Preparation method and device of doped diamond powder

Abstract

The invention provides a preparation method and device of doped diamond powder, and relates to the technical field of semiconductor materials. The preparation method of the doped diamond powder provided by the invention comprises the following steps: taking a cleaned diamond powder substrate, and paving the cleaned diamond powder substrate on a molybdenum circle; the method comprises the following steps: placing a molybdenum circle on a central copper table of microwave plasma chemical vapor deposition (MPCVD) equipment, closing a sealing cover of the equipment, vacuumizing the interior of the equipment, starting the equipment, respectively introducing hydrogen, methane, diborane or diborane / nitrogen mixed gas, and depositing doped diamond on the surface of a diamond powder substrate to obtain doped diamond powder. After the doped diamond powder is prepared, the hybridization mode of carbon at the tail end of the surface of the doped diamond powder is changed through follow-up treatment. The prepared doped diamond powder has enough conductivity, the particle size of the powder and the content of doped boron and nitrogen elements can be adjusted and controlled according to needs, and the high-specific-surface-area and surface-functionalized diamond powder which is uniform in doping degree, different in conductivity and high in specific surface area is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor materials, and in particular to a method and a device for preparing doped diamond powder. Background Art

[0002] Traditional diamonds are not conductive, but by doping other atoms in diamonds to change their electrical, optical and quantum chemical properties, they can become good semiconductor materials or have more special functions, expanding the application range of diamonds. At present, the two most commonly used doping elements are boron and nitrogen. By doping boron into the diamond lattice, diamond can be transformed from an insulator to a typical p-type semiconductor with metal-like conductive properties, which can be used as an electrode material. The incorporation of nitrogen will form specific defect structures in diamonds, such as nitrogen-vacancy (NV) color centers. This color center has good optical stability and long coherence time at room temperature, can be manipulated by lasers and microwaves, and shows great application potential in the field of quantum detection, which can realize the precise measurement of physical quantities such as magnetic fields, electric fields, temperature, and stress. Therefore, different doping elements will give diamonds different characteristics and functions. Compared with traditional materials, boron-doped diamond electrodes have a wide potential window, low background current and extremely high physical and chemical stability in water and non-aqueous electrolytes. Based on the above advantages, the development and application of doped diamond electrodes have developed rapidly. It can not only be used for wastewater treatment and purification, but also has been widely used in environmental monitoring and biomedical measurements.

[0003] In addition, boron-nitrogen co-doping can make diamond not only have semiconductor properties, but also have special optical properties brought by surface nitrogen-vacancies. Compared with boron-doped diamond electrodes, boron-nitrogen doped diamond not only has a wider potential window and faster electron transfer rate, but the synergistic effect of boron-nitrogen co-doping can also improve the electrocatalytic performance of the electrode. The incorporation of the two elements can adjust the electronic structure of the carbon material, polarize the carbon atoms near boron and nitrogen, and produce more strain sites and defect sites. These polarized carbon atoms, strain sites and defect sites can serve as active sites for electrocatalysis, increase the active area of ​​the electrode surface, and further improve the electrochemical performance. At the same time, boron-nitrogen co-doped diamond electrodes have better performance in photoelectric synergistic catalysis.

[0004] Traditional diamond electrodes are usually grown and deposited on flat substrates such as silicon, niobium, and titanium. Their shapes are relatively fixed, and it is difficult to meet the requirements for the shape of doped diamond electrodes under complex conditions. Therefore, in order to obtain doped diamond electrodes with other complex shapes or even three-dimensional structures, using boron (nitrogen) doped diamond powder to prepare electrodes is a promising method.

