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  • 1
    Electronic Resource
    Electronic Resource
    Statistical modeling of capture, association, and exit-channel dynamics in the CH3+/CH3CN system (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 1944-1956 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ion–molecule reaction CH3++CH3CN is known to have an association channel leading to CH3CNCH3+ in competition with the exothermic binary channels H2CN++C2H4 and C2H5++HCN. This reaction has been modeled using a master equation treatment incorporating weak collisions. The parameters required for the Rice–Ramsberger–Kassel–Marcus (RRKM) treatment have been found from an ab initio investigation of the CH3+/CH3CN energy surface. A means of including capture rate coefficients in the RRKM approach is developed, in which only the hindered dipole rotation is coupled with the reaction coordinate at large separations. Existing experimental data from ion cyclotron resonance (ICR) spectroscopy and a selected ion flow tube are fitted by the model in the pressure range 10−7–0.3 Torr. The low pressure experimental results are accounted for by weak collisions of the complex with the bath gas (when M=He, 〈ΔEdown(approximately-greater-than) and 〈ΔRdown(approximately-greater-than)∼100 cm−1) corresponding to a collision efficiency β=0.05 for M=He and 0.14 for M=CH3CN. Unimolecular rate coefficients for the (CH3CNCH3+)* complex are calculated for all product channels at a range of temperatures from 300 to 600 K. The rate coefficient for radiative stabilization was found to be 225 s−1 at the conditions of the ICR experiment. The average lifetime of the complex was calculated to vary between 29 μs at 600 K to 0.47 ms at 300 K and the termolecular association rates from 3.4×10−24–9.8×10−23 cm6 s−1 (M=He) and from 6.7×10−23–2.2×10−21 cm6 s−1 (M=CH3CN) over the temperature range 600–300 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464228
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetoelastic dependence of switching field in TbFe–FeCo giant magnetostrictive spring-magnet multilayers (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5780-5782 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The role of magneto-elastic interactions in controlling the magnitude of switching field and coercivity is investigated using sputter-deposited TbFe/FeCo multilayers. In the absence of long-range anisotropy in amorphous TbFe layers, along with negligible magneto-crystalline anisotropy in FeCo layers, reversal behavior in these multilayers is largely determined by stress-induced anisotropy. Results show that magneto-elastic constraints at the TbFe–FeCo interfaces arising due to different values of saturation magnetostriction in adjacent layers lead to biaxial stresses. This manifests itself as highly square and similar M–H loops measured in different directions in the plane of the films. The measured values of coercivity in these films (between 4.5 and 7.0 mT) are found to be in close agreement with theoretical coercivity values predicted on the basis of biaxial stress-induced anisotropy. Biaxial stresses resulting in corresponding stress-induced anisotropy were found to have interesting consequences vis-à-vis magnetization reversal. In particular, self-organized domain patterns are formed during reversal which are mediated by local stress state in the films. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372520
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  • 3
    Electronic Resource
    Electronic Resource
    Broadband optical limiting based on excited state absorption in Pt:ethynyl (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 1726-1732 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Analytical, numerical, and experimental studies of the nonlinear transmission of a Pt:ethynyl compound have been carried out. Based on a model for the electronic transitions derived from earlier work, optical limiting behavior that is both broadband across the visible and effective over a range of pulse lengths, is predicted. Detailed experimental results are presented which exhibit many of the theoretically predicted characteristics, including a broadband nonlinear response from 450 to 700 nm. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1303054
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  • 4
    Electronic Resource
    Electronic Resource
    Noise and photoconductive gain in AlGaAs/GaAs quantum well intersubband infrared photodetectors (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1889-1894 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We reevaluate the current model of noise gain and photoconductive gain for AlGaAs/GaAs quantum well infrared photodetectors. An experimental study is carried out on samples covering different types of intersubband transitions, i.e., bound-to-continuum, bound-to-quasibound, and bound- to-bound cases. A general difference between gains measured by dark current noise and by responsivity was found for all three cases, while agreement between them was found within some ranges of bias voltages for the bound-to-quasibound and bound-to-continuum samples. The thermal noise contribution to the total white noise is explicitly modeled and discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357713
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  • 5
    Electronic Resource
    Electronic Resource
