Method for preparing blue diamond based on MPCVD method

Abstract

The invention discloses a method for preparing a blue diamond based on an MPCVD method, and aims to solve the problems that in the diamond growth process, boron-doped coloring growth has gray tone, and an electron irradiation method needs to be adjusted according to the growth batch of diamonds. The method for preparing the blue diamond comprises the following steps: S1, pretreating an HPHT diamond seed wafer, and ultrasonically cleaning a silicon wafer and a germanium wafer; s2, placing a cleaned silicon wafer and a cleaned germanium wafer around the pretreated seed crystal, and then performing etching treatment; s3, methane and hydrogen are introduced for microwave plasma chemical vapor deposition growth; s4, the diamond blank is taken out; s5, polycrystals on the surface of the diamond blank are cut off; and S6, high-temperature and high-pressure treatment. According to the method, Si and Ge elements are doped in the crystal growth process, SiV and GeV color centers are formed in a diamond blank, the diamond is blue through absorption of the SiV and GeV color centers in a near-infrared region, gray tone caused by doping of boron elements is avoided, and the method is suitable for batch production of blue diamonds.

Description

Technical Field

[0001] The invention belongs to the field of diamond color modification, and in particular relates to a method for preparing blue diamond based on the MPCVD method. Background Art

[0002] Diamond is mainly composed of carbon, and is a mineral produced in high temperature and high pressure environment deep in the earth. Pure diamond is colorless and transparent. When the growth environment changes or some elements enter the diamond lattice to form some defects, the color of the diamond will change. For example, when the pressure changes suddenly, the diamond lattice changes and produces green, when the nitrogen content of the fluid suddenly increases during the growth process, the diamond turns yellow, and so on. Because diamond has a high dispersion, the cut diamond shows colorful fire under the light, and the dazzling appearance makes diamond deeply loved by people. White diamond is the eternal favorite of jewelers and luxury designers. With the improvement of people's living standards and aesthetic level, the demand for white diamonds continues to increase, and the demand for high-quality colored diamonds has also greatly increased. However, the more demanding growth environment and extremely small production make the price of colored diamonds very expensive.

[0003] At present, the main methods for synthesizing diamonds are HPHT (High Pressure High Temperature) and CVD (Chemical Vapor Deposition). Compared with HPHT, CVD is widely used in the production of synthetic diamonds due to its obvious advantages such as fast crystal growth rate, large crystal output and high crystal quality. With the increasing demand for diamonds and the continuous development of synthetic diamond technology, synthetic diamonds have entered the jewelry market with their advantages such as beauty, low cost, high output, low carbon and environmental protection, which are not inferior to natural diamonds, and are sought after by the public.

[0004] At present, synthetic colored diamonds are mostly blue diamonds, pink diamonds and golden diamonds. There are two methods for preparing blue diamonds: growth method and electron irradiation. The growth method mainly adds boron to the environment during the growth of diamonds to form a blue color center in the diamond. The blue prepared by this method often has a gray tone, which makes the blue not bright enough and affects the value; the electron irradiation method uses a high-energy electron beam to prepare a blue GR1 color center in the diamond, but the irradiation parameters need to be adjusted according to the batch, which affects the production efficiency of blue diamonds and the yield rate of large-carat blue diamonds. In addition, the difficulty in obtaining irradiation sources increases the production cost of blue diamonds. Summary of the invention

[0005] The purpose of the present invention is to solve the problem that the blue diamond grown by boron-doped coloration during the diamond growth process has a gray tone and the electron irradiation method needs to be adjusted according to the growth batch of diamond, and two methods for preparing blue diamond based on the MPCVD method are provided.

