Georgetown College. Georgetown University.

By Megan Weintraub

In the future, our ability to predict a terrorist chemical attack or to trace sources of pollution from combustion processes might lie in molecules 100,000 times smaller than the diameter of a hair. Thanks to a couple of extremely sensitive microscopes and a team of dedicated students, Dr. Paola Barbara, an associate professor in Georgetown’s Department of Physics, investigates the huge promise of the electrical properties of carbon nanotubes, the tiny cylindrical molecules that she constructs in her lab.

Despite their miniscule size, carbon nanotubes hold vast potential to revolutionize technologies such as computer chips. For decades, the computer industry has doubled processing power every 18 months; this trend is known as Moore’s Law. Computers run on silicon chips containing large numbers of miniature transistors; the smaller the transistors, the faster the computer runs. Traditionally, manufacturers have made these chips using a “top-down” approach by patterning transistors and other electronic devices from large silicon crystals. During the patterning process, called lithography, scientists create a polymer layer on top of the silicon. Then they make a hole in the polymer that is shaped like parts of the transistor and deposit material or etch through these holes to create the device. Dr. Barbara and other researchers, on the other hand, are learning how to create transistors using a “bottom-up” strategy.

“We grow carbon nanotubes like crystals,” she explains. “These molecules can function as transistors in their own right, and we can learn how the small size affects their performance.”

After growing the molecules, Dr. Barbara carefully deposits metal contacts to create carbon nanotube transistors, also called “three-terminal devices.” One contact acts like the knob of a faucet, allowing her to control the electrical current between the other two contacts attached to each end of the carbon molecule. Scientists are still learning how the interfaces between the molecule and the contacts affect the properties of the device and how to make the best contacts. These experiments are labor and time intensive; simply creating the three-terminal devices takes significant work.

Carbon nanotube transitors also hold very promising applications as extremely sensitive chemical detectors.

“It’s fascinating to study these systems because all these new properties come into play on such a small level,” Dr. Barbara explains. “We were surprised to find that the interface between the nanotube and the electrodes plays a key role in the mechanism that causes the strong response of carbon nanotubes devices to some chemicals.”

Dr. Barbara’s work on carbon nanotubes is exciting because it opens up new avenues of scientific knowledge. For example, she is investigating whether the tubes can act as superconductors, which are materials that can transfer an electrical current without losing any energy in the process. In order to achieve this, superconductors must operate at a very low temperature, so she is researching whether and under which conditions superconductivity may arise in carbon nanotubes.

To illustrate the contrast between superconductors and traditional conductors, one need only look at a common toaster. Part of its electrical energy is transformed into thermal energy, which is used to toast the bread. In other words, when electrical current flows through a normal conductor, some electrical energy is always dissipated into heat. Superconductors, on the other hand, can carry electrical current without experiencing this dissipation. Carbon nanotubes offer the opportunity to study superconductivity in the smallest possible wires that scientists can fabricate.

Nanometer-sized devices are impossible to see with the naked eye or even an optical microscope. Dr. Barbara and her students rely predominantly on two instruments to facilitate their research: an atomic force microscope and a scanning electron microscope. Both instruments use highly specialized technology to create images of the carbon nanotubes, which allows the research team to run their experiments. Dr. Barbara’s students have contributed significantly to getting the lab ready for such intricate observations.

“My students have helped with every step along the way,” describes Dr. Barbara. “They have learned how to fabricate the carbon nanotubes and how to take measurements. It takes a couple of dedicated semesters just to learn how to work with these materials.”

Dr. Barbara has been working at Georgetown since 2000, and she is excited to be part of the expansion and improvement of the school’s science program. Due to the small size of the Department of Physics, she sees opportunities to collaborate with scientists from other departments, a luxury she would not be afforded at a larger school.

Currently on sabbatical, Dr. Barbara is taking the opportunity to dive deeper into her research, which is funded through the National Science Foundation, the American Chemical Society, and the Research Corporation.

“Would there be another job I’d like more than this one? No way,” she says. “I love the variety of working in the lab, the teaching, and the interactions with students. It seems like I’m always stimulated by new challenges and new topics in this field.”

While it would be impossible to view Dr. Barbara’s work just by looking at it, its potential impact will remain clearly visible in the field of superconductivity and nanotechnology for years to come.

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