Characterization of high-quality MgB2(0001) epitaxial films on Mg(0001)

High-grade MgB2(0001) films were grown on Mg(0001) by means of ultra-high-vacuum molecular beam epitaxy. Low energy electron diffraction and x-ray diffraction data indicate that thick films are formed by epitaxially oriented grains with MgB2 bulk structure. The quality of the films allowed angle-resolved photoemission and polarization dependent x-ray absorption measurements. For the first time, we report the band mapping along the Gamma-A direction and the estimation of the electron-phonon coupling constant l ~ 0.55 for the surface state electrons.Comment: 15 text pages, 6 figures Submitted for publicatio

Carbon-based and other nanostructures obtained via cluster-assembling: a view combining electron spectroscopies and nanospectroscopies

This work will provide an overview of recent experiments devoted to study the nature and properties of materials obtained in situ via cluster-assembling, by using supersonic cluster beam deposition. This technique has proved to be a powerful tool for assembling nanostructured materials with tailored physical properties, in particular for: 1) carbon-based clusters deposited in situ on appropriate substrates in Ultra High Vacuum compatible conditions; 2) a micro-structured pattern based on pristine carbon-based dots and then promoted to the formation of SiC via in situ thermal annealing; 3) thermo-chemically doped nanostructured TiO2, revealing the possibility to control the band gap of this material. The electronic structure of the systems has been studied combining a wide variety of experimental methods, including valence-band and core-level photoemission, Electron Energy Loss Spectroscopy, Scanning Auger Spectroscopy, Atomic Force Microscop

The effects of cold plasma treatments on LDPE wettability and curing kinetic of a polyurethane adhesive

A cold plasma feed with either oxygen or nitrogen was used to modify thin Low Density Polyethylene films. The treatment improved both the surface wettability and the curing kinetic of a polyurethane based adhesive spread on the surface. The chemical functionalities responsible of the observed behaviours were investigated and monitored over time by high resolution x-ray photoelectron spectroscopy. Atomic force microscopy were used to compare the effects of the two feeding gases on the surface morphology of films exposed (to the plasma) for equal times. The effect on the treated films of the atmosphere exposure and of the aging time were also considered

Atomic topography and self-assembly of one-dimensional potassium chains on the InAs(110) surface

One-dimensional (1D) potassium chains, obtained on the InAs(110) surface, are studied by scanning tunneling microscopy (STM). The (2xn) symmetry in the low energy electron diffraction pattern, becoming a c(2x6) structure at the completion of the first layer, is explained by the various spacing D between alkali chains in the [001] direction. The distribution of D as a function of the chain density suggests the presence of a repulsive interaction among the chains, which drives the self-assembling of the 1D structures. The origin of the interaction is discussed in comparison with the model proposed for the Cs/InAs(110) interface, showing the general validity of the model for this class of chain structures. The atomic structure of an isolated chain is investigated by high-resolution STM images, revealing the asymmetry in the charge density induced by K adatoms and a modification of the As-related charge density of the topmost substrate layer

Orientation of C60 molecules in the (3r3 x3r3 )R30\ub0 and (r13 xr13 )R14\ub0 phases of C60/Ge(111) single-layer

The structure of the (33 x 33 )R30\ub0 and (13 x 13 )R14\ub0 phases of C60/Ge(111) single-layer has been studied by Scanning Tunneling Microscopy (STM). Sub-molecular resolution allows to distinguish among differently orientated molecules. In the (33 x 33 )R30\ub0 phase the molecules result to be arranged in rhomboidal groups of 4 molecules, named tetramers. The (2x2) periodicity in the domains of homogeneously oriented tetramers is due to the alternating orientation of the molecules within the tetramer, accounting for the observed (33 x 33 )R30\ub0 Low Energy Electron Diffraction (LEED) pattern. The symmetry of the molecular lattice suggests that the molecules interact only with the first layer of substrate atoms. The orientation of each molecule is mainly determined by the configuration of the substrate atoms in the adsorption site, even though a contribution from the intermolecular interaction is likely present. In the (13 x 13 )R14\ub0 phase the observed sub-molecular features indicate that all the molecules have the same adsorption configuration, with a hexagon facing the substrate. The threefold symmetry of the molecular lattice suggests that the C60 - Ge interaction involves also the atoms of the second layer of the substrate

Morphology of pentacene films deposited on Cu(119) vicinal surface

We investigate the morphology of a pentacene (C22H14) film adsorbed on the Cu(119) vicinal surface by scanning tunnelling microscopy (STM). Thermal treatment of a thick film of molecules generates a long-range ordered structure. Series of molecular rows are alternated with areas where the molecules assume two equivalent orientations. STM data analysis suggests that the ordered structure can be described by a rippled morphology. The behaviour of the film at different annealing temperatures suggests a possible explanation of the film structure as due to an adsorbate-induced modification of the substrat

Structural and electronic properties of one dimensional inorganic and organic structures on surfaces

We investigate one-dimensional (1-D) nanostructures formed by deposition of potassium on InAs(110) surface and of pentacene on the vicinal Cu(119) surface. Scanning tunneling microscopy (STM) reveals the morphology and the long-range ordering of the nanostructures. Voltage-dependent STM images are used to investigate the electronic structure in the real space. The potassium chains give rise to a delocalized continuum of charge density, suggesting their 1-D electronic nature. 1-D pentacene rows, growing beyond the completion of the first layer, do not show a similar behavior. The formation of the 1-D electronic structures is discussed in term of the substrate-adsorbate interaction. (C) 2004 Elsevier B.V. All rights reserved

Long range ordered pentacene chains assembled on Cu(119) vicinal surface

Pentacene (C22H14), deposited on the Cu(119) vicinal surface, forms ordered molecular chains, with the long molecular axis aligned along the step direction. Phase correlation between neighboring chains gives rise to large domains, observed in the low-energy electron-diffraction (LEED) pattern. Scanning tunneling microscopy (STM) images show that the molecules are laying flat on the copper terraces with the molecular axis aligned along the steps, hence, facing the short side of one another. High-resolution STM data suggest that the molecules adsorb, locating the central benzene ring on the hollow site of the Cu(001) surface

Growth morphology and electronic properties of Sn deposited on different InSb surfaces

We present a study of the growth morphology and electronic properties of Sn deposition on ZnSb(111) A-type and ZnSb(110) surfaces, by means of photoemission spectroscopy. Tin grows in a layer-by-layer fashion on the (111) substrate, with a (1x1) symmetry characteristic of pseudomorphic bulk-like Sn(111). A first-ordered monolayer followed by Sn island formation is observed on the (110) surface, and we estimate a fractional area of Sn islands increasing from 60% at two monolayers nominal coverage to about 80% at higher coverages. Both interfaces show the formation of non-metallic Sn adlayer at room temperature, while annealing of a multilayer Sn/InSb(110) produces a light metallic-like response, probably due to Sn clustering. (C) 1999 Elsevier Science B.V. All rights reserved