LU503066B1

LU503066B1 - Graphene-based composite material and its preparation method and application

Info

Publication number: LU503066B1
Application number: LU503066A
Authority: LU
Inventors: Zhaojun Tang; Shengquan Tang
Original assignee: Univ Zhengzhou Aeronautics
Priority date: 2022-11-15
Filing date: 2022-11-15
Publication date: 2023-05-15

Abstract

The present disclosure belongs to the technical field of graphene materials, and discloses a preparation method of a graphene-based composite material, which including the following steps: providing a Si nanoporous column array; depositing a Ni nanocrystal catalyst on the Si nanoporous column array; and by using the Si nanoporous column array with the deposited nickel nanocrystals as a substrate, methane as a carbon source, a mixed gas of argon gas and hydrogen as a carrier gas, carrying out a chemical vapor deposition method to obtain the graphene-based composite material, wherein graphene in the composite material grows parallel to the substrate. The advantages of the present invention are: by depositing a Ni nanocrystal catalyst on the Si nanoporous column array and growing graphene nanosheets parallel to the substrate, the instability of the structure with graphene vertical to the substrate can be overcome through the structure with graphene parallel to the substrate.

Description

DESCRIPTION 0503066

GRAPHENE-BASED COMPOSITE MATERIAL AND ITS PREPARATION METHOD

AND APPLICATION

Technical Field

This disclosure belongs to the technical field of graphene materials, and particularly relates to a graphene-based composite material and its preparation method and application.

Background

Carbon nanotubes are considered to be the preferred materials for cold cathode preparation because of their stable electron emission, low turn-on field strength and high forward emission current density. However, the wide application of carbon nanotube cold cathode materials 1s still plagued by some inherent problems. For example, the tube-like structure of carbon nanotubes limits the electron emission to the top position, so a layered carbon nanotube film will show non- uniform emission. In addition, the electrostatic shielding between carbon nanotubes cannot be ignored. Therefore, it is very scientific and necessary to develop other carbon cathode materials.

As the most promising cold cathode material to replace carbon nanotubes, graphene has attracted more and more attention in recent years. Compared with carbon nanotubes, graphene has higher aspect ratio (lateral dimension to thickness ratio), unique electrical properties, high transparency, inherent flexible structure and good mechanical properties and is more suitable as a flexible cold cathode material than carbon nanotubes. In addition, since edge defect sites of graphene can be used as active field emission sites to amplify the electric field emission intensity of graphene, graphene is better than the carbon nanotubes in the application of low-voltage electron tunneling.

In order to make full use of the high electron emission characteristics of edge defect sites of graphene, in the prior art, a structure in which graphene is vertical to a substrate is adopted to maximize the use of field emission edge sites (FEES) of graphene to obtain high-intensity electron emission. For example, few-layer graphene is prepared by a microwave plasma enhanced chemical vapor deposition (PECVD) method to be aligned perpendicular to the substrate. Graphene films are screen-printed to be vertical to the substrate or to construct a blade- like electron emitter. However, in combination with references, the emission current of the

. . . . . Lo. LU503066 vertically aligned graphene is unstable at a slightly higher voltage, and the emission current density of the material will gradually decrease after multiple voltage cycles: À typical example is graphene grown vertical to the substrate prepared by Alexander Malesevic’s group (Malesevic

A, Kemps R, Vanhulsel A, et al, Field emission from vertically aligned few-layer graphene [J]. J

Appl Phys, 2008, 104: 084301-084301-084305). After five cycles, the emission current density has significantly decreased, and also the field amplification factor has a large floating range, ranging from 3000 to 5000.

Therefore, how to improve the stability of electron emission while maintaining high emission current density is a key problem to be solved in the development of graphene-based cold cathode materials.

Summary of the Invention

The embodiments of this disclosure are intended to provide a preparation method of a graphene- based composite material and to solve the problems in the prior art.

The embodiments of this disclosure are implemented as follows: the preparation method of a graphene-based composite material comprises the following steps: providing a Si nanoporous column array; depositing a Ni nanocrystal catalyst on the Si nanoporous column array; and by using the Si nanoporous column array with the deposited nickel nanocrystals as a substrate, methane as a carbon source, a mixed gas of argon gas and hydrogen as a carrier gas, carrying out a chemical vapor deposition method to obtain the graphene-based composite material, wherein graphene in the composite material grows parallel to the substrate.

