HK1101705B - Ultrahard diamonds and method of making thereof - Google Patents

Description

Superhard diamond and method for manufacturing same

Priority is claimed for U.S. provisional application No. 60/486,435 filed on 14/7/2003, which is incorporated herein by reference.

Statement of government title

The invention was made with U.S. government support under grant number EAR-0135626 from the united states scientific foundation. The government has certain rights in the invention.

Technical Field

The present invention relates to diamonds, and more particularly to superhard diamonds produced using Microwave Plasma Chemical Vapor Deposition (MPCVD) in a deposition chamber.

Background

The mass production of synthetic diamonds has long been a goal of researchers and industry. In addition to the properties of gemstones, diamond is the hardest known material, has the highest known thermal conductivity, and is transparent to a wide variety of electromagnetic radiation. Thus, in addition to its value as a gemstone, diamond is valuable due to its wide range of applications in several industries.

At least during the last 20 years, methods for producing small amounts of diamond by Chemical Vapor Deposition (CVD) have been available. As reported by B.V. Spitsyn et al in "Vapor Growth of Diamond on Diamond and Other Surfaces", Journal of Crystal Growth, Vol.52, p.219-226, the method involves CVD of Diamond on a substrate (substrate) using a combination of methane or another simple hydrocarbon gas and hydrogen gas at reduced pressure and a temperature of 800-. The addition of hydrogen (inclusion) prevents the formation of graphite during diamond nucleation and growth. The growth rate using this technique is reported to reach 1 μm/hr.

Later work, such as that reported by Kamo et al in "Diamond Synthesis from Gas phase in Microwave Plasma", journal of Crystal Growth, vol 62, page 642-644, demonstrated the production of Diamond using Microwave Plasma Chemical Vapor Deposition (MPCVD) at a pressure of 1-8KPa and a temperature of 800-1000 ℃ and a Microwave power of 300-700 Watts at a frequency of 2.45 GHz. Methane gas is used in the Kamo et al process at a concentration of 1-3%. The maximum growth rate using this MPCVD method is reported to be 3 μm/hr.

The hardness of natural diamond is between 80-120 GPa. Most grown or manufactured diamonds, regardless of the method, have a hardness of less than 110 GPa. Unlike type IIa natural diamonds, which have been subjected to annealing, no diamond hardness greater than 120GPa has been reported.

Disclosure of Invention

Accordingly, the present invention is directed to an apparatus and method for manufacturing diamond that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.

One object of the present invention relates to an apparatus and method for manufacturing diamond with increased hardness in a microwave plasma chemical vapor deposition system.

It is another object of the present invention to enhance the optical properties of single crystal diamond.

Additional features and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, a single crystal diamond grown by microwave plasma chemical vapor deposition, annealed at a pressure of more than 4.0GPa and heated to a temperature of more than 1500 ℃ has a hardness of more than 120 GPa.

In another embodiment, the hardness of the single crystal diamond is 160-180 GPa.

According to another embodiment of the invention, a method of making a hard single crystal diamond includes growing a single crystal diamond and annealing the single crystal diamond at a pressure in excess of 4.0GPa and a temperature in excess of 1500 ℃ such that the hardness of the single crystal diamond exceeds 120 GPa.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

Fig. 1 is a picture of an indenter for testing the hardness of diamond.

Fig. 2 is a photograph of an indentation made on a diamond.

Figure 3 is a graph showing the hardness and toughness of annealed microwave plasma CVD-grown single-crystal diamonds compared to type IIa natural diamonds, annealed type Ia natural diamonds, and annealed type Ib HPHT synthetic diamonds.

Detailed Description

Reference will now be made in detail to the preferred embodiments of the present invention, the results of which are illustrated in the accompanying drawings.

Microwave plasma CVD-grown single crystal diamonds as referred to in this application were grown using the Apparatus described in U.S. patent No. 10/288,499 entitled "Apparatus and Method for Diamond Production" filed 11/6/2002, which is hereby incorporated by reference. Typically, the seed diamond is placed in a jig that moves the seed diamond/the growing diamond as it grows. The inventors of the present application are also the inventors of U.S. patent application No. 10/288,499.