[0006] The method for preparing blue diamond based on MPCVD method of the present invention is implemented according to the following steps:

[0007] Step S1, placing a HPHT (high-temperature and high-pressure method) diamond seed crystal in a mixed acid for pretreatment, washing to obtain a pretreated seed crystal, and ultrasonically cleaning the silicon wafer and the germanium wafer respectively to obtain a cleaned silicon wafer and germanium wafer;

[0008] Step S2, in the vacuum chamber of the MPCVD device, placing the pretreated seed crystal on a molybdenum tray, placing the cleaned silicon wafer and germanium wafer around the pretreated seed crystal, evacuating the vacuum chamber, and then introducing hydrogen or oxygen, using hydrogen or oxygen to excite plasma for etching;

[0009] Step S3, after the etching process is completed, methane and hydrogen are introduced into the vacuum chamber, the volume concentration of methane is controlled to be 2% to 10%, the volume concentration of hydrogen is controlled to be 90% to 98%, the growth temperature is controlled to be 700 to 1000°C, and the pressure is controlled to be 10 to 15 kPa for microwave plasma chemical vapor deposition growth;

[0010] Step S4: After the microwave plasma chemical vapor deposition growth is completed, the pressure and temperature in the vacuum chamber are gradually reduced to obtain a diamond blank;

[0011] Step S5, using a laser cutting machine to cut off the polycrystals on the surface of the diamond blank to obtain a diamond blank;

[0012] Step S6, subjecting the diamond blank to high temperature and high pressure treatment at a temperature of 800-1200° C. and a pressure of 800-1000 Pa to obtain blue diamond.

[0013] The method for preparing blue diamond based on the MPCVD method of the present invention is suitable for the growth of large single crystals of 10×10 mm and above. During the growth method, no elements are added in the crystal growth step S3, which avoids the stratification of the crystal due to gas fluctuations and can improve the crystal quality of the large single crystal.

[0014] The method for preparing blue diamond based on MPCVD method of the present invention is implemented according to the following steps:

[0015] Step S1, placing a HPHT (high-temperature and high-pressure method) diamond seed crystal in a mixed acid for pretreatment, and washing to obtain a pretreated seed crystal;

[0016] Step S2, placing the pretreated seed crystal on a molybdenum support in a vacuum chamber of an MPCVD device, evacuating the vacuum chamber, and then introducing hydrogen or oxygen to excite plasma for etching;

[0017] Step S3, after the etching process is completed, methane, hydrogen, SiH4 and GeH4 are introduced into the vacuum chamber, the volume concentration of methane is controlled to be 5% to 8%, the volume concentration of hydrogen is controlled to be 82% to 91%, the volume concentration of SiH4 is controlled to be 2% to 5%, the volume concentration of GeH4 is controlled to be 2% to 5%, the growth temperature is controlled to be 700 to 1000°C, and the pressure is controlled to be 10 to 15 kPa for microwave plasma chemical vapor deposition growth;

[0018] Step S4: After the microwave plasma chemical vapor deposition growth is completed, the pressure and temperature in the vacuum chamber are gradually reduced to obtain a diamond blank;

[0019] Step S5, using a laser cutting machine to cut off the polycrystals on the surface of the diamond blank to obtain a diamond blank;

[0020] Step S6, subjecting the diamond blank to high temperature and high pressure treatment at a temperature of 800-1200° C. and a pressure of 800-1000 Pa to obtain blue diamond.

[0021] The method for preparing blue diamond based on the MPCVD method is suitable for preparing blue diamond of small carat (blank size is below 10×10 mm).

[0022] Compared with the prior art, the method for preparing blue diamond based on the MPCVD method of the present invention has the following beneficial effects:

[0023] The present invention prepares SiV and GeV color centers inside the diamond blank at the same time to make it appear blue. Two preparation methods are proposed according to the size of the diamond. Large carat blue diamonds are suitable for solid-state etching methods, and small carat blue diamonds are suitable for growth doping methods. Both methods can control the required depth of blue by controlling the concentration of Si and Ge. Compared with the currently more common boron doping in the diamond growth process, the blue produced by doping Si and Ge is purer and has no gray tone, which can effectively improve the color quality of blue diamonds and increase their market value; compared with the electron irradiation method, the doping method is simple to operate, does not require complex electron irradiation technology, and also saves irradiation time and cost, improves the blue diamond yield, reduces production costs, and achieves controllable color tone. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a production flow chart for preparing large carat blue diamonds in the first specific implementation mode;

[0025] Figure 2 It is a schematic diagram of the growth of a large carat diamond seed crystal in the first specific implementation mode;

[0026] Figure 3 This is a production flow chart for preparing small carat blue diamonds in specific implementation mode eight;

[0027] Figure 4 It is a schematic diagram of the growth of small carat diamond seed crystals in specific embodiment 8;

