Graphene-Based Material Supports for Ni- and Ru- Catalysts in CO Hydrogenation: Ruling out Performances and Impurity Role.

Laboratory-prepared Gnp using molten salt, commercial Gnp and reduced graphene oxide (rGO) have been characterized and utilized as support for CO hydrogenation catalysts. Ni- and Ru- catalysts supported over Gnp, commercial Gnp and rGO have been deeply characterized at different stages using Raman, IR, XRD, FE-SEM-EDXS, SEM-EDXS, XPS, and TEM, also addressing carbon loss before reaction and evolved species, thus allowing a better comprehension of the produced materials. Ni and Ru/rGO were inactive while Gnp-supported ones were active.

Intercalation and reactions of CO under single layer graphene/Ni(111): the role of vacancies.

We use synchrotron radiation-induced core level photoemission spectroscopy to investigate the influence of vacancies, produced by ion bombardment, on monolayer graphene/Ni(111) exposed to CO at pressures ranging from ultra-high vacuum (10 mbar) up to near ambient (5.6 mbar) conditions. CO intercalates at a rate which is comparable to the one observed in absence of defects and reacts the Boudouard reaction producing additional carbon atoms and CO.

Adsorption of glutamic acid on clean and hydroxylated rutile TiO(110): an XPS and NEXAFS investigation.

Due to its biocompatibility, TiOis a relevant material for the study of bio-interfaces. Its electronic and chemical properties are influenced by defects, which mainly consist of oxygen vacancies or adsorbed OH groups and which affect, consequently, also the interaction with biological molecules. Here we report on an x-ray photoemission spectroscopy and near edge adsorption fine structure study of glutamic acid (Glu) adsorption on the rutile TiO(110) surface, either clean or partially hydroxylated.

Prominence of Terahertz Acoustic Surface Plasmon Excitation in Gas-Surface Interaction with Metals.

The current understanding of the dynamics of gas-surface interactions is that all of the energy lost in the collision is transferred to vibrations of the target. Electronic excitations were shown to play a marginal role except for cases in which the impinging particles have energies of several electronvolts. Here we show that this picture does not hold for metal surfaces supporting acoustic surface plasmons.

Morphological characterization and electronic properties of pristine and oxygen-exposed graphene nanoribbons on Ag(110).

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.

Synthesis of corrugated C-based nanostructures by Br-corannulene oligomerization.

The structure and electronic properties of carbon-based nanostructures obtained by metal surface assisted synthesis is highly dependent on the nature of the precursor molecule. Here, we report on a combined scanning tunneling microscopy, soft X-ray spectroscopy and density functional theory investigation on the surface assisted polymerization of Br-corannulene at Ag(110) and on the possibility of building a mesh of π-conjugated polymers starting from buckyball shaped molecules. Indeed, the corannulene units form one-molecule-wide ribbons in which the natural concavity of the precursor molecule is maintained.

Adatom Extraction from Pristine Metal Terraces by Dissociative Oxygen Adsorption: Combined STM and Density Functional Theory Investigation of O/Ag(110).

The reconstruction and modification of metal surfaces upon O_{2} adsorption plays an important role in oxidation processes and in gauging their catalytic activity. Here, we show by employing scanning tunneling microscopy and the ab initio density functional theory that Ag atoms are extracted from pristine (110) terraces upon O_{2} dissociation, resulting in vacancies and in Ag-O complexes. The substrate roughening generates undercoordinated atoms and opens pathways to the Ag subsurface layer.

Influence of growing conditions on the reactivity of Ni supported graphene towards CO.

Free standing graphene is chemically inert but, as recently demonstrated, CO chemisorption occurs at low crystal 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.

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.

Spontaneous Oxidation of Ni Nanoclusters on MgO Monolayers Induced by Segregation of Interfacial Oxygen.