Preferably, the Si nanoporous column array is prepared by a chemical hydrothermal etching method.

Preferably, the step of preparing the Si nanoporous column array by the chemical hydrothermal etching method specifically comprises: removing organic contaminants from a surface of a Si wafer by using acetone, and then cleaning;

. . . . . LU503066 adding a corrosive solution composed of Fe(NO3)3 and an aqueous solution of HF into an autoclave equipped with teflon lining; clamping the Si wafer in a teflon fixing bracket and then placing the Si wafer into the autoclave; heating the autoclave in a heating furnace; and carrying out temperature holding and cooling to obtain the Si nanoporous column array.

Preferably, the Si wafer is heavily doped P-type monocrystalline silicon, and the doping concentration is 1017-1019 cm-3.

Preferably, the step of depositing the Ni nanocrystal catalyst on the Si nanoporous column array adopts a chemical bath deposition method.

Preferably, the chemical bath deposition method comprises the following steps: preparing a mixed solution containing ammonium fluoride and nickel acetate; and placing the Si nanoporous column array into the mixed solution to have a reaction, and cleaning the the Si nanoporous column array after the reaction to obtain the Si nanoporous column array with the deposited nickel nanocrystals.

Preferably, a molar ratio of the ammonium fluoride to the nickel acetate is 30-80:1.

Preferably, the step of carrying out the chemical vapor deposition method to obtain the graphene- based composite material specifically comprises: placing the Si nanoporous column array with the deposited nickel nanocrystals into a porcelain combustion boat, then pushing the porcelain combustion boat into a cleaned quartz tube, fixing two ends of the quartz tube by flanges, and removing air out of the quartz tube; and introducing a mixed gas of argon gas and hydrogen into the quartz tube, raising a furnace temperature to a specified temperature, introducing methane into the mixed gas, and then pushing the quartz tube out of a heating area to a room temperature area for cooling and continuously introducing the mixed gas of argon gas and hydrogen at the same time to obtain the graphene-based composite material.

Another object of the embodiments of this disclosure is to provide a graphene-based composite material prepared by the above-described preparation method of a graphene-based composite material.

. . Cg . . Lo. LU503066

A further object of the embodiments of this disclosure is to provide an application of the above- described graphene-based composite material in preparation of a field emission device.

The preparation method of a graphene-based composite material provided by the embodiments of this disclosure is provided in view of the problem that the unstable field emission performance in the structure with graphene vertical to the substrate limits its practical application. By depositing a Ni nanocrystal catalyst on the Si nanoporous column array and growing graphene nanosheets parallel to the substrate, the instability of the structure with graphene vertical to the substrate can be overcome through the structure with graphene parallel to the substrate.

Compared with the structure with graphene vertical to the substrate, the structure with graphene parallel to the substrate is greatly enhanced in the emission stability during the electron emission process. Moreover, the lateral nanoscale of graphene has a relatively high perimeter-area ratio and there are a number of edge emission sites, which ensures the field emission density of the material. In addition, the multiple orientations and roughness of the surface of the Si nanoporous column array increase the growth area of graphene, which in turn increases the number of emitters. The special geometry of the Si nanoporous column array will also greatly reduce the electrostatic shielding between the emitters, and greatly increase the field amplification factor B and improve the emission current intensity.

Brief Description of Drawings

FIG. 1 is a schematic structural diagram of the graphene-Si composite material prepared in

Example 1 of this disclosure (where GNS represents graphene nanosheets, and FEES represents field emission edge sites of graphene);

FIG. 2 is an SEM photograph of the graphene-Si composite material prepared in Example 1 of this disclosure;

FIG. 3 is an X-ray diffraction spectrum of the graphene-Si composite material prepared in

Example 1 of this disclosure; and

FIG. 4 shows test charts of the field emission performance and stability of the graphene-Si composite material prepared in Example 1 of this disclosure (where a indicates the J-E curves of

. LU503066 the sample measured at four voltage cycles; b indicates the corresponding F-N diagram of the sample in four measurement cycles).

