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Towards the production of core-shell nanoparticles with fluidized bed ALD
No full textReducing particle size or material structure size to nanometer scale can make the material properties, such as light absorption and electronic structure, change compared to the same materials at normal scale. This gives them properties that can make them suitable for the development of highly efficient and improved micro-electronics, sensor,medicine, batteries, catalysts and third generation solar cells. There are, however some challenges that need to be overcome in the development of nanoparticle-based devices. The first is protection of nanoparticles against corrosion and oxidation. This phenomenon is increased by the large surface area available for corrosion. Furthermore, when nanoparticles or nanostructures are used in electronic devices, lowresistive electrical contacts should be made between electrodes and nanoparticles. The second challenge is, thus how to make electrical contacts without compromising the material’s nanostructure. This thesis deals with the development of a synthesis process for core-shell nanoparticles, existing of a core that is coated with a thin layer of material that is able to provide protection, or electrical contacts. The first chapter describes the electrical contact between titanium nitride (TiN), which is a metallically conductive material that is used as contact material in electronic devices, and cadmium sulfide (CdS), a II-IV semiconductor that is used in (second generation) thin film solar cells and to increase light absorption in Grätzel-type solar cells. The experiments show that indeed we can make a Ohmic contact between TiN and CdS, meaning that the contact resistance between the two materials is low and that current is not blocked by the contact. The use of thin coatings as protective layers is investigated by coating thin CdS films,which can be used as photo-catalyst in solar hydrogen production cells, with thin, inert titanium dioxide (TiO2) to protect the CdS from corrosion under influence of solar radiation. The goal of this research was to deposit a TiO2 layer that was thick enough to provide full protection against corrosion, yet thin enough to enable electrons to be transferred between the CdS electrode and the electrolyte. The TiO2 coating was deposited with Atomic Layer Deposition (ALD), a technique used to deposit extremely thin layers of material by letting two precursors (A and B) react on the surface of a substrate to form product C. The first step in this process is chemisorption of precursor A. This chemisorption reaction is self-limiting and stops whenever the complete substrate is covered with a monolayer of component A. After completion of pulse A, precursor B is fed to the reactor and reacts with component A to form component C and prepare the surface of the substrate for a new pulse of component A. By repeating this cycle coatings can be made atomic layer by atomic layer. The experiments with TiO2-coated CdS films in photoelectrochemical hydrogen production cells show that, even though the samples are coated with protective TiO2 layers, the CdS remains sensitive to photocorrosion. The photocorrosion mechanism is investigated with electrochemical measurements in which the photocurrent over time can be described with a model that strongly resembles the Johnson-Mehl-Avrami model for phase transitions in solids. Analysis of the experimental results with the model shows that the corrosion starts in small defects in the TiO2 coating and that the corrosion spreads mostly in lateral directions. The next step in the research was to deposit coatings on individual nanoparticles with a fluidized bed ALD reactor (FB-ALD) that was specially developed for this purpose. In this reactor, the nanoparticles are agitated by a constant flow of inert carrier gas. The ALD precursors, tetrakis-dimethylaminotitanium (TDMAT) and water, are added to the carrier gas and hence brought into contact with the nanoparticles and layer-by-layer form a TiO2 shell on the particles. In the design of the reactor that, is used for loose nanoparticles, care has been taken to make the reactor both safe and versatile in operation. Furthermore, the possibility of extensive monitoring of the reactor is provided. With this reactor, silica (SiO2) nanoparticles are coated with 1.6 nm TiO2 layers. The growth rate is 0.32 Å per ALD cycle and independent of precursor pulse time and exposure. Electron microscope analysis (TEM) tells us that particles have a core-shell structure in which the SiO2 core is coated by a homogenous TiO2 layer. To show that this deposition technique can also be used to deposit conductive coatings on nanoparticles, SiO2 nanoparticles have been coated with conductive TiN layers. In this case TDMAT and ammonia (NH3) were used as precursors. The growth rate of TiN showed the saturation plateau that is typical for ALD growth but depended on the amount of ALD cycles: more cycles led to a lower growth rate. This decline in growth rate can be attributed to the formation of reaction by-products that can adsorb on the particle surface and hence block the adsorption of precursor molecules. The TiN-coated nanoparticles did show good electrical conductivity, with a resistance that depended strongly on the deposition conditions. The results of this research are a step towards the use of FB-ALD in the synthesis of core-shell nanoparticles, with batteries and nanostructured third generation solar cells as the most promising applications. Future research should focus on technological challenges of the FB-ALD technique itself and, on a fundamental level, on optimization of the core-shell structure. The fundamental questions relate to the electronic structure of the nanoparticles: the behavior of nanostructured materials can be fundamentally different from behavior of "normal materials”. Fundamental studies, based on calculations and simulations of electronic structure, can determine the ideal core-shell material combination for each application. The particles can be synthesized in a fluidized bed ALD reactor. In the further development of the FB-ALD technique, safety, with respect to the processing of loose nanoparticles, will be the most important aspect to be looked at, especially when dealing with (nano-) toxic materials and materials that are easily oxidized in air. This is mostly important for loading fresh particles and in loading of processed particles. The importance of a proper loading and unloading procedure has been demonstrated with the TiN-coated particles that spontaneously ignited when they came in contact with air. Another, more practical challenge is controlling nanoparticle agglomeration and maintaining a stable, homogeneously fluidized particle bed at large scale. Several techniques are available, besides the vibrating fluidized bed described in this thesis, to break agglomeraties and create an homogeneous fluidized bed at lab scale. Scale-up of these techniques should be investigated. Furthermore, the static head (pressure drop) of large scale fluidized beds is often higher than the desired absolute operating pressure of the ALD reaction. The influence of the relatively large pressure drop over the bed on fluidization homogeneity should be thoroughly investigated. Despite the technological challenges that come with scaling up of the technique, FB-ALD is a promising technique for the production of core-shell nanoparticles. The flexibility in materials selection, both for the core and the shell, and the homogeneity and quality of the coatings will provide a large advantage over other techniques.Materials for Energy Conversion and StorageApplied Science
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
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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