WO2018176217A1

WO2018176217A1 - Method of preparing high-density diamond thin film

Info

Publication number: WO2018176217A1
Application number: PCT/CN2017/078429
Authority: WO
Inventors: 唐永炳; 王陶; 张文军
Original assignee: 深圳先进技术研究院
Priority date: 2017-03-28
Filing date: 2017-03-28
Publication date: 2018-10-04

Abstract

A method of preparing a high-density diamond thin film, comprising the following steps: (1) performing a surface-charging process on a surface of a cemented carbide substrate, wherein the surface-charging process comprises a positive or negative charging process; (2) preparing a diamond suspension: adding an organic acid or an amine-containing compound to water to obtain a pretreatment liquid; adding diamond powder to the pretreatment liquid and uniformly dispersing to obtain a nano-diamond suspension; wherein the organic acid comprises one or more of oxalic acid and citric acid, and the amine-containing compound is selected from glutamic acid and aspartic acid, and one or more aliphatic amines having 2 to 5 carbon atoms; (3) placing the surface-charged substrate in the nano-diamond suspension and performing ultrasonic vibration such that the nano-diamond adsorbs on the surface of the substrate, wherein the charge of the nano-diamond suspension is opposite to the charge of the substrate; (4) using a chemical vapor deposition apparatus, growing a diamond thin film on the substrate obtained in step (3).

Description

Method for preparing high-density diamond film

Technical field

The invention belongs to the technical field of nano diamonds, and in particular relates to a preparation method of a high density diamond film.

Background technique

As the hardest material in the world, and with low sliding friction coefficient and highest elastic properties, diamond is considered to be the ideal coating material for cutting tools and other mechanical components in hard alloys (WC-Co). The growth of diamond on a substrate such as a titanium alloy can greatly improve the wear resistance and processing efficiency of tools and components.

However, when depositing a diamond film on a cemented carbide substrate, there is often a problem that the diamond nucleation density is low and the film is not dense, resulting in a hole at the interface between the film and the substrate, so that the bonding force between the film and the substrate is poor. In addition, when the film is not dense, cobalt in the cemented carbide diffuses from the substrate into the diamond film, catalyzing the formation of graphite, which deteriorates the quality of the diamond film. Therefore, how to improve the nucleation density of the diamond film is one of the problems to be solved.

Methods for increasing the density of diamond nucleation include application of an intermediate layer, surface ion implantation, application of a bias voltage, and implantation of diamond powder, etc., and the most effective method to date has been to apply a bias power supply to the susceptor, using the highest form of this method. The nuclear density can reach 0.9×10 ¹⁰ cm ^-2 , but the bias method can not be applied to complex shape substrates, such as sharp edges, complex molds, etc., and the industrial applicability is poor; while other methods have lower diamond nucleation density. Often around 10 ⁷ cm ^-2 .

Summary of the invention

In view of the above, the present invention provides a method for preparing a high-density diamond film, which is suitable for deposition on a workpiece of any shape, in view of the disadvantages of the prior art that the nucleation density is low and the diamond film is not suitable for deposition on a complex shaped workpiece. The diamond film can make the diamond film have a nucleation density of about 10 ¹⁰ cm ^-2 on the substrate, thereby growing a highly dense diamond film.

In a first aspect, the present invention provides a method of preparing a high density diamond film, comprising the steps of:

(1) taking a cemented carbide substrate and performing surface charge treatment on the surface thereof, the surface charge treatment comprising positive or negative electrification;

(2) preparing a diamond suspension: adding an organic acid or an amine-containing compound to water to obtain a pretreatment liquid; adding the diamond raw powder to the pretreatment liquid and uniformly dispersing to obtain a nanodiamond suspension; The organic acid includes one or more of oxalic acid and citric acid, and the amine-containing compound is selected from one or more of glutamic acid and aspartic acid, and an aliphatic amine having 2 to 5 carbon atoms. Species

(3) placing the surface-charged substrate in the nano-diamond suspension for ultrasonic vibration, so that the nano-diamond is adsorbed on the surface of the substrate, wherein the nano-diamond suspension is charged Sexuality is opposite to the electrical properties of the substrate;

(4) A diamond thin film is grown on the substrate obtained in the step (3) by using a chemical vapor deposition apparatus.