Detailed Description of Preferred Embodiments

The present invention will be further described below in conjunction with the drawings and embodiments.

This disclosure relates to a graphene-based composite material, which is a graphene-Si composite material, and its preparation method comprises the following steps:

S1, preparing a Si nanoporous column array: carrying out a chemical hydrothermal etching method, wherein a Si wafer is monocrystalline p- type heavily doped, with a doping concentration of 1017-1019 cm-3 and an orientation of <111>; before etching, the Si wafer is soaked in acetone to remove organic contaminants from its surface and then placed in a sample holder and cleaned by a standard CRA process; an etching solution is composed of Fe(NO3)3 and an aqueous solution and added in an autoclave equipped with teflon lining; the Si wafer is clamped in a teflon fixing bracket and placed in the autoclave, and the autoclave is heated in a heating furnace to 120-140 °C and held at that temperature for 22-30 min, and then cooled in a ventilated place;

S2, depositing a Ni nanocrystalline catalyst on the Si nanoporous column array: preparing Ni nanocrystallines by a chemical water bath deposition method, wherein a mixed solution containing ammonium fluoride and nickel acetate is first prepared, and the Si nanoporous column array is placed into the mixed solution to have a reaction for 5-20 min and then cleaned with deionized water for later use, wherein the molar ratio of the ammonium fluoride to the nickel acetate is (30-80):1; and

S3, preparing the graphene-Si composite material (graphene-silicon composite material): carrying out a chemical vapor deposition method for preparation, wherein a quartz tube is first cleaned with a mixed solution of water and ethanol and then air dried, the Si nanoporous column array with the deposited Ni nanocrystalline catalyst is placed into a porcelain combustion boat, the porcelain combustion boat is then pushed into the cleaned quartz tube, and two ends of the quartz tube are fixed by flanges; the air in the quartz tube is pumped out to 0.1 Pa by a vacuum pump, argon gas is then introduced to the tube until the atmospheric pressure is reached in the tube, the quartz tube is then vacuumized by the vacuum pump again, and such operations are repeated three times until the air in the tube is removed; a mixed gas of argon gas and hydrogen is further introduced into the quartz tube; a furnace temperature is raised to 800-1000°C at a speed of 10 °C/min and then held at that temperature for 18-20 min; CH4 is added to the mixed gas, the quartz tube is then pushed out of a heating area to a room temperature area for cooling and the mixed protective gas of argon gas and hydrogen is further introduced for 8-10 min at the same time to finally obtain the graphene-based composite material.

Specific implementations of this disclosure are described in detail below in conjunction with specific embodiments.

Example 1

A graphene-based composite material, prepared by a method comprises the following steps:

S1, preparing a Si nanoporous column array: carrying out a chemical hydrothermal etching method, wherein a Si wafer with a resistivity of 0.015 Q-cm is monocrystalline p-type heavily doped, with a doping concentration of 1018 cm-3 and an orientation of <111>; before etching, the Si wafer is soaked in acetone to remove organic contaminants from its surface and then placed in a sample holder and cleaned by a standard CRA process; an etching solution is composed of Fe(NO3)3 (0.04 mol/l) and an aqueous solution of

HF (13 mol/l) and added in an autoclave equipped with teflon lining; the Si wafer is clamped in a teflon fixing bracket and placed in the autoclave, and the autoclave is heated in a heating furnace to 140 °C and held at this temperature for 25 min, and then cooled in a ventilated place;

S2, depositing a Ni nanocrystalline catalyst on the Si nanoporous column array: preparing Ni nanocrystallines by a chemical water bath deposition method, wherein 20 ml of a mixed solution containing ammonium fluoride (4 mol/L) and nickel acetate (0.05 mol/L) is first prepared, and the Si nanoporous column array is placed into the mixed solution to have a reaction for 15 min and then cleaned with deionized water for later use;

