Graphene nanoribbons (GNRs) are at the frontier of research on graphene materials since the 1D quantum confinement of electrons allows for the opening of an energy gap. GNRs of uniform and well-defined size and shape can be grown using the bottom-up approach, i.e. by surface assisted polymerization of aromatic hydrocarbons. Since the electronic properties of the nanostructures depend on their width and on their edge states, by careful choice of the precursor molecule it is possible to design GNRs with tailored properties. A key issue for their application in nanoelectronics is their stability under operative conditions. Here, we characterize pristine and oxygen-exposed 1.0 nm wide GNRs with a well-defined mixed edge-site sequence (two zig-zag and one armchair) synthesized on Ag(110) from 1,6-dibromo-pyrene precursors. The energy gap and the presence of quantum confined states are investigated by scanning tunneling spectroscopy. The effect of oxygen exposure under ultra-high vacuum conditions is inferred from scanning tunneling microscopy images and photoemission spectra. Our results demonstrate that oxygen exposure deeply affects the overall system by interacting both with the nanoribbons and with the substrate; this factor must be considered for supported GNRs under operative conditions.

Highly hydrophobic aluminium surfaces fabricated by chemical etching are investigated by Contact Angle Goniometry, Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy in order to correlate the wettability of our samples with their morphology at the sub-micrometer scale and with the chemical composition of the very first surface layers. We find that the etched aluminium surfaces have binary structures with nanoscale block-like convexities and hollows, which provide more space for air trapping. We also demonstrate that both hierarchical micro/nanostructures and surface composition endow these surfaces with excellent hydrophobic properties. XPS analysis shows indeed that the contact angle anti-correlates with the amount of metallic aluminium present at the surface, but also confirms the essential role of the adsorption of airborne carbon compounds. The hydrophobic behaviour depends therefore on the combined effects of surface morphology and surface chemistry.

We investigated the interaction of CO with a Ni(111) sample partially covered with carbide by Near Ambient Pressure (PCO ~ 2 mbar) X-Ray Photoemission Spectroscopy. Above 500 K we observe the formation of strongly and weakly interacting graphene in comparable amount and CO intercalation underneath the latter moiety. Above 600 K, physisorbed CO2 forms, a process which we ascribe to the onset of the Boudouard reaction under the graphene cover.

The chemical reactivity of single layers of supported graphene (G) is affected by the nature of the underlying substrate: in particular CO chemisorption occurs on G/Ni(111), while graphene on Cu is inert. Here, we demonstrate experimentally that doping of the G layer with nitrogen atoms further increases the reactivity of the G/Ni(111) system towards CO. The doped layer is obtained by sputtering pristine G/Ni(111) with N2 + ions. For an ~11% dopant concentration, an additional electron energy loss at 238 meV appears in the HREEL spectra besides the loss around 256 meV present also on pristine G/Ni(111). The new feature corresponds to a CO species with a higher desorption temperature and, consequently, a higher adsorption energy than the one forming on pristine G/Ni(111). At low coverage, the adsorption energy is estimated to be ~0.85 eV/molecule.

Free standing graphene is chemically inert but, as recently demonstrated, CO chemisorption occurs at lowcrystal temperature on the single layer grown by ethene dehydrogenation on Ni(111). Such layer is inhomogeneous since different phases coexist, the relative abundance of which depends on the growth conditions. Here we show by X ray photoemission and high resolution electron energy loss spectroscopies that the attained CO coverage depends strongly on the relative weight of the different phases as well as on the concentration of carbon in the Ni subsurface region. Our data show that the chemical reactivity is hampered by the carbon content in the substrate. The correlation between the amount of adsorbed CO and the weight of the different graphene phases indicates that the top-fcc configuration is the most reactive. Published by AIP Publishing.

We present here a novel approach to achieve the selective formation of different in-plane boron-nitrogen-carbon heterostructures on Pt(111) using a single molecular precursor, namely dimethylamine borane (DMAB). Through thermally activated decomposition and sequential bond activation it is possible to control intermolecular coupling and obtain alternatively a quasi-free-standing continuous monolayer formed by complementary hexagonal boron nitride and graphene (G) large-size domains, or a pure or doped G monolayer, or hybridized layers with non-planar bonds. The selective bond-bond coupling is achieved by controlling the substrate temperature either during or after the deposition of DMAB. This allows on-surface synthesis of B-N-C materials with tunable composition. (C) 2017 Elsevier Ltd. All rights reserved.

We investigate CO adsorption at single vacancies of graphene supported on Ni(111) and polycrystalline Cu. The borders of the vacancies are chemically inert but, on the reactive Ni(111) substrate, CO intercalation occurs. Adsorbed CO dissociates at 380 K, leading to carbide formation and mending of the vacancies, thus preventing their effectiveness in sensor applications.

Graphene is usually considered a chemically inert material. Theoretical studies of CO adsorption on free-standing graphene predict quite low adsorption energies (<0.1eV). However, we show here by vibrational spectroscopy and scanning tunneling microscopy that the nondissociative chemisorption of CO occurs at cold, pristine graphene grown on Ni(111). The CO adlayer remains stable up to 125K, although some coverage survives flashes to 225K. This unexpected result is explained qualitatively by the modification of the density of states close to the Fermi energy induced by the relatively strong graphene-substrate interaction. The value of the adsorption energy allows us to estimate an equilibrium coverage of the order of 0.1monolayers at 10mbar pressure, which thus paves the way for the use of graphene as a catalytically active support under realistic conditions.