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  • 1
    Online Resource
    Online Resource
    Helium Atom Scattering from Surfaces. (1992)
    Berlin, Heidelberg :Springer Berlin / Heidelberg,
    Details
    Keywords: Surfaces (Physics). ; Scattering (Physics). ; Electronic books.
    Type of Medium: Online Resource
    Pages: 1 online resource (331 pages)
    Edition: 1st ed.
    ISBN: 9783662027745
    Series Statement: Springer Series in Surface Sciences Series ; v.27
    URL: https://ebookcentral.proquest.com/lib/geomar/detail.action?docID=6503617
    DDC: 530.417
    Language: English
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    GEOMAR EBL
  • 2
    Electronic Resource
    Electronic Resource
    Refractory graphite skimmers for supersonic free-jet, supersonic arc-jet, and plasma discharge applications (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1640-1648 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The fabrication of molecular beam "skimmers" from electrical discharge machining (EDM) graphite is reported. EDM graphite is highly refractory and is easily machined using conventional cutting and grinding techniques. In its most fine-grained form, EDM graphite can be machined free-standing to a knife-edge lip radius of ∼1 μm, providing excellent skimmer aerodynamics. Being refractory, such EDM skimmers are of particular interest in sampling or collimating high-temperature plasma discharges. Our explicit application is in skimming an electrical discharge supersonic free-jet of molecular nitrogen, forming a molecular beam of A 3Σu+ metastable N2 to be used in the heteroepitaxial growth of III–N wide-band-gap semiconductors. In view of the their economy, ease of manufacture, and excellent aerodynamics, the skimmers may also find use in skimming conventional, nondischarge supersonic free-jets. The performance of the EDM skimmers was tested in a conventional helium supersonic free-jet expansion, measuring the time-of-flight distribution and beam intensity as a function of nozzle pressure and nozzle-skimmer separation. Direct comparison with commercial nickel and copper skimmers showed the EDM graphite skimmers to perform nearly as well as the best commercial metal skimmers. The refractory properties of the skimmers were tested in a high-temperature arc-discharge supersonic free-jet expansion of 10% nitrogen in argon. Exposure to a plasma plume of ∼7500 K for over 6 h produced only relatively minor deterioration of the EDM graphite skimmer. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149645
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Absolute calibration of an atomic helium beam time-of-flight apparatus by flight path variation (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1957-1964 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Virtually all inelastic helium atom scattering experiments utilize time-of-flight (TOF) analysis to energy analyze the scattered beam. To date, the demands upon the accuracy of these TOF measurements have not been particularly great (typically a few percent), and rather rudimentary calibration techniques have sufficed. For certain experiments, e.g., for time-resolved measurements of specular scattering to determine surface-bound states of helium or to observe surface-step interference, this is no longer the case. We describe an in situ calibration technique based upon a variation of the TOF flight path that allows us to calibrate our path length and time origin to within a few millimeters and microseconds, respectively (〈2×10−3). A comparison with "zero flight time'' laser timing measurements shows that finite drawout/transit times through the beam detector can introduce nonnegligible systematic errors into the laser calibration technique, even in the present favorable instance (light beam mass, drawout along the beam axis). We demonstrate the utility of surface diffraction as either a consistency check or to accurately determine unknown reciprocal lattice vectors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140059
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    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Corona discharge supersonic free-jet for III–V nitride growth via A 3Σu+ metastable nitrogen molecules (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 883-892 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A corona discharge supersonic free-jet is shown to be a nearly pure source of A 3Σu+ metastable molecular nitrogen, an electronically excited and chemically active form of N2 that is ideally suited to nitride semiconductor growth. Optical emission spectroscopy at various distances downstream of the supersonic nozzle reveals a cascade through the excited state manifold of N2 triplet states to populate the A 3Σu+ state. Appearance potential spectroscopy (mass spectrometer electron bombardment ionization yield, measured as a function of electron impact energy) delivers the composition of the terminal molecular beam. A 3Σu+ molecules are the dominant activated species in the beam, which otherwise contains only nonreactive X 1Σg+ ground state nitrogen molecules plus a minor amount of 4S0 nitrogen atoms. Up to 1.56% number fraction of the beam is A 3Σu+, providing 1.0×1017 metastables sr−1 s−1. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1331646
