Method for preparing spherical crown-shaped diamond film through hot working treatment

Abstract

The invention provides a method for preparing a spherical crown-shaped diamond film through hot working treatment, and relates to the technical field of diamond film processing. The method comprises the steps that S1, a trace equation is calculated, laser cutting is conducted on a diamond film, and a petal-shaped diamond film is obtained; s2, a graphite mold is designed, and mold preparation is completed; performing high-temperature treatment to finish hot-pressing deformation of the diamond; and S3, chemical vapor deposition equipment is used for carrying out secondary growth on the spherical crown-shaped diamond subjected to hot pressing, and gap filling is completed. The method is simple in process and low in operation difficulty, the diamond film is convenient to deform, the heat-conducting property and the mechanical property are excellent, heat dissipation application of electronic devices with irregular surfaces is easy, and industrial large-scale production and popularization are facilitated.

Description

Technical Field

[0001] This invention relates to the technical field of diamond film processing, and in particular to a method for preparing a crown-shaped diamond film by thermal processing. Background Technology

[0002] Diamond, as the hardest material in nature, is widely used in cutting, grinding, and machining. With continuous technological advancements, diamond sheet processing technology has gradually become a research hotspot. Among these, thermal processing technology has attracted widespread attention in the industry due to its significant advantages in improving diamond sheet performance and extending its service life.

[0003] With the rapid development of the electronics industry, third-generation semiconductor materials have been widely used in electronic components. As electronic devices continue to miniaturize and increase power density, heat dissipation has become a common issue in improving their performance. Diamond has a thermal conductivity of over 2000 W / m·K, which is approximately 5 times that of copper, 13 times that of silicon, and 4 times that of silicon carbide. This means that heat can be transferred and dissipated extremely quickly in diamond. When diamond is used as a passivation layer or substrate layer in devices, it can significantly improve the heat dissipation capacity and increase the power of the devices.

[0004] High-power electronic devices with regular planar surfaces can achieve heat transfer through uniform and close contact with heat dissipation materials. However, irregular shapes lead to problems such as reduced contact area, air gaps, and uneven heat flux density, resulting in a significant decrease in heat dissipation efficiency. Currently, diamond materials are generally grown in planar shapes, which makes it difficult to effectively utilize their heat dissipation advantages when dealing with some irregular flexible electronic devices. Therefore, in order to increase the contact area between diamond films as heat dissipation materials and electronic devices, the deformation processing of diamond films is extremely important.

[0005] The physicochemical properties of diamond films determine their processing difficulty. Traditional processing methods, such as grinding and laser cutting, can only perform simple surface treatments on diamond films, which are insufficient to meet the future application scenarios of curved diamond films.

[0006] Chinese patent CN115261817A discloses a method for preparing a high-toughness diamond film. This diamond film achieves a significant improvement in the fracture toughness of diamond through the combined effects of particle toughening and twinning toughening. Obviously, the increased toughness will further increase the contact area with electronic devices, but the increase effect is not significant. Moreover, it requires the periodic introduction of boronane or silane to finally obtain boron carbide or silicon carbide nanoparticles encapsulated by the grown diamond, which is costly and inefficient. Furthermore, it may have technical defects such as increased interfacial thermal resistance and thermal stress concentration due to insufficient material matching.

[0007] Chinese patent CN118207512A discloses a method for preparing a high-quality waveform diamond film. This method involves processing a three-dimensional pattern on the substrate surface to meet the growth conditions of the diamond film according to its size requirements, followed by pretreatment, chemical vapor deposition, and finally removing the substrate to obtain the diamond film. Although this method can be used to generate diamond films with curved surfaces, it requires not only processing the substrate, but also bias voltage to enhance nucleation and high-cost microwave plasma chemical vapor deposition, without considering surface processing to enhance the contact area.

[0008] Chinese patent CN120734900A discloses a method for polishing the surface of large-size CVD polycrystalline diamond films. The method involves first patterning the diamond film surface, then depositing a metal catalyst layer onto the diamond micropowder surface at high cost, followed by surface polishing with a prepared polishing slurry, and finally annealing. Clearly, this method processes the surface of a pre-prepared diamond film. The laser used in the processing can only construct a micron-scale three-dimensional microgroove array on the diamond film surface, correspondingly reducing the contact area. Although the subsequent preparation and use of the polishing slurry can catalyze the transformation of diamond into an easily machinable non-diamond carbon phase under the high temperature and stress of polishing, its self-healing properties do not enhance the contact area. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing a spherical crown-shaped diamond film through thermal processing, in order to solve the technical problems of existing technologies that use particle toughening and twinning to increase the contact area of ​​the diamond film surface, such as high preparation cost, low efficiency, high operation difficulty, increased interfacial thermal resistance and stress concentration of the prepared material; or processing the substrate or the diamond film surface, which, although increasing the contact area to a certain extent, do not increase it significantly and are not suitable for increasing the contact area of ​​curved diamond films.

[0010] To achieve the above objectives, the technical solution of the present invention is as follows:

[0011] A method for preparing a crown-shaped diamond film by thermal processing, the method comprising:

[0012] S1. Selection and cutting of diamond film: Design the target curvature of the desired crown-shaped diamond film, calculate the required diamond film radius based on the curvature, select the diamond film grown by chemical vapor deposition and perform acid washing; perform laser cutting according to the calculated relevant formula to cut off the excess part before hot pressing deformation to obtain a petal-shaped diamond film.

[0013] S2. High-temperature hot pressing deformation: Prepare a hot pressing deformation mold with the required curvature; fix the petal-shaped diamond film and the hot pressing deformation mold together; set the corresponding parameters of the heating furnace, so that the petal-shaped diamond film is subjected to high-temperature hot pressing deformation in the mold and the heating furnace to obtain a spherical crown-shaped diamond film with gaps.

[0014] S3. Secondary growth of diamond film: The slit-shaped diamond film is placed in a chemical vapor deposition device, and the corresponding parameters are set to perform secondary growth of the diamond film to fill the cut gaps and form a complete slit-shaped diamond film.

