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  • 1
    Electronic Resource
    Electronic Resource
    Magnetic particle–particle interaction in frozen magnetic fluids (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7931-7935 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic resonance is used to study magnetic dipole particle–particle interaction in ionic water-based iron-manganese magnetic fluids. A set of six samples having particle concentration running from 1.2×1016 to 6.3×1016 particles/cm3 were frozen below room temperature and analyzed in the range of 100–250 K. Average values of magnetic particle–particle interaction energy were obtained from the temperature dependence of the resonance linewidth broadening. At 1.2×1016 particles/cm3 magnetic particle–particle interaction energy is found to be of the order of 1.2 meV. However, at 6.3×1016 particles/cm3 magnetic particle–particle interaction energy goes to 32 meV. The enhancement of the magnetic particle–particle interaction energy far beyond the linearity is associated to cluster structuration. A one-dimensional model for cluster structuration is presented. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362407
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  • 2
    Electronic Resource
    Electronic Resource
    Low temperature photoluminescence study in AlxGa1−xAs alloys in the indirect band gap region (x(approximately-greater-than)0.4) (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 5090-5097 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-temperature photoluminescence spectroscopy was used to study AlxGa1−xAs intrinsic epitaxial layers in the range of aluminum content between 0.45〈x〈0.9 in the region where the band gap minimum is indirect. Nonintentionally doped samples were grown by liquid phase epitaxy very near the saturation temperature (∼800 °C). The heterostructures consisted of an AlxGa1−xAs layer grown on top of a GaAs Si-doped (n∼2×1018 cm−3) substrate with orientation (100) 2° toward the (110). There is little information on the zero phonon excitonic lines for Al compositions x(approximately-greater-than)0.6, because the appearance of these lines depends on several factors such as internal strength, crystalline defects, and impurities. In our samples the excitonic lines were observable up to x=0.9. Transitions related to bound-to-free carrier as well as their phonon replicas were observable too. The data obtained from the spectra fitted with multigaussian lines allowed us to estimate the dependencies on the Al composition, x, of the bound exciton peak, the bound exciton binding energy, and the exciton localization energy. The acceptor ionization energy attributed to carbon residual impurities in As sites and its dependence on x was also obtained. Fitting by Gaussian lines the phonon region, the PL spectra fitted better with the TO(X) AlAs-type branch rather than the LO(X) AlAs-type, with a linear dependence with x in the studied range. The phonon energies of the GaAs type seem to behave almost constant and it was difficult to assign them to the LO(X) GaAs type or to TO(X) GaAs type due to the scatter of the data for high values of x. Other phonon replicas from the bound exciton and the electron-to-acceptor carbon transition (e-A°) coincide with the LO(X) AlAs type and TA(X), TA(X)+LA(X) and two LA(X) phonon energies. All the dependencies we present here are valid for aluminum compositions in the range 0.48〈x〈0.90. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359740
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  • 3
    Electronic Resource
    Electronic Resource
    Characterization of the interlayer water in niobyl phosphate hydrates by IR and NMR spectroscopies (1987)
    s.l. : American Chemical Society
    Inorganic chemistry 26 (1987), S. 847-850 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00253a015
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  • 4
    Electronic Resource
    Electronic Resource
    A note on the symmetry group and perturbation algebra of a parabolic partial differential equation (1991)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 32 (1991), S. 1444-1449 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: In this paper, the symmetry group of the parabolic partial differential equation ∂tf=Af is focused on (A is an analytic second-order elliptic linear differential operator on Rn). Following Olver [Applications of Lie Groups to Differential Equations (Springer, New York, 1986)], Ovsjannikov [Group Analysis of Differential Equations (Academic, New York, 1982)], and Rosencrans [J. Math. Anal. Appl. 56, 317 (1976); 61, 537 (1977)], the Lie algebra of infinitesimal symmetries is studied. It will be proven that it is finite dimensional (putting apart the trivial symmetries due to the linearity of the partial differential equation) by relating it to the Lie algebra of infinitesimal homothetic transformations of a Riemannian manifold (Rn,a), thus generalizing results of Ovsjannikov on elliptic equations and making use of the same Riemannian geometric techniques. Thanks to these techniques, the perturbation algebra of A, introduced by Rosencrans, is also shown to be related to geometric characteristics of (Rn,a).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529301
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  • 5
    Electronic Resource
    Electronic Resource
    Line-shape analysis of reflectance spectra from GaAs/AlAs multiple-quantum-well structures (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 2501-2505 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The reflectance spectra from six GaAs/AlAs multiple-quantum-well structures have been analyzed with a multilayer classical dielectric function model which describes in detail the propagation of light through these microstructures. The model predicts accurately the observed line shapes. It can be used for the analysis of the reflectance or transmission spectra of any semiconductor multilayer structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345501
