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Ordering and manipulation of MoS2 platelets on differently charged micas by atomic force microscopy
No full textAtomic force microscopy (AFM) has been used to investigate how dispersed MoS2 platelets (from colloidal suspensions) deposit onto three natural(Muscovite) mica (001) surfaces. Different platelet arrangements are observed, which are attributed to defects and charging effects of the mica (as well as the concentration of starting colloid). The provenance of the mica influences the self-organisation of the platelets into long tape-like assemblies (South Dakota mica) or individual flakes (Alps mica). Atomic scale imaging of the tapes reveals a distorted octahedral (O-h)-based local structure, different from the trigonal prismatic structure found in the 2H-polytype of annealed MoS2, in agreement with previous structural results on water-dispersed MoS2 platelets. The buckling and susceptibility to stripping of the tapes is ascribed to the presence of a water layer between the substrate mica and MoS2, and after stripping by the tip, the platelets ultimately form small clusters. The ordering of these clusters depends not only on the defect and charge structure of the mica, but also on complex hydration reactions between the H2O layer associated with the MoS2 and K+ ions of the mica. Relatively symmetrical squares may be lifted out of the tapes, supporting the presence of weak bonding between tape and mica. Conversely, Alps and Bihar micas give rise to separate platelets, which are resistent to tip manipulation, which is attributed to hydrophobic interaction between MoS2 platelets and the mica surface
[Fe(en)(3)](2)(Hg2Te9): A novel tellurometalate containing one-dimensional chains of weakly bound zintl anions (Hg2Te9)(4-)
No full text[Fe(en)3]2Hg2Te9, a novel tellurometalate containing a new type of Zintl ion (Hg2Te9)4-, has been synthesized from solvothermal reactions. Single-crystal X-ray diffraction analysis shows that this compounds contains one-dimensional chains of weakly bound (Hg2Te9)4- ions separated by iron tris(ethylenediamine). Not only is [Fe(en)3]2Hg2Te9 the first tellurometalate produced from solvothermal reactions, it is also the first example of an interesting structure containing a Zintl ion and transition metal complex (as counterion) in the same phase
Rb2Hg3Te4: A new layered compound synthesized from solvothermal reactions
No full textA layered mercury telluride, Rb2Hg3Te4, was discovered during an exploration of hydro(solvo)thermal synthesis of tellurides at temperatures somewhat above the boiling point of ethylenediamine. Crystals of Rb2Hg3Te4 were grown from solvothermal reactions using ethylenediamine as a solvent. Single crystal X-ray diffraction analysis shows that this compound belongs to the orthorhombic system, space group Pbcn (No. 60) with lattice parameters a=12.177(2) Angstrom, b=7.245(2) Angstrom, c=14.545(2) Angstrom, and Z=4. The structure contains two-dimensional layers of (2)(infinity)[Hg3Te42-] which are separated by the Rb+ counterions. The interlayer Te-Te distances imply weak van der Waals interactions. Rb2Hg3Te4 is the first two-dimensional mercury telluride prepared by an unconventional low-temperature technique
Site differentiation by synchrotron radiation resonant scattering: Case study of BaZn2Ge2
No full textResonance scattering was applied for the first time to the class of solids with the AB(2)X(2) stoichiometry. A few members of this family seem to violate the developed rules describing the structure-property relationship, and the source of ambiguity is often the experimental determination of the structure itself. As an example, the newly synthesized BaZn2Ge2 can in principle adopt either the ThCr2Si2 or the CaBe2Ge2 type structures, and conventional diffraction techniques do not allow discrimination between the two structure models. The resonance scattering method shows, however, that BaZn2Ge2 crystallizes in the ThCr2Si2 structure (tetragonal I4/mmm; alpha = 4.527(2) Angstrom c = 10.555(3) Angstrom, Z =; 2), in agreement with theoretical analyses
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
Assembly and local structure of MoS2 colloidal platelets on quartz and muscovite mica surfaces
No full textAqueous suspensions of MoS2 colloidal platelets and their assembly after casting on quartz and cleaved muscovite mica (001) surfaces have been investigated by optical spectroscopy and atomic force microscopy (AFM). Optical spectra are consistent with the presence of non-metallic distorted pseudo-octahedral (MoS2)n-based moieties. Features observed between 800-1300 nm in single layers, at low platelet stacking order and when traces of Li+ remain (but not in either 2H-MoS2 or 1T-MoS2) are assigned to transitions from a split d x2,yz,xz Oh MoS2 band to other d levels in a complex (rather than band) formulation. Differences in optical spectra of platelets on (001) mica and on quartz, both as-cast and after annealing at > 120°C (when the films undergo a phase transition) are ascribed to differences in platelet assembly involving water bilayers (H2O vibrational combination bands are observed in mica but not in quartz). AFM micro-imaging shows MoS2 colloidal platelets assemble randomly, including as almost vertical packets (as on γ-alumina) on quartz over a wide concentration range. Instead, on mica (001) surfaces the cast assembly orders as a network of laterally developed tape-like structures (albeit with stacking faults). Single tapes are 200-300 nm wide, ca. 4 nm high and > 3 μm long and probably arise via side-on platelet fixture involving a complex platelet parking mechanism. It is suggested that horizontal dispersion and re-stacking of the platelets is directed by the charged mica surface. After annealing at 200°C, MoS2 platelets on mica give single layers of minimum thickness 6.2 ± 0.2 Å, having a0 = 3.2 Å (by AFM) as expected for a 2H-MoS2 structure. [MoS2 films prepared by reaction of MoO3 or MoCl5 + H2S via hard methods (CVD, sputtering, etc.) give vertically-oriented MoS2 platelets.] Colloidal MoS2 cast on GaAs(111) and Si(111) surfaces gives rise to a micro-crystalline environment via platelet scission and surface reactions. At the limit, annealing MoS2 plates on both surfaces at 200°C leads to complete disappearance of MoS2 islands due to reaction of S2- with the surface
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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