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  • 1
    Electronic Resource
    Electronic Resource
    Low temperature epitaxial growth of Ge using electron-cyclotron-resonance plasma-assisted chemical vapor deposition (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1949-1954 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial Ge films have been deposited on Si and Ge substrates at 300 °C using electron-cyclotron-resonance plasma-assisted chemical vapor deposition. Helium was fed into the resonance chamber, and a mixture of helium and germane were fed downstream at a location above the substrate. Surface roughness increased with energetic ion bombardment as quantified by the number of ions striking the surface per Ge atom deposited. Surface roughness also increased with increasing substrate temperature. Films with very rough surface morphology were found to be polycrystalline. The large hydrogen content of the films, particularly those deposited on Si, appeared to prevent the reduction of the epitaxial temperature below 300 °C. In the temperature range between 300 and 325 °C, hydrogen bubbles formed at the Ge/Si interface and caused the films to pucker from the surface. Increasing the substrate temperature above 325 °C eliminated this problem by decreasing the surface coverage of hydrogen during deposition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351189
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  • 2
    Electronic Resource
    Electronic Resource
    Absolute measurements of elastic-wave phase and group velocities in lossy materials (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 3477-3486 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Traditional methods of determining phase and group velocities are often inadequate for many thick-section materials that exhibit greater than 30 dB, frequency-dependent propagation losses across the passband of the transducer. This article describes a measurement method that addresses this problem. Our method is mechanized as a pulsed, swept-frequency interferometer. The method's accuracy and reliability are enhanced by a combination of circuit-design improvements, which increase the signal-to-noise ratio and linearity, and signal-processing methods, which remove circuit-related measurement errors and compensate for diffraction. First we describe the foundations of our measurement method and its mechanization. Then we describe the signal-processing procedures, used to calibrate the instrumentation and to determine the absolute phase and group velocities. To illustrate the method, we determine the phase velocities in a very lossy, 50-mm-thick, glass/epoxy specimen in the 0.3–1.2-MHz region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143752
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Using Soil 13C to Detect the Historic Presence of Schizachyrium scoparium (Little Bluestem) Grasslands on Martha's Vineyard (2003)
    Boston, MA, USA : Blackwell Science Inc
    Restoration ecology 11 (2003), S. 0 
    Details
    ISSN: 1526-100X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract We used differences in soil carbon δ13C values between forested sites and grasslands dominated by the C4 grass Schizachyrium scoparium (little bluestem) to detect the presence of former grasslands in the historical landscape of the coastal sand plain of Martha's Vineyard, Massachusetts, U.S.A. Soil δ13C was measured at (1) sites with long-term forest or grassland vegetation and (2) sites with known histories where forest vegetation invaded grassland and where forest converted to grassland. The δ13C of soil under long-term grassland was –24.1‰ at 0 to 2 cm depth and –23.4‰ at 2 to 10 cm and was enriched by 3.4‰ and 2.8‰ compared with soil under long-term forest. In forests that invaded grasslands dominated by S. scoparium, soil δ13C decreased as C derived from trees replaced C from S. scoparium. This decline occurred faster in surface soils and in the light soil organic matter fraction than in the mineral soil. In forests that converted to grasslands, soil δ13C increased and the rate of increase was similar in surface and mineral soil and in the different soil organic matter fractions. Rates of change indicated that soil δ13C could be used to detect changes in vegetation involving the presence or absence of S. scoparium during the last 150 years. Application of this model to a potential grassland restoration site on Martha's Vineyard where the landscape history was not known indicated that the site was previously unoccupied by S. scoparium during this time. The δ13C of surface mineral soil can be useful for detecting the presence of historic S. scoparium grasslands but only in the period well after European settlement of these coastal sand plain landscapes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1526-100X.2003.00080.x
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  • 4
    Electronic Resource
    Electronic Resource
    Mercury-201 nuclear quadrupole resonance. I. Mercury and halogen NQR in the mercuric halide dioxanates (1973)
    s.l. : American Chemical Society
    Inorganic chemistry 12 (1973), S. 1282-1286 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic50124a014
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  • 5
    Electronic Resource
    Electronic Resource
