1,720,976 research outputs found
Structural and dynamical properties of Bridgman-grown CdSe[subscript x]Te[subscript 1−x] (0<x≤0.35) ternary alloys
No full textMeasurements of the Raman scattering and extended x-ray-absorption fine-structure (EXAFS) spectroscopy are reported on a series of Bridgman-grown zinc-blende CdTe[subscript 1−x]Se[subscript x] (0.35 ≥ x > 0.05) ternary alloys to empathize their lattice dynamical and structural properties. Low-temperature Raman spectra have revealed the classic CdTe-like (TO[subscript 1], LO[subscript 1]) and CdSe-like (TO[subscript 2], LO[subscript 2]) pairs of optical phonons. The composition-dependent peak positions of the LO[subscript 2] modes exhibited shifts towards the higher-energy side, while those of the LO[subscript 1] phonon frequencies have unveiled the slight redshifts. Detailed analyses of EXAFS data by using the first-principles bond orbital model have enabled us to estimate both the lattice relaxations and nearest-neighbor radial force constants around the Se/Te atoms in the CdTe/CdSe matrix. These results are methodically integrated in the “average t-matrix” formalism within the Green's-function theory for defining the impurity perturbations to comprehend the composition-dependent optical phonons in CdTe[subscript 1−x]Se[subscript x] alloys. Based on our comprehensive calculations of impurity modes in the low-composition regime x → 0, we have assigned the weak phonon feature observed near ∼175 cm[superscript −1] in the low-temperature infrared reflectivity spectroscopy study to a Se[subscript Te] localized vibrational mode
Infrared reflectance and transmission spectra in II-VI alloys and superlattices
No full textRoom temperature measurements of the far-infrared (FIR) reflectance spectra are reported for the polar optical phonons in a series of bulk Cd[subscript x]Zn[subscript 1−x]Te (0 ≤ x ≤ 1) and CdSe[subscript x]Te[subscript 1−x] (0 < x ≤ 0.35) crystals grown by Bridgman technique. The composition-dependent spectra exhibited many fundamental aspects of lattice vibrations, while the results of long-wavelength optical modes for the end member binary compounds displayed phonon values in good agreement with the existing inelastic neutron scattering and/or Raman spectroscopy data. Using a standard methodology of multilayer optics with effective-medium dielectric tensors, we simulated the FIR transmission and reflectivity spectra at oblique incidence (Berreman's effect) in many II-VI free-standing thin films, epilayers and superlattices. Berreman's approach provided us with a strong basis for analyzing the infrared experimental data and offered an effective means of estimating the zone-center transverse and longitudinal optical (ω[subscript TO], ω[subscript LO]) phonon frequencies in polar-semiconductor thin films and heterostructure materials of increasing technological importance.Indiana University of Pennsylvania. Graduate School (Innovation Grant)National Science Council (China) (Grant No. NSC 98-2221-E-002-015-MY3)National Science Council (China) (Grant No. NSC 98-3114-E-005-002-CC2
Amorphous InSb and InAs[subscript 0.3]Sb[subscript 0.7] for long wavelength infrared detection
No full textThe structural, electronic, and optical properties of amorphous InSb and InAs[subscript 0.3]Sb[subscript 0.7] films deposited on Corning glass, Al[subscript 2]O[subscript 3] CdZnTe, SiO[subscript 2]-Si, and CaF2 substrates by Radio Frequency (RF) magnetron sputtering have been studied as they relate to Mid and Long Wavelength Infrared (MWIR and LWIR) detection. Depositions at elevated substrate temperature and pressure of <10mTorr Ar show an emergence of crystalline grains with strong X-ray diffraction peaks at the (111) and (220) orientations. Electronically the amorphous InSb and InAs[subscript 0.3]Sb[subscript 0.7] films deposited at 300K show hopping conduction with resistance in InSb ranging from 44 to 1.1E8 Ω-cm at 300K and 84K respectively. Optical analysis using Fourier transform infrared spectroscopy (FTIR) show the absorption of these films has an absorption tail, the equation of which differing activation energies in InSb and InAs0.3Sb0.7. Amorphous InSb and InAs[subscript 0.3]Sb[subscript 0.7] films showed thermal responsivity in excess of 100V/W for 6μm thick films held at 233K. The maxima and minima of the responsivity are shown to correspond to the interference fringes in the film. The response is highly substrate dependent and compares favorably to other thermal detectors
Synchrotron radiation x-ray absorption fine-structure and Raman studies on CdZnTe ternary alloys
No full textThe synchrotron radiation (SR) X-ray absorption fine-structure spectroscopy (XAFS) technology has been employed to obtained Zn K-edge absorption spectra for Cd1[subscript 1-x]Zn[subscript x]Te alloy with x = 0.03, 0.10, 0.20, 0.30, 0.40, 0.50 and 1.00. Their Fourier transform spectra were analyzed, which have shown a bimodal distribution of bond lengths, suggesting distortion of the Te sub-lattice, so that the linear interpolation is true only in an approximate sense. Synthetic CdZnTe crystals can be used for the room temperature-based detection of gamma radiation. The radiation detection properties of CZT crystals vary widely. A common defect found in most high-quality CZT crystals is Te secondary phases, often located along grain boundaries. The secondary phases can be both large inclusions (>50 µm) and smaller precipitates (<50 µm). The Te secondary phases distributed throughout the crystal can cause changes to the detector leakage current, resulting in decreased radiation spectrometer performance. This set of Cd1[subscript 1-x]Zn[subscript x]Te crystals were also measured by Raman scattering at room temperature. The two observed peaks at about 125 and 145 cm[superscript -1] which can be assigned to Te A[subscript 1] and E phonon mode, respectively. The induced damage on the crystal surfaces by Raman laser has been discussed. It is suggested that in the case of highly Zn doping CdZnTe crystals, the ZnTe bond were broken by laser exposing and then free Te atoms are migrating to these heated areas which cause Te precipitate. Further, the results of the soft X-ray measurements have been also presented and this part of the experimental data needs to do more penetrating analysis in the future
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
Far-IR reflectance spectra analysis of CdZnTe and related materials
No full textFar-infrared (FIR) reflectance spectroscopy has been employed to study the optical properties for a series of bulk CdZnxTe1-x and CdSexTe1-x wafers. The zone-centre optical phonons for the ternary alloys show a variety of behavior patterns: they exhibit a "one-mode", "two-mode" or "intermediate-mode" behavior depending on the vibration characteristics of the end binary members. The CdSeTe called CST were found to be single-crystal with the zincblende structure. These four samples labeled with CST5, CST15, CST25, and CST35, which correspond with the composition of Se, 5%, 15%, 25%, 35%, respectively. The intensity of CdTe-like TO band decays with x increasing, and the peak position increases from 140 cm[superscript -1] to 145 cm[superscript -1]. In the other hand, the intensity of CdSe-like TO band grows with x increasing, and the peak position of CdSe-like TO band increases from 174 cm[superscript -1] to 181 cm[superscript -1]. We use the model of dielectric function and using Least-Square fit to find the optical and transport parameters. By the infrared spectra analysis, we found the conductivity of CdZn[subscript x]Te[subscript 1-x] increase with increasing of x value and the conductivity of CdZn[subscript x]Te[subscript 1-x] decrease with increasing of x value
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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