6 research outputs found
NH<sub>3</sub>āNO Coadsorption System on Pt(111). II. Intermolecular Interaction
Coadsorption of ammonia and nitric
oxide on the (111) surface of
platinum causes the mutual stabilization of the two adsorbed species,
arranged in an ordered 2 Ć 2 mixed layer. Furthermore, their
interaction leads also to stable, isolated triangular units, which
we observe on the surface after annealing to 345 K. Having provided
in the preceding article (10.1021/jp406068y) a detailed structural description of the NH<sub>3</sub>āNO
mixed layer, we focus here on the stabilizing intermolecular interactions.
By combining scanning tunneling microscopy (STM) experiments and density
functional theory (DFT) calculations, we identify the isolated triangular
units as formed by one NH<sub>3</sub> and three NO molecules, and
we characterize them in terms of structure, energetics, and charge
rearrangement. Eventually, we investigate the nature of the chemical
bond between the coadsorbed NH<sub>3</sub> and NO both in the mixed
layer and in the isolated triangular units, pointing out the essential
role of the surface mediation in inducing attractive dipoleādipole
interactions and the presence of hydrogen bonds
Experimental and Theoretical Investigation of the Restructuring Process Induced by CO at Near Ambient Pressure: Pt Nanoclusters on Graphene/Ir(111)
The
adsorption of CO on Pt nanoclusters grown in a regular array
on a template provided by the graphene/Ir(111) MoireĢ was investigated
by means of infrared-visible sum frequency generation vibronic spectroscopy,
scanning tunneling microscopy, X-ray photoelectron spectroscopy from
ultrahigh vacuum to near-ambient pressure, and <i>ab initio</i> simulations. Both terminally and bridge bonded CO species populate
nonequivalent sites of the clusters, spanning from first to second-layer
terraces to borders and edges, depending on the particle size and
morphology and on the adsorption conditions. By combining experimental
information and the results of the simulations, we observe a significant
restructuring of the clusters. Additionally, above room temperature
and at 0.1 mbar, Pt clusters catalyze the spillover of CO to the underlying
graphene/Ir(111) interface
Tailoring Bimetallic Alloy Surface Properties by Kinetic Control of Self-Diffusion Processes at the Nanoscale
Achieving control of the nanoscale structure of binary
alloys is
of paramount importance for the design of novel materials with specific
properties, leading to, for example, improved reaction rates and selectivity
in catalysis, tailored magnetic behavior in electronics, and controlled
growth of nanostructured materials such as graphene. By means of a
combined experimental and theoretical approach, we show that the complex
self-diffusion mechanisms determining these key properties can be
mostly defined by kinetic rather than energetic effects. We explain
how in the NiāCu system nanoscale control of self-diffusion
and segregation processes close to the surface can be achieved by
finely tuning the relative concentration of the alloy constituents.
This allows tailoring the material functionality and provides a clear
explanation of previously observed effects involved, for example,
in the growth of graphene films and in the catalytic reduction of
carbon dioxide
Local Electronic Structure and Density of Edge and Facet Atoms at Rh Nanoclusters Self-Assembled on a Graphene Template
The chemical and physical properties of nanoclusters largely depend on their sizes and shapes. This is partly due to finite size effects influencing the local electronic structure of the nanocluster atoms which are located on the nanofacets and on their edges. Here we present a thorough study on graphene-supported Rh nanocluster assemblies and their geometry-dependent electronic structure obtained by combining high-energy resolution core level photoelectron spectroscopy, scanning tunneling microscopy, and density functional theory. We demonstrate the possibility to finely control the morphology and the degree of structural order of Rh clusters grown in register with the template surface of graphene/Ir(111). By comparing measured and calculated core electron binding energies, we identify edge, facet, and bulk atoms of the nanoclusters. We describe how small interatomic distance changes occur while varying the nanocluster size, substantially modifying the properties of surface atoms. The properties of under-coordinated Rh atoms are discussed in view of their importance in heterogeneous catalysis and magnetism
Steering the Chemistry of Carbon Oxides on a NiCu Catalyst
In the perspective of a sustainable
energy economy, CO<sub>2</sub> reduction is attracting increasing
attention as a key step toward the synthesis of fuels and valuable
chemicals. A possible strategy to develop novel conversion catalysts
consists in mimicking reaction centers available in nature, such as
those in enzymes in which Fe, Ni, and Cu play a major role as active
metals. In this respect, NiCu shows peculiar activity for both water-gas
shift and methanol synthesis reactions. The identification of useful
descriptors to engineer and tune the reactivity of a surface in the
desired way is one of the main objectives of the science of catalysis,
with evident applicative interest, as in this case. To this purpose,
a crucial issue is the determination of the relevant active sites
and rate-limiting steps. We show here that this approach can be exploited
to design and tailor the catalytic activity and selectivity of a NiCu
surface
Chemistry of the Methylamine Termination at a Gold Surface: From Autorecognition to Condensation
13The self-assembly of the naphthylmethylamine molecules (NMA) on the Au(111) surface is investigated by a combined experimental and theoretical approach. Three well-defined phases are observed upon different thermal treatments at the monolayer stage. The role played by the methylamine termination is evidenced in both the moleculeāmolecule and moleculeāsubstrate interactions. The autorecognition process of the amino groups is identified as the driving factor for the formation of a complex hydrogen bonding scheme in small molecular clusters, possibly acting also as a precursor of a denitrogenation condensation process induced by thermal annealing.reservedmixedDri, Carlo; Fronzoni, Giovanna; Balducci, Gabriele; Furlan, Sara; Stener, Mauro; Feng, Zhijing; Comelli, Giovanni; Castellarin-Cudia, Carla; Cvetko, Dean; Kladnik, Gregor; Verdini, Alberto; Floreano, Luca; Cossaro, AlbanoDri, Carlo; Fronzoni, Giovanna; Balducci, Gabriele; Furlan, Sara; Stener, Mauro; Feng, Zhijing; Comelli, Giovanni; Castellarin Cudia, Carla; Cvetko, Dean; Kladnik, Gregor; Verdini, Alberto; Floreano, Luca; Cossaro, Alban