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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 92-96 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A normal-incidence modulation mechanism is proposed which uses the Stark effect to induce Γ-L transitions in asymmetrically stepped AlSb/InAs/GaSb/AlSb quantum wells (QWs). A significant feature of this structure is the unusual band alignments which localize two deep wells for the Γ and L bands in adjacent layers, i.e., the Γ-valley minimum is in the InAs while the L-valley minimum is in the GaSb. In contrast to a square QW, where the Stark shifts for both Γ and L subbands are in the same direction, the two step wells for Γ and L valleys in the proposed structure are oppositely biased in the presence of an electric field. Therefore, the first Γ and L subbands move toward each other, making the Γ-L crossover occur more efficiently. Near this point, most of the Γ electrons transfer to the L valleys, where they are allowed to make intersubband transitions under normally incident radiation. As a result, the device switches from being transparent to normal-incidence light to strongly absorbing it. The calculations indicate that excellent on/off ratios can be achieved in this structure operating at T≤150 K with electric fields on the order of ∼100 kV/cm for any infrared wavelength within the range of 3–20 μm.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 4628-4634 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photocurrent excitation spectra of xenon and of the xenon–methane absorber–perturber system were studied in cells equipped with LiF windows cooled to ≈−30 °C. The cooling was needed to shift the LiF cutoff so as to enable measurements at photon energies up to the first ionization potential of Xe (12.13 eV). The spectra observed in methane–xenon mixtures were essentially similar to those in neat xenon, demonstrating that the Hornbeck–Molnar process (excitation of a xenon atom–excimer formation–ionization of an excimer) is feasible even in the presence of the molecular perturber CH4 at pressures up to ≈ 105 Pa. The primary effect of CH4 is to decrease the photocurrent, since photons in the energy range in question are absorbed by the methane molecules as well, without photoionizing them. The dependence of the current on methane concentration showed that the above mechanism is not the only one by which methane quenches the current. Moreover, the degree of quenching of the current by methane is dependent on the photon energy. The analysis of this dependence led to the assumption that an excited xenon atom and a methane molecule may form an excimer. Previous results on the Ar:Xe and Kr:Xe systems support this assumption. Peak inversions observed at high pressures in neat xenon, but absent in the CH4:Xe system, are discussed on the basis of prevailing models.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2048-2050 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel mechanism is proposed for surface-emitting second-harmonic generation at normal incidence using L-valley intersubband transitions in AlSb/GaSb/Ga1−xAlxSb/AlSb stepped quantum wells. The calculations indicate that second-harmonic susceptibilities of at least 9×10−8 m/V should be achievable under double resonance conditions, which is comparable to the best obtainable in GaAs/Ga1−xAlxAs systems for realistic propagation angles (e.g., 45°). Besides the advantage of normal-incidence geometry, the large L-valley conduction band offset between GaSb and AlSb enables doubling to frequencies spanning the entire midwave infrared spectral region. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 3160-3162 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have experimentally and theoretically investigated the Auger recombination lifetime in InAs–Ga1−xInxSb superlattices. Data were obtained by analyzing the steady-state photoconductive response to frequency-doubled CO2 radiation, at intensities varying by over four orders of magnitude. Theoretical Auger rates were derived, based on a k⋅p calculation of the superlattice band structure in a model which employs no adjustable parameters. At 77 K, both experiment and theory yield Auger lifetimes which are approximately two orders of magnitude longer than those in Hg1−xCdxTe with the same energy gap. This finding has highly favorable implications for the application of InAs–Ga1−xInxSb superlattices to infrared detector and nonlinear optical devices.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Wafer temperature, etch rate, and etch uniformity measurements of SiO2 wafers were made to characterize the use of back side helium cooling with an electrostatic wafer holder in an electron cyclotron resonance etching tool. The etch rate was found to be independent of the wafer temperature in the range between 20 and 110 °C. A 7% increase in etch nonuniformity (3σ) at higher backside pressures was attributed to helium, which leaked around the edge of the wafer, displacing the etchant gas. A back side pressure of 2–3 Torr provides a balance between wafer temperature control and helium leak rates.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 545-547 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the observation of multiple photoluminescence peaks due to monolayer thickness fluctuations in HgTe-CdTe superlattices. The spectra for seven different [211]-oriented superlattices with band gaps varying from 133 to 495 meV exhibit double peaks, and in nearly all cases the energy splitting corresponds to a difference of ≈1.5 ML in the quantum well thickness.