Preparation method and application of doped graphite

Abstract

The invention discloses a preparation method and application of doped graphite, and belongs to the technical field of doped graphite. The method comprises the following steps: performing vacuum annealing on a single crystal metal substrate adsorbed with a doped element compound to obtain a doped element embedded single crystal metal substrate; the single crystal metal substrate embedded with the doping elements is attached to a graphite base material, heat preservation is conducted for 1-3 h at the temperature of 1000-1500 DEG C in a non-oxidizing atmosphere, then heat preservation is conducted for 4-12 h at the temperature of 700-900 DEG C, and the doped graphite is obtained after cooling. According to the invention, the doping elements are embedded into the single crystal metal substrate, and the graphite is doped through variable temperature growth, so that the super-lubricity is maintained while the doping uniformity and controllability are ensured, and the method is more suitable for being applied to electronic devices needing to maintain the super-lubricity.

Description

Technical Field

[0001] This invention belongs to the field of doped graphite technology, specifically relating to a method for preparing doped graphite and its application. Background Technology

[0002] Graphite from sp 2 Hybridized carbon atom layers are stacked by van der Waals forces. When two atomically smooth graphite surfaces are stacked at a certain rotation angle, their interface achieves a structurally superlubricated state with near-zero friction and zero wear. Structurally superlubricated interfaces are typically dominated by van der Waals forces (vdW) and are incommensurable contact states (e.g., ...). Figure 32 (As shown). The emergence and development of structural superlubricity has provided a revolutionary solution to the friction and wear problems in fields such as microelectromechanical systems (MEMS) and precision manufacturing. In recent years, prototype devices such as microgenerators and electrostatic actuators developed based on this property have demonstrated breakthrough performance. Graphite, as the basic material for structural superlubricity technology, will play a significant role in improving the performance of related devices by controlling its electrical properties.

[0003] For example, a semiconductor DC microgenerator based on structural superlubricity technology is composed of graphite and semiconductor materials. When the two materials come into contact, due to their different work functions, a depletion layer will form between them to establish electrostatic equilibrium. When the two materials slip relative to each other, the formation and destruction of the depletion layer generates a non-equilibrium electric field, driving electrons to drift and forming direct current. The application of structural superlubricity effectively solves the lifespan problem of microgenerators caused by friction and wear during mechanical energy harvesting. However, although the output current density can reach approximately 21 mA / cm², the actual lifespan is significantly reduced. 2 The output power density is approximately 0.7 mW / cm³. 2 However, this still cannot meet the power supply requirements of low-power micro / nanoelectronic devices. To address this issue, impurity atoms are continuously introduced during graphite growth to obtain doped graphite, thereby forming substitutional doping that alters the interlayer electronic structure of graphite. This, in turn, modulates the work function to control the built-in electric field between materials, improving power generation efficiency. This effectively improves the electromechanical conversion efficiency of semiconductor DC microgenerators based on superlubricated structures, promoting the practical application of microgenerators in various fields. It also opens up new research directions and technical approaches for improving the performance of electronic devices based on superlubricated structures.

[0004] Currently, the main methods for preparing doped graphite include ion implantation, plasma treatment, gas-phase chemical doping, and liquid-phase exfoliation-recombination, but these methods have the following problems.

[0005] Ion implantation or plasma treatment can introduce doped atoms into the graphite layer, but often leads to a large number of defects and lattice damage, destroying the interlayer superlubricity.

[0006] Gas-phase chemical doping: Partial doping is achieved by introducing gaseous doping precursors (such as ammonia or diborane) into the CVD atmosphere. However, this method is difficult to guarantee doping uniformity and has a limited doping depth, making it difficult to apply to multilayer graphite structures.

[0007] Liquid phase exfoliation-recombination method: This method achieves the recombination of graphite or graphene layers through liquid phase doping, but the process is complex and the doping positions are uncontrollable, making it difficult to meet the requirements of device-level applications.

[0008] Therefore, a method is needed to prepare doped graphite that is uniform, controllable, and avoids damaging the graphite lattice. Summary of the Invention

[0009] To overcome the shortcomings of existing technologies, this invention provides a method for preparing doped graphite and its application. This invention employs an embedded pretreatment process combined with simultaneous growth doping, ensuring doping uniformity and controllability while avoiding damage to the graphite lattice, making it more suitable for electronic devices requiring the maintenance of super-lubricating properties.

[0010] The technical solution adopted by this invention to solve its technical problem is: This invention provides a method for preparing doped graphite, comprising the following steps: (1) Vacuum annealing of a single-crystal metal substrate adsorbed with doped element compounds to obtain a single-crystal metal substrate with embedded doped elements; (2) The single crystal metal substrate with embedded doped elements is bonded to the graphite substrate, and kept at 1000-1500℃ for 1-3h in a non-oxidizing atmosphere, and then kept at 700-900℃ for 4-12h. After cooling, doped graphite is obtained.