We report the study of Ni nanoclusters deposited on MgO/Ag(100) ultrathin films (one monolayer) at T = 200 K. We show by STM analysis and DFT calculations that in the limit of low Ni coverage the formation of nanoclusters of four to six atoms occurs and that these aggregates are flat rather than 3D, as expected for Ni tetramers, pentamers, or hexamers. Both the shape of the clusters and the interatomic distance between neighboring Ni atoms are indicative that the nanoparticles do not consist of pure metal atoms but that a NiyOx structure has formed thanks to the availability of atomic oxygen accumulated at the MgO/Ag interface, with Ni clusters acting as oxygen pumps.

Anisotropic dispersion and partial localization of acoustic surface plasmons on an atomically stepped surface: Au(788).

Understanding acoustic surface plasmons (ASPs) in the presence of nanosized gratings is necessary for the development of future devices that couple light with ASPs. We show here by experiment and theory that two ASPs exist on Au(788), a vicinal surface with an ordered array of monoatomic steps. The ASPs propagate across the steps as long as their wavelength exceeds the terrace width, thereafter becoming localized.

Morphology of monolayer MgO films on Ag(100): switching from corrugated islands to extended flat terraces.

The ability to engineer nearly perfect ultrathin oxide layers, up to the limit of monolayer thickness, is a key issue for nanotechnological applications. Here we face the difficult and important case of ultrathin MgO films on Ag(100), for which no extended and well-ordered layers could thus far be produced in the monolayer limit. We demonstrate that their final morphology depends not only on the usual growth parameters (crystal temperature, metal flux, and oxygen partial pressure), but also on aftergrowth treatments controlling so far neglected thermodynamics constraints.

Accretion disc origin of the Earth's water.

Earth's water is conventionally believed to be delivered by comets or wet asteroids after the Earth formed. However, their elemental and isotopic properties are inconsistent with those of the Earth. It was thus proposed that water was introduced by adsorption onto grains in the accretion disc prior to planetary growth, with bonding energies so high as to be stable under high-temperature conditions.

Unraveling the self-assembly of the (S)-glutamic acid "flower" structure on Ag(100).

(S)-Glutamic acid adsorbed on Ag(100) organizes in different self-assembled structures depending on surface temperature [Smerieri, M.; Vattuone, L.; Kravchuk, T.

Spectroscopic evidence for neutral and anionic adsorption of (S)-glutamic acid on Ag(111).

We report here on a combined photoemission and vibrational spectroscopy investigation of (S)-glutamic acid adsorption on Ag(111). We show that, in the temperature range 250 K ≤ T ≤ 400 K, non-zwitterionic adsorption takes place and the anionic form prevails at nonvanishing coverage. Significant conformational changes of the self-assembled layer must occur above 300 K, corresponding to a substantial reduction of the sticking probability and a modification of the vibrational spectrum.

Correlated motion of electrons on the Au(111) surface: anomalous acoustic surface-plasmon dispersion and single-particle excitations.

The linear dispersion of the low-dimensional acoustic surface plasmon (ASP) opens perspectives in energy conversion, transport, and confinement far below optical frequencies. Although the ASP exists in a wide class of materials, ranging from metal surfaces and ultrathin films to graphene and topological insulators, its properties are still largely unexplored. Taking Au(111) as a model system, our combined experimental and theoretical study revealed an intriguing interplay between collective and single particle excitations, causing the ASP associated with the Shockley surface state to be embedded within the intraband transitions without losing its sharp character and linear dispersion.

Coupling scanning tunneling microscope and supersonic molecular beams: a unique tool for in situ investigation of the morphology of activated systems.

We report here on a new experimental apparatus combining a commercial low temperature scanning tunneling microscope with a supersonic molecular beam. This setup provides a unique tool for the in situ investigation of the topography of activated adsorption systems and opens thus new interesting perspectives. It has been tested towards the formation of the O/Ag(110) added rows reconstruction and of their hydroxylation, comparing data recorded upon O(2) exposure at thermal and hyperthermal energies.

The effect of step geometry in copper oxidation by hyperthermal O2 molecular beam: Cu(511) vs Cu(410).

