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Direct evidence of the dependence of surface state density on the size of SnO2 nanoparticles observed by scanning tunneling spectroscopy
No full textIn this work, we report a scanning tunnelling spectroscopy (STS) study of 30 and 10 nm tin dioxide nanoparticles.
The STS spectra give a surface band gap of 2.5 eV for both samples and show that the density of surface states in the
band gap is around 6 times higher for the 30 nm particles than for the 10 nm particles. This provides direct experimental
evidence for our theoretical model, which predicts a decrease in the surface state density as the particle size decreases,
and partly accounts for the improved sensitivity of gas sensing devices fabricated with nanoparticles
STM and XPS characterisation of vacuum annealed nanocrystalline WO3 films
No full textScanning tunnelling microscopy and X-ray Photoelectron Spectroscopy were conducted on magnetron sputtered WO3 thin films, following a sequence of ultra high vacuum anneals from 100 degrees C to 900 degrees C. Annealing from 100 degrees C to 400 degrees C induced an upward surface band bending of about 0.3 eV, attributed to the oxygen migration from the bulk to the surface, but no changes in the surface topography. Chemical changes occurred from 600 degrees C to 800 degrees C, associated with the formation of secondary oxide species. STM imaging showed that the film surface consists of amorphous particles 35 nm in size up to 600 degrees C, while higher temperatures resulted in an increase in particle size. Crystallisation of the nanoparticles started to occur after annealing at 600 degrees C. The implications in terms of gas sensing are discussed. (c) 2007 Elsevier B.V. All rights reserved
Evidence of band bending flattening of 10 nm polycrystalline SnO2
No full textWe developed a model for n-type metal-oxide semiconductors, which allows one to calculate the density of charged surface states on
nanostructured grains, once the Schottky barrier height is known.We characterised structurally and electrically two sets of polycrystalline
SnO2 films with average grain radius of 30 and 10 nm. The purpose of this experiment was to observe the flattening of the bandbending
and the corresponding decrease in the density of charged surface states which are, in turn, responsible for the pinning of the Fermi level.
Finally, we highlighted how this phenomenon affects the characteristics of the films as gas sensors
Photo-induced unpinning of Fermi level in WO3
No full textAtomic force and high resolution scanning tunneling analyses were carried out on
nanostructured WO3 films. It turned out that the band gap measured by scanning tunneling
spectroscopy at surface is lower than the band gap reported in the literature. This effect is
attributed to the high density of surface states in this material, which allows tunneling into
these states. Such a high density of surface states pins the Fermi level resulting in modest
surface activity at room temperature. Photo activation of WO3 results in unpinning of the
Fermi level and thereby in higher chemical activity at surface
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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