Preparation method of diamond self-supporting film

Abstract

The invention relates to the field of diamond processing and preparation, in particular to a preparation method of a diamond self-supporting film. Based on a microwave plasma or hot filament chemical vapor deposition method, a diamond film with the thickness larger than 10 microns grows on a (001) monocrystalline silicon or titanium alloy or molybdenum substrate, or monocrystalline diamond is directly used as a substrate; selectively etching the diamond film or the monocrystal diamond substrate by adopting a micro-nano processing method to prepare a diamond one-dimensional nano array structure with the length of more than 10 microns; the diamond one-dimensional nano array structure is further put into microwave plasma chemical vapor deposition equipment for diamond regrowth, so that in the diamond one-dimensional nano array structure, nanowires located on the upper portion serve as a seed layer to transversely and longitudinally grow to form a diamond continuous film; the nanowire located at the lower portion does not grow due to the shielding effect of plasma, and the diamond one-dimensional nano array structure and the substrate are broken through mechanical stripping to obtain the diamond self-supporting film.

Description

Technical Field

[0001] The invention relates to the field of diamond processing and preparation, in particular to a method for preparing a diamond self-supporting film. Background Art

[0002] As we all know, diamond has excellent mechanical, optical, electrical and thermal conductivity properties, and has important application value in the fields of high-performance tool coatings, optical windows and heat sinks. In particular, diamond has very high visible light and near-infrared transmittance, and its thermal conductivity is more than 10 times that of single-crystal silicon. Therefore, large-sized diamond self-supporting films can be used as high-power laser window materials and heat sink materials for high-power electronic devices. Chemical vapor deposition (CVD) is a common method for preparing high-quality diamond thick films, and the prepared diamond thick films usually need to be peeled off from the substrate for use.

[0003] The common peeling methods can be divided into four categories:

[0004] The first type is to use laser to cut the diamond thick film or single crystal diamond substrate along the interface between the substrate and the epitaxial layer to obtain a self-supporting film. Since the laser has a certain cone angle, it will cause a large loss of diamond when cutting large-sized diamonds; while using laser to perform vertical hidden cutting along the surface of the substrate, high-energy laser irradiation will cause defects inside the outermost diamond film. The second type is to grow a diamond film on a silicon substrate and remove the silicon substrate by wet chemical etching. However, this method makes the single crystal silicon substrate non-reusable, resulting in a significant increase in the preparation cost; a metal transition layer (such as a titanium / molybdenum transition layer) can also be pre-deposited on the silicon substrate, and then a diamond film is grown. The silicon substrate and the diamond film are separated by corroding the metal transition layer to obtain a self-supporting film. However, in this method, the bubbles generated under the diamond film during the process of etching the metal with an acid solution are not easy to be discharged, resulting in the film being easy to crack (Chinese patent application with publication number CN104561925A). The third class is, adopts the hydrogen ion implantation method to form the hydrogen layer to the silicon substrate, then grows the diamond film, separates the diamond from the silicon substrate by the method of electrochemical stripping hydrogen to prepare the diamond self-supporting film, but the hydrogen transition layer thickness of the method is very thin, and the efficiency of adopting electrochemical separation will be very low (publication number is the Chinese patent application of CN107400871A). The fourth class is, grows the polycrystalline diamond layer at the polycrystalline diamond substrate growth nano diamond layer transition layer, utilizes high temperature heat treatment that nano diamond is changed into graphite, utilizes electrochemical method etching graphite to separate the upper and lower layers of polycrystalline diamond, prepares the diamond self-supporting film, but because the nano diamond / graphite transition temperature is very high, in the process that changes, micron diamond also changes and causes the quality variation of the self-supporting film (publication number is the Chinese patent application of CN112430803A). In summary, the preparation of the diamond self-supporting film is currently faced with the problem of low efficiency. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a method for preparing a diamond self-supporting film, which adopts a diamond with a one-dimensional diamond array structure as a substrate, and utilizes a microwave plasma chemical vapor deposition method or a hot wire chemical vapor deposition method to carry out diamond regrowth, so that the diamond at the top of the array quickly nucleates and continuously forms a film, while the diamond at the bottom of the array does not form a film continuously, which serves as a weak area connecting the epitaxial film and the substrate. Under the action of thermal stress during the cooling process, the epitaxial film is automatically peeled off, thereby forming a large-sized diamond self-supporting film.

