1,721,043 research outputs found
Study of hydrogen absorption in a novel three-dimensional graphene structure: Towards hydrogen storage applications
Full text linkThe use of a novel three-dimensional graphene structure allows circumventing the limitations of the two-dimensional nature of graphene and its application in hydrogen absorption. Here we investigate hydrogen-bonding on monolayer graphene conformally grown via the epitaxial growth method on the (0001) face of a porousified 4H-SiC wafer. Hydrogen absorption is studied via Thermal Desorption Spectroscopy (TDS), exposing the samples to either atomic (D) or molecular (D
) deuterium. The graphene growth temperature, hydrogen exposure temperature, and the morphology of the structure are investigated and related to their effect on hydrogen absorption. The three-dimensional graphene structures chemically bind atomic deuterium when exposed to D
. This is the first report of such an event in unfunctionalized graphene-based materials and implies the presence of a catalytic splitting mechanism. It is further shown that the three-dimensional dendritic structure of the porous material temporarily retains the desorbed molecules and causes delayed emission. The capability of chemisorbing atoms after a catalytic splitting of hydrogen, coupled to its large surface-to-volume ratio, make these structures a promising substrate for hydrogen storage devices
Polycrystalline cubic silicon carbide thin films for MEMS
Full text linkBereits vor 60 Jahren wurde Silizium (Si) aufgrund seiner gut etablierten Technologie zur bevorzugten Materialwahl für Mikro elektromechanische Systeme (MEMS). Seine begrenzten elektrischen, thermischen und mechanischen Eigenschaften, wie etwa die relativ geringe Bandlücke, schränken jedoch seine Leistung in Hochtemperatur- oder rauen Umgebungen erheblich ein. Um diese Herausforderungen zu überwinden, hat sich Siliziumkarbid (SiC) als vielversprechende Alternative etabliert. Einkristallines SiC weist überlegene Eigenschaften auf, darunter eine breite Bandlücke, eine hohe Durchbruchfeldstärke und eine ausgezeichnete thermische Stabilität. Damit ist es ideal für Hochleistungs- und Hochtemperaturanwendungen, sowie Anwendungen in chemisch aggressiven Umgebungen geeignet. Diese Arbeit konzentriert sich auf polykristallines 3C-SiC, welches durch seine hohe Härte, thermische Stabilität, Verschleißfestigkeit und erstklassige Biokompatibilität überzeugt. SiC ist daher ein perfekter Ersatz für Silizium in thermomechanisch belasteten Komponenten wie Cantilevern und Membranen. Die kontrollierte Abscheidung von 3C-SiC auf Si oder SiO2 beschichteten Si Substraten ermöglicht maßgeschneiderte Dünnschichteigenschaften und die Herstellung von polykristallinen 3C-SiC-on-Insulator (SiCOI-ähnlichen) Strukturen. Diese Fortschritte in den Materialeigenschaften können die Leistung von 3C-SiC-basierten MEMS-Geräten erheblich verbessern, die Einschränkungen von Silizium überwinden und den Weg für die nächste Generation leistungsfähiger Anwendungen in extremen Umgebungen ebnen. In dieser Arbeit werden die Abscheidung, Charakterisierung und das Anwendungspotenzial von polykristallinen 3C-SiC-Dünnschichten untersucht, die auf Si und SiO2 beschichteten Si Substraten gewachsen sind. Ein alternierender Ansatz wird verwendet, um die Precursor-Gase Silan und Propan in die Reaktionskammer einzuleiten. Die Studie konzentriert sich primär auf den Einfluss der Prozessgasflussraten auf das Wachstum und die daraus resultierenden Eigenschaften der Dünnschichten. Eine höhere Wachstumsrate pro Zyklus wurde konsistent bei geringerer Trägergasflussrate beobachtet, was auf die Hemmung durch Wasserstoff und Passivierungseffekte an der Oberfläche zurückgeführt wird. Tiefenprofilanalysen mittels Röntgenphotoelektronenspektroskopie (XPS) zeigten einen erhöhten Sauerstoffgehalt von 7,5 % in auf SiO2 gewachsenen Schichten, was zu signifikanten Unterschieden im Vergleich zu auf Si gewachsenen Schichten führte. Verglichen mit SiO2, wurden höhere Wachstumsraten pro Zyklus von 37 % auf Si Substraten gemessen, während die Karbonisierungsschichtdicke für das jeweilige Substrat konstant blieb. Dabei wurde eine 20 nm