U.S. patent number RE41,189 [Application Number 12/362,529] was granted by the patent office on 2010-04-06 for method of making enhanced cvd diamond.
This patent grant is currently assigned to Carnegie Institution of Washington. Invention is credited to Russell J. Hemley, Wei Li, Ho-kwang Mao, Chih-shiue Yan.
United States Patent |
RE41,189 |
Li , et al. |
April 6, 2010 |
Method of making enhanced CVD diamond
Abstract
Single crystal CVD diamond is heated to temperatures of
1500.degree. C. to 2900.degree. C. under a pressure that prevents
significant graphitization. The result is a CVD diamond with
improved optical properties.
Inventors: |
Li; Wei (Ann Arbor, MI),
Hemley; Russell J. (Washington, DC), Mao; Ho-kwang
(Washington, DC), Yan; Chih-shiue (Washington, DC) |
Assignee: |
Carnegie Institution of
Washington (Washington, DC)
|
Family
ID: |
29731931 |
Appl.
No.: |
12/362,529 |
Filed: |
January 30, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
10161266 |
Jun 3, 2002 |
06811610 |
Nov 2, 2004 |
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Current U.S.
Class: |
117/88; 427/902;
427/444; 427/372.2; 427/370; 427/249.8; 427/249.7 |
Current CPC
Class: |
C23C
16/27 (20130101); C23C 16/56 (20130101); C30B
29/04 (20130101); C30B 33/02 (20130101); Y10S
427/103 (20130101) |
Current International
Class: |
C23C
16/27 (20060101) |
Field of
Search: |
;427/249.7,249.8,370,372.2,444,902 ;117/88 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 480 895 |
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Apr 1992 |
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EP |
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0480895 |
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Apr 1992 |
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EP |
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0 616 954 |
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Aug 1994 |
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EP |
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0616954 |
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Aug 1994 |
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EP |
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0 671 482 |
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Sep 1995 |
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EP |
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0671482 |
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Sep 1995 |
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EP |
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WO 04/022821 |
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Mar 2004 |
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WO |
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Other References
AV. Khomich et al, Effect of High Temperature Annealing on Optical
and Thermal Properties of CVD Diamond, 2001 Elsevier Science B.V.
pp. 546-551. cited by examiner .
About CVD Diamond: Manufacture-Afford Industrial Diamond, PI
Diamond Inc., Website printout of Apr. 30, 2002. cited by examiner
.
CVD Diamond-a new Technology for the Future, Paul W. May, School of
Chemistry, University of Briston, download from CVD Diamond
Review-Endeavor Magazine, Apr. 29, 2002. cited by examiner.
|
Primary Examiner: Meeks; Timothy H
Assistant Examiner: Burkhart; Elizabeth
Attorney, Agent or Firm: Morgan Lewis & Bockius LLP
Claims
What is claimed is:
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.degree. 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.degree. C. to about 2900.degree. 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.degree. 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 single crystal CVD diamond to
about 2200.degree. 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
diamond to ambient temperature while maintaining the pressure on
the single crystal CVD diamond.
Description
BACKGROUND
This invention relates to a method of improving the optical,
electrical, thermal, and mechanical properties of chemical vapor
deposition (CVD) diamond. CVD diamond can be classified as either
single crystal or polycrystalline. Either type can be manufactured
to produce materials that range from opaque to fully transparent.
Typical impurities within CVD diamond are graphite and hydrogen,
although trace amounts of other materials may be present, such as
nitrogen. In addition to impurities, there are structural defects
which occur that further degrade the material and its properties as
compared to a defect free natural diamond. As a result, CVD diamond
is often opaque or very dark
Most industrial applications for diamond require high quality
crystals or films. Common applications include lenses that require
high optical transmission of light, heat sinks that require very
high heat conductivity, and electrical insulators. Prior work to
improve these materials by high temperature treatment has shown
that heating above 850.degree. C. significantly degrades the
sample. In fact, temperatures above 1600.degree. C. have totally
destroyed sample integrity due to formation of cracks thought to be
the result of loss of bonded hydrogen or conversion of the diamond
carbon to graphite.
Natural or synthetic diamond, on the other hand, can withstand
treatment to very high temperatures. In fact, it has been shown
that annealing of synthetic and natural type I or type II diamonds
in the range of 1900.degree. C. to 2600.degree. C. at pressures in
the range of 50 to 80 kbars causes the visible color of the diamond
to change. In the case of natural diamond type I, the color changes
from brown to yellow or yellow-green. For type II natural diamond,
the color changes from brown to colorless or, on rare occasions,
blue or pink. Synthetic diamond will change from yellow to lighter
yellow.
It would be advantageous if a method were devised that would
significantly improve the properties of CVD diamond after it is
grown. It would also be desirable to form CVD diamond with fewer
defects that serve to degrade the intrinsic properties of a perfect
crystalline diamond material in order to enhance its usage in many
applications.
SUMMARY
According to the present invention, there is provided a method of
improving the optical properties of CVD diamond, which includes the
steps of:
1. creating a reaction mass by placing the CVD diamond in a
pressure transmitting medium that completely encloses the diamond;
and
2. subjecting the reaction mass to a temperature of at least
1500.degree. C. and, preferably, in the range of about 1800.degree.
C. to about 2900.degree. C. under a pressure of at least 4.0
GPA.
The period of time during which the sample is subjected to HPHT
conditions is from less than about one minute to about 30 minutes.
The preferred time is between one to five minutes. The actual
conditions can be varied depending on the grade and the size of the
CVD sample.