[0006] The technical solution of the present invention is:

[0007] A method for preparing a diamond self-supporting film comprises the following steps: growing a diamond film with a thickness greater than 10 μm on a (001) single crystal silicon or titanium alloy or molybdenum substrate based on a microwave plasma or hot wire chemical vapor deposition method, or directly using a single crystal diamond as a substrate, selectively etching the diamond film or the single crystal diamond substrate using a micro-nano processing method to prepare a diamond one-dimensional nano array structure with a length greater than 10 μm; further placing the diamond one-dimensional nano array structure in a microwave plasma chemical vapor deposition device for diamond regrowth, so that the nanowires located at the upper part of the diamond one-dimensional nano array structure act as a seed layer to grow laterally and longitudinally to form a diamond continuous film, while the nanowires located at the lower part do not grow due to the shielding effect of plasma; finally mechanical stripping is used to break the diamond one-dimensional nano array structure and the substrate to obtain a diamond self-supporting film.

[0008] The method for preparing the diamond self-supporting film specifically comprises the following steps:

[0009] a. Substrate cleaning: Select (001) single crystal silicon or titanium alloy or molybdenum as the substrate, and use acetone, ultrapure water and anhydrous alcohol to ultrasonically clean its surface for 5 to 15 minutes respectively to remove surface contaminants;

[0010] b. Pre-nucleation treatment: Place the cleaned substrate in a diamond seed solution and ultrasonicate for 30 to 60 minutes to form a substrate with uniform distribution of diamond seeds;

[0011] c. Thin film growth: placing the substrate obtained in step b in a microwave plasma or hot wire chemical vapor deposition device, using methane and hydrogen as reaction gases, with a flow ratio of methane to hydrogen of 3% to 8%, a methane flow concentration of 12 to 32 sccm, and growing for different times to obtain a diamond film with a thickness greater than 10 μm;

[0012] d. Micro-nano processing: The diamond film obtained in step c or the single crystal diamond substrate is directly used for micro-nano processing to prepare a diamond one-dimensional nanoarray structure, and the diamond one-dimensional nanoarray structure is surface treated with a mixed solution of sulfuric acid and nitric acid to remove non-diamond phases;

[0013] e. CVD regrowth of self-supporting film: Place the diamond one-dimensional nanoarray structure in step d into a microwave plasma chemical vapor deposition device, use methane and hydrogen as reaction gases, and the flow ratio of methane to hydrogen is 6% to 10%. Grow a diamond continuous film on the top of the nanowires of the diamond one-dimensional nanoarray structure. The diamond continuous film is automatically peeled off during the cooling process after the growth is completed to form a diamond self-supporting film.

[0014] In the method for preparing the diamond self-supporting film, in step a, (001) single crystal silicon or titanium alloy or molybdenum is selected as a substrate to perform epitaxial growth of diamond.

[0015] In the method for preparing the diamond self-supporting film, in step b, the composition of the diamond seed solution is an aqueous solution containing 3-5wt% diamond nanocrystals, and the average grain size of the diamond nanocrystals is 4-6nm.

[0016] In the method for preparing the diamond self-supporting film, in steps a and b, the substrate needs to be ultrasonically cleaned with alcohol and deionized water for 3 to 6 minutes before and after the diamond seed pre-nucleation treatment, and then dried to obtain a substrate with uniform diamond seed distribution.

[0017] The method for preparing the diamond self-supporting film, in step c, uses microwave plasma chemical vapor deposition equipment to control microwave power, working gas pressure and growth time so that the thickness of the diamond film is greater than 10μm; wherein the microwave power is 6-10kW, the working gas pressure is 60-80mbar, the growth temperature is 800-975℃, and the growth time is greater than 8h.

[0018] The method for preparing the diamond self-supporting film, in step d, during the micro-nano processing process, ultraviolet lithography and reactive ion etching process are used to selectively etch the diamond film or diamond substrate to prepare a diamond one-dimensional nanoarray structure, the reaction gas used is an oxygen-containing source, and the length of the one-dimensional nanowire of the diamond one-dimensional nanoarray structure is greater than 10μm.

[0019] In the method for preparing the diamond self-supporting film, in step d, the volume ratio of sulfuric acid and nitric acid mixed solution used for surface treatment of the diamond one-dimensional nanoarray structure is 3:1, the temperature is 150° C., the concentration of sulfuric acid is 98wt%, and the concentration of nitric acid is 96wt%.

[0020] The method for preparing the diamond self-supporting film, in step e, when performing microwave plasma chemical vapor deposition, the microwave power, working gas pressure and growth time are controlled, the microwave power is 6-10 kW, the working gas pressure is 60-80 mbar, the growth temperature is 800-975°C, and the growth time is more than 1 hour.

