Two years after construction on the press began, it was finally finished and the physicists involved in the team set about running failed experiment after failed experiment with it. Hall thought GE and the team that designed the machine were approaching the problem wrong and believed there was a better, simpler way. In fact, he thought with a few modifications and a custom designed apparatus, he could use a leaky, 35 year old Watson-Stillman press to do the job.
After all, a team of extremely well educated physicists thought it could only be done with their shiny new, very expensive, machine. An old Watson-Stillman press could never be sufficient for the job, no matter how much he modified it.
Aside from denying him the money to make the modifications, GE also gave priority in the machining shop to the physicists on the Project Superpressure team, making it so Hall could not continue working on his idea that way either.
Thanks to the intervention of a sympathetic supervisor, Herman Liebhafksy, who had been integral to Hall getting the job in the first place when he insisted they needed to add a chemist to the Project Superpressure team, GE purchased the expensive carboloy for Hall.
With his machine finally built, Hall set about experimenting with it. It took him several attempts at creating synthetic diamonds before he discovered the correct method. But on December 16, , Hall worked alone at the GE laboratory after the rest of the staff had gone home for the Christmas holiday. My eyes had caught the flashing light from dozens of tiny… crystals. He then asked his colleague, Hugh H.
Woodbury, to conduct the test himself. When Hall informed his bosses at GE about the success he achieved with his makeshift device, they were skeptical. Their skepticism disappeared when they witnessed the experiment themselves. Hall left the building before the test specifically so that they could not claim he doctored the results somehow.
However, they initially claimed it was more of a team effort by physicists and other researchers as part of Project Superpressure, rather than it being mostly just Hall working on the project on the side and simply modifying an old press to suit his purposes.
And because semiconducting diamond can generate a wider range of potentials than other electrode materials, electrodes made of this material can be used to study redox reactions that can't be studied with conventional electrodes, notes assistant professor of chemical engineering Heidi B. Martin of Case Western. That and the many other excellent properties of diamond have led chemistry professor Greg M. Swain of Michigan State University and many other scientists to use CVD to grow polycrystalline boron-doped diamond electrodes that can detect--and in some cases degrade--redox-reactive organic contaminants in water supplies.
In addition, Martin is using CVD to grow highly conductive boron-doped polycrystalline diamond microelectrodes that could directly sense a variety of redox-active neurotransmitters during neurotransmission. The diamond microelectrodes should be more sensitive, stable, and versatile than ones made of other materials, Martin says. The company markets its polycrystalline diamond for use as heat spreaders in high-power electronic devices.
It also uses the material to fashion surgical blades that are resistant to dulling and optical windows for high-powered CO 2 lasers. Because the C—C bonds that hold its patchwork of tiny crystals together are weaker than C—C bonds in single-crystal diamond, polycrystalline diamond isn't quite as thermally conductive, as optically transparent, or as strong as single-crystal diamond.
For diamond to live up to its promise as an alternative to silicon for fabricating electronic devices, "what's required is high-quality, single-crystal CVD diamond in usable sizes," Coe adds.
Coe and his colleagues at Element Six proved this was possible just over a year ago [ Science , , ] and now can grow high-quality, single-crystal diamond wafers that are 5 mm square.
He predicts that within the next four years the company will be cranking out 4-inch square wafers. Both Coe and Linares suggest that, thanks to its high thermal conductivity and electrical carrier mobility, single-crystal semiconducting diamond will be the ultimate material for fashioning high-powered electronic devices. Element Six is already making some simple prototype devices, such as switches, from p-type semiconducting diamonds, Coe says.
But most devices will require both hole-conducting p-type and electron-conducting n-type diamond semiconductors. The former is easy: Both Element Six and Apollo report that they can use their CVD methods to make boron-doped single-crystal diamond wafers that are excellent p-type semiconductors. Producing n-type semiconducting diamond has proven more challenging, however. A number of potential n-type dopants have been investigated, most notably phosphorus.
A group led by Hisao Kanda of Japan's National Institute for Materials Science has shown that doping diamond with phosphorus gives n-type semiconducting diamond. The team has gone on to show that phosphorus-doped and boron-doped diamond can be combined to make a simple electrical device called a p-n junction. But so far neither phosphorus nor any other n-type dopant has demonstrated exactly the right electrical properties, according to Butler. Despite this promising development, Angus--whose own lab is doping CVD diamond with a combination of boron and sulfur to get n-type semiconductivity--comments that "all of the n-type work, including ours, is interesting in a scientific sense but not yet practical for devices.
The payoff for such work is potentially huge: Today's microchips are running hotter and hotter because more and more transistors are being crammed onto them. If the trend continues, silicon may not be able to take the heat. Diamond could be the perfect solution. Despite its superior combination of electrical, optical, thermal, and chemical properties, though, diamond may never totally replace silicon for two reasons: Silicon is both cheap and firmly entrenched in the computer industry.
Still, Reza Abbaschian, a professor of materials science and engineering at the University of Florida, Gainesville, whose lab helped to perfect Gemesis' diamond-growing method, believes that "for certain specialized applications, such as devices that run at high power or high temperature, diamond may be just the ticket.
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