Graphene nanoribbon breakthrough paves way for new generation of quantum devices
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A new 'templated growth' technique for fabricating nanoribbons of epitaxial graphene has produced structures that are 15 to 40nm wide and can conduct current with almost no resistance. According to researchers at the Georgia Institute of Technology, these structures could address the challenge of connecting graphene devices made with conventional architectures and pave the way for a new generation of electronics that take advantage of the quantum properties of electrons.
"We can now make very narrow, conductive nanoribbons that have quantum ballistic properties," said Walt de Heer, a professor in the School of Physics at Georgia Tech. "These narrow ribbons become almost like a perfect metal. Electrons can move through them without scattering, just like they do in carbon nanotubes."
According to Professor de Heer, the new technique begins with etching patterns into the silicon carbide surfaces on which epitaxial graphene is grown. The patterns, which serve as templates, direct the growth of graphene structures, allowing the formation of nanoribbons and other structures of specific widths and shapes without the use of cutting techniques that produce rough edges.
In creating these graphene nanostructures, de Heer and his research team first used conventional microelectronics techniques to etch tiny 'steps', or contours, into a silicon carbide wafer that had been made extremely flat. They then heated the contoured wafer to approximately 1,500°C to initiate melting and to polish any rough edges left by the etching process.
Established techniques were then used for growing graphene from silicon carbide by driving off the silicon atoms from the surface. Instead of producing a consistent layer of graphene across the entire surface of the wafer, however, the researchers limited the heating time so that the graphene grew only on portions of the contours. According to the professor, the width of the resulting nanoribbons was proportional to the depth of the contours, providing a mechanism for precisely controlling the nanoribbon structures.
"This technique allowed us to avoid the complicated e-beam lithography steps that people have been using to create structures in epitaxial graphene," de Heer noted. "We are seeing very good properties that show these structures can be used for real electronic applications."
While the Georgia Tech team is continuing to develop high frequency transistors, its primary efforts are now focused on developing quantum devices, de Heer said. "Using the quantum properties of electrons rather than the standard charged particle properties means opening up new ways of looking at electronics. This is probably the way that electronics will evolve and it appears that graphene is the ideal material for making this transition."
