1,721,002 research outputs found
Unusually Large Franz-Keldysh Oscillations at Ultraviolet Wavelengths in Single-Walled Carbon Nanotubes
No full textWe report large electroabsorption susceptibilities in the ultraviolet region for single-walled carbon nanotubes (SWNT) supported on quartz that are approximately 10[superscript 3] larger than the highest values reported to date for any system. The oscillatory behavior is described using a convolution of Airy functions in photon energy ascribing the effect to Franz-Keldysh oscillations. The metallic and semiconducting SWNT composition is varied, and it is shown that the confinement energy correlates with the average band gap for semiconducting SWNT in the film. The large susceptibilities arise from a subpercolated network of metallic SWNT that enhances the local electric field
Complementary p- and n-Type Doping using Polymer Electrolyte Gates for Low-Power Graphene Inverters
No full textGraphene has extensively attracted great interest to replace Si-based electronics due to its outstanding electrical properties. However, ambipolar characteristics of graphene field-effect transistors (FETs) and low on/off current ratio due to the absence of bandgap in graphene are unfavorable for logic gates. In addition, conventional back-gated structure using SiO2 as a dielectric has a high operating voltage. To overcome this problem, several researchers have used top-gated device structure with high-k dielectrics. However, the use of high-k materials requires expensive and complex processes. In this regard, polymer electrolyte gating was successfully demonstrated in carbon nanotube and graphene FETs. Here, we report a low-power unipolar p- and n-type graphene FETs by using polymer electrolytes. For p- or n-type conduction in graphene, we selected a surface charge transfer doping method by using poly(ethyleneimine) (PEI) and poly(acrylic acid) (PAA), respectively. Lithium perchlorate (LiClO4) known as a salt for electrolyte was added in PEI or PAA matrix to obtain high gate efficiency. We demonstrated the low-power graphene inverter with polymer electrolyte gates, which is compatible with the CMOS technologies. The maximum voltage gain is 1.11 at VDD = 1 V. This value is ~80 times higher than that of back-gated polymer-doped graphene inverter. This demonstration will be useful in the development of low-cost, low-power flexible electronic devices.Maste
Synthesis, characterization, and electrochemical properties of nanostructured materials for enhanced lithium storage properties
No full textThe morphology, porosity, and electronic properties of material play a key role in improving the performance and durability of lithium batteries such as Lithium-ion battery (Li-ion), Lithium-sulfur battery (Li-S), and Lithium metal-air battery (Li-M). Improved lithium storage properties can be obtained through the design of the morphology of active material and carbon support by using a various synthetic method. In this thesis, novel nanostructured materials have been synthesized and characterized as active materials for lithium storage reaction in lithium battery systems. Firstly, α-Fe2O3 hollow spheres in different sizes were successfully synthesized via a glycerol emulsion template method. The sizes of α-Fe2O3 hollow sphere could be easily controlled by adjusting glycerol amount over the Fe precursor during hydrothermal synthesis process. Thin carbon layer was subsequently coated on the surface of α-Fe2O3 hollow spheres via a hydrothermal treatment with glucose for the carbonization process. In which, the carbon phases could serve as a conductive layer for the efficient charge transfer, but also as a buffer layer for the accommodation of volume vibration of the electrode material during cycling. The stability and cycling performance were also significantly improved by the presence of carbon layer, indicating that the C/α-Fe2O3 hollow sphere could be a promising metal oxide anode material for the lithium-ion batteries. Secondly, an anode material system of Co3O4 nanowires composited with reduced graphene oxide (Co3O4 NWs/rGO) and protected by N-doped carbon layer (Co3O4 NWs/rGO@NC) was prepared. The N-doped carbon layer could serve as stress relief matter to reduce volume changes of the Co3O4 NWs/rGO during repeated charge/discharge cycles, and also enhance the reaction kinetics as a highly conductive layer between the Co3O4 NWs and electrolyte. The Co3O4 NWs/rGO@NC electrode delivered a high discharge capacity of ca. 995 mAh g-1 at 0.1 C after 65 cycles, and showed a much better rate performance of 428 mAh g-1 even at a high current rate of 5 C as compared to those of Co3O4 NWs/rGO electrode (203 mAh g-1). The demonstrated electrochemical properties suggested that the N-doped carbon coating on the composite of Co3O4 NWs and rGO could significantly enhance the durability and rate capability of the anode material for high performance lithium-ion batteries. Lastly, novel three-dimensional (3D) honeycomb-like N-doped carbon nanowebs (HCNs) have been synthesized through a facile aqueous solution route for use as a cathode material in lithium-sulfur batteries. The Li2S@HCNs cathode delivers a high discharge capacity of ca. 815 mAh g-1 after 65 cycles at 0.1 C, along with a superior rate capacity of ca. 568 mAh g-1 even at 2 C. The outstanding electrochemical rate performance is ascribed to their unique 3D honeycomb-like nanoweb structure, consisting of nanowires derived from polypyrrole. These properties greatly enhance the electrochemical reaction kinetics by providing efficient electron pathways and hollow channels for electrolyte transport. Nitrogen doping in the carbon nanowebs also considerably improves the chemisorption properties by tuning affinity between sulfur and oxygen functional groups on the carbon framework. The simple synthesis strategy and the resulting unique electrode structure could present a new avenue in nanostructure research for high performance lithium-sulfur batteries.Docto
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
Combined effects of shape and doping on piezoelectric properties of ZnO nanostructures on graphene
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