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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 366 (1993), S. 725-727 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A STEM equipped with an electron energy spectrometer can select a specific energy loss, and scan the focused 0.3-nm-wide electron probe over the sample12 thereby mapping the locations at which that loss occurs. Our observations are tuned to the carbon K-edge (that is, excitations from the carbon ...
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 3146-3148 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial LiTaO3 thin films were grown on (0001) sapphire in a low pressure chemical vapor deposition reactor of a new design, using lithium tantalum hexa-t-butoxide as the precursor. X-ray diffraction shows that the LiTaO3 c axis is normal to the sapphire surface. The x-ray pole figure and cross-section transmission electron microscopy diffraction show that the films were also in-plane oriented, with sapphire [101¯0] parallel to lithium tantalate [101¯0]. The refractive index of the film compares well with bulk values, over a wide wavelength range.
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 3105-3107 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial MgO thin films were grown on (100) GaAs substrates by reactive rf magnetron sputtering. Coupled x-ray diffraction, off-axis φ scan, and transmission electron microscopy indicated in-plane alignment of the MgO film with the GaAs substrate such that MgO[100](parallel)GaAs[100]. PbTiO3 ferroelectric thin films, grown on this MgO surface, were found to be oriented with PbTiO3{100}(parallel) MgO(001)(parallel) GaAs(001) and PbTiO3〈100〉(parallel) MgO[100](parallel) GaAs[100].
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 3958-3960 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A reliable high temperature substrate heater for thin film deposition was constructed. The heater has a modular design and is built from parts that are easy to fabricate. The heater consists of a square arrangement of four tungsten filaments in a disk-shaped molybdenum susceptor. The electrical connections are placed near the edge where they are easily accessed. A finite element analysis shows that this design produces a more uniform temperature distribution than typical radial arrangements of filaments. The excellent performance of the new heater is demonstrated by thickness variations of less than 2% in thin films of lithium tantalate films grown on a 3.75 cm diam substrate by a high vacuum metal-organic chemical vapor deposition process. © 1996 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 1323-1325 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial thin films of KNbO3 were deposited on SrTiO3 (100) substrate by laser ablation. In the orthorhombic phase, the four possible domain variants in the KNbO3 (110) film growth plane were determined to be KNbO3[11¯0](parallel)SrTiO3[001], [001¯], [010], and [01¯0] denoted as X+, X−, Y+, and Y−, respectively. Using a fundamental beam of 1064 nm transmitted normal to the film, the second harmonic generation (SHG) signal at 532 nm was measured and correlated to the area fractions AX+, AX−, AY+, and AY− of the four domain variants X+, X−, Y+, and Y−, respectively, in the growth plane of the film. At room temperature, the area fractions δAx=AX+−AX− and δAy=AY+−AY− were determined to be ∼3.3% and ∼2.2%, respectively. In-situ SHG measurements revealed the phase transitions to be 210±10 °C for orthorhombic–tetragonal and 450±10 °C for tetragonal–cubic transitions. In the tetragonal phase (between 210 °C and 450 °C) the KNbO3 〈100〉(parallel)SrTiO 3 〈100〉. The use of SHG as a sensitive, non-destructive and real-time probe of phase transitions and evolution of domains in ferroelectric thin films is demonstrated. © 1996 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The oxidation behavior of SiCN–ZrO2 fibers and SiCN at 1350°C are compared. The as-measured parabolic rate constants for the two materials are nearly the same (15–20 × 10−18 m2/s). However, after implementing a correction for the difference in the compositions, the rate constant is 13.2 × 10−18 m2/s for the fiber, and 29.4 × 10−18 m2/s for SiCN. The lower oxidation rate of the fiber is ascribed to the lower carbon content in the fiber material.
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  • 7
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The oxidation kinetics of amorphous silicon carbonitride (SiCN) was measured at 1350°C in ambient air. Two types of specimens were studied: one in the form of thin disks, the other as a powder. Both specimens contained open nanoscale porosity. The disk specimens exhibited weight gain that saturated exponentially with time, analogous to the oxidation behavior of reaction-bonded Si3N4. The saturation value of the weight gain increased linearly with specimen volume, suggesting the nanoscale pore surfaces oxidized uniformly throughout the specimen. This interpretation was confirmed by high-resolution electron microscopy and secondary ion mass spectroscopy. Experiments with the powders (having a particle size much larger than the scale of the nanopores) were also consistent with measurements of the disks. However, the powder specimens, having a high surface-to-volume ratio, continued to show measurable weight gain due to oxidation of the exterior surface. The wide range of values for the surface-to-volume ratio, which included all specimens, permitted a separation of the rate of oxidation of the free surface and the oxidation of the internal surfaces of the nanopores. Surface oxidation data were used to obtain the rate constant for parabolic growth of the oxidation scale. The values for the rate constant obtained for SiCN lay at the lower end of the spectrum of oxidation rates reported in the literature for several Si3N4 and SiC materials. Convergence in the behavior of SiCN and CVD-SiC is ascribed to the purity of both materials. Conversely, it is proposed that the high rates of oxidation of sintered polycrystalline silicon carbides and nitrides, as well as the high degree of variability of these rates, might be related to the impurities introduced by the sintering aids.
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  • 8
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Polycrystalline coatings of an oxide, with a columnar grain morphology, were grown on metal substrates from metalorganic precursors using the pulsed-CVD process. In a model study, films of the rutile phase of titanium dioxide were grown on nickel by thermal decomposition of titanium isopropoxide. Growth rates of up to 0.3 µm/min were obtained with conversion efficiencies (mole oxide per mole precursor) approaching 100%. The high growth rates and conversion efficiencies portend the application of this method for the manufacture of films and coatings on large surface areas, as, for example, required in the deposition of zirconium dioxide on nickel-based superalloys to serve as thermal barrier coatings on turbine blades.
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  • 9
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Needlelike, free-floating ß-crystals of silicon nitride, precipitated within a supersaturated Y-Si-Al-O-N oxynitride glass, apparently approach an equilibrium value of the aspect ratio. An expression that relates this aspect ratio to the anisotropy in the interfacial energies of the longitudinal and transverse interfaces of the crystal is derived. The prediction agrees reasonably well with theoretical estimates of the interfacial energies. Kinetic and stearic effects that often lead to nonequilibrium values of the aspect ratio are discussed.
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  • 10
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The oxidation kinetics of non-oxides depend on the inward diffusion of oxygen from the environment through the passivating silica overgrowth, the outward diffusion of the effluent species, e.g., CO, produced by the oxidation reaction at the interface, and the chemical driving forces for diffusion. An analysis that combines these factors into a unified theory is presented. The analysis is applied to experiments on the oxidation of polymer-derived amorphous silicon oxycarbide (SiCO) ceramics containing different amounts of carbon. The comparison between theory and experiment suggests that the activity of the so-called “free carbon” in SiCO is likely to be less than unity, which explains why the oxidation of SiCO is passive in nature. Further, the analysis provides quantitative answers to the following questions: (a) How is the effective diffusivity for the parabolic rate constant related to the composition of the substrate, the inward diffusivity of oxygen, and the outward diffusivity of CO? (b) How does the rate constant depend on the activity of carbon in the substrate and on the activity of carbon in the environment? (c) How is the pressure of CO generated at the interface related to the carbon activity and the diffusion coefficients? The analysis points towards the need for systematic experiments in controlled O2/CO2 environments for a more complete understanding of the oxidation kinetics of carbon-based ceramics.
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