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  • Springer  (123)
  • Wiley  (51)
  • American Institute of Physics (AIP)  (47)
  • Cambridge University Press  (4)
  • 1990-1994  (225)
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Publisher
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Polymerization of anilines by the use of copper(II) perchlorate as an oxidative coupling agent (1991)
    Springer
    Polymer bulletin 26 (1991), S. 403-408 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Polyaniline and polyalkylaniline perchlorates were prepared by oxidative coupling polymerization of anilines by the use of copper(II) perchlorate in acetonitrile as an oxidant. The corresponding polymer bases obtained by treating the perchlorates with alkaline solution were soluble in dimethylsulfoxide and partly soluble in tetrahydrofuran. The molecular weights of the THF-soluble components were 2000–6000. The charge transport of the perchlorates is influenced by the chain length and the steric effect of alkyl substituents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00302607
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  • 2
    Electronic Resource
    Electronic Resource
    Influence of refilling effects on deep-level transient spectroscopy measurements in Se-doped AlxGa1−xAs (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 525-530 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Deep-level transient spectroscopy (DLTS) and constant-capacitance DLTS (CC-DLTS) techniques have been used to investigate selenium-related DX centers in AlGaAs alloys. The value of the thermal activation energy obtained by both techniques was the same (0.21 eV); however, experimental curves show some important differences. While CC-DLTS curves show only one peak, which reveals that there exists only one DX center in Se-doped AlGaAs, in DLTS curves it is possible to resolve up to two peaks lying at a lower temperature than the one observed by CC-DLTS. This disagreement may be due to the fact that DLTS measurements are strongly affected by refilling effects which occur in the edge zone of the space-charge region during capacitance transients performed at constant voltage. These effects accelerate the capacitance transients and can lead to too high thermal-emission rates. In contrast, these effects do not affect CC-DLTS curves, because in constant-capacitance voltage transients the edge of the space-charge region remains unchanged and refilling effects do not take place. These effects are rather important on DX levels because they exhibit thermally activated capture cross sections and very low ionization factors at the experimental temperatures and, therefore, capture processes are slow and their time constants can be similar to those of the emission processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351883
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of the structure and composition of lead glasses on the thermal lensing of pulsed laser radiation (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3693-3700 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The thermal lensing characteristics of several silicate, germanate, phosphate, and borate glasses were studied using a laser with a 7 ns pulse at 457 nm in a tight focus geometry. A geometric model was developed to describe the quadratic radial profile of the refractive index resulting from the laser-induced temperature profile. This model was utilized to interpret the effects of some of the relevant experimental parameters on the fluence transmission experiments. The influence of material properties such as different types of network former and modifier ions on the nonlinear optical properties of these materials were also studied. It was found that: (i) the greatest influence of the network modifier ions was due to their effect on the absorption coefficient of the glasses; (ii) in lead glasses, the thermo-optic coefficients dn/dT of the germanates and silicates with random network structures were greater than those of the borate and phosphate glasses with ring and chain structures; and (iii) the main contribution to the thermo-optic coefficient comes from the thermally induced changes in the electronic polarizability of the glass components. In these glasses, the oxygen polarizability provides the dominant contribution and is affected by the variations in the polarizing power (charge to radius-squared ratio) of the network former ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350879
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of Nd3+ concentration on the emission spectra of CaF2:Nd layers grown by molecular-beam epitaxy (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4485-4489 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nd3+-doped CaF2 monocrystalline films have been grown by molecular-beam epitaxy using CaF2 and NdF3 evaporation on CaF2 (100) substrates. Auger electron spectrometry and high-energy electron diffraction have been used as in situ techniques to characterize the grown layers. No degradation of crystallinity was observed even for the highest levels of doping considered. The effect of Nd3+ concentration is studied by means of the photoluminescence signal of Nd3+ ions. The results can be compared favorably with those of bulk CaF2:Nd crystals. For a given Nd3+ concentration a lower quantity of Nd3+ aggregate centers is observed. Nd3+ ions can, therefore, be efficiently incorporated in isolated Nd3+-F− centers up to concentrations of 3.7 wt % Nd3+ without emission quenching of the associated line at 1.0457 μm. The results are related to the thermodynamic conditions imposed by the molecular-beam epitaxy technique.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349082
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  • 5
    Electronic Resource
    Electronic Resource
