New Process Promises Bigger, Better Diamond Crystals

Oct 27, 2008
Diamonds such as these grown in the laboratory using a chemical vapor deposition process can be treated by a new high temperature, low pressure method to improve their color and optical clarity. Credit: Carnegie Institution for Science

(PhysOrg.com) -- Researchers at the Carnegie Institution have developed a new technique for improving the properties of diamonds—not only adding sparkle to gemstones, but also simplifying the process of making high-quality diamond for scalpel blades, electronic components, even quantum computers. The results are published in the October 27-31 online edition of the Proceedings of the National Academies of Science.

A diamond may be forever, but the very qualities that make it a superior material for many purposes—its hardness, optical clarity, and resistance to chemicals, radiation, and electrical fields― can also make it a difficult substance with which to work. Defects can be purged by a heating process called annealing, but this can turn diamond to graphite, the soft, grey form of carbon used in pencil leads. To prevent graphitization, diamond treatments have previously required high pressures (up to 60,000 times atmospheric pressure) during annealing, but high pressure/high temperature annealing is expensive and there are limits on the size and quantities of diamonds that can be treated.

Yu-fei Meng, Chih-shiue Yan, Joseph Lai, Szczesny Krasnicki, Haiyun Shu, Thomas Yu, Qi Liang, Ho-kwang Mao, and Russell Hemley of the Carnegie Institution's Geophysical Laboratory used a method called chemical vapor deposition (CVD) to grow synthetic diamonds for their experiments. Unlike other methods, which mimic the high pressures deep within the earth where natural diamonds are formed, the CVD method produces single-crystal diamonds at low pressure. The resulting diamonds, which can be grown very rapidly, have precisely controlled compositions and comparatively few defects.

The Carnegie team then annealed the diamonds at temperatures up to 2000° C using a microwave plasma at pressures below atmospheric pressure. The crystals, which are originally yellow-brown if produced at very high growth rates, turned colorless or light pink. Despite the absence of stabilizing pressure there was minimal graphitization. Using analytical methods such as photoluminescence and absorption spectroscopy, the researchers were also able to identify the specific crystal defects that caused the color changes. In particular, the rosy pink color is produced by structures called nitrogen-vacancy (NV) centers, where a nitrogen atom takes the place of a carbon atom at a position in the crystal lattice next to a vacant site..

"This low-pressure/high-temperature annealing enhances the optical properties of this rapid-grown CVD single crystal diamond." says Meng. "We see a significant decrease in the amount of light absorbed across the spectrum from ultraviolet to visible and infrared. We were also able to determine that the decrease arises from the changes in defect structure associated with hydrogen atoms incorporated in the crystal lattice during CVD growth."

"It is striking to see brown CVD diamonds transformed by this cost-efficient method into clear, pink-tinted crystals," says Yan. And because the researchers pinpointed the cause of the color changes in their diamonds, "Our work may also help the gem industry to distinguish natural from synthetic diamond."

"The most exciting aspect of this new annealing process is the unlimited size of the crystals that can be treated. The breakthrough will allow us to push to kilocarat diamonds of high optical quality" says coauthor Ho-kwang Mao. Because the method does not require a high pressure press, it promises faster processing of diamonds and more types of diamonds to be de-colored than current high-pressure annealing methods. There is also no restriction on the size of crystals or the number of crystals, because the method is not limited by the chamber size of a high pressure press. The microwave unit is also significantly less expensive than a large high-pressure apparatus.

"The optimized process will produce better diamond for new-generation high pressure devices and window materials with improved optical properties in the ultraviolet to infrared range." concludes laboratory director Russell Hemley. "It has the advantage of being applicable in CVD reactors as a subsequent treatment after growth."

The high-quality, single crystal diamond made possible by the new process has a wide variety of applications in science and technology, such as the use of diamond crystals as anvils in high-pressure research and in optical applications that take advantage of diamond's exceptional transparency. Among the more exotic future applications of the pink diamonds made in this way is quantum computing, which could use the diamonds' NV centers for storing quantum information.

Source: Carnegie Institution

Explore further: Faster switching helps ferroelectrics become viable replacement for transistors

add to favorites email to friend print save as pdf

Related Stories

First Swedish hard-rock diamonds discovered

22 hours ago

An Uppsala-led research group has presented the first verified discovery of diamonds in Swedish bedrock. The diamonds are small, but provide important clues to the geological evolution of rocks.

Serendipitous holography reveals hidden cracks

Oct 15, 2014

In a recent article published in the Review of Scientific Instruments, a research team led by scientists at Lawrence Livermore National Laboratory describe a technique for 3D-image processing of a high-s ...

Solar cell compound probed under pressure

Sep 25, 2014

Gallium arsenide, GaAs, a semiconductor composed of gallium and arsenic is well known to have physical properties that promise practical applications. In the form of nanowires and nanoparticles, it has particular ...

Smallest possible diamonds form ultra-thin nanothreads

Sep 21, 2014

For the first time, scientists have discovered how to produce ultra-thin "diamond nanothreads" that promise extraordinary properties, including strength and stiffness greater than that of today's strongest ...

Recommended for you

High-intensity sound waves may aid regenerative medicine

18 hours ago

Researchers at the University of Washington have developed a way to use sound to create cellular scaffolding for tissue engineering, a unique approach that could help overcome one of regenerative medicine's ...

Formula could shed light on global climate change

22 hours ago

Wright State University researchers have discovered a formula that accurately predicts the rate at which soil develops from the surface to the underlying rock, a breakthrough that could answer questions about ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

Scalziand
not rated yet Oct 28, 2008
I wonder if the increased understanding of the nitrogen impurities will lead to synthesis of beta carbon nitride.
Yes
not rated yet Nov 04, 2008
Why is this need to be able to discriminate an industrial diamond from a natural diamond?:)
From my point of view it would be a great advancement if you couldn't see the difference.
Yes
not rated yet Nov 04, 2008
I also want to share this recipe for a nice refreshing soda.
Take a 6 krt diamond and heat it up to 2500C in the presence of oxygen. Carefully save the gas that is formed and dissolve the gas in water.
Put this solution in the fridge and drink on a hot day.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.