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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We communicate a detailed study of the epitaxial growth of CeO2 on MgO. The key feature of the growth is the dependence of the in-plane orientation of the CeO2 epitaxial layer on the MgO surface morphology. Atomic force microscopic (AFM) measurements, x-ray analyses, as well as high-resolution transmission electron microscopy (HRTEM) investigations reveal that on rough substrates a cube-on-cube growth of CeO2 on MgO occurs while on smooth substrates the CeO2 unit cell is rotated around the surface normal by 45° with respect to the MgO unit cell when the deposition rate is low (∼0.3 A(ring)/s) during the first stages of growth. This growth mechanism can be used for a defined fabrication of 45° grain boundaries in the CeO2 layer by controlling the surface roughness of the MgO substrate. This report demonstrates that these 45° grain boundaries may be used to fabricate YBa2Cu3O7−x Josephson junctions. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3337-3339 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial thin films of Y-doped SrZrO3 have been grown on MgO(001) by pulsed laser deposition. The deposition process has been performed at temperatures of 1000–1200 °C and at an oxygen pressure of 1.5×10−1 mbar. The samples are characterized by Rutherford backscattering spectrometry/channeling (RBS/C) and x-ray diffraction (XRD). We found an epitaxial relationship of SrZrO3 (0k0) [101](parallel)MgO (001) [100]. Good crystalline quality is confirmed by RBS/C minimum yield values of 9% and a FWHM of 0.35° of the XRD rocking curve. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 4358-4360 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to study the local atomic environments of both B and Fe in Fe3B1−xCx (0.1≤x≤0.4), NMR measurements of the hyperfine field distributions for 10B, 11B, and 57Fe have been performed at 4.2 K and from 10 to 60 MHz. It was found that the 11B and 57Fe NMR frequencies do not change with C concentration. From these results, the 11B NMR frequency characteristic of orthorhombic Fe3B was unambiguously determined to be 36.3 MHz, which is in good agreement with the value obtained for the orthorhombic Fe3B phase prepared by annealing amorphous Fe80B20. Our results show that the substitution of C atoms for B atoms has a small effect on the hyperfine field at both the B and Fe nuclei as well as on the magnetic moment of the Fe atoms.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 4349-4351 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The rapidly quenched, crystalline, Fe-rich Fe100−xMx system has been studied by 57Fe Mössbauer effect spectrometry. Boron and carbon alloys were found to have regions with cementite local structure. Small amounts of fcc γ-Fe were also observed in some of the cases. Furthermore, almost half of the carbon was concluded to be in interstitial solution. Upon annealing the carbon alloy, the fcc phase disappears to benefit formation of the cementite. In contrast, the alloys with aluminum, silicon, and phosphorous are substitutional solid solutions. After being annealed at 1073 K, they do not show changes in their hyperfine interactions nor in their crystalline structure. However, the lattice parameter of the alloy with phosphorous unexpectedly increased from a value below that corresponding to pure iron to another above it. These results are discussed on the basis of the metalloid solubilities in iron and their atomic sizes.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 3231-3233 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Based on a knowledge of the NMR spectra for FeB, Fe2B, orthorhombic Fe3B (o-Fe3B), and body-centered-tetragonal Fe3B (bct-Fe3B), the phases produced during the annealing of Fe-B amorphous alloys can be identified with greater sensitivity by NMR techniques than by x-ray diffraction. In the present work, a combination of x-ray diffraction experiments and spin-echo NMR measurements of the hyperfine field distributions for the 10B, 11B, and 57 Fe nuclei has been performed on both as-quenched and annealed Fe100−xBx (14≤x≤25) amorphous alloys. In general terms, it was found that annealing at temperatures near 400 °C resulted in crystallization products which included bct-Fe3B, while annealing at approximately 800 °C leads to the formation of o-Fe3B. The behavior of the B hyperfine field indicates that, for the Fe100−xBx amorphous alloys, an o-Fe3B-like local order is favored in the low B concentration regime, and a bct-Fe3B-like local order is favored in the high B concentration regime.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 1671-1675 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The crystallization of Fe100−xBx amorphous alloys (x=14, 20, and 25), prepared by rapid quenching from the melt, was studied by Mössbauer effect spectroscopy. In general, the present results support recent nuclear magnetic resonance studies (performed on the same samples used in this work), which indicated that the amorphous material had a body-centered-tetragonal Fe3B-like short-range order for x=25 but an orthorhombic Fe3B-like one for x=14. For x=25, annealing at about 400 °C led to the formation of almost pure body-centered-tetragonal Fe3B. On the other hand, thermal treatments at about 800 °C produced a mixture of phases for all the compositions. For x=14, formation of body-centered-tetragonal Fe3B was not observed in any case. In addition, the present Mössbauer results, combined with the previous nuclear magnetic resonance ones, show that boron and iron atomic surroundings evolve differently when alloys with x=14 are annealed at 390–420 °C. In the boride phase, the 57Fe Mössbauer signal remained "amorphouslike'' in contrast with the 11B nuclear magnetic resonance signals which became sharp and corresponded to those in tetragonal and orthorhombic Fe3B and in Fe2B. These results would indicate that under these experimental conditions the surroundings of the boron atoms become ordered before the surroundings of the iron atoms.