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Posted: Oct 11, 2013

Quantum conductors benefit from growth on smooth foundations

(Nanowerk News) Imagine if the "information superhighway" had HOV lanes so that data could be stored, processed and disseminated many times faster than possible with today’s electronics. Researchers in the United States and China have teamed to develop such a speedway for future devices, an exotic type of electrical conductor called a topological insulator (TI). In a new paper in the journal AIP Advances ("Molecular beam epitaxial growth of Bi2Te3 and Sb2Te3 topological insulators on GaAs (111) substrates: a potential route to fabricate topological insulator p-n junction"), the international collaborators report that they grew two types of TI materials inside an ultra-high vacuum chamber on both smooth and rough surfaces and then evaluated their abilities to transport electrons.
A TI harnesses not only the charge of electrons, but also their spin and magnetic properties. The interior of this unusual structure is an insulator, something that blocks the flow of current, while the surface acts as a highly efficient conductor of electricity. So efficient, in fact, that the electrons never deviate from their path.
"This makes the TI promising for applications such as future high-speed, dissispationless [does not involve energy dissipation] computers where massive quantities of information would be carried by electrons in quantum channels," said physicist and corresponding author Jian Wang at Peking University’s International Center for Quantum Materials. "Avoiding the scattering of electrons that occurs in today’s computers would keep high-speed devices from experiencing chip overheating, destruction of the data stream, and a slowdown of operational speed."
In their study, the researchers grew two types of TI materials, bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3), one atomic layer at a time on both vicinal (rough) and non-vicinal (smooth) forms of a substrate material commonly used by the semiconductor industry, gallium arsenide (GaAs).
"Higher quality, better-electron-conducting TI films were grown on the smoother surface substrate and that was unexpected," says Timothy Morgan, co-author and nanotechnologist at the Arkansas Institute for Nanoscale Material Sciences and Engineering. "Typically, rough spots would provide anchor points for film growth kind of like putting the first pieces of a tile floor up against a wall so that the rest fall in alignment. This new finding tells us we need to do more investigations of the growth mechanisms involved."
Now that the researchers have shown that they can grow high-quality TI materials on industry standard substrates, they say the next step is to put them to work. "We will try to design and fabricate some fundamental devices using TI materials to see how well they perform tasks such as electronic switching and photodetection," says Zhaoquan Zeng, lead author an and postdoctoral researcher at Ohio State University’s Electrical and Computer Engineering Department.
Source: American Institute of Physics
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