dicke amorphe Kohlenstoffschicht an der 3C-SiC/Si Grenzfläche festgestellt, während an der Grenzfläche auf SiO2 eine 10 nm dicke Graphitschicht identifiziert wurde. Darüber hinaus wurden glattere Oberflächen bei 3C-SiC-Dünnschichten auf SiO2 Substraten mit einer minimalen RMS-Rauheit von 2,6 nm im Vergleich zu 3,5 nm auf Si gemessen. Röntgenbeugungsanalysen (XRD) bestätigten die polykristalline Natur der Schichten, wobei die Kristallorientierung am stärksten ausgeprägt war. Eine höhere Kristallqualität wurde für SiO2 beschichtete Si Substrate festgestellt, was durch geringere Werte der Halbwertsbreite (FWHM) der XRD-Rockingkurven von 1,112 ° für Si und 0,446 ° für SiO2 belegt wurde. Des Weiteren wurde der Wärmeausdehnungskoeffizient (CTE) von 3C-SiC-Dünnschichten untersucht, der eine signifikante Abhängigkeit von den Prozessgasflussraten zeigte. Die CTE-Werte variierten zwischen 4,37 und 13,96 ppm/K bei 900 °C, was zu einem minimalen CTE-Mismatch von 3,8 % zwischen 3C-SiC und Si führte. Der Einfluss dieses CTE-Mismatches wurde auf Bauteilebene an Mikroheizplatten (μHP) mit strukturierten Platin- (Pt-) Heizstrukturen demonstriert. Wie erwartet zeigte sich eine signifikante Reduktion der thermisch induzierten Verformungen bei geringerem Mismatch der CTE-Werte. Elektrische Charakterisierungen von nominal undotierten 3C-SiC-Schichten zeigten, dass durch eine sorgfältige Auswahl der Prozessgasflussraten Filme mit niedrigen Verunreinigungsniveaus erreicht wurden, was sich in hohen spezifischen Schichtwiderständen von 2,3 Ω·cm äußerte. Für n-dotierte 3C-SiC-Schichten, die mit dem alternierenden Precursor einleite-Ansatz hergestellt wurden, wurde ein minimaler spezifischer Widerstand von 0,02 Ω·cm bei Raumtemperatur gemessen, was die Effektivität des neu entwickelten in-situ Dotierungsschemas bestätigte. Weitere Analysen zeigten, dass eine übermäßige Stickstoffinkorporation aufgrund hoher Ammoniakflussraten zur Bildung einer amorphen isolierenden SiCxNy Schicht führte. Auf Geräteebene zeigten 3C-SiC-basierte μHP-Strukturen reduzierte thermisch induzierte Auslenkungen im Vergleich zu Pt-basierten Strukturen, was das Potenzial integrierter 3C-SiC-Heizstrukturen unterstreicht. Zusammenfassend hebt diese Arbeit die signifikanten Auswirkungen von Abscheidungsparametern auf das Wachstum, die Struktur und die elektrischen Eigenschaften von polykristallinen 3C-SiC-Dünnschichten hervor, mit vielversprechenden Anwendungen für MEMS und Hochtemperaturbauteilen.Starting already 60 years ago silicon (Si) has been the material of choice for micro electromechanical systems (MEMS), thanks to its well-established technology base. However, its limitations in terms of electrical, thermal and mechanical properties, such as its relatively low band gap, restrict its performance in high-temperature or harsh environments applications. To overcome these challenges, silicon carbide (SiC) has emerged as a promising alternative. Single crystal SiC exhibit superior properties, including a wide band gap, high breakdown electric field strength and thermal stability, making it ideal for high-power, high-temperature and chemically aggressive applications. This work focuses on polycrystalline 3C-SiC featuring high hardness, thermal stability, wear resistance and biocompatibility, making it a perfect substitute for Si for thermo-mechanically loaded components, such as cantilevers and membranes. The controlled deposition of 3C-SiC on Si or SiO2 coated Si substrates offers the potential for tailored thin film properties, enabling the creation of polycrystalline 3C-SiC-on-insulator (SiCOI-like) structures. This advancement in material properties can significantly improve the performance of 3C-SiC-based MEMS devices, surpassing the limitations of Si and paving the way for next-generation, high-performance applications in extreme environments. This work investigates the deposition, characterization and application potential of polycrystalline 3C-SiC thin films grown on both Si and SiO2 covered Si substrates. An alternating approach is used to feed the precursor gases of silane and propane into the reaction chamber. The study primarily focuses on the influence of process