In the present invention, the diamond raw powder is added to a pretreatment solution containing an organic acid or an amine-containing compound to obtain a nanodiamond suspension. Under the action of organic acid or amine-containing compound, the obtained nano-diamond can be uniformly dispersed and stably suspended in the solution, and the hydrated particle size is in a small range, which solves the problem of agglomeration and sedimentation of the diamond raw powder, and the obtained nanometer. The diamond surface can have different electrical properties. Wherein, when the organic acid is added to water, the surface of the obtained nanodiamond is negatively charged; when the amine group-containing compound is added to water, the surface of the obtained nanodiamond is positively charged.

The invention provides a method for electrostatically attracting implanted diamond seeds, and ultrasonically oscillates the substrate after surface electro-oxidation treatment with a suspension of nano-diamonds whose surface is electrically opposite, and performs diamond pre-nucleation on the surface of the substrate. It can effectively increase the nucleation density of the diamond film and make the nucleation density above 10 ¹⁰ cm ^-2 , which is 20-1000 times reported at the present stage. At such a high nucleation density, a highly dense diamond film can be grown. Improve the bonding ability between the film and the substrate.

Further, when the organic acid is contained in the pretreatment liquid, the substrate is subjected to a positive electrolysis treatment.

Wherein, the positive electro-chemical treatment is surface hydrotreating, specifically comprising: placing the substrate in a vacuum chamber of the coating device, introducing high-purity hydrogen, controlling the gas pressure in the vacuum chamber to be 0.5-20 kPa, and the substrate temperature being 900-1100 °C. The hydrogenation treatment at a higher temperature (900-1100 °C) on the one hand hydrogenates the surface of the cemented carbide substrate, and the surface is positively charged; on the other hand, the cobalt on the surface of the cemented carbide substrate can be removed to reduce the diffusion of the subsequent cobalt.

Preferably, the hydrogenation treatment time is from 0.5 to 1 h. Hydrogen forms hydrogen radicals in the plasma and interacts with the surface of the substrate to connect the outermost atomic layer on the surface of the substrate to the hydrogen atom. After the surface hydrogenated substrate is placed in water, the surface of the substrate is positively charged.

Further, when the pretreatment liquid contains the amine group-containing compound, the substrate is subjected to a negative electron treatment.

Wherein, the negative electro-oxidation treatment comprises any one of the following methods: oxidative etching of the cemented carbide substrate with a Caro mixed acid; or, the cemented carbide substrate is placed in an oxygen plasma cleaning machine for cleaning.

Further, the oxidizing etching time is 0.5 to 1 min. The oxygen plasma cleaning time may be 2-15 min.

Specifically, the Caro mixed acid (H ₂ SO ₄ :H ₂ O ₂ =1:10) is used to oxidize the hard alloy substrate, and part of Co can be removed, and the surface of the substrate is oxidized to negatively charge the surface of the substrate; Plasma cleaning can bring the surface of the substrate with a group such as -OH.

The particle size of the nanodiamond in the nanodiamond suspension (particle size less than 50 nm) is significantly reduced compared to the diamond powder. In the present application, the diamond raw powder is a commercially available product, obtained by an explosion method (also referred to as nano-diamond aggregate), without any treatment, and the particle size ranges from several hundred nanometers to ten micrometers, and the average particle diameter thereof. On the micron level.

Preferably, in the nano-diamond suspension, the nano-diamond has a particle diameter of 5 to 35 nm.

Preferably, in the nano-diamond suspension, the nano-diamond has a particle diameter of 5-15 nm. More preferably, it is 5-10 nm.

Preferably, in the nano-diamond suspension, the nano-diamond has a particle diameter of 10-35 nm. It is further preferably 10-30 nm or 10-25 nm.

Preferably, the mass of the diamond raw powder is 0.005% to 0.5% of the sum of the mass of the diamond raw powder and the treatment liquid.