S3, preparing the graphene-Si composite material:

carrying out a chemical vapor deposition method for preparation, wherein a quartz tube is first LUS03066 cleaned with a mixed solution of water and ethanol and then air dried, the Si nanoporous column array with the deposited Ni nanocrystalline catalyst is placed into a porcelain combustion boat, the porcelain combustion boat is then pushed into the cleaned quartz tube, and two ends of the quartz tube are fixed by flanges; the air in the quartz tube is pumped out to 0.1 Pa by a vacuum pump, 200 sccm of argon gas is then introduced to the tube until the atmospheric pressure is reached in the tube, the quartz tube is then vacuumized by the vacuum pump again, and such operations are repeated three times until the air in the tube is removed; a mixed gas of 200 sccm of argon gas and 65 sccm of hydrogen is further introduced into the quartz tube; a furnace temperature is raised to 1000 °C at a speed of 10 °C/min and then held at this temperature for 20 min; 10 sccm of CH4 is added to the mixed gas, the quartz tube is then pushed out of a heating area to a room temperature area for cooling and the mixed protective gas of argon gas and hydrogen is further introduced for 10 min at the same time to finally obtain the graphene-based composite material.

Performance test: (1) The structural diagram of the graphene-Si composite material is shown in FIG. 1. (2) The graphene-Si composite material was scanned by an electron microscope, and the result is shown in FIG. 2. (3) X-ray diffraction was carried out on the graphene-Si composite material, and the result is shown in FIG. 3. (4) The graphene-Si composite material was tested for field emission performance as follows:

Tested by a Hall tester according to a Four Point Probe Theory, the graphene-Si composite material had a carrier concentration of 5.45 [J 1024cm-3, and a plane resistivity of 2.52 [1 10-8 © cm.

At room temperature, the test was carried out by using a diode structure model in a vacuum chamber with a pressure of about 2 x 10-4 Pa. Indium tin oxide (ITO)-coated glass (p=8x10-4

Q-cm) was used as an anode, the graphene-Si composite material was used as a cathode, and the anode and the cathode were separated by a mica insulating sheet with a thickness of 375 um. The current-voltage data was recorded with a digital multimeter (Sourcemeter-2400, Keithley). The LUS03066 results are shown in FIG. 4, where the typical turn-on field intensity is 2.85V/um, and under the electric field of 4.2V/um, a current density of 53.9uA/cm2 can be obtained, and after 4 cycles, the current intensity does not change significantly, and the F-N curves do not change significantly.

To sum up, tested by the Hall tester through the Four Point Probe Theory, the composite system prepared in the embodiment of this disclosure has a high carrier concentration of 5.45 [J 1024 cm-3 and a low plane resistivity of 2.52 [1 10-8 Q-cm which is two orders of magnitude lower than that of most metals, thereby providing enough conduction electrons for electron-emitting graphene to ensure a stable and continuous emission current.

Compared with the structure with graphene vertical to the substrate, the graphene-Si-based material prepared in the embodiment of this disclosure has greatly improved field emission stability. Considering that the emission area of graphene/Si-NPA is 1 cm2, graphene-based field emission cathode materials have quite strong field emission performance. For example, according to what is disclosed in the prior art, nitrogen-passivated vertically aligned few-layer graphene has an emission area of 0.2 cm2 and a turn-on electric field high up to 4.6 V/um (10.0 uA/em2). Similarly, the field electrons emitted from the edge of the graphene film with a size of 1.0 x 1.0 cm require a turn-on field intensity of 50 V/um, and it was tested by the Hall tester according to the Four Point Probe Theory that the on-current at a turn-on voltage was only 10-4 uA/em2. It can be clearly seen that under the same field intensity, its current density is not as strong as that of the composite material prepared in the embodiment of this disclosure and its emission area is smaller than that of the composite material in the embodiment of this disclosure, and in the case of the same emission area, its turn-on field intensity is not as strong as that of the composite material prepared in the embodiment of this disclosure. In addition, the embodiment of this disclosure has a simple preparation process, can be put into large-area and large-scale production, and is suitable for low-voltage cold cathode devices.

