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Au-Co Thin Films and Nanostructures for MagnetoPlasmonics
Full text linkThis thesis develops in the framework of the Material Science for MagnetoPlasmonic purposes.
MagnetoPlasmonics is a recent and fast growing research _eld that aims at coupling the plasmonic properties typical of nanostructured noble metals (as, for instance, the local enhancement of electromagnetic _eld or the extraordinary optical transmission) with magnetic functionalities.
Promising applications, just to mention a few, span from sensing to the realization of active optical circuits at a nanoscale level.
MagnetoPlasmonic systems, so far mostly studied in the literature, are based on thin layers or nanostructures of noble metals coupled with ferromagnetic materials. Nevertheless, the requirement to increase the performances of such systems, and/or extend their functionalities, prompts the search for innovative compounds, which, displaying synergistic properties not otherwise achievable in phase segregated mixtures, can hold both plasmonic and magnetic features.
The aim of the present thesis is the realization and study of Au:Co alloyed thin _lms and nanostructures: gold is among the best performing materials in Plasmonics, while cobalt is known for its ferromagnetic properties. Unfortunately, the two metals are immiscible as bulk phases.
Au:Co thin _lms have been prepared by magnetron sputtering deposition technique in co-focusing geometry. Three di_erent compositions have been investigated, i.e., Au2Co1, Au1Co1 and Au1Co2, combined with three different values of thickness, i.e., ≈ 15 nm, ≈ 30 nm and ≈ 100 nm.
A full structural investigation has been carried out by X-Ray Di_raction integrated with XRay Absorption Spectroscopy and Transmission Electron Microscopy. The results demonstrate that the major fraction of the _lm is composed of an Au:Co alloy, typically richer in gold with respect to the nominal Au:Co atomic ratios.
The alloy fraction, its stoichiometry and the local order depend on the initial Au:Co ratio.
In the case of Au2Co1 sample, the alloy is, indeed, amorphous, while in the case of alloy richer in cobalt, there are some FCC crystalline seeds, elongated along the direction of the _lm growth. These grains are highly textured, with the (111) planes parallel to the substrate, and show a lattice constant that shortens as the Co content increases.
Besides this alloyed phase, there are segregated clusters of Cobalt, extremely nanostructured.
The presence of two magnetic phases is con_rmed by SQUID measurements, which, furthermore, allowed to characterize the hysteresis loops of the Au:Co _lms and to estimate the values of saturation magnetization.
The optical properties of the _lms have been characterized by transmittance UV-Vis measurements and Ellipsometry.
A thermal stability study demonstrated that the alloy is stable up to 200_ C; then, as the temperature increases, a de-alloying process occurs leading to two segregated phases of gold and cobalt.
The as-prepared Au-Co materials have been employed as metallic component in nanostructured periodic arrays, i.e., Semi Nano-Shell Array and Nano Hole Array. The morphological as well as the optical characterizations of the arrays demonstrate that these systems are promising candidates for future magneto-plasmonic studies and applications.Il presente lavoro si inserisce nell'ambito della scienza e ingegneria dei materiali per la MagnetoPlasmonica. Questa ultima è una recente, ma allo stesso tempo crescente, area di ricerca che mira a combinare le proprietà plasmoniche tipiche dei metalli nobili nanostrutturati (quali, ad esempio, l’intensificazione del campo elettromagnetico locale o la trasmissione ottica straordinaria) con funzionalità di tipo magnetico.
Promettenti applicazioni spaziano dalla sensoristica alla realizzazione di nanocircuiti totalmente ottici, solo per citarne alcuni.
Tradizionalmente i sistemi per MagnetoPlasmonica più considerati in letteratura prevedono l’accoppiamento di un film sottile o arrangiamento nanostrutturato di metalli nobili con materiale ferromagnetico. Tuttavia, al fine di migliorare le prestazioni di suddetti sistemi e/o esplorare nuove funzionalità è necessario ricercare nuovi composti in cui già il materiale innovativo presenta proprietà plasmoniche e magnetiche.
Scopo della presente tesi è la realizzazione e lo studio di film sottili e nanostrutture a base di lega Au-Co: l’oro è, infatti, un metallo nobile tra i migliori per applicazioni in plasmonica e il cobalto è un materiale ferromagnetico. I due metalli allo stato bulk sono notoriamente immiscibili.
Con la tecnica di deposizione magnetron sputtering sono stati depositati (in geometria di codeposizione) film sottili Au:Co, caratterizzati da tre diverse composizioni, ovvero Au2Co1, Au1Co1 e Au1Co2 e tre diversi spessori, rispettivamente ≈ 15 nm, ≈ 30 nm e ≈ 100 nm.
Una ricerca estesa è stata condotta con l’obiettivo di studiare attentamente le proprietà strutturali dei film, combinando diffrazione a raggi X, con misure di Assorbimento X svolte al Sincrotrone e Microscopia elettronica. I risultati dimostrano che la parte predominante del film è costituita da una lega Au-Co che è tipicamente più ricca in oro rispetto ai rapporti atomici nominali di Au e Co.
La frazione di lega, la sua stechiometria e l’ordine locale dipendono dal rapporto Au/Co inizialmente presente. Inoltre, mentre nel campione Au2Co1 la lega è prevalentemente amorfa, nel caso delle leghe più ricche in cobalto vi è la presenza di grani FCC cristallini, allungati lungo la direzione di crescita del film, fortemente tessiturati (in cui i piani (111) sono prevalentemente paralleli al substrato) e caratterizzati da un parametro reticolare che diminuisce all'aumentare del contenuto di cobalto.