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 875-880 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transformation of the Fe0.91B0.09 rapidly quenched crystalline alloy from its original metastable state to its equilibrium state has been studied by Mössbauer effect spectroscopy. It was found that the alloy transforms in a single step from a fine dispersion of orthorhombic-Fe3B-like complexes embedded in metallic bcc iron to a system consisting of Fe2B precipitates in the α-Fe matrix. The kinetics and temperature dependence of the process have been measured. It was determined that the relative fraction of Fe2B increases as Ω=1−exp(−kt3/2) with k=k0 exp(−Ea/kBT), indicating a diffusion-controlled, Arrhenius-type transformation, where k0=(1.92±0.26)×1014 s3/2 and Ea=(3.56±0.07) eV/atoms. Magnetization versus temperature scans have been simulated and compared to previously measured scans. A simple picture of the transformation process is given.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 2081-2091 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Schottky barrier photovoltaic detectors have been fabricated on n-AlxGa1−xN(0≤x≤0.35) and p-GaN epitaxial layers grown on sapphire. Their characteristics have been analyzed and modeled, in order to determine the physical mechanisms that limit their performance. The influence of material properties on device parameters is discussed. Our analysis considers front and back illumination and distinguishes between devices fabricated on ideal high-quality material and state-of-the-art heteroepitaxial AlxGa1−xN. In the former case, low doping levels are advisable to achieve high responsivity and a sharp spectral cutoff. The epitaxial layer should be thin (〈0.5 μm) to optimize the ultraviolet/visible contrast. In present devices fabricated on heteroepitaxial AlxGa1−xN, the responsivity is limited by the diffusion length. In this case, thick AlxGa1−xN layers are advisable, because the reduction in the dislocation density results in lower leakage currents, larger diffusion length, and higher responsivity. In order to improve bandwidth and responsivity, and to achieve good ohmic contacts, a moderate n-type doping level (∼1018 cm−3) is recommended. © 2000 American Institute of Physics.
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  • 9
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The hydrogenation–disproportionation–desorption–recombination process is known as a novel method for producing permanent magnets. The hydrogen driven reactions involved in this process are carefully studied here using Mössbauer effect, x-ray diffraction and scanning microscopy, in the Nd13.67Co15.74Al0.77Ga0.27Zr0.03Fe62.2B7.33 alloy. The temperature dependence of the hydrogenation disproportionation in the 119 kPa isochore line was obtained. Hydrogen absorption seems to occur in two steps: absorption from Nd at the grain boundaries followed by absorption from the Nd2Fe14B type phase. In order to determine the recombination kinetics, a typical mass of the alloy was submitted to disproportionation reaction at 800 °C under a hydrogen pressure of 119 kPa, followed by recombination, which was achieved by vacuum desorption at 800 °C and subsequent quenching to room temperature after various time intervals. It was found that the relative fraction of the Nd2(Fe,Co)14B phase, as obtained from the Mössbauer effect, increases as f=1−exp(−ktn) with n=0.99±0.05. From this growing law it is inferred that recombination occurs without long range diffusion and starts at the grain boundaries with zero nucleation rate. An activation energy of 0.64±0.13 eV/atom was obtained for this process. © 1998 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5870-5872 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Rapidly quenched crystalline Fe95M5 alloys were studied by spin-echo NMR experiments for frequencies ranging from 10 to 300 MHz at 4.2 K. While x-ray diffraction for all these samples show the same bcc Fe pattern, NMR measurements reveal the details of their local structural character. The C atoms form an interstitial bcc solid solution with Fe as well as Fe3C-like short-range order (SRO). Similarly, an orthorhombic Fe3B-like SRO exists in the B-containing alloy. The Si- and P-containing alloys are substitutional bcc solid solutions in which the Si and P atoms replace Fe randomly. A SRO is also found in Fe95Al5 the Al atoms avoid being close to each other. The results demonstrate that atomic size plays a key role in forming the various kinds of atomic configurations in these alloys.
    Type of Medium: Electronic Resource
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