Luca Gavioli

Healing of structural defects in the topmost layer of graphite by chemical vapor deposition.

Very recently, Lahiri et al. reported the controlled production of extended line defects in graphene and suggested that such structures might function as metallic wires. [ 16 ] Studies such as these have demonstrated that defect engineering in graphitic systems is a promising approach towards controlling a variety of material properties. Despite this, defects are well-known for their ability to scatter charge carriers and phonons, thereby decreasing the ballistic transport path length and adversely affecting carrier mobility and thermal conductivity. The detrimental effects of defects are particularly pronounced in graphene fi lms. For example, defects were held responsible for a dramatic reduction in charge carrier mobility in graphene fi lms obtained by micromechanical cleavage. [ 17 ] The transport properties of graphene fi lms produced by chemical methods, such as the exfoliation and chemical reduction of graphene oxide platelets, have also been ascribed to defects (introduced by the chemical treatments used). [ 18 ] In this respect, defects are undesirable, and the ability to “heal” them is important for generating carbon nanostructures with high electrical and thermal conductivities and, potentially, enhanced mechanical strength. Improvements in these characteristics are of central importance because the successful realization of graphene-based electronic devices

Directed assembly of Au and Fe nanoparticles on a TiOx/Pt(111) ultrathin template: the role of oxygen affinity

The essential role of O affinity in the directed assembly of size-selected Au and Fe nanoparticles (NPs) on a TiO(x)/Pt(111) ultrathin oxide phase, an effective template for size selected metal NP growth, is revealed through scanning tunneling microscopy and density-functional calculations. A weakly interacting element (Au) diffuses rapidly and gets trapped in the vacancy defects (picoholes) located inside parallel rows (troughs, spaced 1.44 nm apart) peculiar to the film structure, producing size-selected NPs arranged in regular linear arrays aligned along the troughs. In contrast, an element with greater O affinity (Fe) experiences higher diffusion barriers, and the growth is dominated by kinetic effects, with a less effective preferential nucleation and the appearance of irregular NP morphologies.

Molecular gap and energy level diagram for pentacene adsorbed on filled d-band metal surfaces

The authors present a combined photoemission and scanning-tunneling spectroscopy study of the filled electronic states, the molecular energy gap, and the energy level diagram of highly ordered arrays of pentacene deposited on the Cu(119) vicinal surface. The states localized at the interface are clearly singled out, comparing the results at different pentacene thicknesses and with gas-phase photoemission data. The molecular gap of 2.35eV, the hole injection barrier of 1.05eV, and the electron injection barrier of 1.30eV determine the energy level diagram of the states localized at the pentacene molecules.

Au nanoparticles on a templating TiOx/Pt(111) ultrathin polar film: a photoemission and photoelectron diffraction study

We present an in-depth investigation of Au nanoparticles self-assembled on a zigzag-like TiO(x)/Pt(111) ultrathin polar film, whose structure is known in great detail. The peculiar pattern of defects (picoholes) templates a linear array of size-selected (ca. 1 nm) Au nanoparticles without disruption of the titania layer, as observed by scanning tunneling microscopy. Their structure and electronic properties have been investigated by several large-area spectroscopic tools, i.e. high-resolution core and valence level photoemission and angle-scanned and energy-scanned photoelectron diffraction. The comparison between experimental data and density functional theoretical calculations indicates that the Au atoms landing on the oxide film are rather mobile, and that the picoholes can act as effective trapping and nucleation centers for the growth of the Au nanoparticles. All the experimental results are in concord in indicating that the Au NPs are flat islands with a maximum thickness of 2-3 layers exposing the (111) surface.

Highly bactericidal Ag nanoparticle films obtained by cluster beam deposition

UNLABELLED The recent emergence of bacterial pathogens resistant to most or all available antibiotics is among the major global public health problems. As indirect transmission through contaminated surfaces is a main route of dissemination for most of such pathogens, the implementation of effective antimicrobial surfaces has been advocated as a promising approach for their containment, especially in the hospital settings. However, traditional wet synthesis methods of nanoparticle-based antimicrobial materials leave a number of key points open for metal surfaces: such as adhesion to the surface and nanoparticle coalescence. Here we demonstrate an alternative route, i.e. supersonic cluster beam deposition, to obtain antimicrobial Ag nanoparticle films deposited directly on surfaces. The synthesized films are simple to produce with controlled density and thickness, are stable over time, and are shown to be highly bactericidal against major Gram positive and Gram negative bacterial pathogens, including extensively drug-resistant strains. FROM THE CLINICAL EDITOR The use of silver nanoparticle in health care is getting more widespread. The authors here describe the technique of cluster beam deposition for spraying silver on surfaces used in health care sectors. This may open a new avenue for future anti-bacterial coatings.

