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  • Articles  (43)
  • American Association for the Advancement of Science (AAAS)  (23)
  • American Institute of Physics (AIP)  (20)
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  • Articles  (43)
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  • 1
    Electronic Resource
    Electronic Resource
    Picosecond pulse response characteristics of GaAs metal-semiconductor-metal photodetectors (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2435-2448 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a comprehensive theoretical and experimental analysis of the current response of GaAs metal-semiconductor-metal Schottky photodiodes exposed to 70 fs optical pulses. Theoretical simulations of the carrier transport in these structures by a self-consistent two-dimensional Monte Carlo calculation reveal the strong influence of the distance between the finger electrodes, the external voltage, the GaAs layer thickness and the excitation intensity on the response time and the corresponding frequency bandwidth of these photodetectors. For many experimental conditions, the model demonstrates a clear temporal separation of the electron and hole contributions to the output current due to the different mobilities of the two carrier types. For a diode with an electrode separation of 0.5 μm, an electric-field strength above 10 kV/cm and low intensity of the incident light the theory predicts a pulse rise time below 2 ps, an initial rapid decay as short as 5 ps associated with the electron sweep out and a subsequent slower tail attributed to the hole current. For weaker electric fields and/or higher light intensities a significant slowing down of the detector speed is predicted because of effective screening of the electric field by the photoexcited carriers. Heterostructure layer-based devices are shown to provide superior performance compared to diodes manufactured on bulk substrates. Experimental data obtained by photoconductive or electro-optic sampling on diodes with electrode separation between 0.5 and 1.2 μm agree fairly well with the theoretical predictions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349395
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  • 2
    Electronic Resource
    Electronic Resource
    Laser induced thermal desorption: A time resolved study (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 4040-4043 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Real time monitoring of laser induced thermal desorption of NH3 from Re(0001) at ns time scale was performed utilizing optical SHG. Coverage dependent desorption kinetic parameters determined under equilibrium conditions were found to correctly describe the 8 orders of magnitude faster desorption rates. The role of strong repulsive interactions is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461857
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis of gadolinium oxide magnetoliposomes for magnetic resonance imaging (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6208-6210 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method for the synthesis of gadolinium oxide magnetoliposomes, i.e., nanosized gadolinium oxide magnetic particles coated by a phospholipid membrane, is presented. Magnetoliposomes were prepared by reacting lauric acid coated gadolinium oxide nanoparticles with dimyristoylphosphatidylcholine liposomes prepared using a direct injection method. The gadolinium oxide magnetoliposomes were characterized using transmission electron microscopy imaging, x-ray diffraction, and fluorescence. The magnetic properties of the magnetoliposomes were investigated with a superconducting quantum interference device magnetometer and nuclear magnetic resonance (NMR) spectrometry. Our results indicate that the magnetoliposomes contain approximately spherical nanoparticles averaging 20 nm in diameter. The occurrence of a phospholipid bilayer surrounding the magnetic particles is confirmed both by transmission electron micrographs of samples negatively stained with uranyl acetate and by digital fluorescence imaging microscopy measurements of magnetoliposomes labeled with fluorescein. The particles are paramagnetic at room temperature. NMR measurements show that the ratio between the relaxivities of the particles depends largely on their preparation. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372656
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  • 4
    Electronic Resource
    Electronic Resource
    A new method for the synthesis of magnetoliposomes (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5699-5701 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new method for the synthesis of magnetoliposomes, i.e., nanosized magnetic particles coated by a phospholipid membrane, is presented. Magnetoliposomes are prepared by directly using the phospholipid vesicles as nanoreactors for the precipitation of the magnetic particles. The magnetoliposomes have been characterized using transmission electron microscopy imaging and x-ray powder diffraction. The magnetic properties of the magnetoliposomes have been investigated with a superconducting quantum interference device magnetometer. Our results indicate that the magnetoliposomes contain approximately spherical maghemite nanoparticles averaging 25 nm in diameter. The occurrence of a phospholipid bilayer surrounding the magnetic particles is confirmed both by transmission electron micrographs of samples negatively stained with uranyl acetate and by digital fluorescence imaging microscopy measurements of magnetoliposomes labeled with fluorescein. The temperature dependence of the zero field cooled and field cooled susceptibilities of the magnetoliposomes is consistent with their expected superparamagnetic nature. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370256
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  • 5
    Electronic Resource
    Electronic Resource
