A one-atom thick billiard table
A team of physicists at the University of California at Riverside (UCR) have found that graphene, which was isolated experimentally only less than three years ago, and which is a one-atom thick sheet of carbon atoms arranged in hexagonal rings, can act as an atomic-scale billiard table. They found that electrons in graphene behave like quantum billiard balls. This research could lead to new kinds of transistors based on quantum physics. In fact, it's possible that graphene can replace silicon as the basic electronic material in a few years. For example, it could be used to develop ballistic transistors.
This research effort was led by Chun Ning (Jeanie) Lau , Assistant Professor of Physics at UC Riverside, and several members of her research group (Caution: Flash-based site) The image above, which comes from her lab, shows a sheet of graphene, "which can act as an atomic-scale billiard table, with electric charges acting as billiard balls." (Credit: Lau lab, UCR) Here is a link to a larger version.
As writes Science in its September 14, 2007 issue, "Graphene acts as a quantum billiard table, the edges of which scatter the wave functions of electrons and holes, producing interference effects that depend on the sheet geometry." And the UCR news release adds that Lau "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."
How did she and her colleagues found that? "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."
And what can be done with graphene, isolated experimentally only less than three years ago? "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.
Other applications are possible. "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."
For more information, this research work has been published in Science under the name "Phase-Coherent Transport in Graphene Quantum Billiards" (Volume 317, Issue 5844, Pages 1530-1533, September 14, 2007). Here is the beginning of the abstract. "As an emergent electronic material and model system for condensed-matter physics, graphene and its electrical transport properties have become a subject of intense focus. By performing low-temperature transport spectroscopy on single-layer and bilayer graphene, we observe ballistic propagation and quantum interference of multiply reflected waves of charges from normal electrodes and multiple Andreev reflections from superconducting electrodes, thereby realizing quantum billiards in which scattering only occurs at the boundaries."
Finally, here is what Lau writes about graphene on her Flash-based website (sorry, no URL). "Graphene, a two-dimensional (2D) a honey-comb lattice of carbon atoms, exhibits unusual energy dispersion relations – the low-lying electrons in single layer graphene behave like massless relativistic Dirac fermions with vanishing density of states at the Dirac point, and a bilayer’s band structure resembles a zero band gap semiconductor. Since recent experimental isolation and measurement of graphene, it has attracted tremendous attention, as the special band structures in single and bi-layer graphenes yield novel aspects to the physics of two-dimensional electron systems. The Dirac spectrum in graphene is predicted to give rise to a number of phenomena, such as quantum spin hall effects, enhanced Coulomb interaction, and suppression of weak localization. Technologically, graphene is an attractive material for nanoscale electronics engineering. As a two-dimensional (2D) relative of carbon nanotubes, it manifests high mobility, high current carrying-capacity and extraordinary thermal conductivity; but in contrast to nanotubes, traditional lithographic techniques can potentially be employed for device synthesis and tailoring transport properties. We are interested in investigating the electrical transport properties of graphene."
Sources: University of California at Riverside news release, September 14, 2007; and various websites
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