[0028] Figure 5 The UV-visible spectra of diamond grown from 10×10 mm seed crystal, irradiated diamond and untreated diamond in Example 1 are shown. DETAILED DESCRIPTION

[0029] Specific implementation method 1: The method for preparing blue diamond based on the MPCVD method in this implementation method is implemented according to the following steps:

[0030] Step S1, placing a HPHT (high-temperature and high-pressure method) diamond seed crystal in a mixed acid for pretreatment, washing to obtain a pretreated seed crystal, and ultrasonically cleaning the silicon wafer and the germanium wafer respectively to obtain a cleaned silicon wafer and germanium wafer;

[0031] Step S2, in the vacuum chamber of the MPCVD device, placing the pretreated seed crystal on a molybdenum tray, placing the cleaned silicon wafer and germanium wafer around the pretreated seed crystal, evacuating the vacuum chamber, and then introducing hydrogen or oxygen, using hydrogen or oxygen to excite plasma for etching;

[0032] Step S3, after the etching process is completed, methane and hydrogen are introduced into the vacuum chamber, the volume concentration of methane is controlled to be 2% to 10%, the volume concentration of hydrogen is controlled to be 90% to 98%, the growth temperature is controlled to be 700 to 1000°C, and the pressure is controlled to be 10 to 15 kPa for microwave plasma chemical vapor deposition growth;

[0033] Step S4: After the microwave plasma chemical vapor deposition growth is completed, the pressure and temperature in the vacuum chamber are gradually reduced to obtain a diamond blank;

[0034] Step S5, using a laser cutting machine to cut off the polycrystals on the surface of the diamond blank to obtain a diamond blank;

[0035] Step S6, subjecting the diamond blank to high temperature and high pressure treatment at a temperature of 800-1200° C. and a pressure of 800-1000 Pa to obtain blue diamond.

[0036] The method for preparing blue diamond by MPCVD method described in this embodiment is to simultaneously dope Si and Ge elements in the crystal during the growth process, so as to form SiV and GeV color centers in the diamond blank, and the absorption of SiV and GeV color centers in the near-infrared region makes the diamond appear green-blue. This method can not only control the blue tone concentration of diamond by controlling the concentration of Si and Ge, avoiding the gray tone caused by the doping of boron elements, but also does not need to use electron irradiation equipment to prepare GR1 color centers. This method has simple process, short production time, low production cost, high repeatability, and is more suitable for mass production of blue diamonds.

[0037] Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that the mixed acid described in step S1 is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1. The HPHT diamond seed wafer is placed in the mixed acid, heated to 250-300°C and soaked for 2-3 hours, and then ultrasonically cleaned using anhydrous ethanol and pure water in turn.

[0038] Specific implementation method three: The difference between this implementation method and specific implementation method one or two is that in step S2, the surface area ratio of the silicon wafer and the germanium wafer is controlled to be 1:1.

[0039] If only SiV color centers are introduced in this embodiment, the color centers will absorb light at 737nm. The absorption in the near-infrared region can only make the diamond appear blue, and the color concentration is not enough. GeV color centers will produce 602nm absorption, which can effectively enhance the blue color and make the diamond appear blue.

[0040] In this embodiment, the concentration of Si and Ge in the plasma is controlled by etching time, thereby controlling the depth of the blue-purple color of the diamond; the concentration of Si and Ge in the plasma is controlled by increasing the number of Si and Ge sheets.

[0041] Specific implementation method 4: The difference between this implementation method and any one of specific implementation methods 1 to 3 is that in step S2, the surface area ratio of the pre-treated seed crystal, the silicon wafer and the germanium wafer is controlled to be (3-6):1:1.

[0042] Specific implementation mode 5: This implementation mode is different from specific implementation modes 1 to 4 in that the etching treatment time in step S2 is 30 to 60 minutes.

[0043] Specific implementation method 6: The difference between this implementation method and any one of specific implementation methods 1 to 5 is that the growth thickness of the diamond blank in step S4 is 5 to 7 mm.

[0044] Specific embodiment 7: This embodiment is different from any one of specific embodiments 1 to 6 in that the high temperature and high pressure treatment time in step S6 is 2 to 3 hours.

