1,721,082 research outputs found
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
Growth of curved graphene sheets on graphite by chemical vapor deposition
No full textWe report a synthesis route of a carbon-based structure, curved graphene sheet (CGS). The CGS grows by catalytic chemical vapor deposition autoselectively at the stacked bilayer edges of graphite support, providing an atomically smooth connection of the edges. We propose a growth mechanism based on Fe nanoparticle diffusion along the step edges, acting as a nanozipper. The work addresses with a simple experimental method, the edge engineering in graphene bilayer systems. The results may have a significant impact on the fabrication of new carbon nanostructures and their integration into nanoelectronics
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
The Role of Substrate on Thermal Evolution of Ag/TiO2 Nanogranular Thin Films
Full text linkIn multicomponent thin films, properties and functionalities related to post-deposition annealing treatments, such as thermal stability, optical absorption and surface morphology are typically ra-tionalized, neglecting the role of the substrate. Here, we show the role of the substrate in deter-mining the temperature dependent behaviour of a paradigmatic two-component nanogranular thin film (Ag/TiO2) deposited by gas phase supersonic cluster beam deposition (SCBD) on silica and sapphire. Up to 600 °C, no TiO2 grain growth nor crystallization is observed, likely inhibited by the Zener pinning pressure exerted by the Ag nanoparticles on the TiO2 grain boundaries. Above 600 °C, grain coalescence, formation of anatase and rutile phases and drastic modification of the optical absorption are observed. However, the two substrates steer the evolution of the film morphology and optical properties in two different directions. On silica, Ag is still present as NPs distributed into the TiO2 matrix, while on sapphire, hundreds of nm wide Ag aggregates appear on the film surface. Moreover, the silica-deposited film shows a broad absorption band in the visi-ble range while the sapphire-deposited film becomes almost transparent for wavelengths above 380 nm. We discuss this result in terms of substrate differences in thermal conductivity, thermal expansion coefficient and Ag diffusivity. The study of the substrate role during annealing is possi-ble since SCBD allows the synthesis of the same film independently of the substrate, and suggests new perspectives on the thermodynamics and physical exchanges between thin films and their substrates during heat treatments
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
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
Thermal evolution of ZnS nanostructures: effect of oxidation phenomena on structural features and photocatalytical performances
No full textZnS nanosystems are being extensively studied for their possible use in a wide range of technological applications. Recently, the gradual oxidation of ZnS to ZnO was exploited to tune their structural, electronic, and functional properties. However, the inherent complexity and size dependence of the ZnS oxidation phenomena resulted in a very fragmented description of the process. In this work, different-sized nanosystems were obtained through two different low temperature wet chemistry routes, namely, hydrothermal and inverse miniemulsion approaches. These protocols were used to obtain ZnS samples consisting of 21 and 7 nm crystallites, respectively, to be used as reference material. The obtained samples were then calcinated at different temperatures, ranging from 400 to 800 °C toward the complete oxidation of ZnO, passing through the coexistence of the two phases (ZnS/ZnO). A thorough comparison of the effects of thermal handling on ZnS structural, chemical, and functional evolution was carried out by TEM, XRD, XAS, XPS, Raman, FT-IR, and UV-Vis. Finally, the photocatalytic activity in the H2 evolution reaction was also compared for selected ZnS and ZnS/ZnO samples. A correlation between size and the oxidation process was observed, as the smaller nanosystems showed the formation of ZnO at lower temperature, or in a larger amount in the case of the ZnS and ZnO co-presence. A difference in the underlying mechanism of the reaction was also evidenced. Despite the ZnS/ZnO mixed samples being characterized by an increased light absorption in the visible range, their photocatalytic activity was found to be much lower.</p
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
Poly vinyl alcohol re-usable masters for microneedle replication
No full textWe present the first results of microstructure replica with re-usable masters in poly vinyl alcohol (PVA). Microneedles of heights ranging from 500 to 1100 pm were fabricated through double-exposure deep Xray lithography (DXRL) process and successfully replicated. A single PVA master was used as a template to successfully replicate up to 10 PMMA microneedle arrays, suggesting that this method might be a possible alternative to PDMS processes. A preliminary characterization of the relationship between the surface roughness of the substrates and the force required for demoulding was also performed. (C) 2009 Elsevier B.V. All rights reserved
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