[0015] Optionally, the selection and cutting of the diamond film for S1 includes:

[0016] S11. Select a circular self-supporting polycrystalline diamond film with a size of 1-16 inches. First, acid-wash the circular self-supporting polycrystalline diamond film with concentrated acid, then ultrasonically clean and wash it with water, and dry it under a protective atmosphere.

[0017] S12, Calculation formula for the trace of removing excess parts before hot pressing deformation;

[0018] S13. Input the trace calculation formula program into the laser cutting machine, place the circular self-supporting polycrystalline diamond film in the laser cutting machine, and input the target spherical cap radius R, target spherical cap height H and wedge cutting times n; use the laser cutting machine to cut the circular self-supporting polycrystalline diamond film, and take out the petal-shaped diamond film after cutting.

[0019] Optionally, in S12, the formula for removing part of the trace is:

[0020] ;

[0021] in: It refers to a positive natural number; R is the radius of the target spherical cap, in mm; H is the height of the target spherical cap, in mm; n is the number of wedge cuts; the trace formula is a polar coordinate equation, where p is the independent variable of the equation; ρ is the dependent variable of the equation.

[0022] Optionally, the high-temperature hot-pressing deformation in S2 includes:

[0023] S21. Select an ultra-high purity fine-grained graphite mold. Based on the measured original radius of the diamond film and the required curvature, and combined with the size of the heating furnace, design the graphite mold using 3D modeling software, draw the model, and process it. Place the mold in the heating furnace and fix it to the cut petal-shaped diamond film.

[0024] S22. Set the heating furnace parameters, mainly including the furnace temperature and load size to achieve the transformation of some diamonds in the petal-shaped diamond film into graphitized material, and provide the temperature and compressive stress conditions for directional deformation; complete the hot pressing process to obtain a spherical crown-shaped diamond film with gaps.

[0025] Optionally, in S21, the lower mold is a curved bowl-shaped graphite mold, and the upper mold is a flat-topped, arc-shaped graphite mold. The graphite mold is placed flat in the heating furnace, and the petal-shaped diamond film is placed in the graphite mold, making it parallel to the bottom surface of the furnace. The hot-pressing graphite mold is placed above the horizontal diamond film, with the arc surface facing down, so that the lowest point of the mold is placed in the center of the diamond film. The hot-pressing table is moved up and down to fix the mold, diamond film and the mold relatively and concentrically aligned. It is ensured that when pressure is applied in the furnace, the pressure head on the heating furnace will match the upper surface of the upper graphite mold.

[0026] Optionally, in S22, the furnace temperature needs to reach above 1300℃, and the target temperature needs to be reached within 10 minutes, followed by rapid cooling; set the furnace load, and apply a pressure of 100-600N to the upper surface of the mold according to the size and thickness of the diamond film, and the load needs to reach its maximum value within 10 minutes.

[0027] Optionally, the secondary growth of the diamond film in S3 includes:

[0028] S31. Immerse the spherical crown diamond film in a suspension containing nanodiamond powder, then sonicate it, and wash it dry;

[0029] S32. Place the pretreated spherical diamond film stably on the sample stage in the chemical vapor deposition reaction chamber, ensuring that the surface to be filled faces the plasma region; close the reaction chamber, start the mechanical pump, and evacuate to a high vacuum level to ensure a pure reaction chamber environment; introduce methane and hydrogen and raise the temperature for growth; after cooling to room temperature, close all gas paths, fill the chamber with atmospheric air, open the reaction chamber, and remove the sample; a complete and seamless spherical diamond film is obtained.

[0030] Optionally, in the S32 CVD furnace, the flow ratio of hydrogen to methane gas is 300:(1-30), the working pressure is 6-20 kPa, the growth temperature range is 750-900℃, the heating time is 10-20 min, the holding time is 10-20 min, the cooling time is 5-10 min, and the growth time is 80-150 min.

[0031] The key to the implementation of this invention lies in

[0032] (1) The circular diamond film is laser-cut according to the existing formula to form a petal-shaped diamond film with gaps.

[0033] (2) Hot-press deformation of petal-shaped diamond film to a temperature of over 1300℃, and rapid heating and cooling are required to ensure the conditions for partial diamond to transform into graphitization. After applying load, a crown-shaped diamond film with gaps is obtained.

[0034] (3) Place the crown diamond with gaps into a suspension containing nanodiamonds, and then place the diamond in a CVD furnace to perform secondary growth on the crown diamond, thereby filling the gaps and making the surface complete.

[0035] Technical principle of the invention:

[0036] 1. Selection of laser cutting process parameters

[0037] To ensure that the laser cutting process does not adversely affect the surface structure of the diamond film, a technology solution based on an ultraviolet picosecond or femtosecond laser should be selected. The key parameters are configured as follows: a short wavelength of 355nm or 266nm is used to improve the diamond's absorption efficiency of laser energy; the pulse width needs to be controlled within 10 picoseconds to achieve a cold processing mechanism, fundamentally avoiding melting or graphitization caused by thermal diffusion; the single pulse energy should be set at a level slightly higher than the diamond ablation threshold, at tens of microjoules, combined with a high repetition frequency of 100kHz to 500kHz, ensuring both precise layer-by-layer removal and efficient cutting; a high-speed scanning speed of several hundred millimeters per second is used to reduce heat accumulation, and a small focused spot of approximately 20μm is used to ensure cutting accuracy and kerf quality; high-purity nitrogen or argon is used as a coaxial purging gas to effectively remove processing debris and prevent surface oxidation. This set of parameters ensures that the cut edges are vertical and neat, the inner wall of the gap is smooth and free of micro-cracks, and the diamond phase structure is fully maintained, laying a damage-free substrate foundation for subsequent hot pressing deformation and secondary growth.

[0038] 2. Selection of process parameters for hot pressing deformation

[0039] Hot pressing deformation (S2 step) is the key step in transforming a diamond film from a planar petal shape to a spherical crown shape. The main process parameters include temperature, heating and cooling rates, load, and mold design. The selection of these parameters is based on the properties of the diamond material and the deformation mechanism.