Example 2

S1, preparing a Si nanoporous column array:

carrying out a chemical hydrothermal etching method, wherein a Si wafer is monocrystalline p-L 7803066 type heavily doped, with a doping concentration of 1017 cm-3 and an orientation of <111>; before etching, the Si wafer is soaked in acetone to remove organic contaminants from its surface and then placed in a sample holder and cleaned by a standard CRA process; an etching solution 1s composed of Fe(NO3)3 and an aqueous solution of HF and added in an autoclave equipped with teflon lining; the Si wafer is clamped in a teflon fixing bracket and placed in the autoclave, and the autoclave is heated in a heating furnace to 120 °C and held at this temperature for 30 min, and then cooled in a ventilated place;

S2, depositing a Ni nanocrystalline catalyst on the Si nanoporous column array: preparing Ni nanocrystallines by a chemical water bath deposition method, wherein a mixed solution containing ammonium fluoride and nickel acetate is first prepared, and the Si nanoporous column array is placed into the mixed solution to have a reaction for 15 min and then cleaned with deionized water for later use, wherein the molar ratio of the ammonium fluoride to the nickel acetate is 30:1; and

S3, preparing the graphene-Si composite material: carrying out a chemical vapor deposition method for preparation, wherein a quartz tube is first cleaned with a mixed solution of water and ethanol and then air dried, the Si nanoporous column array with the deposited Ni nanocrystalline catalyst is placed into a porcelain combustion boat, the porcelain combustion boat is then pushed into the cleaned quartz tube, and two ends of the quartz tube are fixed by flanges; the air in the quartz tube is pumped out to 0.1 Pa by a vacuum pump, 200 sccm of argon gas is then introduced to the tube until the atmospheric pressure is reached in the tube, the quartz tube is then vacuumized by the vacuum pump again, and such operations are repeated three times until the air in the tube is removed; a mixed gas of 200 sccm of argon gas and 65 sccm of hydrogen is further introduced into the quartz tube; a furnace temperature is raised to 800 °C at a speed of 10 °C/min and then held at this temperature for 20 min; 10 sccm of CH4 is added to the mixed gas, the quartz tube is then pushed out of a heating area to a room temperature area for cooling and the mixed protective gas of argon gas and hydrogen is further introduced for 10 min at the same time to finally obtain the graphene-based composite material.

Example 3: LU503066 a preparation method of a Y203-MgO infrared transparent ceramic material, including the following steps:

S1, preparing a Si nanoporous column array: carrying out a chemical hydrothermal etching method, wherein a Si wafer is monocrystalline p- type heavily doped, with a doping concentration of 1017 cm-3 and an orientation of <111>; before etching, the Si wafer is soaked in acetone to remove organic contaminants from its surface and then placed in a sample holder and cleaned by a standard CRA process; an etching solution is composed of Fe(NO3)3 and an aqueous solution and added in an autoclave equipped with teflon lining; the Si wafer is clamped in a teflon fixing bracket and placed in the autoclave, and the autoclave is heated in a heating furnace to 130 °C and held at this temperature for 25 min, and then cooled in a ventilated place;

S2, depositing a Ni nanocrystalline catalyst on the Si nanoporous column array: preparing Ni nanocrystallines by a chemical water bath deposition method, wherein a mixed solution containing ammonium fluoride and nickel acetate is first prepared, and the Si nanoporous column array is placed into the mixed solution to have a reaction for 15 min and then cleaned with deionized water for later use, wherein the molar ratio of the ammonium fluoride to the nickel acetate is 40:1; and

S3, preparing the graphene-Si composite material: carrying out a chemical vapor deposition method for preparation, wherein a quartz tube is first cleaned with a mixed solution of water and ethanol and then air dried, the Si nanoporous column array with the deposited Ni nanocrystalline catalyst is placed into a porcelain combustion boat, the porcelain combustion boat is then pushed into the cleaned quartz tube, and two ends of the quartz tube are fixed by flanges; the air in the quartz tube is pumped out to 0.1 Pa by a vacuum pump, and argon gas is then introduced to the tube until the atmospheric pressure is reached in the tube, the quartz tube is then vacuumized by the vacuum pump again, and such operations are repeated three times until the air in the tube is removed; a mixed gas of argon gas and hydrogen is further introduced into the quartz tube; a furnace temperature is raised to 850°C at a speed of ps . 2 . . LU503066 °C/min and then held at this temperature for 18 min; CH4 is added to the mixed gas, the quartz tube is then pushed out of a heating area to a room temperature area for cooling and the mixed protective gas of argon gas and hydrogen is further introduced for 8 min at the same time to finally obtain the graphene-based composite material.

