by Catherine Brahic
Diamonds are a girl’s best friend, they say - and soon they could be
every girl’s best friend.
A team in the US has brought the world one step closer to cheap,
mass-produced, perfect diamonds. The improvement also means there is
no theoretical limit on the size of diamonds that can be grown in
A team led by Russell Hemley, of the Carnegie Institute of
Washington, makes diamonds by chemical vapour deposition (CVD),
where carbon atoms in a gas are deposited on a surface to produce
The CVD process produces rapid diamond growth, but impurities from
the gas are absorbed and the diamonds take on a brownish tint.
These defects can be purged by a costly high-pressure,
high-temperature treatment called annealing. However, only
relatively small diamonds can be produced this way: the largest so
far being a 34-carat yellow diamond about 1 centimetre wide.
Now Hemley and his team have got around the size limit by using
microwaves to “cook” their diamonds in a hydrogen plasma at 2200 C
but at low pressure. Diamond size is now limited only by the size of
the microwave chamber used.
“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 Hemley’s Carnegie Institute colleague Ho-kwang Mao.
“The microwave unit is also significantly less expensive than a
large high-pressure apparatus,” adds Yufei Meng, who also
participated in the experiments.
The new technique is so efficient that the synthetic diamonds
contain fewer impurities than those found in nature, says Meng. “We
once sent one of our lab-grown diamonds for jewellery
identification, it wasn’t told apart from natural ones,” she says.
One immediate application will be to make ultra-high quality windows
that are optically transparent to lasers. Threat to commerce
The team’s method “could be routinely run in any laboratory where it
is needed,” says Alexandre Zaitsev, a physicist at the City
University of New York, whose work also includes diamonds. “When
considered in combination with the high-growth-rate technique of CVD
diamonds, it seems to be a starting point of mass-scale production
of perfect diamond material at a low price.”
Zaitsev considers low-pressure annealing at temperatures greater
than 2000 C to be a “breakthrough in diamond research and
The improving quality of synthetic diamonds threatens the natural
diamond market. While 20 tonnes of natural diamonds are mined
annually, some 600 tonnes of synthetic diamonds are produced each
year for industrial use alone.
They are used in a range of high-end technologies, such as lasers and
high-pressure anvils. Some companies have also started to sell
synthetic diamonds as In response, diamond giant De Beers
has set up a “Gem Defensive Programme” with the aim of finding ways
to tell apart synthetic and natural diamonds.