The reaction mass may be subjected to any number of such
treatments. Thus, if the desired results were not achieved the
first time, the sample may be re-treated at HPHT until such time
that the desired improvement in characteristics or properties is
achieved.
The greatest improvements will be noted for single crystal CVD
diamond that is void of defects, such as surface pits, microscopic
inclusions, and that is at least partially translucent. Such CVD
material may be so improved as to even be polished and faceted to
produce a gem quality diamond to be used in jewelry.
BRIEF DESCRIPTION OF THE DRAWING
The various features, advantages and other uses of the present
invention will be come more apparent by referring to the following
detailed description and drawing in which:
FIG. 1 is a cross sectional view of the inner portion of a high
pressure cell used to treat CVD diamond according to the present
invention.
DETAILED DESCRIPTION
The present invention is a process to heat treat single crystal CVD
diamond at high temperature and high pressure. It is not certain
what happens to the CVD material when it is subjected to such
conditions. Possibly, internal atoms shift position to more
correctly align themselves to the diamond crystalline structure or
perhaps the bonding mechanism shifts such that SP.sup.2 type bonds
become SP.sup.3 type bonds causing carbon atoms to change from
impurity status to becoming part of the diamond crystal
lattice.
Whatever the mechanism, it has been found that treating CVD diamond
at high pressure and high temperature (HPHT) causes the optical
properties to change so much that opaque material become clear.
This same mechanism also improves the thermal conductivity and the
electrical resistance for the CVD diamond. This is very unexpected
since prior work has shown just the opposite occurs when CVD
diamond is annealed in a vacuum to 1600.degree. C. (A. V. Khomich
et al., Diam. Relat. Mater. 10 (2001), pp. 546-551), Heating CVD
diamond in vacuum has caused diamond to darken at temperatures as
low as 850.degree. C. (S. Mitra, K. I. Gleason, Diam. Relat. Mater.
2 (1993) p. 126).
Thus, one would expect that when diamond is heated to temperatures
above 850.degree. C., at pressures where graphite is the stable
phase, significant degradation of the sample would result. However,
very unexpected behavior occurs in CVD diamond at high temperatures
where the pressure is raised above atmospheric pressure but still
remains within the graphite stable region. Under certain conditions
of temperature and pressure, CVD diamond does not degrade; instead
the opposite occurs: the sample is transformed into a more perfect
diamond crystalline material
FIG. 1 shows a cross section of the inner portion of an assembly
that may be employed to treat CVD diamond 1 according to the
present invention. The outer body 2 is cylindrical in shape and is
designed to fit within a central cavity of an ultrahigh pressure
and ultrahigh temperature cell, such as that described in U.S. Pat.
Nos. 3,745,623 or 3,913,280.
The outer body 2 is composed of graphite or other material that
will readily transmit pressure and remain stable and non-reactive
to the CVD diamond 1 at high temperature and high pressure. Other
materials for the outer body 2 include, but are not limited to,
salt, MgO, or talc. The CVD diamond 1 is encapsulated in the outer
body 2. The CVD sample 1 is a stand alone CVD diamond or a CVD
coating on diamond or other materials. This assembly should be
consolidated to greater than 90% of its theoretical density and
made to fit snugly into a HPHT reaction cell, such as that used to
manufacture PCD.
The entire cell is subjected to pressures in excess of 4.0 GPA and
heated to temperature in excess of 1500.degree. C. for a time of
five minutes. Then the cell is allowed to cool enough so that the
CVD diamond does not back-convert to graphite after the pressure is
released.
After pressing, the sample 1 is removed from the graphite outer
body by mechanical means, such as by tapping with a mallet. The
sample can then be further heated in an oven to 725.degree. C. for
approximately ten minutes in order to obtain a clean and smooth
outer diamond surface. This treatment removes any graphite that may
have adhered to the sample. The surface can also be polished in a
manner as traditionally used on natural diamond single crystals or
polycrystalline diamond compacts.
EXAMPLE #1
A cubed-shaped CVD coated synthetic type Ib diamond, approximately
one centimeter square, was encapsulated in a graphite cylinder. The
CVD portion was a layer on one side of the cube-shaped natural
diamond, approximately one millimeter thick and was opaque to
optical transmission. The synthetic diamond substrate was light
yellow.
The graphite cylinder was loaded into a HPHT reaction vessel that
was configured for indirect heating of the reaction mass. Various
reaction vessel configurations, which provide the indirect or
direct heating, are disclosed in the patent literature and are also
useful for carrying out the present HPHT process.
Reaction vessels of this type usually of a plurality of
interfitting cylindrical members and end plugs or discs for
containing a sample in the innermost cylinder. For the indirectly
heated type of reaction vessel, one of the cylindrical members is
made of graphite that is heated by the passage of electric current
through the cylinder. For this case, the reaction mass, if composed
of graphite, must be electrically insulated from the graphite
heater tube by an insulating material, such as talc or salt, to
prevent passage of electrical current through the reaction mass. In
the directly heated type of reaction vessel, the insulating sleeve
is not required as the sample is heated by simply passing electric
current through the reaction mass provided it is composed of an
electrically conducting material, such as used in this example.
The reaction vessel was placed in a conventional HPHT apparatus.
First, the pressure was increased to 5.0 GPA, and then the
temperature was rapidly brought up to 2200.degree. C. The sample
was maintained at these conditions for five minutes, then the
temperature was decreased over a period of about one minute to room
temperature before the pressure was released.
The sample was removed from the reaction mass and examined under an
optical microscope. The opaque CVD diamond layer turned clear and
remained firmly bonded to the yellow synthetic type Ib diamond.
* * * * *