[0040] Temperature: The furnace temperature needs to reach above 1300℃. This is because diamond undergoes partial graphitization at high temperatures (usually above 1200℃), meaning that the sp in diamond will undergo a partial graphitization transformation. 3 carbon atoms towards sp 2 The graphite-carbon transformation reduces the material's hardness and brittleness, while improving its plastic deformation capacity. A temperature above 1300℃ ensures that the diamond film possesses sufficient plasticity during hot pressing, facilitating directional bending.

[0041] Heating and cooling rates: The target temperature must be reached within 10 minutes, followed by rapid cooling. Rapid heating reduces the time diamond spends at high temperatures, preventing excessive graphitization that could lead to material performance degradation; rapid cooling helps to "freeze" the deformed structure, preventing the graphitized area from expanding or recrystallizing, thus maintaining the stability of the spherical crown shape.

[0042] Load: Depending on the size and thickness of the diamond film, apply a pressure ranging from 100 to 600 N. The load must reach its maximum value within 10 minutes. The load provides the necessary compressive stress, causing the petal-shaped diamond film to undergo plastic deformation in the mold. The load magnitude is related to the size and thickness of the diamond film: thicker or larger films require higher loads to ensure uniform deformation, but excessive loads may lead to cracking or over-graphitization.

[0043] Mold Design: Ultra-high purity fine-grained graphite molds are used. The lower mold is a curved bowl-shaped mold, while the upper mold is flat on top and rounded at the bottom. The curvature of the mold directly determines the curvature of the target spherical crown. The graphite mold has high thermal conductivity and high temperature resistance, ensuring uniform temperature distribution and reducing chemical reactions with the diamond film.

[0044] 3. Gap filling mechanism

[0045] A spherical diamond film with gaps is immersed in a suspension containing nanodiamond powder and then sonicated. The purpose of this step is to adsorb nanodiamond powder onto the gap surface, serving as nucleation sites for secondary growth. Nanodiamond powder possesses high surface energy, effectively promoting heterogeneous nucleation for diamond deposition. Under plasma conditions, CH4 decomposes to generate carbon-based active species (such as CH3 radicals), while H2 acts as a carrier gas and etchant, removing non-diamond carbon (such as graphite) and promoting diamond growth. The nanodiamond powder acts as a seed, attracting carbon species to deposit and grow in the gaps, gradually filling them. The growth process proceeds from the gap edge towards the center, forming a continuous diamond layer. The hydrogen to methane flow ratio (300:1-30) and operating pressure control the growth rate and quality: higher methane concentrations (e.g., a flow ratio of 300:30) accelerate growth but may introduce non-diamond carbon; lower methane concentrations (e.g., 300:1) result in slower but higher quality growth. Secondary growth primarily improves surface integrity and structural continuity, with little or no impact on curvature. By controlling growth conditions, curvature stability and surface smoothness can be ensured.

[0046] The above technical solution has at least the following advantages compared with the existing technology:

[0047] The above-described method of the present invention, which prepares a crown-shaped diamond film by thermal processing, involves hot pressing at a specific temperature to permanently deform a large-sized diamond film, resulting in a crown-shaped diamond film with gaps.

[0048] The slit-shaped diamond film obtained by the method of the present invention has a large curvature, good integrity, and maintains the high thermal conductivity and mechanical properties of diamond, which can meet the heat dissipation requirements of some electronic devices with irregular surfaces.

[0049] In summary, compared with traditional methods for increasing the contact area of ​​diamond films, the method of this invention uses the selection and cutting of diamond films, high-temperature hot pressing deformation, and secondary growth of diamond films to obtain spherical crown-shaped diamond films with high contact area. This method has a simple process, low operation difficulty, convenient diamond film deformation, excellent thermal conductivity and mechanical properties, is easy to use for heat dissipation of electronic devices with irregular surfaces, and is conducive to large-scale industrial production and promotion. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 This is a process flow diagram of a method for preparing a crown-shaped diamond film by thermal processing according to the present invention;

[0052] Figure 2 This is a laser cutting trace and petal diamond shape diagram of a method for preparing a crown-shaped diamond film by thermal processing according to the present invention; wherein: (1) is the diagram corresponding to the number of wedge cuttings n=3, (2) is the diagram corresponding to the number of wedge cuttings n=4, (3) is the diagram corresponding to the number of wedge cuttings n=7, and (4) is the diagram corresponding to the number of wedge cuttings n=8;

[0053] Figure 3 This is a schematic diagram of the hot-pressing deformation part of a method for preparing a crown-shaped diamond film by thermal processing according to the present invention. Detailed Implementation

[0054] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0055] In embodiments of the present invention, words such as "exemplarily," "for example," etc., are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the word "exemplary" is intended to present the concept in a concrete manner. Furthermore, in embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one.

[0056] In the embodiments of the present invention, the terms "image" and "picture" may sometimes be used interchangeably. It should be noted that when the distinction is not emphasized, their intended meanings are consistent.

[0057] In this embodiment of the invention, sometimes a subscript such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, the meaning they express is the same.

[0058] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0059] A method for preparing a crown-shaped diamond film by thermal processing, the method combining Figure 1 include:

[0060] S1. Selection and Cutting of Diamond Film: Design the target curvature of the desired crown-shaped diamond film, calculate the required diamond film radius based on the curvature, select the diamond film grown by chemical vapor deposition and perform acid washing; perform laser cutting according to the calculated formula to remove the excess part before hot pressing deformation; the laser cutting trace and the petal-shaped diamond film after cutting are as follows... Figure 2 As shown;

[0061] S2. High-Temperature Hot Press Deformation: Prepare a hot press deformation mold with the required curvature; fix the petal-shaped diamond film to the hot press deformation mold; set the corresponding parameters of the heating furnace to perform high-temperature hot press deformation of the diamond film in the mold and heating furnace, obtaining a slit-shaped diamond film; the hot press deformation part is as follows: Figure 3 As shown;

[0062] S3. Secondary growth of diamond film: The slit-shaped diamond film is placed in a chemical vapor deposition device, and the corresponding parameters are set to perform secondary growth of the diamond film to fill the cut gaps and form a complete slit-shaped diamond film.

[0063] Specifically, the selection and cutting of the diamond film for S1 includes:

[0064] S11. Select a circular self-supporting polycrystalline diamond film with a size of 1-16 inches. First, acid-wash the circular self-supporting polycrystalline diamond film with concentrated acid, then ultrasonically clean and wash it with water, and dry it under a protective atmosphere.

