3 research outputs found
Solution-Synthesized Chevron Graphene Nanoribbons Exfoliated onto H:Si(100)
There
has been tremendous progress in designing and synthesizing graphene
nanoribbons (GNRs). The ability to control the width, edge structure,
and dopant level with atomic precision has created a large class of
accessible electronic landscapes for use in logic applications. One
of the major limitations preventing the realization of GNR devices
is the difficulty of transferring GNRs onto nonmetallic substrates.
In this work, we developed a new approach for clean deposition of
solution-synthesized atomically precise chevron GNRs onto H:Si(100)
under ultrahigh vacuum. A clean transfer allowed ultrahigh-vacuum
scanning tunneling microscopy (STM) to provide high-resolution imaging
and spectroscopy and reveal details of the electronic structure of
chevron nanoribbons that have not been previously reported. We also
demonstrate STM nanomanipulation of GNRs, characterization of multilayer
GNR cross-junctions, and STM nanolithography for local depassivation
of H:Si(100), which allowed us to probe GNR–Si interactions
and revealed a semiconducting-to-metallic transition. The results
of STM measurements were shown to be in good agreement with first-principles
computational modeling
Interfacial Self-Assembly of Atomically Precise Graphene Nanoribbons into Uniform Thin Films for Electronics Applications
Because of their
intriguing electronic and optical properties, atomically precise graphene
nanoribbons (GNRs) are considered to be promising materials for electronics
and photovoltaics. However, significant aggregation and low solubility
of GNRs in conventional solvents result in their poor processability
for materials characterization and device studies. In this paper,
we demonstrate a new fabrication approach for large-scale uniform
thin films of nonfunctionalized atomically precise chevron-type GNRs.
The method is based on (1) the exceptional solubility of graphitic
materials in chlorosulfonic acid and (2) the original interfacial
self-assembly approach by which uniform films that are single-GNR
(∼2 nm) thick can be routinely prepared. These films can be
transferred to various substrates including Si/SiO<sub>2</sub> and
used for the streamlined fabrication of arrays of GNR-based devices.
The described self-assembly approach should be applicable to other
types of solution-synthesized atomically precise GNRs as well as large
polyaromatic hydrocarbon (PAH) molecules and therefore should facilitate
and streamline their device characterization
Nitrogen-Doping Induced Self-Assembly of Graphene Nanoribbon-Based Two-Dimensional and Three-Dimensional Metamaterials
Narrow
graphene
nanoribbons (GNRs) constructed by atomically precise bottom-up synthesis
from molecular precursors have attracted significant interest as promising
materials for nanoelectronics. But there has been little awareness
of the potential of GNRs to serve as nanoscale building blocks of
novel materials. Here we show that the substitutional doping with
nitrogen atoms can trigger the hierarchical self-assembly of GNRs
into ordered metamaterials. We use GNRs doped with eight N atoms per
unit cell and their undoped analogues, synthesized using both surface-assisted
and solution approaches, to study this self-assembly on a support
and in an unrestricted three-dimensional (3D) solution environment.
On a surface, N-doping mediates the formation of hydrogen-bonded GNR
sheets. In solution, sheets of side-by-side coordinated GNRs can in
turn assemble via van der Waals and π-stacking interactions
into 3D stacks, a process that ultimately produces macroscopic crystalline
structures. The optoelectronic properties of these semiconducting
GNR crystals are determined entirely by those of the individual nanoscale
constituents, which are tunable by varying their width, edge orientation,
termination, and so forth. The atomically precise bottom-up synthesis
of bulk quantities of basic nanoribbon units and their subsequent
self-assembly into crystalline structures suggests that the rapidly
developing toolset of organic and polymer chemistry can be harnessed
to realize families of novel carbon-based materials with engineered
properties