[0021] In the method for preparing the diamond self-supporting film, in step e, the flow ratio of methane to hydrogen is 6% to 10%, so that the upper surface of the nanowire grows rapidly in the in-plane direction and forms a continuous film; while in the area near the substrate on the lower surface of the nanowire, due to the shielding effect of plasma, no diamond regrowth occurs, and the area is a region with discontinuous distribution, stress concentration and low mechanical strength. During the cooling process after the growth is completed, the diamond film or the diamond substrate breaks due to thermal stress mismatch, thereby obtaining a diamond self-supporting film.

[0022] The design concept of the present invention is:

[0023] Diamond self-supporting film is the main means of preparing large-sized single crystals or polycrystalline. At present, there are many methods for preparing large-sized diamond self-supporting film, which vary for different substrates. For diamond films grown on Mo-based substrates, the high stress generated by the difference in thermal expansion coefficients between diamond and Mo is usually used to make the diamond automatically peel off during the cooling process. However, thermal stress also causes cracks in the diamond self-supporting film, making it impossible to prepare large-sized diamonds. For diamond films grown on silicon substrates, the silicon substrate is mainly etched by wet chemical etching. The bubbles generated in the etching of the silicon substrate by this method may cause microcracks in the diamond film. At the same time, the strong acid used in the chemical reagents has a large environmental pollution. More importantly, the silicon substrate cannot be reused. For diamond films grown on single-crystal diamond substrates, the substrate can only be peeled off by laser cutting. The wide cone angle of the laser beam spot causes a large loss of the diamond substrate and the film, which is not suitable for the preparation of large-sized self-supporting films.

[0024] The preparation method of the present invention is based on constructing a discontinuous region with weak mechanical connection between a diamond film and a substrate, namely a diamond one-dimensional nanoarray structure, which is very easy to break under the action of thermal stress and external shear force, so that the diamond film is peeled off from the substrate to obtain a diamond self-supporting film. The specific method is: first, a diamond film is grown on a heterogeneous or homogeneous substrate, and a diamond one-dimensional nanoarray structure is prepared on the substrate by a micro-nano processing method; then, a microwave plasma chemical vapor deposition or hot wire chemical vapor deposition method is used to make the top of the nanowire of the diamond one-dimensional nanoarray structure grow diamond quickly and form a film continuously, while the bottom of the nanowire does not grow diamond continuously, becoming a mechanically weak area, which breaks under the action of thermal stress and external shear force, so that the diamond film is peeled off from the substrate without cracks, thereby obtaining a diamond self-supporting film.

[0025] Compared with the existing preparation technology of diamond self-supporting film, the advantages and beneficial effects of the present invention are mainly reflected in:

[0026] (1) The present invention mainly adopts a one-dimensional nanostructure constructed in a heterogeneous or homogeneous diamond film as a weak mechanical connection area between the top diamond film and the substrate. Due to the flexibility of the nanowires and the discontinuity of the nanowire array, the thermal stress between the diamond film and the substrate can be reduced, thereby avoiding the generation of microcracks inside the top diamond film.

[0027] (2) The present invention can avoid the use of chemical reagents for heterogeneous substrates, so that the substrates can be reused.

[0028] (3) The present invention can prepare diamond self-supporting films on large-sized single-crystal diamond substrates, thereby avoiding material loss caused by laser processing.

[0029] In summary, the method for preparing the diamond self-supporting film of the present invention uses a one-dimensional nanowire array as a connection with weak mechanical strength of the diamond film or diamond substrate. This method is independent of the substrate and has strong universality. It is suitable for the preparation of large-size, high-quality diamond self-supporting films and has very important scientific value and engineering significance in the fields of high-power electronic device heat sinks, optical windows, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Flowchart for preparing diamond free-standing films on foreign substrates.

[0031] Figure 2 Flowchart for the preparation of diamond free-standing films for homogeneous substrates.

[0032] Figure 3 This is a scanning electron microscope image of a diamond continuous film grown on a diamond one-dimensional micro-nanostructure using microwave plasma chemical vapor deposition. In the figure, 1 is a diamond continuous film, 2 is a diamond nanowire, 3 is a substrate, and 4 is a diamond self-supporting film.

[0033] Figure 4 This is a scanning electron microscope image of the surface layer of a diamond continuous film grown on a diamond one-dimensional micro-nanostructure using microwave plasma chemical vapor deposition.

