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  • 1
    Electronic Resource
    Electronic Resource
    Ultrathin delta doped GaAs and AlAs tunnel junctions as interdevice ohmic contacts (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4207-4212 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ultrathin (200 A(ring)), highly conductive GaAs and AlAs p/n junction tunnel diodes were fabricated using delta doping. The current carrying capacity of these tunnel diodes is the highest reported to date. The GaAs tunnel junction is capable of handling over 30 A/cm2 at a voltage drop of only 0.02 V, and the AlAs tunnel diode is capable of handling 27 A/cm2 at 0.10 V. These tunnel junctions are useful for interconnecting three-dimensional integrated circuits, integrated optoelectronic devices, and monolithic multijunction solar cells. The delta doping of tunnel junctions to form interdevice ohmic contacts can also be applied to other material systems as well as any devices requiring vertical interconnection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354425
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  • 2
    Electronic Resource
    Electronic Resource
    Filament formation in semiconductor laser gain regions (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2921-2925 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have linearized the equations for propagation of the beam of light in a semiconductor optical amplifier about an operating point and have derived the rate of growth of small sinusoidal perturbations of the phase and modulus of the complex field amplitude. The perturbations grow if the spatial frequency is below a critical value that depends on the intensity of the field at the operating point. For spatial frequencies above the critical value, the perturbations die out. The critical spatial frequency decreases as the intensity increases above a certain value. In other words, the tendency to filament becomes weaker as the intensity increases above a certain value. Computer-generated solutions of the propagation and gain equations are included to illustrate the growth of filaments as the plane-wave intensity changes in an amplifier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350349
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  • 3
    Electronic Resource
    Electronic Resource
    Close-coupled wave-packet calculations of the direct inelastic scattering of NO(X 2Π) from Ag(111) (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6175-6189 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this article we report an application of the time-dependent close-coupled wave-packet (CCWP) method to the rotationally inelastic scattering of NO(X 2Π) molecules from a rigid, flat Ag(111) surface. Previous applications of the CCWP method have been restricted to either direct scattering off purely repulsive potentials requiring short propagation times, or weakly physisorbed systems in which only a few internal states are coupled. The calculations reported here were performed for a molecule in an initial state with a momentum distribution peaked around E=6700 cm−1 scattering off a strongly anisotropic potential with a well depth of 4400 cm−1 and a long-range tail. Numerical procedures were introduced which enhance the efficiency of the CCWP method whenever a large number of internal states or a large number of grid points are needed to simulate the collision. For the current application to NO–Ag these techniques reduced the required CPU time by more than an order of magnitude. The resulting state–to–state transition probabilities are compared with previous time-independent close-coupled calculations, and with the semiclassical self-consistent eikonal method (SCEM). The agreement between the two quantum-mechanical methods is well within the accuracy of both numerical procedures. A comparison of the instantaneous transition probabilities calculated throughout the propagation shows good agreement between the CCWP and the SCEM calculations at high collision energies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458341
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  • 4
    Electronic Resource
    Electronic Resource
    Photoelectron spectroscopy of free radicals with cm−1 resolution: The benzyl cation (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 8665-8668 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report four vibrational bands from 0–650 cm−1 for benzyl+−h7, benzyl+−αd2, and benzyl+−d7. The exocyclic C—C bond of benzyl cation has substantial double bond character. Band assignments from ab initio frequencies illuminate the mechanism of vibronic coupling in the 1 2A2–2 2B2 system of neutral benzyl. The adiabatic ionization potential of benzyl−h7 is 7.2484±0.0006 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461249
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  • 5
    Electronic Resource
    Electronic Resource
    Close-coupled wave packet calculations of the scattering of oriented molecules from surfaces (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 767-776 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report time-dependent close-coupled wave packet calculations of transition probabilities for the direct rotationally inelastic scattering of oriented NO(X 2Π) molecules from a rigid, flat Pt surface. A comparison is made with the recent experiments of Kuipers, Tenner, Kleyn, and Stolte [Phys. Rev. Lett. 62, 2152 (1989); J. Vac. Sci. Technol. A 8, 2692 (1990)] on NO molecules which were state selected with an electrostatic hexapole lens and oriented in a Stark field. Compared with unoriented molecules, the mean rotational energy is increased (decreased) by approximately 15% when the O end (N end) of the molecule is directed towards the surface, in qualitative agreement with experiment. An analysis of the rotational excitation mechanism in this collision system shows that the steric effect is strongly influenced by the dependence of the attractive region of the gas–surface potential on molecular orientation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460345
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  • 6
    Electronic Resource
    Electronic Resource
