1,720,973 research outputs found
Fe2O3-WO3 and Fe2O3-CuO nanoheterostructures by XPS
Full text linkThe detrimental effects of gaseous nitrogen oxides (NOx, with x = 1 and 2) on both human health and the environment have triggered efforts aimed at the development of solar-activated photocatalysts for their efficient removal. In this regard, Fe2O3-WO3 and Fe2O3-CuO nanoheterostructures were prepared by a two-step vapor phase route. In particular, chemical vapor deposition (CVD) of β-Fe2O3, a scarcely investigated iron(III) oxide polymorph, was followed by radio frequency-sputtering of WO3 or CuO under mild conditions. The adopted strategy enabled the obtainment of nanoheterostructures with a peculiar pyramidal morphology and a uniform dispersion of CuO or WO3 onto the pristine iron(III) oxide. In this work, the chemical composition of the target systems was investigated by means of x-ray photoelectron and x-ray excited-Auger electron spectroscopies. In addition to the identification of elemental chemical states, the reported results confirmed the formation of pure and O-deficient systems, in which the direct interplay between the single components opens the door to air purification using the developed systems as photocatalysts
MnO2nanomaterials functionalized with Ag and SnO2: An XPS study
No full textThe present study is devoted to the characterization of MnO2-Ag and MnO2-SnO2 nanocomposites of technological interest as gas sensors for food quality control and security applications. In particular, MnO2 nanomaterials were deposited on polycrystalline alumina substrates by plasma enhanced-chemical vapor deposition and functionalized with either Ag or SnO2 nanoparticles by means of radio frequency-sputtering. The target materials were investigated by a multitechnique approach, evidencing the successful formation of nanocomposites with tailored morphology, featuring an intimate contact of their components. Herein, the attention is dedicated to the characterization of system surface composition by x-ray photoelectron spectroscopy. Besides wide scan spectra, data obtained by the analysis of the C 1s, O 1s, Mn 2p, Mn 3s, Ag 3d, Sn 3d, and silver Auger signal spectral features are presented and critically discussed. The results highlight the occurrence of phase-pure MnO2 and SnO2 free from other Mn and Sn oxidation states and of appreciable silver surface oxidation in the target nanomaterials
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
Hydrogen gas sensing performances of p-type Mn3O4 nanosystems: The role of built-in Mn3O4/Ag and Mn3O4/SnO2 junctions
Full text linkAmong oxide semiconductors, p-type Mn3O4 systems have been exploited in chemo-resistive sensors for various analytes, but their use in the detection of H2, an important, though flammable, energy vector, has been scarcely investigated. Herein, we report for the first time on the plasma assisted-chemical vapor deposition (PA-CVD) of Mn3O4 nanomaterials, and on their on-top functionalization with Ag and SnO2 by radio frequency (RF)-sputtering, followed by air annealing. The obtained Mn3O4-Ag and Mn3O4-SnO2 nanocomposites were characterized by the occurrence of phase-pure tetragonal α-Mn3O4 (hausmannite) and a controlled Ag and SnO2 dispersion. The system functional properties were tested towards H2 sensing, yielding detection limits of 18 and 11 ppm for Mn3O4-Ag and Mn3O4-SnO2 specimens, three orders of magnitude lower than the H2 explosion threshold. These performances were accompanied by responses up to 25% to 500 ppm H2 at 200 °C, superior to bare Mn3O4, and good selectivity against CH4 and CO2 as potential interferents. A rationale for the observed behavior, based upon the concurrence of built-in Schottky (Mn3O4/Ag) and p-n junctions (Mn3O4/SnO2), and of a direct chemical interplay between the system components, is proposed to discuss the observed activity enhancement, which paves the way to the development of gas monitoring equipments for safety end-uses
XPS characterization of Mn2O3nanomaterials functionalized with Ag and SnO2
No full textX-ray photoelectron spectroscopy was used to characterize the chemical composition and elemental states of bare and composite Mn2O3 (Mn2O3-Ag, Mn2O3-SnO2) nanomaterials. The target systems were prepared by the initial plasma enhanced-chemical vapor deposition of manganese oxides on alumina substrates, followed by annealing in inert atmospheres and functionalization with Ag and SnO2 by radio frequency-sputtering on the Mn2O3 surface. The survey scans of the fabricated samples, along with detailed spectra of the C 1s, O 1s, Mn 2p, Mn 3s, and, eventually, Ag 3d, Ag MVV, and Sn 3d regions, were collected and analyzed in detail. The obtained results revealed the formation of composite systems characterized by the presence of Mn2O3 free from other manganese oxides and pure SnO2, whereas appreciable Ag oxidation was observed. The O 1s photoelectron peaks could be fitted by means of two components related to lattice oxygen and to hydroxyl groups/oxygen species chemisorbed on surface O defects. The occurrence of the latter could exert a beneficial effect on the system functional behavior in gas sensing and electrocatalytic applications
Quasi-1D MnO2 nanocomposites as gas sensors for hazardous chemicals
No full textQuasi-1D MnO2 nanocomposite materials (A/MnO2 with A = CuO, SnO2) were developed by a two-step plasma-assisted process, involving the plasma enhanced-chemical vapor deposition (PE-CVD) of MnO2 nanomaterials and their functionalization with copper or tin oxides by radio frequency (RF)-sputtering. A thorough characterization by means of specific surface analytical techniques highlighted the formation of high purity nanocomposites, endowed with a controlled morphology and a tailored spatial dispersion of the functionalizing agents. The target materials were tested as gas sensors for the recognition of hazardous gases [H2 and di(propyleneglycol) monomethyl ether (DPGME) / dimethyl methyl phosphonate (DMMP), the latter used as simulants for chemical warfare agents]. Functional data evidenced the obtainment of low detection limits and promising gas responses, whose improvement with respect to the pristine MnO2 was traced back to the formation of built-in p-n and n-n junctions for CuO/MnO2 and SnO2/MnO2 systems, respectively. The possibility of discriminating between the target analytes depending on the functionalizing species already at moderate working temperatures demonstrates the potential of the developed materials for eventual gas sensing applications under real-world conditions
Tailoring Vapor-Phase Fabrication of Mn3O4 Nanosystems: From Synthesis to Gas-Sensing Applications
No full textSupported p-Type α-Mn3O4 nanosystems were fabricated by means of chemical vapor deposition (CVD) on polycrystalline alumina substrates at temperatures of 400 and 500 °C, using Mn(hfa)2·TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N′,N′-Tetramethylethylenediamine) as precursor compound. The structure, chemical composition, and morphology of the obtained deposits were characterized in detail, devoting particular attention to the influence of the used reaction atmosphere (dry O2 vs O2 + H2O) on the system characteristics. For the first time, the gas-sensing performances of the obtained CVD Mn3O4 nanomaterials were investigated toward ethanol and acetone vapors, with concentrations ranging from 10 to 50 and from 25 to 100 ppm, respectively. The developed systems showed the best activity ever reported in the literature for Mn3O4 chemoresistive sensors in the detection of the target gases, a result that, along with their low detection limits and good selectivity, is an appealing starting point for eventual technological applications
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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