[0034] Figure 5 This is the Raman curve of the surface layer of a continuous diamond film grown on a diamond one-dimensional micro-nanostructure using microwave plasma chemical vapor deposition. In the figure, the horizontal axis Raman shift is the Raman shift (cm -1 ), the vertical axis Intensity is the relative intensity (au). DETAILED DESCRIPTION

[0035] In the specific implementation process, the present invention provides a method for preparing a diamond self-supporting film on a heterogeneous substrate, and the preparation process is as follows: growing a diamond film on a heterogeneous substrate by CVD → micro-nano processing a one-dimensional nanostructure → growing a diamond continuous film by CVD → removing the substrate to obtain a diamond self-supporting film. Figure 1 As shown, the present invention firstly grows a diamond film on a foreign substrate by CVD, and prepares a diamond one-dimensional nanoarray structure on the substrate by a micro-nano processing method; then, microwave plasma chemical vapor deposition or hot wire chemical vapor deposition is used to make diamonds grow rapidly and continuously form a film at the top of the nanowires of the diamond one-dimensional nanoarray structure, while the bottom of the nanowire does not grow diamonds continuously, forming a mechanically weak area, which breaks under the action of thermal stress and external shear force, so that the diamond film is peeled off from the substrate without generating cracks, thereby obtaining a diamond self-supporting film with an area of ​​up to 4 inches.

[0036] In addition, the present invention provides a method for preparing a diamond self-supporting film on a homogeneous substrate, and the preparation process is as follows: using micro-nano processing of a one-dimensional nanostructure on a homogeneous substrate → growing a diamond continuous film by CVD → removing the substrate to obtain a diamond self-supporting film. Figure 2 As shown, the present invention first utilizes a micro-nano processing method to prepare a diamond one-dimensional nanoarray structure on a single crystal diamond substrate; then utilizes a microwave plasma chemical vapor deposition method or a hot wire chemical vapor deposition method to rapidly grow diamonds at the top of the nanowires of the diamond one-dimensional nanoarray structure and continuously form a film, while the bottom of the nanowires does not continuously grow diamonds, forming a mechanically weak area, which breaks under the action of thermal stress and external shear force, causing the diamond film to be peeled off from the substrate without generating cracks, thereby obtaining a diamond self-supporting film with an area of ​​up to 4 inches.

[0037] Two points are the most critical. The first is based on constructing a discontinuous area with weak mechanical connection between the diamond film and the substrate, namely the diamond one-dimensional nanoarray structure, on which the length of the one-dimensional nanowire is greater than 10μm. The second is to use chemical vapor deposition to make diamond grow rapidly at the top of the nanowire and form a continuous film. The reason is that the micro-nano structure will redistribute the electromagnetic field and plasma and produce a shielding effect. The plasma density at the top of the nanowire is the highest, and the diamond growth rate is the fastest to form a continuous film, while the plasma density at the bottom of the nanowire is the lowest, and diamond does not grow to form a discontinuous structure.

[0038] The present invention is further described below in conjunction with specific implementations, but the protection scope of the present invention is not limited thereto:

[0039] Embodiment 1:

[0040] In this embodiment, the method for preparing the diamond self-supporting film is as follows:

[0041] (1) A single crystal silicon substrate with a diameter of 20 mm and a thickness of 0.5 mm was cleaned with acetone, ultrapure water and anhydrous alcohol for 10 min respectively to remove surface pollutants. The cleaned silicon wafer was inoculated with a diamond seed aqueous solution (with an average diamond grain size of 5 nm and a content of 2.5 wt%) for pre-nucleation treatment, and anhydrous ethanol and deionized water were used for ultrasonic cleaning for 3 min to remove the seeds that were aggregated and loosely combined on the substrate surface, so that the diamond seeds were evenly distributed on the substrate surface and formed a tight combination, and dried to obtain a pre-nucleation treated substrate.

[0042] (2) The inoculated single crystal silicon substrate was placed at the center of the sample stage of a microwave plasma chemical vapor deposition equipment, and hydrogen and methane were introduced. The gas flow ratio of methane to hydrogen was set to 6%, the methane flow concentration was 24 sccm, the microwave power and the working gas pressure were set to 8 kW and 75 mbar, the growth temperature was 875 °C, the growth time was 9 h, and a diamond film with a thickness of 10.5 μm was obtained.

