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06/01/2005
Diodes and Diamonds
I’ve never been “into” jewelry, as my wife can attest. My Sigma
Chi fraternity pin served as the only engagement token for my
bride-to-be. Fortunately, she was content to be a sweetheart of
Sigma Chi. Hey, I couldn’t afford more on my meager $100 a
month stipend as a graduate assistant in the chemistry department
at Pitt. However, one precious stone, diamond, has fascinated
me ever since I learned that ultrahard diamond and soft graphite
were just different forms of the same element, carbon.
Last week, I spotted a very brief item in the June issue of
National Geographic stating that recent studies support the belief
that the famed 45-carat Hope Diamond was cut from an even
larger stone, a 69-carat bauble stolen during the French
Revolution. Some owners or wearers of the Hope or its larger
parent suffered grievous misfortunes, leading to a belief that it
carried a curse. Notable examples were Louis XVI and Marie
Antoinette, both separated from their heads by the guillotine.
The Materials Research Society (MRS) sends e-mails alerting
members to new developments in materials science and
technology. Last week’s e-mail alerted me to a major
breakthrough in the growth of large diamonds. Not as large as
the Hope, but a 10-carat rock isn’t too shabby! In the past, I’ve
mentioned my own ill-fated attempts to grow diamonds some
four decades ago while at Bell Labs. In one experiment, my
assistant and I tried passing the vapor of an organic compound
over a diamond seed crystal. All we got was soot. Others,
notably John Angus at Case Western University, tried pretty
much the same experiment except that he added hydrogen and
voila - he grew diamond! This spurred a worldwide effort on
growing diamonds from vapor, a process known as chemical
vapor deposition, CVD.
For those who might not know or remember, diamond is
thermodynamically unstable at ordinary pressures and
temperatures. It should convert to graphite, the stable phase.
However, once diamond is formed, the chances of that happening
in a million lifetimes are virtually zero. At very high pressures
and high temperatures, diamond is stable and Nature used high
temps and pressures to make the diamonds we dig out of the
ground. Prior to Angus’ work, researchers at General Electric
had grown diamonds using a process involving very high
pressures and temperatures. The last I heard, GE still grows
industrial diamonds this way. The neat thing about CVD is that
at relatively low temperatures and ordinary pressures you trick
the carbon atoms from the vapor into sitting down on a diamond
seed crystal and extending the underlying diamond structure.
The carbon atoms don’t know they should be forming the softer
graphite structure.
Two weeks ago, Russell Hemley and his team at the Carnegie
Institution’s Geophysical Laboratory in Washington, D.C.
reported their breakthrough results at the Applied Diamond
Congress meeting in Illinois. They have used CVD to grow 10-
carat single crystal diamonds a half inch thick! You can see
pictures of these babies on the Web site carnegieinstitution.org or
on other sites reporting their work. Not only have Hemley and
crew grown the diamonds big, they’ve learned to grow them fast.
Their standard rate is 0.1 millimeter per hour but they’ve also
gone to 0.3 millimeters an hour and hope to raise that as high as
1 millimeter per hour. If you’re not comfortable with metric
units, achieving the latter millimeter per hour rate would yield an
inch thick diamond in just 25 hours! In diamond growth terms,
that’s like driving a car 200 mph on the Indianapolis Speedway.
As it is, their 10-carat diamonds are reportedly five times bigger
than other synthetic diamonds made by CVD or by high
pressure/high temperature methods. They’ve also made them
colorless, transparent to light in the range from ultraviolet to
infrared wavelengths. Typically, large CVD and high-pressure/
high-temperature diamonds are colored brown or yellow. The
achievement of colorless diamond paves the way for optical
applications and I would think indicates a control of impurities
and defects to a degree that augurs well for diamond’s future as
an electronic material. Incidentally, the Hope is a bluish color
due to boron impurity, according to the Smithsonian, where it
now resides. Harry Winston, its last owner, donated it to the
Smithsonian in 1958.
The same MRS e-mail contained an alert on a new light-emitting
diode (LED). At Bell Labs, I had considerably more success
with LEDs than with diamond growth, or lack thereof. Now
researchers at Los Alamos National Lab have come up with an
LED that can emit two colors at the same time. This represents a
step forward towards an LED that, if it could emit three colors of
the right wavelengths, would achieve the goal of an LED that
emits white light. The Los Alamos LED makes use of a
compound of gallium and nitrogen, gallium nitride, and colloidal
particles of an unidentified material. These very tiny colloidal
particles are so-called “quantum dots”. It has been known for
some time that, by varying the size of these quantum dots, light
of different colors could be achieved. The problem has been
trying to make electrical contacts to these very tiny specks of
material.
The Los Alamos workers have solved that problem by placing
the quantum dots at the junctions of different layers of the
gallium nitride. It’s at these junctions that electrons are whizzing
around doing their thing. It’s not clear to me but I’m guessing
that the dots get in the way of the electrons and it’s as though
there are electrical contacts without the wires normally needed.
You may recall that gallium nitride LEDs have an interesting
history. Red, green and yellow LEDs were common but blue
was out of reach until Shuji Nakamura, working for a small
Japanese company, came up with a gallium nitride blue LED. It
was a major achievement and Nakamura ended up coming to the
U.S. and suing his former company for what he considered his
just compensation for his invention. I was shocked to read some
time ago that a Japanese court awarded Nakamura 840 million
yen, or about $8 million dollars. Had I come up with a blue LED
at Bell Labs, I might have gotten a modest increase in salary
and/or a bonus of at most a few thousand dollars. Nakamura’s
company appealed the decision and recently a Tokyo court
lowered the amount 608 million yen plus interest, still about $6
million dollars I would guess.
Which brings me to an article by Otis Port in the May 23
Business Week that Brian Trumbore called to my attention. The
article is about Nick Holonyak, a former colleague at Bell Labs
who went on to the University of Illinois, where he became a
superstar in the world of LEDs. Port’s article quotes Nick as
predicting in the February 1963 issue of Reader’s Digest, of all
places, that incandescent light was doomed. Thanks in large
measure to Holonyak’s work, LEDs became brighter and brighter
and among his awards are the 1995 Japan Prize and the 2004
Lemelson-MIT Prize, worth a cool $500,000 each! Not bad for a
university professor! And his 1963 prediction looks closer to
becoming reality, perhaps in this century.
But Holonyak isn’t finished yet. He and another professor at
Illinois, Milton Feng, have come up with a light-emitting
transistor, an LET. This LET emits infrared light, which you and
I can’t see. However, it’s the kind of light that is used in
transmitting signals over our fiber optic networks. There is also
the long awaited optoelectronic circuit on a chip on which the
signals don’t travel over wires but on light beams traveling from
one component to another. This concept has been around for
many decades but still has to be consummated. Could the LET
be the answer? If it is, Nick might pick up another cool million!
Back to electrical connections, I plead guilty to allowing a very
important centennial to pass by last November without any
notice. A short article in the June Geographic by Pete Gwin
marked the awarding in November 1904 of a patent to Harvey
Hubbell for his “separable plug”. His plug and companion
socket surely must rate as one of the key inventions of the
twentieth century. Without them, think of having to wire
everything from curling irons to toasters directly into the home
electrical system. Hubbell’s patent rightfully declared that his
invention would allow “persons having no electrical knowledge
or skill” to connect appliances requiring electrical current.
Here’s to Harvey Hubbell, whose company still makes those
plugs.
Allen F. Bortrum
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