July 01, 1991

Article at Reuters

Scientists make cheap diamonds from pencil graphite

Cheap diamonds from the soft grey graphite of pencils

By Wilson da Silva

SYDNEY – Australian scientists have found a new way to make cheap diamonds: by blasting the soft grey graphite of pencils with an electric welder’s arc.

Amorphous diamond, a new type of carbon identified by University of Sydney researchers, is cheap enough to spawn a miniaturisation boom in computers, while boasting many of the useful properties of natural diamonds, scientists say.

By stripping carbon atoms off graphite with a low-voltage electric arc and filtering the residue through a magnetic field, the Australians found they could compress a carbon layer onto a substrate such as glass, plastic or ceramic.

This produces thin sheets of artificial diamond that are purer and cheaper than those made with conventional methods, say the university’s David McKenzie and Bernard Pailthorpe.

The sheets are only 500 atoms thick, or 20 times thinner than the silicon chips that carry computer circuitry.

Diamond, the hardest substance known, is also a superb electrical insulator. U.S. scientists estimate that a diamond microchip could pack one billion transistors in a one-cm (half-inch) wafer, compared with 16 million in the most advanced microchip.

McKenzie and Pailthorpe say that, using supercomputers, they understand better how their sheets of “glassy” diamond are made. This may have stolen them a world lead in fine- tuning their methods for eventual application.

Pailthorpe said in a statement the method could allow diamond film, expensive to produce and made in small amounts today, to go into large-scale production within a few years.

In April, U.S. scientists detailed experimental methods which use high-powered pulsed ultraviolet lasers to shear carbon atoms from graphite and deposit a thin diamond layer on a copper base.

Pailthorpe said that although the laser method produces the densest and purest artificial diamonds, it requires particle accelerators worth tens of millions of dollars and may prove too expensive to be used commercially.

“We think we have an edge,” Pailthorpe said by telephone.

He said the Australian team, working with Britain’s University of Cambridge, has successfully implanted working diamond diodes on a silicon chip, and believes it may be close to installing transistors, something yet to be achieved.

Cheap diamonds could make possible ball bearings that never wear out, computer chips that survive temperatures approaching 4,500 degrees Celsius (8,130 Farenheit), scratch-resistant lenses, and razor blades that never go blunt.

“People have been trying to make diamond from graphite for ages, because they know that both are just different types of carbon,” Pailthorpe said.

The Australians use a technique called Vacuum Arc Deposition (VAD), developed by Soviet scientists in 1978 and being applied in hardening tools with titanium nitride deposits.

Commercial methods have since the late 1950s produced tiny, gritty diamonds by subjecting graphite to extreme pressures, but the process is extremely expensive. It is used to harden tools or to protect camera lenses used in space.

A new method, Chemical Vapour Deposition (CVD), has allowed large sheets of diamond film to be made. But the sheets, per diamond carat, are more expensive than those made under the standard high-pressure technique.

The CVD diamond film is 300 times thicker than that produced by the Australian method, and scientists have been unable to implant an efficient working diode in one, McKenzie said.

Pailthorpe said the group had made amorphous diamonds with a density of 3.0 grams per cubic centimetre, close to natural diamond’s 3.5 grams.

The CVD method produces crystalline diamond with a density equal to natural diamond, as does the pressure method. Amorphous diamond made by the Australian group is more “glassy” but in many ways more useful.

“Its structure is not regular like a natural diamond. It’s a tangled network which makes the glassy diamond film harder than the crystalline diamond because it is more resistant to distortion,” McKenzie said.