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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 7739-7746 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spectroscopic ellipsometry (SE) has been used to study the effects of interface roughness on the optical properties of ultrathin short-period 3×3 GaAs/AlAs superlattices grown by molecular-beam epitaxy (MBE). The complex dielectric function and thickness of the whole superlattice and the thickness of the native oxide overlayer were simultaneously determined by an inversion technique from data in the 1.5–5.0 eV region. The main optical critical points E0, E0+Δ0, E1, E1+Δ1, and E2 were deduced by line-shape fitting of the second derivative of the complex dielectric function of the superlattice to the analytical line-shape expression. The interface roughness is found to shift the optical transitions, except E2, to higher energy and broaden their line shapes. A simple interpretation of the shift and broadening is given. The interface roughness and layer thicknesses obtained by SE are found to be consistent with the results of x-ray diffraction and Raman scattering studies previously reported. The results in this study demonstrate the capability of the post-growth nondestructive characterization by SE to provide useful information about the interface quality of superlattice structures, and consequently to optimize the MBE growth conditions in order to achieve the desired structural parameters.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5819-5821 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Temperature-dependent longitudinal and transverse magnetoresistance measurements have been carried out on a series of five Fe-Ni multilayer thin films. The samples were prepared by sputtering onto glass substrates that were nominally at room temperature and proved to be highly textured with the (111) direction perpendicular to the substrate. The multilayer wavelength ranged from 21 to 155 A(ring) with each sublayer composed of an equal number of monolayers of Fe and Ni. For the larger-wavelength films the magnetoresistance data shows a preferred direction of in-plane magnetization associated with the film growth parameters. With the field perpendicular to the plane the data shows the characteristic break at the applied magnetic field required for saturation. This saturation field is not temperature dependent and does not vary much or in any systematic manner with wavelength. Above the saturation field the magnetoresistance varies linearly with applied field with a slope, dR/dH, that varies systematically with temperature but very little with wavelength. For the smaller-wavelength samples where both the Fe and Ni are in the fcc crystal structure there is evidence in both the magnetization and dR/dH for a more complicated magnetic structure than either the long-wavelength films or bulk materials. In particular there is evidence for atomic scale magnetic anisotropy that differs from the film average.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4469-4469 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Compositionally modulated multilayer samples of Fe/Ni have been prepared in a dual-ion-beam sputtering system in which one beam is used to deposit the film and the other is directed at the substrate to increase the surface mobility of the arriving atoms. The multilayers had equal thicknesses of Fe and Ni, and wavelengths λ varying between 15 and 120 A(ring). The composition modulation was investigated by measuring the satellite intensities. The phases present have been studied by x-ray diffraction and extended x-ray-absorption fine-structure measurements. The x-ray investigations included Read photographs. The Ni layers have fcc structure. For λ=120 A(ring) the Fe layers primarily have the usual structure of Fe, namely bcc. For λ〈40 A(ring) the Fe layers have fcc structure. For λ=50 A(ring) the Fe layers are a mixture of fcc and bcc phases. The magnetic properties have been investigated by vibrating-sample-magnetometer measurements. For λ=35 A(ring), T=298 K, and the magnetic field parallel to the substrate, the coercive force is only a few gauss and, of more importance, the saturation magnetization is approximately the sum of the magnetization expected for bcc Fe and fcc Ni. For λ=35 A(ring), T=298 K, and the magnetic field perpendicular to the substrate, a field of 20 kOe is required to achieve saturation.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 6563-6566 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have grown thin films of (100)-oriented La0.67(CaxSr1−x)0.33MnO3 on (100) NdGaO3 substrates by off-axis sputtering. We have looked at the changes in the resistivity and magnetoresistance of the samples as the Ca/Sr ratio was varied. We find that as the calcium fraction is decreased, the lattice match to the substrate decreases, and the films become more disordered, as observed in transport measurements and the variation in Curie and peak resistance temperatures. We find a correlation between the temperature independent and T2 terms to the low temperature resistivity. The room temperature magnetoresistance exhibits a maximum as the peak temperature is increased by the substitution of Sr for Ca, and a change in the field dependence to the resistivity at room temperature is observed.