    Analytical criteria for nonlinear instability of thermal structures (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 4127-4133 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Analytical criteria for supercritical and asymptotic stability and for subcritical and superexponential instability are obtained for slab-like, spherical, and cylindrical thermal structures. It is assumed that both, the thermal conductivity κ(T) and the gain/loss function Q(T), can be written as continuous functions of the temperature and they have continuous derivatives. Conditions on κ and Q under which the symmetry of the structure determines the kind of instability (or stability) are obtained. Additionally, it is found that the response of the structure not only depends on the amplitude of the disturbance, but also on whether the disturbance increases or decreases the initial steady temperature. In particular, the threshold value for the amplitude of the disturbances beyond which a linearly stable configuration destabilizes, and explicit conditions for catastrophic heating or cooling are obtained. Applications to structures constituted by atomic and molecular gas are outlined. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871036
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  • 6
    Electronic Resource
    Electronic Resource
    Optical gain and spontaneous emission in InGaAs/GaAs multiple quantum well laser diodes (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 582-584 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present gain and spontaneous emission measurements in In0.35Ga0.65As/GaAs multiple quantum well lasers. First, the gain is extracted from measured amplified spontaneous emission through a laser facet. Second, unamplified spontaneous emission is detected through the transparent GaAs-substrate. Taking advantage of the fundamental relationship between gain and spontaneous emission, the separation of the electron and hole quasi-Fermi levels, ΔEF, at various bias currents below laser threshold is accurately determined. Theoretically, ΔEF is calculated utilizing a simple two-subband structure model. Fitting the theoretical predictions to the experimental data allows us to determine the threshold carrier density (nth=2.0×1018 cm−3), the in-plane hole effective mass (mv1=0.21m0), and the amount of band gap shrinkage at threshold (ΔEg,th=33 meV). © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362721
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  • 7
    Electronic Resource
    Electronic Resource
    Subpicosecond characterization of carrier transport in GaAs-metal-semiconductor-metal photodiodes (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1410-1412 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temporal evolution of the photocurrent in interdigitated GaAs metal-semiconductor- metal Schottky photodiodes is directly measured in the time domain by photoconductive and electro-optic sampling with subpicosecond resolution. Excellent agreement is found between experiment and theoretical data obtained by two-dimensional self-consistent Monte Carlo calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105208
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  • 8
    Electronic Resource
    Electronic Resource
    Transit time limited response of GaAs metal-semiconductor-metal photodiodes (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 2503-2505 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The response of GaAs metal-semiconductor-metal (MSM) photodiodes at low temperatures has been investigated in the time domain by photoconductive sampling. The dependence of the response time on temperature for T(approximately-greater-than)50 K can be described by phonon mediated intervalley and intravalley scattering. The pulse width drops from 10.8 ps at 300 K to 5.6 ps at 70 K and then grows rapidly with decreasing temperature below 50 K. These results demonstrate that the response is limited by the electron/hole transport in the semiconductor rather than by external capacitances or inductances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104857
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  • 9
    Electronic Resource
    Electronic Resource
    Subpicosecond carrier lifetimes in radiation-damaged GaAs (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1881-1883 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate the dependence of carrier lifetimes in radiation-damaged, GaAs on proton implantation dose by means of time-resolved reflectivity and photoconductivity experiments with subpicosecond resolution. The carrier lifetimes decrease with increasing implantation dose at low implantation levels whereas beyond the "amorphization dose'' a saturation at 0.5 ps can be observed due to a saturation of the defect density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105061
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  • 10
    Electronic Resource
    Electronic Resource
    Wavelength selective infrared microscopy: A nondestructive and quick method for the investigation of buried structures in optoelectronic devices (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 3401-3406 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper we present an optical method to control the geometry of buried layers in optoelectronic heterostructures. The technique uses an optical microscope equipped for infrared applications and relies on the fact that the different layers of the multilayer structure have different band gaps. Accordingly transmission/absorption, reflectance, and photoluminescence of the inidividual layers exhibit their characteristic near-band-gap spectral variations at different wavelengths. By appropriate selection of the wavelength range used for image formation, any layer of interest can be made visible. As an example we investigated a mushroom-type InGaAsP/InP 1500-nm laser structure with subsequent mass transport. Both technological steps, the formation of the mushroom by underetching, and the regrowth by mass transport represent critical processes in the fabrication of these index-guided lasers. Our results show clearly that the successful accomplishment of the process can be controlled by images of the selected buried layer. Contrast and resolution of the pictures are sufficient to show any irregularity in etching or regrowth. The main advantage of the method is that it offers the possibility of investigating whole wafers without sample preparation and in a nondestructive way, which is in marked contrast to observation with a scanning electron microscope, where only profiles along cleaved facets can be inspected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337637
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