[0005] The use of high temperature and high pressure method to directly synthesize boron (nitrogen) doped diamond powder and CVD method to prepare boron (nitrogen) doped diamond film, and then mechanical grinding to obtain doped diamond powder has the following disadvantages: First, it is necessary to grow a boron (nitrogen) doped diamond film first, and it takes a long time to grow to obtain a film sample with a certain thickness. Second, the grinding process will cause the surface structure of the diamond to be destroyed, affecting the performance of the doped diamond powder. Therefore, how to quickly and mass-produce boron (nitrogen) doped diamond powder with surface uniformity and controllable surface structure and morphology is still a problem that needs to be solved urgently. Summary of the invention

[0006] In order to solve the above problems, the present invention aims to provide a method and device for preparing doped diamond powder. The prepared boron (nitrogen) doped diamond powder has sufficient conductivity, and the morphology, particle size and content of the doped boron (nitrogen) element of the powder can be adjusted as needed to obtain doped diamond powder with different morphological characteristics and high surface uniformity. The technical solution of the present invention is as follows: A method for preparing doped diamond powder, the method comprising the following steps: (1) Take diamond powder and spread it flat on the molybdenum circle; (2) Place a molybdenum circle on the central copper table of a microwave plasma chemical vapor deposition (MPCVD) device, close the sealing cover of the device, evacuate the interior of the device and start the device, introduce hydrogen, methane and diborane or a diborane / nitrogen mixed gas, and obtain doped diamond powder by depositing doped diamond on the surface of the diamond powder substrate. Preferably, the diamond powder is washed before being placed in step (1), and the washing process is to wash the diamond powder with aqua regia (HCl:HNO3=3:1), hydrogen peroxide, deionized water, and acetone, and the washing time is 25-35min, 20-40min, 5-15min, and 5-15min, respectively. Preferably, there is a groove in the center of the molybdenum circle for placing and fixing the diamond powder substrate.

[0007] Preferably, in step (2), the flow ratio of hydrogen, methane and diborane is (91-104):4:(1-5); The flow ratio of hydrogen, methane, and diborane / nitrogen mixed gas is (91-104):4:(1-10); In the step (2), during the deposition process, the equipment temperature is 780-810° C., the system pressure is 90-100 torr, and the microwave power is 3500-4000 W.

[0008] Further preferably, the concentration of the hydrogen, methane, diborane, and diborane / nitrogen mixed gas is > 99.99%, Diborane is composed of B2H4 and H2 in a volume ratio of (0.5-3): (97-99); diborane / nitrogen mixed gas is composed of N2, B2H4, H2 in a volume ratio of (0.5-1.5): (0.5-1.5): (97-99); More preferably, diborane is composed of B2H4 and H2 in a volume ratio of 1:99, and the diborane / nitrogen mixed gas is composed of N2, B2H4, H2 in a volume ratio of 1:1:98.

[0009] Preferably, in step (2), during the deposition process, the equipment temperature is 780-810° C., the system pressure is 90-100 torr, and the microwave power is 3500-4000 W.

[0010] Preferably, the subsequent treatment includes heat treatment of the doped diamond powder in oxygen plasma for 1 h to produce oxygen termination (C-sp 2 ), heat treated in hydrogen plasma for 1 h to produce hydrogen termination (C-sp 3 ).

[0011] The method for preparing doped diamond powder adopts a diamond powder deposition device, which includes a base, a vibration container and a vibrator. The base is equipped with a vibration container, and the bottom of the vibration container is equipped with a vibrator. The vibration container is made of molybdenum alloy, or the bottom of the vibration container is made of molybdenum alloy.

[0012] Preferably, the vibration container comprises an oscillation ring, a vibration base plate and a movable cup, the vibration base plate is fixedly connected to the lower end of the oscillation ring, the upper end of the oscillation ring is connected to the base, and the vibrator is installed at the bottom of the vibration base plate; the movable cup is made of molybdenum alloy, and the movable cup is detachably mounted on the vibration base plate; Further preferably, a recessed platform is provided on the vibration base plate, and the movable cup is threadedly screwed into the recessed platform.

[0013] Preferably, a support platform is provided at the upper end of the base, a flange extending outward is provided at the upper end of the oscillation ring, and the support platform and the flange are connected by an elastic member.

