U.S. patent application number 11/802425 was filed with the patent office on 2007-12-20 for annealing single crystal chemical vapor deposition diamonds.
This patent application is currently assigned to Carnegie Institution of Washington. Invention is credited to Russell J. Hemley, Ho-Kwang Mao, Chih-shiue Yan.
Application Number | 20070290408 11/802425 |
Document ID | / |
Family ID | 34079231 |
Filed Date | 2007-12-20 |
United States Patent
Application |
20070290408 |
Kind Code |
A1 |
Hemley; Russell J. ; et
al. |
December 20, 2007 |
Annealing single crystal chemical vapor deposition diamonds
Abstract
A method to improve the optical clarity of CVD diamond where the
CVD diamond is single crystal CVD diamond, by raising the CVD
diamond to a set temperature of at least 1500 degrees C. and a
pressure of at least 4.0 GPa outside of the diamond stable
phase.
Inventors: |
Hemley; Russell J.; (Chevy
Chase, MD) ; Mao; Ho-Kwang; (Washington, DC) ;
Yan; Chih-shiue; (Washington, DC) |
Correspondence
Address: |
MORGAN LEWIS & BOCKIUS LLP
1111 PENNSYLVANIA AVENUE NW
WASHINGTON
DC
20004
US
|
Assignee: |
Carnegie Institution of
Washington
|
Family ID: |
34079231 |
Appl. No.: |
11/802425 |
Filed: |
May 22, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10889171 |
Jul 13, 2004 |
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11802425 |
May 22, 2007 |
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60486435 |
Jul 14, 2003 |
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Current U.S.
Class: |
264/346 |
Current CPC
Class: |
C01B 32/25 20170801;
H04N 5/765 20130101; H04N 5/76 20130101; H04N 5/781 20130101; H04N
9/8042 20130101; C30B 33/02 20130101; G11B 2220/20 20130101; C23C
16/279 20130101; H04N 9/8205 20130101; C23C 16/274 20130101; G11B
2220/65 20130101; C30B 25/105 20130101; C23C 16/277 20130101; H04N
5/775 20130101; C01B 32/26 20170801; C30B 33/00 20130101; C30B
29/04 20130101 |
Class at
Publication: |
264/346 |
International
Class: |
B29C 71/02 20060101
B29C071/02 |
Goverment Interests
STATEMENT OF GOVERNMENT INTEREST
[0002] This invention was made with U.S. government support under
grant number EAR-0135626 from the National Science Foundation. The
U.S. government has certain rights in the invention.
Claims
1. A method to improve the optical clarity of CVD diamond where the
CVD diamond is single crystal CVD diamond, by raising the CVD
diamond to a set temperature of at least 1500 degrees C. and a
pressure of at least 4.0 GPa outside of the diamond stable
phase.
2. The method of claim 1 wherein, the CVD diamond is a single
crystal coating upon another material.
3. The method of claim 1, wherein the step of raising the
temperature of the single crystal CVD diamond further comprises the
step of: raising the single crystal CVD diamond to a set
temperature of about 1800 degrees C. to about 2900 degrees C.
4. The method of claim 1, wherein the step of raising the
temperature of the single crystal CVD diamond further comprises the
step of: maintaining the temperature of the single crystal CVD
diamond at the set temperature for less than about one minute.
5. The method of claim 1, wherein the step of raising the
temperature of the single crystal CVD diamond further comprises the
step of: raising the temperature of the single crystal CVD diamond
to at least 1500 degrees C. over a time period of about one minute
to five minutes.
6. The method of claim 1, wherein the step of raising the
temperature of the single crystal CVD diamond comprises of the step
of: raising the temperature of the CVD diamond to about 2200
degrees C. at a pressure of about 5.0 GPa.
7. The method of claim 1, further comprising the step of: after
reaching the set temperature, decreasing the temperature of the CVD
to ambient temperature while maintaining the pressure on the single
crystal CVD diamond.
8. The method of claim 1, wherein the single crystal CVD diamond
initially has a brown color and becomes colorless.
9. The method of claim 1, further comprising the step of: growing
the single crystal brown diamond at a temperature of about
1400-1460 degrees C. in an atmosphere containing 4-5%
N.sub.2/CH.sub.4.
Description
[0001] The present invention claims the benefit of priority from
U.S. Provisional Application Ser. No. 60/486,435 filed Jul. 14,
2003, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to annealing diamond, and more
particularly, to annealing single crystal CVD diamond.