Steps are known to be often the active sites for the dissociation of O(2) molecules and the nucleation sites of oxide films since they provide paths for subsurface migration and oxygen incorporation. In order to unravel the effect of their morphology on the oxidation of Cu surfaces, we present here a detailed investigation of the O(2) interaction with Cu(511) and compare it with previous results for Cu(410), a surface exhibiting terraces of similar size and geometry but different step morphology. As for Cu(410) we find, by x-ray photoemission spectroscopy performed with synchrotron radiation, that Cu(2)O formation gradually starts above half a monolayer oxygen coverage and that the ignition of oxidation can be lowered to room temperature by dosing O(2) via a supersonic molecular beam at hyperthermal energy.

Poisoning and non-poisoning oxygen on Cu(410).

We have investigated ethene and oxygen co-adsorption on Cu(410) by high resolution electron energy loss spectroscopy. We find that these two species compete for the adsorption sites and that pre-exposure to oxygen affects ethene adsorption more or less strongly depending on oxygen coverage and the kind of occupied sites. The c(2 × 2) O overlayer is inert with respect to ethene adsorption, while when some oxygen is removed by thermally induced subsurface incorporation, ethene chemisorption is restored.

Stoichiometry-dependent chemical activity of supported MgO(100) films.

Here, we show that the stoichiometry and, consequently, the chemical activity toward hydroxylation of MgO(100) films grown by reactive deposition on Ag(100) strongly depend on the O(2) partial pressure during film growth. Oxygen-deficient films undergo dramatic relative oxygen uptake either by exposure to a partial pressure of water vapor or by aging in vacuum for a sufficiently long time. Conversely, on stoichiometric monolayer MgO islands, photoemission analysis of the O 1s level and scanning tunneling microscopy images are consistent with the prediction that dissociative adsorption of water occurs only at the borders of the islands.

O(2) dissociation before the onset of added row nucleation on Ag(110): an atomistic scanning tunnelling microscopy view.

We present here a scanning tunnelling microscopy (STM) study on O(2) adsorption at Ag(110) at T = 175 K, i.e. in the temperature range between the onset of O(2) dissociation and the formation of the added row reconstruction.

(S)-glutamic acid on Ag(100): self-assembly in the nonzwitterionic form.

The fundamental understanding of adsorption and self-organization of biological molecules at surfaces is of greatest importance for a huge variety of possible applications, ranging from molecular electronics to the study of biocompatible materials, hygiene, and biofouling. In spite of that, the characterization of the interactions of organic molecules of biological interest with surfaces is far from being complete. In the present paper we report on a combined microscopic (scanning tunneling microscopy (STM)) and spectroscopic (X-ray photoemission spectroscopy and high-resolution electron energy loss spectroscopy) study of glutamic acid (Glu) adsorption and self-assembly on Ag(100) at different temperature.

Self-assembly of (S)-glutamic acid on Ag(100): a combined LT-STM and ab initio investigation.

Self-assembly of organic molecules at metal surfaces is of greatest importance in nanoscience; in fact, it opens new perspectives in the field of molecular electronics and in the study of biocompatible materials. Combining an experimental low-temperature scanning tunneling microscopy investigation with ab initio calculations, we succeeded to describe in detail (S)-glutamic acid adsorption on Ag(100) at T = 350 K. We find that (S)-glutamic acid organizes in a squared structure and, at variance with the majority of cases reported in literature, it adsorbs in the neutral form, 4.

Ethene stabilization on Cu(111) by surface roughness.

The molecular vibrations of ethene adsorbed on roughened Cu(111) surfaces have been investigated with high resolution electron energy loss spectroscopy and density-functional-theory calculations. The roughness was introduced by sputtering or evaporation of copper, respectively, on the cooled surface. We found stabilization of the ethene layer compared to ethene adsorbed on pristine Cu(111).

Selective production of reactive and nonreactive oxygen atoms on Pd(001) by rotationally aligned oxygen molecules.

Sticking together: The occupation of different sites by oxygen atoms that are produced by the dissociation of O(2) on Pd(100) is determined by the initial rotational alignment of the parent molecules. The atom locations are characterized by different chemical reactivities in the reaction with CO to form CO(2) (see picture), which are followed by synchrotron radiation (SR) experiments with a supersonic molecular beam (SMB).