[0045] Specific embodiment 8: The method for preparing blue diamond based on MPCVD method in this embodiment is implemented according to the following steps:

[0046] Step S1, placing a HPHT (high-temperature and high-pressure method) diamond seed crystal in a mixed acid for pretreatment, and washing to obtain a pretreated seed crystal;

[0047] Step S2, placing the pretreated seed crystal on a molybdenum support in a vacuum chamber of an MPCVD device, evacuating the vacuum chamber, and then introducing hydrogen or oxygen to excite plasma for etching;

[0048] Step S3, after the etching process is completed, methane, hydrogen, SiH4 and GeH4 are introduced into the vacuum chamber, the volume concentration of methane is controlled to be 5% to 8%, the volume concentration of hydrogen is controlled to be 82% to 91%, the volume concentration of SiH4 is controlled to be 2% to 5%, the volume concentration of GeH4 is controlled to be 2% to 5%, the growth temperature is controlled to be 700 to 1000°C, and the pressure is controlled to be 10 to 15 kPa for microwave plasma chemical vapor deposition growth;

[0049] Step S4: After the microwave plasma chemical vapor deposition growth is completed, the pressure and temperature in the vacuum chamber are gradually reduced to obtain a diamond blank;

[0050] Step S5, using a laser cutting machine to cut off the polycrystals on the surface of the diamond blank to obtain a diamond blank;

[0051] Step S6, subjecting the diamond blank to high temperature and high pressure treatment at a temperature of 800-1200° C. and a pressure of 800-1000 Pa to obtain blue diamond.

[0052] Specific embodiment nine: The difference between this embodiment and specific embodiment eight is that in step S3, the volume concentration of methane is controlled to be 5%, the volume concentration of hydrogen is controlled to be 90%, the volume concentration of SiH4 is controlled to be 2.5%, and the volume concentration of GeH4 is controlled to be 2.5%, and the growth temperature is controlled to be 800-900°C and the pressure is controlled to be 11-13 kPa for microwave plasma chemical vapor deposition growth.

[0053] Specific embodiment ten: This embodiment is different from specific embodiment eight in that the blue diamond is further cut and polished in step S6.

[0054] In this embodiment, the diamond is cut in a radiant, emerald or princess cut to make the color of the diamond more obvious.

[0055] Embodiment 1: The method for preparing blue diamond based on MPCVD method in this embodiment is implemented according to the following steps:

[0056] Step S1, selecting a HPHT seed wafer with a flat surface, no obvious impurities under a 20x microscope, and a crystal face of (100), placing the HPHT (high-temperature and high-pressure method) diamond seed wafer in a mixed acid heated to 280° C. and soaking for 2 hours, wherein the mixed acid is a mixture of 98% sulfuric acid and 67% nitric acid in a volume ratio of 3:1, and washing to obtain a pretreated seed wafer, and ultrasonically cleaning the silicon wafer and the germanium wafer respectively, wherein the ultrasonic cleaning is performed by sequentially using anhydrous ethanol and pure water for 30 minutes each, to obtain the cleaned silicon wafer and the germanium wafer;

[0057] Step S2, in the vacuum chamber of the MPCVD device, placing the pretreated seed crystal on a molybdenum tray, placing the cleaned silicon wafer and germanium wafer around the pretreated seed crystal, controlling the surface area ratio of the HPHT seed crystal, the silicon wafer and the germanium wafer to be 5:1:1, evacuating the vacuum chamber, and then introducing hydrogen, controlling the temperature to reach 750° C., the microwave energy to be 3 kW, and the pressure to be 10 kPa, using hydrogen to excite plasma for etching for 60 minutes;

[0058] Step S3, after the etching treatment is completed, methane and hydrogen are introduced into the vacuum chamber, the volume concentration of methane is controlled to be 5%, the volume concentration of hydrogen is controlled to be 95%, the growth temperature is controlled to be 800°C, the microwave energy is 5kW, and the pressure is 12kPa to perform microwave plasma chemical vapor deposition growth, and the 10×10mm diamond blank is grown for 400h;

[0059] Step S4: After the microwave plasma chemical vapor deposition growth is completed, the pressure and temperature in the vacuum chamber are gradually reduced, and air is filled into the chamber to make the pressure in the chamber close to the atmospheric pressure, and the diamond blank is taken out;

[0060] Step S5, using a laser cutting machine to divide the diamond blank into blocks, and cutting off the black polycrystals on the surface of the diamond blank to obtain a diamond blank;

[0061] Step S6, selecting a nearly pure blank with no color stratification on the side and internal impurities that cannot be observed under a 20x microscope from the cut blanks, placing the blank in a six-sided top press, and subjecting the diamond blank to a high temperature and high pressure treatment for 2.5 hours at a temperature of 900° C. and a pressure of 1000 Pa, thereby obtaining a blue diamond.

