2 research outputs found
Mechanisms of Covalent Coupling Reaction of Dibromofluoranthene on Au(111)
The
reaction mechanism of on-surface coupling of 7,10-dibromofluoranthene
(Br<sub>2</sub>FL) on Au(111) was studied on the basis of density
functional theory calculations, as a possible route for fabricating
graphene nanoribbons (GNRs) including pentagonal rings. The reaction
pathways and energy barriers of debromination, radical coupling, and
diffusion processes were investigated. The results indicate that the
reaction mechanism is substantially different for Br<sub>2</sub>FL
compared to that for the phenyl radical, which has been extensively
studied as a model system. The rate-limiting step was radical coupling
associated with the formation of a gold-metallic intermediate, which
is rarely observed on Au(111), because of steric repulsion between
the two radicals and that between the radicals and the substrate.
The energy barriers were comparable with those for cyclohexa-<i>m</i>-phenylene on Ag(111), and the reaction rate estimated
using transition state theory was consistent with the experimental
results. These results suggest that Br<sub>2</sub>FL is preferred
as a precursor of the coupling reaction to fabricate fluoranthene
polymers. Well-defined GNRs including pentagonal rings would be formed
by further cyclodehydrogenation
Solvation Effects on OH Adsorbates on Stepped Pt Surfaces
Density functional theory calculations
were applied to OH formations
on stepped Pt electrodes of PtÂ[<i>n</i>(111) × (111)]
(<i>n</i> = 3, 4, and 6) for examining solvation effects
on the OH adsorbates. Results indicated that OH adsorbates at terrace
sites are slightly destabilized by water molecules adsorbed at step
sites forming 1-dimensional water chains whereas OH adsorbates at
step sites are significantly destabilized by water molecules adsorbed
at terrace sites forming 2-dimensional honeycomb structures. On stepped
Pt surfaces with narrow terrace widths, water molecules cannot exist
at terrace sites, and therefore, the solvation effects on OH adsorbates
at step sites disappear. Hence, OH adsorbates are formed at step sites
at a low potential region, ca. 0.3 V (standard hydrogen electrode
(SHE)). When high-coverage CO adsorbates are present on the stepped
Pt surfaces, water molecules cannot exist at the terrace sites either
because strongly bound CO molecules exclude the water molecules. In
such conditions, OH formation potentials decrease significantly, too.
Thermodynamic stabilities of OH adsorbates are, therefore, controlled
not only by the local surface morphology but also by long-ranged interfacial
solvation environments. In other words, the stability and presence/absence
of OH adsorbates should be considered to be totally different with
water adsorbates (like in inert conditions) and without them (like
in the CO oxidation)