Nov. 23, 1998 Consider these possibilities: A TV set, only slightly thicker than paper, which could be hung on a wall or rolled up and moved from room to room within a home; A laptop computer screen that would remain battery-powered for weeks at a time instead of just a few hours; Or a device that would make future Star Trek-like travel to Mars possible on electrically powered space capsules.
These are just a few of the uses of diamond technology envisioned by the team of Vanderbilt University engineering professors Jim Davidson and Weng Poo Kang. Their lab includes two machines that can deposit diamond coating.
"The only common thread in these potential applications is the diamond material itself," Davidson said. He and Kang have had as many as nine sponsored research projects underway at the same time. In tune with current funding trends, their research is aimed at practical applications.
The two engineer's work with diamond emitter tips "could revolutionize flat panel display technology," according to Davidson. While the vacuum tubes and copper wiring used on early television sets have long since been replaced by tiny semiconductor chips and circuit boards, television and computer screens are still using the cathode ray tube (CRT), which retains most of the bulk and inefficiency of a half century ago. In the CRT, a heated filament sends out a flow of electrons that light up phosphors on the image screen.
Davidson and Kang's technology involves using an electric field rather than heat to release the electrons that light up computer screens. They started with a pyramidal mold and filled it with diamond. They added terminals and backing, using traditional semiconductor fabrication techniques. Finally, the mold material was etched away. The result was a uniform pattern of tiny diamond pyramids. The tips of the tightly packed pyramids (more than one million in an area no bigger than the capital letter "O") release the electrons in a very efficient manner and require much less power. The pyramidal diamond array emitter could lead to slimmer, more energy-efficient and portable displays for personal computers and television sets. Davidson said the emitter "could significantly outperform silicon devices in speed, power consumption and reliability" once some practical problems are solved. Among these is a tendency to get reverse current flow.
The emitters are also being used to make a diamond neutralizer that would allow for electric propulsion of future interplanetary space vehicles. Not surprisingly, NASA is extremely interested in the research and has been funding the project.
Davidson said that future space vehicles will use a beam of positively charged particles discharged from the back of the vehicle for propulsion. The problem is that the vehicle itself will become charged and the beam of ions used for propulsion will get weaker and weaker without a neutralizer. "You have to retain charge neutrality or your ion propulsion won't work," Davidson said. He and Kang have developed a device using the diamond pyramids that neutralizes the ions so that the vehicle will retain its thrust and will not become charged. They just finished the first phase of the project and will apply for additional NASA funding with their technology partner, Physitron, Inc.
Kang, through Vanderbilt, has a patent on a hydrogen sensor for the launch area at Cape Canaveral. Kang said that diamond has unique electro-chemical properties that make it very sensitive to certain gasses. NASA is interested in the sensor because it fuels its rockets with liquid hydrogen and liquid oxygen at the launch site. Kang's sensor shows the presence of potentially explosive hydrogen gasses much quicker than present technology.
The two engineers, teamed with Physitron, have also designed a high bandwidth pressure sensor for NASA's Mach 15 wind tunnel in Langley, Va. The wind tunnel conditions can include extreme heat and high frequency mechanical pressure fluctuations. The diamond sensor can withstand heat up to a thousand degrees Fahrenheit without being harmed.
With the emphasis on non-polluting automotive emission systems, Davidson said he can foresee the day when there are "smart" sensors in every automotive tailpipe and in every factory smoke stack in the country. The diamond sensor's ability to withstand extreme heat and still function efficiently make it an ideal candidate for such applications.
Davidson and Kang have also designed a high G-force accelerometer for the U.S. Air Force. It is being tested at Eglin Air Force Base in Florida. The accelerometer, which will probably be located on a missile, measures large changes in velocity to more than 50,000 G's, according to Davidson. By comparison, he said the G forces in the very worst automobile accidents is about 300 G's.
"The military may have information that the enemy is in a bunker that is built of three feet of concrete followed by an air pocket and then another three feet of steel-reinforced concrete," Davidson said. "The accelerometer would be the 'brain' that tells the missile that it has penetrated a multi-layered bunker and should explode. Our diamond sensor can help provide that information."
The same technology could be used in making a "smarter" airbag for automobiles or by petroleum companies for profiling geological structures far beneath the ground, according to Davidson. He said several oil companies have expressed an interest in the research.
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