Experiments the team conducted have shown they can cause carbon nanotubes, a new form of carbon discovered about a decade ago, to generate intense electron beams that bombard a metal "target" to produce X-rays. Researchers say they have demonstrated that their cold-cathode device can generate sufficient X-ray flux to create images of extremities such as the human hand.
The advantage of using carbon nanotubes is that machines incorporating them can work at room temperature rather than the 1500 or so degrees Celsius that conventional X-ray machines now require and produce.
"If this works as well as we think it will, we can make such machines a lot smaller and cooler and be able to turn them on and off much faster," said Dr. Otto Z. Zhou, associate professor of physics and materials sciences. "Other advantages are that they should be cheaper, be safer in terms of the lower heat generated, last longer, use less electricity and produce higher resolution images.
"We believe we have made a major breakthrough in X-ray technology, and we are extremely excited about it."
A report on their experiments appears in the July 8 issue of Applied Physics Letters, a science and technology journal. Patents on the UNC work are pending.
Besides Zhou, authors are Dr. Guo Z. Yue, a former UNC faculty member now with United Solar Systems; Qi Oiu and Drs. Bo Gao and Hideo Shimoda of Applied Nanotechnologies Inc., students Yuan Cheng and Jian Zhang, and Dr. Jian Ping Lu, associate professor of physics and astronomy and applied and materials sciences. Dr. Sha Chang, associate professor of radiation oncology at the UNC School of Medicine, also participated in the project.
"Scientists and others, including the popular press, have shown a lot of interest in carbon nanotubes because of numerous potential applications," Zhou said. "They are very strong tubular structures formed from a single layer of carbon atoms and are only about a billionth of a meter in diameter."
In the past, UNC scientists and others have used carbon nanotubes to produce electrons, he said. What's new is that until now, no one could generate enough electrons to create distinct images like conventional X-rays do. Nanotubes replace traditional metal filaments that must be heated to high temperatures before being subjected to an electric field. The tubes shed electrons easily because, being so small, they are extremely sharp.
"We already have taken pictures of human hands and fish that are as good as standard X-rays," Zhou said. "We think our images eventually will be clearer than conventional ones since we have a more pointed, tunable source of electrons. That would help doctors, for example, get more useful information from pictures of broken bones, for example."
The physicists are working with manufacturers to turn their discovery into working machines and expect to have them on the market within a year or two, he said.
Being able to miniaturize X-ray devices could have more major benefits, Zhou said, including allowing technicians to take X-rays inside or outside ambulances before ever leaving the scenes of accidents. No major technical obstacles remain in their way.
In addition, the new X-ray technology will allow manufacturing of large-scale X-ray scanning machines for industrial inspections, airport security screening and customs inspections.
Other uses of carbon nanotubes include flat panel display and telecommunications devices, fuel cells, high-strength composite materials and novel molecular electronics for the next generation of computers, he said. People have raised the possibility of using them to improve batteries, but no one demonstrated that they might work better than conventional materials until Zhou and his UNC team published a paper on the subject in January in Physical Review Letters.
That paper showed they could potentially improve electric batteries by using single-wall carbon nanotubes to help store electrical charges. They have patented the process of creating such nanotubes.
Zhou directs the N.C. Center for Nanoscale Materials at UNC. Applied Nanotechnologies Inc., which seeks to develop new industrial and medical applications for carbon nanotubes, is a new spin-off company resulting from his group's work. Support for the experiments came from the Office of Naval Research and private sources.
Note: Zhou can be reached at (919) 962-3297 or Zhou@email.unc.edu
Contact: David Williamson, (919) 962-8596
By DAVID WILLIAMSON
UNC News Services
Journal
Applied Physics Letters