[0011] In some embodiments, the material of the single-crystal metal substrate in step (1) is one of single-crystal nickel, single-crystal iron, single-crystal cobalt, single-crystal platinum, single-crystal palladium, single-crystal nickel-based alloy, single-crystal iron-based alloy, and single-crystal cobalt-based alloy.

[0012] In some embodiments, the graphite substrate in step (1) is graphite paper; the thickness and area are adjusted according to the carbon source and area required to prepare doped graphite.

[0013] In some embodiments, the dopant compound in step (1) is a nitrogen-containing compound that can be decomposed by vacuum annealing.

[0014] In some embodiments, the dopant compound in step (1) is one or more of melamine, urea, and dicyandiamide.

[0015] In some embodiments, the method for preparing the single-crystal metal substrate adsorbed with doped element compounds in step (1) is as follows: immerse the single-crystal metal substrate in a solution of doped element compounds, remove it and dry it to obtain the single-crystal metal substrate adsorbed with doped element compounds.

[0016] In some embodiments, the soaking time is 3-20 minutes.

[0017] In some embodiments, the concentration of the solution of the dopant compound is 0.1-1 mg / ml.

[0018] In some embodiments, the drying is vacuum drying.

[0019] In some embodiments, the vacuum annealing temperature in step (1) is 1000-1500°C and the time is 3-10 minutes.

[0020] In some embodiments, the non-oxidizing atmosphere in step (2) is a non-oxidizing gas stream.

[0021] In some embodiments, the flow rate of the non-oxidizing gas stream is 100-500 sccm.

[0022] In some embodiments, the non-oxidizing atmosphere in step (2) is a reducing atmosphere; this can better protect graphite from oxidation.

[0023] In some embodiments, the reducing atmosphere is a mixture of an inert gas and hydrogen.

[0024] In some embodiments, the volume ratio of the inert gas to hydrogen is 10:(0.1-3).

[0025] In some embodiments, the graphite-doped single-crystal metal substrate obtained in step (2) is peeled off.

[0026] In some embodiments, the method for stripping the graphite-doped single-crystal metal substrate is ferric chloride solution etching.

[0027] In some embodiments, the method for stripping the doped graphite from the single-crystal metal substrate is as follows: the doped graphite obtained in step (2) is immersed in a ferric chloride solution, the nickel sheet is removed, washed, and dried to obtain the doped graphite stripped from the single-crystal metal substrate.

[0028] In some embodiments, the concentration of the ferric chloride solution is 0.01-0.2 mg / ml.

[0029] In some embodiments, the soaking time is 12-72 hours.

[0030] In some embodiments, the washing is a sequential washing with ethanol and deionized water.

[0031] In some embodiments, the drying is vacuum drying.

[0032] In some embodiments, the graphite surface of the doped graphite obtained in step (2) is bonded to a silicon wafer or glass plate and then immersed in a ferric chloride solution; this can better maintain the integrity of the doped graphite from being damaged.

[0033] This invention provides a doped graphite prepared by the above-described preparation method.

[0034] This invention provides an application of the above-mentioned doped graphite in the preparation of superlubricated micro-generators, superlubricated relays, or nano-switches.

[0035] The mechanism of graphite doping in this invention is that substitutional doping (such as replacing C atoms with N or B atoms) can effectively regulate the local electronic structure of graphite, thereby changing the band width, work function and electrical transport characteristics.

[0036] The catalytic effect of single-crystal metals in this invention: single-crystal nickel and other metals can promote the decomposition of carbon sources and the precipitation of graphite at high temperatures, and can also serve as a carrier for dopant sources, realizing the co-precipitation process of carbon and dopant atoms.

[0037] The application prospects of graphite doping in this invention: This invention achieves controllable and effective doping of multilayer structures during graphite growth, while maintaining the superlubricating properties of the graphite interface. This overcomes the bottleneck of existing technologies that cannot adjust the graphite band structure and limit device performance improvement. Doped graphite not only maintains the superlubricating interface structure for applications in microelectromechanical systems (MEMS) and precision manufacturing, but also further enhances the performance of devices such as triboelectric generators, superlubricating relays, and nano-switches, providing new solutions for low-power electronic devices.