[0014] Further preferably, the vibrator is a vibration motor; preferably, the vibrator is an ultrasonic vibrator.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses diamond powder as a substrate to directly deposit doped diamond on the particles, and can obtain doped diamond powder with a large specific surface area and good surface uniformity in a small growth space (10 mm×20 mm×1 mm). Due to the flexibility of the powder morphology, the present invention can be plated on objects of different three-dimensional shapes to prepare electrodes, breaking through the limitations of traditional electrode shapes (such as from flat plates and meshes to complex three-dimensional shapes). In addition, the boron-doped diamond powder material itself has good stability and corrosion resistance, which allows it to be used in various harsh environmental conditions while ensuring that it has a sufficiently long service life, reducing maintenance costs and replacement frequency, thereby reducing long-term operating costs. Compared with the existing technology, it is a new strategy with broad application prospects.

[0016] 2. Diamond powder in the prior art has different uses, such as being used to make molds (non-conductive), while the doped powder in the present invention is used for electrode preparation, which has better effects than conventional powder. Due to its tiny particle size, high surface area, controllable morphology, and good surface uniformity, it can provide larger active sites, thereby enhancing the reaction efficiency and catalytic activity of the electrode, and can solve some problems faced by the in-situ growth method (such as being limited by the size of the furnace and the limited growth shape).

[0017] 3. Diamond particles are directly used as seeds for growth. Only a layer of doped diamond film with a thickness of hundreds of nanometers to several microns needs to be deposited to obtain a powder sample with good conductive properties, which can greatly shorten the growth cycle, save time and reduce production costs.

[0018] 4. By installing a vibrator at the bottom of the vibration container, the diamond powder substrate in the vibration container will vibrate continuously during the preparation process. The diamond powder substrate is in a continuous vibration suspension state. During the entire deposition preparation process, the boron atoms are evenly wrapped on the diamond powder substrate, thereby forming boron-doped diamond powder.

[0019] 2. The movable cup is detachably mounted on the vibration base plate. When in use, the diamond powder substrate is placed into the movable cup. The movable cup vibrates along with the vibration base plate. After the deposition preparation is completed, the movable cup is removed to facilitate pouring out the boron-doped diamond powder in the movable cup. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the Raman spectrum of the doped diamond powder prepared in Example 1; Figure 2 This is a scanning electron microscope image of the doped diamond powder prepared in Example 1; Figure 3 The cyclic voltammogram of the doped diamond powder prepared in Example 1 after heat treatment; Figure 4 The Raman spectrum of the product prepared in Example 2; Figure 5 The Raman spectrum of the product prepared in Example 3; Figure 6 The state diagram of the present invention before and after deposition, the left side is the original yellow powder, and the right side is the grown black powder; Figure 7 It is a schematic diagram of the three-dimensional structure of an embodiment of a deposition device of the present invention; Figure 8 is a schematic cross-sectional structural diagram of an embodiment of a deposition device of the present invention; In the figure, there are a base 10 , a support platform 11 , an elastic member 12 , an oscillation ring 20 , a flange 21 , a vibration container 30 , a vibration bottom plate 40 , a screw 41 , a recessed platform 42 , a vibrator 50 , an ultrasonic source 60 , and a movable cup 70 . DETAILED DESCRIPTION

[0021] The following will be combined with the specific embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. The embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0022] Example 1 Weigh 2g of diamond powder with a particle size of 5μm and place it in a 100ml beaker. Add 50ml of aqua regia and ultrasonicate for 30min at 40℃. Then transfer the diamond powder to hydrogen peroxide and ultrasonicate for 30min under the same conditions to remove the graphite phase and metal impurities in the diamond powder. Finally, wash it in deionized water and acetone for 10min respectively to remove oil and other impurities.

[0023] Take a molybdenum circle with a diameter of 60mm and a thickness of 5.5mm and place it in the center of the laser cutting machine. Set the scanning area to 40×40mm, the laser intensity to 95%, and scan continuously for 30 minutes until a 10×20×1mm groove is scanned in the center of the molybdenum circle. After the above process is completed, use sandpaper with a roughness of 400 mesh to polish the molybdenum circle to remove surface impurities, and scan it under the laser cutting machine for 2 minutes to increase the surface roughness.

