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Atomic Scale Insights into the Early Stages of Metal Oxidation: A Scanning Tunneling Microscopy and Spectroscopy Study of Cobalt Oxidation
No full textAtomic scale investigation of the early stages of cobalt oxidation
Get PDFLAUREA MAGISTRALEIn questo lavoro di tesi sono state studiate le prime fasi di ossidazione di
un film ultrasottile di cobalto metastabile. Il film di cobalto é stato depositato,
con la tecnica Molecular Beam Epitaxy (MBE), sul substrato Fe
(001)-p(1x1)O. La successiva ossidazione (da 2 L fino a 120 L) é stata eseguita
con la tecnica di post-ossidazione riscaldando il campione a 200 C.
Per studiare il suddetto campione sono state utilizzate Auger Electron
Spectroscopy (AES), Low Energy Electron Diffraction (LEED) e Scanning
Tunneling Microscopy (STM).
Una struttura cristallina del substrato di ferro e del film di cobalto é
stata indagata con il LEED. Dai dati AES, é stato possibile osservare che
l’ossigeno segrega sulla superficie durante la deposizione di cobalto e che si
verifica un ridotto intermixing di ferro con il film soprastante. Inoltre, é stato
osservato che l’ossidazione avviene solo alla superficie di cobalto. Comunque,
una ridotta ossidazione del substrato di ferro non é stata esclusa.
Dai dati STM, é stato possibile distinguere il cobalto metallico dalle isole
di ossido, che presentano una variazione di altezza (misurata dal substrato
di cobalto) cambiando i parametri di tunneling. Un’analisi di coverage (ricoprimento)
del primo e del secondo strato di ossido, confermano una modalitá
di crescita layer-by-layer.
L’analisi topografica evidenzia la presenza di stati nella gap dell’ossido, i
quali sono stati attribuiti alla presenza di difetti superficiali e all’accoppiamento
all’interfaccia dell’ossido con il cobalto metallico. Una gap di 2.3 eV é stata
stimata con le misure STS (Scanning Tunneling Spectroscopy). É stato inoltre
rilevato un band bending dell’ossido, attribuito ad un trasferimento
di carica in corrispondenza della superficie e/o all’interfaccia con il cobalto
sottostante.
Sulla base dei risultati topografici, CoO é stato visto crescere con la struttura
rocksalt ruotata di 45 rispetto al reticolo bct del cobalto, esponendo la
faccia CoO(001) alla superficie.In this thesis work early stages of oxidation of a ultra-thin film of metastable
cubic cobalt was studied. The film was deposited, with the Molecular Beam
Epitaxy (MBE) technique, on a Fe(001)-p(1x1)O substrate. The subsequent
oxidation (from 2 L up to 120 L) was performed with the post oxidation
technique heating the film at 200 C.
To study the above sample Auger Electron Spectroscopy (AES), Low
Energy Electron Diffraction (LEED) and Scanning Tunneling Microscopy
(STM) were used.
The crystalline structure of the iron substrate and the cobalt film was
investigated by LEED. From the AES data, it was possible to observe that
oxygen floats to the surface during the cobalt deposition and that there is
low intermixing of iron with the uppermost film. Moreover, it was observed
that the oxidation takes place only on the surface of the cobalt film. A small
oxidation of the iron substrate was anyway not excluded.
From the STM data, it was possible to distinguish metallic cobalt from
oxide islands, which present a relative height variation with respect to the
different tunneling parameters. The coverage analysis of the first and the
second oxide layers confirm a layer-by-layer growth mode.
A topographic study evidences the presence of states in the oxide gap,
whose nature is attributed to surface defects and to the coupling at the interface
with the metallic cobalt. An electronic gap of 2.3 eV was estimated by
Scanning Tunnelling Spectroscopy (STS) measurements. It was also detected
a band bending in the oxide, attributed to a charge transfer at the surface
and/or at the interface with the underlying cobalt.
Supported by the topographic study, CoO was seen to grow in the rocksalt
structure rotated in plane by 45 , with respect to the bct cobalt lattice,
exposing the CoO(001) 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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