[0038] This invention pre-embeds a dopant source in a single-crystal metal substrate and uses variable-temperature growth to dope graphite. At a high temperature of approximately 1000-1500 degrees Celsius, carbon is fully released to establish carbon transport channels within the single-crystal metal substrate. The temperature is then lowered to 700-900 degrees Celsius, allowing carbon and the dopant element in the single-crystal metal substrate to precipitate simultaneously. This enables synchronous substitutional doping of graphite during growth, overcoming the bottleneck of uniform and effective doping of multilayer graphite structures in existing technologies. The method of this invention does not damage the layered van der Waals structure of graphite, ensuring that the near-zero friction and zero wear characteristics of the interface are maintained after doping, making it suitable for application in ultralubricated electronic devices. By controlling the dopant source concentration, this invention effectively adjusts the graphite band structure, work function, and carrier concentration, thereby improving the energy conversion efficiency and functional performance of graphite-based ultralubricated electronic devices. Based on mature chemical vapor deposition (CVD) technology, combined with rapid thermal annealing and other process steps, this invention possesses good process repeatability and compatibility with existing microelectronic manufacturing technologies. In the process of separating graphite from a single-crystal metal substrate, the present invention adopts a support-based retrieval method to effectively protect the structural and morphological integrity of the graphite layer, thereby improving the stability and usability of doped graphite samples.

[0039] The beneficial effects of this invention are: This invention embeds doping elements into a single-crystal metal substrate and uses variable-temperature growth to dopant graphite. This ensures doping uniformity and controllability while not damaging the graphite lattice, thus maintaining super-lubricating properties. It is more suitable for electronic devices that require maintaining super-lubricating characteristics. Attached Figure Description

[0040] Figure 1 The process flow diagram for preparing doped graphite in Example 1 is shown.

[0041] Figure 2 This is a photograph of the nitrogen-embedded single-crystal nickel sheet prepared in Example 1.

[0042] Figure 3 This is a SEM image of the nitrogen-embedded single-crystal nickel wafer prepared in Example 1.

[0043] Figure 4 The image shows the EDS diagram of the nitrogen-embedded single-crystal nickel wafer prepared in Example 1.

[0044] Figure 5 The images show the SEM and EDS images of the nitrogen-doped graphite surface away from the single-crystal nickel sheet prepared in Example 1.

[0045] Figure 6 The image shows the Raman spectrum of the nitrogen-doped graphite obtained in Example 1 on the side of the single-crystal nickel sheet away from the surface.

[0046] Figure 7The image shows the frictional force test results of the nitrogen-doped graphite prepared in Example 1.

[0047] Figure 8 This is a graph showing the friction test results for undoped graphite.

[0048] Figure 9 This is a diagram showing the positional relationship between the carbon source graphite paper and the nitrogen-deposited single-crystal nickel sheet in Comparative Example 1.

[0049] Figure 10 This is a photograph of the nitrogen-deposited single-crystal nickel wafer prepared in Comparative Example 1.

[0050] Figure 11 The image shows a SEM image of a nitrogen-deposited single-crystal nickel wafer prepared in Comparative Example 1.

[0051] Figure 12 EDS image of the nitrogen-deposited single-crystal nickel wafer prepared in Comparative Example 1.

[0052] Figure 13 The total elemental distribution spectrum of the nitrogen-deposited single-crystal nickel wafer prepared in Comparative Example 1 is shown.

[0053] Figure 14 The image shows the EDS pattern of the nitrogen-doped graphite surface away from the single-crystal nickel sheet prepared in Comparative Example 1.

[0054] Figure 15 The total elemental distribution spectrum is shown on the surface of the nitrogen-doped graphite away from the single-crystal nickel sheet prepared in Comparative Example 1.

[0055] Figure 16 The image shows the Raman spectrum of the nitrogen-doped graphite obtained in Comparative Example 1 on the side of the single-crystal nickel sheet away from the surface.

[0056] Figure 17 XPS image of the nitrogen-doped graphite surface away from the single-crystal nickel sheet prepared in Comparative Example 1.

[0057] Figure 18 EDS image of the thickness-direction cross-section of the nitrogen-doped graphite prepared in Comparative Example 1.

[0058] Figure 19 The total elemental distribution spectrum is shown in the cross-section of the nitrogen-doped graphite prepared in the thickness direction of Comparative Example 1.

[0059] Figure 20 The image shows the EDS plot of the nitrogen-doped graphite prepared in the thickness direction, which is a comparative example 1.

[0060] Figure 21 The total elemental distribution spectrum is obtained by line scanning along the thickness direction of nitrogen-doped graphite prepared in Comparative Example 1.

[0061] Figure 22 SEM image of the nitrogen-doped graphite surface away from the single-crystal nickel sheet prepared in step (2) of Comparative Example 2.