gas flow rates on thin film growth and properties. A higher growth per cycle was consistently observed with a lower carrier flow rate, attributed to hydrogen inhibition and surface passivation effects. X-ray photoelectron spectroscopy (XPS) depth profiling revealed an increased oxygen content of 7.5 % in thin films grown on SiO2, causing substantial differences when compared to those grown on Si. Higher rates in growth per cycle were measured for Si substrates compared to SiO2. The carbonization layer thickness, however, was consistent for each substrate, featuring a 20 nm amorphous carbon layer at the 3C-SiC/Si interface, while a 10 nm graphite layer was identified at the interface on SiO2. Furthermore, smoother surfaces of 3C-SiC thin films grown on SiO2 compared to Si were measured with a minimum RMS roughness of 2.6 and 3.5 nm, respectively. X-ray diffraction (XRD) analysis confirmed the polycrystalline nature of the films, with the crystallographic orientation being most prominent. Higher crystal quality was confirmed for SiO2 covered Si substrates, indicated by lower full-width at half maximum (FWHM) values of XRD rocking curves of 1.112 ° for Si and 0.446 ° for SiO2. Next, the coefficient of thermal expansion (CTE) of 3C-SiC thin films was investigated, showing significant variation with process gas flow rates. The CTE values ranged from 4.37 to 13.96 ppm/K at 900 °C, resulting in a minimal CTE-mismatch between 3C-SiC and Si of 3.8 %. The impact of the CTE-mismatch is demonstrated on device level with micro hotplate (μHP) structures featuring thermal excitation with patterned platinum (Pt) structures. As expected, significant reduction of thermally-induced deflections was demonstrated when a lower mismatch of the individual CTE values was achieved. Electrical characterization of nominally undoped 3C-SiC films showed that a carefully selected process gas flow ratio resulted in films with low impurity levels, indicated by high film resistivities of 2.3 Ω·cm. For n-doped 3C-SiC thin films, using the alternating feed approach, a minimum film resistivity of 0.02 Ω·cm was measured at room temperature, confirming the effectiveness of the newly designed in-situ doping scheme. Further analysis showed that excessive nitrogen incorporation leads to the formation of an amorphous insulating SiCxNy layer due to the presence of high ammonia flow rates. On the device level, 3C-SiC-based μHP structures exhibited reduced thermally-induced deflections compared to those with Pt-based structures, confirming the potential of integrated 3C-SiC heating structures as minimal deflections resulted. In conclusion, this work highlights the significant impact of deposition parameters on the growth, structural and electrical properties of polycrystalline 3C-SiC thin films, with promising applications in MEMS and high-temperature device applications
Intrinsic Losses in Silicon, Polycrystalline Diamond, and Silicon Carbide MEMS Resonators
Full text linkSeit ihrem Start in den frühen 1960er Jahren hat sich die Microsystemtechnik zu einem außergewöhnlich erfolgreichen Bereich der Wissenschaft und Technik entwickelt. Unzählige bahnbrechende Entdeckungen haben den Weg für den heutigen Multimilliarden-Dollar-Markt geebnet, der durch mikroelektromechanische Systeme (MEMS) weltweit angetrieben wird. Neben dem piezoresistiven Effekt, der hauptsächlich für Bauteildesigns im niederfrequenten Bereich ohne Resonanz (z.B. Drucksensoren) zum Einsatz kommt, sind aktiv getriebene Systeme, die die Eigenfrequenzen der MEMS-Strukturen nutzen, von Interesse und Teil einer großen Bandbreite an Sensorsystemen und signalverarbeitenden Technologien. Silizium, ein etabliertes Basismaterial in der Halbleiterindustrie, ist dank der Errungenschaften der CMOS-Mikroelektronik auch in der MEMS-Industrie weit verbreitet. Dennoch gibt es Hochtemperaturanwendungen und solche unter herausfordernden Bedingungen bei denen Silizium an seine Grenzen stößt und andere Materialien, wie z.B. Siliziumkarbid und Diamant als vielversprechende Alternativen in Betracht gezogen werden. Polykristalline Materialien innerhalb dieser Halbleiter kombinieren herausragende mechanische, chemische und