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  • 1
    Electronic Resource
    Electronic Resource
    On the structure and stability of the H2O− ion (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 2913-2918 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potential energy surfaces of the three lowest bound electronic states (1 2A′, 2 2A′, and 2A″) of H2O− have been investigated by ab initio calculations using highly correlated electronic wave functions. Minima resulting from ion–quadrupole interactions between the O−(2P) and H2(1Σ+) fragments were found for linear 2Σ+ and 2Π O−⋅⋅⋅H2 structures. The corresponding dissociation energies amount to about 0.2 eV. The 2Σ+ (2A′) minimum is separated by a barrier from the H2O+e continuum, while the 2Π (2A″) state is connected via a similar barrier to another local minimum of 2Π symmetry originating from the ion–dipole interaction of OH(X 2Π) and H−(1S). Hence, in accordance with recent experimental findings of de Koning and Nibbering, the H2O− ion is found to be a bound species in ion–quadrupole or ion–dipole cluster structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453079
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  • 2
    Electronic Resource
    Electronic Resource
    Defect-induced redistribution of Fe- or Ti-implanted and annealed GaAs, InAs, GaP, and InP (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 3514-3521 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structural properties of GaAs, InAs, GaP, and InP implanted by Fe or Ti at 150 keV/400 keV and doses of 1012–1×1015 cm−2 and the depth distribution of the implants are comparatively studied before and after annealing with and without a Si3N4 cap. Results of Rutherford backscattering, x-ray double-crystal diffractometry, and secondary-ion mass spectroscopy experiments are presented. Fe redistributes strongly in all materials upon annealing, Ti does not redistribute at all. The driving force of redistribution of Fe is not classical diffusion but reaction with implantation-induced defects and stoichiometric imbalances. The actual defect chemistry of the as-implanted arsenides is found to be fundamentally different from the as-implanted phosphides since in the latter case the mass ratio of the constituents is much larger and the specific energy for amorphization is much lower. Consequently, redistribution of Fe in the phosphides and the arsenides differs qualitatively from each other.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351429
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  • 3
    Electronic Resource
    Electronic Resource
    Surface phase behavior in binary polymer mixtures. I. Miscibility, phase coexistence, and interactions in polyolefin blends (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 8786-8794 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have used composition depth profiling of polymer bilayers, based on nuclear reaction analysis, to determine miscibility, phase coexistence, and critical temperatures in mixtures of random olefinic copolymers of mean composition E1−x/EEx; here E is the ethylene group −(C4H8)−, EE is the ethylethylene group −[C2H3(C2H5)]−, and one of the copolymers is partially deuterated. The components in each binary mixture have different values x1,x2 of the EE fraction. Using a simple Flory–Huggins mixing model, our results enable us to extract an interaction parameter of the form χ(x1,x2,T)=A(x1,x2)/T, where for given x1,x2, A is a constant. Calculated binodals using this form fit our measured coexistence curves well, while allowing χ a weak composition dependence improves the fit further. Within the range of our parameters, our results suggest that in such binary polyolefin mixtures the interaction parameter increases roughly linearly with the extent of chemical mismatch expressed as the difference in degree of ethyl branching between the two components. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471568
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  • 4
    Electronic Resource
    Electronic Resource
    Surface phase behavior in binary polymer mixtures. II. Surface enrichment from polyolefin blends (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 8795-8806 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using nuclear reaction analysis, we have measured the enrichment by one of the components at the surface of a binary mixture of random olefinic copolymers, with components of monomer structure E1−x1EEx1 and E1−x2EEx2. Here E and EE are the linear ethylene and branched ethylethylene groups (C4H8) and [C2H3(C2H5)], respectively, and x represents the fraction of the EE group randomly distributed on the chains. We examined 12 different couples covering a range x=0.38–0.97. The mixtures, whose thermodynamic behavior was established in our earlier paper, were cast in the form of films on both a silicon and on a gold-covered silicon surface, and were investigated in the one-phase region of the binodal in the vicinity of the critical temperature. We find that it is always the more flexible component—the one with a shorter statistical step length, corresponding to the higher ethylethylene fraction (higher x)—that is enriched at the polymer/air surface. Within our resolution neither component is enriched at the polymer/solid interface. These results show clearly that enthalpic rather than entropic factors dominate the surface potential driving the surface enrichment. For two of the mixtures we determined the excess of the surface-preferred species as a function of mixture composition along an isotherm in the one-phase region of the binodal. A consistent description of our data in terms of a mean-field model is provided by including in the surface potential a term in the mixture composition gradient at the polymer surface. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471569
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  • 5
    Electronic Resource
    Electronic Resource
    Measurements of polycapillary x-ray optics (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 5933-5939 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Assemblies of hollow capillary tubes, termed "Kumakhov optics,'' can be used to control x rays for a large variety of applications. Measurements of x-ray transmission in polycapillary glass tubes were performed for the purpose of understanding their behavior in such devices. X-ray transmission was measured for straight, uniformly curved, and nonuniformly bent fibers. The data agree well with a computer simulation based on classical ray tracing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355204
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  • 6
    Electronic Resource
    Electronic Resource