[0062] The ultraviolet-visible spectrum of the blue diamond obtained in this example is shown in Figure 5 As shown, it can be seen that the diamond sample appears blue.

[0063] Embodiment 2: The method for preparing blue diamond based on MPCVD method in this embodiment is implemented according to the following steps:

[0064] Step S1, selecting a HPHT seed crystal with a flat surface, no obvious impurities under a 20x microscope, and a crystal face of (100), placing the HPHT (high-temperature and high-pressure method) diamond seed crystal in a mixed acid heated to 280° C. and soaking for 2 hours, wherein the mixed acid is composed of 98% sulfuric acid and 67% nitric acid in a volume ratio of 3:1, and washing to obtain a pretreated seed crystal;

[0065] Step S2, in the vacuum chamber of the MPCVD device, placing the pretreated seed crystal on a molybdenum support, evacuating the vacuum chamber, introducing hydrogen, controlling the temperature to reach 750° C., the microwave energy to 3 kW, and the pressure to 10 kPa, using hydrogen to excite plasma for etching for 60 minutes;

[0066] Step S3, after the etching treatment is completed, methane, hydrogen, SiH4 and GeH4 are introduced into the vacuum chamber, the volume concentration of methane is controlled to be 5%, the volume concentration of hydrogen is controlled to be 90%, the volume concentration of SiH4 is controlled to be 2.5%, and the volume concentration of GeH4 is controlled to be 2.5%. The growth temperature is controlled to be 800°C, the microwave energy is controlled to be 5kW, and the pressure is controlled to be 12kPa for microwave plasma chemical vapor deposition growth, and the 7×7mm diamond blank is grown for 350h;

[0067] Step S4: After the microwave plasma chemical vapor deposition growth is completed, the pressure and temperature in the vacuum chamber are gradually reduced, and air is filled into the chamber to make the pressure in the chamber close to the atmospheric pressure, and the diamond blank is taken out;

[0068] Step S5, using a laser cutting machine to divide the diamond blank into blocks, and cutting off the black polycrystals on the surface of the diamond blank to obtain a diamond blank;

[0069] Step S6, selecting a nearly pure blank with no color stratification on the side and internal impurities that cannot be observed under a 20x microscope from the cut blanks, placing the blank in a six-sided top press, and subjecting the diamond blank to a high temperature and high pressure treatment for 2.5 hours at a temperature of 900° C. and a pressure of 1000 Pa, thereby obtaining a blue diamond.

[0070] The method for preparing blue diamond of the present invention is to prepare SiV and GeV color centers in diamond so that the diamond appears blue. According to the size of the diamond, two methods are designed: doping Si and Ge during the etching process and doping Si and Ge during the growth process. Both methods can control the depth of blue by regulating the concentration of Si and Ge in the plasma. The blue diamond prepared by this method is simple to operate, avoids the phenomenon that the blue diamond color turns gray due to boron doping, can effectively improve the color quality of the diamond and increase its value. In addition, this method does not require the use of electron irradiation equipment, avoids the tedious attempts of irradiation parameters and the problem of difficulty in obtaining irradiation sources, reduces the production cost of blue diamonds and shortens the production time of blue diamonds. In comparison, the blue diamond prepared by this method has high repeatability and stability, simple process flow, low production cost, and high market application value.