elektrische Eigenschaften mit hoher Kompatibilität zu Silizium-Substraten. Diese Arbeit fokussiert sich auf polykristalline Siliziumkarbid- und Diamant-Dünnschichten zur Anwendung als resonante MEMS-Bauteile. Durch die Verwendung maßgeschneiderter Herstellungsprozesse werden MEMS-Resonatoren aus polykristallinen Siliziumkarbid- und Diamant-Schichten auf Siliziumsubstraten hergestellt und ihre Schwingungseigenschaften, insbesondere die Resonanzfrequenz und der Gütefaktor (Q-Faktor), bei Frequenzen bis zu 1 MHz untersucht. Die hervorragenden mechanischen Eigenschaften der Materialien werden ausgenutzt, um möglichst hohe Gütefakturen für Anwendungen, z.B. als Taktgeber, zu erzielen. Um dieses Ziel zu erreichen, untersucht diese Arbeit die Möglichkeiten einer automatisierten optischen Charakterisierung der statischen und dynamischen Eigenschaften von MEMS-Resonatoren. Ein optischer Ansatz basierend auf Weißlichtinterferometrie (WLI) und Laser-Doppler-Vibrometrie (LDV) wird entwickelt, um die lokalen Schichtdicken- und Stresswerte sowie die Resonanzfrequenzen und die Gütefaktoren zu bestimmen und damit statische und dynamische Bauteileigenschaften zu verbinden. Durch die Untersuchung verschiedener Resonanzmoden werden die Energieverluste in den Resonatoren ermittelt. Zudem wird die automatisierte Vermessung von hunderten Resonatoren mit tausenden and Resonanzmoden auf einem einzelnen 4-zoll Wafer für die Entwicklung der design-dependent Q-factor spectroscopy (DDQS) verwendet. Bei der DDQS wird die Breite der untersuchten einseitig geklemmten plattenförmigen MEMS-Resonatoren variiert, was dazu führt, dass sich die Resonanzmoden im Frequenzspektrum auffächern und Rückschlüsse auf moden- und frequenzabhängige Verlustmechanismen ermöglichen. Durch begleitende analytische und numerische Simulationen kann eine Landkarte der dominierenden Verlustmechanismen im Frequenzspektrum erstellt werden. Darüber hinaus wird die DDQS angewendet, um die Einflüsse der Oberflächenoxidation in monokristallinen Siliziumresonatoren, der Oberflächenreibungsverluste in nicht-Diamantbindungen in polykristallinen Diamantresonatoren und der Reibungsverluste in dotierten polykristallinen Siliziumkarbidresonatoren zu untersuchen. Alles in allem streicht diese Arbeit die Notwendigkeit von statistischen Analysen einer großen Zahl von MEMS-Resonatoren hervor, um dominierende Verlustmechanismen zu identifizieren und dadurch ein verbessertes Verständnis der Dünnfilmeigenschaften und des MEMS-Bauteildesigns für die Resonatorperformance zu ermöglichen.Starting in the early 1960s, microsystem technology evolved into an extraordinarily successful field of science and industry, thanks to its numerous groundbreaking discoveries, which paved the way for today's multi-billion-dollar market, driven by microelectromechanical systems (MEMS) worldwide. Besides the piezoresistive effect, used mainly within off-resonance, low-frequency device designs (e.g., pressure sensors), actively driven systems utilizing the eigenfrequencies of MEMS structures are of great interest and part of a wide range of sensor systems and signal-processing technologies. Silicon is a well-established base material in the semiconductor industry; therefore, it is widely used within the MEMS industry, thanks to the achievements of CMOS microelectronics. However, there are high-temperature or harsh environment applications where silicon reaches its limitations, and other materials, e.g., silicon carbide and diamond, have emerged as promising alternatives. Polycrystalline materials within these semiconductors combine both the outstanding physical, chemical, and electrical properties with the good compatibility with silicon substrates. This work focuses on polycrystalline silicon carbide and diamond thin films for the application of resonant MEMS devices. Due to tailored integration process steps, flexural MEMS resonators are fabricated on silicon substrates from polycrystalline silicon carbide and diamond device layers, and their vibrational properties, especially resonance frequency and quality factor (Q-factor), are studied up to frequencies of 1 MHz. Furthermore, the exceptional mechanical properties of