Microwave plasma CVD-grown single-crystal diamonds with a thickness greater than 1 mm were deposited on type Ib {100} synthetic diamonds. In order to increase the growth rate (50-150 μm/h) and promote the growth of smooth {100} crystal planes, in N₂/CH₄＝0.2-5.0％、CH₄/H₂Single crystal diamond was grown from microwave induced plasma in a CVD chamber in an atmosphere of 12-20%, a total pressure of 120-. Raman spectroscopy shows a small amount of hydrogenated amorphous carbon (a-C: H) giving rise to brown diamonds at < 950 ℃ and > 1400 ℃⁴And nitrogen-containing a-C: H (N: a-C: H)⁴. Photoluminescence (PL) spectra show nitrogen-vacancy (N-V) impurities. Single crystal diamond up to 4.5mm in thickness is produced at a growth rate two orders of magnitude higher than conventional polycrystalline CVD growth methods.

The microwave plasma CVD-grown single-crystal diamond is heated to a temperature exceeding 1500 deg.c (e.g., 1800-. The reaction vessel may be a cell, such as the cell described in U.S. Pat. No. 3,745,623 or 3,913,280, which are incorporated herein by reference. Such annealing reduces or eliminates the color of the microwave plasma CVD-grown single crystal diamond crystals and lightens the color of the type Ib HPHT artificial seed crystal (seed crystal). Furthermore, the hardness of the annealed CVD diamond (at least 140GPa) of the annealed microwave plasma CVD-grown single crystal diamond exceeds the hardness of either the annealed or unannealed type Ib HPHT synthetic diamond (-90 GPa), the annealed type Ia natural diamond (-100 GPa), type IIa natural diamond (-110 GPa), and the annealed type IIa natural diamond (-140 GPa), as well as the sintered (sintered) polycrystalline diamond (120-140 GPa).

Example 1

Using N in a ratio of 5% at a temperature of about 1500 deg.C₂/CH₄Single crystal diamonds were grown on yellow type Ib HPHT synthetic diamonds in a microwave CVD chamber. The microwave plasma CVD-grown single-crystal diamond had a size of 1 cm square and a thickness of slightly more than 1 mm. The color of the microwave plasma CVD-grown single-crystal diamond was brown. Then, brown microwave plasma CVD-grown single-crystal diamond on type Ib HPHT synthetic seed diamond (seed diamond) was placed as a sample in a reaction vessel.

The reaction vessel was placed in a conventional HPHT apparatus. First, the pressure was increased to a pressure of 5.0GPa, and then the temperature was raised to 2200 ℃. The sample was held under such annealing conditions for 5 minutes and then the temperature was reduced to room temperature over a period of about 1 minute before releasing the pressure.

The samples were removed from the reaction kettle and examined under an optical microscope. The brown microwave plasma CVD-grown single crystal diamond had turned to a transparent pale green color and remained firmly bonded to the yellow type Ib HPHT synthetic diamond. The yellow color of the type Ib HPHT synthetic diamond turned to a lighter yellow or more transparent yellow. The hardness was about 160 GPa.

Example 2

The same as in example 1 above, except that the annealing conditions were maintained for 1 hour. The brown microwave plasma CVD-grown single crystal diamond turned a light green color, which was more transparent than the light green color obtained in example 1, and remained firmly bonded to the type Ib HPHT synthetic diamond. The yellow color of the type Ib HPHT synthetic diamond turned to a lighter yellow or more transparent yellow. The hardness was about 180 GPa.

Example 3

At a temperature of about 1450 ℃ with a ratio of 5% N₂/CH₄Single crystal CVD diamonds were grown on yellow type Ib HPHT synthetic diamonds in a microwave CVD chamber. The microwave plasma CVD-grown single-crystal diamond had a size of 1 cm square and a thickness of slightly more than 1 mm. The color of the microwave plasma CVD-grown single-crystal diamond was light brown or yellow. In other words, a yellow color or light brown color which is not as dark as the brown color of the microwave plasma CVD-grown single-crystal diamond in the above-described example 1. Yellow or light brown microwave plasma CVD-grown single crystal diamonds on type Ib HPHT synthetic diamonds were then placed as samples in a reaction vessel. The hardness is more than 160 GPa.

