1,721,018 research outputs found
Spectroelectrochemistry of Nanomaterials
No full textAs the development and application of novel nanomaterials is continually expanding, so is the need for versatile characterization methods that can probe nanoscale processes as they occur. Such characterization techniques would permit non-destructive and parallel spectroscopy and imaging of nanomaterials. The objective of this work is to address the need for such techniques. First, a new spectroelectrochemical characterization technique, Micro-Extinction Spectroscopy (MExS), is presented, including instrumental design as well as data acquisition and analysis algorithms. Two nanomaterial systems are then studied with MExS: two-dimensional transmission metal dichalcogenides (TMDs) and plasmonic nanoparticles. For TMDs, in situ and hyperspectral reflectance studies coupled with cyclic voltammetry and chronocoulometry enable the time-resolved observation of the process of electroablation, an oxidative technique recently developed for the synthesis of monolayer TMDs. For plasmonic nanoparticles, dark-field microscopy is used in conjunction with chronocoulometry to observe, in a hyperspectral manner, single-particle electrodeposition, a technique developed for nanoparticle surface modification. Together, these two techniques position spectroelectrochemistry as a rich tool for optical nanomaterials, capable of both synthesis and concurrent characterization
Investigation of Light-Matter Interactions in Nanomaterials via Correlated Optical-Electron Microscopy
No full textNanomaterials have become more relevant in several sectors (environmental, energy storage, nanomedicine, etc) over recent years, where their unique properties compared to bulk are exploited. The difference in surface area is one of the reasons nanomaterials display tailorable chemical, mechanical, and physical properties due to extremely small grain size. Unfortunately, the properties of most of the nanomaterials are still to be characterized due to the need of precise instrumentation, preventing from making them convenient for consumer/industry applications. This thesis addresses the study and understanding of the relationship of nanomaterials’ optical properties and their physical structure, as well as the creation of protocols to facilitate characterization. By understanding this relationship, nanomaterials can be tailored to exploit their properties for many applications in many sectors. Based on this premise, two different systems were studied and correlated. First, the sensitivity-structure correlation of gold nanoparticles (NPs) for biosensing applications is studied. In such study, a single-nanoparticle approach was used, and statistical models were applied to correlate the refractive index sensitivity of gold NPs with their shape and size. Based on such correlation, rounder NP resulted to be more sensitive to surface events, providing insights on particle selection for biosensors. Furthermore, the nanoparticles were functionalized as DNA sensors as a proof of concept. Next, the Micro Extinction Spectroscopy development is described, as well its use as an
analytical tool to study the influence of defects in 2D semiconductors. With such tool, a monolayer transition metal dichalcogenides library was create by detecting excitons with their local absorption. Finally, monolayer MoS2 was treated by both oxygen plasma exposure and hydrogen treatment to create defects and alter its band gap. The material was characterized before and after the treatment using optical spectroscopy, and information about its composition, bandgap, and optical response was revealed. In sum, the projects presented here are unified by the need for structure-function correlations, which are achieved with optical spectroscopy and electron microscopy
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
Ultrathin Chalcogens
No full textTwo-dimensional (2D) materials, which are only one or a few atoms thick, can possess exciting and tunable optical/electronic properties unique from their 3D counterparts, providing a platform to tailor physics through chemistry and engineering. Structure-property relationships in 2D materials, including the room-temperature quantum Hall effect in graphene, have inspired the search for new 2D materials, amongst which are those from non-layered parent crystals, such as germanene. In this research, I have designed novel synthesis routes aimed to exploit attractive properties in 2D and ultrathin ( lies in the plane of the substrate on highly-oriented pyrolytic graphite (HOPG) but aligns orthogonally to MgO(100) substrates. Complementary high-resolution transmission electron microscopy (HRTEM), polarized Raman spectroscopy, and Hall effect measurements unravel a correlation between this tunable orientation and optical/electrical anisotropy in ultrathin Te, providing both a rational handle to access desired properties and a simple platform for device fabrication. Also, Raman signals are acutely dependent on film thickness from 20-2.5 nm displaying dramatic blue shifts of both basal plane and axial modes—a phenomenon not observed in layered 2D materials. The relative shifts between modes are orientation-dependent, suggesting that optical anisotropy persists and is even enhanced at the ultrathin limit. Lastly, vapor transport deposition is demonstrated for 0.85-3.0 nm-thick Se and Te, and TEM/scanning transmission electron microscopy (STEM) reveal a novel 2D α-phase in the case of three-atom-thick Te. This research has resulted in the first ultrathin chalcogens grown by a truly scalable technique with rational control of orientation and large-area uniformity, pushing these materials toward practical utility. Furthermore, evidence of thickness-dependent optical properties and 2D α-phase reconstruction reveals the quasi-2D nature of ultrathin Te
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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