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  • 1
    Electronic Resource
    Electronic Resource
    Evidence of an off-center position of thulium in GaAs and excitonic excitation of the Tm3+ emission (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6457-6459 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: By photoluminescence and by Zeeman spectroscopy we study the characteristic 4f luminescence transition 3H5 → 3H6 at 1.0 eV of thulium in gallium arsenide which has been reported recently. It turns out that optically active Tm3+, which is present in mainly one specific type of center, does not occupy a simple substitutional lattice site. The results show a considerable tetragonal crystal field. The excitation mechanism of the 1.0-eV luminescence is investigated by photoluminescence excitation. The 3H5 → 3H6 is pumped most efficiently by trapping of free excitons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355133
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  • 2
    Electronic Resource
    Electronic Resource
    Electronic properties of semiconducting FeSi2 films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 1726-1734 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polycrystalline iron disilicide thin films are prepared by furnace annealing of electron-beam deposited iron layers. As substrates we use single-crystal silicon wafers, epitaxial silicon thin films on sapphire substrates, and low-pressure chemical vapor deposited polycrystalline silicon thin films on oxidized silicon wafers. X-ray diffraction indicates that orthorhombic β-FeSi2 is obtained for growth temperatures in the range 800–900 °C. Photothermal deflection spectroscopy reveals a direct band-gap of 0.85 eV. Optical transitions at energies above 1.4 eV are investigated by spectroscopic ellipsometry. Measurements of the subgap defect absorption, photoluminescence, conductivity, and of the Hall mobility suggest that lower growth temperatures yield material of better quality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346601
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  • 3
    Electronic Resource
    Electronic Resource
    Erratum: "Photoluminescence study of impurity states in aluminum antimonide'' [J. Appl. Phys. 67, 1478 (1990)] (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 1944-1944 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347200
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  • 4
    Electronic Resource
    Electronic Resource
    Deep level transient spectroscopy on focused ion beam written in-plane capacitances (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6088-6093 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We discuss defects created by focused Ga ion beam implantation in GaAs or AlGaAs/GaAs heterostructures using deep level transient spectroscopy (DLTS). A novel contact configuration which is sensitive to defects located at the boundary between implanted and unperturbed regions at a well-defined depth is presented. The DLTS spectra for these samples are dominated by a peak with an activation energy of Ea=0.38 eV. The results show that this peak is associated with implantation-induced damage independent of the ion species. The defect is also found in a sample with Schottky contacts on top of a Ga-implanted GaAs layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355193
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  • 5
    Electronic Resource
    Electronic Resource
    Implantation and diffusion of noble gas atoms during ion-beam etching of silicon (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 6179-6186 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The excessive damage and high defect density generated during ion-beam etching of crystalline Si is characterized by Rutherford backscattering, photoluminescence, and transmission electron microscopy. In samples etched at room temperature, a highly damaged surface layer (d≈5 nm) with a large concentration of noble gas atoms is detected and analyzed using Rutherford backscattering in axial channeling geometry. Point defects due to the low-energy noble gas ion implantation are produced within a depth of 100 nm and deeper, and are monitored by their characteristic photoluminescence. The intensity of the noble-gas-defect photoluminescence is studied for different ion-beam energies (200–2000 eV) and crystal orientations. A threshold to produce the defects can then be determined, leading to an estimate of the number of vacancies contained in the noble gas defect. Annealing of etched samples at 650 °C causes the formation of different new photoluminescent centers. Although little is known about the structure of these defects, it is observed that the defects effectively getter copper. Further annealing of the Ar-etched samples at 1050 °C causes the formation of Ar bubbles with an average diameter of about 5 nm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346908
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  • 6
    Electronic Resource
    Electronic Resource
    Influences of a high excitation frequency (70 MHz) in the glow discharge technique on the process plasma and the properties of hydrogenated amorphous silicon (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5665-5674 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hydrogenated amorphous silicon has been prepared at a plasma excitation frequency in the very-high-frequency band at 70 MHz with the glow discharge technique at substrate temperatures between 280 and 50 °C. The structural properties have been studied using hydrogen evolution, elastic recoil detection analysis, and infrared spectroscopy. The films were further characterized by dark and photoconductivity and by photothermal deflection spectroscopy. With respect to films prepared at the conventional frequency of 13.56 MHz considerable differences concerning the electronic and structural properties are observed as the substrate temperature is decreased from 280 to 50 °C. Down to a substrate temperature of 150 °C the electronic film properties change only a little and the total hydrogen content cH and the degree of microstructure that can be directly correlated to cH increase only moderately. Below 150 °C the electronic properties deteriorate in the usual manner but still the total hydrogen content does not exceed 21 at. % even at a substrate temperature of 50 °C. It is argued that the influence of the higher excitation frequency on the plasma and on the growth kinetics plays a key role in this context by allowing a highly effective dissociation of the process gas with the maximum ion energies remaining at low levels. It is concluded that deposition processes at higher excitation frequencies can have important technological implications by allowing a decrease of the deposition temperature without losses in the material quality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350500
