1,720,973 research outputs found
One- and Two-Dimensional Systems: Scanning Tunneling Microscopy and Spectroscopy of Organic and Inorganic structures
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Orientation of C60 molecules in the (3r3 x3r3 )R30° and (r13 xr13 )R14° phases of C60/Ge(111) single-layer
No full textThe structure of the (33 x 33 )R30° and (13 x 13 )R14° 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° 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° 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° 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
Carbon-based and other nanostructures obtained via cluster-assembling: a view combining electron spectroscopies and nanospectroscopies
No full textThis 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
Scanning Tunneling Microscopy Studies of Nanotube-like Structures on the HOPG Surface
No full textWe have studied the scanning tunneling microscopy tip interaction with the naturally formed nanotube-like (NTL) structures on highly oriented pyrolytic graphite (HOPG) surface. Shape variations of the NT-like structures, caused by the modulation of scanning parameters, were observed and analyzed
Ag island nucleation on Ge(111)-c(2 x 8)
No full textWe present a study of the thermal evolution of the Ag/Ge(1 1 1)
interface by combining Scanning Electron Microscopy (SEM), Low Energy
Electron Diffraction (LEED), Spatially Resolved Auger Electron
Spectroscopy (SR-AES), and Atomic Force Microscopy (AFM). We followed
the morphological and structural changes of a thick Ag film grown onto
Ge(1 1 1)-c(2 x 8) at 300 K after annealing at selected temperatures
between 370 and 800 K. The morphology of the system evolves from a flat
film up to the nucleation of islands through the formation of dendritic
structures. The diffraction pattern shows different intermediate surface
reconstructions. We report evidences of Ge intermixing into the Ag
growing layer and segregation on top of it. (C) 2003 Elsevier Science
B.V. All rights reserved
Atomic topography and self-assembly of one-dimensional potassium chains on the InAs(110) surface
No full textOne-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
Morphology of pentacene films deposited on Cu(119) vicinal surface
No full textWe 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
Long range ordered pentacene chains assembled on Cu(119) vicinal surface
No full textPentacene (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
Effect of substrate surface defects on the Fe film morphology deposited on graphite
No full textWe have studied Fe films on Ar+ ion sputtered highly oriented pyrolitic graphite (HOPG) using scanning tunnelling microscopy
(STM). The adsorbed Fe atoms form nanoparticles uniformly distributed over the substrate surface with narrow size distribution. Comparing
these data with Fe deposited on non-sputtered HOPG indicates the role of substrate defects, acting as nucleation sites, on the
overall film structure. However, the shape and size of individual defects do not seem to influence the shape of the nanoparticles. The correlation between the Fe film morphology and the sputtered substrate morphology is discussed taking into account the different capturing properties of sputtering-induced defects
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