2 research outputs found
Termini of Bottom-Up Fabricated Graphene Nanoribbons
Atomically precise graphene nanoribbons (GNRs) can be
obtained
via thermally induced polymerization of suitable precursor molecules
on a metal surface. This communication discusses the atomic structure
found at the termini of armchair GNRs obtained via this bottom-up
approach. The short zigzag edge at the termini of the GNRs under study
gives rise to a localized midgap state with a characteristic signature
in scanning tunneling microscopy (STM). By combining STM experiments
with large-scale density functional theory calculations, we demonstrate
that the termini are passivated by hydrogen. Our results suggest that
the length of nanoribbons grown by this protocol may be limited by
hydrogen passivation during the polymerization step
On-Surface Synthesis and Characterization of 9‑Atom Wide Armchair Graphene Nanoribbons
The bottom-up approach
to synthesize graphene nanoribbons strives
not only to introduce a band gap into the electronic structure of
graphene but also to accurately tune its value by designing both the
width and edge structure of the ribbons with atomic precision. We
report the synthesis of an armchair graphene nanoribbon with a width
of nine carbon atoms on Au(111) through surface-assisted aryl–aryl
coupling and subsequent cyclodehydrogenation of a properly chosen
molecular precursor. By combining high-resolution atomic force microscopy,
scanning tunneling microscopy, and Raman spectroscopy, we demonstrate
that the atomic structure of the fabricated ribbons is exactly as
designed. Angle-resolved photoemission spectroscopy and Fourier-transformed
scanning tunneling spectroscopy reveal an electronic band gap of 1.4
eV and effective masses of ≈0.1 <i>m</i><sub>e</sub> for both electrons and holes, constituting a substantial improvement
over previous efforts toward the development of transistor applications.
We use <i>ab initio</i> calculations to gain insight into
the dependence of the Raman spectra on excitation wavelength as well
as to rationalize the symmetry-dependent contribution of the ribbons’
electronic states to the tunneling current. We propose a simple rule
for the visibility of frontier electronic bands of armchair graphene
nanoribbons in scanning tunneling spectroscopy