Oltre alla fase di lega, sono presenti dei clusters di cobalto, caratterizzati da un basso ordine strutturale.
L’interfaccia tra due fasi magnetiche è stata confermata da misure SQUID che hanno inoltre permesso di caratterizzare i cicli di isteresi dei film Au:Co e di stimarne i valori di magnetizzazione di saturazione.
Le proprietà ottiche dei film sono state caratterizzate con misure di trasmittanza (nel range UV-Vis) ed Ellissometria.
Da un punto di vista termico, la lega Au-Co si dimostra stabile fino a 200° C; al crescere della temperatura ha lungo una de-alligazione che porta alla formazione di fasi metalliche separate di oro e cobalto.
I materiali Au-Co così preparati e caratterizzati sono stati poi impiegati come componente metallica in array periodici nanostrutturati, i.e., Semi Nano-Shell Array e Nano Hole Array. Gli array sono stati caratterizzati da un punto di vista morfologico e ottico dimostrandosi promettenti piattaforme per future caratterizzazioni MagnetoPlasmoniche
Preliminary synchrotron radiation characterization of first multilayer mirrors for the soft X-ray water window
No full textA vacuum soft x-ray reflectometer for the characterization of multilayer mirrors by synchrotron radiation at DAφNE
No full text
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
Au-Co Thin Films and Nanostructures for MagnetoPlasmonics
Full text linkThis thesis develops in the framework of the Material Science for MagnetoPlasmonic purposes.
MagnetoPlasmonics is a recent and fast growing research _eld that aims at coupling the plasmonic properties typical of nanostructured noble metals (as, for instance, the local enhancement of electromagnetic _eld or the extraordinary optical transmission) with magnetic functionalities.
Promising applications, just to mention a few, span from sensing to the realization of active optical circuits at a nanoscale level.
MagnetoPlasmonic systems, so far mostly studied in the literature, are based on thin layers or nanostructures of noble metals coupled with ferromagnetic materials. Nevertheless, the requirement to increase the performances of such systems, and/or extend their functionalities, prompts the search for innovative compounds, which, displaying synergistic properties not otherwise achievable in phase segregated mixtures, can hold both plasmonic and magnetic features.
The aim of the present thesis is the realization and study of Au:Co alloyed thin _lms and nanostructures: gold is among the best performing materials in Plasmonics, while cobalt is known for its ferromagnetic properties. Unfortunately, the two metals are immiscible as bulk phases.
Au:Co thin _lms have been prepared by magnetron sputtering deposition technique in co-focusing geometry. Three di_erent compositions have been investigated, i.e., Au2Co1, Au1Co1 and Au1Co2, combined with three different values of thickness, i.e., ≈ 15 nm, ≈ 30 nm and ≈ 100 nm.
A full structural investigation has been carried out by X-Ray Di_raction integrated with XRay Absorption Spectroscopy and Transmission Electron Microscopy. The results demonstrate that the major fraction of the _lm is composed of an Au:Co alloy, typically richer in gold with respect to the nominal Au:Co atomic ratios.
The alloy fraction, its stoichiometry and the local order depend on the initial Au:Co ratio.
In the case of Au2Co1 sample, the alloy is, indeed, amorphous, while in the case of alloy richer in cobalt, there are some FCC crystalline seeds, elongated along the direction of the _lm growth. These grains are highly textured, with the (111) planes parallel to the substrate, and show a lattice constant that shortens as the Co content increases.
Besides this alloyed phase, there are segregated clusters of Cobalt, extremely nanostructured.
The presence of two magnetic phases is con_rmed by SQUID measurements, which, furthermore, allowed to characterize the hysteresis loops of the Au:Co _lms and to estimate the values of saturation magnetization.
The optical properties of the _lms have been characterized by transmittance UV-Vis measurements and Ellipsometry.
A thermal stability study demonstrated that the alloy is stable up to 200_ C; then, as the temperature increases, a de-alloying process occurs leading to two segregated phases of gold and cobalt.
The as-prepared Au-Co materials have been employed as metallic component in nanostructured periodic arrays, i.e., Semi Nano-Shell Array and Nano Hole Array. The morphological as well as the optical characterizations of the arrays demonstrate that these systems are promising candidates for future magneto-plasmonic studies and 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
Ricoprimenti contenenti nanoparticelle di ZnO e TiO2 per applicazioni fotovoltaiche
Full text linkQuesto lavoro è relativo al progetto che ho svolto presso il Settore Materiali del Dipartimento di Ing. Meccanica dell'Università di Padova. Si colloca all'interno del progetto europeo ORION. Il lavoro sperimentale presentato in queste pagine si inserisce nel più ampio lavoro di ricerca sulle nanostrutture di semiconduttori e quantum dots, volto all !"ottimizzazione dei coating di ricoprimento e dei materiali assorbenti per celle fotovoltaiche. Più specificatamente mi sono occupata della sintesi via colloidale di nanoparticelle di ZnO e TiO2 e della loro deposizione via spin coating al fine di ottenere films con spessori e caratteristiche ottiche diverse. E' da sottolineare che sono state impiegate sintesi già collaudate nella realizzazione di materiali nanostrutturati per svariate applicazione nel campo dell'ottica e della fotonica: il mio lavoro è stato, più in dettaglio, rivolto alla deposizione dei ricoprimenti e alla loro caratterizzazioneopenEmbargo per motivi di segretezza e di proprietà dei risultati e informazioni sensibil
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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