Atomic carbon billiards

Physicists at UC Riverside have demonstrated that graphene – a one-atom thick sheet of carbon atoms arranged in hexagonal rings – can act as an atomic-scale billiard table, with electric charges acting as billiard balls.

The finding underscores graphene’s potential for serving as an excellent electronic material, such as silicon, that can be used to develop new kinds of transistors based on quantum physics. Because they encounter no obstacles, the electrons in graphene roam freely across the sheet of carbon, conducting electric charge with extremely low resistance.

Study results appear in today’s issue of Science.

The research team, led by Chun Ning (Jeanie) Lau, found that the electrons in graphene are reflected back by the only obstacle they meet: graphene’s boundaries.

“These electrons meet no other obstacles and behave like quantum billiard balls,” said Lau, an assistant professor who joined UCR’s Department of Physics and Astronomy in 2004. “They display properties that resemble both particles and waves.”

Lau observed that when the electrons are reflected from one of the boundaries of graphene, the original and reflected components of the electron can interfere with each other, the way outgoing ripples in a pond might interfere with ripples reflected back from the banks.

Her lab detected the “electronic interference” by measuring graphene’s electrical conductivity at extremely low (0.26 Kelvin) temperatures. She explained that at such low temperatures the quantum properties of electrons can be studied more easily.

“We found that the electrons in graphene can display wave-like properties, which could lead to interesting applications such as ballistic transistors, which is a new type of transistor, as well as resonant cavities for electrons,” Lau said. She explained that a resonant cavity is a chamber, like a kitchen microwave, in which waves can bounce back and forth.

In their experiments, Lau and her colleagues first peeled off a single sheet of graphene from graphite, a layered structure consisting of rings of six carbon atoms arranged in stacked horizontal sheets. Next, the researchers attached nanoscale electrodes to the graphene sheet, which they then refrigerated in a cooling device. Finally, they measured the electrical conductivity of the graphene sheet.

Graphene, first isolated experimentally less than three years ago, is a two-dimensional honeycomb lattice of carbon atoms, and, structurally, is related to carbon nanotubes (tiny hollow tubes formed by rolling up sheets of graphene) and buckyballs (hollow carbon molecules that form a closed cage).

Scientifically, it has become a new model system for condensed-matter physics, the branch of physics that deals with the physical properties of solid materials. Graphene enables table-top experimental tests of a number of phenomena in physics involving quantum mechanics and relativity.

Bearing excellent material properties, such as high current-carrying capacity and thermal conductivity, graphene ideally is suited for creating components for semiconductor circuits and computers. Its planar geometry allows the fabrication of electronic devices and the tailoring of a variety of electrical properties. Because it is only one-atom thick, it can potentially be used to make ultra-small devices and further miniaturize electronics.

Source : Scientist Live

New Development : Bendable Battery

It's a battery that looks like a piece of paper and can be bent or twisted, trimmed with scissors or molded into any shape needed. While the battery is only a prototype a few inches square right now, the researchers at Rensselaer Polytechnic Institute who developed it have high hopes for it in electronics and other fields that need smaller, lighter power sources."We would like to scale this up to the point where you can imagine printing batteries like a newspaper. That would be the ultimate," Robert Linhardt a professor at the Center for Biotechnology and Interdisciplinary Studies at RPI said in a telephone interview.The development is reported in this week's online edition of Proceedings of the National Academy of Sciences. Unlike other batteries, Linhardt explained, it is an integrated device, not a combination of pieces. The battery uses paper infused with an electrolyte and carbon nanotubes that are embedded in the paper. The carbon nanotubes form the electrodes, the paper is the separator and the electrolyte allows the current to flow.Students at the school in Troy, N.Y., were the inspiration for the work, said Linhardt, whose students were working on methods to dissolve paper and cast it into membranes for use in dialysis machines. Meanwhile, students of Pulickel Ajayan in RPI's materials science department were trying to make carbon nanotube composites using polymers. The two groups got together and realized they could use paper instead of polymers and combine the two projects.Then came Omkaram Nalamasu's students, also at RPI, who said the project—a thin sheet black on one side and white on the other—looked like an electrical device. And over about 18 months, the groups developed the projects, into a battery, a capacitor, which stores electricity and a combination of the two. Ajayan sees potential uses in combination with solar cells, perhaps layers of the paper batteries that could store the electricity generated until it is needed, he said in a telephone interview.Perhaps it could be scaled up and shaped into something like a car door, offering moving electrical storage and power when needed. That might be an expensive proposition, however, cautioned Peter Kofinas, an engineering professor at the University of Maryland."The advantage of a flexible device would be that you could roll it in a film or a sheet. However, carbon nanotubes are very expensive," said Kofinas, who was not involved in the research."So from the commercial standpoint, this would be very expensive if you want to make a large sheet out of this material," he said via e- mail. In addition, he said, "It does not look like it performs better than currently available batteries and supercapacitors in the market."Because of its flexibility, however, it does have potential, Kofinas said.The research was funded by the New York State Office of Science, Technology and Academic Research and the National Science Foundation.