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  • 1
    Electronic Resource
    Electronic Resource
    Al–Ga interdiffusion, carbon acceptor diffusion, and hole reduction in carbon-doped Al0.4Ga0.6As/GaAs superlattices: The As4 pressure effect (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2450-2460 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Al–Ga interdiffusion, carbon acceptor diffusion, and hole reduction were studied in carbon doped Al0.4Ga0.6As/GaAs superlattices (SL) annealed under different ambient As4 pressure conditions in the temperature range of 825 °C–960 °C. The SL were doped with carbon to an initial acceptor concentration of ∼2.9×1019 cm−3. Al–Ga interdiffusion was found to be most prominent under Ga-rich annealing ambient conditions, with interdiffusivity values, DAl–Ga, turned out to be about two orders of magnitude smaller than those predicted by the Fermi-level effect model. Under As-rich ambient conditions, the DAl–Ga values are in approximate agreement with those predicted by the Fermi-level effect model. The hole concentrations in the SL decreased significantly after annealing under As-rich and As-poor ambient conditions, while those after annealing in the Ga-rich ambient were almost totally intact. By analyzing the measured hole concentration profiles, it has been found that both carbon acceptor diffusion and reduction have occurred during annealing. Both the carbon acceptor diffusivity data and the carbon acceptor reduction coefficient data are characterized approximately by a dependence on As4 pressure values to the one-quarter power. These As4 pressure dependencies indicate that carbon diffuses via the interstitialcy or interstitial–substitutional mechanism, while hole reduction is governed by a carbon acceptor precipitation mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354682
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  • 2
    Electronic Resource
    Electronic Resource
    Disordering in 69GaAs/71GaAs isotope superlattice structures (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5206-5212 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Undoped 69GaAs/71GaAs isotope superlattice structures grown by molecular beam epitaxy on n-type GaAs substrates, doped by Si to ∼3×1018 cm−3, have been used to study Ga self-diffusion in GaAs by disordering reactions. In the temperature range of 850–960 °C, the secondary ion mass spectrometry (SIMS) measured Ga self-diffusivity values showed an activation enthalpy of 4 eV, and are larger than previously compiled Ga self-diffusivity and Al-Ga interdiffusivity values obtained under thermal equilibrium and intrinsic conditions, which are characterized by a 6 eV activation enthalpy. Characterizations by SIMS, capacitance-voltage (C-V), and transmission electron microscopy showed that the as-grown superlattice layers were intrinsic which turned into p type with hole concentrations of ∼2×1017 cm−3 after annealing, because the layers contain carbon. Dislocations of a density of ∼106–107 cm−2 were also present. However, the factor responsible for the presently observed larger Ga self-diffusivity values appears to be Si out-diffusion from the substrate, which was determined using C-V measurements. Out-diffusion of Si decreases the electron concentration in the substrate which causes the release of Ga vacancies into the superlattice layers where they become supersaturated. This Ga vacancy supersaturation leads to enhanced Ga self-diffusion in the superlattice layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352002
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  • 3
    Electronic Resource
    Electronic Resource
    Raman scattering and x-ray diffractometry studies of epitaxial TiO2 and VO2 thin films and multilayers on α-Al2O3(112¯0) (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 2841-2847 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial thin films of TiO2 and VO2 single layers and TiO2/VO2 multilayers were grown on (112¯0) sapphire (α-Al2O3) substrates using the metalorganic chemical vapor deposition technique and were characterized using Raman scattering and four-circle x-ray diffractometry. X-ray diffraction results indicate that the films are high quality single crystal material with well defined growth plane and small in-plane and out-of-plane mosaic. Single-layer films are shown to obey the Raman selection rules of TiO2 and VO2 single crystals. The close adherence to the Raman selection rules indicates the high degree of orientation of the films, both parallel and perpendicular to the growth plane. Selection rule spectra of two and three layer TiO2/VO2 multilayers are dominated by the VO2 layers with only minimal signature of the TiO2 layers. Due to the low band gap of semiconducting vanadium dioxide, we attribute the strong signature of the VO2 layers to resonant enhancement of the VO2 Raman component accompanied with absorption of the both the incident and scattered laser light from the TiO2 layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353036
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of layering and doping on the magnetic anisotropy of the layered manganites La2−2xSr1+2xMn2O7 (x=0.3–0.4) (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6621-6623 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization experiments were performed on a series of single crystals of the bilayer manganites La2−2xSr1+2xMn2O7. The magnetic anisotropy constants were determined by fitting expressions based on the tetragonal anisotropy energy to the magnetization curves. It is shown that there is a significant dipolar contribution to the first order anisotropy constant arising from the layered crystal structure. This contribution determines the magnetization direction in the doping range x=0.32–0.33 where the anisotropy due to the electronic structure is small. With increasing doping the magnetic anisotropy changes from strong uniaxial anong the c axis (K(approximate)2.5×106 erg/cm3) at x=0.3 to strong easy plane (K(approximate)−3.7×106 erg/cm3) at x=0.4 in an almost linear fashion. This evolution is explained through the change of the orbital nature of the eg electrons from predominantly d3z2−r2 to predominantly dx2−y2. On the samples displaying easy-plane anisotropy a small anisotropy in the basal plane of about −7×104 erg/cm3 was determined with (110) being the easy axis. An estimate of the spin-wave gap based on these results is in reasonable agreement with experimental determinations. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1357136
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  • 5
    Electronic Resource
    Electronic Resource
    On the use of electronic tilt sensors as angle encoders for synchrotron applications : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1712-1714 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have tested several electrolytic tilt sensors produced by Applied Geomechanics, Inc. A pair of sensors were tested by mounting them on the Chi circle of a Huber 4 circle diffractometer. The angles were scanned in 1° intervals over a range of ±35°. In these tests the resolution was about ±5 μrad but the repeatability depended on angle and varied from 70 μrad (one standard deviation) at large angles to 7 μrad at small angles. This type of tilt sensor may be too slow (2–10 s settling time) as a primary angle encoder for a monochromator or diffractometer, but for a system run by stepping motors, they would prove quite useful as secondary angle encoders. Other models which have a narrower angular range would be useful in setting and tuning focusing mirrors. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145826
