  We report the growth of single-crystalline Bi2Se3 nanoribbons with lengths up
to several millimeters via a catalyst-free physical vapor deposition method.
Scanning transmission electron microscopy analysis reveals that the nanoribbons
grow along the (1120) direction. We obtain a detailed characterization of the
electronic structure of the Bi2Se3 nanoribbons from measurements of
Shubnikov-de Haas (SdH) quantum oscillations. Angular dependent
magneto-transport measurements reveal a dominant two-dimensional contribution
originating from surface states and weak contribution from the bulk states. The
catalyst-free synthesis yields high-purity nanocrystals enabling the
observation of a large number of SdH oscillation periods and allowing for an
accurate determination of the pi-Berry phase, one of the key features of Dirac
fermions in topological insulators. The long-length nanoribbons can empower the
potential for fabricating multiple nanoelectronic devices on a single
nanoribbon.