    Watt-range, coherent, uniphase powers from phase-locked arrays of antiguided diode lasers (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 2070-2072 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Twenty-element near-resonant AlGaAs/GaAs arrays of antiguides have been optimized for maximum intermodal discrimination and large Strehl ratio. It is found that 1000-μm-long devices with two intracavity Talbot-type spatial filters, and a 3 to 1 ratio between element core and interelement spacing provide the best results. The intermodal discrimination is discussed for both Talbot and uniform devices. For devices with two Talbot-type spatial filters, diffraction-limited-beam operation is obtained to 1 W pulsed power, and operation in a beam with lobewidth 1.5× diffraction limit is obtained to 2 W and 19× threshold. cw diffraction-limited-beam operation is obtained to 0.5 W, limited by thermal considerations. Uniform devices operate in beams with lobewidth ≈3× diffraction limit to 5 W and 45× threshold. At 5 W total output the coherent uniphase power is 1.6 W, and the coherent power in the main lobe is 0.94 W.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105013
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    cw high-power diffraction-limited-beam operation from resonant optical waveguide arrays of diode lasers (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 22-24 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Monolithic phase-locked resonant arrays of antiguides, resonant optical-waveguide (ROW) arrays, have been optimized for efficient in-phase-mode operation. Diffraction-limited, in-phase-mode continuous-wave (cw) operation is obtained from 20-element uniform arrays to 250 mW output power, with (front facet) external differential quantum efficiencies of 41%. Single longitudinal mode operation is observed below 100 mW cw. In-phase-operating devices with and without Talbot-type spatial filters are compared, and it is found that for ROW arrays Talbot-type spatial filters are not required.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104425
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  • 7
    Electronic Resource
    Electronic Resource
    Spectrographic Microdetermination of Beryllium in Air Dust Samples (1950)
    s.l. : American Chemical Society
    Analytical chemistry 22 (1950), S. 1197-1200 
    Details
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ac60045a033
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  • 8
    Electronic Resource
    Electronic Resource
    High-power, narrow single-lobe operation from 20-element phase-locked arrays of antiguides (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 2060-2062 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pure in-phase-mode operation is obtained from 20/21-element AlGaAs/GaAs antiguided arrays grown by two-step metalorganic chemical vapor deposition. Oscillation of out-of-phase modes is substantially suppressed by a built-in spatial filter: two sets of noncollinear antiguides separated by a 50-μm-long laterally unguided region, corresponding to the half-Talbot distance. Design considerations for 20- vs 10-element arrays are discussed. Diffraction-limited-beam operation (i.e., 0.8° lobewidth) is obtained to 1.5×threshold (90 mW, both facets). Beams with 1.3° lobewidth (1.6×diffraction limit) are obtained at 3×threshold and 300 mW (both facets). Devices with optimized facet coatings operate in a single, 1.5°-wide lobe (i.e., 1.8×diffraction limit) at 330 mW front-facet emitted power. The main lobe contains 80–87% of the total power.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102105
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  • 9
    Electronic Resource
    Electronic Resource
    Dependence of external differential efficiency on laser length and reflectivities in multiple quantum well lasers (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 825-827 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The external efficiency ηd of quantum well (QW) lasers is maximum at some characteristic laser length, which is dependent upon mirror reflectivities and the number of QWs in the active layer. The observed decrease in ηd in short lasers is caused by increased optical absorption associated with a high concentration of free carriers in the QW and the surrounding waveguide layer. The carriers spill into the waveguide because of QW subband filling in short cavity lasers with high threshold gains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101771
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    Resonant optical transmission and coupling in phase-locked diode laser arrays of antiguides: The resonant optical waveguide array (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 2183-2185 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Uniform linear arrays of antiguides have 100% optical transmission between elements when the interelement spacing is an integer number of leaky wave half-wavelengths in the lateral direction. Resonant in-phase-mode and out-of-phase-mode coupling occurs when the number of half-wavelengths is odd and even, respectively. Such devices are called resonant optical waveguide (ROW) arrays. The discrimination between the resonant array mode and adjacent array modes reaches a maximum in close proximity to the resonance. An AlGaAs/GaAs ROW diode laser array operating close to resonance is demonstrated. Devices with virtually uniform near-field intensity profiles operate in stable, diffraction-limited in-phase modes to drive levels in excess of three times threshold.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101159
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