the materials are utilized, aiming for the highest possible quality factors for applications in e.g., timing devices. To achieve this goal, this work investigates the opportunities of an automated approach to optically characterize the static and dynamic properties of MEMS resonators. An optical approach based on white light interferometry (WLI) and laser Doppler vibrometry (LDV) is developed to screen local device layer thickness and stress values, as well as resonance frequency and quality factor, thereby combining information on both static and vibrational device properties. Investigating several different mode shapes enables to study energy losses in the resonators. Furthermore, the automated approach, applied to hundreds of resonators with thousands of resonance modes on one single 4-inch wafer, is utilized in the novel technique of design-dependent Q-factor spectroscopy (DDQS). The width of the studied single-side clamped plate-shaped (SSCP) MEMS resonators is varied within the DDQS, resulting in resonance modes spread across a wide frequency range, which enables the study of mode shape and frequency-dependent loss mechanisms. From accompanying analytical and numerical simulations, it is possible to draw a map of dominating loss mechanisms in the frequency spectrum. Even more, the DDQS is applied to investigate the influences of surface oxidation in monocrystalline silicon resonators, surface friction losses in non-diamond bonds in polycrystalline diamond resonators, and bulk friction losses in doped polycrystalline silicon carbide resonators. All in all, this work highlights the need for statistical analysis of a large number of MEMS resonator devices, enabling the identification of dominant loss contributions, thus paving the way to an improved understanding of thin film properties as well as MEMS device designs on resonator performance
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
Out-of-plane excitation of MEMS resonators in the MHz range with a planar electrostatic transducer arrangement
Full text linkMEMS (micro electro-mechanical systems) resonators can be excited into a defined mechanical oscillation state in different ways. In this work, a concept for the electrostatic actuation of out-of-plane modes is presented, where both electrodes of the transducer element are located in one plane. The fabrication steps for this transducer are reduced to a minimum in order to enable a simplified production. The material used for the resonators are thin layers of polycrystalline silicon and polycrystalline diamond just a few micrometers thin. The excitation possibilities of different modes are tested and compared with different electrode configurations. Both long, narrow bars and wide plate resonators are used as the resonator geometry. Furthermore, this excitation method is compared with thermo-mechanical actuation, which is carried out contactlessly with alaser. In addition to the characterization of material-specific properties of MEMS resonators, the potential application of this transducer in process monitoring at wafer level during the manufacture of MEMS is also discussed.MEMS (micro electro-mechanical systems) Resonatoren in einen definierten, mechanischen Schwingungszustand anzuregen kann auf unterschiedliche Arten erfolgen. In dieser Arbeit wird ein Konzept für die elektrostatische Anregung von out-of plane Moden präsentiert, wobei sich beide Elektroden des Transducerelementes in einer Ebene befinden. Die Fabrikationsschritte für diesen Transducer sind auf ein Minimum reduziert, um eine einfache Herstellung zu ermöglichen. Als Material für die Resonantoren kommen wenige Mikrometer dünne Schichten aus polykristallinem Silizium und polykristallinem Diamant zum Einsatz. Die Anregemöglichkeit von unterschiedlichen Moden wird mit verschiedenen Elektrodenkonfigurationen getestet und verglichen. Als Resonatorgeometrie kommen sowohl lange, schmale Balken als auch breiten Plattenresonatoren zum Einsatz. Des Weiteren erfolgt ein Vergleich dieser Anregungsmethode mit einer thermo-mechanischen Anregung, die kontaktlos mit einem Laser erfolgt. Neben der Charakterisierung von materialspezifischen Eigenschaften von MEMS Resonatoren wird darüber hinaus die potentielle Anwendung dieses Transducers im Prozessmonitoring auf Waferebene während der Herstellung von MEMS diskutiert
