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STM study of the nanostructures prepared bydeposition of NiO on Ag(001)
No full textSubmonolayers of nickel oxide were grown on the Ag(001) surface by evaporation of Ni in the presence of O2 at a pressure of 1 × 10−6 mbar. In the early stages of deposition, two-dimensional oxide islands with a (2 × 1) periodicity grow on Ag(001). After annealing at about 500 K, the (2 × 1) single atomic layer transforms into NiO(001) double layer islands. The 1:1 stoichiometry of the film is not influenced by whether the annealing is carried out in vacuum or in the presence of oxygen. However, the oxide islands exhibit different morphologies depending on the O2 pressure during the annealing process
Epitaxial growth of TiO2 films with the rutile(110) structure on Ag(100)
No full textUltrathin films of TiO2 were grown on Ag(100) by evaporation of titanium in the presence of O2 at a pressure in the 10-4 Pa range and annealing at 770 K. The composition of the deposited films was monitored by XPS and LEIS. The morphology at the nanometric scale of the TiO2 films and their crystallographic structure were investigated by means of STM, LEED and XPD. Above the monolayer coverage (at which the oxide film has a lepidocrocite-like structure), STM images show the formation of multilayer islands with a distribution of heights. XPD results indicate that these oxide islands have the rutile (110) structure and are epitaxially oriented with the sides of the oxide unit cell parallel to those of the substrate unit cell. The results of the DFT calculations justify the 3D growth of rutile (110) on Ag(100). The
calculated strain energy required to match the metal substrate can explain the incommensurate growth of the overlayer in the direction of the long side of the oxide unit cell. The results of
the calculations indicate that a commensurate growth of rutile (110) may be possible along the short side of the oxide unit cell, taking into account the relatively small strain energy to fit the
lattice parameter of the substrate. The DFT calculations predict a considerable increase of the work function upon deposition of titania films on Ag(100), which can be attributed to a charge
transfer from the metal to the 3d Ti empty states
Ultrathin nickel oxide films grown on Ag(0 0 1): a studyby XPS,LEIS and LEED intensity analysis
No full textThe structure of a nickel oxide film 2 ML thick has been investigated by LEED intensity analysis. The NiO film was prepared by evaporating Ni in presence of O2 at a pressure in the 10-6 mbar range. The growth of the oxide film was followed by XPS, LEIS and LEED. In the early stages of deposition, the film shows a (2 × 1) superstructure in LEED. After deposition of 2 ML of NiO, a sharp (1 × 1) LEED pattern is observed. The intensity versus electron energy curves of the LEED spots were measured for this NiO(1 × 1) film and analysed by means of the tensor LEED method. A good level of agreement of the experimental LEED intensities with those calculated for a pseudomorphic NiO(0 0 1) film was obtained. We found that oxygen atoms at the oxide-substrate interface are on-top silver atoms. The interlayer distance in the oxide does not differ significantly from that in bulk NiO(001), within the accuracy of the analysis. An outward displacement (0.05 ± 0.05 Å) of oxygen atoms with respect to nickel atoms was found at the oxide film surface. The interlayer distance at the silver-nickel oxide interface is 2.43 ± 0.05 Å. © 2003 Elsevier Science B.V. All rights reserved
Early Stages of NiO Growth on Ag(001): A Study LEIS, XPS and LEED
No full textUltrathin nickel oxide films were grown on the Ag(001) surface by evaporation of Ni in an O-2 atmosphere. The growth mechanism, composition, and structure of the NiO layers formed in the early stages of deposition have been investigated by LEIS, XPS, XPD, and LEED. We found that at O-2 pressures in the 10(-7)-10(-1) mbar range and sample temperatures between room temperature and 373 K, a nickel oxide layer forms showing a (2 x 1) LEED pattern. This is a phase of monatomic thickness which gradually covers the substrate surface upon increasing the surface coverage. LEIS and XPS data show that before the (2 x 1) layer is completed NiO(001) islands start to nucleate. The substrate surface is completely covered by NiO(001) for coverages higher than 2 ML. When NiO is deposited with the sample held at 453 K, we found that in the early stages of deposition metallic Ni is present in the subsurface region of the substrate. Upon further NiO deposition the oxide becomes the prevalent species on the surface. Under these conditions, the (2 x 1) phase is not observed. We found that the (2 x 1) phase is not stable upon annealing at 473-600 K and transforms into NiO(001). LEIS and XPD results indicate the formation of NiO islands 2 ML thick upon annealing. The structure of the (2 x 1) phase has been investigated by LEED intensity analysis (tensor LEED method). The best agreement with the experimental data is obtained for a structural model similar to the (111) surface of NiO. The effects of surface temperature and O-2 pressure on nickel oxide growth are discussed in terms of the low sticking probability of O-2 on Ag(001) and of the interaction between nickel and silver
