Method Developed For Measuring Single Carbon Nanotubes
Scientists at Purdue University (West Lafayette, IN; 765-494-2081), are the first to develop a simple method for accurately measuring the electrical properties of a single carbon nanotube. The technique already has shown that nanotubes may conduct electricity with little resistance—a result that confirms their potential value in making extremely small circuits and computer chips.
How It Works (Back to Top)
A major obstacle in producing ever-smaller circuits and electronic components is the self-destructive heat they generate. The smaller the electronic circuit, the more susceptible it is to heat damage. Materials that conduct electrons with little resistance are needed for these applications, says Ronald Reifenberger, professor of physics at Purdue. Measurements made by the Purdue team suggest that nanotubes do, in fact, possess this low-heat characteristic.
Preliminary data from the Purdue research also confirms a theoretical characteristic of nanotubes—that they conduct electrons by "ballistic transport"—meaning the electrons collide with few impurities as they flow from one end of the nanotube to the other. Lack of collisions means low resistance and low heat production.
"It is difficult to test theories about nanotubes because of their small size," Reifenberger says. "The best way to reliably analyze the electrical characteristics of a nanotube is to connect it on both ends with metallic contacts and then run a current through it. But, until now, scientists have been unable to manipulate an individual nanotube and make reliable contacts."
The Purdue team devised a method using an atomic force microscope to precisely position a nanotube so that both ends are bridging a circuit. They then coated the ends with gold, using a process known as shadow masking, creating strong contacts at both ends. Having solid contacts at both ends ensures that passing a current through the nanotube will yield accurate data about its electrical characteristics such as resistance, Reifenberger says.
Applications (Back to Top)
"Now we can measure standard things that electrical engineers are interested in," Reifenberger says, noting that the new method is especially attractive to researchers because, unlike other techniques, it does not require elaborate facilities.
"The thing that's appealing is the simplicity of the idea," he says. "A small college can do these measurements now, because all you need is a steady hand. You can make a half dozen samples in a week and get data on them."
Carbon nanotubes, elongated molecules that are as small as a few atoms in diameter, were discovered less than 10 years ago. In theory, they might be used to build devices to replace much larger silicon-based devices in electronic circuits.
Engineering professors Ronald Andres and Supriyo Datta, and graduate students Pedro de Pablo, Elton Graugnard, and Brian Walsh worked with Reifenberger on the research project.
The technique was presented March 23, 1999, during a meeting of the American Physical Society (Atlanta). The research was funded by the National Science Foundation.
For more information, call 765-494-2081.