[0024] After cleaning, lay the diamond powder flat and place it in the groove of the molybdenum circle. Use a scraper to scrape off the excess diamond powder on the surface to ensure the flatness of the surface of the diamond powder substrate.

[0025] Place the molybdenum circle with diamond powder substrate on the central copper table of the microwave plasma chemical vapor deposition (MPCVD) equipment, close the sealing cover of the equipment, evacuate the inside of the equipment to vacuum, set the system pressure to 90 torr, and start the equipment with a microwave pressure of 3500W.

[0026] After the equipment is started, the cavity pressure and the corresponding microwave power are gradually increased after the low-pressure ignition to make the plasma ball reach the appropriate state, and the shape and color of the ball are observed to see if they are normal. After the plasma ball is generated normally, the equipment increases the pressure and power according to the set parameters until the temperature stabilizes at around 800°C.

[0027] While the equipment automatically increases the gas pressure and power, hydrogen, methane and diborane are introduced respectively, with the gas volume not exceeding 10sccm each time until the flow ratio reaches 100:4:4. The entire ventilation process lasts about 15 minutes, which can effectively prevent the tiny diamond particles from being blown away. After the temperature stabilizes, the diamond powder substrate grows and deposits for 3 hours.

[0028] The concentrations of the hydrogen, methane, diborane, and diborane / nitrogen mixed gas are greater than 99.99%, and diborane is composed of B2H4 and H2 in a volume ratio of 1:99.

[0029] After the growth is completed, the pressure and power of the equipment are reduced until the temperature stabilizes at around 700°C. At the same time, the introduction of methane and diborane is stopped, and only hydrogen / oxygen is introduced for 2 hours of heat treatment to obtain boron-doped diamond powder.

[0030] The prepared doped diamond powder was characterized using Raman spectroscopy, scanning electron microscopy and electrochemical workstation. The Raman spectroscopy scanning wavelength was 785nm. Figure 1 As shown, except for the -1 In addition to the characteristic diamond peaks, two peaks at 475 cm -1 Nearby and 1220cm -1 The reason for the two peaks is related to boron doping, and the peak positions can be used to estimate the boron doping content in the lattice. At the same time, due to the influence of the Fano effect, the peak at 1332cm -1 The characteristic diamond peak at 1500-1600cm -1 Found near sp 2 Peaks related to carbon impurities. These phenomena all prove that boron is doped into diamond and the product is doped diamond.

[0031] The particle size was measured by scanning electron microscopy, e.g. Figure 2 shown.

[0032] The heat-treated doped diamond powder was tested with the aid of an electrochemical workstation to obtain its cyclic voltammetry curve. The solution used was 10 mM K3[Fe(CN)6] + 0.1 M KCl. Figure 3 As shown in the figure, after the powder was treated with oxygen plasma, [Fe(CN)6]3 - / [Fe(CN)6] 4 - The redox process becomes very slow and the reversibility is poor. The separation between the anodic potential (Ea) and cathodic potential (Ec) peaks is large, and the line is a typical c-sp 2 In contrast, the powder treated with hydrogen plasma showed a fast redox couple response, chemically and electrochemically reversible, and a small separation between Ea and Ec, showing a typical c-sp 3 .

[0033] See the actual pictures before and after deposition. Figure 6 .

[0034] Example 2 The preparation method is basically the same as that of Example 1, except that the flow ratio of hydrogen, methane and diborane is adjusted to 100:4:8 sccm.

[0035] This method increases the amount of diborane introduced, so the Raman spectrum of the product (Figure 4) shows that the -1 Nearby and 1220cm -1 The peak is more obvious, located at 1332cm -1 The intensity of the diamond peak at the lattice is weakened, and the shift of the diamond peak is more obvious, which indicates that more boron elements are incorporated into the crystal lattice.

[0036] Example 3 The preparation method is basically the same as that of Example 1, except that the flow ratio of hydrogen, methane and diborane is adjusted to 100:4:1 sccm.

[0037] This method reduces the amount of diborane introduced, so the Raman spectrum of the product ( Figure 5 ) shows that at 475cm -1 Nearby and 1220cm -1 There is no obvious characteristic peak, only one at 1332cm -1 The diamond peak is not shifted, which indicates that almost no boron element is incorporated into the crystal lattice.