Bistable SiC MEMS membranes: the potential for medical applications
Full text linkThe aim of this thesis is to fabricate and characterize silicon carbide coated and hence, biocompatible, bistable membranes, which are controlled by integrated piezoelectric thin film actuators. Due to different membrane configurations and electrical excitation signals it is possible to switch the buckled membrane from one stable state to the other and vice versa. The first part of this work concentrates on the stress behaviour of a-SiC:H thin layers. By coating the top surface of the membranes, biocompatibility to any human tissue is ensured with an electrically insulating material. Silicon carbide as thin layer can be deposited by PECVD in different compositions of silicon and carbon, which has a huge impact on the thickness and layer stress of the resulting thin layer. However, not only the stress behaviour of a-SiC:H layers will be characterised, but also its biocompatibility and the likeliness of CaCo-2 cells attaching to the substrates surface. Epithelial cells of the small intestine were used to characterise the adhesiveness and proliferation on a-SiC:H layers, deposited with different gas flow ratios of silane and methane. Silicon is known as a hydrophile material, while SiC with an increasing amount of carbon gets more hydrophobic, which tends to directly influence the attachment behaviour of cells. The more hydrophile a surface is, the more likely is the attachment of a cell. Living mammalian cells adhere especially well to surfaces, whose electrochemical potential is similar to their own. Since carbon fits this aspect very well, carbon-rich surfaces are preferred with respect to the attachment behaviour of such cells, which stands in contradiction with the hydrophobicity of SiC substrates with high contents of carbon. This work found a balanced composition of silicon and carbon in an a-SiC:H thin layer, where cells adhere best, and compares the stress behaviour of different SiC composed layers with the proliferation and adhesiveness of cells. For this purpose, 50.000 CaCo-2 cells were placed on 13 different processed 6 x 6 mm2 a-SiC:H coated silicon samples. To get a broader result, each of the 13 samples was produced six times, whereby every sample was either pre-treated in an O2-plasma or additionally coated with collagen or Poly-D-Lysine in order to create different growing surroundings, while the same procedures for cell planting, feeding, growing and measuring were applied. After finding the right deposition conditions for a preferably low stress state, the SiC layer got deposited on several different diaphragms, which were produced with diameters from 600 800 m. The fabrication process starts with an SOI-wafer as base material, where different thin film layers were subsequently deposited. These layers were treated with several etching steps, until the final structure of the membrane was created. Through a careful adjustment of the layer stress of all other thin films involved, the diaphragm buckled randomly in one of its two stable states. As piezoelectric layer aluminium nitride (AlN) was used as the material of choice. Secondly, the vibrational behaviour of bistable membranes under the load of an electrical signal was measured, as well as the directly related characteristic resonance frequencies, to predict the switching behaviour of such biocompatible diaphragms in air and different fluids. These measurements were conducted with a Laser-Doppler-Vibrometer, a White-Light- Interferometer, wafer-bow-measurements, contact angle measurements and an oscilloscope. In this thesis, the fabrication process, the measurements approach as well as the results of the switching behaviour of bistable membranes in both air and fluids are described and discussed. Finally, the correlation of living cells growing on substrates of different Si-C compositions and its correlation to the mechanical stress state will be presented
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
- …