In an embodiment of the invention, when the organic acid or the amine-containing compound is added to the water, the method further comprises: adjusting the pH by using a pH adjuster, and setting the pH of the pretreatment liquid to 2-10. The pH adjuster can be sodium hydroxide or hydrochloric acid.

Preferably, when the organic acid is added to water, the pH of the pretreatment liquid is 2-9. The pH of the pretreatment liquid needs to be controlled within a certain range to prevent the organic acid from being more dissociated, resulting in instability of the suspension and sedimentation of the diamond particles. At this time, the surface of the nanodiamond in the obtained nano-diamond suspension is negatively charged, mainly because the carboxyl group in the organic acid (oxalic acid, citric acid) is adsorbed on the diamond raw powder particles, and the entire diamond particle is negatively charged.

Further, when the organic acid added to the water is citric acid, the pH of the pretreatment liquid is 3.5-9; when the organic acid added to the water is specifically oxalic acid, the pH of the pretreatment liquid is 2 -8.

Further, the concentration of the organic acid in the pretreatment liquid is 10 ^-5 to 10 ^-3 mol/L. The proper concentration of the organic acid in the pretreatment liquid can ensure that the organic acid is completely covered with the diamond particles; the concentration of the organic acid cannot be too large, otherwise the ionic strength in the pretreatment liquid is increased and the Debye length of the diamond particles in the water is shortened. (Debye length), and caused by the Coulomb force to attract diamond particles together to cause agglomeration and precipitation.

In the present invention, when the amine group-containing compound is added to water, the obtained nanodiamond suspension is positively charged. When the amine group-containing compound is a glutamic acid or aspartic acid having both a carboxyl group and an amino-NH ₂ group, the carboxyl group in the molecule preferentially attracts the surface of the diamond particle, and the amino group obtains a proton in the water to make the diamond The outermost layer of water in the particles is positively charged. When the amine-containing compound is a fatty amine, the fatty amine forms positively charged NH ₃ + in water, which is attracted to the surface of the diamond particles to disperse the diamond particles.

Preferably, the fatty amine is at least one of ethylenediamine and n-propylamine.

Further, the concentration of the amine-containing compound in the pretreatment liquid is from 10 ^-5 to 10 ^-3 mol/L.

Further, when the pretreatment liquid contains the fatty amine, the pH of the pretreatment liquid is 3-10.

Further, when the pretreatment liquid contains glutamic acid, the pH of the pretreatment liquid is 3-10. More preferably, it is 3-5. The concentration of the glutamic acid in the pretreatment liquid is preferably from 10 ^-5 to 10 ^-4 mol/L.

Further, when the pretreatment liquid contains aspartic acid, the pH of the pretreatment liquid is 5-10.

In the step (3) of the present invention, the ultrasonic oscillation time is 10 min-2 h, and the power is 200-500 W.

Preferably, after the ultrasonic vibration of the step (3), the method further comprises: taking out the substrate, sequentially placing it in water, ethanol, ultrasonic cleaning, and drying with nitrogen.

In the step (4) of the present invention, the diamond thin film may be grown by hot filament vapor deposition, microwave plasma enhanced chemical vapor deposition, or by other chemical vapor deposition methods. The diamond grains in the diamond film can be on the order of nanometers or micrometers, and can be achieved by controlling the content of the reaction gas, as well as the pressure in the vacuum chamber, the temperature of the substrate, and the like.

In an embodiment of the invention, a diamond film is prepared by hot filament vapor deposition, and the deposition conditions are as follows:

Using hydrogen and methane as reaction gases, methane accounts for 0.6%-2% of total gas volume, vacuum chamber pressure is 2-10 kPa, filament temperature is 1800-2800 °C, and substrate temperature during deposition is 700-800 °C; deposition A diamond film was prepared at a time of 1-4 h. At this time, the diamond crystal grains of the diamond thin film layer are on the order of micrometers.

Optionally, the diamond film has a thickness of 0.2 to 5 μm.