[0038] Example 4 See also Figure 7-8 The diamond powder deposition device used in the methods of Examples 1-4 includes a base 10, a vibration container 30 and a vibrator 50. The vibration container 30 is installed on the base 10, and the vibrator 50 is installed at the bottom of the vibration container 30. The vibration container 30 is made of molybdenum alloy, or the bottom of the vibration container 30 is made of molybdenum alloy.

[0039] The base 10 is used to fix and support the vibration container 30, and the vibrator 50 is used to vibrate the vibration container 30 so that the diamond powder substrate in the vibration container 30 can vibrate continuously. During the entire deposition preparation process, boron atoms are evenly wrapped on the diamond powder substrate to form boron-doped diamond powder.

[0040] The vibration container 30 includes an oscillation ring 20, a vibration base plate 40 and a movable cup 70. The vibration base plate 40 is fixedly connected to the lower end of the oscillation ring 20, the upper end of the oscillation ring 20 is installed and connected to the base 10, and the vibrator 50 is installed at the bottom of the vibration base plate 40; the movable cup 70 is made of molybdenum alloy, and the movable cup 70 is detachably installed on the vibration base plate 40.

[0041] When in use, the diamond powder substrate is put into the movable cup 70. The movable cup 70 vibrates along with the vibration base plate 40. After the deposition preparation is completed, the movable cup 70 is removed to facilitate pouring out the boron-doped diamond powder in the movable cup 70.

[0042] In one embodiment, a recessed platform 42 is disposed on the vibration base plate 40 , and the movable cup 70 is screwed into the recessed platform 42 .

[0043] In addition to being installed on the vibration base plate 40 by means of threaded connection, the movable cup 70 can also be installed on the vibration base plate 40 by means of other methods, for example, the movable cup 70 is installed on the vibration base plate 40 by means of a rotating buckle.

[0044] In this embodiment, the oscillation ring 20 is a bellows-shaped structure. The oscillation ring 20 can not only play the role of the side wall of the container, but also enable the oscillation ring 20 to elastically expand and contract axially, thereby enabling the vibration base plate 40 to vibrate up and down.

[0045] When in use, the diamond powder substrate is placed on the vibration base plate 40 .

[0046] A support platform 11 is provided at the upper end of the base 10, and a flange 21 extending outward is provided at the upper end of the oscillation ring 20, and the support platform 11 and the flange 21 are connected by an elastic member 12. The elastic member 12 is provided to reduce vibration of the oscillation ring 20, so that the vibration of the oscillation ring 20 is not transmitted to the base 10.

[0047] In this embodiment, the elastic member 12 may be a rubber ring or a plurality of rubber pads. The elastic member 12 may be bonded between the support platform 11 and the flange 21 .

[0048] In one embodiment, the vibrator 50 is a vibration motor.

[0049] In another embodiment, the vibrator 50 is an ultrasonic vibrator. Figure 8When the ultrasonic vibrator is installed, a screw 41 is fixed to the lower side of the vibration base plate 40, and the ultrasonic vibrator is screwed to the screw 41, and the ultrasonic vibrator is also bonded to the vibration base plate 40. When in use, the ultrasonic vibrator is electrically connected to the ultrasonic source 60 through a wire.

[0050] The working principle or action process is as follows: When preparing doped diamond powder by deposition, the deposition device is installed in a microwave plasma chemical vapor deposition (MPCVD) device, and an appropriate amount of cleaned diamond powder substrate is taken and laid flat on the vibration base plate 40 or in the movable cup 70. The vibrator 50 is powered on, and the diamond powder substrate in the vibration container vibrates continuously. The diamond powder substrate is in a continuous vibration suspension state, and the sealing cover of the device is closed. After the inside of the device is evacuated to a vacuum, the device is started, and hydrogen, methane and doping gas (diborane or diborane / nitrogen mixed gas) are introduced respectively to make the boron atoms evenly wrapped on the diamond powder substrate, thereby forming boron-doped diamond powder.

