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  • 1
    Electronic Resource
    Electronic Resource
    Bandwidth enhanced metal-semiconductor-metal photodetectors based on backgated ip structures (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2223-2225 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on theoretical and experimental results on a novel metal-semiconductor-metal (MSM) photodetector with a backgate provided by a p-doped layer. The backgate allows extremely short sweep-out times for the holes, due to strong electric fields normal to the surface. Thus, long tails due to slow moving holes and screening of the external drift fields by hole space charge accumulation at high optical power, which lead to a degradation of the time response of conventional MSM photodetectors, are avoided. The high frequency performance measured up to 8 GHz in the time and frequency domain showed a significant reduction of the bandwidth limiting hole tail compared to standard MSM photodetectors. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112767
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  • 2
    Electronic Resource
    Electronic Resource
    Diffusion of ammonia on Re(001): A monolayer grating optical second harmonic diffraction study (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 8277-8283 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Diffusion of ammonia was studied over the smooth Re(001) surface utilizing optical second harmonic diffraction from surface coverage grating. The decay of the first order diffraction peak as a function of surface temperature for different initial coverages was measured and then simulated by numerical solution of Fick's second diffusion equation, employing a coverage dependent diffusion constant. For the first time the second order diffracted second harmonic signal was monitored during the diffusion process, supporting the calculated initial coverage profile and the diffusion model. The resulting diffusivity D(θ)=D0exp[−Em(θ)/RT], is defined by a barrier for diffusion Em(θ)=E0−ωZθ, with activation energy at zero coverage E0=3.4±0.6 kcal/mol, D0=2.8×10−3 cm2 sec−1 and the repulsion energy between the pair of nearest neighbor molecules ω=0.2±0.06 kcal/mol. The magnitude and effect of the repulsive interactions on diffusion are compared to their strong effect on the activation energy for desorption.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464533
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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Demonstration of electron beam self-focusing in plasma wake fields (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1376-1383 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper, the direct observation of wake-field self-focusing of an electron beam in plasma is reported. The dynamics of beam self-pinching and the fast collisionless evolution of a Bennett-like, near-equilibrium profile are examined theoretically and computationally. The experimental results are compared to predictions of the analysis and discussed in the context of application to the plasma lens and the plasma wake-field accelerator.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859559
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  • 5
    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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  • 6
    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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  • 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
    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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  • 9
    Electronic Resource
    Electronic Resource
    Time-resolved photocurrent response of metal-semiconductor-metal photodetectors to double-pulse excitation (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 2780-2782 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The photocurrent response of a GaAs metal-semiconductor-metal (MSM) photodetector was measured after excitation with two femtosecond pulses having a variable delay Δt of 0 ps≤Δt≤100 ps. At low excitation densities the influence of the first pulse on the pulse shape of the second is negligible for Δt≥20 ps. This corresponds to a resolvable pulse train of 50 GHz repetition rate for the detectors used in our experiments. The influence of space charge effects at higher excitation density and/or lower bias could be shown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110332
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  • 10
    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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