Dynamics of the Si(100) surface

Abstract The Si(100) surface is constituted by asymmetric dimers and presents complex dynamical behaviour. To understand the influence of dimer motion on the surface electronic properties, we investigate the dynamics of the Si(100) surface experimentally and theoretically in a wide temperature range (150–1200 K). High-resolution electron energy-loss spectroscopy measurements are compared to a microscopic tight-binding calculation of the dielectric function. An instantaneous symmetric-like flat dimer configuration due to fast dimer-flipping is responsible for the electronic transition at 0.8 eV and for the surface metallization observed at 900 K, well below the suggested incomplete melting temperature (1400 K).

Adsorption sites at Cs nanowires grown on the InAs(110) surface

We present a high-resolution ultraviolet photoelectron spectroscopy study of the room temperature Cs chain formation on InAs(1 1 0), analysing the valence band spectra and core levels in the whole coverage range from the self-assembling of the Cs chains to the cluster uptake at saturation coverage. The valence band data shows an insulating behaviour up to saturation coverage. The adsorption sites have been monitored by means of Cs-4d, In-4d and As-3d core levels. The Cs-4d core-level data shows two distinct components, consistent with the presence of two unequivalent Cs adsorption sites in the Cs nanowire. The In-4d and As-3d levels show Cs-induced extra components due to electronic level re-hybridization to the substrate atoms, and predominant charge transfer from Cs adatoms to In, in agreement with recent theoretical calculations.

Surface electronic structure at Si(100)-(2x1)

Abstract The surface electronic structure of the clean Si(100)-(2x1) surface at room temperature is studied by high-resolution electron-energy-loss spectroscopy. Main absorption edge is detected at ∼ 0.4 eV, which corresponds to the energy gap of the system, further structures are singled out at 0.8 and 1.25 eV and ascribed to interband electronic transitions between dimer-related levels. The paramount importance of cleanness is addressed, showing and quantifying the effect of the residual gas atmosphere (that can be present in ultrahigh vacuum) on the electronic structure.

Direct synthesis of antimicrobial coatings based on tailored bi-elemental nanoparticles

Ultrathin coatings based on bi-elemental nanoparticles (NPs) are very promising to limit the surface-related spread of bacterial pathogens, particularly in nosocomial environments. However, tailoring the synthesis, composition, adhesion to substrate, and antimicrobial spectrum of the coating is an open challenge. Herein, we report on a radically new nanostructured coating, obtained by a one-step gas-phase deposition technique, and composed of bi-elemental Janus type Ag/Ti NPs. The NPs are characterized by a cluster-in-cluster mixing phase with metallic Ag nano-crystals embedded in amorphous TiO2 and present a promising antimicrobial activity including also multidrug resistant strains. We demonstrate the flexibility of the method to tune the embedded Ag nano-crystals dimension, the total relative composition of the coating, and the substrate type, opening the possibility of tailoring the dimension, composition, antimicrobial spectrum, and other physical/chemical properties of such multi-elemental systems. ...

Stability and chemisorption properties of ultrathin TiOx/Pt(111) films and Au/TiOx/Pt(111) model catalysts in reactive atmospheres

The stability of three ultrathin TiO(x)/Pt(111) films with different stoichiometry and defectivity and the corresponding Au/TiO(x)/Pt(111) model catalysts in CO or a CO-O(2) (1 : 1) gas mixture up to a pressure of 100 mbar has been investigated. According to previous studies, the ultrathin films proved to be effective substrates to deposit in UHV Au nanoparticles with specific morphologies and lateral sizes ranging between 1 and 6 nm. The films have been characterized before and after the exposure using X-ray photoemission spectroscopy (XPS), low-energy electron diffraction (LEED) and scanning tunnelling microscopy (STM). Additional in situ measurements of the CO chemisorption behavior were performed using polarization-modulation infrared reflection-absorption spectroscopy (PM-IRAS). A fully oxidized film is stable in CO and CO-O(2) (1 : 1) ambient, while the reduced films undergo an oxidative dewetting process at RT in the latter atmosphere. This process ultimately produces a nano-composite surface, where very tiny (from 0.5 to 3 nm lateral sizes) titania nanograins are mixed with open, uncovered areas of the Pt substrate. IRAS measurements on the corresponding Au/TiO(x)/Pt(111) model catalysts demonstrated that the CO chemisorption strongly depends on the Au nanoparticle size and morphology, while the actual Ti oxidation state of the oxide support does not seem to play a significant role.