In the method for preparing a high-density diamond film provided by the invention, the nucleation density of the diamond film can be greatly improved by inoculating the surface-electrolyzed substrate with a small-diameter nano-diamond opposite to its electrical property, so that the nucleation density reaches 10 ¹⁰ More than cm ^-2 , which is 20-1000 times reported at the present stage, can produce a dense and dense diamond film. Compared with the current biasing method with the best nucleation density, the process is simpler and does not require a bias power supply. It is uniformly coated on the surface of an irregularly shaped workpiece, and the bias method cannot uniformly coat the sharp edge due to the tip discharge effect. The method solves the problems of low density of nanodiamond nucleation and poor density of diamond film in the prior art, and is simple in operation and suitable for large-scale production.

The advantages of the invention will be set forth in part in the description which follows.

DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the description of the prior art will be briefly described below. Obviously, the drawings in the following description are only It is a certain embodiment of the present invention, and other drawings can be obtained from those skilled in the art without any creative work.

1 is a scanning electron microscope (SEM) diagram of a diamond film nucleation process according to Embodiment 1 of the present invention;

2 is a (a) surface SEM secondary electron image, (b) cross-sectional SEM backscatter image, and (c) Raman spectrum of the diamond thin film in Example 1 of the present invention.

detailed description

The technical solutions of the present invention will be clearly and completely described below. It is apparent that the described embodiments are only a part of the embodiments of the invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts are within the scope of the present invention. The following are the preferred embodiments of the embodiments of the present invention, and it should be noted that those skilled in the art can make some improvements and refinements without departing from the principles of the embodiments of the present invention. And retouching is also considered to be the scope of protection of the embodiments of the present invention.

Example 1

A method for preparing a high density diamond film, comprising:

Step one, the surface of the substrate is negatively treated:

The YG6X (WC-6%Co) cemented carbide insert sold on the domestic market was used as the substrate, which was ultrasonically cleaned in acetone and alcohol for 10 minutes, and then immersed in a ratio of KOH:K ₃ [Fe(CN). ₆ ]: H ₂ O = 1:1: 10 (mass ratio) solution for 10 minutes to enhance the contact area of the matrix with the subsequent diamond film and mechanical occlusion (this step can also be omitted), then immerse the substrate in the distribution Oxidation etching was carried out for 30 seconds in a Caro mixed acid solution having a ratio of H ₂ SO ₄ :H ₂ O ₂ = 1:10 (volume ratio) to negatively charge the surface of the substrate.

Step 2: Prepare a suspension of positively charged diamond nanoparticles:

Adding glutamic acid to water and adjusting its pH to 4, a pretreatment liquid is obtained, wherein the concentration of glutamic acid in the pretreatment liquid is 7×10 ^-5 mol/L; then the commercially available nanodiamond powder is added to the above pretreatment The treatment liquid is uniformly dispersed to obtain a nano-diamond suspension; wherein the mass concentration of the nano-diamond in the nano-diamond suspension is 0.005 wt.%.

Step 3, the cemented carbide substrate processed in the first step is placed in the nano-diamond suspension in the second step for ultrasonic vibration for 30 minutes, and the ultrasonic power is 250 W, so that the nano-diamond particles are adsorbed on the surface of the cemented carbide substrate, wherein the adsorption is carried out. The particle size of the nanodiamond on the surface of the cemented carbide substrate is less than 50 nm (specifically 35-45 nm).

In step four, the cemented carbide substrate is taken out, sequentially placed in water, alcohol, ultrasonically cleaned, and finally dried with nitrogen.

Step 5: The processed sample is placed in a vacuum chamber of a hot wire chemical vapor deposition apparatus, and the diamond film is grown for 2.5 hours using the following parameters to obtain a high-density diamond film: hydrogen and methane are used as reaction gases to control the flow of hydrogen and methane. They were 800 sccm and 16 sccm, respectively, and the deposition pressure was 4 kPa, the filament temperature was 2400 ° C, and the substrate temperature was 850 ° C.