[0005] 2. Discussion Of The Related Art
[0006] Chemical vapor deposition growth of diamonds is achieved by
imparting energy into a gas-phase carbon containing precursor
molecules. For example, microwave energy can be used to create
plasma that deposits carbon so as form diamond upon a seed diamond.
Up until recently, all CVD techniques for growing diamond resulted
in polycrystalline diamond or very thin layers of single crystal
diamond. The present inventors of this application have developed a
microwave plasma CVD technique to grow large single crystal CVD
that is disclosed in copending patent application Ser. No.
10/288,499 filed on Nov. 6, 2002, which is hereby incorporated by
reference.
[0007] The present inventors' microwave plasma CVD technique can
grow a single crystal diamond on a seed diamond, such as a yellow
type Ib HPHT synthetic diamond, at rates of up to 150 micrometers
an hour. The color of the diamonds produced by the present
inventors' microwave plasma CVD technique depends on the
temperature at which the diamond is grown. More particularly, when
diamond is grown within a certain temperature range, which is
dependent upon the mixture of gases in the plasma, a colorless
diamond can be produced. However, diamonds produced at temperatures
outside of the certain range are yellow or brown in color.
SUMMARY OF THE INVENTION
[0008] Accordingly, the present invention is directed to a
annealing a single crystal CVD diamond that substantially obviates
one or more problems due to limitations and disadvantages of the
related art.
[0009] An object of the present invention is to lighten or remove
the color from a single crystal CVD diamond.
[0010] Another object of the present invention is to eliminate
defects from a single crystal CVD diamond.
[0011] Another object of the present invention is to enhance the
optical characteristics of a single crystal CVD diamond.
[0012] Additional features and advantages of the invention will be
set forth in part in the description which follows, and in part
will be apparent from the description, or may be learned from
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.
[0013] To achieve these objects and other advantages and in
accordance with the purpose of the invention, as embodied and
broadly described, a method to improve the optical clarity of
single crystal CVD diamond that includes raising the CVD diamond to
a set temperature of at least 1500 degrees C. at a pressure of at
least 4.0 GPa.
[0014] 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.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Reference will now be made in detail to the preferred
embodiments of the present invention.
[0016] The present inventors have used their microwave plasma CVD
technique to grow single crystal diamonds with thickness of greater
than one millimeter on a seed diamond, such as a type Ib {100} HPHT
synthetic diamond. In order to enhance the growth rate to about
50-150 .mu.m/h and promote smooth {100} face growth, the
single-crystal CVD diamond was grown in an atmosphere of
N.sub.2/CH.sub.4=0.2-5.0%, CH.sub.4/H.sub.2=12-20% with a 120-220
torr total pressure, and at a temperature of 900-1500 degrees C.
Raman spectra show a small amount of hydrogenated amorphous carbon
(a-C:H).sup.4 and nitrogen-containing a-C:H (N:a-C:H).sup.4 that
cause the single crystal CVD diamond to have a brown or yellow
color when the diamond is grown at <950.degree. C. or
>1400.degree. C. Further, photoluminescence (PL) spectra
indicate nitrogen-vacancy (N-V) impurities.
[0017] The CVD single crystal diamond grows faster at the higher
temperatures of 1400-1500 degrees but the resulting diamond has a
brown color. Regardless of the color, the single crystal CVD
diamonds resulting from the present inventors' microwave plasma CVD
technique can still have impurities. Of course, a lighter colored
diamond, a more translucent diamond or a diamond having no color is
desired.
[0018] The lightening of the brown color in brown natural diamonds,
as well as a decrease in impurities by high pressure high
temperature annealing has been reported by I. M. Reinitz et al.
Gems & Gemology 36, 128-137 (2000). However, the present
inventors have discovered that HPHT annealing of a single crystal
yellow or brown CVD diamond at a temperature of 1800-2900.degree.
C. and at a pressure of 5-7 GPa for about 1-60 minutes using a
reaction vessel in a conventional high pressure high temperature
apparatus so as to transform some single crystal brown CVD diamonds
into transparent colorless single crystal diamond. More
particularly, a single crystal yellow or light brown CVD diamond
grown with high growth rate at a temperature of about 1400-1460
degrees C. in an atmosphere containing 4-5% N.sub.2/CH.sub.4 ratio
can be annealed to become a colorless single crystal diamond.
Further, Raman and PL spectra of such an annealed CVD diamond
demonstrate the disappearance of hydrogenated amorphous carbon and
a significant decrease in N-V impurities in such a colorless single
crystal diamond. These changes appear to be similar to the report
by I. M. Reinitz et al. of transparency enhancement produced by
HPHT annealing of brown natural diamond.
