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  • 1
    Electronic Resource
    Electronic Resource
    Growth-induced shallow acceptor defect and related luminescence effects in molecular beam epitaxial GaAs (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 741-754 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a study of a defect responsible for the "g'' bound exciton line at 1.5112 eV that is frequently detected in photoluminescence spectra of GaAs grown by molecular beam epitaxy (MBE). A direct correlation has been observed between this line and a transition at 1.4946 eV, which is shown to result from a conduction band-to-acceptor recombination involving a shallow, unidentified acceptorlike defect that is labeled "A.'' The activation energy of the defect is 24.8±0.2 meV, about 1.7 meV lower than that of CAs acceptor. Upon hydrogenation the defect is passivated more extensively than any known shallow acceptor species in GaAs. This result is analyzed in terms of a passivation model, from which it can be inferred that the A defect is not due to a simple substitutional Group II impurity on a Ga site. Incorporation of the A defect strongly affects the luminescence properties of the material. An almost complete quenching of the donor-bound exciton lines, profound changes in the line shape and relative intensity of the free exciton recombination, and appearance of a sharp transition of unknown origin at 1.5138 eV were observed with increasing defect concentration. Apparently "donorless'' low temperature exciton recombination spectra are reported for defect-rich p-type MBE GaAs layers with donor concentrations as high as 7×1014 cm−3 and compensation ratios of ∼0.3. The dependence of the defect incorporation on MBE growth parameters is discussed. The feasibility of MBE growth of high purity, nearly shallow defect-free p-type GaAs layers at marginally As-stabilized surface conditions over an about 1–5 μm/h range of deposition rates is demonstrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346779
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  • 2
    Electronic Resource
    Electronic Resource
    Investigation of the thermal dissociation of PH3 and NH3 using quadrupole mass spectrometry (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 8025-8030 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The thermal dissociation of PH3 and NH3 injected through a Ta-based high-pressure gas-injection cell were studied. Using a quadrupole mass spectrometer, the Ta was found to effectively dissociate the PH3 into primarily P2, P4, and H2 molecules with an injector temperature as low as 550 °C. The introduction of NH3 through this same injector resulted in dissociation into N2 and H2 for an injector temperature greater than 900 °C. When NH3 and PH3 were coinjected, again P2, P4, N2, and H2 were the primary molecules produced; however, an additional dimer, PN, was also detected. The PN concentration was maximum at a cell temperature of 700 °C. This dimer was found to be an effective source for introducing nitrogen as an isoelectronic trap in GaP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347447
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of post-growth cooling ambient on acceptor passivation in carbon-doped GaAs grown by metalorganic chemical vapor deposition (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 1248-1250 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The degree of unintentional hydrogen passivation of acceptors in heavily C-doped GaAs (p(approximately-greater-than)1018 cm−3) grown by metalorganic chemical vapor deposition has been found to be a strong function of post-growth cool-down ambient. The carbon concentration in the GaAs and the amount of AsH3 in the cool-down ambient are the most important factors affecting passivation. Carbon acceptors can be reactivated by annealing in N2, then repassivated by heating and re-cooling in an AsH3/H2 or PH3/H2 ambient. Secondary ion mass spectrometry analysis shows that the hydrogen concentration is significantly higher in a C-doped GaAs surface layer which is exposed to the cool-down ambient than in a layer which is buried beneath n-type GaAs. This result is consistent with observations in n-p-n heterojunction bipolar transistor structures, where the fraction of C acceptors passivated in the base region is found to be less than in a single layer grown under identical conditions. Be-doped GaAs grown by gas-source molecular beam epitaxy has also been heated and cooled in AsH3-containing ambients, but no acceptor passivation is detectable by Hall effect measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108748
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  • 4
    Electronic Resource
    Electronic Resource
    p-type InGaAs/InP quantum well infrared photodetector with peak response at 4.55 μm (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3209-3211 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Lattice-matched InGaAs/InP quantum well intersubband photodetectors (QWIPs) have been grown on an InP substrate by gas source molecular beam epitaxy. Detection at 4.55 μm was observed for a narrow well p-type InGaAs QWIP which, when complimented by a high responsivity 8.93 μm n-type InGaAs/InP QWIP, demonstrates the possibility of dual band, monolithically integrated QWIPs on the same InP substrate. Theoretical calculations of the photocurrent spectra are in excellent agreement with the experimental data. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117963
