4 research outputs found
Electronic transport across quantum dots in graphene nanoribbons: Toward built-in gap-tunable metal-semiconductor-metal heterojunctions
The success of all-graphene electronics is severely hindered by the
challenging realization and subsequent integration of semiconducting channels
and metallic contacts. Here, we comprehensively investigate the electronic
transport across width-modulated heterojunctions consisting of a graphene
quantum dot of varying lengths and widths embedded in a pair of armchair-edged
metallic nanoribbons, of the kind recently fabricated via on-surface synthesis.
We show that the presence of the quantum dot enables the opening of a
width-dependent transport gap, thereby yielding built-in one-dimensional
metal-semiconductor-metal junctions. Furthermore, we find that, in the vicinity
of the band edges, the conductance is subject to a smooth transition from an
antiresonant to a resonant transport regime upon increasing the channel length.
These results are rationalized in terms of a competition between
quantum-confinement effects and quantum dot-to-lead coupling. Overall, our work
establishes graphene quantum dot nanoarchitectures as appealing platforms to
seamlessly integrate gap-tunable semiconducting channels and metallic contacts
into an individual nanoribbon, hence realizing self-contained carbon-based
electronic devices
Edge Disorder in Bottom-Up Zigzag Graphene Nanoribbons: Implications for Magnetism and Quantum Electronic Transport
We unveil the nature of the structural disorder in bottom-up zigzag graphene
nanoribbons along with its effect on the magnetism and electronic transport on
the basis of scanning probe microscopies and first-principles calculations. We
find that edge-missing m-xylene units emerging during the cyclodehydrogenation
step of the on-surface synthesis are the most common point defects. These
"bite'' defects act as spin-1 paramagnetic centers, severely disrupt the
conductance spectrum around the band extrema, and give rise to spin-polarized
charge transport. We further show that the electronic conductance across
graphene nanoribbons is more sensitive to "bite" defects forming at the zigzag
edges than at the armchair ones. Our work establishes a comprehensive
understanding of the low-energy electronic properties of disordered bottom-up
graphene nanoribbons
Quantum Electronic Transport Across "Bite" Defects in Graphene Nanoribbons
On-surface synthesis has recently emerged as an effective route towards the
atomically precise fabrication of graphene nanoribbons of controlled topologies
and widths. However, whether and to which degree structural disorder occurs in
the resulting samples is a crucial issue for prospective applications that
remains to be explored. Here, we experimentally identify missing benzene rings
at the edges, which we name "bite" defects, as the most abundant type of
disorder in armchair nanoribbons synthesized by the bottom-up approach. First,
we address their density and spatial distribution on the basis of scanning
tunnelling microscopy and find that they exhibit a strong tendency to
aggregate. Next, we explore their effect on the quantum charge transport from
first-principles calculations, revealing that such imperfections substantially
disrupt the conduction properties at the band edges. Finally, we generalize our
theoretical findings to wider nanoribbons in a systematic manner, hence
establishing practical guidelines to minimize the detrimental role of such
defects on the charge transport. Overall, our work portrays a detailed picture
of "bite" defects in bottom-up armchair graphene nanoribbons and assesses their
effect on the performance of carbon-based nanoelectronic devices