The reaction vessel was placed in a conventional HPHT apparatus. The pressure was increased to a pressure of about 5.0GPa and then the temperature was rapidly raised to about 2000 ℃. The sample was held under such annealing conditions for 5 minutes and then the temperature was reduced to room temperature over a period of about 1 minute before releasing the pressure.

The samples were removed from the reaction kettle and examined under an optical microscope. The light brown microwave plasma CVD-grown single crystal diamond had become colorless and remained firmly bonded to the yellow type Ib HPHT synthetic diamond. The yellow color of the type Ib HPHT synthetic diamond also changed to a lighter yellow or more transparent yellow.

Example 4

Except that colorless microwave plasma single crystal CVD-grown diamond was allowed to stand at a temperature of-1200 deg.C under N₂/CH₄Except annealing in 5% atmosphereSame as in example 1 above. After annealing, the microwave plasma single crystal CVD-grown diamond was blue in color. This blue microwave plasma single crystal CVD-grown diamond had > 20MPam^1/2Very high toughness. The hardness is about 140 GPa.

Example 5

Except that colorless microwave plasma single crystal CVD-grown diamond was allowed to stand at a temperature of-1200 deg.C under N₂/CH₄Same as example 1 above except that annealing was performed in an atmosphere of 5%. The microwave plasma single crystal CVD-grown diamond was still colorless. This colorless microwave plasma single crystal CVD-grown diamond had a hardness of 160GPa and 10MPam^1/2The toughness of (3).

Fig. 1 is a picture of an indenter for testing the hardness of diamond. Vickers hardness tests were performed on annealed microwave plasma CVD-grown single-crystal diamonds with an indenter 1 shown in fig. 1. The indenter 1 in fig. 1 has an impact material 2 mounted on a base 3. The impact material 2 may be silicon carbide, diamond or some other hard material. The impact material has a face (face) in the shape of a conical vickers indenter, wherein the angle on both sides of the conical vickers indenter shape is 136 °.

The indenter applies a point load (point load) to the test diamond 2 until an indentation or crack is formed in the test diamond 2. To prevent elastic deformation of the indenter, the load varies between 1 and 3kg on the {100} crystal plane in the <100> direction of the test diamond. The size of the indentation and the cracks associated with the indentation were measured by optical microscopy. Fig. 2 is a photograph of an indentation made on a microwave plasma CVD-grown single-crystal diamond.

By measuring the length D and height H of the indentation, the hardness H of the test diamond can be determined from the following equation (1)_v：

(1)：H_v＝1.854×P/D²

P is the maximum load used on the indenter to form the indentation on the test diamond. D is the length of the longest crack formed by the indenter in the test diamond and h is the depth of the indentation in the test diamond, as shown in fig. 1.

By using the hardness H obtained from equation (1) in the following equation (2)_vThe fracture toughness K of the test diamond can be determined_c：

(2)：K_c＝(0.016±0.004)(E/H_v)^1/2(P/C^3/2)

E is the Young's modulus, which is assumed to be 1000 GPa. P is the maximum load used on the indenter to form the indentation on the test diamond. The term d is the average length of the indentation cavity in the test diamond, as shown in fig. 2, such that d ═ d (d ═ d)₁+d₂)/2. The term c is the average length of the radial cracks in the test diamond, as shown in fig. 2, such that c ═ c₁+c₂)/2。

The same measurements were also made on other diamonds due to uncertainties in hardness determination. The measurements on the other diamonds were found to be consistent with published data for the other diamonds. The vickers hardness test is performed on the (100) crystal plane of the (100) direction of each type of diamond.

