1,720,962 research outputs found
Cumulenic sp‐Carbon atomic wires wrapped with polymer for supercapacitor application
Full text linkCarbyne, the ideal linear atomic wire consisting of a single-atom thick chain of sp-carbon, is theoretically predicted to have around five times higher surface area than graphene, notable charge mobilities, as well as excellent optical and thermal properties. Despite these impressive properties, the exploitation of carbyne-like system as an electrochemical energy-storage electrode has not been reported so far. To address this challenge, we focused on experimentally available finite and short linear atomic chain of sp-carbon. Herein, we prepare solution-processed thin films of tetraphenyl [3]cumulenic sp-carbon atomic wires embedded in a polymer matrix, in which sp-carbon atomic wires feature three cumulated carbon-carbon double bonds terminated at each end by two phenyl groups. Raman and UV–visible spectroscopy confirms the presence of sp-carbons inside the polymeric matrix. Finally, we investigate the supercapacitor performance of cumulenic sp-carbon atomic wires embedded polymer in three aqueous electrolytes, namely 1 M Na2SO4 (neutral), 1 M H2SO4 (acidic), and 6 M KOH (basic). The results suggest 6 M KOH is the best electrolyte to obtain high charge-storage performance of device with areal capacitance of 2.4 mF/cm2 at 20 mV/s, 85 % cycle stability after 10000 charge-discharge cycles, and excellent frequency response
Exploring the Growth Dynamics of Size‐Selected Carbon Atomic Wires with In Situ UV Resonance Raman Spectroscopy
Full text linkShort carbon atomic wires, the prototypes of the lacking carbon allotrope carbyne, represent the fundamental 1D system and the first stage in carbon nanostructure growth, which still exhibits many open points regarding their growth and stability. An in situ UV resonance Raman approach is introduced for real-time monitoring of the growth of carbon atomic wires during pulsed laser ablation in liquid without perturbing the synthesis environment. Single-chain species' growth dynamics are tracked, achieving size selectivity by exploiting the peculiar optoelectronic properties of carbon wires and the tunability of synchrotron radiation. Diverse solvents are systematically explored, finding size- and solvent-dependent production rates linked to the solvent's C/H ratio and carbonization tendency. Carbon atomic wires' growth dynamics reveal a complex interplay between formation and degradation, leading to an equilibrium. Water, lacking in carbon atoms and reduced polyynes solubility, yields fewer wires with rapid saturation. Organic solvents exhibit enhanced productivity and near-linear growth, attributed to additional carbon from solvent dissociation and low relative polarity. Exploring the dynamics of the saturation regime provides new insights into advancing carbon atomic wires synthesis via PLAL. Understanding carbon atomic wires' growth dynamics can contribute to optimizing PLAL processes for nanomaterial synthesis.Time-resolved, in situ UV resonance Raman approach to monitor carbon atomic wires growth via pulsed laser ablation in liquid. This approach tracks solvent-dependent, size-selected wires formation, correlating their Raman responses with concentration as a function of ablation time. It elucidates the synthesis, formation, and degradation mechanisms of carbon atomic wires via pulsed laser ablation and solvent-dependent production rates. imag
Probing the Stability of Halogenated Carbon Atomic Wires in Electrospun Nanofibers via Raman Spectroscopy
Full text linkCarbon atomic wires (CAWs) are one-dimensional (1D) sp-carbon nanostructures with remarkable electronic, mechanical, and optical properties, but their instability limits their practical applications. Embedding them in solid matrices can enhance their stability. This work reports the first example of electrospun nanofibers embedding halogenated CAWs. A solution of poly(methyl methacrylate) and CAWs in N,N-dimethylformamide was electrospun using various parameters to investigate the effects on fiber morphology and diameter. Halogenated CAWs were successfully incorporated with a minimal morphological impact. Raman spectroscopy confirmed effective embedding and CAWs stability during electrospinning. The halogenated CAWs showed resistance to degradation for at least six months and demonstrated enhanced thermal stability when embedded within nanofibers. Additionally, our work investigated the influence of different halogen terminations on the degradation kinetics of CAWs upon exposure to these conditions. Similarly, photodegradation studies revealed improved photostability within fibers and demonstrated how CAWs chemical structure affects degradation pathways, including possible homolytic C-X bond cleavage. This work introduces electrospun nanofibers as a novel platform for stabilizing CAWs, offering advantages over thin films, such as better homogeneity, larger surface area, and comparable stability. These findings open new perspectives for CAWs-based nanocomposites in electronics, electrochemistry, and energy-related applications
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
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
