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  • 1990-1994  (7)
  • 1994  (4)
  • 1991  (3)
Material
Years
  • 1990-1994  (7)
Year
  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 259-262 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used time-resolved reflection high energy electron diffraction (RHEED) measurements to study anion exchange reactions in molecular beam epitaxy (MBE) grown III-V semiconductors. In the experiment, InAs surfaces are exposed to Sbx fluxes and subsequent changes in the crystals RHEED patterns are examined. We find that when an InAs surface is initially exposed to an Sb flux the specular spot intensity first decreases, then recovers back toward its initial value. The shape of the intensity versus time curves is extremely reproducible if the absolute Sb flux and the Sb species are kept constant. The length of time required for the RHEED pattern to stabilize is much shorter for cracked Sb than for uncracked Sb. The RHEED dynamics are also faster if the total Sb flux increases. The behavior of the RHEED dynamics as a function of Sb flux and Sb species is consistent with the changes in the RHEED pattern being due to an Sb/As exchange reaction on the crystal's surface. The RHEED data are compared to previously published x-ray photoelectron spectroscopy (XPS) data which studied exchange reactions on InAs surfaces exposed to Sb fluxes. The XPS study confirmed that the incident Sb did indeed exchange with As in the epilayer and estimated the exposure time needed to complete the Sb/As exchange reaction. The time scales for exchange associated with the RHEED and XPS data are in good agreement. This further indicates that RHEED could be used to indirectly probe anion exchange reactions, potentially opening up several avenues of research ranging from basic materials science to MBE process control in manufacturing.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1673-1675 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report experimental observation of room-temperature current gains as large as 50 in a novel transistor grown in the InAs/GaSb/AlSb material system. Due to the unique degree of flexibility this material system offers in choosing band alignments, the base and collector terminals are separated by a quantum barrier while electrons traveling between the emitter and collector terminals do not tunnel across any classically forbidden regions, even though a quasi-bound state exists in the quantum well collector. This asymmetry in current conduction between the terminals of the device leads to transistor action: applying a bias to the base terminal electrostatically modulates the emitter-collector current through Stark shifts of the energy levels in the quantum well collector, while the quantum barrier between the base and collector terminals suppresses the base current. Because transport through the structure is dependent on resonant transmission, this novel transistor holds promise for the fabrication of high-speed circuits.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant breeding 107 (1991), S. 0 
    ISSN: 1439-0523
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: There is a large hectarage of tall fescue in Alabama. Recognition of the deleterious effects of the endophytic fungus Acremonium coenophialum has resulted in substantial acceptance of new endophyte-free cultivars. Destruction of old pastures and the concomitant loss of potentially valuable adapted germplasm could be a valid cause for concern. The objectives of this study were to evaluate genetic variation for maturity and plant morphological traits, both among and within tall fescue cv. ‘Kentucky 31’ populations from 18 to 38 year-old pastures in Alabama. Ten populations of approximately 50 plants each were collected from old Alabama tall fescue pastures. Two pastures were sampled in each of five counties, representing the five major land use areas of the state. In 1990, spaced plants of all populations were evaluated at heading time for maturity, morphological, and disease traits at two locations in central Alabama. Endophyte infection level of the populations ranged from 2 to 100 %. Maturity was highly correlated with tiller length and flag leaf width and was used as a covariate for these traits in the analysis of variance. Leaf rust and net blotch ratings were negatively correlated. Significant variation among populations was observed for maturity and flag leaf dimensions, most variation being due to differences among source counties. Significant variation was observed within all populations for maturity and morphological traits, but only in seven populations for leaf rust. No within-population variation was detected for net blotch. The average precipitation for the month of May explained 81 % of the variation among populations for maturity. Age of the pasture sampled had a significant effect on tiller diameter (r2= 0.55), and latitude of the pasture sampled was the best individual predictor of leaf width (r2= 0.42). This study reveals that considerable genetic diversity, largely influenced by climatic conditions, exists among ‘Kentucky 31’ tall fescue ecotypes from Alabama.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 47 (1991), S. 678-682 
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 5
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    Unknown
    London, etc. : Periodicals Archive Online (PAO)
    Slavonic and East European review. 72:4 (1994:Oct.) 763 
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Archiv der Mathematik 62 (1994), S. 1-11 
    ISSN: 1420-8938
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
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  • 7
    facet.materialart.
    Unknown
    London, etc. : Periodicals Archive Online (PAO)
    Slavonic and East European review. 72:4 (1994:Oct.) 748 
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