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 8082-8086 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Anisotropic Cu–O islands form striped periodic supergratings upon annealing an oxygen-exposed Cu(110) surface. While the formation of these striped phases has been attributed to long-range repulsive forces between stripes, we show using the one-dimensional lattice gas model and Monte Carlo simulations that short range adsorbate–adsorbate interactions are capable of producing striped phases.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 187-193 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Impurity photocurrents of fluid CH4:CH3I were studied in the region of the (2E1/2)nd Rydberg series of CH3I and also beyond the 2E1/2 ionization potential up to the LiF cutoff. In the gas, a step-like rise of the photocurrent was observed at a photon energy somewhat lower (by about 20 meV) than the 2E1/2 ionization potential, indicating that high members of the (2E1/2)nd Rydberg series of methyl iodide can be ionized by further processes besides the well-known autoionization into the 2E3/2 continuum. At the high-energy side of the 2E1/2 limit further peaks appear, corresponding to simultaneous excitation of (2E1/2)nd Rydberg states and one or two quanta of the ν2(a1) vibration of CH3I. In the photon energy region of 10.8–11.8 eV a series of at least eight peaks were observed, due to excitation of vibronic levels of the Jahn–Teller split 4s Rydberg state of methane. The value of the adiabatic ionization potential 2E3/2 of CH3I in liquid CH4 near the critical point was found to be 8.30 eV, while in neat dilute CH3I gas it is 9.48 eV. The overall variation of 2E3/2 in the liquid phase (from 190 to 132 K, 6.4×1021 to 1.5×1022 cm−3) is 70 meV. In the densest (and coolest) liquid samples studied a series of peaks, with intervals of ≈60 meV appeared in the photon energy range 8.37〈hν〈8.5 eV on top of the continuous background.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of oral rehabilitation 6 (1979), S. 0 
    ISSN: 1365-2842
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: In the first part of this study, the microstructures and the mechanical properties of precious, semi-precious, and nonprecious dental casting alloys for the porcelainbaked- to-metal technique have been determined. The semi-precious alloys contained only 50 % gold, and palladium, silver, and some base metals. The nonprecious alloys were of the nickel-chromium type. Discs and miniaturized tensile bars have been cast and tested either in the as cast condition, or after a simulation of the various porcelain bakes. Proof stress, ultimate tensile strength, elongation, and plastic stiffness have been measured and results compared by use of analyses of variance. The microstructure examination shows that the simulation of the porcelain bakes improves the homogeneity of the precious and semi-precious alloys. Simultaneously, the mechanical properties of the same alloys are also improved. One semi-precious alloy, still under development at the time of these tests, has its mechanical characteristics markedly dovv'ngraded by the thermal treatments. The nickel-chromium alloys exhibit the best range of mechanical properties for the porcelain-baked-to-metal technique, when considering the three most relevant properties: proof stress, plastic stiffness, and modulus of elasticity.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 174 (1994), S. 121-131 
    ISSN: 1432-1351
    Keywords: Grasshopper stridulation ; Laser interfer ometry ; Laser vibrometry ; Tympanic membrane ; Auditory information processing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract During stridulation in the gomphocerine grasshopper Omocestus viridulus the leg movements, sound pattern and either summed auditory nerve activity or single interneuron activity were recorded. Simultaneous laser interferometric and vibrometric measurements of the displacement and velocity of the tympanic membrane were performed at the pyriform vesicle (d-receptor group). Slow displacements of the tympanic membrane occur in phase with the ventilatory and stridulatory rhythm and reach 10 μmpeak-peak and 1–3 μmpeak-peak in amplitude, respectively. Additionally, the tympanic membrane oscillates maximally in the range 5–10 kHz. These high-frequency oscillations are due to sound production and motor activity and correspond in amplitude to oscillations evoked by sound pressures of 90-dB SPL. They activate the auditory receptors during most of the stridulatory cycle even during mute stridulation. Only at the lower reversal point of the leg movement are membrane vibrations and receptor activity at a minimum. As a consequence the response of receptors and interneurons to auditory stimuli are generally impaired and an auditory response of receptors and interneurons can be elicited only during a short period at the lower reversal point. Although in this phase of the stridulatory cycle auditory sensitivity is present, males do not show phonotactic responses towards female songs during ongoing own stridulation.
    Type of Medium: Electronic Resource
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