Optimization of polyynes production by Pulsed Laser Ablation in Liquid through a recirculation system
Full text linkLAUREA MAGISTRALEIn questa tesi, ho indagato la produzione di poliine attraverso l’Ablazione Laser Pulsata in Liquido (PLAL) utilizzando un innovativo metodo di ricircolo. Ho progettato un sistema di ricircolo che consente di ablare un target solido di grafite immerso in un solvente in condizioni di flusso all’interno di una cella di ablazione. Questo flusso è generato da una pompa peristaltica a membrana. Le ablazioni sono state eseguite utilizzando un laser Nd:YAG ns-pulsato alla lunghezza d’onda fondamentale di 1064 nm. In ogni ablazione il target viene ablato per 90 minuti in presenza di 100 ml di solvente. Ho esplorato gli effetti di due solventi organici: metanolo (MeOH) e acetonitrile (ACN). Tra questi, l’ACN è stato scelto per gli esperimenti a causa della sua maggiore produzione di poliine, infatti la concentrazione di HC8H in ACN è risultata circa doppia rispetto a quella in MeOH. Le ablazioni sono state eseguite con una configurazione della cella in cui il volume della cella era completamente riempito dal solvente. In tale configurazione ho investigato l’impatto della fluenza e del raggio dello spot sulla concentrazione finale di poliine. Un aumento sia delle dimensioni dello spot che della fluenza ha dimostrato di migliorare la produzione di poliine fino a una certa soglia, oltre la quale si verifica un’inversione del trend. Ad esempio, la concentrazione di HC8H è aumentata del 90% grazie a un incremento del raggio del 24% a fluenza costante. Un’ ablazione in condizioni di produzione batch (statica) è stata eseguita con gli stessi parametri utilizzati in condizioni di ricircolo per confrontare i due metodi. Ablando in condizioni di flusso, la concentrazione di poliine corte ha mostrato un lieve aumento (15% per HC8H), mentre le poliine più lunghe hanno subito una diminuzione (50% per HC14H). Il risultato più promettente riguarda il tasso di produzione, che diminuisce nel tempo ma con un gradiente più basso nel caso di ricircolo. Infatti, negli ultimi 15 minuti di ablazione, il tasso di produzione ottenuto nel sistema di ricircolo è superiore del 30% per HC8H e approssimativamente di un ordine di grandezza superiore per HC14H rispetto al caso statico. Questi risultati suggeriscono prospettive future promettenti per uno scale-up della tecnica.In this thesis work, I investigated the production of polyynes by Pulsed Laser Ablation in Liquid (PLAL) through a novel recirculation method. I designed a recirculation system that allows to ablate a solid graphite target immersed in a solvent in flow conditions within an ablation cell. This flow is generated by a peristaltic membrane pump. The ablations were performed using an Nd:YAG ns-pulsed laser at the fundamental wavelength of 1064 nm. The laser ablated the graphite target for 90 minutes in the presence of 100 ml of solvent. I explored the effects of two organic solvents: methanol (MeOH) and acetonitrile (ACN). Among these, ACN was chosen for the experiments due to its higher production of polyynes (i.e., the concentration of HC8H in ACN was twice the one in MeOH). Ablations were performed in a cell configuration where the cell volume was entirely filled by the solvent. The impact of fluence and spot radius on the final concentration of polyynes was investigated. An increase in both spot size and fluence was shown to enhance polyynes production up to a threshold, where a trend inversion occurs. For instance, the concentration of HC8H was increased by 90% thanks to a radius increase of 24% at constant fluence. An ablation in batch (static) conditions using the same parameters of the recirculation system was performed to compare the two methods. Ablating in flow conditions, the concentration of short polyynes showed a slight increase (15% for HC8H), while longer polyynes experienced a decrease (50% for HC14H). The most promising result regards the rate of production, which decreased over time but with a lower gradient in the recirculation case. Indeed, in the last 15 minutes of ablation, the rate of production obtained in the recirculation system is more than 30% higher for HC8H and approximately an order of magnitude higher for HC14H compared to the static case. These results show promising future perspectives for the scalability of the technique
Polyynes production by pulsed laser ablation in liquid: recirculation design for upscaling strategies
Full text linkLAUREA MAGISTRALEI fili atomici di carbonio (CAWs) sono strutture di carbonio ibridate sp, che presentano
proprietà elettroniche, ottiche e meccaniche uniche. La sintesi dei CAW mediante metodi
fisici è impegnativa a causa della loro instabilità e reattività, e richiede metodi innovativi per una produzione stabile. L’ ablazione laser pulsata in liquido (PLAL) offre un
approccio promettente, ecologico e scalabile, sfruttando i laser pulsati ad alta intensità
in mezzi liquidi per produrre nanostrutture. Questo studio indaga la sintesi di CAWs
in particolare poliine, attraverso PLAL, concentrandosi sull’ottimizzazione dei sistemi di
ricircolo con flusso dentro cella di ablazione, per migliorare la scalabilità della produzione.
