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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1306-1311 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The phenomenon of simultaneous compositional disordering and the formation of electrical resistive layers induced by oxygen implantation in InGaAs/InP superlattices has been investigated. The disordering characteristics have been studied as a function of implantation temperature and ion dose. It was found that implantation at elevated temperatures (referred to as the IM or ion mixing process) usually leads to much more efficient disordering compared to implantation at room temperature followed by annealing at the same elevated temperature (referred to as the implantation plus annealing process). Of particular interest is the observation that ion mixing at 550 °C with 1×1013 O+/cm2 leads to significantly more disordering than implantation with the same dose at room temperature followed by annealing at 550 °C for the same period of ion mixing time. In addition, the electrical resistance of the ion-mixed layer at 550 °C increases 2600 times for the p-type InGaAs/InP superlattice structure, whereas the sample implanted at room temperature and annealed at 550 °C showed only a 20 times increase in electrical resistance. These results indicate a distinct advantage for the IM process in achieving simultaneous compositional disordering and electrical isolation for optoelectronic applications.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 1763-1771 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of strain-induced band-gap modulation has been studied in a GaAs/AlGaAs multiple-quantum-well structure with the wells located at various depths in the structure. The energy change in the quantum wells was calculated based on simple elasticity theory and measured using photoluminescence on the structure where a thin-film stressor array was deposited. Metallic thin-film stressors were made by conventional thin-film deposition techniques followed by photolithography. It was found that the elasticity theory describes the energy changes reasonably well in comparison with the experimental results. For stressor layers that react with the heterojunction structure, the situation was more complex and requires more detailed analysis. Based on the calculated and experimental results it appears possible to fabricate quantum wire with lateral dimensions of less than 100 nm using thin-film technology and e-beam lithography. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4270-4272 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Raman scattering studies were performed on ZnSe–ZnS strained-layer superlattices with different strains. In the optical phonon regime, the Raman spectra of the ZnSe–ZnS superlattices with a superlattice axis along [001] show optical phonons confined in the ZnSe well and ZnS barrier layers, and display a two-mode behavior corresponding to ZnSe-like and ZnS-like modes. We report the experimental results, by means of Raman scattering of confined longitudinal optical phonons in ZnSe–ZnS strained-layer superlattices. The Raman frequency shift dependence on the layer thickness, superlattice period, and interface strain is presented and discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 2478-2481 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: At 77 K, stimulated emission from n=1 light-hole excitons in a ZnSe-Zn0.8Cd0.2Se superlattice is observed and the oscillation mode properties of n=1 light-hole and heavy-hole excitons are analyzed. It is noticed that the ZnSe-Zn0.8Cd0.2Se superlattice with the shorter Fabry–Pérot cavity length d has the larger threshold excitation. The threshold of each mode has been determined using its time delay curve. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 7619-7620 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Brillouin scattering studies were performed on ZnSe-ZnSe1−xSx strained-layer superlattices with the composition x∼0.2. We have observed scattering from longitudinal guided modes (LGM) whose velocities are determined primarily by the C11 elastic constant. From the measured velocity of the first-order LGM of the quasitransverse acoustic mode and of the quasilongitudinal acoustic mode, the C11 and C44 elastic constants in ZnSe-ZnSe1−xSx superlattice film have been observed. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the use of thin film technology to introduce controllable and thermally stable stress into semiconductor heterostructures. Two simple schemes are used. The first scheme is to use interfacial reactions between a metal and the substrate, such as Ni, Co, Pd, and Pt on GaAs/AlGaAs. The induced stress in the structure is reproducible and controllable because the volumetric change for a given reaction is fixed, as long as the deposited film is fully reacted to form a compound. The stability of the stress depends on the stability of the compound. In the case of Ni and Co on GaAs/AlGaAs, the induced stress is thermally stable up to 600 °C. Evaporated films and reacted films are usually under tension. The second scheme is to use rf sputtered W or WNi alloy films where W or WNi is sputtered onto a negative dc biased substrate. This scheme effectively provides highly compressed films. The thermal stability depends on the concentration of Ni in the WNi alloy. Using the two schemes above, we have fabricated low-loss (∼1 dB/cm at 1.52 μm wavelength) photoelastic waveguides in GaAs/AlGaAs heterostructures, and explored the interrelationship between the photoelastic waveguide characteristics and the stress. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5905-5908 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Longitudinal acoustic and optical phonon modes of a ZnSe/ZnSxSe1−x (x(approximately-equal-to)0.20) lattice-mismatched superlattice, prepared with atmospheric metal organic chemical vapor deposition method, have been investigated by light scattering measurements. Despite a lattice mismatch as large as 1% between the alternating layers, the measured longitudinal elastic constants are in agreement with the calculated values of an unstrained effective medium model. Furthermore, a correlative study was made by fitting the spectra to a spatial correlation model, which reproduces line shapes of the observed confined longitudinal-optical modes without incorporating the strain effects. The results demonstrate that a combination of Brillouin and Raman spectroscopy provides a good method to determine accurately the elastic constants and strain information of the lattice-mismatched superlattices and heterostructures.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Efficient 1.3 and 1.55 μm InP-based electroabsorption waveguide modulators with planar device structures have been demonstrated. Elevated temperature oxygen ion implantation and/or the photoelastic effect induced by W metal stressor stripes deposited on the semiconductor surface have been used to produce these self-aligned planar guided-wave devices. The oxygen ion mixing process has been used to simultaneously achieve compositional disordering and electrical isolation of superlattice material while the photoelastic effect has been used to improve the lateral mode confinement. A 1.3 μm Franz–Keldysh modulator with a (approximately-greater-than)10 dB extinction ratio at 2 V and a 1.55 μm device with a (approximately-greater-than)10 dB extinction ratio at 7 V are reported. These single growth step planar processing techniques have also been used to fabricate relatively low-loss (〈4 dB/cm) double heterostructure InGaAs(P)/InP single-mode optical waveguides which demonstrate their usefulness in developing InP-based photonic integrated circuits.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 625-627 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The principle of solid phase regrowth (SPR)has been used to induce compositional disordering in AlGaAs/GaAs superlattice structures in the temperature range of 400 °C (30 min)–650 °C (30 s) as compared to the conventional diffusion method in the temperature range of 600–850 °C for hours. The SPR process is simple to implement, requiring only thin-film deposition and annealing. The crystal quality as well as the photoluminescence signals emerging from the disordered region generally improve with increasing processing temperature. The simplicity, the low process temperature, and the short process duration of the SPR technique are distinct advantages for optoelectronic applications, especially for self-aligned devices.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Protein levels of different acetylcholinesterase (AChE) splice variants were explored by a combination of immunoblot techniques, using two different antibodies, directed against the C-terminus of the AChE-R splice variant or the core domain common to all variants. Both AChE-R and AChE-S splice variants as well as several heavier AChE complexes were detected in brain homogenates from the parietal cortex of patients with or without Alzheimer's disease (AD) as well as the cerebrospinal fluid (CSF) of AD patients, compatible with the assumption that CSF AChEs might originate from CNS neurons. Long-term changes in the composition of CSF AChE variants were further pursued in AD patients treated with rivastigmine (n = 11) or tacrine (n = 17) in comparison to untreated AD patients (n = 5). In untreated patients, AChE-R was markedly reduced as compared with the baseline level (37%), whereas the medium size AChE-S complex was increased by 32%. Intriguingly, tacrine produced a general and profound up-regulation of all detected AChE variants (up to 117%), whereas rivastigmine treatment caused a mild and selective up-regulation of AChE-R (∼10%, p 〈 0.05). Moreover, the change in the ratio of AChE-R to AChE-S (R/S-ratio) strongly and positively correlated with sustained cognition at 12 months (p 〈 0.0001). Thus, evaluation of changes in the composition of CSF AChE variants may yield important information referring to the therapeutic efficacy and/or development of drug tolerance in AD patients treated with anti-cholinesterases.
    Type of Medium: Electronic Resource
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