1,720,979 research outputs found
Synthesis and characterization of plasmon resonant gold nanoparticles and graphene for photovoltaics
No full textHere we discuss the use in solar cells of graphene grown by chemical vapor deposition (CVD) and of plasmonic gold nanoparticles (Au NPs) deposited by sputtering. The Au NPs have been coupled with a-Si heterojunction solar cells, with an organic active layer used in organic photovoltaics, and with graphene. Extensive characterization of those three systems by the optical technique of spectroscopic ellipsometry, which is suitable to monitor and analyze the plasmon resonance of the Au NPs, by the microstructural technique of Raman spectroscopy, which is suitable to analyze graphene properties and doping, and by atomic force microscopy has been carried out. Those techniques highlighted interactions between Au NPs and silicon, polymer and graphene, which lead to variation in the plasmon resonance of Au NPs and consequently in the characteristics of the Au NPs/Si, Au NPs/polymer and Au NPs/graphene hybrids. Specifically, we found that an optimal size and density of Au NPs are able to enhance the efficiency of c-Si/a-Si heterojunction solar cells and that exceeding with Au NPs size and density causes device shortcut because of interface interdiffusion between silicon and gold. To discuss organic photovoltaics, Au NPs have been combined with an electro-donating conjugated polymer, the poly[1,4bis(2-thienyl)-2,5-bis-(2-ethyl-hexyloxyphenylenes)]. We found that there is a strong correlation between the thickness and morphology of the organic active layer, which affects the energy and amplitude of the Au NPs plasmon resonance. Finally, Au NPs have been deposited on graphene. We found that Au NPs show the plasmon resonance in the region where graphene is transparent and also yield p-type doping of graphene decreasing its sheet resistance. © 2012 Elsevier B.V. All rights reserved
Defect healing and doping of CVD graphene by thermal sulfurization
No full textCVD graphene layers are intrinsically polycrystalline; depending on grain size, their structure at the atomic level is scarcely free of defects, which affects the properties of graphene. On the one hand, atomic-scale defects act as scattering centers and lead to a loss of carrier mobility. On the other hand, structural disorder at grain boundaries provides additional resistance in series that affects material conductivity. Graphene chemical functionalization has been demonstrated to be an effective way to improve its conductivity mainly by increasing carrier concentration. The present study reports the healing effects of sulfur doping on the electrical transport properties of single-layer CVD graphene. A post-growth thermal sulfurization process operating at 250 degrees C is applied on single layers of graphene on Corning-glass and Si/SiO2 substrates. XPS and Raman analyses reveal the covalent attachment of sulfur atoms in graphene carbon lattice without creating new C-sp3 defects. Measurements of transport properties show a significant improvement in hole mobility as revealed by Hall measurements and related material conductivity. Typically, Hall mobility values as high as 2500 cm2 V-1 s-1 and sheet resistance as low as 400 Ohm per square are measured on single-layer sulfurized graphene.Selective healing action of morphological defects in CVD graphene by sulfur leaves unchanged chemical defects that are potentially useful for subsequent chemical functionalization
Chemically functionalized Eggs capsules of Sea Snail (ess) banded dye-murex for bioremediation applications
Get PDFamong materials proposed in literature to remediate the environment, biohybrid composites at the interface between material science, chemistry and biology are the most promising. In this paper, we first contemplate the use of porous capsules, released by marine murex snails after eggs hatching, as a natural matrix capable of adsorbing organic pollutants. This study starts to investigate chemical and morphological features of this envisaging, unexplored protein material. Then, the chemical topography of egg capsules has been potentiated via a surface decoration with the polyphenol gallic acid, leading to enhance the bioremediation potential of the final biohybrid material. This moiety helped to give a huge activation of the adsorption towards a specific organic pollutant: the drug Tetracycline. The bioorganic methodology begins with bioconjugation via direct targeting of the exposed Lysine residues with polyphenol moieties. The material was morphologically investigated via high-resolution X-ray micro-computed tomography (HR X-ray μ-CT), and characterized using Raman spectroscopy, Fourier Transformed Infrared-attenuated total reflectance (FTIR-ATR), micro-IR, elemental, and BET analysis, after the bioorganic decoration. For the in vitro environmental remediation test, Tetracycline was chosen as a model drug molecule, and the specific adsorption was tested concerning the mass of the investigated material, different pH conditions (considering limit values), till evaluating the recycle of the material. The functionalization efficiently sparked the properties of the starting material, leading to an increase in the biosorption of the model urban pharmaceutical pollutant Tetracycline. Compared to the natural material, the functionalized matrix showed a sorbing capacity 12.5 times higher, leading to the sorption of about 25 mmol of Tetracycline per g of sorbent. In addition, the functionalized material remained active up to 5 sorption cycles. This outcome represents an achievement made from the combination of natural materials and Nature inspired molecular moieties to act as efficient platforms for self-cleaning, leading to environmental remediation
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
Direct epitaxial CVD synthesis of tungsten disulfide on epitaxial and CVD graphene
No full textThe direct chemical vapor deposition of WS2 by W(CO)(6) and elemental sulfur as precursors onto epitaxial-graphene on SiC and CVD-graphene transferred on SiO2/Si substrate is presented. This methodology allows the epitaxial growth of continuous WS2 films with a homogeneous and narrow photoluminescence peak without inducing stress or structural defects in the graphene substrates. The control of the WS2 growth dynamics for providing the localized sulfide deposition by tuning the surface energy of the graphene substrates is also demonstrated. This growth methodology opens the way towards the direct bottom-up fabrication of devices based on TMDCs/graphene van der Waals heterostructures
Structural, optical, and electrical characterization of ZnO and Al-doped ZnO thin films deposited by MOCVD
No full textA novel approach is used to deposit transparent Al-doped zinc oxide (AZO) films by metal-organic (MO) CVD using a Zn/Al safe, friendly to use, easily to handle, multimetal, liquid precursor source. Films are highly crystalline, (002) textured, and exhibit good transparency in the visible region (90%). The effects of Al doping on morphological, optical, and electrical performances are scrutinized. Al doping causes an energy gap (Eg) blue shift and a slight decrease in refractive index. Moreover, it favors sizeable changes in grain size and a surface integrity that are responsible for a reduced carrier mobility. Nevertheless, a minimum resistivity value of 5 × 10-2Ω cm is obtained for thin (∼150nm) AZO films. Time resolved photoluminescence (TRPL) confirms the high crystal quality of deposited films. All features render present AZO films well suited for transparent conductive oxide (TCO) applications and suggest a great potential for the proposed fabrication method. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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
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