[0062] Figure 23 EDS image of the nitrogen-doped graphite surface away from the single-crystal nickel sheet prepared in step (2) of Comparative Example 2.

[0063] Figure 24 The total elemental distribution spectrum of the nitrogen-doped graphite on the side of the single-crystal nickel sheet away from the surface prepared in step (2) of Comparative Example 2 is shown.

[0064] Figure 25 EDS image of the cross-section of nitrogen-doped graphite in the thickness direction prepared in step (2) of Comparative Example 2.

[0065] Figure 26 For comparative example 2, the nitrogen-doped graphite spectrum prepared in step (2) is shown. Figure 5 The element distribution diagram.

[0066] Figure 27 EDS image of the nitrogen-doped graphite prepared in step (2) of Comparative Example 2, showing the thickness direction line scan.

[0067] Figure 28 The elemental distribution map of the nitrogen-doped graphite prepared in step (2) of Comparative Example 2 is obtained by line scanning along the thickness direction.

[0068] Figure 29 The optical mirror image of the nitrogen-doped graphite near the single-crystal nickel sheet prepared in step (3) of Comparative Example 2.

[0069] Figure 30 Raman spectrum of nitrogen-doped graphite near the surface of single-crystal nickel sheet prepared in step (3) of Comparative Example 2.

[0070] Figure 31 XPS image of the nitrogen-doped graphite near the single-crystal nickel sheet surface prepared in step (3) of Comparative Example 2.

[0071] Figure 32 This is a schematic diagram of the contact state between commensurable and incommensurable graphite in the background technology. Detailed Implementation

[0072] The present invention will be further described below with reference to embodiments.

[0073] The following will clearly and completely describe the concept, specific solutions, and technical effects of the present invention with reference to embodiments, so as to fully understand the purpose, features, and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention. The various technical features in the present invention can be combined interactively without contradicting each other.

[0074] This invention pre-treats the single-crystal metal substrate by using vacuum high-temperature rapid thermal annealing to pre-dope the substrate and introduce a doping source. Then, using chemical vapor deposition (CVD) in a tube furnace under specific atmosphere and temperature, carbon and doping elements are simultaneously precipitated on the surface of the single-crystal metal substrate to form multilayer doped graphite. After the doped graphite growth is completed, in order to separate the single-crystal metal substrate from the grown doped graphite phase, ferric chloride solution is used to etch and oxidize the single-crystal metal substrate.

[0075] This invention provides a method for preparing doped graphite, comprising the following steps: (1) Vacuum annealing of a single crystal metal substrate adsorbed with doped element compounds decomposes the doped element compounds and embeds the doped elements into the single crystal metal substrate to obtain a single crystal metal substrate with embedded doped elements. (2) A single crystal metal substrate with embedded doped elements is bonded to a graphite substrate and held at 1000-1500℃ (e.g., 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, 1500℃) for 1-3h (e.g., 1h, 1.5h, 2h, 2.5h, 3h) in a non-oxidizing atmosphere, and then held at 700-900℃ (e.g., 700℃, 750℃, 800℃, 850℃, 900℃) for 4-12h (e.g., 4h, 5h, 6h, 8h, 10h, 12h) and cooled to obtain doped graphite.

[0076] Optionally, the material of the single-crystal metal substrate in step (1) is one of single-crystal nickel, single-crystal iron, single-crystal cobalt, single-crystal platinum, single-crystal palladium, single-crystal nickel-based alloy, single-crystal iron-based alloy, and single-crystal cobalt-based alloy.

[0077] Optionally, the thickness of the single crystal metal substrate in step (1) is 50-500 μm, such as 50 μm, 100 μm, 150 μm, 200 μm, 300 μm, 400 μm, or 500 μm.

[0078] Optionally, the dopant compound in step (1) is a nitrogen-containing compound, which can be decomposed by vacuum annealing.

[0079] Optionally, the dopant compound in step (1) is one or more of melamine, urea, and dicyandiamide.

[0080] Optionally, the graphite substrate in step (1) is graphite paper; the thickness and area are adjusted according to the carbon source and area required to prepare doped graphite.

[0081] Optionally, the thickness of the graphite substrate in step (1) is 1-10 mm, such as 1 mm, 2 mm, 3 mm, 5 mm, 8 mm, or 10 mm.

[0082] Optionally, the method for preparing the single-crystal metal substrate adsorbed with doped element compounds in step (1) is as follows: immerse the single-crystal metal substrate in a solution of doped element compounds, take it out and dry it to obtain the single-crystal metal substrate adsorbed with doped element compounds.

[0083] Alternatively, the soaking time is 3-20 minutes.

[0084] Alternatively, the solvent for the solution of the dopant compound may be an organic solvent, such as ethanol.

