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Field-effect Tuning of the Hole Density in Nd1.2Ba1.8Cu3Oy Thin Films
No full textUsing a field effect device we modified the number of holes in the surface layers of 4 to 10 unit cell Nd1.2Ba1.8Cu3Oy (NBCO) epitaxial films grown on (100) SrTiO3 substrates. The results obtained on a set of 12 devices demonstrate that it is possible to induce reversible changes of the hole density of NBCO films by field effect. It is found that the field effect becomes less pronounced increasing the film thickness. Insulating–superconducting transition was observed in one 8 unit cell NBCO field effect device. © 2004 American Institute of Physics
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
Field-effect experiments on oxide superconductors thin films
No full text[ITALIANO] Negli ultimi anni la ricerca nell’ambito della fisica dello stato solido ha rivolto grande interesse allo studio delle proprietà dei sistemi fortemente correlati ed in particolare degli ossidi perovskitici dei metalli di transizione. Questi materiali presentano una grande varietà di notevoli proprietà, quali alti costanti dielettriche, ferroelettricità, effetti di magnetoresistenza colossale e superconduttività ad alta temperatura critica. La comune struttura perovskitica permette inoltre di poter integrare tali diverse funzionalità in eterostrutture multistrato.
Esperimenti di effetto di campo elettrico (field-effect) permettono la modulazione dei portatori senza alterare le caratteristiche strutturali dei materiali investigati, consentendo lo studio del ruolo intrinsico della concentrazione dei portatori nel modificare le proprieà degli ossidi perovskitici. Inoltre, l’effetto di campo elettrico è alla base del funzionamento dei transistors ad effetto di campo a semiconduttore (Metal Oxide Semiconductor Field Effect Transistor, MOSFET); quindi lo studio della risposta di nuovi materiali a tale tipo di sollecitazione può, in linea di principio, condurre anche all’individuazione di materiali candidati alla sostituzione del silicio nella realizzazione di dispositvi elettronici. Parametri critici in questo tipo di esperimenti sono lo spessore e la concentrazione di portatori del materiale studiato, lo spessore e le caratteristiche dielettriche dell’isolante attraverso cui viene applicato il campo, l’interfaccia tra i due.
Oggetto del lavoro di tesi è stato lo studio di field-effect su film sottili di ossidi superconduttori. Il lavoro è stato svolto in parte presso i laboratori di superconduttività del Dipartimento di Scienze Fisiche presso la facoltà di Ingegneria dell’Università degli Studi di Napoli e in parte presso il Département de Physique de la Matière Condensée (DPMC) dell’ Università di Ginevra sotto la supervisione del prof. J.-M. Triscone.
L’attività svolta a Napoli è stata concentrata sullo studio dell’effetto di campo su film ultrasottili (da 4 a 10 celle elementari) di Nd1,2Ba1,8Cu3Oy a valle della caratterizzazione delle loro proprietà di trasporto in funzione dello spessore. Allo scopo è stata allestita una stazione di misura che consentisse di effettuare misure di resistività in funzione della temperatura (in particolare di film isolanti) per diversi campi applicati e contemporaneamente permettesse il monitoraggio di eventuali correnti di perdita attraverso l’isolante. Il field-effect è stato studiato sia su film superconduttori (10 celle elementari di spessore) sia su film isolanti (4 e 8 celle elementari di spessore). A tal fine sono stati realizzati dispositivi in cui l’ Nd1,2Ba1,8Cu3Oy è stato depositato su substrati di STO e ricoperto da un sottile strato di ossido di alluminio (Al2O3). Entrambi sono stati impiegati per l’applicazione del campo modulante. Oltre all’effetto sull’andamento in temperatura della resistività, è stata indagata anche l’influenza del campo modulante sulle caratteristiche IV dei dispositivi realizzati.