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  • 5
    Electronic Resource
    Electronic Resource
    III-N semiconductor growth with activated nitrogen: State-specific study of A3Σu+ metastable N2 molecules (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 3030-3032 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High quality epitaxial III-N semiconductor films, ranging in thickness from 300 to 900 Å, have been grown using A3Σu+ metastable nitrogen molecules. The work employed a corona discharge supersonic free-jet to generate a molecular beam containing exclusively the A3Σu+ activation state in an otherwise ground state N2 beam. AlN films were grown on 6H–SiC(0001) and Si(001) substrates. GaN films were grown on the same substrates and on buffer layers of AlN deposited in situ on 6H–SiC(0001). The N-atom incorporation efficiency (the number of N atoms attaching to a III–N surface per incident A3Σu+ molecule) approached 100% and was independent of substrate temperature from 600 to 900 °C, implying direct molecular chemisorption of the A3Σu+. These measurements support theoretical predictions that A3Σu+ is an ideal precursor for III–N growth. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1323739
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  • 6
    Electronic Resource
    Electronic Resource
    Influence of 6H–SiC(0001) substrate surface morphology on the growth of AlN epitaxial layers (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 985-987 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial AlN films were grown on 6H–SiC(0001) substrates using an ammonia supersonic seeded beam. The films grown on substrates etched in hydrogen at high temperatures were shown by ion beam channeling to exhibit a higher degree of order relative to those grown on the as-received substrates. Cross-sectional electron microscopy revealed sharper SiC–AlN interfaces with extended flat terraces. In particular, very few stacking mismatch boundaries were observed to originate from the 1.5 nm steps which correspond to the 6H stacking sequence of the substrate. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123431
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Low-energy electron microscopy observations of GaN homoepitaxy using a supersonic jet source (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 989-991 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A study of the homoepitaxial growth of GaN(0001) layers was conducted in situ and in real time using the low-energy electron microscope. The Ga flux was supplied by an evaporative cell while the NH3 flux was supplied via a seeded-beam supersonic jet source. At growth temperatures of 665 °C and 677 °C, smooth GaN(0001) layers with well-defined step structures were grown on GaN(0001) substrates prepared by metalorganic chemical vapor deposition. In general, nonfaceted homoepitaxial layers were achieved when the Ga/NH3 flux ratios exceeded 2, starting with a Ga-covered substrate surface, in the temperature range of 655–710 °C. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124575
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  • 8
    Electronic Resource
    Electronic Resource
    Growth of AlN and GaN on 6H–SiC(0001) using a helium supersonic beam seeded with ammonia (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 1365-1367 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have grown AlN and GaN layers on 4° off-axis 6H–SiC (0001) substrates using He supersonic beams seeded with NH3. The AlN films were used as buffer layers for GaN growth at 800°C. We estimate 39% incorporation of the NH3 molecules impinging on the substrate surface during GaN film growth. High structural quality of the epitaxial GaN layers was confirmed by transmission electron microscopy and electron channeling patterns. The GaN films, which had a thickness of ∼105 nm, contained a defect density of ∼2×1010 cm−2. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119895
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  • 9
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    Diffraction from cells yields protein structure [Biophysics and Computational Biology] (2014)
    National Academy of Sciences
    Details
    Publication Date: 2014-09-03
    Description: It has long been known that toxins produced by Bacillus thuringiensis (Bt) are stored in the bacterial cells in crystalline form. Here we describe the structure determination of the Cry3A toxin found naturally crystallized within Bt cells. When whole Bt cells were streamed into an X-ray free-electron laser beam we...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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