[0085] Further optionally, the concentration of the solution of the dopant compound is 0.1-1 mg / ml.

[0086] Alternatively, the drying process can be vacuum drying at a temperature of 60-80°C.

[0087] Optionally, the vacuum annealing temperature in step (1) is 1000-1500℃ (e.g., 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, 1500℃), and the time is 3-10 minutes (e.g., 3 minutes, 5 minutes, 8 minutes, 10 minutes).

[0088] Optionally, the vacuum degree of the vacuum annealing in step (1) is less than or equal to 10 Pa, preferably less than or equal to 3 Pa.

[0089] Optionally, the non-oxidizing atmosphere in step (2) is a non-oxidizing gas stream.

[0090] Further optionally, the flow rate of the non-oxidizing gas stream is 100-500 sccm, such as 100 sccm, 200 sccm, 300 sccm, or 500 sccm.

[0091] Optionally, the non-oxidizing atmosphere in step (2) is a reducing atmosphere; this can better protect graphite from oxidation.

[0092] Further optionally, the reducing atmosphere is a mixture of inert gas and hydrogen.

[0093] Further optionally, the volume ratio of the inert gas to hydrogen is 10:(0.1-3), such as 10:0.1, 10:0.3, 10:0.5, 10:1, 10:2, or 10:3.

[0094] Optionally, in step (2), the temperature is maintained at 1200-1300℃ for 1-3 hours in a non-oxidizing atmosphere, and then maintained at 750-850℃ for 6-10 hours.

[0095] Optionally, the single-crystal metal substrate doped with graphite obtained in step (2) can be peeled off.

[0096] Alternatively, the method for stripping the graphite-doped single-crystal metal substrate is ferric chloride solution etching.

[0097] Further optionally, the method for stripping the doped graphite from the single crystal metal substrate is as follows: the doped graphite obtained in step (2) is immersed in a ferric chloride solution, the nickel sheet is removed, washed, and dried to obtain the doped graphite stripped from the single crystal metal substrate.

[0098] Further optionally, the concentration of the ferric chloride solution is 0.01-0.2 mg / ml.

[0099] Alternatively, the solvent for the ferric chloride solution may be an organic solvent, such as ethanol.

[0100] Further optionally, the soaking time is 12-72 hours, such as 12 hours, 18 hours, 24 hours, 36 hours, 48 ​​hours, or 72 hours.

[0101] Alternatively, the washing may be performed by washing with ethanol and deionized water in sequence.

[0102] Alternatively, the drying process can be vacuum drying at a temperature of 60-80°C.

[0103] Further, optionally, the graphite surface of the doped graphite obtained in step (2) is bonded to a silicon wafer or glass plate, and then immersed in a ferric chloride solution; this can better maintain the integrity of the doped graphite and prevent it from being damaged.

[0104] The doped graphite surface prepared above was qualitatively and quantitatively analyzed by means of SEM, EDS (energy dispersive X-ray spectroscopy), Raman spectroscopy (intensity ratio of D peak and D' peak), XPS (X-ray photoelectron spectroscopy), etc., and the doped graphite was cut open by FIB to observe the cross section.

[0105] Example 1 A method for preparing doped graphite, the process flow diagram is shown below. Figure 1 This includes the following steps: (1) Preparation of nitrogen-embedded single-crystal nickel wafers (1.1) Take 20 mg of melamine powder and put it into a beaker. Pour 50 ml of anhydrous ethanol into the beaker and place it in an ultrasonic machine to sonicate the solution to disperse it evenly, thus obtaining a melamine solution.

[0106] (1.2) Place the single crystal nickel sheet (10mm*10mm*100μm) into the melamine solution in step (1.1), and take it out after 5 minutes to allow the melamine to be fully adsorbed on the surface of the single crystal nickel sheet. Place it in a vacuum drying oven at 60℃ for 5 minutes to allow the alcohol on the surface of the single crystal nickel sheet to be fully evaporated, and obtain the single crystal nickel sheet adsorbed with melamine.

[0107] (1.3) Place the melamine-adsorbed single-crystal nickel sheet from step (1.2) onto the corundum plate in the rapid thermal annealing device, and place the entire device in a vacuum furnace for pre-vacuum treatment. The vacuum time is 15 minutes, and the vacuum degree reaches between 2-3 Pa. Turn on the rapid thermal annealing device and perform vacuum rapid thermal annealing on the single-crystal nickel sheet. After the annealing temperature reaches 1300 degrees and is held for 5 minutes, turn off the rapid thermal annealing device. After the device cools down for 10 minutes, slowly introduce air into the vacuum furnace to make the furnace pressure consistent with the atmospheric pressure. Then, open the vacuum furnace and take out the single-crystal nickel sheet sample. The pre-embedding treatment of the single-crystal nickel sheet is completed, and a single-crystal nickel sheet with embedded nitrogen element is obtained.