A Ginevra è stato studiato l’effetto di campo su strati superficiali di titanato di stonzio ridotto mediante plasma ad idrogeno. L’STO è un isolante nel suo stato normale e presenta interessanti proprietà dielettriche. Se drogato mediante sosituzione o deviazione del contenuto di ossigeno dal suo valore stechiometrico (introduzione di vacanze di ossigeno o riduzione), presenta caratteristiche metalliche ed anche una transizione superconduttiva a bassissime temperature, anche a basse concentrazioni di portatori. Anche in questo caso tali proprietà sono fortemente dipendenti dal livello di drogaggio e quindi dalla concentrazione dei portatori. La riduzione mediante plasma ad idrogeno ha permesso di trattare solo strati superficiali di cristalli di STO portando alla realizzazione di dispositivi in cui le proprietà dielettriche dell’STO normale e quelle metalliche dell’STO ridotto fossero integrate in un unico cristallo. In un primo momento si è proceduo alla caraterizzazione delle proprietà di trasporto elettronico delle superfici ottenute in termini di resistenza, magnetoresistenza ed effetto Hall in funzione della temperatura. Poi è stata investigata la riposta di tali superfici all’effetto di campo applicando il campo modulante attraverso la parte non ridota del cristallo di STO. Infine, allo scopo di verificare l’effettiva modulazione della concentrazione dei portatori da parte dell’effetto di campo, sono state effettuate misure simultanee di field-effect e di effetto Hall. Quest’ultimo tipo di indagine è stata eseguita anche su alcuni campioni di Nd1,2Ba1,8Cu3Oy realizzati a Napoli. / [ENGLISH] In last decade a lot of interest has been focused on the field of the oxides electronics, in particular possible device application of the transition metals perovskite oxides have been investigated. In fact, these strongly correlated systems show ineteresting multifunctional properties such as high temperature superconductivity (HTS) in cuprates, colossal magnetoresistance (CMR) in manganites, ferroelectricity in titanates or high dielectric constant. The attention paid to this class of material is mainly due to the possibility of integrating these different poperties in a single multy-layered structure thanks to the structural compatibility they present, leading to the implementation of new electronic devices.
Recently, field effect approach was successfully employed in order to verify the intrinsic role of the carrier concentration in determining perovskite oxides electronic transport behaviour. Interesting results have been obtained in modulating transport characteristics such as high temperature superconductivity and colossal magnetoresistance. In addition, field effect principle could leads to the realization of an all perovskite electronic switch device, wich could be a possible candidate in substituting the Si-based electronic technology. Unfortunately, field effect experiments present some problems related to both the characteristics of the materials employed and the needed experimental set-up. The former consist mainly in the thickness of the layer affected by the electrostatic modulation, governed by the carrier concentration via the Thomas-Fermi screening length; in the dielectric costant value of the insulating material employed to apply the modulating electric field; in possible interface related problems between the two. The latter are mainly due to the need of monitoring the very little leakage currents that can flow across the dielectric material during the experiment and to the possibility of measuring very high resistance values because of the little carrier concentrations desired to observe substantial electrostatic modulation effects.
In this thesis the results obtained in field effect experiments on very thin supercondcuting films are reported. The principal aim of the work was acquire more informations about the field effect mechanism on superconductor thin films by studying two different systems characterised by low carrier density and no interface related problems, paying attention to the instrumentation related problems. The work was performed between the Dipartimento Scienze Fisiche at the Univeristà degli studi di Napoli and the Département de Physique de la Matière Condensée at the Université de Genève.
In Naples, underdoped Nd1,2Ba1,8Cu3Oy very thin films were employed as channels in field effect devices. This compound, a classical example of cuprate superconductors, has shown a dependence of its electronic transport features as a function of the film thickness, presenting even Mott insulating behaviour in thinnest samples. In order to perform field-effect experiments on this material, devices consisting in Nd1,2Ba1,8Cu3Oy thin films deposited on STO substrates and covered by an Al2O3 thin layer were realised. Thanks to the deposition technique employed, completely in-situ, interfaces between the Nd1,2Ba1,8Cu3Oy films and both the STO substrate and the Al2O3 layer result of great quality. In this way both the materials could be exploited as dielectric to apply the modulating field across. A great effort was devoted to arrange a masurement set-up capable of measuring high resistance values in order to mainly investigate the elecrostatic modulation of the thinnest insulating samples.
In Geneva an STO single crystal field effect device was realised and tested. The interest in the strontium titanate arises from the observation of an insulator-metal transition occurring in it at very low doping levels. In addition, the posibility of integrating in a single device both these transport features and the dielectric characteristics of its undoped state make this material very attractive. A new hydrogen plasma reducing technique was employed to obtain very thin surface doped layers on STO syngle crystals. The characterization of the obtained doped surface layers electronic transport in terms of resistivity, magnetresistance and Hall effect, all as a function of the temperature, was carried out first. Then the field effect response of these thin doped surface regions was studied exploiting the dielectric fatures of the remaining non-doped STO substrate. The low carrier density and the defect free interfaces obtained, at least in principle, promise great modulation effects can be achieved. In order to verify the applying modulating field acts on the carrier concentration, Hall effect and field effect measurements were performed simultaneously. These measurements have been also performed on few Nd1,2Ba1,8Cu3Oy samples exploiting the instrumental apparatus in Geneva
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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