Example 4:

S1, preparing a Si nanoporous column array: carrying out a chemical hydrothermal etching method, wherein a Si wafer is monocrystalline p- type heavily doped, with a doping concentration of 1018 cm-3 and an orientation of <111>; before etching, the Si wafer is soaked in acetone to remove organic contaminants from its surface and then placed in a sample holder and cleaned by a standard CRA process; an etching solution is composed of Fe(NO3)3 and an aqueous solution and added in an autoclave equipped with teflon lining; the Si wafer is clamped in a teflon fixing bracket and placed in the autoclave, and the autoclave is heated in a heating furnace to 140 °C and held at this temperature for 30 min, and then cooled in a ventilated place;

S2, depositing a Ni nanocrystalline catalyst on the Si nanoporous column array: preparing Ni nanocrystallines by a chemical water bath deposition method, wherein a mixed solution containing ammonium fluoride and nickel acetate is first prepared, and the Si nanoporous column array is placed into the mixed solution to have a reaction for 20 min and then cleaned with deionized water for later use, wherein the molar ratio of the ammonium fluoride to the nickel acetate is 50:1; and

S3, preparing the graphene-Si composite material: carrying out a chemical vapor deposition method for preparation, wherein a quartz tube is first cleaned with a mixed solution of water and ethanol and then air dried, the Si nanoporous column array with the deposited Ni nanocrystalline catalyst is placed into a porcelain combustion boat, the porcelain combustion boat is then pushed into the cleaned quartz tube, and two ends of the quartz tube are fixed by flanges; the air in the quartz tube is pumped out to 0.1 Pa by a vacuum pump, and argon gas is then introduced to the tube until the atmospheric pressure is reached in

. . . . LU503066 the tube, the quartz tube is then vacuumized by the vacuum pump again, and such operations are repeated three times until the air in the tube is removed; a mixed gas of argon gas and hydrogen is further introduced into the quartz tube; a furnace temperature is raised to 900°C at a speed of °C/min and then held at this temperature for 18 min; CH4 is added to the mixed gas, the quartz tube is then pushed out of a heating area to a room temperature area for cooling and the mixed protective gas of argon gas and hydrogen is further introduced for 10 min at the same time to finally obtain the graphene-based composite material.

Example 5:

S1, preparing a Si nanoporous column array: carrying out a chemical hydrothermal etching method, wherein a Si wafer is monocrystalline p- type heavily doped, with a doping concentration of 1019 cm-3 and an orientation of <111>; before etching, the Si wafer is soaked in acetone to remove organic contaminants from its surface and then placed in a sample holder and cleaned by a standard CRA process; an etching solution is composed of Fe(NO3)3 and an aqueous solution and added in an autoclave equipped with teflon lining; the Si wafer is clamped in a teflon fixing bracket and placed in the autoclave, and the autoclave is heated in a heating furnace to 120 °C and held at this temperature for 30 min, and then cooled in a ventilated place;

S2, depositing a Ni nanocrystalline catalyst on the Si nanoporous column array: preparing Ni nanocrystallines by a chemical water bath deposition method, wherein a mixed solution containing ammonium fluoride and nickel acetate is first prepared, and the Si nanoporous column array is placed into the mixed solution to have a reaction for 18 min and then cleaned with deionized water for later use, wherein the molar ratio of the ammonium fluoride to the nickel acetate 1s 60:1; and

S3, preparing the graphene-Si composite material: carrying out a chemical vapor deposition method for preparation, wherein a quartz tube is first cleaned with a mixed solution of water and ethanol and then air dried, the Si nanoporous column array with the deposited Ni nanocrystalline catalyst is placed into a porcelain combustion boat,

