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Reduzierung des Kontaktwiderstands in organischen Dünnschicht-Feldeffekttransistoren mit p- und n-Kanal
No full textPerformance of organic field-effect transistors (OFETs) is generally defined by two processes: injection of charge carriers at the electrode-organic interface and transport of charge carriers across the conduction channel at the gate dielectric-organic interface. In recent years, progress in understanding the electronic structure of π-conjugated organic solids and advancements in methods of chemical synthesis have allowed to develop organic semiconductor (OSC), whose effective mobility in devices exceeds that of amorphous silicon. However, as the efficiency of charge transport in the conduction channel increases, the inefficiency of the charge-carrier injection starts to play an ever more important role in the performance of OFETs. Nowadays contact resistance – a property that summarizes the effects of an inefficient charge-carrier injection in a device – is one of the main factors limiting the performance of OFETs. Therefore, in order to further advance the field of organic electronics, it is crucial to be able to understand the physical origin of contact resistance and its interplay with other performance characteristics of a device.
While contact resistance has been a topic of extensive research in recent years, its effects on the device performance are not yet completely understood. In particular, this is influenced by the fact that methods used for characterisation of OFETs are often adopted directly from the field of inorganic semiconductors. However, the van der Waals nature of intermolecular bonds in organic solids results in a much higher rates of disorder in comparison to inorganic semiconductors. Therefore, even extremely pure organic single crystals only exhibit a band-like transport, while the theory of inorganic semiconductors mostly deals with ideal electronic band structures. Another contribution stems from the specifics of thin films of OSCs not being taken into account during the preparation and electrical characterisation of devices. This includes, in particular, exposure to ambient air, which is known to affect the current-voltage characteristics of both p- and n-channel OFETs. Furthermore, the measured current-voltage characteristics implicitly include a complex interplay of phenomena at metal-organic and dielectric-organic interfaces, making the development of a simple analytical model a rather challenging task. As a result, unravelling the effects of individual interfaces on the device performance is often not possible. Finally, the importance of investigating devices with well-defined interfaces to establish a proper physical understanding of the involved phenomena cannot be underestimated.
To address the aforementioned issues, it was decided to develop a full-high vacuum (HV) process chain, which encompasses preparation and electrical characterisation of OFETs. Devices with a bottom gate-bottom contact geometry are used, which ensures well-defined interfaces between the organic layer, the source-drain electrodes and the gate dielectric. The use of a full-vacuum process allows to exclude the effects of exposure to ambient air and thus isolate the influence of the interfaces on the device performance. This makes it possible to demonstrate an interplay between the contact resistance and the effective mobility in OFETs. Furthermore, it is shown that even a short exposure to ambient air drastically alters the current-voltage characteristics, influencing extracted performance characteristics. To allow a deeper insight into the charge-carrier injection and transport phenomena in OFETs, a variable-temperature transfer length method (TLM) analysis is developed and used in combination with the full-HV process chain. As a result, a connection between the height of the injection barrier and the activation energy of charge transport is uncovered in both ?- and ?-channel devices. This connection indicates that a low activation energy of charge transport is required to ensure a low contact resistance. Furthermore, the reproducibility of the TLM analysis is investigated, whereby the importance of precisely defining the actual channel length of devices is demonstrated.
The results of this dissertation advance the understanding of the contact resistance and its relation with charge transport in the conduction channel of OFETs. The developed full-HV process chain and analysis methods are flexible and have great potential for future studies, in particular in investigation of electrode functionalisation techniques to achieve true ohmic contacts in organic electronics.Die Leistung der organischen Feldeffeckttransistoren (OFET) ist generell durch zwei Prozessen zu definieren: die Injektion der Ladungsträger an der elektrod-organischen Schnittstelle und der Transport der Ladungsträger über den Leitungskanal am Gate-Dielektrikum-organischen Schnittstelle. In letzter Zeit, Fortschritt des Verständnis der elektronischen Struktur von π-konjugierten molekularen Festkörper und Verbesserung der organischen Synthesemethoden haben es erlaubt, organische Halbleiter (OSC) zu entwickeln, deren Effektivmobilität in Geräte übersteigt die vom amorphen Silizium. Aber je höher die Effizienz der Ladungstransport im Ladungskanal wird, desto größere Rolle spielt die Ineffizienz der Ladungsträgerinjektion in der Leistung der OFET. Heutzutage ist der Kontaktwiderstand – eine Eigenschaft, die die Effekte von der ineffizienten Ladungsträgerinjektion in einem Gerät charakterisiert, – ein der Hauptfaktoren, die die Leistung von OFET limitieren. Deswegen ist es entscheidend, den physikalischen Grund des Kontaktwiderstandes und das Zusammenspiel davon mit anderer Leistungscharakteristika des Gerätes zu verstehen, um weitere Fortschritte im Bereich organischer Elektronik zu machen.