[0108] (2) Preparation of single-crystal nickel wafers with nitrogen-doped graphite. Nitrogen-embedded single-crystal nickel sheets and carbon-source graphite paper (20mm*20mm*2mm) are tightly arranged on a corundum plate, with the carbon-source graphite paper on the corundum plate and the single-crystal nickel sheets on the carbon-source graphite paper. After pressing, they are made to make full contact and placed in a CVD furnace. Argon gas is introduced for initial furnace cleaning. After 5 minutes, the flow rates of argon and hydrogen are adjusted to 100 sccm and 10 sccm, respectively. The CVD furnace is rapidly heated to 1300 degrees Celsius and held for 2 hours. Then, it is cooled to 800 degrees Celsius and held for 6 hours to grow nitrogen-doped graphite. After that, the CVD furnace is cooled down until it reaches room temperature. The furnace is then slowly opened and the sample is removed to obtain a single-crystal nickel sheet with nitrogen-doped graphite.

[0109] (3) Nitrogen-doped graphite was obtained by stripping single-crystal nickel sheets. (3.1) After the nitrogen-doped graphite is grown, the graphite is effectively separated from the nickel metal catalyst by using ferric chloride solution. First, 5 mg of ferric chloride is weighed and placed in a 100 ml volumetric beaker, 50 ml of anhydrous ethanol is poured in, and the beaker is placed in an ultrasonic machine to sonicate the solution to disperse it evenly, thus obtaining the ferric chloride solution.

[0110] (3.2) The graphite surface of the nitrogen-doped graphite single crystal nickel wafer is inverted on the silicon wafer to make the graphite and silicon wafer fully adhere, and then placed in ferric chloride solution for 48 hours.

[0111] (3.3) After fully soaking and oxidizing, use flat-tipped tweezers to slowly lift the silicon wafer and the graphite on the surface out of the solution horizontally, and slowly remove the graphite paper on the surface and the nickel sheet remaining underneath, so that the graphite and the bottom silicon wafer can be well bonded.

[0112] (3.4) After taking out the sample, repeatedly put it into alcohol to dissolve the residual ferric chloride on the surface. During the process, keep the silicon wafer in a horizontal state during repeated picking to ensure the integrity of the graphite on the silicon surface. Put it into alcohol and pick it up 3 times. Put the sample into deionized water and repeat the above process 3 times and take it out.

[0113] (3.5) Place the sample with the single crystal nickel sheet removed into a vacuum drying oven and dry it at 60 degrees for 10 minutes to allow the surface water residue to evaporate fully. Then take out the sample and attach conductive tape to the edge of the graphite to prevent the doped graphite from falling off during subsequent experiments.

[0114] Test results and analysis: (1) A photograph of the nitrogen-embedded single-crystal nickel wafer prepared in step (1.3) of this embodiment is shown below. Figure 2 SEM image as follows Figure 3 EDS diagram as follows Figure 4 The elemental contents are shown in Table 1.

[0115] Table 1:

[0116] This indicates that nitrogen has been fully incorporated into the single-crystal nickel wafer.

[0117] (2) The SEM and EDS images of the nitrogen-doped graphite surface away from the single-crystal nickel sheet prepared in step (3.5) of this embodiment are as follows: Figure 5 Raman spectra as follows Figure 6 This indicates that nitrogen doping occurs on the surface of nitrogen-doped graphite away from the single-crystal nickel sheet, and nitrogen doping occurs throughout the entire nitrogen-doped graphite.

[0118] (3) The frictional force test of the nitrogen-doped graphite prepared in step (3.5) of this embodiment is as follows: Figure 7 Compared to undoped graphite (friction test, etc.), the graphite was used as a control. Figure 8 This indicates that the nitrogen-doped graphite prepared in this embodiment still has superlubricating properties.

[0119] Comparative Example 1 In contrast, this invention also employs magnetron sputtering to introduce nitrogen onto a single-crystal nickel wafer.