. . . . LU503066 the porcelain combustion boat is then pushed into the cleaned quartz tube, and two ends of the quartz tube are fixed by flanges; the air in the quartz tube is pumped out to 0.1 Pa by a vacuum pump, and argon gas is then introduced to the tube until the atmospheric pressure is reached in the tube, the quartz tube is then vacuumized by the vacuum pump again, and such operations are repeated three times until the air in the tube is removed; a mixed gas of argon gas and hydrogen is further introduced into the quartz tube; a furnace temperature is raised to 950°C at a speed of °C/min and then held at this temperature for 20 min; CH4 is added to the mixed gas, the quartz tube is then pushed out of a heating area to a room temperature area for cooling and the mixed protective gas of argon gas and hydrogen is further introduced for 10 min at the same time to finally obtain the graphene-based composite material.

Example 6:

S1, preparing a Si nanoporous column array: carrying out a chemical hydrothermal etching method, wherein a Si wafer is monocrystalline p- type heavily doped, with a doping concentration of 1019 cm-3 and an orientation of <111>; before etching, the Si wafer is soaked in acetone to remove organic contaminants from its surface and then placed in a sample holder and cleaned by a standard CRA process; an etching solution is composed of Fe(NO3)3 and an aqueous solution and added in an autoclave equipped with teflon lining; the Si wafer is clamped in a teflon fixing bracket and placed in the autoclave, and the autoclave is heated in a heating furnace to 140 °C and held at this temperature for 28 min, and then cooled in a ventilated place;

S2, depositing a Ni nanocrystalline catalyst on the Si nanoporous column array: preparing Ni nanocrystallines by a chemical water bath deposition method, wherein a mixed solution containing ammonium fluoride and nickel acetate is first prepared, and the Si nanoporous column array is placed into the mixed solution to have a reaction for 20 min and then cleaned with deionized water for later use, wherein the molar ratio of the ammonium fluoride to the nickel acetate is 70:1; and

S3, preparing the graphene-Si composite material:

carrying out a chemical vapor deposition method for preparation, wherein a quartz tube is first LUS03066 cleaned with a mixed solution of water and ethanol and then air dried, the Si nanoporous column array with the deposited Ni nanocrystalline catalyst is placed into a porcelain combustion boat, the porcelain combustion boat is then pushed into the cleaned quartz tube, and two ends of the quartz tube are fixed by flanges; the air in the quartz tube is pumped out to 0.1 Pa by a vacuum pump, and argon gas is then introduced to the tube until the atmospheric pressure is reached in the tube, the quartz tube is then vacuumized by the vacuum pump again, and such operations are repeated three times until the air in the tube is removed; a mixed gas of argon gas and hydrogen is further introduced into the quartz tube; a furnace temperature is raised to 1000°C at a speed of °C/min and then held at this temperature for 20 min; CH4 is added to the mixed gas, the quartz tube is then pushed out of a heating area to a room temperature area for cooling and the mixed protective gas of argon gas and hydrogen is further introduced for 10 min at the same time to finally obtain the graphene-based composite material.

Example 7:

S1, preparing a Si nanoporous column array: carrying out a chemical hydrothermal etching method, wherein a Si wafer is monocrystalline p- type heavily doped, with a doping concentration of 1019 cm-3 and an orientation of <111>; before etching, the Si wafer is soaked in acetone to remove organic contaminants from its surface and then placed in a sample holder and cleaned by a standard CRA process; an etching solution is composed of Fe(NO3)3 and an aqueous solution and added in an autoclave equipped with teflon lining; the Si wafer is clamped in a teflon fixing bracket and placed in the autoclave, and the autoclave is heated in a heating furnace to 120 °C and held at this temperature for 22 min, and then cooled in a ventilated place;

S2, depositing a Ni nanocrystalline catalyst on the Si nanoporous column array: preparing Ni nanocrystallines by a chemical water bath deposition method, wherein a mixed solution containing ammonium fluoride and nickel acetate is first prepared, and the Si nanoporous column array is placed into the mixed solution to have a reaction for 5 min and then cleaned with deionized water for later use, wherein the molar ratio of the ammonium fluoride ta 803066 the nickel acetate 1s 80:1; and

