  Graphene electronics has motivated much of graphene science for the past
decade. A primary goal was to develop high mobility semiconducting graphene
with a band gap that is large enough for high performance applications.
Graphene ribbons were thought to be semiconductors with these properties,
however efforts to produce ribbons with useful bandgaps and high mobility has
had limited success. We show here that high quality epitaxial graphene
nanoribbons 40 nm in width, with annealed edges, grown on sidewall SiC are not
semiconductors, but single channel room temperature ballistic conductors for
lengths up to at least 16 micrometers. Mobilities exceeding one million
corresponding to a sheet resistance below 1 Ohm have been observed, thereby
surpassing two dimensional graphene by 3 orders of magnitude and theoretical
predictions for perfect graphene by more than a factor of 10. The graphene
ribbons behave as electronic waveguides or quantum dots. We show that transport
in these ribbons is dominated by two components of the ground state transverse
waveguide mode, one that is ballistic and temperature independent, and a second
thermally activated component that appears to be ballistic at room temperature
and insulating at cryogenic temperatures. At room temperature the resistance of
both components abruptly increases with increasing length, one at a length of
160 nm and the other at 16 micrometers. These properties appear to be related
to the lowest energy quantum states in the charge neutral ribbons. Since
epitaxial graphene nanoribbons are readily produced by the thousands, their
room temperature ballistic transport properties can be used in advanced
nanoelectronics as well.