    Cap and capless annealing of Fe-implanted InGaAs (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 4825-4830 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The distribution of Fe implanted at medium (1–4×1014 cm−2) and low (2×1012 cm−2) doses into InGaAs and annealed with or without a cap is investigated and the degree of compensation of such implanted regions is assessed. Secondary ion mass spectrometry profiles of low dose implanted Fe reveal a substantial role of the capping layer. Fe concentrations below as well as above the estimated metal vacancy concentration produced by implantation are observed. The effect of the cap strongly depends on the wet chemical surface preparation before insulator deposition. A correlation of the magnitude of the Fe accumulation at the InGaAs surface with defect related photoluminescence intensity is established. On the basis of the substitutional-interstitial diffusion model the barrier effects of the various caps for host and dopant atoms are analyzed. The best semi-insulating properties were obtained for plasma enhanced chemical vapor deposition SiO2 caped samples using a H2SO4:H2O2:H2O=1:1:125 surface preparation before deposition resulting in a 53% incorporation of Fe. A high electrical activation is proved directly by capacity-voltage profiles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353797
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  • 7
    Electronic Resource
    Electronic Resource
    Fe and Ti doping of InP grown by metalorganic chemical-vapor deposition for the fabrication of thermally stable high-resistivity layers (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3870-3881 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optimum conditions for the fabrication of semi-insulating InP epitaxial layers grown by metalorganic chemical-vapor deposition are investigated in a comparative study of the structural, electrical, and diffusive properties of Fe- and Ti-doped material. Thermally stable InP:Fe layers with resistivities approaching the intrinsic limit can be prepared in an environment of n-type material if the Fe concentration does not exceed but is close to its solubility limit of 8×1016 cm−3 at 640 °C. In contact with p-type layers, however, semi-insulating characteristics of InP:Fe turn out to be difficult to reproduce because of a pronounced interdiffusion of Fe and p-type dopants. Here, Ti doping of InP is shown to be a useful scheme for the fabrication of high-resistivity layers. New processes for the deposition of InP:Ti using (C5H5)2Ti(CO)2 and Ti[N(CH3)2]4 as metalorganic precursors are described in detail. Ti is found to compensate up to 2×1016 cm−3 of shallow acceptors in metalorganic chemical-vapor-phase-deposition-grown InP. Ti-doped InP layers containing more electrically active deep Ti donors than net shallow acceptors exhibit semi-insulating characteristics with a resistivity of 5×106 Ω cm. Codoping of InP:Fe with Ti turns out to be a universal process for the preparation of thermally stable high-resistivity layers. If the material is appropriately grown, Fe+Ti doping compensates both excess shallow donors and excess shallow acceptors up to concentrations of 8×1016 and 2×1016 cm−3, respectively. In contrast to InP:Fe, resistivities in excess of 107 Ω cm are obtained in contact with both symmetric n- and p-type current injecting contacts. Moreover, codoping of semi-insulating InP:Fe with Ti is found to suppress the interdiffusion of Fe and p-type dopants. Therefore, the outdiffusion and accumulation of Fe in other regions of complex device structures can be significantly reduced. The interdiffusion of Fe and p-type dopants as well as its suppression by additional doping with Ti, finally, is studied in detail, which enables a comprehensive model accounting for this phenomenon to be developed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356067
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  • 8
    Electronic Resource
    Electronic Resource
    Superconducting properties of (Bi,Pb)2Sr2Ca2Cu3Ox tapes (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 4440-4442 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: (Bi,Pb)2Sr2Ca2Cu3Ox Ag-sheathed tapes were fabricated by the standard "powder in tube'' technique. Because of the platelike growth of the Bi HTc-phase, it is possible to texture the wires by a rolling process, which improves the mechanical density. This implies an increase of the critical current density not only in zero magnetic field, but also in all external magnetic fields. By measuring ρ(T,B) curves, we have estimated the activation energy for thermically activated flux creep, U0, to vary between 200 and 20 meV in magnetic fields between 0.005 and 10 T. These low U0 values are approximately ten times smaller than in Y1Ba2Cu3O7−δ. For the Bi 2223 tapes, a power law U0∼B−α with α=0.277±0.030 was obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350785
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  • 9
    Electronic Resource
    Electronic Resource
    Redistribution of Fe and Ti implanted into InP (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2604-2609 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The redistribution of Fe and Ti implanted into InP and its recrystallization is studied using 〈m1;37.6p〉various thermal annealing techniques. Fe and Ti profiles are measured by secondary-ion mass spectroscopy and recrystallization by Rutherford backscattering channeling. Ti shows absolutely superior thermal stability under any circumstances as compared to Fe. Iron always accumulates at the surface and at a depth of approximately twice the projected range Rp. After high-dose implantation Fe additionally accumulates in the 0.8Rp region. At similar doses Ti still shows no diffusion and only faint accumulation between the surface and Rp.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349370
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  • 10
    Electronic Resource
    Electronic Resource
    A thin film CdS-self-electro-optic effect device with identically contrasted (0.95/1) optical and electro-optical loops at 210 K (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 7357-7359 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report an investigation of the improved photothermal bistable features of a thin (6 μm) CdS Self-Electro-optic Effect Device prepared by spray deposition on pyrex. For the excitation, the 514.5 nm laser line was used. Optical, optoelectronic, electrical, and electrooptical bistabilities were observed at 210 K. It is shown that it is possible to reach with thin CdS films comparable contrasted ratios in the optical and optoelectronic bistabilities. The function of the device is explained by the measured transmission dependence of the temperature. A generalized model basing on Urbach's rule for calculating the temperature dependence of the absorption coefficient is presented, leading to a fairly good agreement with the measured curve. Furthermore, the switch-off time of the optical bistability is observed to be unusually small (5 ms) for the used laser focus diameter (400 μm).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347595
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