Claims

1. A method for preparing blue diamond based on MPCVD method, characterized in that The method for preparing blue diamond is achieved by following steps: Step S1, placing the HPHT diamond seed crystal in mixed acid for pretreatment, washing to obtain the pretreated seed crystal, and ultrasonically cleaning the silicon wafer and the germanium wafer respectively to obtain the cleaned silicon wafer and the germanium wafer; Step S2, in the vacuum chamber of the MPCVD device, placing the pretreated seed crystal on a molybdenum tray, placing the cleaned silicon wafer and germanium wafer around the pretreated seed crystal, evacuating the vacuum chamber, and then introducing hydrogen or oxygen, using hydrogen or oxygen to excite plasma for etching; Step S3, after the etching process is completed, methane and hydrogen are introduced into the vacuum chamber, the volume concentration of methane is controlled to be 2% to 10%, the volume concentration of hydrogen is controlled to be 90% to 98%, the growth temperature is controlled to be 700 to 1000°C, and the pressure is controlled to be 10 to 15 kPa for microwave plasma chemical vapor deposition growth; Step S4: After the microwave plasma chemical vapor deposition growth is completed, the pressure and temperature in the vacuum chamber are gradually reduced to obtain a diamond blank; Step S5, using a laser cutting machine to cut off the polycrystals on the surface of the diamond blank to obtain a diamond blank; Step S6, subjecting the diamond blank to high temperature and high pressure treatment at a temperature of 800-1200° C. and a pressure of 800-1000 Pa to obtain blue diamond.

2. The method for preparing blue diamond based on MPCVD method according to claim 1, characterized in that The mixed acid described in step S1 is composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:

1. The HPHT diamond seed wafer is placed in the mixed acid, heated to 250-300° C. and soaked for 2-3 hours, and then ultrasonically cleaned with anhydrous ethanol and pure water in turn.

3. The method for preparing blue diamond based on MPCVD method according to claim 1, characterized in that In step S2, the surface area ratio of the silicon wafer to the germanium wafer is controlled to be 1:

1.

4. The method for preparing blue diamond based on MPCVD method according to claim 1, characterized in that In step S2, the surface area ratio of the pre-treated seed crystal, the silicon wafer and the germanium wafer is controlled to be (3-6):1:

1.

5. The method for preparing blue diamond based on MPCVD method according to claim 1, characterized in that The etching treatment time in step S2 is 30 to 60 minutes.

6. The method for preparing blue diamond based on MPCVD method according to claim 1, characterized in that The growth thickness of the diamond blank in step S4 is 5 to 7 mm.

7. The method for preparing blue diamond based on MPCVD method according to claim 1, characterized in that The high temperature and high pressure treatment time in step S6 is 2 to 3 hours.

8. A method for preparing blue diamond based on MPCVD method, characterized in that The method for preparing blue diamond is achieved by following steps: Step S1, placing the HPHT diamond seed crystal in mixed acid for pretreatment, and washing to obtain a pretreated seed crystal; Step S2, placing the pretreated seed crystal on a molybdenum support in a vacuum chamber of an MPCVD device, evacuating the vacuum chamber, and then introducing hydrogen or oxygen to excite plasma for etching; Step S3, after the etching process is completed, methane, hydrogen, SiH4 and GeH4 are introduced into the vacuum chamber, the volume concentration of methane is controlled to be 5% to 8%, the volume concentration of hydrogen is controlled to be 82% to 91%, the volume concentration of SiH4 is controlled to be 2% to 5%, the volume concentration of GeH4 is controlled to be 2% to 5%, the growth temperature is controlled to be 700 to 1000°C, and the pressure is controlled to be 10 to 15 kPa for microwave plasma chemical vapor deposition growth; Step S4: After the microwave plasma chemical vapor deposition growth is completed, the pressure and temperature in the vacuum chamber are gradually reduced to obtain a diamond blank; Step S5, using a laser cutting machine to cut off the polycrystals on the surface of the diamond blank to obtain a diamond blank; Step S6, subjecting the diamond blank to high temperature and high pressure treatment at a temperature of 800-1200° C. and a pressure of 800-1000 Pa to obtain blue diamond.

9. The method for preparing blue diamond based on MPCVD method according to claim 8, characterized in that In step S3, the volume concentration of methane is controlled to be 5%, the volume concentration of hydrogen is controlled to be 90%, the volume concentration of SiH4 is controlled to be 2.5%, and the volume concentration of GeH4 is controlled to be 2.5%. The growth temperature is controlled to be 800-900°C and the pressure is controlled to be 11-13 kPa for microwave plasma chemical vapor deposition growth.

10. The method for preparing blue diamond based on MPCVD method according to claim 8, characterized in that In step S6, the blue diamond is further cut and polished.

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