[0065] S12, Calculation formula for the trace of removing excess parts before hot pressing deformation;

[0066] S13. Input the trace calculation formula program into the laser cutting machine, place the circular self-supporting polycrystalline diamond film in the laser cutting machine, and input the target spherical cap radius R, target spherical cap height H and wedge cutting times n; use the laser cutting machine to cut the circular self-supporting polycrystalline diamond film, and take out the petal-shaped diamond film after cutting.

[0067] Specifically, in S12, the formula for removing part of the trace is:

[0068] ;

[0069] in: It refers to a positive natural number; R is the radius of the target spherical cap, in mm; H is the height of the target spherical cap, in mm; n is the number of wedge cuts; the trace formula is a polar coordinate equation, where p is the independent variable of the equation; ρ is the dependent variable of the equation.

[0070] Specifically, the high-temperature hot-pressing deformation in S2 includes:

[0071] S21. Select an ultra-high purity fine-grained graphite mold. Based on the measured original radius of the diamond film and the required curvature, and combined with the size of the heating furnace, design the graphite mold using 3D modeling software, draw the model, and process it. Place the mold in the heating furnace and fix it to the cut petal-shaped diamond film.

[0072] S22. Set the heating furnace parameters, mainly including the furnace temperature and load size to achieve the transformation of some diamonds in the petal-shaped diamond film into graphitized material, and provide the temperature and compressive stress conditions for directional deformation; complete the hot pressing process to obtain a spherical crown-shaped diamond film with gaps.

[0073] Specifically, in S21, the lower mold is a curved bowl-shaped graphite mold, and the upper mold is a flat-topped, arc-shaped graphite mold. The graphite mold is placed flat in the heating furnace, and the petal-shaped diamond film is placed in the graphite mold, making it parallel to the bottom surface of the furnace. The hot-pressing graphite mold is placed above the horizontal diamond film, with the arc surface facing down, so that the lowest point of the mold is placed in the center of the diamond film. The hot press table is moved up and down to fix the mold, diamond film and the mold relatively and concentrically aligned. This ensures that when pressure is applied in the furnace, the pressure head on the heating furnace will match the upper surface of the upper graphite mold.

[0074] Specifically, in S22, the furnace temperature needs to reach above 1300℃, and the target temperature needs to be reached within 10 minutes, followed by rapid cooling; the furnace load is set, and pressures ranging from 100-600N are applied to the upper surface of the mold according to the size and thickness of the diamond film, and the load needs to reach its maximum value within 10 minutes.

[0075] Specifically, the secondary growth of the diamond film in S3 includes:

[0076] S31. Immerse the spherical crown diamond film in a suspension containing nanodiamond powder, then sonicate it, and wash it dry;

[0077] S32. Place the pretreated spherical diamond film stably on the sample stage in the chemical vapor deposition reaction chamber, ensuring that the surface to be filled faces the plasma region; close the reaction chamber, start the mechanical pump, and evacuate to a high vacuum level to ensure a pure reaction chamber environment; introduce methane and hydrogen and raise the temperature for growth; after cooling to room temperature, close all gas paths, fill the chamber with atmospheric air, open the reaction chamber, and remove the sample; a complete and seamless spherical diamond film is obtained.

[0078] Specifically, in the S32 CVD furnace, the flow rate ratio of hydrogen to methane is 300:(1-30), the working pressure is 6-20 kPa, the growth temperature range is 750-900℃, the heating time is 10-20 min, the holding time is 10-20 min, the cooling time is 5-10 min, and the growth time is 80-150 min.

[0079] Example 1

[0080] A method for preparing a crown-shaped diamond film by thermal processing, the method combining Figure 1 include:

[0081] S1. Selection and Cutting of Diamond Film: Design the target curvature of the desired spherical crown-shaped diamond film, calculate the required diamond film radius based on the curvature, select the diamond film grown by chemical vapor deposition and perform acid etching; perform laser cutting according to the calculated formulas to remove the excess part before hot pressing deformation; the laser cutting trace and the shape of the diamond after cutting are as follows... Figure 2 As shown;

[0082] The required final radius of curvature (design value 150mm) was calculated to be 149.2mm for the graphite mold. A circular self-supporting polycrystalline diamond film with a diameter of 6 inches was selected, and its initial radius (76.2mm), thickness (0.8mm), and initial curvature (flatness) were measured. It was placed in a mixed acid solution of concentrated nitric acid and concentrated sulfuric acid (volume ratio 3:1) and acid-washed at 120℃ for 30min to remove surface metallic impurities. Subsequently, the diamond film was placed in an ethanol solution and ultrasonically cleaned 3 times, 10min each time. Finally, it was rinsed with deionized water and transferred to a drying oven filled with high-purity nitrogen (purity ≥99.999%) and dried at 80℃ for 2 hours.

[0083] Formula for calculating the traces after removing excess material before hot pressing deformation;

[0084] ;

[0085] Input the trace calculation formula program into the laser cutting machine, place the circular self-supporting polycrystalline diamond film in the laser cutting machine, and input the target spherical cap radius R, target spherical cap height H and wedge cutting times n; use the laser cutting machine to cut the circular self-supporting polycrystalline diamond film, and after the cutting is completed, take out the petal-shaped diamond film;

[0086] S2. High-Temperature Hot Press Deformation: Ultra-high purity fine-grained graphite was selected as the mold material. A cylindrical graphite blank was fixed using a CNC milling lathe. A diamond-coated cutting tool was used, with a feed rate of 0.1 mm / r and a spindle speed of 2000 r / min to machine a matching lower mold (bowl-shaped, radius of curvature 149.2 mm) and an upper mold (flat upper surface, matching arc-shaped lower surface). The lower mold was then placed stably at the bottom of the microwave plasma chemical vapor deposition (MPCVD) furnace, and then the cutting... The cut petal-shaped diamond film is precisely placed on the concave surface of the lower mold; then the convex surface of the upper mold is placed downwards, aligned and gently placed on top of the diamond film, ensuring that the three are concentrically aligned; the reaction chamber door is closed, and the mechanical pump and molecular pump are started in sequence to evacuate to a high vacuum state. After evacuation, the heating program is started: the temperature is increased to 1700℃ at a rate of 2000℃ / min and then rapidly cooled within 30 seconds. At the same time, a final pressure of 300N is applied when the temperature reaches 1700℃ and maintained until the end, to obtain a slit crown-shaped diamond film;