[0019] The reaction vessel can be a cell, such as that described in
U.S. Pat. Nos. 3,745,623 or 3,913,280, which are hereby
incorporated by reference. The entire cell is subjected to
pressures in excess of 4.0 GPa, such as 5-7 GPa, and heated to
temperature in excess of 1500 degrees C., such as 1800-2900 degrees
C., such that the pressure/temperature conditions in the cell or
reaction vessel are within the graphite stable phase or just within
the diamond stable phase for a time period that can be as short as
1 minute or as long as an hour. The cell is allowed to cool prior
to the pressure being released so that the single crystal CVD
diamond does not become graphite.
EXAMPLE #1
[0020] A single crystal CVD diamond was grown with a
N.sub.2/CH.sub.4 ratio of 5% at a temperature of approximately 1500
degrees C. on a yellow type Ib HPHT synthetic diamond at the
Carnegie Institution of Washington. The dimension of the single
crystal diamond CVD diamond was one centimeter square and a little
larger than one millimeter in thickness. The color of the single
crystal diamond CVD diamond was brown. The brown single crystal CVD
diamond on the type Ib HPHT synthetic seed diamond was then placed
as a sample in the reaction vessel.
[0021] The reaction vessel was placed in a conventional HPHT
apparatus. First, the pressure was increased to a pressure of 5.0
GPa, and then the temperature was rapidly brought up to 2200
degrees C. The sample was maintained at these annealing conditions
for five minutes, and then the temperature was decreased over a
period of about one minute to room temperature before the pressure
was released.
[0022] The sample was removed from the reaction vessel and examined
under an optical microscope. The brown single crystal CVD diamond
had turned to a light green color and remained firmly bonded to the
yellow type Ib HPHT synthetic diamond. The yellow color of the
synthetic type Ib diamond became a lighter yellow or a more
translucent yellow.
EXAMPLE #2
[0023] Same as example #1 above, except the annealing conditions
were maintained for 1 hour. The dark brown single crystal CVD
diamond turned to a light green color, which was more translucent
than the light green color resulting in example #1, and remained
firmly bonded to the yellow type Ib HPHT synthetic diamond. The
yellow color of the type Ib HPHT synthetic diamond became a lighter
yellow or a more translucent yellow.
EXAMPLE #3
[0024] A single crystal CVD diamond was grown with a
N.sub.2/CH.sub.4 ratio of 5% at a temperature of approximately 1450
degrees C. on a yellow synthetic type Ib diamond at the Carnegie
Institution of Washington. The dimension of the single crystal
diamond CVD diamond was one centimeter square and a little larger
than one millimeter in thick. The color of the single crystal
diamond CVD diamond was a light brown or yellow. In other words, a
light brown that was not as dark as the brown of the single crystal
CVD diamond in example #1 above. The yellow or light brown single
crystal CVD diamond on type Ib HPHT synthetic seed diamond was then
placed as a sample in a reaction vessel.
[0025] The reaction vessel was placed in a conventional HPHT
apparatus. The pressure was increased to about to a pressure of 5.0
GPa, and then the temperature was rapidly brought up to about 2000
degrees C. The sample was maintained at these annealing conditions
for five minutes, and then the temperature was decreased over a
period of about one minute to room temperature before the pressure
was released.
[0026] The sample was removed from the reaction vessel and examined
under an optical microscope. The light brown or yellow single
crystal CVD 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 became a lighter yellow or
a more translucent yellow.
EXAMPLE #4
[0027] Same as example #1 except a colorless microwave plasma
single-crystal CVD-grown diamond in an atmosphere of
N.sub.2/CH.sub.4=5% at a temperature of 1200 degree C. was
annealed. After annealing, the microwave plasma single-crystal
CVD-grown diamond was blue. This blue microwave plasma
single-crystal CVD-grown diamond had a very high toughness of
>20 MPa mn.sup.1/2. The hardness was about 140 GPa.
EXAMPLE #5
[0028] Same as example #1 except a colorless microwave plasma
single-crystal CVD-grown diamond in an atmosphere of
N.sub.2/CH.sub.4=0.5% at a temperature of .about.1200 degree C. was
annealed. The microwave plasma single-crystal CVD-grown diamond was
still colorless. This colorless microwave plasma single-crystal
CVD-grown diamond had a hardness of 160 GPa and toughness of
.about.10 MPa m.sup.1/2.
[0029] 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.
* * * * *