1,720,963 research outputs found
Coexistence of the Cu3Au type ordered structure and the fine modulation in CdxZn1-xTe epilayers grown on GaAs substrates
No full textSelected-area electron diffraction pattern (SADP) and transmission electron microscopy (TEM) measurements were carried out to investigate the spontaneously ordered structure in CdxZn1-xTe epitaxial layers grown on (001) GaAs substrates. The SADP showed superstructure reflections with symmetrical intensity, and the high-resolution TEM (HRTEM) image showed doublet periodicity in the contrast of the {100} and {110} lattice planes. The results of the SADP and HRTEM measurements showed that Cu3Au type ordered structures were formed in the CdxZn1-xTe epitaxial layers. The dark-field TEM image showed that the size of the Cu3Au type ordered domains with a rectangular-like shape was approximately 15similar to30 nm thick, with widths ranging from 30 to 200 nm. Fine modulations in the ordered domains were also observed. These results provide important information on the microstructural properties for enhancing the efficiencies of CdxZn1-xTe-based optoelectronic devices operating at the blue-green region of the spectrum. (C) 2002 American Institute of Physics
CuPt-type ordering and ordered domains in CdxZn1-xTe epilayers grown on ZnTe buffer layers
No full textWe have studied ordering and ordered domains in CdxZn1-x Te grown molecular beam epitaxy on ZnTe buffer layer. The composition of CdxZn1-xTe films films was determined by X-ray diffraction patterns using Vegard's law. Selected area diffraction patterns and transition in order to investigate ordered domains in CdxZn1-xTe thin films. The strong contrast modulations along the [110] direction perpendicular to the growth direction were observed in samples with composition x = 0.15 similar to 0.76. Superstructure reflection spots corresponding to a CuPt type ordering were observed. Ordered domain regions were randomly distributed in CdxZn1-xTe thin films. These results provide important information on the microstructural properties for enhancing efficiencies of devices operating in the blue-green region of the spectrum
Simultaneous existence and atomic arrangement of CuPt-type and CuAu-I type ordered structures near ZnTe/ZnSe heterointerfaces
No full textSelected area electron diffraction pattern and high-resolution transmission electron microscopy measurements on a ZnTe/ZnSe heterointerface grown on a GaAs(001) substrate showed two structures of the CuPtB-type ordering structures, one for each direction of the doublet periodicity on the {111} lattice planes along the [110] axis, and superstructure spots related to CuAu-I-type ordering. Auger electron spectroscopy measurements showed that the Se atoms were interdiffused into the ZnTe thin film and that the diffused Se atoms formed a ZnSexTe1-x layer, which might be related to the coexistence of the two types of ordered structures. The coexisting behavior of the two ordered structures are discussed. The present results can help improve the understanding of the formation mechanism and the coexisting behaviors of the two ordered structure near the ZnTe/ZnSe heterointerface. (C) 2002 American Institute of Physics
Existence and atomic arrangement of the CuPt-type ordered structure near the ZnTe/GaAs heterointerface due to residual impurities
No full textTransmission electron microscopy (TEM) and selected area electron diffraction pattern (SADP) measurements were carried out to investigate the ordered structures near ZnTe/GaAs heterointerfaces, and Auger electron spectroscopy (AES) and secondary ion mass spectroscopy (SIMS) measurements were performed to determine the compositions of the ZnTe/GaAs interfacial layer. The SADP showed two sets of {1/2 1/2 1/2} extra spots with symmetrical intensity, and the corresponding high-resolution TEM image showed doublet periodicity in contrast of the {111} lattice planes. The results of the SADP and the high-resolution TEM measurements showed that a CuPt-type ordered (Cd, Zn)Te structure was observed near the ZnTe/GaAs heterointerface, and the AES and SIMS results showed that the ordered structure was formed due to the diffusion of Cd atoms into the ZnTe layer. Two variants, one for each direction of the doublet periodicity on the {111} lattice, were observed in the ordering, and each variant had its own domain structure with a similar probability. The formation of the CuPt-type ordered structure near the ZnTe/GaAs heterointerface originated from both the existence of the Cd residual impurities during the initial growth stage of the ZnTe epilayer and the strain relaxation of the ZnTe epilayer. These results can help to improve the understanding of the microstructural properties of the ZnTe/GaAs heterointerface. (C) 2001 American Institute of Physics
Dependence of the InAs size distribution on the growth times for vertically stacked InAs/GaAs quantum dots
No full textVertically stacked InAs/GaAs quantum dots (QDs) were grown on (001) GaAs substrates by using molecular beam epitaxy (MBE). The dependence of the InAs quantum-dot size distribution on the growth time of InAs/GaAs QDs was investigated by using atomic force microscopy (AFM), transmission electron microscopy (TEM), and photoluminescence (PL) measurements. AFM and TEM images showed that the size of the QDs increased with increasing number of stacked layers when the growth time of the InAs QDs was held constant. However, the size distribution uniformity of the QDs was improved when the deposition time of the InAs QDs gradually decreased while the number of stacked layers increased. These results can help improve understanding of how to control the sizes of the QDs in InAs/GaAs QD arrays
Microstructural and optical properties of InAs/GaAs quantum dots embedded in modulation-doped AlxGa1-xAs/GaAs heterostructures
No full textThe microstructural and the optical properties of InAs/GaAs quantum-dot (QD) arrays inserted into undoped GaAs barriers embedded in an AlxGa1-xAs/GaAs were investigated by using transmission electron microscopy (TEM) and photoluminescence (PL) measurements. The TEM images and the selected-area electron diffraction patterns showed that vertically stacked InAs QD self-assembled arrays were embedded in the GaAs barriers. The temperature-dependent PL spectra showed that the peak corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole band of the InAs QDs shifted to lower energy with increasing temperature. The PL intensity of the InAs dots was significantly enhanced by the modulation-doped AlxGa1-xAs/GaAs heterostructure, and the thermal activation energy of the InAs dots was decreased by the addition of the modulation-doped AlxGa1-xAs/GaAs heterostructure. The present results can help to improve the understanding of the microstructural and the optical properties in InAs QD arrays inserted into GaAs barriers embedded in a modulation-doped AlxGa1-xAs/GaAs heterostructure. (C) 2002 American Institute of Physics
Coexisting phenomena of the CuPt-type and the Cu3Au-type ordered structures near ZnTe/ZnSe heterointerfaces in ZnxCd1-xTe/ZnSySe1-y quantum wells
No full textTransmission electron microscopy (TEM) measurements were carried out to investigate the ordered structures near the ZnTe/ZnSe heterointerfaces in ZnxCd1-xTe/ZnSySe1-y quantum wells. The high-resolution TEM micrographs and selective-area electron-diffraction patterns showed a CuPt-type ordered structure and a Cu3Au-type ordered structure near the ZnTe/ZnSe heterointerfaces in ZnxCd1-yTe/ZnSySe1-y quantum wells. The present results can help improve understanding for the appli cation of ZnxCd1-xTe/ZnSySe1-y quantum wells in optoelectronic devices in the blue-green spectral region. (C) 2001 Elsevier Science Ltd. All rights reserved
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
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