© 1999 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 4985-4993 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Structural and light-emitting properties of nanoparticles of ZnS:Mn annealed in vacuum at temperatures up to 525 °C are presented. Annealing the 3.5 nm particles at temperatures up to 350 °C caused growth of some particles without substantial change in the luminescence or ZnS lattice. After annealing at 400–525 °C, the high-temperature wurtzite phase of ZnS appeared, accompanied by an increase of the average particle diameter to approximately 100 nm and a rearrangement of the Mn ions. Dramatic increase in cathodoluminescence emission was also observed and is compared to the structural information obtained from electron microscopy, x-ray diffraction, x-ray absorption fine structure, and electron paramagnetic resonance measurements. © 2000 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 115-119 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Studies of pressure induced phase transformations of ZnS nanoparticles using diamond anvil cells and synchrotron radiation were carried out to 20.0 GPa. Nanoparticles initially in the zinc-blende and wurtzite phases both transformed to the NaCl phase under the application of pressure. The zinc-blende particles, which were of 2.8 nm size, and the wurtzite particles, which were of 25.3 nm size, transformed to the NaCl phase at 19.0 and 15.0 GPa, respectively. Nanoparticles of the wurtzite phase never regained their initial wurtzite structure but returned to the zinc-blende phase upon downloading the pressure. The resultant zinc-blende nanoparticles transformed to the NaCl phase upon the reapplication of a pressure of 15.0 GPa. Nanoparticles initially in the zinc-blende phase returned to their original phase. © 2001 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3517-3520 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The thermal expansion coefficients along the a axis (αa) and c axis (αc) of barium hexaferrite were measured from room temperature to 850 °C. The thermal expansion of barium hexaferrite along the a axis and c axis was found to be linear as a function of temperature, indicating constant thermal expansion coefficients over this temperature range. The specific values for αc and αa were calculated to be 12.2±0.9 and 9.99±1.1 ppm/°C, respectively. The measurements were performed using a standard x-ray powder diffraction setup equipped with a high temperature stage. © 1996 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 7850-7859 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The phase evolution during annealing of Al/Ni multilayer samples prepared by ion-beam sputtering with composition modulation wavelengths Λ between 10 and 400 nm was determined using x-ray diffraction and differential scanning calorimeter measurements. Samples with average compositions of Al0.40Ni0.60 and Al0.75Ni0.25 were investigated. For the Al0.40Ni0.60 samples the following results were obtained. A measure of the degree of periodicity and the sharpness of the interfaces in a sample with Λ=80 nm was the large number (over 20) of peaks observed in small-angle x-ray scattering measurements. A sample with Λ=10 nm was transformed by heat treatment directly to the AlNi phase. In the Λ=80 nm sample, the first phase formed after annealing was the metastable η phase. The η phase was identified as Al9Ni2. In the 400 nm wavelength sample, both the metastable η phase and the stable Al3Ni formed after the first exothermic reaction. For the Al0.75Ni0.25 samples two results were obtained. A Λ=11.4 nm sample transformed directly on annealing into Al3Ni. The η phase was the first phase formed on annealing a Λ=100 nm sample. The difference in the component diffusivities and the concentration gradient play an important role in controlling phase formation and evolution. © 1994 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1783-1785 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the growth of a new closely lattice-matched II-VI heterostructure: ZnTe/CdSe (Δa/a∼0.3%). Epilayers of zinc blende CdSe grown on ZnTe buffer layers are shown to have much better quality than those grown earlier (with a 7% mismatch) on GaAs substrates. This permitted the first successful growth of high quality superlattices of ZnTe/CdSe. The superlattices were studied by x-ray diffraction, transmission electron microscopy, and optical techniques. Results of photoluminescence and optical transmission measurements show that ZnTe/CdSe superlattices have a very small valence-band offset.
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 2680-2682 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the growth of cubic (zinc blende) CdSe epilayers on [100] GaAs substrates by molecular beam epitaxy. The lattice constant of the CdSe epilayers is 6.077 A(ring), and the energy gap is 1.75, 1.74, and 1.67 at 10, 80, and 300 K, respectively.
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