Among them, the surface morphology of diamond nucleation 10 minutes before growth is shown in Fig. 1, and the nucleation density is calculated to be as high as 1.1×10 ¹⁰ cm ^-2 . After the deposition for 1.5 h, the surface morphology, cross-sectional morphology and Raman spectrum of the film are shown in Fig. 2. The thickness of the obtained diamond film is 2 μm, and the grain size of the diamond is 1 μm. It can be seen from (a) and (b) in Fig. 2 that the diamond film is uniform and dense, and the sharp diamond peak at 1338 cm ^-1 in the Raman spectrum ((c) in Fig. 2) is 1400 cm ^-1 to The peak of the broad peak of the graphite phase at 1600 cm ^-1 is very low, indicating that the diamond is of high quality.

Example 2

A method for preparing a high density diamond film, comprising:

Step one, the surface of the substrate is subjected to hydrogenation treatment:

The YG8 (WC-8%Co) cemented carbide insert sold on the domestic market was used as the substrate, which was ultrasonically cleaned in acetone and alcohol for 10 minutes, and then placed in the vacuum chamber of the microwave plasma enhanced chemical vapor deposition equipment. Only high-purity hydrogen gas is introduced into the vacuum chamber, and the deposition pressure range is 3 kPa, the substrate temperature is 1000 ° C, and the microwave power is 1000 W, so that the surface of the substrate is positively charged.

Step 2, preparing a suspension of negatively charged diamond nanoparticles:

Adding oxalic acid to water and adjusting the pH to 6 to obtain a pretreatment liquid, wherein the concentration of glutamic acid in the pretreatment liquid is 10 ^-4 mol/L; then, the commercially available nanodiamond powder is added to the above pretreatment liquid, The nano-diamond suspension is obtained by uniformly dispersing; wherein the mass concentration of the nano-diamond in the nano-diamond suspension is 0.5 wt.%.

Step 3, the cemented carbide substrate after the first step is placed in the nano-diamond suspension in the second step for ultrasonic vibration for 15 minutes, and the ultrasonic power is 300 W, so that the nano-diamond particles are adsorbed on the surface of the cemented carbide substrate, wherein the adsorption is carried out. The size of the nanodiamond on the surface of the cemented carbide substrate is less than 50 nm. (specifically 20-25nm).

Step 5: The processed sample is placed in a vacuum chamber of a microwave plasma enhanced chemical vapor deposition apparatus, and the diamond film is grown for 2 hours by using the following parameters: hydrogen gas and methane are used as reaction gases, and the flow rates of hydrogen and methane are controlled to be 500 sccm and respectively. 20 sccm, deposition pressure 3 kPa, substrate temperature 800 ° C.

In the second embodiment, the thickness of the diamond film formed after deposition is 3 μm, the grain size of diamond in the diamond film is 80 nm, and the nucleation density in the nucleation stage 20 minutes before deposition growth is as high as 1.3×10 ¹⁰ cm ^{-2 .} .

Example 3

A method for preparing a high density diamond film, comprising:

Step one, the surface of the substrate is negatively treated:

The YT15 (WC-15%TiC) carbide indexing blade sold on the domestic market was used as a substrate, which was ultrasonically cleaned in acetone and alcohol for 10 minutes in sequence, and dried with nitrogen; then the substrate was placed in an oxygen plasma machine. Cleaning for 4 minutes to make the surface of the substrate negatively charged;

Step 2: Prepare a suspension of positively charged diamond nanoparticles:

Adding aspartic acid to water and adjusting its pH to 7 to obtain a pretreatment liquid, wherein the concentration of aspartic acid in the pretreatment liquid is 7×10 ^-5 mol/L; then the commercially available nano diamond raw powder is obtained. Adding to the above pretreatment liquid and uniformly dispersing to obtain a nanodiamond suspension; wherein the mass concentration of the nanodiamond in the nanodiamond suspension is 0.01 wt.%.

Step 3, the cemented carbide substrate after the first step is placed in the nano-diamond suspension in the second step for ultrasonic vibration for 40 minutes, and the ultrasonic power is 280 W, so that the nano-diamond particles are adsorbed on the surface of the cemented carbide substrate, wherein the adsorption is carried out. The particle size of the nanodiamond on the surface of the cemented carbide substrate is less than 50 nm (specifically (specifically 10-20 nm).

