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nanotimes News in Brief

11-02/03 :: February / March 2011

Nanomaterial // UCLA Advance With new Nanomaterials Good News for Next-Generation Electronic Devices

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n recent years, topological insulators have become one of the hottest topics in physics. These new

materials act as both insulators and conductors, with their interior preventing the flow of electrical cur- rents while their edges or surfaces allow the move- ment of a charge.

Perhaps most importantly, the surfaces of topological insulators enable the transport of spin-polarized elec- trons while preventing the “scattering” typically asso- ciated with power consumption, in which electrons deviate from their trajectory, resulting in dissipation.

Because of such characteristics, these materials hold great potential for use in future transistors, memory devices and magnetic sensors that are highly energy efficient and require less power.

Researchers from UCLA‘s Henry Samueli School of Engineering and Applied Science and from the mate- rials division of Australia‘s University of Queensland show the promise of surface-conduction channels in topological insulator nanoribbons made of bismuth telluride and demonstrate that surface states in these nanoribbons are “tunable” – able to be turned on and off depending on the position of the Fermi level.

“Our finding enables a variety of opportunities in building potential new-generation, low-dissipation nanoelectronic and spintronic devices, from ma- gnetic sensing to storage,” said Kang L. Wang, the Raytheon Professor of Electrical Engineering at UCLA Engineering, whose team carried out the research.

Bismuth telluride is well known as a thermoelec- tric material and has also been predicted to be a three-dimensional topological insulator with robust and unique surface states. Recent experiments with bismuth telluride bulk materials have also suggested two-dimensional conduction channels originating from the surface states. But it has been a great challenge to modify surface conduction, because of dominant bulk contribution due to impurities and thermal excitations in such small-band-gap semicon- ductors.

The development of topological insulator nanorib- bons has helped. With their large surface-to-volume ratios, these nanoribbons significantly enhance sur- face conditions and enable surface manipulation by external means.

Wang and his team used thin bismuth telluride nanoribbons as conducting channels in field-effect