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  • 6
    Electronic Resource
    Electronic Resource
    Infrared absorption and photoconductive gain of quantum well infrared photodetectors (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 592-594 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have conducted a detailed study on the properties of a multiple quantum well infrared photodetector (QWIP) with a single bound state. From the optical absorption experiment, we found that the peak absorption energy is determined by the resonant states associated with each individual well and not by the global miniband structure. From the transport experiment, we observed that the photoelectron distribution over the QWIP is extremely narrow and close to the top of the quantum well barriers, indicative of the diffusive nature of the hot-electron transport in this structure. At large bias, the photoelectron distribution begins to shift up in energy, and is found strongly correlated to the observed photoconductive gain of the detector.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106591
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  • 7
    Electronic Resource
    Electronic Resource
    Fermi level pinning in low-temperature molecular beam epitaxial GaAs (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 1585-1587 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Fermi level position in low temperature (LT) GaAs has been studied by photoreflectance (PR). By etching the LT-GaAs to a different thickness, we find the Fermi level in the as-grown as well as the annealed LT-GaAs is firmly pinned. The pinning position, however, occurs at different energies: 0.47 eV below the conduction band edge for the as-grown samples and 0.65 eV below the conduction band edge for the annealed samples. The pinning in the as-grown LT-GaAs is believed to be the result of a high degree of charge compensation by deep levels, while the pinning in the annealed LT-GaAs is due to the depletion of carriers by the Schottky barrier at the metallic As precipitates. From the measured Fermi level and ionization ratio of As antisites, the (0/+) donor level of the As antisite in LT-GaAs is, for the first time, determined at Ec−0.57 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107504
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  • 8
    Electronic Resource
    Electronic Resource
    High detectivity InGaAs base infrared hot-electron transistor (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 3303-3305 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An infrared hot-electron transistor with a thin (300 A(ring))InGaAs base layer is constructed. By adopting a thin base material with a large Γ-L valley separation, the photocurrent transfer ratio is improved by a factor of four in comparison with the GaAs base transistor. As a result, the detectivity of the transistor is increased to 1.4×1010 cm(square root of)Hz/W at 77 K with a cutoff wavelength of 9.5 μm, two times as large as the companion state-of-the-art GaAs quantum well photoconductor. Combined with the lower dark current, the voltage responsivity and the noise equivalent temperature difference of a detector array can be improved by more than an order of magnitude.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105713
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  • 9
    Electronic Resource
    Electronic Resource
    Low dark current infrared hot-electron transistor for 77 K operation (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 908-910 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recently, thermal imaging using quantum well infrared photodetector (QWIP) focal plane arrays has been demonstrated. However, the operating temperature needs to be kept around 60 K due to the large dark current occurring at higher temperatures. In order to achieve thermal imaging at 77 K, we have designed and demonstrated two infrared hot-electron transistor structures, whose dark current is two to three orders of magnitude lower than that of a QWIP. The resultant dark current falls within the limit of the charge handling capacity of a readout circuit, and the infrared detection is demonstrated to be background limited at 77 K. The noise equivalent temperature difference of the detectors is estimated to be 14 and 26 mK, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109869
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  • 10
    Electronic Resource
    Electronic Resource
    Wavelength tuning and absorption line shape of quantum well infrared photodetectors (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 1781-1783 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have conducted a systematic theoretical and experimental study on wavelength tuning and absorption lineshape of single-bound-state quantum well infrared photodetectors. By computing the oscillator strength using the exact quantum well eigen functions, we show that an intersubband transition is from the ground state to the first resonant state in one extreme when the ground state is totally localized in the well, or to the second miniband in another extreme when the ground state wave function is delocalized. In the intermediate cases, the absorption wavelength is determined by the energy of a final state with which the oscillator strength is maximum. We also calculated the absorption lineshape and show that it depends sensitively on the position of the final state relative to the global band structure of the detector.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108425
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