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  • 7
    Electronic Resource
    Electronic Resource
    Aero-acoustic levitation: A method for containerless liquid-phase processing at high temperatures (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 456-465 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A method for containerless liquid-phase processing was developed which has practical application in process and property research on virtually any material which is involatile at the melting point. It combines aerodynamic and acoustic forces to support and position the levitated material. The design provides forced convection control of the thermal boundary in the gas surrounding beam-heated specimens, which stabilizes the acoustic forces and allows acoustic positioning necessary to stabilize the aerodynamic levitation forces on molten materials. Beam heating and melting at very high temperatures was achieved. Experiments were conducted on specimens with diameters in the range 0.25–0.4 cm, of density up to 9 g/cm3, at temperatures up to 2700 K, and in oxygen, air, or argon atmospheres. Unique liquid-phase processing results included deep undercooling of aluminum oxide, glass formation at exceptionally small cooling rates, complete melting and undercooling of YBa2Cu3Ox superconductor materials, direct formation of the YBa2Cu3Ox from the liquid phase, and the vaporization of volatile constituents from a low-liquefaction point glass to form a refractory, high melting material. The application of rapid containerless batch processing operations to materials synthesis is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145157
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  • 8
    Electronic Resource
    Electronic Resource
    Laser hearth melt processing of ceramic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 522-524 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new technique for synthesizing small batches of oxide-based ceramic and glass materials from high purity powders is described. The method uses continuous wave CO2 laser beam heating of material held on a water-cooled copper hearth. Contamination which would normally result during crucible melting is eliminated. Details of the technique are presented, and its operation and use are illustrated by results obtained in melting experiments with a-aluminum oxide, Y–Ba–Cu–O superconductor material, and the mixtures, Al2O3–SiO2, Bi2O3–B2O3, Bi2O3–CuO. Specimen masses were 0.05–1.5 g. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146631
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  • 9
    Electronic Resource
    Electronic Resource
    Intracellular Free Calcium Dynamics in Stretch-Injured Astrocytes (1998)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 70 (1998), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: We have previously developed an in vitro model for traumatic brain injury that simulates a major component of in vivo trauma, that being tissue strain or stretch. We have validated our model by demonstrating that it produces many of the posttraumatic responses observed in vivo. Sustained elevation of the intracellular free calcium concentration ([Ca2+]i) has been hypothesized to be a primary biochemical mechanism inducing cell dysfunction after trauma. In the present report, we have examined this hypothesis in astrocytes using our in vitro injury model and fura-2 microphotometry. Our results indicate that astrocyte [Ca2+]i is rapidly elevated after stretch injury, the magnitude of which is proportional to the degree of injury. However, the injury-induced [Ca2+]i elevation is not sustained and returns to near-basal levels by 15 min postinjury and to basal levels between 3 and 24 h after injury. Although basal [Ca2+]i returns to normal after injury, we have identified persistent injury-induced alterations in calcium-mediated signal transduction pathways. We report here, for the first time, that traumatic stretch injury causes release of calcium from inositol trisphosphate-sensitive intracellular calcium stores and may uncouple the stores from participation in metabotropic glutamate receptor-mediated signal transduction events. We found that for a prolonged period after trauma astrocytes no longer respond to thapsigargin, glutamate, or the inositol trisphosphate-linked metabotropic glutamate receptor agonist trans-(1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid with an elevation in [Ca2+]i. We hypothesize that changes in calcium-mediated signaling pathways, rather than an absolute elevation in [Ca2+]i, is responsible for some of the pathological consequences of traumatic brain injury.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1998.70062377.x
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  • 10
    Electronic Resource
    Electronic Resource
    Hydrogen in amorphous and microcrystalline silicon films prepared by hydrogen dilution (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4971-4975 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hydrogen incorporation in silicon layers prepared by plasma-enhanced chemical-vapor deposition using silane dilution by hydrogen has been studied by infrared spectroscopy (IR) and elastic recoil detection analysis (ERDA). The large range of silane dilution investigated can be divided into an amorphous and a microcrystalline zone. These two zones are separated by a narrow transition zone at a dilution level of 7.5%; here, the structure of the material cannot be clearly identified. The films in/near the amorphous/microcrystalline transition zone show a considerably enhanced hydrogen incorporation. Moreover, comparison of IR and ERDA and film stress measurements suggests that these layers contain a substantial amount of molecular hydrogen probably trapped in microvoids. In this particular case the determination of the total H content by IR spectroscopy leads to substantial errors. At silane concentrations below 6%, the hydrogen content decreases sharply and the material becomes progressively microcrystalline. The features observed in the IR-absorption modes can be clearly assigned to mono- and/or dihydride bonds on (100) and (111) surfaces in silicon crystallites. The measurements presented here constitute a further indication for the validity of the proportionality constant of Shanks et al. [Phys. Status Solidi B 110, 43 (1980)], generally used to estimate the hydrogen content in "conventional'' amorphous silicon films from IR spectroscopy; additionally, they indicate that this proportionality constant is also valid for the microcrystalline samples. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363541
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