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  • 5
    Electronic Resource
    Electronic Resource
    Deep structure of an Archaean greenstone terrane (1990)
    [s.l.] : Nature Publishing Group
    Nature 344 (1990), S. 327-330 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/344327a0
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  • 6
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    THE AMERICAN AGRICULTURAL PRESS, by A. L. Demaree (Book Review) (1941)
    Brunswick, Me., etc. : Periodicals Archive Online (PAO)
    New England Quarterly. 14:1/4 (1941) 393 
    Details
    ISSN: 0028-4866
    Topics: English, American Studies
    Notes: BOOK REVIEWS
    URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pao:&rft_dat=xri:pao:article:1170-1941-001-00-000059
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  • 7
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    SOME ANCESTORS OF THE EXTENSION COURSE. (1941)
    Brunswick, Me., etc. : Periodicals Archive Online (PAO)
    New England Quarterly. 14:1/4 (1941) 505 
    Details
    ISSN: 0028-4866
    Topics: English, American Studies
    URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pao:&rft_dat=xri:pao:article:1170-1941-001-00-000081
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  • 8
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    AGAINST THE CURRENT: THE LIFE OF KARL HEINZEN, 1809-1880, by Carl Wittke. (1945)
    Brunswick, Me., etc. : Periodicals Archive Online (PAO)
    New England Quarterly. 18:1/4 (1945) 282 
    Details
    ISSN: 0028-4866
    Topics: English, American Studies
    Notes: SHORT NOTICES
    URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pao:&rft_dat=xri:pao:article:1170-1945-001-00-000049
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  • 9
    Electronic Resource
    Electronic Resource
    The dynamic behavior of cytoplasmic F-actin in growing hyphae (1993)
    Springer
    Protoplasma 173 (1993), S. 23-34 
    Details
    ISSN: 1615-6102
    Keywords: Tip growth ; Actin ; Rhodamine phalloidin ; Electroporation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A dynamic population of cytoplasmic F-actin was observed with electroporated rhodamine phalloidin (RP) staining in growing hyphae ofSaprolegnia ferax. This central actin population was distinct from the fibrillar peripheral network previously described in chemically fixed hyphae in that it was diffuse, pervaded the entire cytoplasm and was most concentrated in the central cytoplasm 8.4 μm from the tip. The peripheral network did not stain with electroporated RP. The apical concentration of central cytoplasmic actin was only present in growing hyphae and developed prior to tip extension. It co-localized with the polarized distribution of mitochondria and endoplasmic reticulum in the tip, suggesting that it functions in positioning these organelles during tip growth. Within the central actin there was a consistent apical cleft which only occurred in growing hyphae and whose position predicted the direction of tip growth. This cleft was coincident with the known accumulation of apical wall vesicles, suggesting that it is either established by vesicle exclusion of the central actin network or is permeated by a portion of the in vivo unstained peripheral network. Photobleaching studies showed that in both growing and non-growing hyphae, cytoplasmic actin continually and rapidly moved from subapical regions to the tip where it accumulated. It mostly moved forward at the rate of tip growth, while some also left the tip, presumably to populate subapical regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01378859
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  • 10
    Electronic Resource
    Electronic Resource
    Changes in intracellular pH during zoosporogenesis inPhytophthora cinnamomi (1996)
    Springer
    Protoplasma 191 (1996), S. 79-83 
    Details
    ISSN: 1615-6102
    Keywords: Cytoplasmic pH ; pH-sensitive carboxyfluorescein ; Zoospore ; Fungus ; Intracellular alkalinisation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Changes in intracellular pH (pHi) have been examined during zoosporogenesis inPhytophthora cinnamomi in order to elucidate the molecular mechanisms that bring about initiation of the orderly cleavage of the sporangium. By microinjecting a dextranconjugated pH-sensitive fluorescent indicator, 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF dextran), and using fluorescence ratio image analysis, the pHi of a sporangium was monitored throughout the process of zoosporogenesis. The pHi of mature sporangia was found to remain constant at pH 6.84 ± 0.05 (mean ± SE, n=6) at room temperature (24 °C), but increased to 7.04 ± 0.04 (p 〈 0.001) during a 20 min cold treatment at 19 °C. As the process of zoosporogenesis proceeded, the increased level of pHi was maintained for 30–40 min after initiation of the cold shock. Zoosporogenesis was blocked when the pHi of the sporangium was held constant by microinjecting with 10 mM HEPES buffer (pH 7.0) before cytoplasmic cleavage was induced by a cold shock. In contrast, no inhibitory effect was observed when sporangia were microinjected with HEPES buffer after the cold shock. These results indicate that initiation of cytoplasmic cleavage requires a rise in pHi.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01280827
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