    Quantum theory and collisional propensity rules for rotationally inelastic collisions between polyatomic molecules (NH3 and CO2) and an uncorrugated surface (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 790-800 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the general quantum theory of collisions of a symmetric top molecule with an uncorrugated surface. The similarities between the description of collisions of a molecule with a structureless atom and a flat surface allow us to exploit earlier gas-phase results. We then derive several collisional propensity rules: (1) In experiments in which both inversion states in the initial J,K doublets of para-NH3 are equally populated, both inversion states of all collisionally excited levels must also be equally populated. If, however, the initial inversion level can be state selected, then unequal populations will be observed in collisionally excited inversion doublets. (2) For transitions from the J=0 level of ortho-NH3 into rotational levels of the K=3 stack, a strong propensity will exist toward conservation of the inversion symmetry for transitions into levels with J' odd, but toward a change in the inversion symmetry for transitions into levels with J' even. (3) If the odd terms in the angular expansion of the potential dominate, then for transitions out of rotational levels with J〉0 in the K=0 stack of ortho-NH3 into rotational levels of the K=3 stack, a strong propensity will exist toward population of the upper level of the inversion doublet if the initial state has even J, and toward population of the lower level if the initial state has odd J. Using the similarities between the wave functions of a symmetric top and those of a linear polyatomic molecule with degenerate bending modes, we derived several propensity rules for the specific case of collisions of CO2 (0000) with an uncorrugated surface. In collisions which excite the low-lying (0110) bending vibration, if the initial rotational quantum number is small, then we predict that the probability of transition into a final state with J' odd will be much larger than for transition into a final state with J' even.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455202
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  • 7
    Electronic Resource
    Electronic Resource
    Pseudospectral method for solving the time-dependent Schrödinger equation in spherical coordinates (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 4115-4126 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we describe a numerically efficient pseudospectral method for solving the time-dependent Schrödinger equation in spherical coordinates. In this method the translational kinetic energy operator is evaluated with a Fourier transform. The angular dependence of the wave function is expanded on a two-dimensional grid in coordinate space and the angular part of the Laplacian is evaluated by a Gauss–Legendre–Fourier transform between the coordinate and conjugate angular momentum representations. The potential energy operator is diagonal. Calculations performed for a model system representing H2 scattering from a static corrugated surface yield transition probabilities identical to those obtained with the close coupled wave packet (CCWP) method. The new algorithm will be more efficient than the CCWP method for problems in which a large number of rotational states are coupled.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463916
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  • 8
    Electronic Resource
    Electronic Resource
    Novel alignment techniques used in multiphoton ionization experiments for laser plasma beat wave (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 2133-2137 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This paper describes the techniques used to create a fully ionized plasma by the multiphoton ionization of gases at pressures of a few Torr to give an initial electron density precision of better than a few percent, necessary for beat-wave experiments. A gas containment vessel has been constructed using high vacuum techniques with a temperature control system to maintain the fill gas pressure constant. Novel alignment techniques are used that do not require an alignment target placed in the vessel. This involves the use of a rotating pencil beam to determine the focusing of the optics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141380
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  • 9
    Electronic Resource
    Electronic Resource
    Subnanosecond polarized microfluorimetry in the time domain: An instrument for studying receptor trafficking in live cells (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 540-543 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe an instrument designed to monitor molecular motions in multiphasic, weakly fluorescent microscopic systems. It combines synchrotron radiation, a low irradiance polarized microfluorimeter, and an automated, multiframing, single-photon-counting data acquisition system, and is capable of continually accumulating subnanosecond resolved anisotropy decays with a real-time resolution of about 60 s. The instrument has initially been built to monitor ligand–receptor interactions in living cells, but can equally be applied to the continual measurement of any dynamic process involving fluorescent molecules, that occurs over a time scale from a few minutes to several hours. As a particularly demanding demonstration of its capabilities, we have used it to monitor the environmental constraints imposed on the peptide hormone epidermal growth factor during its endocytosis and recycling to the cell surface in live cells. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148691
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  • 10
    Electronic Resource
    Electronic Resource
    A high sensitivity time-resolved microfluorimeter for real-time cell biology (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 3716-3721 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe an instrument based on the novel combination of synchrotron radiation, a high sensitivity time-resolved microfluorimeter, and a multiframe single photon counting data acquisition system. This instrument has been designed specifically to measure kinetic events in live cells using fluorescence resonance energy transfer, and is capable of rapidly collecting multiple consecutive decay profiles from a small number of fluorophores. The low irradiance on the samples (〈10 mW/cm2) greatly reduces probe photobleaching and specimen photodamage during prolonged exposures. The Daresbury Synchrotron Radiation Source provides fully wavelength tunable light pulses that have a full width half-maximum of 160 ps at a repetition rate of 3.125 MHz, with the high temporal stability required for continuous measurements over periods of hours. A very low limit of detection (〈104 molecules/mW/cm2) is accomplished by combining a high-gain single photon counting detection system with a low fluorescence background optical layout. The latter is achieved by the inclusion of collimating optics, a reflecting objective, and a specially designed beam stop situated in the epi-fluorescence light-path. A typical irradiance of 8 mW/cm2 on a sample of ∼105 fluorescein molecules gives, in under 20 s, a fluorescence decay profile with a peak height of 104 counts, over 400 channels, and a signal to background ratio better than 40. The data acquisition system has been developed to have a real-time time-resolved fluorescence collection capability (denoted as TR2) so that fluorescence lifetime data can be continually collected throughout a changing process. To illustrate the potential of this instrument, we present the results of a TR2 experiment in which lifetime measurements of fluorescence resonance energy transfer are used to monitor the degree of clustering of epidermal growth factor receptors during endocytosis, over a period of about 1 h, with a 5 s resolution. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147138
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