    Raman study under resonant conditions of defects near the interface in a GaAs/Si heterostructure (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4777-4781 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A Raman study has been performed, under resonant conditions, on a GaAs bevelled-edge layer grown on a Si substrate to characterize the optical and crystalline properties of the epilayer near the interface. According to the geometrical characteristics of the sample, a theoretical expression for the Raman intensities profile has been established and compared to the experimental data. This fitting procedure enables us to investigate the absorption coefficient of the GaAs layer due to the disorder-induced softening of the E1 edge. A quantitative analysis of the lattice disorder has been carried out on both longitudinal and transverse optical modes by studying the Raman line-shape evolution versus the laser spot position on the bevel edge. From this study, we have followed the recovery of the crystalline quality of the epilayer while going away from the interface, and evaluated the "Raman thickness'' of the dislocated layer. Using the spatial correlation model as a relationship between the disorder amount and the outcoming effects on the Raman line peaks, we have estimated the dislocation density at the heterostructure interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346133
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  • 6
    Electronic Resource
    Electronic Resource
    Tin diffusion and segregation in GaAs processed with a pulsed ruby laser (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 3832-3837 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tin-diffused GaAs layer samples, with mean concentrations larger than 1019 cm−3, were obtained by irradiating with a ruby laser GaAs substrates covered with thin tin layers. Mobilities between 100 and 200 cm2/V s were obtained. Both carrier concentration and mobility decrease with increasing energy density. Strong segregation effects were observed in the samples processed with large energy densities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346267
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  • 7
    Electronic Resource
    Electronic Resource
    Generalization of Bragg reflector geometry: Application to (Ga,Al)As-(Ca,Sr)F2 reflectors (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 5366-5368 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Bragg reflectors based on (Ca,Sr)F2 and (Ga,Al)As are studied. Modeling and fabrication of these structures by molecular-beam epitaxy were performed. Quarter-wave Bragg reflectors were found to present an excellent reflectance around the wavelength of interest, 870 nm, for only three periods of bilayers. However, the structures grown exhibited cracks after epitaxy due to thermal stress between both materials. To alleviate this problem, other reflector geometries were investigated consisting of deviations from the classical Bragg reflector. The new geometries enable one to reduce the absolute or relative fluoride thickness within the structure. The results obtained show that the use of adequate geometries allows one to overcome the stress problem, and good heteroepitaxial reflectors with a crack-free surface morphology were obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347034
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of sintering atmosphere on magnetic aftereffect in polycrystalline yttrium iron garnet samples : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6301-6303 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time effects associated with domain-wall stabilization processes are investigated at temperatures ranging from 80 to 420 K, for yttrium iron garnet polycrystalline samples sintered in different atmospheres. A very different behavior for samples sintered in high and low oxygen partial pressures is found. Above 0.1 atm the isochronal relaxation spectra show a peak around 180 K that could be associated with an electron diffusion controlled domain-wall relaxation. The activation energy for the process is close to 0.4 eV. Below this pressure, the spectra show both positive and negative peaks as a result of the competition between disaccommodation and accommodation processes. These peaks are closely temperature spaced in the neighborhood of 130 K, and the relaxation mechanism responsible for this behavior is not yet clear.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352677
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  • 9
    Electronic Resource
    Electronic Resource
    ac impedance analysis on crystalline layered and polycrystalline bismuth titanate (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 404-408 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A comparison is made on the dielectric properties of the ferroelectric perovskite bismuth titanate for both crystalline (along different directions) and polycrystalline (with and without flux) samples, using the complex ac impedance technique. Results for the impedance, conductivity activation energies, bulk dielectric constant, and temperature behavior of the low-frequency dielectric constant are presented. We discuss these results in terms of the conduction mechanisms depending on the nature of the sample, and compare results for crystalline and polycrystalline samples. Also, we show the important influence of the flux on the dielectric properties of the different samples, which must be taken into account in the use of these materials as substrates for the growth of superconducting thin-film ceramic oxides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347730
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  • 10
    Electronic Resource
    Electronic Resource
    Polar phonon-intersubband plasmon coupling in Si delta-doped GaAs (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 1072-1078 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The present work is devoted to Raman scattering by coupled phonon-intersubband plasmon excitations in Si δ-doped GaAs. The signature of the coupled modes is pointed out by means of difference Raman scattering, and their symmetry determined according to the selection rules. A good agreement is found between the experimental spectra and those calculated in the frame of the dielectric response theory. Raman depth profiling measurements have been performed for two locations of the Si-doped sheet with respect to the sample surface. These results give evidence for electron localization in the vicinity of the doped sheet and allow the spatial extent of the electron gas to be estimated. The change undergone by the Raman signal of the coupled phonon-plasmon system is studied as a function of doping level, and the ion spreading effects are discussed. The measurements performed in a wide range of temperature are also presented and analyzed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354954
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