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  • 6
    Electronic Resource
    Electronic Resource
    Cell design for in situ x-ray scattering studies of metal/solution interfaces under electrochemical control (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 2199-2205 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: During the last decade, there has been an increasing use of synchrotron x-ray techniques for the in situ investigation of the structure and composition of metal/solution interfaces under electrochemical control. While a number of experimental cell designs have been utilized in the past, every one of them has exhibited some shortcomings. This paper describes the development of a wide-angle-accessible, transmission-geometry, sandwich-type, x-ray/electrochemical cell. From an x-ray physics standpoint, this cell allows uninterrupted access over a 180° in-plane angle for all incident and scattering angles between 0° and 75° with respect to the sample surface. It is especially advantageous at small scattering angles because of the uniform and insignificant background scattering. From an electrochemical standpoint, this cell provides a uniform current distribution and continuous, precise potential control of the working-electrode surface; at the same time, it permits easy flushing of the working solution and even accommodates operating with flowing solution. Its only disadvantage is its inability to permit in situ cyclic voltammetry of only one surface of the single crystal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144727
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  • 7
    Electronic Resource
    Electronic Resource
    Substrate effects on the structure of epitaxial PbTiO3 thin films prepared on MgO, LaAlO3, and SrTiO3 by metalorganic chemical-vapor deposition (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 2607-2622 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial PbTiO3 films were prepared by metalorganic chemical-vapor deposition on MgO(001)-, SrTiO3(001)-, and LaAlO3(001)-oriented substrates. Four-circle x-ray diffraction, transmission electron microscopy, Rutherford backscattering (RBS) channeling, and optical waveguiding were performed to characterize the deposited films. Epitaxial, single-crystal films were obtained on all three substrate materials under the same growth conditions. However, the defect structure of the films, including grain tilting, threading dislocation density, and 90° domain formation, was strongly dependent on the choice of substrate material. Films grown on MgO(001) and LaAlO3(001) (pseudocubic indices) substrates are nominally c-axis oriented; however, the PbTiO3 grains in the film form a fourfold domain structure, with the grains tilted ∼0.6° and ∼0.7°, respectively, toward the [100] directions (cubic or pseudo-cubic) of the substrates. In addition, these films contain a significant volume fraction of 90°-domain (a-axis) structures with a critical thickness hc for domain formation below the detection level of our experiments (hc≥100 A(ring)). Together, these structural defects result in a low RBS channeling yield reduction. In contrast, films grown on SrTiO3(001) substrates showed no tilting of the c-axis grains and a minimum RBS channeling yield of as low as ∼3%. In addition, we observed that below a critical film thickness of hc∼1500 A(ring), 90° domain formation was completely suppressed resulting in a nearly perfect single-crystal structure.The refractive indices and optical birefringence of the films were measured as a function of wavelength using the film-prism coupling method. Both the ordinary and extraordinary refractive indices for films grown on MgO(001) and LaAlO3(001) were higher than that of single-crystal PbTiO3; however, the optical birefringence of films grown on MgO(001) was reduced from that of the bulk. For films grown on SrTiO3(001), the ordinary refractive index was very close to that of single-crystal PbTiO3. We correlate the refractive index values and the reduced birefringence to the degree of residual strain and the volume fraction of 90° domains in the samples, respectively. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360121
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  • 8
    Electronic Resource
    Electronic Resource
    Acceptor proteins of rat prostate residual chromatin (1984)
    s.l. : American Chemical Society
    Biochemistry 23 (1984), S. 5326-5329 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00317a034
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  • 9
    Electronic Resource
    Electronic Resource
    Phase relationships in Cu-O thin films prepared by sputtering (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 3174-3176 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The conditions for deposition of Cu and Cu-oxide thin films by reactive dc sputtering have been investigated by characterizing the crystal structure of growing films both during and immediately following deposition using an in situ x-ray diffraction technique. The relationship between sputtering conditions and the phases deposited was established for a variety of conditions. At each temperature studied, increasing the oxygen pressure in the system resulted in a systematic change in the phases deposited. Of significant importance was the identification of temperature-pressure regimes in which CuO was stable during deposition but reverted to Cu2O after the sputtering plasma was extinguished, suggesting a shift in the oxidizing potential in the plasma environment. These results also suggest that the in situ analysis technique may be ideally suited for the investigation of phase relationships and phase diagrams in other systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105775
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  • 10
    Electronic Resource
    Electronic Resource
    Denuded zone formation in carbon-implanted silicon and its application to device quality silicon-on-insulator preparation (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 970-972 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For producing ultrathin (〈0.1 μm) device quality silicon-on-insulator (SOI) films, commercially available 4-in. diameter (100) SOI wafers with single-crystal layer thickness of 1.5±0.5 μm were carbon-implanted (190 keV and 3×1016 cm−2) followed by bonding to oxidized Si wafers. The buried oxide in the SOI wafers was used as the first etch stop and the second etch was stopped at the implanted carbon peak. The formation of a carbon denuded zone allowed us to obtain ≤900±50 A(ring) SOI films free of carbon precipitation. Since precision polishing to thin one wafer of a bonded pair down to ±0.5 μm in thickness variation is available in industry, it should be possible to start the described SOI process with a bulk Si wafer, rather than an expensive SOI wafer, and obtain similar results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108536
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