[0087] S3. Secondary growth of diamond film: After completion, open the vent valve and take out mold 1 and mold 2 one after another. Continue to place the pretreated substrate stably on the sample stage in the CVD reaction chamber, ensuring that the surface to be filled faces the plasma region. Then, introduce high-purity hydrogen and methane, controlling the hydrogen to methane flow ratio to be 50:1; the working pressure is 15 kPa; start the microwave plasma, heat the substrate temperature and maintain it at 750℃ for growth, the heating time is 20 min, the holding time is 10 min, the cooling time is 10 min, and the growth time is 120 min, forming a complete spherical crown-shaped diamond film.

[0088] The 6-inch complete spherical diamond film processed according to the above embodiments has a radius of curvature that meets the design requirements (150±5mm), and a smooth surface without defects such as cracks.

[0089] Example 2

[0090] A method for preparing a crown-shaped diamond film by thermal processing, the method combining Figure 1 include:

[0091] S1. Selection and Cutting of Diamond Film: Design the target curvature of the desired spherical crown-shaped diamond film, calculate the required diamond film radius based on the curvature, select the diamond film grown by chemical vapor deposition and perform acid etching; perform laser cutting according to the calculated formulas to remove the excess part before hot pressing deformation; the laser cutting trace and the shape of the diamond after cutting are as follows... Figure 2 As shown;

[0092] The required final radius of curvature (design value 150mm) was calculated to be 149.5mm for the graphite mold. An 8-inch (200mm) diameter chemical vapor deposition (CVD) diamond self-supporting film was selected, and its initial parameters were precisely measured using a laser interferometer: radius 100.0±0.05mm, thickness 1.2±0.03mm, and initial curvature flat (radius of curvature > 1500mm). It was then placed in a mixed acid solution of concentrated nitric acid and concentrated sulfuric acid (volume ratio 3:1) and acid-washed at 120℃ for 30 minutes to remove surface metallic impurities. Subsequently, the diamond film was placed in an ethanol solution and ultrasonically cleaned three times, 10 minutes each time. Finally, it was rinsed with deionized water and transferred to a drying oven filled with high-purity nitrogen (purity ≥ 99.999%) and dried at 80℃ for 2 hours.

[0093] Formula for calculating the traces after removing excess material before hot pressing deformation;

[0094] ;

[0095] Input the trace calculation formula program into the laser cutting machine, place the circular self-supporting polycrystalline diamond film in the laser cutting machine, input the predetermined formula, set the crown height and radius to 149.5mm, the wedge cutting number to 8, cut the circular self-supporting polycrystalline diamond film, and take out the petal-shaped diamond film after the cutting is completed.

[0096] S2. High-Temperature Hot Press Deformation: Using ultra-high purity fine-grained graphite material with dimensions Φ250mm×120mm, the lower mold (Mold 2) is designed with a precisely curved bowl shape using 3D modeling software, while the upper mold (Mold 1) has a flat upper surface and a rounded lower surface. The lower mold is placed stably at the bottom of the hot press furnace. Then, the pre-cut petal-shaped diamond film is precisely placed on the concave surface of the lower mold. Next, the convex surface of the upper mold is placed downwards, aligned, and gently placed on top of the diamond film, ensuring concentric alignment of all three. The hot press furnace is then closed and a vacuum is applied. The furnace was filled with high-purity argon as a protective atmosphere. A heating program was set: the furnace temperature was raised to 1800℃ at a rate of 1500℃ / min using an inductive coupling module. At the same time, a loading program was set: a constant pressure of 200N was applied to the upper mold within 1 minute. This caused the diamond film to undergo plastic deformation and fit tightly into the mold cavity, completing the graphitization-induced directional bending deformation. Subsequently, the furnace was cooled to room temperature and the pressure was released. The sample was then taken out of the furnace, resulting in a primary diamond spherical crown with a crown-like shape but obvious cracks in the gaps between the petals.

[0097] S3. Secondary growth of diamond film: Place the pretreated spherical diamond sample, with the surface to be repaired facing upwards, stably on the sample stage of the microwave plasma CVD equipment; close the reaction chamber and evacuate the background vacuum to 5×10⁻⁶. -4 Below Pa; then high-purity hydrogen and methane are introduced, with the hydrogen flow rate controlled at 300 sccm and the methane flow rate at 10 sccm (flow ratio 30:1), and the working pressure stabilized at 10 kPa; microwave plasma is started to heat the substrate temperature and maintain it at 850℃ for growth, with a heating time of 20 min, a holding time of 10 min, a cooling time of 10 min, and a growth time of 120 min; after growth, the methane supply is stopped, and the temperature is lowered to room temperature in a hydrogen atmosphere; finally, the chamber is filled with atmosphere, and the sample is taken out to obtain a complete spherical crown-shaped diamond film.

[0098] The 8-inch complete spherical diamond film processed by the above embodiments has a radius of curvature that meets the design requirements (150±1mm), and has a smooth surface without defects such as cracks.

[0099] Example 3

[0100] A method for preparing a crown-shaped diamond film by thermal processing, the method combining Figure 1 include:

[0101] S1. Selection and Cutting of Diamond Film: Select a circular, self-supporting polycrystalline diamond film with a diameter of 10 inches and a thickness of 1.5 mm. Immerse the diamond film in a boiling mixture of concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4) (volume ratio 1:3) for 30 minutes to thoroughly remove surface contaminants such as metals and organic matter. After acid washing, remove the diamond film and ultrasonically clean it three times in deionized water for 10 minutes each time. Then, ultrasonically clean it again in anhydrous ethanol for 5 minutes. Finally, transfer the diamond film to a drying oven filled with high-purity nitrogen (N2) and dry it at 80°C for 1 hour. Design the target spherical cap radius R = 50 mm and the target spherical cap height H = 15 mm. Determine the number of wedge cuts n = 8. Substitute R, H, and n into the provided trace calculation formula. Precisely fix the pretreated circular diamond film onto the worktable of the laser cutting machine. Input the parameters in the control interface: R = 50 mm, H = 15 mm, n = 8. The laser cutting program is initiated. The laser cuts along eight calculated petal-shaped lines, precisely removing excess material while ensuring the width and edge quality of the cut.

