E _on "represents the open field, and "E _1.0 "represents the corresponding applied electric field strength when the field emission current density reaches 1.0mA/cm ² , "J _max " indicates the maximum field emission current density, and "↓" indicates the decrease.

Table 1

Claims (7)

1. A method for improving the field emission performance of a graphene sheet-silicon nanowire array composite material, comprising: first utilizing a metal-catalyzed corrosion method to prepare a silicon nanowire array, and then using energy-carrying silver ions to bombard with a dip Silicon nanowire arrays, and then use microwave plasma enhanced chemical vapor deposition to prepare thin graphene sheets on silicon nanowire arrays, and use microwave nitrogen and hydrogen plasma to treat the resulting graphene sheets-silicon nanowire arrays at room temperature , by adjusting the microwave power to 120-160W, the pressure in the treatment chamber to 1.5kPa, and the treatment time to 20-60 minutes to control the morphology of the graphene sheet, and then anneal the obtained nitrogen-doped graphene sheet-silicon nanowire array for 2 hour, finally obtain the nitrogen-doped graphene sheet-silicon nanowire array composite material after high-temperature heat treatment; the nitrogen-doped graphene sheet-silicon nanowire array composite material is deposited by The number of edge layers is 2-5 layers, rich in defects, densely distributed, and nitrogen-doped graphene sheets; the diameter of the graphene sheets is mostly 50-100 nanometers; the prepared nitrogen-doped graphene sheets-silicon nanowires The average open field of the array composite material is only 2.53-2.77V/μm, the average maximum field emission current density can reach 9.32-11.63mA/cm ² , and the average field emission current density is as high as 9.19mA/cm ² , and the current within 20 hours Attenuation is only 0.76%. 2. The method according to claim 1, further comprising a pretreatment process in which the silicon single wafer is ultrasonically cleaned with 50W power for 5 minutes in deionized water and absolute ethanol successively. 3. The method according to claim 1, further comprising the step of soaking the ultrasonically cleaned silicon single wafer in hydrofluoric acid with a volume ratio of 4% for 5 minutes. 4. The method according to claim 1, characterized in that the obtained nitrogen-doped graphene sheet-silicon nanowire array is annealed for 2 hours at 1000 degrees Celsius under normal pressure in a hydrogen atmosphere. 5. a kind of method for promoting graphene sheet-silicon nanowire array composite material field emission performance according to claim 1, is characterized in that, carries out as follows: Step (1) Preparation of silicon nanowire arrays by metal-catalyzed corrosion method: first cut the silicon single wafer into small pieces of 2 cm × 2 cm, and then use 50 W ultrasonic cleaning in deionized water and absolute ethanol for 5 minutes, and then The silicon single wafer was immersed in hydrofluoric _acid with a volume ratio of ₄ % for 5 minutes, and then the obtained silicon single wafer with a clean surface was successively inserted into the Soak in the solution for 1 minute, and soak in the solution with a volume ratio of H ₂ O ₂ :HF:H ₂ O=1:10:39 for 45 minutes to obtain the silicon nanowire array; the concentrations of AgNO ₃ , HF acid and hydrogen peroxide used above are respectively 0.01, 4 and 0.176mol/L; Step (2) silver ion bombardment pretreatment of silicon nanowire array: the silicon nanowire array obtained in step (1) is subjected to energy-carrying silver ion bombardment pretreatment in a metal vapor vacuum arc ion source (MEVVA source), during bombardment, The angle between the incident direction of silver ions and the axial direction of silicon nanowires is 10 degrees, and the sample stage is kept rotating at a constant speed. The bias voltage of the sample stage is set to -15kV, the beam current is 10 mA, and the bombardment time is 10 minutes; Step (3) Preparation of graphene sheet by microwave plasma enhanced chemical vapor deposition method: place the silicon nanowire array bombarded by silver ions obtained in step (2) on the graphite sample stage in the microwave plasma system, and vacuum the reaction chamber After pumping to 1.0×10 ^-3 Pa, introduce 10 sccm hydrogen, adjust the pressure regulator to 1 kPa, heat the sample stage with a heater until the temperature is stable at 800 degrees Celsius, start the microwave source, adjust the microwave power to 180W, and feed 5 sccm of acetylene gas , adjust the air pressure again to 1kPa, that is, start the growth of the graphene sheet, the growth time is 3 hours, and the final result is the graphene sheet-silicon nanowire array; Step (4) nitrogen and hydrogen plasma treatment of graphene sheet-silicon nanowire array: on the basis of step (3), cool the sample to room temperature in a 10sccm hydrogen atmosphere, and carry out nitrogen treatment on the obtained graphene sheet-silicon nanowire array 1. Hydrogen plasma treatment. The gas used to generate plasma is a mixed gas composed of nitrogen and hydrogen. The flow rates of nitrogen and hydrogen are 5 and 10 sccm respectively, and the air pressure is adjusted to 1.5kPa. After the air pressure is stable, start the microwave source and adjust The microwave power is 120-160W, and the processing time is 20-60 minutes, and the nitrogen-doped graphene sheet-silicon nanowire array is obtained; Step (5) high-temperature annealing: the nitrogen-doped graphene sheet-silicon nanowire array obtained in step (4) is subjected to high-temperature annealing treatment in a quartz tube furnace, the treatment temperature is 1000 degrees Celsius, and the protective gas used is 400 sccm hydrogen, and the quartz tube The medium pressure is normal pressure, and the treatment time is 2 hours. 6. A method for improving the field emission performance of the graphene sheet-silicon nanowire array composite material according to claim 5, wherein the purity of various gases used is 5N. 7. A nitrogen-doped graphene sheet-silicon nanowire array composite material prepared according to the method of claim 1, wherein the nitrogen-doped graphene sheet-silicon nanowire array composite material is made of silver The ion-bombarded silicon nanowires are composed of 2-5 layers of deposited edge layers, rich in defects, densely distributed, and nitrogen-doped graphene sheets; the diameter of the graphene sheets is mostly 50-100 nanometers; the prepared nitrogen The average open field of the doped graphene sheet-silicon nanowire array composite material is only 2.53-2.77V/μm, the maximum field emission current density can reach an average of 9.32-11.63mA/cm2, and the average field emission current density is as high as 9.19mA/cm2. cm2, the current decay within 20 hours is only 0.76%.