CO chemisorption at vacancies of supported graphene films: a candidate for a sensor?

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

Influence of Defects and Heteroatoms on the Chemical Properties of Supported Graphene Layers

A large and growing number of theoretical papers report the possible role of defects and heteroatoms on the chemical properties of single-layer graphene. Indeed, they are expected to modify the electronic structure of the graphene film, allow for chemisorption of different species, and enable more effective functionalisation. Therefore, from theoretical studies, we get the suggestion that single and double vacancies, Stone–Wales defects and heteroatoms are suitable candidates to turn nearly chemically inert graphene into an active player in chemistry, catalysis, and sensoristics. Despite these encouraging premises, experimental proofs of an enhanced reactivity of defected/doped graphene are limited because experimental studies addressing adsorption on well-defined defects and heteroatoms in graphene layers are much less abundant than theoretical ones. In this paper, we review the state of the art of experimental findings on adsorption on graphene defects and heteroatoms, covering different topics such as the role of vacancies on adsorption of oxygen and carbon monoxide, the effect of the presence of N heteroatoms on adsorption and intercalation underneath graphene monolayers, and the role of defects in covalent functionalisation and defect-induced gas adsorption on graphene transistors

Ethylene adsorption on clean and oxygen covered flat and stepped Ag(001)

In the present paper we review our findings on ethylene adsorption on clean and oxygen covered Ag(001) surfaces investigated by dosing the gas with a Supersonic Molecular Beam and analysing the adsorption state either by High Resolution Electron Energy Loss Spectroscopy or by High Resolution X Rays Photoemission Spectroscopy. The final adsorption state depends on the translational and on the internal energy of the gas-phase molecules and on the presence of defects. At low translational energy ethylene either physisorbs or very weakly chemisorbs at flat terrace sites. The physisorption probability is thereby hindered by rotational excitation. A more strongly bound, pi bonded, state forms at higher translational energy, the activation barrier being related to the energy needed to form the relevant defect at which chemisorption takes place. A further even more strongly bound state forms only when dosing vibrationally excited molecules from the gas phase

Phonons in Thin Oxide Films

Thin oxide films have physical and chemical properties which may be significantly different from those of the corresponding bulk materials. For their complete characterization the information on the lattice dynamics which can be retrieved by vibrational spectroscopy is mandatory. Here we show that the number of observed phonon modes and their frequencies can indeed provide relevant information about stoichiometry, structure and thickness of the film

Surface plasmon dispersion on sputtered and nanostructured Ag(001)

The surface plasmon dispersion of ion bombarded Ag(001) is investigated by angle resolved high resolution electron energy loss spectroscopy. We find it to be parabolic and dominated by the quadratic term, contrary to the case of flat Ag(001) where the linear term is dominant. The case is reminiscent of surface plasmon dispersion on the oxygen covered, missing row reconstructed Ag(001) surface, for which case the change of the dispersion from nearly linear to quadratic was attributed to the removal of a surface plasmon decay channel associated to the surface interband transition at (X) over bar. We show moreover, that for the sputtered surface, slope and curvature of the dispersion depend on surface morphology at the nanoscale. When sputtering is performed at low crystal temperature and no ordered superstructure forms, the quadratic term coincides with the isotropic value dictated by bulk properties, reported for flat Ag(110) and Ag(111) and for reconstructed Ag(001). When on the contrary sputtering is performed at room temperature and the checkerboard superstructure develops, the quadratic term becomes twice as large

Interaction of ethylene and oxygen with stepped Ag surfaces

The active role of defects in some catalytic reactions was predicted in the very early days of surface science. Most of the studies on gas adsorption at solid surfaces dealt, however, so far with nearly perfect low Miller index surfaces, which are rather unlike the active powders employed as catalysts in industrial reactors. The structure gap between the systems studied by surface scientists and the surface structure of real catalyst powders was therefore often indicated as the reason for the failure in reproducing some chemical reactions, which occur readily in industrial reactors, also in controlled conditions. Overcoming this limit without losing control over the experiment at the nanoscopic level is therefore an issue of pivotal importance, which could be addressed only now that the understanding of adsorption processes at flat surfaces is reasonably established. In this paper we shall review our most recent results on O-2 and C2H4 interaction with Ag(410) and Ag(210), which are vicinal surfaces of Ag(100) characterised by open (110)-like steps and narrow (100) terraces. The gases were dosed with a supersonic molecular beam, allowing to perform experiments at selected and well defined angles of incidence of the gas-phase particles. For both gases we find that the open steps affect gas-surface interaction considerably, changing the energy barriers to adsorption as well as the final chemisorption state