[0102] S2. High-Temperature Hot Press Deformation: Ultra-high purity fine-grained graphite (purity > 99.99%) is selected as the mold material. Based on the original radius of the diamond film (127mm) and the target spherical crown curvature, the mold is designed using SolidWorks. Lower mold: A bowl-shaped spherical crown mold with a curvature radius of 50mm. Upper mold: A pressure head with a flat upper surface and an arc-shaped lower surface matching the lower mold. The processed lower graphite mold is placed smoothly at the center of the furnace bottom of the hot press sintering furnace. The petal-shaped diamond film is carefully placed in the groove of the lower mold, ensuring it is parallel to the furnace bottom. Then, the arc-shaped upper graphite mold is gently placed on top of the diamond film, ensuring its lowest point (center) is concentrically aligned with the center of the diamond film and the center of the lower mold. The position of the upper pressure head of the hot press furnace is checked and adjusted to ensure it presses completely and flatly onto the plane of the upper graphite mold during descent. The furnace chamber was closed and evacuated to a vacuum, with argon gas introduced as a protective gas. The target temperature inside the furnace was set to 1350°C. The heating program was to raise the temperature from room temperature to 1350°C within 8 minutes. Based on the size and thickness of the diamond film, the maximum load was set to 300N. The loading program was to uniformly load from 0N to 300N within 8 minutes. Hot pressing was then performed: the hot pressing program was initiated. Under the combined action of high temperature and pressure, the petal-shaped diamond film underwent plastic deformation, with the petals bending downwards and adhering to the bowl-shaped curved surface of the lower mold. Simultaneously, under high temperature and pressure, a localized, minute phase transition from diamond to graphite occurred in the area of ​​highest contact stress in the center of the diamond film. The hot pressing was allowed to complete. After the furnace temperature dropped to room temperature (approximately <60°C), the protective gas was turned off, and the furnace chamber was opened. The assembly was removed, and the mold was carefully separated to obtain a preliminarily formed, but spherical, crown-shaped diamond film with gaps between the petals.

[0103] S3: Chemical Vapor Deposition (CVD) Secondary Growth for Gap Filling: The hot-pressed spherical diamond film is immersed in an ethanol suspension of nanodiamond powder (particle size 5-10 nm) at a concentration of 0.1 mg / mL. It is ultrasonically treated for 30 minutes to ensure uniform adhesion of the nanodiamond particles to the film surface, especially at the gap edges, serving as nucleation sites for secondary growth. It is then rinsed with ethanol and dried under a nitrogen atmosphere. The pretreated spherical diamond film is then stably placed on the molybdenum sample stage of the microwave plasma CVD (MPCVD) reaction chamber, ensuring the gap to be filled faces the plasma sphere region. The reaction chamber is closed, the vacuum system is activated, and the chamber pressure is evacuated to 1.0 × 10⁻⁶. -3 Below Pa. High-purity hydrogen (H2) and methane (CH4) are introduced into the reaction chamber at a flow rate ratio of H2:CH4 = 100:3 (sccm). The working pressure is stabilized at 10 kPa. The microwave source and heating system are started, and the substrate temperature is raised to 850°C within 15 minutes. The growth is carried out at 850°C for 120 minutes. After growth, the microwave and heating are stopped, and the sample is allowed to cool to below 400°C within 8 minutes under continuous ventilation, followed by natural cooling to room temperature. All gas paths are closed, and high-purity nitrogen is introduced into the chamber to atmospheric pressure. The reaction chamber is then opened. The final sample is carefully removed. At this point, the original gaps have been completely filled by the newly grown high-quality diamond, resulting in a structurally complete, dense, seamless, spherical, self-supporting polycrystalline diamond film.

[0104] Example 4

[0105] A method for preparing a crown-shaped diamond film by thermal processing, the method combining Figure 1 include:

[0106] S1. Selection and Cutting of Diamond Film: A spherical crown-shaped diamond film was designed based on a target curvature radius of 100mm. The calculated curvature radius of the graphite mold was 99.7mm. A CVD diamond self-supporting film with a diameter of 6 inches was selected. Its radius was measured to be 75.0±0.05mm and its thickness to be 1.0±0.03mm. The initial curvature was flat (curvature radius > 1200mm). The film was placed in a mixed acid solution of concentrated nitric acid and concentrated sulfuric acid (2:1 volume ratio) at 110℃ for 40 minutes to remove surface impurities. Then, it was ultrasonically cleaned three times with isopropanol solution and rinsed with deionized water. Finally, it was dried at 85℃ for 1.5 hours in a drying oven under high-purity argon protection. Next, the program was programmed according to the calculation formula for removing excess parts before hot pressing deformation. The crown height and radius parameters were set to 99.7mm and the number of wedge cuts was set to 12. The pre-treated circular diamond film was precisely cut using an ultraviolet laser cutter to obtain a petal-shaped structure.

[0107] S2. High-temperature hot pressing deformation: Using ultra-high purity fine-grained graphite material of Φ200mm×100mm, the lower mold is designed as a bowl-shaped mold with a curvature of 99.7mm through 3D modeling, and the upper mold is a flat upper and rounded lower structure. The lower mold is placed at the bottom of the hot pressing furnace, and the petal-shaped diamond film is precisely positioned on its concave surface. Then the upper mold is covered to ensure that the three are concentrically aligned. After the furnace is closed and vacuumed, high-purity argon gas is introduced. The temperature is raised to 1600℃ at a rate of 1200℃ / min and a constant pressure of 400N is applied within 2 minutes to cause the diamond film to undergo graphitization-induced plastic deformation and fit into the mold cavity. After cooling with the furnace, a primary spherical crown with interlobular cracks is obtained.

