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  • 1
    Electronic Resource
    Electronic Resource
    Collisional quenching of CO B 1Σ+(v′=0) probed by two-photon laser-induced fluorescence using a picosecond laser (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 3046-3054 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report measurements of room-temperature, species-specific quenching cross sections of CO B 1Σ+ (v′=0) in collisions with He, Ne, H2, N2, Ar, CO, Kr, CH4, O2, Xe, CO2, C3H8, and H2O. The measured quenching cross sections (in Å2) were 0.25±0.02, 0.54±0.04, 11.0±0.4, 24.6±0.5, 27.7±0.5, 37±2, 42±2, 81±4, 85±5, 99±6, 133±5, 144±7, and 170±8, respectively. Two-photon excitation of the CO molecules via the Hopfield–Birge system (X 1Σ+→→B 1Σ+) was performed using the frequency-tripled 690 nm emission of a custom-built picosecond dye laser. Blue-to-green fluorescence in the Angström bands (B 1Σ+→A 1Π) was detected using a microchannel-plate photomultiplier tube and recorded with a digital storage oscilloscope. The quenching cross sections were directly obtained by time resolving the temporal decay of the fluorescence signal and observing its variation as a function of the quencher pressure. The effect of radiative trapping on the observed fluorescence was also quantitatively modeled. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287144
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  • 2
    Electronic Resource
    Electronic Resource
    Production of radioactive ion beams using the in-flight technique (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 380-387 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Reactions with a heavy projectile incident on a light target can be used for the efficient in-flight production of secondary radioactive beams. An overview of this technique is given using data on 17F beams produced via the p(17O, 17F)n and d(16O, 17F)n reactions. With primary 16,17O beam currents of 100 pnA, intensities of up to 2×106 17F/s on target were achieved. Using this beam, the p(17F,α)14O reaction was measured. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150211
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  • 3
    Electronic Resource
    Electronic Resource
    The origin of photoluminescence from thin films of silicon-rich silica (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 9291-9300 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have carried out a study of the photoluminescence properties of silicon-rich silica. A series of films grown using plasma enhanced chemical vapor deposition over a range of growth conditions were annealed under argon at selected temperatures. Photoluminescence spectra were measured for each film at room temperature and for selected films at cryogenic temperatures. The photoluminescence spectra exhibit two bands. Fourier transform infrared and electron spin resonance spectroscopies were used to investigate bonding and defect states within the films. The data obtained strongly suggest the presence of two luminescence mechanisms which exhibit different dependencies on film growth conditions and postprocessing. We make assignments of the two mechanisms as (1) defect luminescence associated with oxygen vacancies and (2) radiative recombination of electron-hole pairs confined within nanometer-size silicon clusters ("quantum confinement''). © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362605
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  • 4
    Electronic Resource
    Electronic Resource
    Internal waves in xenon near the critical point (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 8 (1996), S. 1464-1475 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Just above the liquid-vapor critical point, a fluid's large compressibility causes a stable stratification in which the density varies by as much as 10% in 1 cm. This stratification supports internal gravity waves which we observed with an oscillator immersed in a near-critical xenon sample. We found the number and frequencies of the observable modes depended on the sample cell's orientation, with only two modes seen in the horizontal cell. The frequencies of the two modes had different temperature dependences: with decreasing temperature, the higher frequency increased monotonically from 0.7 to 2.8 Hz, but the lower frequency varied nonmonotonically, with a maximum of 1.0 Hz at 20 mK above the critical temperature. These temperature dependences continued to 20 mK below the critical temperature, where the xenon was separated into liquid and vapor phases. We calculated these two frequencies by solving the eigenvalue problem of internal waves in a box containing a stratified fluid. The fluid's density profile was obtained from xenon's equation of state. The calculated and measured frequencies agree to within 15%. Analytical calculations based on simple approximations of the density profile provide insight into the observed temperature dependences. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868923
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  • 5
    Electronic Resource
    Electronic Resource