    Anisotropic optical scatter from moisture patches in thin films deposited obliquely (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 1453-1455 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Moisture adsorption patches in magnesium-fluoride spacer layers of metal-dielectric-metal interference filters deposited obliquely are known to possess elliptical symmetry. The spatial distribution of light scattered from these patches at normal incidence is shown to exhibit the same elliptical symmetry with the major and minor axes interchanged.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336498
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  • 6
    Electronic Resource
    Electronic Resource
    Two-photon intersubband transitions in quantum well infrared photoconductors (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 1560-1562 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate that a symmetric GaAs/GaAlAs quantum well photodetector with a peak responsivity centered at 8.1 μm shows a significant quadratic power response at 10.6 μm. This is due to intersubband two-photon transitions from the ground level to continuum states. The two-photon responsivity agrees with a theoretical prediction based on a perturbative approach and photoconductive gain estimations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113004
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  • 7
    Electronic Resource
    Electronic Resource
    Low dark current dual band infrared photodetector using thin AlAs barriers and Γ-X mixed intersubband transition in GaAs quantum wells (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 475-477 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A low dark current dual band quantum well infrared photodetector is demonstrated by adding thin AlAs barriers to the usual detector structure, which consists of Si-doped GaAs wells separated by thick AlGaAs barriers. The advantages of adding the thin AlAs barriers to clad the quantum wells are that (a) the detector displays a low dark current and (b) intersubband photocurrents result from transitions from both the Γ ground to the first excited state, and from the Γ ground to a mixed Γ-X excited state because the X-valley band edge forms a well in AlAs and intrinsic Γ-X mixing occurs. The spectral peaks of these two transitions, which occur at 8.5 and 5.5 μm in our test structure, can be varied by changing device parameters during growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111134
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  • 8
    Electronic Resource
    Electronic Resource
    Second-harmonic generation from silicon nanocrystals embedded in SiO2 (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 766-768 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present observations of optical second-harmonic generation (SHG) from silicon nanocrystals embedded in SiO2. SHG sensitivity to Si/SiO2 interface states, charge on the nanocrystals, and particle density gradients is demonstrated. SHG is proven to be a powerful noncontact nondestructive diagnosis tool for characterization of Si-nanocrystal-based devices and materials. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1345825
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  • 9
    Electronic Resource
    Electronic Resource
    Nonlinear luminescence spectroscopy in a Pt:ethynyl compound (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 1337-1341 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report pulsed laser studies of nonlinear luminescence in a platinum ethynyl complex which, from 560 to 700 nm, shows strong two-photon absorption from the ground singlet state to an excited singlet state. The spectral dependence of the photoluminescence peaks indicates that in the region from 560 to 700 nm the two-photon absorption cross section is independent of excitation wavelength. Through the use of a simple calibration we have been able to estimate the number of states (NS1) formed from two-photon absorption, and have found good agreement with theory using the value of β=0.34 cm/GW measured previously. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369264
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  • 10
    Electronic Resource
    Electronic Resource
    Liquid-to-crystal nucleation: Automated lag-time apparatus to study supercooled liquids (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 7599-7608 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The statistics of liquid-to-crystal nucleation are studied using an automated lag-time apparatus. A single 500 μL sample of distilled water is repeatedly supercooled to a fixed temperature below its equilibrium freezing temperature, held until freezing occurred, and then thawed. Our raw data is then a set of approximately 300 lag-times for each of three set supercooling temperatures. In each case, a small insoluble AgI crystal was added to ensure heterogeneous nucleation and average nucleation temperatures around ΔT=8 K. The distribution of lag-times is analyzed, and shown to be well approximated by a single exponential decay, with average lag-times in the range of 1000–3000 seconds. This average lag-time decreases markedly at deeper levels of supercooling, and for the present data, this decrease is fit equally well by exponential, power law decay, and classical nucleation functional forms. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1407290
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