[0108] S3: Chemical Vapor Deposition (CVD) Secondary Growth to Fill Gaps: Secondary growth of diamond film is performed: The spherical cap sample is placed with the side to be repaired facing upwards in a microwave plasma CVD device, and a vacuum of 8×10⁻⁶ is applied. -4 After passing through hydrogen (400 sccm) and methane (15 sccm) at 15 kPa pressure, the diamond film is grown at 900°C for 90 minutes (including 15 minutes of heating, 15 minutes of holding, and 8 minutes of cooling) to obtain a complete spherical diamond film. The 6-inch diamond film treated in this example has a radius of curvature of 100 ± 0.8 mm and a smooth, crack-free surface.

[0109] Example 5

[0110] A method for preparing a crown-shaped diamond film by thermal processing, the method combining Figure 1 include:

[0111] S1. Selection and Cutting of Diamond Film: First, a circular self-supporting polycrystalline diamond film with a diameter of 10 inches and a thickness of 1.2 mm was selected. After acid washing with a mixture of concentrated nitric acid and concentrated sulfuric acid (volume ratio 1:3) at 180°C for 30 minutes, it underwent ultrasonic cleaning and rinsing with deionized water, and finally dried under argon protection. Based on the target spherical cap radius R=150mm, height H=50mm, and wedge cutting times n=16, the cutting path was calculated using a trace formula. Cutting was completed using a 500W nanosecond pulsed laser (wavelength 1064nm) to obtain a petal-shaped diamond film.

[0112] S2. High-Temperature Hot Press Deformation: A lower mold (152mm radius of curvature) and an upper mold (148mm radius of curvature) are fabricated using ultra-high purity fine-grained graphite. The petal-shaped diamond film is precisely fixed within the mold and placed in a hot press furnace. The hot pressing program is set: the temperature is raised to 1400℃ within 2 minutes, while a pressure of 450N is applied. After holding at this temperature and pressure for 15 minutes, the temperature is rapidly cooled to below 800℃, resulting in a crown-shaped diamond film with 16 wedge-shaped slits.

[0113] S3: Chemical vapor deposition (CVD) secondary growth to fill gaps: The diamond film was immersed in a 0.5 mg / mL isopropanol suspension of nanodiamond powder (particle size 5-10 nm) and ultrasonically treated for 20 minutes. After drying, it was placed in a chemical vapor deposition device and grown for 120 minutes under the conditions of hydrogen flow rate 600 sccm, methane flow rate 18 sccm (flow ratio 300:9), working pressure 12 kPa, and substrate temperature 850℃. All gaps were successfully filled, and a complete and dense spherical crown-shaped diamond film product was finally obtained.

[0114] Example 6

[0115] A method for preparing a crown-shaped diamond film by thermal processing, the method combining Figure 1 include:

[0116] S1. Selection and Cutting of Diamond Film: First, a spherical crown-shaped diamond film with a target radius of curvature of 320 mm was designed. The radius of curvature of the graphite mold was calculated to be 318.2 mm. A circular self-supporting polycrystalline diamond film with a diameter of 16 inches was selected, and its initial radius (203.2 mm), thickness (1.5 mm), and initial curvature (flat) were measured. It was placed in a mixed acid solution of concentrated nitric acid and concentrated sulfuric acid (volume ratio 1:2) and acid-washed at 155°C for 35 min to thoroughly remove surface metallic impurities. Subsequently, the diamond film was placed in an acetone solution and ultrasonically cleaned 5 times, 10 min each time. Finally, it was rinsed with deionized water and transferred to a drying oven filled with high-purity argon gas (purity ≥99.999%) and dried at 90°C for 2 hours.

[0117] S2. High-Temperature Hot Press Deformation: The trace calculation formula is input into a 1500W femtosecond laser cutting machine. The target spherical crown radius R = 320mm, target spherical crown height H = 110mm, and wedge cutting times n = 32 are set. After cutting, a diamond film with 32 petal units is obtained. In the high-temperature hot press deformation stage, ultra-high purity fine-grained graphite is selected as the mold material. A five-axis CNC machining center is used to fix the cylindrical graphite blank. A diamond-coated milling cutter is selected, with a feed rate of 0.05mm / r and a spindle speed of 3000r / min to process the matching lower mold (bowl-shaped, radius of curvature 318.2mm) and upper mold (flat upper surface, matching arc lower surface). The lower mold is placed stably at the bottom of a large hot press furnace. Then, the cut petal-shaped diamond film is precisely placed on the concave surface of the lower mold. The convex surface of the upper mold is then aligned and gently placed on top of the diamond film, ensuring concentric alignment of all three. After closing the furnace door and evacuating to a high vacuum state, the heating program is started: the temperature is increased to 1600℃ at a rate of 1200℃ / min and then rapidly cooled within 60 seconds. At the same time, a final pressure of 800N is applied when the temperature reaches 1600℃ and maintained until the end of the process to obtain a crown-shaped diamond film with 32 wedge-shaped slits.

[0118] S3: Secondary Chemical Vapor Deposition (CVD) for Gap Filling: In the secondary growth stage of the diamond film, the hot-pressed substrate is stably placed on the sample stage within a large MPCVD reaction chamber, ensuring the surface to be filled faces the plasma region. High-purity hydrogen and methane are introduced, with the hydrogen to methane flow ratio controlled at 60:1 and the working pressure at 16 kPa. Microwave plasma is activated to heat the substrate to 820°C for growth. The heating time is 25 min, the holding time is 20 min, the cooling time is 12 min, and the growth time is 180 min, forming a complete large-size spherical crown-shaped diamond film. The 16-inch complete spherical crown-shaped diamond film processed in the above example has a radius of curvature that meets the design requirements (320±5 mm), a surface finish Ra≤15 nm, and is free of cracks and other defects, fully meeting the application requirements of large-size optical windows.

[0119] The above-described method of the present invention, which prepares a crown-shaped diamond film by thermal processing, involves hot pressing at a specific temperature to permanently deform a large-sized diamond film, resulting in a crown-shaped diamond film with gaps.

[0120] The slit-shaped diamond film obtained by the method of the present invention has a large curvature, good integrity, and maintains the high thermal conductivity and mechanical properties of diamond, which can meet the heat dissipation requirements of some electronic devices with irregular surfaces.