It is clear from optical microscopy that the indented surface of the annealed microwave plasma CVD-grown single-crystal diamond is different from the indented surface of other (softer) diamonds. The annealed microwave plasma CVD-grown single crystal diamond exhibited a rectangular crack pattern along <110> or <111>, with no intersecting crack lines along <100>, and the tapered vickers indenter produced a watermark-like distortion mark on the surface of the annealed microwave plasma CVD-grown single crystal diamond. In contrast, annealed type IIa natural diamond has fewer rectangular crack patterns along (110) and (111), but still exhibits crossing (100) cracks of softer diamond. These results show that annealed microwave plasma CVD-grown single crystal diamond is harder than the indenter, and the pressure generated by the elastic deformation of the indenter causes the slip of the softer 111 crystal planes.

Typically, the vickers indenter broke after-15 measurements on unannealed microwave plasma CVD-grown single crystal diamond and type Ib natural diamond. Also, typically, the vickers indenter broke after-5 measurements were made on annealed type IIa natural diamond, annealed type Ia natural diamond, and annealed type Ib HPHT synthetic diamond. However, the vickers indenter broke after only one or two measurements on the annealed microwave plasma CVD-grown single-crystal diamond. These observations further indicate that the annealed microwave plasma CVD-grown single crystal diamond is harder than indicated by the measured values. In fact, many annealed microwave plasma CVD-grown single crystal diamonds completely damaged the softer indenter. In such an example, the indenter does not leave any imprint on the surface of the annealed microwave plasma CVD-grown single-crystal diamond whatsoever.

Figure 3 is a graph showing the hardness and toughness of annealed microwave plasma CVD-grown single-crystal diamonds in comparison to type IIa natural diamonds, annealed type Ia natural diamonds, and annealed type Ib HPHT synthetic diamonds. As shown in fig. 3, the hardness of the annealed microwave plasma CVD-grown single-crystal diamond was much higher than that of type IIa natural diamond, as shown by the dashed box 10 in fig. 3. All annealed microwave plasma CVD-grown single crystal diamonds also had higher hardness than reported ranges of hardness for polycrystalline CVD diamonds, as indicated by the dashed box 20 in fig. 3. The fracture toughness of the microwave plasma CVD-grown single-crystal diamond shown in FIG. 3 was 6-10MPam^1/2Hardness of 140-180GPa, there is an indication that the hardness may be higher.

As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to be embraced by the appended claims.

Claims (13)

1. A single crystal diamond grown by microwave plasma chemical vapour deposition annealed at a temperature in excess of 1500 ℃ under a pressure in excess of 4.0GPa and having a hardness in excess of 120 GPa.

2. The single crystal diamond of claim 1, having a fracture toughness of 6-10MPam^1/2。

3. The single crystal diamond of claim 1, wherein the hardness is 160-180 GPa.

4. The single crystal diamond of claim 3, having a fracture toughness of 6-10MPam^1/2。

5. A single crystal diamond with the hardness of 160-180 GPa.

6. The single crystal diamond of claim 5, having a fracture toughness of 6-10MPam^1/2。

7. A method of making a hard single crystal diamond comprising:

growing single crystal diamond; and

the single crystal diamond is annealed at a pressure in excess of 4.0GPa and a temperature in excess of 1500 ℃ to a hardness in excess of 120 GPa.

8. The method of claim 7, wherein growing single crystal diamond comprises microwave plasma chemical vapor deposition.

9. The method of claim 7, wherein growing single crystal diamond is at N₂/CH₄0.2-5.0% and CH₄/H₂12-20% atmosphere at a total pressure of 120 torr to 220 torr.

10. The method as recited in claim 7, wherein annealing the single crystal diamond results in a single crystal diamond having a hardness in excess of 160 and 180 GPa.

11. The method of claim 7 wherein growing single crystal diamond occurs in an atmosphere having a temperature of 900-1500 ℃.

12. The method of claim 7, wherein said annealing is performed for 1-60 minutes.

13. The method as recited in claim 7, wherein annealing the single crystal diamond results in a single crystal diamond having a hardness in excess of 140 and 180 GPa.