    Photopyroelectric detection of hydrogen/oxygen mixtures (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 3563-3571 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: It has been found that the photopyroelectric (PPE) sensor made of thin-film polyvinylidene fluoride, sputter coated with palladium, can detect trace hydrogen gas in the presence of pure oxygen without significant drift and stabilization problems. Presently, hydrogen concentration as low as 0.1% in flowing 99.9% oxygen has been detected under standard temperature and pressure conditions. The detector has been used without a reference sensor (single mode) which simplifies the sensor system compared to previous work, at the expense of sensitivity limits. This paper describes the detection of hydrogen gas in hydrogen/oxygen mixtures, and deals with some instrumental aspects of the PPE sensor device such as background noise and signal drift. Some techniques for stabilization are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144283
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  • 6
    Electronic Resource
    Electronic Resource
    Influence of the recharging process on the dark current noise in quantum-well infrared photodetectors (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 862-864 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We show that the dark curent noise spectrum of an In0.30Ga0.70As/GaAs quantum-well infrared photodetector (QWIP) is characterized by two plateau-like frequency regions. At high frequencies, the observed noise current is due to the generation–recombination noise of carriers, which have been emitted thermionically from the quantum wells into the continuum. In the low-frequency regime, an additional contribution to the noise current is caused by the redistribution of space charges, that occurs on a time scale similar to the dielectric relaxation time. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1435071
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  • 7
    Electronic Resource
    Electronic Resource
    Noise gain and detectivity of n-type GaAs/AlAs/AlGaAs quantum well infrared photodetectors (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1251-1253 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated noise currents in GaAs/AlAs/AlGaAs quantum well infrared photodetectors (QWIPs). The specific design of these detectors implies a carrier mean-free path of exactly one period of the superlattice with N=20 periods, leading to a carrier capture probability pc(approximate)1 associated with a noise gain gn=1/N at sufficiently small applied bias voltages. The gain values obtained from our measurements are analyzed using three different noise gain models, which predict different dependencies of the detectivity on the capture probability. Our results indicate that a photoconductive QWIP with pc(approximate)1 should have a higher detectivity than a conventional GaAs/AlGaAs QWIP. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122142
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  • 8
    Electronic Resource
    Electronic Resource
    Response to "Comment on ‘Noise gain and detectivity of n-type GaAs/AlGaAs quantum well infrared photodetectors' " [Appl. Phys. Lett. 74, 892 (1999)] (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 892-892 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123958
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  • 9
    Electronic Resource
    Electronic Resource
    Luminescence efficiency measurements of silicon nanoclusters (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 523-525 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present the results of what we believe to be the first study of the power efficiency of room temperature photoluminescence from thin films of silica containing silicon nanoclusters. Films were prepared by plasma enhanced chemical vapor deposition from silane and nitrous oxide precursors. Luminescence was excited using the 476 nm line of an argon-ion laser. We have measured power efficiencies for samples that exhibit luminescence solely due to radiative recombination of quantum confined excitons. Efficiencies around 0.04% are reported. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121921
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  • 10
    Electronic Resource
    Electronic Resource
    How methanol affects the surface of blue and red emitting porous silicon (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 3669-3671 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of liquid methanol on the photoluminescence intensity and FTIR spectra of red and blue emitting porous silicon were investigated. Hydrogen passivated red emitting samples exhibit quenching and recovery of photoluminescence intensity and broadening of the Si-Hx stretch bands upon exposure to liquid methanol. Oxygen passivated red emitting samples exhibit no photoluminescence quenching. The sensitivity of the red emitting sample is due to the microstructure of porous silicon at the surface and the ability of methanol to penetrate the pores. The blue photoluminescence of thermally oxidized samples is quenched upon exposure to methanol. This is attributed to the solvent's ability to change the surface passivation which modifies existing traps and introduces competitive recombination channels for electrons. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114135
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