Obwohl der Kontaktwiderstand schon seit Jahren extensiv recherchiert wird, seine Wirkung auf der Geräteleistung ist noch nicht komplett klar. Das wird insbesondere von der Tatsache beeinflusst, dass die Methoden der OFET-Charakterisierung oft direkt aus dem Bereich anorganischer Halbleiter angenommen werden. Aber die van der Waals Natur der Molekularkräfte der molekularen Festkörper erzeugt Unordnungsrate, die viel höher ist, als bei anorganischer Halbleiter. Deswegen sogar extrem reine organische Einzelkristalle zeigen nur Bandgetreuetransport, während die Theorie der anorganischen Halbleiter handelt von idealer Bandstrukturen. Weiterer Beitrag dazu kommt aus dem nicht-Berücksichtigung der Einzelheiten der molekularen Dünnschichten während der Herstellung und Charakterisierung der Geräten. Das beinhaltet insbesondere die Luftaussetzung, die sowohl auf die Strom-Spannung-Kennlinie der p-, als auch n-Kanal Transistoren auswirkt. Zudem bezieht die gemessene Strom-Spannung-Kennlinie eine komplexe Zusammenspiel von Phänomenen am metalorganischen- und dielektrikorganischen Schnittstellen implizit ein, womit die Entwicklung eines einfaches analytisches Modells nur herausfordernd wird. Hierauf ist oft das Enträtseln der Wirkung einzelner Schnittstellen auf die Geräteleistung nicht möglich. Schließlich ist es schwer zu überbewerten, die Wichtigkeit der Untersuchungen von Geräte mit scharf umgerissener Schnittstellen, um eine richtige Verständnis der Grundphänomen zu erstellen.
Um es zu versuchen, die obengenannte Fragen zu antworten, wurde es entschieden, eine Vollhochvakuumprozesse zu erstellen, die Herstellung und elektrische Charakterisierung der OFET umfasst. Geräte mit einer bottom-Gate-bottom-Kontakt Geometrie werden benutzen, um scharf umgerissene Schnittstellen zwischen der organischen Schichte, der Source-Drain-Elektroden und der Gate-Dielektrikum sicherzustellen. Die Verwendung einer Vollvakuumprozesse erlaubt den Ausschluss der Wirkung von Luftaussetzung und damit die Isolierung des Einflusses der Schnittstellen auf die Geräteleistung. Damit ist es möglich, ein Zusammenspiel zwischen den Kontaktwiderstand und die Effektivmobilität in OFETs zu zeigen. Zudem wird es demonstriert, dass sogar eine kurze Luftaussetzung in der Strom-Spannung-Kennlinie eine drastische Änderung erzeugt, die die extrahierende Leistungscharakteristika stark beeinflusst. Um neue Erkenntnisse über die Ladungsträgerinjektion und Ladungstransport in OFET zu gewinnen, eine temperaturvariabele Transfer-Length-Methode wird entwickelt und zusammen mit der Vollhochvakuumprozesse verwendet. Infolge wird eine Verbindung zwischen die Höhe der Injektionsbarriere und die Aktivierungsenergie der Ladetransport sowie in ?-, als auch in ?-Kanalgeräte entdeckt. Diese Verbindung deutet auf eine Voraussetzung hin, um einen niedrigen Kontaktwiderstand sicherzustellen, nämlich dass die Aktivierungsenergie der Ladetransport auch niedrig sein muss. Weiterhin wird die Reproduzierbarkeit der TLM-Analyse untersucht, womit die Wichtigkeit von der Festlegung der tatsächlichen Kanallänge der Geräte veranschaulicht wird.
Die Ergebnisse dieser Dissertation bringen das Verständnis des Kontaktwiderstandes und seine Verbindung mit der Ladetransport im Ladekanal der OFET voran. Die entwickelte Vollhochvakuumprozesse und Analysemethoden sind flexibel und verfügen über großes Potenzial an künftige Forschung, insbesondere an Untersuchungen der Elektrodenmodifikation, die eine Möglichkeit zu wahren ohmischen Kontakten für organische Elektronik bietet
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
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
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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