[0043] (3) Spin-coating the diamond surface with photoresist, performing patterned exposure using ultraviolet photolithography, then developing and removing the resist, and then etching the uncoated area using reactive ion etching to obtain a diamond one-dimensional nanowire array with a nanowire length of 10.5 μm. The prepared diamond one-dimensional nanowire array sample was placed in a mixed solution of sulfuric acid and nitric acid with a volume ratio of 3:1 (the concentration of sulfuric acid was 98wt% and the concentration of nitric acid was 96wt%), and placed on a magnetic stirrer, the solution temperature was set to 150°C, and a stirring bar was used for stirring to etch the non-diamond phase.

[0044] (4) The diamond one-dimensional nanowire array sample was placed in a tube furnace, and hydrogen and methane were introduced into the center of the sample stage of the microwave plasma chemical vapor deposition equipment. The gas flow ratio of methane and hydrogen was set to 8%, the microwave power and the working pressure were set to 8 kW and 62 mbar, the growth temperature was 820°C, and the growth time was 2 h to prepare a diamond film. Figure 3 and Figure 4 As shown, the diamond nanowires at the upper part grow into a diamond continuous film 1, while the diamond nanowires 2 at the lower part do not grow into a diamond continuous film, and the lower end of the diamond nanowires 2 separates from the substrate 3 to form a diamond self-supporting film 4. In the diamond self-supporting film of this embodiment, the thickness of the diamond continuous film is 2 μm.

[0045] Embodiment 2:

[0046] In this embodiment, the preparation method of the diamond self-supporting film is as follows:

[0047] (1) A (001) oriented single crystal diamond substrate with a length of 10 mm, a width of 10 mm, and a thickness of 0.5 mm was cleaned by ultrasonic treatment with acetone, ultrapure water, and anhydrous alcohol for 10 min each to remove surface contaminants.

[0048] (2) Spin-coating the diamond surface with photoresist, performing patterned exposure using ultraviolet photolithography, then developing and removing the resist, and then etching the uncoated area using reactive ion etching technology to obtain a diamond one-dimensional nanowire array with a nanowire length of 12 μm. The prepared diamond one-dimensional nanowire array sample was placed in a mixed solution of sulfuric acid and nitric acid with a volume ratio of 3:1 (the concentration of sulfuric acid was 98wt% and the concentration of nitric acid was 96wt%), and placed on a magnetic stirrer, the solution temperature was set to 150°C, and a stirring bar was used for stirring to etch the non-diamond phase.

[0049] (4) The diamond one-dimensional nanowire array sample is placed in a tube furnace, and hydrogen and methane are introduced into the center of the sample stage of the microwave plasma chemical vapor deposition equipment. The gas flow ratio of methane and hydrogen is set to 8%, the microwave power and the working pressure are set to 8 kW and 72 mbar, the growth temperature is 860°C, and the growth time is 2 hours. The prepared diamond film has continuous film formation on the upper part of the nanowires and separation from the substrate at the lower part to form a self-supporting film. In the diamond self-supporting film of this embodiment, the thickness of the diamond continuous film is 2.5 μm.

[0050] like Figure 5 As shown in the figure, the crystal quality of the diamond self-supporting film can be seen from the Raman curve. The Raman shift of the one-dimensional nanowire continuous film is 5.12cm -1 The Raman shift of single crystal diamond one-dimensional nanowire is 3.38 cm -1 .

[0051] The results of the examples show that the diamond self-supporting film provided by the method of the present invention has the characteristics of simple preparation process, strong universality and high efficiency, and provides a completely different preparation method for preparing diamond support films over a large area.

Claims

1. A method for preparing a diamond self-supporting film, characterized in that: Based on microwave plasma or hot wire chemical vapor deposition method, a diamond film with a thickness greater than 10 μm is grown on a (001) single crystal silicon or titanium alloy or molybdenum substrate, or a single crystal diamond is directly used as a substrate, and a micro-nano processing method is used to selectively etch the diamond film or single crystal diamond substrate to prepare a diamond one-dimensional nanoarray structure with a length greater than 10 μm; the diamond one-dimensional nanoarray structure is further placed in a microwave plasma chemical vapor deposition device for diamond regrowth, so that in the diamond one-dimensional nanoarray structure, the nanowires located at the upper part act as a seed layer to grow horizontally and vertically to form a diamond continuous film, while the nanowires located at the lower part do not grow due to the shielding effect of plasma, and finally mechanical stripping is used to break the diamond one-dimensional nanoarray structure and the substrate to obtain a diamond self-supporting film.