Step 5: The treated sample is placed in a vacuum chamber of a hot wire chemical vapor deposition apparatus, and hydrogen gas and methane are used as reaction gases, and the diamond film is grown for 2 hours by using the following parameters: controlling methane to account for 1% of the total gas volume during deposition. The vacuum chamber has a gas pressure range of 6 kPa, a filament temperature of 2800 ° C, and a substrate temperature of 880 ° C to obtain a diamond coating having a thickness of 3 μm. In the diamond coating, the diamond grain size is 2 μm.

Example 4

A method for preparing a high density diamond film, comprising:

Step one, the surface of the substrate is negatively treated:

The YG6X (WC-6%Co) cemented carbide insert sold on the domestic market was used as the substrate, which was ultrasonically cleaned in acetone and alcohol for 10 minutes, and then immersed in a ratio of KOH:K ₃ [Fe(CN). ₆ ]: H ₂ O = 1:1: 10 (mass ratio) solution for 30 minutes to enhance the contact area of the matrix with the subsequent diamond film and mechanical occlusion (this step can also be omitted), then immerse the substrate in the distribution Oxidation etching was carried out for 25 seconds in a Caro mixed acid solution having a ratio of H ₂ SO ₄ :H ₂ O ₂ = 1:10 (volume ratio) to negatively charge the surface of the substrate.

Step 2: Prepare a suspension of positively charged diamond nanoparticles:

The positive propylamine was added to the water, and the pH was adjusted to 6, to obtain a pretreatment liquid, wherein the concentration of glutamic acid in the pretreatment liquid was 6×10 ^-5 mol/L; then the commercially available nanodiamond powder was added to the above pretreatment. In the liquid, uniformly dispersed, a nano-diamond suspension is obtained; wherein the mass concentration of the nano-diamond in the nano-diamond suspension is 0.05 wt.%.

In the third step, the cemented carbide substrate after the first step is placed in the nano-diamond suspension in the second step for ultrasonic vibration for 30 minutes, and the ultrasonic power is 300 W.

Step 5: The processed sample is placed in a vacuum chamber of a hot wire chemical vapor deposition apparatus. First, the flow rates of hydrogen and methane are 500 sccm and 10 sccm, respectively, for 0.5 h; then the methane flow rate is decreased to 5 sccm, and the hydrogen flow rate remains unchanged. Lasts for 2.5h. A high-density diamond film was obtained: hydrogen gas and methane were used as reaction gases, and the flow rates of hydrogen and methane were controlled to be 800 sccm and 16 sccm, respectively. During the deposition process, the vacuum chamber pressure range was 3 kPa, the filament temperature was 2500 ° C, and the substrate temperature was 850 ° C to obtain a diamond coating having a thickness of 4 μm. In the diamond coating, the diamond grain size was 3 μm.

To highlight the beneficial effects of the present invention, the present invention also provides the following comparative examples:

Comparative Example 1: On the basis of Example 1, the substrate of the ultrasonically cleaned acetone and alcohol was directly implanted with diamond seeds by using an aqueous suspension of commercially available diamond raw powder, and the diamond film was grown by the same film growth process. It was tested that the nucleation density of diamond was only 10 ⁷ cm ^-2 10 minutes before growth. And there is a porous structure in the diamond film, which is not so dense. This indicates that the nano-diamond suspension prepared by the present invention is inoculated when the substrate is not subjected to charge treatment, and the nucleation density when the diamond film is grown is still low.

Comparative Example 2: On the basis of Example 1, a substrate prepared by ultrasonically cleaning acetone and alcohol was directly implanted with a suspension of positively charged diamond nanoparticles (glutamic acid, water, pH=7). For the seed crystal, the diamond film was grown by the same film growth process, and the nucleation density of the diamond was 10 ⁸ cm ^-2 10 minutes before the growth. The above comparison shows that the pH and other parameters of the glutamic acid-containing pretreatment liquid have an important influence on the nucleation density of the final diamond coating, and need to be controlled within the scope of the present invention.