S3, preparing the graphene-Si composite material: carrying out a chemical vapor deposition method for preparation, wherein a quartz tube is first cleaned with a mixed solution of water and ethanol and then air dried, the Si nanoporous column array with the deposited Ni nanocrystalline catalyst is placed into a porcelain combustion boat, the porcelain combustion boat is then pushed into the cleaned quartz tube, and two ends of the quartz tube are fixed by flanges; the air in the quartz tube is pumped out to 0.1 Pa by a vacuum pump, and argon gas is then introduced to the tube until the atmospheric pressure is reached in the tube, the quartz tube is then vacuumized by the vacuum pump again, and such operations are repeated three times until the air in the tube is removed; a mixed gas of argon gas and hydrogen is further introduced into the quartz tube; a furnace temperature is raised to 800°C at a speed of °C/min and then held at this temperature for 18 min; CH4 is added to the mixed gas, the quartz tube is then pushed out of a heating area to a room temperature area for cooling and the mixed protective gas of argon gas and hydrogen is further introduced for 8 min at the same time to finally obtain the graphene-based composite material.

Claims

CLAIMS LU503066

1. À preparation method of a graphene-based composite material, comprising the following steps: providing a Si nanoporous column array; depositing a Ni nanocrystal catalyst on the Si nanoporous column array; and by using the Si nanoporous column array with the deposited nickel nanocrystals as a substrate, methane as a carbon source, a mixed gas of argon gas and hydrogen as a carrier gas, carrying out a chemical vapor deposition method to obtain the graphene-based composite material, wherein graphene in the composite material grows parallel to the substrate.

2. The preparation method of a graphene-based composite material according to claim 1, wherein the Si nanoporous column array is prepared by a chemical hydrothermal etching method.

3. The preparation method of a graphene-based composite material according to claim 2, wherein the step of preparing the Si nanoporous column array by the chemical hydrothermal etching method specifically comprises: removing organic contaminants from a surface of a Si wafer by using acetone, and then cleaning, adding a corrosive solution composed of Fe(NO3)3 and an aqueous solution of HF into an autoclave equipped with teflon lining; clamping the Si wafer in a teflon fixing bracket and then placing the Si wafer into the autoclave; heating the autoclave in a heating furnace; and carrying out temperature holding and cooling to obtain the Si nanoporous column array.

4. The preparation method of a graphene-based composite material according to claim 3, wherein the Si wafer is heavily doped P-type monocrystalline silicon, and the doping concentration is 1017-1019 cm-3.

5. The preparation method of a graphene-based composite material according to claim 1, wherein the step of depositing the Ni nanocrystal catalyst on the Si nanoporous column array adopts a chemical bath deposition method.

6. The preparation method of a graphene-based composite material according to claim 5, wherein the chemical bath deposition method comprises the following steps:

. . . . . . . ; LU503066 preparing a mixed solution containing ammonium fluoride and nickel acetate; and placing the Si nanoporous column array into the mixed solution to have a reaction, and cleaning the the Si nanoporous column array after the reaction to obtain the Si nanoporous column array with the deposited nickel nanocrystals.

7. The preparation method of a graphene-based composite material according to claim 6, wherein a molar ratio of the ammonium fluoride to the nickel acetate 1s 30-80:1.

8. The preparation method of a graphene-based composite material according to claim 1, wherein the step of carrying out the chemical vapor deposition method to obtain the graphene-based composite material specifically comprises: placing the Si nanoporous column array with the deposited nickel nanocrystals into a porcelain combustion boat, then pushing the porcelain combustion boat into a cleaned quartz tube, fixing two ends of the quartz tube by flanges, and removing air out of the quartz tube; and introducing a mixed gas of argon gas and hydrogen into the quartz tube, raising a furnace temperature to a specified temperature, introducing methane into the mixed gas, and then pushing the quartz tube out of a heating area to a room temperature area for cooling and continuously introducing the mixed gas of argon gas and hydrogen at the same time to obtain the graphene-based composite material.

9. A graphene-based composite material prepared by one of the preparation method of a graphene-based composite material according to claim 1-8.

10. An application of the graphene-based composite material in preparation of a field emission device according to claim 9.