UNC discovery shows properties of gas depend on container size

November 15, 2001

(Embargoed) CHAPEL HILL -- Hydrogen gas behaves the same whether confined to a laboratory test tube or a huge storage tank, but a new discovery shows that its properties changes markedly when the container is only a few nanometers in diameter, about 10 millionths of an inch.

That discovery, being reported Friday (Nov. 16) in the journal Science, is potentially useful because it shows a new way of tailoring the properties of matter through nanotechnology, say scientists at University of North Carolina at Chapel Hill. Possible applications range from boosting understanding of amorphous silicon-based solar cell efficiency to exploration of quantum space.

UNC authors of the report, all in the physics and astronomy department, are doctoral student Jonathan Baugh; Dr. Alfred Kleinhammes, research assistant professor; Dr. Daxing Han, research associate professor; and Dr. Yue Wu, associate professor. Dr. Qi Wang, a staff scientist at the National Renewable Energy Laboratory in Golden, Colo., contributed to the research. In April at the 2001 Materials Research Society spring meeting, Baugh won a gold medal in the graduate student research competition with the project.

To work in collecting solar energy, amorphous silicon films are impregnated with hydrogen atoms, Wu said. A fraction of those atoms are trapped as hydrogen molecules in an array of cigar- or football-shaped pockets a few nanometers in size in the amorphous silicon film. Roughly 500 hydrogen molecules fill each pocket.

Using a technique called nuclear magnetic resonance, Baugh, Wu and the others found for the first time that confining hydrogen molecules to such small spaces created measurable magnetic interactions. Normally, those interactions cancel one another out in larger containers and average zero when measured.

The discovery provides a convenient sensor of nanometer-scaled structures inside hydrogenated amorphous silicon and could lead to a better understanding of solar cell efficiency, they said.

"The amorphous form of silicon is important because it's what people use to make solar cells to create electricity from solar energy," Wu said. "The key issue in converting one form of energy to another is cost, and the cost is directly related to the efficiency."

The UNC team believes most fluids, including both gases and liquids, should behave similarly when contained in such small spaces, he said.

"This is one of those discoveries where you really can't say at the moment what concrete applications it will have, but it is fundamental enough, we think, that it should have applications in the future," Baugh said. "The science of nanomaterials is really in its infancy."
Note: The authors can be reached at (919) 962-0307 or yuewu@physics.unc.edu.
Contact: David Williamson, (919) 962-8596.

UNC News Services

University of North Carolina at Chapel Hill

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