2. The method for preparing a diamond self-supporting film according to claim 1, wherein: The specific steps include: a. Substrate cleaning: Select (001) single crystal silicon or titanium alloy or molybdenum as the substrate, and use acetone, ultrapure water and anhydrous alcohol to ultrasonically clean its surface for 5 to 15 minutes respectively to remove surface contaminants; b. Pre-nucleation treatment: Place the cleaned substrate in a diamond seed solution and ultrasonicate for 30 to 60 minutes to form a substrate with uniform distribution of diamond seeds; c. Thin film growth: placing the substrate obtained in step b in a microwave plasma or hot wire chemical vapor deposition device, using methane and hydrogen as reaction gases, with a flow ratio of methane to hydrogen of 3% to 8%, a methane flow concentration of 12 to 32 sccm, and growing for different times to obtain a diamond film with a thickness greater than 10 μm; d. Micro-nano processing: The diamond film obtained in step c or the single crystal diamond substrate is directly used for micro-nano processing to prepare a diamond one-dimensional nanoarray structure, and the diamond one-dimensional nanoarray structure is surface treated with a mixed solution of sulfuric acid and nitric acid to remove non-diamond phases; e. CVD regrowth of self-supporting film: Place the diamond one-dimensional nanoarray structure in step d into a microwave plasma chemical vapor deposition device, use methane and hydrogen as reaction gases, and the flow ratio of methane to hydrogen is 6% to 10%. Grow a diamond continuous film on the top of the nanowires of the diamond one-dimensional nanoarray structure. The diamond continuous film is automatically peeled off during the cooling process after the growth is completed to form a diamond self-supporting film.

3. The method for preparing a diamond self-supporting film according to claim 2, characterized in that: In step a, (001) single crystal silicon or titanium alloy or molybdenum is selected as a substrate for epitaxial growth of diamond.

4. The method for preparing a diamond self-supporting film according to claim 2, characterized in that: In step b, the diamond seed solution is composed of an aqueous solution containing 3-5 wt% diamond nanocrystals, and the average grain size of the diamond nanocrystals is 4-6 nm.

5. The method for preparing a diamond self-supporting film according to claim 2, characterized in that: In steps a and b, the substrate needs to be ultrasonically cleaned with alcohol and deionized water for 3 to 6 minutes before and after the diamond seed pre-nucleation treatment, and then dried to obtain a substrate with uniform distribution of diamond seeds.

6. The method for preparing a diamond self-supporting film according to claim 2, characterized in that: In step c, microwave plasma chemical vapor deposition equipment is used to control microwave power, working gas pressure and growth time so that the thickness of the diamond film is greater than 10 μm; wherein the microwave power is 6 to 10 kW, the working gas pressure is 60 to 80 mbar, the growth temperature is 800 to 975° C., and the growth time is greater than 8 hours.

7. The method for preparing a diamond self-supporting film according to claim 2, characterized in that: In step d, during the micro-nano processing, ultraviolet lithography and reactive ion etching processes are used to selectively etch the diamond film or diamond substrate to prepare a diamond one-dimensional nanoarray structure. The reaction gas used is an oxygen-containing source, and the length of the one-dimensional nanowire of the diamond one-dimensional nanoarray structure is greater than 10 μm.

8. The method for preparing a diamond self-supporting film according to claim 2, characterized in that: In step d, the volume ratio of sulfuric acid and nitric acid mixed solution used for surface treatment of the diamond one-dimensional nanoarray structure is 3:1, the temperature is 150° C., the concentration of sulfuric acid is 98wt%, and the concentration of nitric acid is 96wt%.

9. The method for preparing a diamond self-supporting film according to claim 2, characterized in that: In step e, when performing microwave plasma chemical vapor deposition, the microwave power, working gas pressure and growth time are controlled, the microwave power is 6 to 10 kW, the working gas pressure is 60 to 80 mbar, the growth temperature is 800 to 975° C., and the growth time is more than 1 hour.

10. The method for preparing a diamond self-supporting film according to claim 2, characterized in that: In step e, the flow ratio of methane to hydrogen is 6% to 10%, so that the upper surface of the nanowire grows rapidly in the in-plane direction and forms a continuous film; however, due to the shielding effect of plasma, the area on the lower surface of the nanowire close to the substrate does not undergo diamond regrowth. This area is a region of discontinuous distribution, stress concentration and low mechanical strength. During the cooling process after the growth is completed, the diamond film or the diamond substrate breaks due to thermal stress mismatch, thereby obtaining a diamond self-supporting film.

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