It should be noted that those skilled in the art to which the invention pertains may also make modifications and changes to the embodiments described above. Therefore, the invention is not limited to the specific embodiments disclosed and described herein, and the equivalents of the invention are intended to be included within the scope of the appended claims. In addition, although specific terms are used in the specification, these terms are merely for convenience of description and do not limit the invention.

Claims

A method for preparing a high-density diamond film, comprising the steps of:

(1) taking a cemented carbide substrate and performing surface charge treatment on the surface thereof, the surface charge treatment comprising positive or negative electrification;

(2) preparing a diamond suspension: adding an organic acid or an amine-containing compound to water to obtain a pretreatment liquid; adding the diamond raw powder to the pretreatment liquid and uniformly dispersing to obtain a nanodiamond suspension; The organic acid includes one or more of oxalic acid and citric acid, and the amine-containing compound is selected from one or more of glutamic acid and aspartic acid, and an aliphatic amine having 2 to 5 carbon atoms. Species

(3) placing the surface-charged substrate in the nano-diamond suspension for ultrasonic vibration, so that the nano-diamond is adsorbed on the surface of the substrate, wherein the nano-diamond suspension is charged Sexuality is opposite to the electrical properties of the substrate;

(4) A diamond thin film is grown on the substrate obtained in the step (3) by using a chemical vapor deposition apparatus.
The preparation method according to claim 1, wherein when the organic acid is contained in the pretreatment liquid, the substrate is subjected to a positive electrolysis treatment; and when the pretreatment liquid contains the amine group In the case of a compound, the substrate is subjected to a negative electron treatment.
The preparation method according to claim 1 or 2, wherein the positive electro-chemical treatment is surface hydrotreating, specifically comprising: placing the substrate in a vacuum chamber of the coating device, introducing high-purity hydrogen gas, and controlling the gas pressure in the vacuum chamber It is 0.5 to 20 kPa, and the substrate temperature is 900 to 1100 °C.
The process according to claim 3, wherein the hydrogenation treatment time is from 0.5 to 1 h.
The preparation method according to claim 1 or 2, wherein the negative ionization treatment comprises any one of the following methods:

The cemented carbide substrate is oxidized and etched using a Caro mixed acid;

Alternatively, the cemented carbide substrate is placed in an oxygen plasma cleaner for cleaning.
The preparation method according to claim 5, wherein the oxidizing etching time is 0.5 to 1 min.
The preparation method according to claim 5, wherein the oxygen plasma cleaning time is 2 to 15 minutes.
The method according to claim 1, wherein when the organic acid or the amine-containing compound is added to the water, the method further comprises: adjusting the pH by using a pH adjuster, and setting the pH of the pretreatment liquid to 2-10.
The treatment method according to claim 8, wherein when the organic acid added to the water is citric acid, the pH of the pretreatment liquid is 3.5-9;

When the organic acid added to the water is oxalic acid, the pH of the pretreatment liquid is 2-8.
The preparation method according to claim 8, wherein when the amine group-containing compound added to water is glutamic acid or a fatty amine, the pH of the pretreatment liquid is 3-10;

When the amine group-containing compound added to water is aspartic acid, the pH of the pretreatment liquid is 5-10.
The process according to claim 1, wherein the concentration of the organic acid or amine-containing compound in the pretreatment liquid is from 10 -5 to 10 -3 mol/L.
The method according to claim 1, wherein the mass of the diamond raw powder is 0.005% to 0.5% of the sum of the mass of the diamond raw powder and the treatment liquid.
The method according to claim 1, wherein the fatty amine is at least one of ethylenediamine and n-propylamine.
The preparation method according to claim 1, wherein the nanodiamond suspension has a particle diameter of less than 50 nm.
The preparation method according to claim 1, wherein in the nano-diamond suspension, the nano-diamond has a particle diameter of 5 to 35 nm.
The preparation method according to claim 1, wherein the nanodiamond raw powder is obtained by an explosion method without any treatment, and has a particle size ranging from several hundred nanometers to ten micrometers, and an average particle diameter of the micron order.