[0051] The technical solution of the present invention is explained through the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above specific embodiments to be implemented. Any improvements made by technicians in the relevant field based on the present invention, or equivalent replacement of the materials selected by the present invention, etc., fall within the scope of protection of the patent.

Claims

1. A method for preparing doped diamond powder, characterized in that: The method comprises the following steps: (1) Take diamond powder and spread it flat on the molybdenum circle; (2) Place a molybdenum circle on the center table of a microwave plasma chemical vapor deposition device, close the sealing cover of the device, evacuate the interior of the device and start the device, introduce hydrogen, methane, diborane or a diborane / nitrogen mixed gas, and obtain doped diamond powder by depositing boron or nitrogen-doped diamond on the surface of diamond powder particles.

2. The method for preparing doped diamond powder according to claim 1, characterized in that: The diamond powder is cleaned and then placed in step (1). The cleaning process is to clean the diamond powder with aqua regia, hydrogen peroxide, deionized water, and acetone, respectively. The cleaning time is 25-35 minutes, 20-40 minutes, 5-15 minutes, and 5-15 minutes, respectively.

3. The method for preparing doped diamond powder according to claim 1, characterized in that: There is a groove in the center of the molybdenum circle for placing and fixing the diamond powder substrate.

4. The method for preparing doped diamond powder according to claim 1, characterized in that: In the step (2), The flow ratio of hydrogen, methane and diborane is (91-104):4:(1-5); The flow ratio of hydrogen, methane, and diborane / nitrogen mixed gas is (91-104):4:(1-10); In the step (2), during the deposition process, the equipment temperature is 780-810° C., the system pressure is 90-100 torr, and the microwave power is 3500-4000 W.

5. The method for preparing doped diamond powder according to claim 1, characterized in that: The concentration of hydrogen, methane, diborane, and diborane / nitrogen mixed gas is > 99.99%, Diborane is composed of B2H4 and H2 in a volume ratio of (0.5-3): (97-99); diborane / nitrogen mixed gas is composed of N2, B2H4, H2 in a volume ratio of (0.5-1.5): (0.5-1.5): (97-99); Preferably, the composition of diborane is: B2H4 and H2 in a volume ratio of 1:99, and the diborane / nitrogen mixed gas is composed of N2, B2H4, H2 in a volume ratio of 1:1:

98.

6. The method for preparing doped diamond powder according to claim 1, characterized in that: The subsequent treatment of the method includes heat treating the doped diamond powder in oxygen plasma for 1 hour to produce oxygen termination, and heat treating the doped diamond powder in hydrogen plasma for 1 hour to produce hydrogen termination.

7. The diamond powder deposition device used in the method for preparing doped diamond powder according to any one of claims 1 to 6 is characterized in that: The device comprises a base (10), a vibration container (30) and a vibrator (50); the vibration container (30) is mounted on the base (10); the vibrator (50) is mounted on the bottom of the vibration container (30); the vibration container (30) is made of a molybdenum alloy, or the bottom of the vibration container (30) is made of a molybdenum alloy.

8. The diamond powder deposition device according to claim 7, characterized in that: The vibration container (30) comprises an oscillating ring (20), a vibrating base plate (40) and a movable cup (70); the vibrating base plate (40) is fixedly connected to the lower end of the oscillating ring (20); the upper end of the oscillating ring (20) is connected to the base (10); and the vibrator (50) is installed at the bottom of the vibrating base plate (40); the movable cup (70) is made of molybdenum alloy and is detachably installed on the vibrating base plate (40); Preferably, a concave platform (42) is provided on the vibration base plate (40), and the movable cup (70) is screwed into the concave platform (42).

9. The diamond powder deposition device according to claim 7, characterized in that: A support platform (11) is provided at the upper end of the base (10), a flange (21) extending outward is provided at the upper end of the oscillation ring (20), and the support platform (11) and the flange (21) are connected via an elastic member (12).

10. The diamond powder deposition device according to claim 7, characterized in that: The vibrator (50) is a vibration motor; preferably, the vibrator (50) is an ultrasonic vibrator.

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