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  • 1
    Electronic Resource
    Electronic Resource
    Carbon-doped p-type AlGaAs/InAs superalloy by metalorganic chemical-vapor deposition (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 504-507 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: C doping in InGaAlAs lattice matched to InP with a p-type carrier concentration as high as 3×1019 cm−3 was demonstrated using trimethylarsenic (C source) and a superalloy approach (16 A(ring) Al0.1Ga0.9As/17 A(ring) InAs). A superalloy approach was necessary to permit C incorporation since the carbon doping was accomplished during the growth of Al0.1Ga0.9As. The carbon concentration was verified by both Hall-effect and secondary-ion-mass-spectrometry measurements. Hydrogen passivation was significant in as-grown samples but the hydrogen concentration decreased after the sample was annealed in a He atmosphere without the presence of hydrogen or arsine. The oxygen concentration in the superalloy needs to be further reduced in order for the superalloy to be effective as a base layer in a heterojunction bipolar transistor. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360858
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  • 2
    Electronic Resource
    Electronic Resource
    InAlAs/InGaAs high electron mobility transistors on low temperature InAlAs buffer layers by metalorganic chemical vapor deposition (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 212-214 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: InAlAs/InGaAs high electron mobility transistors (HEMT) with excellent high frequency performance were demonstrated. Device sizes of 0.25×50 μm and 0.10×50 μm showed current gain cutoff frequencies of 143 and 205 GHz, respectively. The HEMT structures were grown on a low temperature InAlAs buffer layers designed to eliminate conductive impurity spikes situated at the epitaxial/substrate interface. The highly resistive buffer layer (2×105 Ω cm) was obtained at a growth temperature of 475 °C using a combination of trimethylarsenic and arsine as the arsenic sources. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113137
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  • 3
    Electronic Resource
    Electronic Resource
    Statistical rate theory description of beam-dosing adsorption kinetics (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 5667-5676 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Absolute rate theory and the sticking probability approach have been previously examined as possible means of predicting the rate of adsorption. However, when applied to examine adsorption kinetics, they have been found not to contain the coverage and pressure dependence required for several important systems including CO–Ni(111). Statistical rate theory (SRT) is being developed with the objective of predicting the rate of molecular (or atomic) transport across the interface between macroscopic phases in terms of experimentally controllable variables and material properties of the two phases. Previous applications of SRT to adsorption have been limited to systems for which both the gas phase pressure and the temperature could be assumed to be constant. Herein, the SRT approach is extended to systems in which the number of molecules in the system (and hence the gas phase pressure) is not constant. To examine this extension, SRT is used to formulate the equations governing the rate of adsorption in isothermal, beam-dosing experiments. These equations are then combined with the values of certain material properties that have previously been established and a hypothesis that the value of the equilibrium adsorption cross section is given by the area of an adsorption site. The kinetic data for CO adsorbing on Ni(111) data reported by three different laboratories are then examined. For each set of experimental data, constants had to be inferred that were related to the experimental apparatus used and as such they were not expected to have any coverage or pressure dependence. The good agreement found between the predicted and measured adsorption kinetics indicates that all of the necessary coverage and pressure dependence was explicitly predicted from the SRT approach. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473587
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  • 4
    Electronic Resource
    Electronic Resource
    Temperature programmed desorption: A statistical rate theory approach (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 5677-5684 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The equation traditionally used to interpret temperature programmed desorption (TPD) spectra, the Polanyi–Wigner equation, does not contain explicitly the coverage and temperature dependence necessary to predict TPD spectra in several important systems including CO–Ni(111). Herein, the statistical rate theory (SRT) approach is used to formulate equations for temperature programmed desorption which are then used to examine TPD spectra reported in the literature for CO–Ni(111). The molecular and material properties for the CO–Ni(111) system have been previously established. One experimental spectrum has been chosen to determine the apparatus constants. The material properties and the apparatus constants are then used in the SRT equations to predict the eight additional TPD spectra for different initial coverages. A critical comparison can then be made between the theory and these eight experimental spectra, since no fitting constants were used in these eight cases. The results show that there is clearly qualitative agreement. The SRT equations are then used along with the heat of adsorption to derive an equation for the pre-exponential factor appearing in the Polanyi–Wigner equation. A prediction is made for the pre-exponential factor that is in agreement with that found empirically. The agreement found between the SRT predictions and the measured spectra indicates that all of the coverage and temperature dependence necessary to predict TPD spectra is given explicitly by the SRT approach. Hence, the experimental support for the SRT approach is enhanced. The SRT equations are then used to predict CO–Ni(111) spectra that would occur if the heating rate were varied. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473588
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  • 5
    Electronic Resource
    Electronic Resource
    Vapor–liquid equilibria of vibrating square well chains (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1293-1301 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrating square well (SW) 2-mer, 4-mer, and 8-mer with average reduced bond lengths of 0.97±0.03, 0.60±0.03, and 0.40±0.03 were studied by discontinuous molecular dynamics (DMD) simulation in the NVE ensemble. Average bond angles for the reduced bond length of 0.4 were constrained to 127±16° while the longer bond lengths were freely jointed. Vapor–liquid equilibria of the vibrating SW fluids were determined based on DMD simulation by isochoric integration and compared to that of rigid SW chains from Gibbs ensemble Monte Carlo (MC) simulation. The binodals of vibrating chains show a shift to higher temperatures relative to rigid chains, reflecting their less repulsive (more attractive) nature. Vapor pressures of the vibrating chains were computed through isochoric integration with Clausius–Clapeyron consistency to 5% or better. Vapor pressure behavior for each chain model was characterized in terms of critical temperature, critical pressure, and acentric factor. The trend in acentric factor vs. chain length showed that shorter bond lengths gave improved agreement with the experimental trend for n-alkanes. Nevertheless, the trends in acentric factor did not support any molecular model for alkanes which represented methylene segments as individual SW interaction sites. If SW chains are to be applied as models of alkanes, each interaction site must be assigned more than one methylene segment. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479315
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  • 6
    Electronic Resource
    Electronic Resource
    Vapor-liquid equilibria of square-well spheres (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 3043-3048 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Results of molecular dynamics (MD) simulations on square-well fluids with λ=1.25, 1.375, 1.5, 1.75, and 2.0 are presented. The calculation of vapor-liquid equilibrium was performed by isochoric integration of the liquid NVE data to obtain the free energy of the liquid and equating this to the vapor free energy from a modified virial equation. The saturation pressure was investigated and compared with that from Monte Carlo simulation and second-order analytical perturbation theory. The vapor pressures from the isochoric integration technique are shown to be smoother than previous results, permitting accurate estimation of the effect of the square-well width on acentric factor. With the saturated properties from molecular dynamics, the f value used in Kofke's Gibbs-Duhem integration was calculated and was found to be nearly constant. The related integration of the Clapeyron equation was implemented as a check on thermodynamic consistency. Vapor pressures presented here are consistent to within 2%. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477899
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