Le ablazioni sono state eseguite utilizzando un laser Nd:YAG ns pulsato alla lunghezza
d’onda fondamentale di 1064 nm, con un sistema di flusso dentro cella di ablazione specificamente personalizzato, alimentato da una pompa a membrana peristaltica, progettato
appositamente per gli esperimenti, e configurazioni statiche (utilizzate per il confronto con
il design con flusso dentro cella di ablazione e per esperimenti che non richiedono flusso di
liquido) con una varietà di target. In questo lavoro vengono studiati alcuni parametri chiave della PLAL, come la velocità di ripetizione del laser e la portata del solvente, che non
sono stati testati prima, comprendendo il loro effetto sulla resa produttiva delle catene.
La scalabilità del sistema utilizzato è stata testata quantificando l’effetto che un aumento
del solvente utilizzato nelle ablazioni (acetonitrile) ha sull’efficienza della produzione e
confrontandolo con casi di configurazione statica. È stata inoltre studiata la possibilità
di eseguire ablazioni in solventi riciclati, al fine di ridurre i costi e andare verso una produzione più rispettosa dell’ambiente e sostenibile. I risultati ottenuti sono promettenti e
aprono la strada ad altri studi per proseguire ulteriormente nella ricerca. Inoltre, sottolineano il fatto che la PLAL, in particolar modo se effettuata in configurazione con flusso
dentro cella di ablazione, è la principale candidata per un ingrandimento della produzione
di CAWs.Carbon atomic wires (CAWs) are sp-hybridized carbon structures, which exhibit unique
electronic, optical, and mechanical properties. CAWs synthesis by physical methods is
challenging due to their instability and reactivity, necessitating innovative methods for stable production. Pulsed Laser Ablation in Liquid (PLAL) offers a promising, eco-friendly,
and scalable approach, leveraging high-intensity pulsed lasers in liquid media to produce
the nanostructures. This study investigates the synthesis of CAWs, specifically polyynes,
through PLAL, focusing on optimizing flow-through cell recirculation systems to enhance
production scalability. Ablations were performed using an Nd:YAG ns-pulsed laser at the
fundamental wavelength of 1064nm, using a specifically customized flow-through cell system, powered by a peristaltic membrane pump, designed appositely for the experiments,
and static configurations (used for comparison with the flow-through cell design and for
experiments not requiring liquid flow) with a variety of targets. Key PLAL parameters,
like repetition rate and flow rate of the solvent, that haven’t been tested before are studied
in this work, understanding their effect on the production yield of the chains. Scalability
of the utilized system was tested by quantifying the effect that an increase of the solvent
used in the ablations (acetonitrile) has on the efficiency of production and comparing it
to static configuration cases. Possibility of performing ablations in recycled solvents in
order to cut costs and go towards a more eco-friendly and sustainable production was
also investigated. The results obtained are promising and pave the way for other studies
to go further in research of the matter. Moreover, they underline the fact that PLAL,
in particular combined with a flow-through chamber recirculation system, is the prime
candidate for upscaling the production of CAWs
Investigation of polyynes in polymeric electrospun nanofibers
Full text linkLAUREA MAGISTRALEI Carbon Atomic Wires (CAWs) sono catene lineari composte da soli atomi di carbonio con ibridazione sp, e rappresentano un vero materiale unidimensionale tra gli allotropi del carbonio. A seconda della loro struttura si possono suddividere in poliine e cumuleni: le prime presentano un'alternanza di legami C-C singoli e tripli, mentre i secondi sono costituiti solo da doppi legami equivalenti. I CAWs possono essere terminati da diversi eteroatomi o gruppi chimici, che ne influenzano la struttura e le proprietà optoelettroniche (ad esempio, la differenza di lunghezza del legame, il gap energetico, la coniugazione elettronica). Nonostante le teoriche proprietà meccaniche, ottiche ed elettroniche siano molto incoraggianti, i CAWs non sono ampiamente diffusi a causa della facilità con cui degradano; in letteratura, la stabilizzazione e la rilevazione di poliine è stata ottenuta con successo incorporando queste molecole all'interno di film polimerici. I Carbon atomic wires sono sintetizzati sfruttando metodi chimici o di ablazione fisica; questi ultimi sono processi versatili e scalabili, ma permettono di ottenere solo poliine a bassa concentrazione. In questi casi, a causa della bassa concentrazione, il rilevamento e la caratterizzazione possono essere eseguiti con l'ausilio di nanoparticelle metalliche, sfruttando l'effetto SERS (Surface Enhanced Raman Scattering).