[0121] In summary, compared with traditional methods for increasing the contact area of ​​diamond films, the method of this invention uses the selection and cutting of diamond films, high-temperature hot pressing deformation, and secondary growth of diamond films to obtain spherical crown-shaped diamond films with high contact area. This method has a simple process, low operation difficulty, convenient diamond film deformation, excellent thermal conductivity and mechanical properties, is easy to use for heat dissipation of electronic devices with irregular surfaces, and is conducive to large-scale industrial production and promotion.

[0122] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. Additionally, the character " / " in this article generally indicates an "or" relationship between the preceding and following related objects, but it can also represent an "and / or" relationship. Please refer to the context for a more accurate understanding.

[0123] In this invention, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of a single item or a plurality of items. For example, at least one of a, b, or c can represent: a, b, c, ab, ac, bc, or abc, where a, b, and c can be a single item or multiple items.

[0124] It should be understood that, in various embodiments of the present invention, the sequence number of each process does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0125] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for producing a spherical cap diamond film by a heat treatment process, characterized by, The method includes: S1. Selection and cutting of diamond film: Design the target curvature of the desired crown-shaped diamond film, calculate the required diamond film radius based on the curvature, select the diamond film grown by chemical vapor deposition and perform acid washing; perform laser cutting according to the calculated relevant formula to cut off the excess part before hot pressing deformation to obtain a petal-shaped diamond film. S2. High-temperature hot pressing deformation: Prepare a hot pressing deformation mold with the required curvature; fix the petal-shaped diamond film and the hot pressing deformation mold together; set the corresponding parameters of the heating furnace, so that the petal-shaped diamond film is subjected to high-temperature hot pressing deformation in the mold and the heating furnace to obtain a spherical crown-shaped diamond film with gaps. S3. Secondary growth of diamond film: The slit-shaped diamond film is placed in a chemical vapor deposition device, and the corresponding parameters are set to perform secondary growth of the diamond film to fill the cut gaps and form a complete slit-shaped diamond film.

2. The method for preparing a spherical cap diamond film by heat processing according to claim 1, wherein The selection and cutting of the diamond film for S1 includes: S11. Select a circular self-supporting polycrystalline diamond film with a size of 1-16 inches. First, acid-wash the circular self-supporting polycrystalline diamond film with concentrated acid, then ultrasonically clean and wash it with water, and dry it under a protective atmosphere. S12, Calculation formula for the trace of removing excess parts before hot pressing deformation; S13. Input the trace calculation formula program into the laser cutting machine, place the circular self-supporting polycrystalline diamond film in the laser cutting machine, input the target spherical cap radius R, the target spherical cap height H and the number of wedge cuts n; use the laser cutting machine to cut the circular self-supporting polycrystalline diamond film, and take out the petal-shaped diamond film after the cutting is completed.

3. The method for preparing a spherical cap diamond film by thermal processing according to claim 2, wherein In S12, the formula for removing part of the trace is: ； in: It refers to a positive natural number; R is the radius of the target sphere, in mm; H is the height of the target sphere, in mm; n is the number of wedge cuts; the trace formula is a polar coordinate equation, where p is the independent variable of the equation; ρ is the dependent variable of the equation.

4. The method for preparing a crown-shaped diamond film by heat treatment according to claim 1, characterized in that, S2 high-temperature hot pressing deformation includes: S21. Select an ultra-high purity fine-grained graphite mold. Based on the measured original radius of the diamond film and the required curvature, and combined with the size of the heating furnace, design the graphite mold using 3D modeling software, draw the model, and process it. Place the mold in the heating furnace and fix it to the cut petal-shaped diamond film. S22. Set the heating furnace parameters, mainly including the furnace temperature and load size to achieve the transformation of some diamonds in the petal-shaped diamond film into graphitized material, and provide the temperature and compressive stress conditions for directional deformation; complete the hot pressing process to obtain a spherical crown-shaped diamond film with gaps.

5. The method for preparing a crown-shaped diamond film by heat treatment according to claim 4, characterized in that, In S21, the lower mold is a curved bowl-shaped graphite mold, and the upper mold is a flat-topped, arc-shaped graphite mold. The graphite mold is placed flat in the heating furnace, and the petal-shaped diamond film is placed in the graphite mold, making it parallel to the bottom surface of the furnace. The hot-pressing graphite mold is placed above the horizontal diamond film, with the arc surface facing down, so that the lowest point of the mold is placed in the center of the diamond film. The hot-pressing table is moved up and down to fix the mold, diamond film and the mold relatively and concentrically aligned. It is ensured that when pressure is applied in the furnace, the pressure head on the heating furnace will match the upper surface of the upper graphite mold.

6. The method for preparing a crown-shaped diamond film by heat treatment according to claim 4, characterized in that, In S22, the furnace temperature needs to reach above 1300℃ and must reach the target temperature within 10 minutes, followed by rapid cooling; set the furnace load, apply pressure of 100-600N to the upper surface of the mold according to the size and thickness of the diamond film, and the load needs to reach the maximum value within 10 minutes.

7. The method for preparing a crown-shaped diamond film by heat treatment according to claim 1, characterized in that, The secondary growth of the diamond film in S3 includes: S31. Immerse the spherical crown diamond film in a suspension containing nanodiamond powder, then sonicate it, and wash it dry; S32. Place the pretreated spherical diamond film stably on the sample stage in the chemical vapor deposition reaction chamber, ensuring that the surface to be filled faces the plasma region; close the reaction chamber, start the mechanical pump, and evacuate to a high vacuum level to ensure a pure reaction chamber environment; introduce methane and hydrogen and raise the temperature for growth; after cooling to room temperature, close all gas paths, fill the chamber with atmospheric air, open the reaction chamber, and remove the sample; a complete and seamless spherical diamond film is obtained.

8. The method for preparing a crown-shaped diamond film by heat treatment according to claim 7, characterized in that, In the S32 CVD furnace, the hydrogen to methane gas flow ratio is 300:(1-30), the working pressure is 6-20 kPa, the growth temperature range is 750-900℃, the heating time is 10-20 min, the holding time is 10-20 min, the cooling time is 5-10 min, and the growth time is 80-150 min.

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