[0120] A method for preparing doped graphite includes the following steps: (1) Preparation of nitrogen-deposited single-crystal nickel wafers Using a single-crystal nickel wafer as a substrate, the substrate is ultrasonically cleaned with acetone for 10 min, ultrasonically cleaned with anhydrous ethanol for 10 min, rinsed with DI water, dried with nitrogen, dried on a hot plate at 120℃ for 10 min, and then treated with oxygen plasma for 3-5 min. Using a BN ceramic target as the sputtering target, the BN ceramic target was fixed on the magnetron sputtering / electron beam deposition cathode, and the pretreated single-crystal nickel substrate was fixed on the substrate fixture. The substrate was heated to 100°C, and Ar was used as the working gas (flow rate: 10 sccm, working pressure: 0.5 Pa). A radio frequency (RF) magnetron sputtering / electron beam deposition system was used to pre-sputter and clean the target. Then, RF power of 150 W was used to deposit the boron nitride single-crystal nickel substrate for 60 min to obtain the deposited boron nitride.

[0121] (2) The operation of growing nitrogen-doped graphite is the same as step (2) in Example 1. The positional relationship between the carbon source graphite paper and the nitrogen-deposited single-crystal nickel sheet is as follows: Figure 9 The carbon source graphite paper is on the corundum plate, and the single crystal nickel sheet is on the carbon source graphite paper. The side of the single crystal nickel sheet where nitrogen is deposited is in contact with the carbon source graphite paper.

[0122] Test results and analysis: (1) A photograph of the nitrogen-deposited single-crystal nickel wafer prepared in step (1) of this comparative example is shown below. Figure 10 SEM image as follows Figure 11 EDS diagram as follows Figure 12 The total number of elements in the distribution map is as follows: Figure 13 The elemental contents are shown in Table 2.

[0123] Table 2:

[0124] This indicates that nitrogen is deposited on the surface of the single-crystal nickel sheet.

[0125] (2) The EDS image of the nitrogen-doped graphite surface away from the single-crystal nickel sheet prepared in step (2) of this comparative example is shown in the figure. Figure 14 The total number of elements in the distribution map is as follows: Figure 15 The elemental contents are shown in Table 3, and the Raman spectra are shown below. Figure 16 XPS graph as shown Figure 17 .

[0126] Table 3:

[0127] This indicates that the surface of the nitrogen-doped graphite away from the single-crystal nickel sheet is not doped with nitrogen.

[0128] (3) The EDS diagram of the cross-section of the nitrogen-doped graphite in the thickness direction prepared in step (2) of this comparative example is shown in the figure. Figure 18 The total number of elements in the distribution map is as follows: Figure 19 The elemental contents are shown in Table 4.

[0129] Table 4:

[0130] This indicates that nitrogen-doped graphite does not have nitrogen doping in the thickness direction, meaning that nitrogen-doped graphite was not prepared in this comparative example.

[0131] (4) The EDS plot of the nitrogen-doped graphite obtained in step (2) of this comparative example is shown in the thickness direction line scan. Figure 20 Element distribution map as follows Figure 21 This also indicates that nitrogen-doped graphite does not have nitrogen doping in the thickness direction, meaning that nitrogen-doped graphite was not prepared in this comparative example.

[0132] Comparative Example 2 In contrast, the present invention also adjusts the temperature at which nitrogen-doped graphite is grown.

[0133] A method for preparing doped graphite includes the following steps: (1) Step (1) is the same as in Example 1.

[0134] (2) Nitrogen-embedded single-crystal nickel sheets and carbon source graphite paper (20mm*20mm*2mm) are tightly arranged on a corundum plate, with the carbon source graphite paper on the corundum plate and the single-crystal nickel sheets on the carbon source graphite paper. After pressing, they are made to make full contact. They are then placed in a CVD furnace, and argon gas is introduced for the initial furnace in-furnace rinsing treatment. After 5 minutes, the flow rates of argon and hydrogen are adjusted. The argon flow rate is 100 sccm and the hydrogen flow rate is 10 sccm. The CVD furnace is rapidly heated to 1300 degrees and held for 6 hours. After growing nitrogen-doped graphite, the CVD furnace begins to cool down until it reaches room temperature. Then, the furnace is slowly opened and the sample is taken out to obtain a single-crystal nickel sheet with nitrogen-doped graphite.

[0135] (3) Step (3) is the same as in Example 1.

[0136] Test results and analysis: (1) The SEM image of the nitrogen-doped graphite surface away from the single-crystal nickel sheet prepared in step (2) of this comparative example is shown below. Figure 22 EDS diagram as follows Figure 23 The total number of elements in the distribution map is as follows: Figure 24 The elemental contents are shown in Table 5.

[0137] Table 5:

[0138] This indicates that the surface of the nitrogen-doped graphite away from the single-crystal nickel sheet is not doped with nitrogen.

[0139] (2) The EDS diagram of the cross-section of the nitrogen-doped graphite in the thickness direction prepared in step (2) of this comparative example is shown in the figure. Figure 25 , spectrum Figure 4 Elemental contents are shown in Table 6, and the spectrum is also shown. Figure 5 Element distribution map as follows Figure 26 , spectrum Figure 5 The elemental contents are shown in Table 7.