Lo scopo di questa tesi è in continuità con lo studio di poliine a bassa concentrazione in matrici polimeriche. In questo lavoro, le poliine sono state integrate in nanofibre polimeriche ottenute tramite elettrofilatura. Il rilevamento delle poliine all'interno di nanofibre elettrofilate è stato condotto per due gruppi di catene con diverse terminazioni, cioè poliine alogenate e idrogenate. Entrambi i sistemi sono stati caratterizzati a bassa concentrazione di poliine; pertanto, è stato necessario l'uso di nanoparticelle d'argento (AgNP) per sfruttare l'effetto SERS. Sono state effettuate misurazioni in liquido e in film di PVA, al fine di studiare l'interazione delle poliine con le AgNP; una buona risposta di entrambe le catene di carbonio è stata verificata. L'indagine riguardo le poliine all'interno delle fibre polimeriche è stata condotta con diverse configurazioni SERS, al fine di verificare quale fosse la più efficace: nanoparticelle a varie concentrazioni sono state poste sopra, sotto e all'interno di nanofibre di PVA o PMMA. È stato riscontrato che nanofibre elettrofilate da una soluzione di PVA contenente AgNP concentrate erano efficaci nel rilevare i segnali caratteristici delle poliine idrogenate; all'interno di queste nanofibre sono state incorporate e rilevate con successo sia una miscela di catene di varia lunghezza che una soluzione di catene con dimensione selezionata (HC8H). La loro stabilità nel tempo è stata verificata fino ad un mese. Questi sono i primi esempi di rilevamento di poliine a bassa concentrazione prodotte con metodi di ablazione fisica e integrate in nanofibre elettrofilate. Al contrario, le poliine alogenate non sono state rilevate con questa o qualsiasi altra configurazione, confermando così come i diversi gruppi chimici terminali possano influenzare l'interazione delle poliine con le AgNP, influenzando il rilevamento SERS di queste molecole.Carbon Atomic Wires (CAWs) are linear chains composed by only sp-hybridized carbon atoms, representing a true unidimensional material among carbon allotropes. Depending on their structures, they can be divided into polyynes and cumulenes: the firsts present an alternation of single and triple C-C bonds, while the seconds are made only by equal double bonds. CAWs can be terminated by different heteroatoms or chemical groups, which affect their structure and opto-electronical properties (i.e., bond length alternation, energy gap, π-electron conjugation). Despite having very appealing theoretically predicted mechanical, optical, and electronic properties, CAWs are not widely diffused due to the easiness of their degradation; in literature, stabilization and detection of polyynes has been successfully achieved embedding these molecules inside polymeric films. Carbon wires have been synthesized exploiting chemical routes or physical ablation methods; the latter are versatile and scalable processes, but only low concentrated polyynes are obtainable. In these cases, due to low concentration, the detection and characterization can be performed with the aid of metallic nanoparticles, exploiting Surface Enhanced Raman Scattering (SERS) effect.
The purpose of this thesis is in continuity with the investigation of low concentrated polyynes in polymeric matrices. In this work, polyynes were integrated in polymeric nanofibers obtained from electrospinning. The detection of polyynes inside electrospun nanofibers was conducted for two different terminated chains, halogenated and hydrogenated polyynes. Both systems were characterized at low polyynes concentration, therefore the use of silver nanoparticles (AgNP) was necessary to exploit SERS effect. Measurements in liquid and in PVA films were done to study the interaction of polyynes with AgNP, showing a good response for both carbon chains. The investigation of polyynes inside polymeric fibers was conducted with several SERS configurations, in order to verify which one was the most effective: AgNP at various concentrations were placed above, under and inside nanofibers of PVA or PMMA. It was found that nanofibers electrospun from a PVA solution containing concentrated AgNP were effective to detect characteristic signals of hydrogenated polyynes; both a mixture of chains with various length and a solution of size-selected chains (HC8H) were successfully embedded and detected inside these nanofibers. Their stability in time was verified up to one month. These are the first examples of detection of low concentrated polyynes produced by physical ablation methods and embedded in electrospun nanofibers. On the contrary, halogenated polyynes were not detected in this or any other configuration, thus confirming how different chemical end-groups can affect the interaction of polyynes with AgNP, influencing the SERS detection of these molecules
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