1,720,988 research outputs found
Understanding spectroscopic phonon-assisted defect features in CVD grown 3C-SiC/Si(1 0 0) by modeling and simulation
No full textSymmetry adapted impurity modes in as grown n-type GaP:X and GaSb:X (X = S, Se and Te)
No full textA comprehensive average-t-matrix Green\u27s function (ATM-GF) theory is used, in the framework of a realistic rigid-ion-model, to simulate the symmetry induced vibrational modes of different defect centers in GaP:X and GaSb:X (X = S, Se and Te) crystals. Explicit calculations are performed for isolated 32SP+ (34SP+) defects, nearest-neighbor 32SP+-CuGa2- (34SP+-CuGa2-) pairs in GaP, and next-nearest-neighbor complex 32SSb+-GaSb2-(34SSb+-GaSb2-) center in GaSb by using apposite perturbation (P↔) and Green\u27s function (G↔o) matrix elements. For the isolated closest mass isoelectronic and charged (donor and acceptor) defects, the study has provided a convincing empirical relationship associating the increase or decrease of force constant change between impurity-host atoms to the increase or decrease of covalency of impurity-host bond. The rule has accurately predicted the observed isotopic shifts of local vibrational and/or gap modes of isolated impurities and offered modes for different “donor–acceptor” pairs of reduced symmetry. We feel that the ATM-GF method will play a significant role identifying the site selectivity of defects for estimating their mode frequencies in the technologically important semiconductor materials
Composition-Dependent Structural, Phonon, and Thermodynamical Characteristics of Zinc-Blende BeZnO
No full textBoth ZnO and BeO semiconductors crystallize in the hexagonal wurtzite (wz), cubic rock salt (rs), and zinc-blende (zb) phases, depending upon their growth conditions. Low-dimensional heterostructures ZnO/BexZn1-xO and BexZn1-xO ternary alloy-based devices have recently gained substantial interest to design/improve the operations of highly efficient and flexible nano- and micro-electronics. Attempts are being made to engineer different electronic devices to cover light emission over a wide range of wavelengths to meet the growing industrial needs in photonics, energy harvesting, and biomedical applications. For zb materials, both experimental and theoretical studies of lattice dynamics ωj(q→)
have played crucial roles for understanding their optical and electronic properties. Except for zb ZnO, inelastic neutron scattering measurement of ωj(q→)
for BeO is still lacking. For the BexZn1-xO ternary alloys, no experimental and/or theoretical studies exist for comprehending their structural, vibrational, and thermodynamical traits (e.g., Debye temperature ΘD(T);
specific heat Cv(T))
. By adopting a realistic rigid-ion model, we have meticulously simulated the results of lattice dynamics, and thermodynamic properties for both the binary zb ZnO, BeO and ternary BexZn1-xO alloys. The theoretical results are compared/contrasted against the limited experimental data and/or ab initio calculations. We strongly feel that the phonon/thermodynamic features reported here will encourage spectroscopists to perform similar measurements and check our theoretical conjectures
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
Impact of stacking sequence on the tight-binding electronic band structures of (BeX)m/(ZnX)m, X = S, Se and Te superlattices
No full textBy using a semi-empirical tight-binding sp3s* method, the results of comprehensive electronic band structures are reported for the zinc-blende beryllium- and zinc-chalcogenides (BeX and ZnX; X = S, Se, Te) as well as their representative (BeX)m/(ZnX)m (0 0 1) superlattices (SLs). For the bulk BeX and ZnX materials, the simulations of energy band dispersions Ejk→ have offered the correct band gaps in very good agreement with the first-principles calculations. The band-mixing effect through the interfaces of two constituent compounds (BeX indirect- and ZnX direct-band gap) has played an important role for determining the overall band lineup in the (BeX)m /(ZnX)m SLs over the entire Brillouin zone. Based on the quantum confinement effects, the impact of stacking sequence m ≤ 10 is carefully examined for assessing the band structures of SLs. The results have clearly revealed that the nature of energy bandgaps is quite sensitive to the choice of well (BeX) and barrier (ZnX) layer thickness. Obviously, this intuition has implied that controlling m to achieve direct bandgaps in novel (BeX)m/(ZnX)m SLs is probably an effective way of assessing their potential use in technologically important optoelectronic devices
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
Comparative study of interfacial strain dependent phonon localization in the beryllium-zinc chalcogenide superlattices
No full textA comprehensive study is reported for the novel (BeX)m/(ZnX)n (X = S, Se and Te) superlattices (SLs) to assess their acoustic and optical phonon characteristics. The use of an elastic continuum model has offered implicit equations for assessing folded acoustic modes (FAMs) and their splitting at the center and at the edge of mini-Brillouin zone. In (BeTe)m/(ZnSe)n SLs grown with Zn–Te interfaces, the Raman spectroscopy measurements revealed well resolved first order doublet and frequency shifts which compared favorably well with the simulated results. For the graded (BeX)10-Δ/(Be0.5Zn0.5X)Δ/(ZnX)10-Δ/(Be0.5Zn0.5X)Δ SLs, we have adopted a modified linear-chain model by meticulously integrating the effects of alloying and interfacial layer thickness Δ to study phonon dispersions (ωj(q→SL)) and Raman intensity profiles. By changing Δ from 1 to 3 monolayers, our study has distinctly revealed (a) a dramatic increase in the Raman scattering intensity of ZnX quasi-confined optical modes (Q-COMs) with slight upward shifts in frequencies, (b) an insignificant change in Raman intensity lines of BeX confined optical modes (COMs) with appreciable downward shifts (up to ∼ - 113 cm−1) in frequencies, and (c) trivial modifications in the FAMs. These atypical effects noticed in the optical modes are attributed to the localization of atomic displacements at the BeX-ZnX interfacial region. The variations of phonon mode frequencies and enhancement of Raman lines for the ZnX Q-COMs can be used as vital tools for establishing interfacial structures in graded SLs of technological importance
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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