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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 5318-5324 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Radiative and compositional properties of spark-processed silicon are studied by photoluminescence and x-ray photoelectron spectroscopy measurements. Spark processing of silicon is performed in different atmospheres composed of nitrogen and oxygen. As a result of the process, room-temperature radiative transitions occur at 2.35 eV and vary in intensity over five orders of magnitude depending on the N2/O2 ratio. After processing in pure nitrogen or pure oxygen, however, the green photoluminescence (PL) is wiped out and weak blue (2.7 eV) or orange (1.9 eV) PL bands, respectively, are discernable. The temperature-dependent features of the 2.35 eV emission are characterized by an intensity increase in conjunction with a red shift of the peak position at lowered temperatures. A cross-sectional study reveals that the green PL is mainly generated in a near-surface layer having a chemical composition close to SiO2 and a nitrogen concentration below 1 at. %. Nearly no PL was observed from a deeper SiO2 layer enriched by silicon clusters and with an increased density of nitrogen (up to 7 at. %). The findings do not support a quantum-dot-related PL mechanism in spark-processed silicon. It is proposed that nitrogen additions reduce the density of nonradiative centers introduced by silicon dangling bonds. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 653-656 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: This paper reports on resistance and capacity measurements of ohmic contacts which were deposited on heteroepitaxially grown, Si-doped GaAs layers on Si substrates. It is observed that the process of rapid thermal annealing (RTA) considerably affects the ohmic properties of subsequently deposited contacts. With rising annealing temperature, the electrical resistivity in the GaAs layer and thus, the contact resistance increased essentially. Although the chemical concentration profile of Si dopants is not changed by RTA, the number of electrically active carriers is lowered. Photoluminescence measurements confirm that Si donors on Ga sites perform a site exchange to As vacancies, thereby forming Si acceptors. The extent of this exchange process is considerably enhanced by the presence of a high dislocation density in the heteroepitaxial GaAs films. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2542-2544 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The structure of spark-processed silicon was examined in a comparative study of optical micrographs utilizing ultraviolet laser light and electron beams for excitation. Whereas the photoluminescence (PL) was found to be dominantly generated in granular structures near the surface, the cathodoluminescence (CL) mainly propagates from holes which were created during the preparation process. PL and CL spectra are not identical in their spectral distributions. Low temperature luminescence measurements for both excitation modes reveal a high degree of local disorder. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 347-349 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The kinetics of growth of GaN/(0001) sapphire heteroepitaxial films have been examined in the relatively low substrate temperature range, 560–640 °C, using the reflection high energy electron diffraction (RHEED) specular reflection intensity monitoring technique. In particular, an alternate element exposure method of growth was employed in which Ga and N atoms were supplied separately (rather than simultaneously, as in conventional molecular beam epitaxy) to the substrate with the inclusion of a time delay between successive Ga flux and N flux exposures. We interpret the observed time dependent recovery of the RHEED specular reflection intensity during the time delay phases to be associated with Ga–N surface molecule migration on Ga-terminated surfaces and the activation energy for this migration process was determined to be 1.45±0.25 eV. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have determined that the surface stoichiometry maintained during the first five monolayers of ZnSe epitaxial growth can have a significant influence on the stacking fault concentration in 2 μm thick epilayers. In particular, we have been able to minimize the stacking fault concentration to a level in the 104 cm−2 range (comparable to the stacking fault concentration in the ZnSe substrates used for epitaxy) by appropriate selection of a delay time (∼30 s for a substrate temperature of 300 °C) employed during an alternate element (Zn and Se) exposure phase of growth. The delay time in question is the time elapsed between closing the Se shutter and opening the Zn shutter. We show that the surface stoichiometry (Zn to Se atomic ratio) can be tailored during the delay phase since Se thermal desorption occurs at the growth temperature in a controlled fashion from an initially Se-terminated surface, and, it is postulated that selection of an optimum delay time corresponding to the attainment of a near-stoichiometric surface results in the growth of low stacking fault concentration material. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 2544-2544 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Cambridge : Cambridge University Press
    Journal of Germanic linguistics 10 (1998), S. 297-302 
    ISSN: 1470-5427
    Quelle: Cambridge Journals Digital Archives
    Thema: Germanistik. Niederlandistik. Skandinavistik
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Der Gynäkologe 32 (1999), S. 220-224 
    ISSN: 1433-0393
    Schlagwort(e): Key words Early pregnancy • Pregnancy outcome • Transvaginal ultrasound • Fetal heart rate • First trimester of pregnancy ; Schlüsselwörter Transvaginalsonographie • Frühschwangerschaft • Fehlgeburt • Fetale Herzfrequenz • Erstes Trimenon der Schwangerschaft • Embryo
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Durch den Einsatz der Transvaginalsonographie läßt sich bereits frühzeitig eine Beurteilung der zeitgerechten Schwangerschaftsentwicklung vornehmen. Diese reicht von der Darstellung einer intrauterinen Fruchthöhle, über den ersten Nachweis einer Embryonalanlage, der Dottersackentwicklung bis hin zur embryonalen Herzaktion als Vitalitätsnachweis der bestehenden Gravidität. Des weiteren erlaubt die sonographische Überwachung der Frühschwangerschaft eine Abgrenzung zur gestörten embryonalen Entwicklung. Aufgrund verschiedener Risikokonstellationen wie vaginaler Blutungen, intrauteriner Hämatome, einem erhöhten mütterlichen Alter, dem nicht zeitgerechten Schwangerschaftswachstum oder dem Auftreten einer frühen fetalen Bradykardie läßt sich eine Vorhersage hinsichtlich eines Abortgeschehens treffen.
    Notizen: Summary Transvaginal ultrasound provides an early and accurate technique to assess first trimester pregnancy. Beginning with the demonstration of an intrauterine gestational sac, sonography enables further evaluation of normal pregnancy development, such as identification of the embryo, visualization of the yolk sac, and the presence of fetal cardiac activity as a reassurance of fetal viability. Furthermore it allows closed sonographic monitoring of early intrauterine pregnancy and distinction between normal and abnormal development of pregnancy. A prediction in terms of pregnancy outcome can be made regarding pregnancy complications or specific risks like vaginal bleeding, the demonstration of intrauterine hematoma, advanced maternal age, early growth delay or fetal bradycardia.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Der Gynäkologe 32 (1999), S. 71-72 
    ISSN: 1433-0393
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Douglas Saunders vom “North shore assisted reproductive technology programme, Sidney, Australien” ist der “senior author” des Artikels “Medical and developmental outcome at 1 year for children conceived by intracytoplasmic sperm injection” (Lancet, 1998; 351:1529–1534), der in der letzten Ausgabe von “Für Sie gelesen” wiedergegeben und diskutiert wurde. Es erscheint sehr interessant, daß hier ein Autor die Ergebnisse seiner eigenen Arbeitsgruppe hinterfragt. Da das Thema von großer Wichtigkeit, gerade auch in Deutschland ist, erscheint es sinnvoll, diese “ongoing debate” wiederzugeben.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 51 (1995), S. 210-213 
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
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