5 research outputs found
Phenyl Functionalization of Atomically Precise Graphene Nanoribbons for Engineering Inter-ribbon Interactions and Graphene Nanopores
Graphene
nanoribbons (GNRs) attract much attention from researchers
due to their tunable physical properties and potential for becoming
nanoscale building blocks of electronic devices. GNRs can be synthesized
with atomic precision by on-surface approaches from specially designed
molecular precursors. While a considerable number of ribbons with
very diverse structures and properties have been demonstrated in recent
years, there have been only limited examples of on-surface synthesized
GNRs modified with functional groups. In this study, we designed a
nanoribbon, in which the chevron GNR backbone is decorated with phenyl
functionalities, and demonstrate the on-surface synthesis of these
GNRs on Au(111). We show that the phenyl modification affects the
assembly of the GNR polymer precursors through π–π
interactions. Scanning tunneling spectroscopy of the modified GNRs
on Au(111) revealed that they have a band gap of 2.50 ± 0.02
eV, which is comparable to that of the parent chevron GNR. The phenyl
functionalization leads to a shift of the band edges to lower energies,
suggesting that it could be a useful tool for the GNR band structure
engineering. We also investigated lateral fusion of the phenyl-modified
GNRs and demonstrate that it could be used to engineer different kinds
of atomically precise graphene nanopores. A similar functionalization
approach could be potentially applied to other GNRs to affect their
on-surface assembly, modify their electronic properties, and realize
graphene nanopores with a variety of structures
Autonomous Molecular Structure Imaging with High-Resolution Atomic Force Microscopy for Molecular Mixture Discovery
Due
to its single-molecule sensitivity, high-resolution atomic
force microscopy (HR-AFM) has proved to be a valuable and uniquely
advantageous tool to study complex molecular mixtures, which hold
promise for developing clean energy and achieving environmental sustainability.
However, significant challenges remain to achieve the full potential
of the sophisticated and time-consuming experiments. Automation combined
with machine learning (ML) and artificial intelligence (AI) is key
to overcoming these challenges. Here we present Auto-HR-AFM, an AI
tool to automatically collect HR-AFM images of petroleum-based mixtures.
We trained an instance segmentation model to teach Auto-HR-AFM how
to recognize features in HR-AFM images. Auto-HR-AFM then uses that
information to optimize the imaging by adjusting the probe-molecule
distance for each molecule in the run. Auto-HR-AFM is the initial
tool that will lead to fully automated scanning probe microscopy (SPM)
experiments, from start to finish. This automation will allow SPM
to become a mainstream characterization technique for complex mixtures,
an otherwise unattainable target
Hydrogen-Bonded Cyclic Water Clusters Nucleated on an Oxide Surface
We
report the observation and molecular-scale scanning probe electronic
structure (<i>dI</i>/<i>dV</i>) mapping of hydrogen-bonded
cyclic water clusters nucleated on an oxide surface. The measurements
are made on a new type of cyclic water cluster that is characterized
by simultaneous and cooperative bonding interactions among molecules
as well as with both metal and oxygen sites of an oxide surface. Density
functional theory + U + D calculations confirm the stability of these
clusters and are used to discuss other potential water-oxide bonding
scenarios. The calculations show that the spatial distributions of
electronic states in the system are similar in character to those
of the lowest unoccupied molecular orbitals of hydrogen-bonded water
molecules. On the partially oxidized Cu(111) investigated here, experiment
and theory together suggest that Cu vacancies in the growing islands
of cuprous oxide inhibit water adsorption in the centers of the islands
(which have reached thermodynamic equilibrium). A stoichiometric,
less stable cuprous oxide likely exists at island edges (the growth
front) and selectively binds these water clusters
Orbital-Resolved Imaging of the Adsorbed State of Pyridine on GaP(110) Identifies Sites Susceptible to Nucleophilic Attack
Artificial photosynthesis by photoelectrocatalytic
CO<sub>2</sub> reduction is dependent, as is natural photosynthesis,
on interfacial
electron transfer to couple light excitation energy to reaction centers.
For heterogeneous systems, in the context of frontier orbital theory
artificial reaction centers are defined through the interactions of
filled and empty orbitals within a few electronvolts of the Fermi
energy of the adsorbate complex. Here we report a scanning tunneling
microscopy (STM) and density functional theory investigation of the
orbital-resolved adsorption state defining the dative bonding interaction
between a III–V semiconductor surface [GaP(110)] and a N-containing
heteroaromatic (pyridine). This system was selected for its relevance
to photoelectrocatalysis utilizing heteroaromatic cocatalysts, which
has been reported to yield highly selective CO<sub>2</sub> reduction
to fuels. By examining the distribution of unoccupied molecular orbitals,
we show that STM images can be used to positively identify the sites
on pyridine susceptible to nucleophilic attack, consistent with frontier
orbital theory. This indicates that STM can be used to explore the
local reaction centers of adsorbed ambidentate electrophiles and nucleophiles
relevant to artificial photosynthesis, and more broadly to generate
critical mechanistic information for various heterogeneous acid–base
reactions
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