1,720,958 research outputs found
Gold nanosponges (AuNS): a versatile nanostructure for surface-enhanced Raman spectroscopic detection of small molecules and biomolecules
No full textPrepared by simple pour and mix chemistry, gold nanosponges (AuNS) are versatile structures for surface-enhanced Raman spectroscopy (SERS). An investigation into the enhancement is performed by relating the nanostructure's morphology to the SERS signal. The potential of the AuNS in SERS-based molecular and biomolecular detection is introduced
Tip-Enhanced Raman Spectroscopy of Self-Assembled Thiolated Monolayers on Flat Gold Nanoplates Using Gaussian-Transverse and Radially Polarized Excitations
No full textTip-enhanced Raman spectroscopy (TERS) is a highly sensitive spectroscopic technique that combines the spatial resolution of scanning near-field techniques with the chemical specificity of vibrational spectroscopy. TERS is based on the excitation of the localized surface plasmon resonance at the apex of an AFM metallized tip, producing a confined and enhanced electromagnetic field. Due to the inherent local nature of TERS and its confinement in the optical near-field of the object, TERS measurements can also be used to probe monolayers adsorbed onto surfaces providing better surface specificity in addition to higher spatial resolution. We implement here gap-mode TERS using gold nanoplates functionalized with thiolated reference molecules such as alkoxy substituted azobenzene thiol and 4-nitrothiophenol. The monolayer is probed with a silver coated AFM tip in order to obtain the largest electromagnetic field enhancement from the surface plasmon localized between the silver tip and the functionalized gold surface. More specifically, we have measured the TERS spectra of the self-assembled monolayer on gold using 532 nm excitation that is linearly (Gaussian-transverse TEM00) and radially polarized. We report the nature of the collected TERS spectra for the thiolated molecules (azobenzene thiol and nitrothiophenol) that appear to be dependent on the polarization of the excitation light at the tip/substrate interface
High-resolution Raman imaging of bundles of single-walled carbon nanotubes by tip-enhanced Raman spectroscopy
No full textBundles of single-walled carbon nanotubes (SWCNTs) prepared by plasma torch method and further purified, are deposited over a glass coverslip to estimate the spatial resolution of tip-enhanced Raman spectroscopy measurements. For this purpose, near-field Raman maps and spectra of isolated bundles of carbon nanotubes are collected using optimized experimental conditions such as a tightly focused beam using a 1.4 numerical aperture oil immersion microscope objective and a gold coated atomic force microscope probe illuminated by a radially polarized 632.8 nm wavelength to selectively excite the localized surface plasmon confined at the extremity of the tip. The near-field nature of the collected Raman signals is evaluated through measuring the decay of the Raman signal with respect to the tip-sample separation
Electrochemistry of robust gold nanoparticle-glassy carbon hybrids generated using a patternable photochemical approach
No full textPhotolysis of diazirine modified small (3.9 +/- 0.9 nm) gold nanoparticles (AuNP) generates a reactive interfacial carbene that then reacts via an insertion reaction to covalently attach the AuNP onto glassy carbon (GC) electrodes. This yields GC surfaces that are densely and homogeneously functionalized with AuNP. The AuNP hybrid glassy carbon electrode has been characterised by atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The system is found to be robust to physical and electrochemical stresses due to the covalent bond between the AuNP and the surface formed through the carbene insertion reaction. The conductivity of the AuNP functionalized GC electrode is found to be similar to clean GC, and the AuNP serve to switch on electron transfer. The AuNP can be oxidatively desorbed from the electrode at surprisingly low potential (0.99 V). This yields a monolayer of insulator thiol/thiolate ligands that previously anchored the AuNP to the GC, which gives an interesting switch off effect of the electron transfer. We demonstrate that because the method is photoinitiated this methodology allows for spatial control and the AuNP, which can be photopatterned onto GC surfaces easily. The high stability, the good electrical conductivity, the facility of making patterns, and the ability to tune the physical and chemical properties of AuNP through its ligands, make this new functionalization method suitable for the development of sensors and electronic devices
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
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