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Hyperspectral Imaging and Machine Learning for Nanomaterials Characterization
Get PDFNanoscale material systems are of great importance for answering open questions in funda- mental science and enabling advancements in next-generation technologies. This dissertation explores the structural, electronic, and optical properties of several nanomaterial systems at the atomic-, nano-, and micro- length scales. A collection of analytical characterization tools, non-trivial imaging methods, and advanced data analysis techniques are presented. This methodology is essential for finding and understanding new physics in nanomaterial systems; it is also an important tool for characterizing new nanomaterial systems and determining the relationship between synthetic parameters and relevant material properties. Applications of these techniques to a wide array of scientific questions are given throughout the thesis.A newly discovered source of highly localized light emission in hexagonal boron nitride (h-BN) is presented. This luminescent color center is closely related to unique impurities and native defects that occur exclusively in high-quality samples grown using a special high-pressure, high-temperature synthetic routine. An electron beam is used as a probe to characterize the luminescence, as well as activate and deactivate the light emission. The electron beam can also be used to deterministically create arbitrary nanoscale light emission patterns in h-BN synthesized using more conventional methods. A variety of h-BN polytypes are discussed and the effects of growth parameters, geometry, dimensionality, impurity concentration, and sample preparation on light emission are discussed.Transition-metal dichalcogenides (TMDs) are an exciting class of Van der Waals (VDW) materials that display a variety of unique phenomena in their 2D (monolayers) and 1D (nanotubes and nanoribbons) forms that are absent in the bulk material. A special synthesis method which allows for targeted growth of specific nanostructures is presented along with characterization of the TMD nanomaterials. A combination of special transmission electron microscopy (TEM) techniques and advanced data analysis methodology allows for rapid determination of the grain structure of continuous, nanocrystalline, monolayer TMD films.Gallium chalcogenides (GCs) are another class of VDW materials, closely related to TMDs, that are of significant interest to the nanoscience community. The type and concentration of chalcogen atoms in these materials can be varied, resulting in a alloys with tunable structural, electronic, and optical properties. A combination of TEM, angle-resolved photoemission spectroscopy (ARPES), and photoluminescence (PL) is used to fully characterize the quasiparticle band structure, optical bandgap, and crystalline phase of the alloys across their compositional range. Monolayers of these materials exhibit a distinct change in band structure, resulting in the material transitioning from direct bandgap in the bulk to indirect bandgap in the 2D limit.The characterization and analysis methods discussed here are broadly applicable to a wide variety of nanomaterial systems. Widespread adoption of machine learning and automation in the nanoscience community is a promising route toward high-throughput scientific inquiry
Long-Range Order in Nanocrystal Assemblies Determines Charge Transport of Films
Get PDFSelf-assembly of semiconductor nanocrystals (NCs) into two-dimensional patterns or three-dimensional (2-3D) superstructures has emerged as a promising low-cost route to generate thin-film transistors and solar cells with superior charge transport because of enhanced electronic coupling between the NCs. Here, we show that lead sulfide (PbS) NCs solids featuring either short-range (disordered glassy solids, GSs) or long-range (superlattices, SLs) packing order are obtained solely by controlling deposition conditions of colloidal solution of NCs. In this study, we demonstrate the use of the evaporation-driven self-assembly method results in PbS NC SL structures that are observed over an area of 1 mm à 100 Î1⁄4m, with long-range translational order of up to 100 nm. A number of ordered domains appear to have nucleated simultaneously and grown together over the whole area, imparting a polycrystalline texture to the 3D SL films. By contrast, a conventional, optimized spin-coating deposition method results in PbS NC glassy films with no translational symmetry and much shorter-range packing order in agreement with state-of-the-art reports. Further, we investigate the electronic properties of both SL and GS films, using a field-effect transistor configuration as a test platform. The long-range ordering of the PbS NCs into SLs leads to semiconducting NC-based solids, the mobility (Î1⁄4) of which is 3 orders of magnitude higher than that of the disordered GSs. Moreover, although spin-cast GSs of PbS NCs have weak ambipolar behavior with limited gate tunability, SLs of PbS NCs show a clear p-type behavior with significantly higher conductivities
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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