Composition and structure of ultrathin vanadium oxidelayers deposited on SnO2(110)
No full textUltrathin layers of vanadium oxides on SnO2(1 1 0) were prepared by evaporation of metallic vanadium in oxygen atmosphere (partial pressure of O2: 1 × 10-5 Pa) at room temperature (RT). Vanadium oxide layers were deposited on the (4 × 1) reconstructed surface of SnO2(1 1 0). The substrate surface was prepared by cycles of sputtering and annealing in vacuum. X-ray photoelectron spectroscopy (XPS) and low-energy ion scattering (LEIS) results show that the growth mechanism of the oxide layers involves the migration of tin atoms from the substrate onto the surface of the film already at RT. Although no LEED pattern is observed, the X-ray photoelectron diffraction (XPD) measurements reveal that the vanadium oxide films grow epitaxially on the substrate surface. The similarity between the Sn3d XPD pattern measured for the clean SnO2(1 1 0) surface and the V 2p pattern measured for the oxide layers suggests that these films have a structure close to that of the substrate (rutile-type lattice). The present results can be explained with a formation of a vanadium oxide of the series VnO2n-1 with 4 ≤ n ≤ 8. These so called Magnéli phases of vanadium oxides have structures similar to that of rutile VO2. This interpretation was confirmed by comparison of multiple scattering calculations with the experimental XPD curves. The vanadium oxide films are stable and the formation of mixed vanadium-tin oxide does not occur after annealing in vacuum at ≈800 K. The XPD data seem to indicate that tin atoms are present at the surface as a two-dimensional phase. STM images collected for the annealed phases reveal a morphology consistent with the XPS and LEIS results. © 2002 Elsevier Science B.V. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Mechanism of growth and structure of titanium oxide ultrathin films deposited on Cu(001) Surface Science 602 (2008) 1101-1113
No full textThe growth mechanism, composition and structure of ultrathin films of titanium oxide deposited on the Cu(001) surface were investigated by means of XPS, LEIS, LEED and STM. Titanium oxide films were deposited on the Cu(001) surface previously saturated witha (p2 2p2)R45 structure of chemisorbed oxygen. The oxide films were prepared by evaporation of titanium in O2 atmosphere (pO2 in the 106 mbar range) while the substrate temperature was kept at 573 K. The Cu LEIS signal versus the amount of deposited titanium (as determined by means of XPS) indicates the growth of 2D islands in the early stages of deposition. Upon increasing the amount of deposited
titanium multilayer islands begin to grow. The XPS results indicate that the oxide phases formed for Ti coverages above 1ML have a
TiO2 stoichiometry. At very low coverages, a LEED pattern with a centred rectangular unit cell is observed. STM measurements show that at this stage of the growth the oxide islands are incorporated in the outermost layer of the substrate and the removed copper atoms form islands around the oxide regions. The very early stages of titanium oxide growth corresponding to the formation of this rectangular phase were also investigated by Ti deposition on the oxygen chemisorbed phase under UHV conditions at 573 K. In this way it is possible to study the reaction of Ti with chemisorbed oxygen. Upon increasing the Ti coverage above 0.5 ML, an oxide film with a slightly distorted
hexagonal unit cell begins to grow. The quasi-hexagonal phase of titanium oxide can also be formed by annealing at 773 K the
rectangular phase. At higher coverages, when the substrate surface is completely covered by the oxide, the film exhibits a LEED pattern with a regular hexagonal unit cell
Substrate mediated interaction of terbium(iii) double-deckers with the TiO2(110) surface
No full textA terbium(iii)-bis(phthalocyaninato) neutral complex was deposited on the rutile TiO2(110) surface, and their interaction was studied by Scanning Tunneling Microscopy (STM) and X-ray Photoelectron Spectroscopy (XPS). It was found that the TiO2 rutile surface favours the adsorption of isolated molecules adopting a lying down configuration with the phthalocyanine planes tilted by about 30° when they lie in the first layer. The electronic and chemical properties of the molecules on the surface were studied by XPS as a function of the TiO2(110) substrate preparation. This study evidences that strong molecule-substrate interactions are present and a charge transfer process occurs from the molecule to the surface
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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