[0140] Table 6:

[0141] Table 7:

[0142] This indicates that the single-crystal nickel sheet has a small amount of nitrogen doping, while nitrogen-doped graphite has almost no nitrogen doping, meaning that nitrogen-doped graphite was not prepared in this comparative example.

[0143] (3) The EDS plot of the nitrogen-doped graphite prepared in step (2) of this comparative example is shown in the thickness direction line scan. Figure 27 Element distribution map as follows Figure 28 This also indicates that the single-crystal nickel sheet has a small amount of nitrogen doping, while nitrogen-doped graphite has almost no nitrogen doping, meaning that nitrogen-doped graphite was not prepared in this comparative example.

[0144] (4) The optical mirror image of the nitrogen-doped graphite near the single-crystal nickel sheet prepared in step (3) of this comparative example is shown below. Figure 29 This indicates that the surface of the doped graphite near the single-crystal nickel sheet clearly shows traces of nickel annealing; the Raman spectra of the light and dark areas in the optical microscopy image are as follows. Figure 30 (The top image shows the light-colored area, and the bottom image shows the dark-colored area), XPS chart as follows. Figure 31 (The top image shows the light-colored area, and the bottom image shows the dark-colored area), indicating that nitrogen elements will appear at the connection between the doped graphite and the single-crystal nickel sheet.

[0145] This comparative example illustrates that nitrogen is not suitable for uniform doping in graphite at high temperatures (1300℃), and carbon has a reducing effect on nitrogen, inhibiting nitrogen doping in graphite.

[0146] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of the present invention.

Claims

1. A method for preparing doped graphite, characterized in that, Includes the following steps: (1) Vacuum annealing of a single-crystal metal substrate adsorbed with doped element compounds to obtain a single-crystal metal substrate with embedded doped elements; (2) The single crystal metal substrate with embedded doped elements is bonded to the graphite substrate, and kept at 1000-1500℃ for 1-3h in a non-oxidizing atmosphere, and then kept at 700-900℃ for 4-12h. After cooling, doped graphite is obtained.

2. The preparation method according to claim 1, characterized in that, The material of the single-crystal metal substrate in step (1) is one of single-crystal nickel, single-crystal iron, single-crystal cobalt, single-crystal platinum, single-crystal palladium, single-crystal nickel-based alloy, single-crystal iron-based alloy, and single-crystal cobalt-based alloy; The graphite substrate in step (1) is graphite paper; The dopant compound in step (1) is a nitrogen-containing compound, which can be decomposed by vacuum annealing; or, the dopant compound in step (1) is one or more of melamine, urea, and dicyandiamide.

3. The preparation method according to claim 1, characterized in that, The method for preparing the single-crystal metal substrate adsorbed with doped element compounds in step (1) is as follows: immerse the single-crystal metal substrate in a solution of doped element compounds, take it out and dry it to obtain the single-crystal metal substrate adsorbed with doped element compounds.

4. The preparation method according to claim 3, characterized in that, The soaking time is 3-20 minutes; The concentration of the solution of the doped element compound is 0.1-1 mg / ml.

5. The preparation method according to claim 1, characterized in that, The vacuum annealing temperature in step (1) is 1000-1500℃, and the time is 3-10 minutes.

6. The preparation method according to claim 1, characterized in that, The non-oxidizing atmosphere mentioned in step (2) is a non-oxidizing gas stream; The non-oxidizing atmosphere mentioned in step (2) is a reducing atmosphere; The reducing atmosphere is a mixture of inert gas and hydrogen. The volume ratio of the inert gas to hydrogen is 10:(0.1-3).

7. The preparation method according to claim 1, characterized in that, The single-crystal metal substrate doped with graphite obtained in step (2) is peeled off; The method for removing graphite-doped single-crystal metal substrates is etching with ferric chloride solution. The specific method for stripping the doped graphite from the single crystal metal substrate is as follows: the doped graphite obtained in step (2) is immersed in ferric chloride solution, the nickel sheet is removed, washed, and dried to obtain the doped graphite stripped from the single crystal metal substrate.

8. The preparation method according to claim 7, characterized in that, The concentration of the ferric chloride solution is 0.01-0.2 mg / ml; The soaking time is 12-72 hours; The graphite surface of the doped graphite obtained in step (2) is bonded to a silicon wafer or glass plate and then immersed in a ferric chloride solution.

9. Doped graphite prepared by the preparation method according to any one of claims 1-8.

10. The application of the doped graphite according to claim 9 in the preparation of superlubricated micro-generators, superlubricated relays or nano-switches.

Images