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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6562-6568 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method for determination of the lattice parameters, parallel to the sample surface as well as normal to the sample surface, in the individual layers of single-crystalline superlattices is derived. The method is based on simulations of low angle reflectivity measurements in combination with x-ray diffraction reciprocal space mapping. The number of unknown simulation parameters is reduced from three to one, namely the layer thickness of one of the layers which constitutes the bilayer period, if compared to techniques based only on simulations of the high angle diffraction pattern. The technique is demonstrated by characterizing a single-crystalline Mo/V(001) superlattice grown by dual-target magnetron sputtering onto MgO(001) substrates. The lattice parameters of the tetragonally distorted layers were aMo=0.309 nm, cMo=0.319 nm, aV=0.305 nm, and cV=0.298 nm which correspond to a misfit dislocation density of ∼0.056 dislocations per nm at each interface and a relaxation of ∼1/3 of the coherency strain. The lattice parameters obtained by the method were confirmed by comparing a kinematical calculation of the high angle Mo/V(002) θ–2θ diffraction pattern (using the obtained values as input parameters) with the experimentally determined pattern. © 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 91 (2002), S. 3551-3555 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial aluminum nitride thin films have been grown on silicon carbide (6H-SiC) substrates by pulsed low-energy ion-assisted reactive magnetron sputter deposition (+5/−20 V of bias pulses), with ion-assisted energy (Ei)≅22 eV, under ultrahigh-vacuum conditions. Surface ion interactions during the negative bias pulse gave rise to enhanced surface mobility of adatoms with beneficial effects, which extended over the limit of ion repelling in the positive pulse as the film thickness increased. High-resolution electron microscopy shows that a large (〉90 nm) AlN domain width can form on the substrate. Domain-boundary annihilation and domain suppression during film growth have been observed. The growth rate also increased by a factor of ∼4 compared to growth conditions with no ion assistance (Ei=2 eV) and by a factor of 2 from dc ion-assisted growth. This indicates that the supply of nitrogen is a limiting factor for AlN formation and that the reactivity of nitrogen is increased on the growing AlN film surface for pulse ion-assisted deposition. High-resolution x-ray diffraction shows a reduction in the full width at half maximum of the rocking curve from 1490 to 1180 arcsec when pulsed ions are used. The cathodoluminescence shows high intensity of near-band edge emissions at wavelengths of 206 (6.02 eV) and 212 nm (5.84 eV) at a measured temperature of 5 K, with relatively low defect and oxygen and carbon impurity related emission, which is indicative of a high quality electronic material. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two different types of dislocation arrangements have been observed in hydride vapor-phase epitaxial GaN films grown on sapphire substrates using both undoped and Si-doped GaN templates grown by metalorganic chemical vapor deposition: (i) predominantly straight threading dislocations parallel to the [0001] direction in the layer grown on an undoped template, and (ii) a network of interacting dislocations of edge, screw, and mixed character in the layer grown on a Si-doped template. The two types of defect distribution result in essentially different surface morphologies, respectively: (i) low-angle grain boundaries formed by pure edge dislocations around spiral grown hillocks, and (ii) smooth surface intersected by randomly distributed dislocations. The Si doping of the GaN templates was found to enhance defect interaction in the templates and to enable a reduction of the dislocation density in the overgrown thick GaN films, although it does not lead to an improvement of the overall structural properties of the material. © 2000 American Institute of Physics.
    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 70 (1991), S. 4963-4968 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single-crystal TiN/VN superlattices with layer thicknesses lTiN=lVN and period Λ ranging from 0.96 to 12.4 nm have been grown on MgO(001) substrates at 750 °C by reactive magnetron sputtering. The superlattice structures had uniform layer thicknesses as observed by cross-sectional transmission electron microscopy and a comparison of x-ray superlattice diffraction spectra with calculated spectra indicated that any interfacial mixing had to be less than ± three atomic layers, (i.e., 〈±0.6 nm). Electrical resistivity and Hall measurements carried out as a function of Λ showed that the room-temperature electron carrier concentration n remained constant at 4.5×1022 cm−3 while the resistivity ρ increased and the electron mobility μ decreased rapidly with Λ〈6 nm. For superlattices with longer periods, ρ∼30 μΩ cm, the expected value for bulk TiN and VN connected in parallel, and μ∼5 cm2 V−1 s−1. The temperature coefficient of resistivity between 80 and 300 K decreased with decreasing Λ but remained positive (i.e., metallic). A modified quantum size effect model accounting for diffuse and specular scattering of electrons at superlattice interfaces was used to explain the electronic transport properties. Best fit results showed that the fraction of specularly scattered electrons was ∼0.3.
    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 74 (1993), S. 1663-1669 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Reactive magnetron sputtering in a mixed Ar/CH4 discharge has been used to deposit 3C-SiC films on (111)-oriented Si substrates. The carbon content as well as the crystalline structure was found to depend on both the CH4 and Ar pressures. At a total pressure of 3 mTorr and a CH4 partial pressure of 0.6 mTorr, epitaxial stoichiometric films were obtained at growth temperatures as low as 850 °C. The epitaxial nature of the films was established by x-ray diffraction using a combination of reciprocal space maps, texture scans, and 360° φ scans. Based on these analyses it could also be concluded that double-positioning domains rotated 60° to one another as well as other defects, giving rise to a mosaic broadening in the reciprocal space maps, were present in the films. Furthermore, based on plasma probe measurements and determination of the electron energy distribution functions in the near-substrate vicinity, the low growth temperature of 850 °C is suggested to be a consequence of an effective decomposition of CH4 molecules in the plasma.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thick hydride vapor phase epitaxy GaN layers have been grown on a-plane sapphire using high-temperature ion-assisted reactively sputtered AlN as a buffer layer. Transmission electron microscopy and atomic force microscopy were carried out to study the formation of the two interfaces sapphire/AlN and AlN/GaN, and their influence on the microstructure of both the buffer layer and the main GaN layer. It was demonstrated that the high-temperature reactively sputtered buffer layer provides a good alternative for hydride vapor phase epitaxy growth of GaN layers. In particular, the buffer promotes a specific interface ordering mechanism different from that observed on low-temperature buffers. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 2302-2304 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The deformation potentials of the E1(TO) mode in AlN are experimentally determined by combining infrared reflection spectroscopy and x-ray diffraction measurements and using a reported value of the Raman-stress factor for hydrostatically stressed bulk AlN. The deformation potentials are found to strongly depend on published stiffness constants of AlN. A comparison with earlier theoretically calculated values of the deformation potentials is made.© 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2636-2638 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Grazing incidence x-ray diffraction (GIXRD) using a standard laboratory x-ray source was used to study the structure of thin palladium films, with nominal thicknesses varying between 0.5 and 40 nm. The films were grown by electron beam evaporation on MgO(001) at 600 °C. Epitaxial [001]-oriented grown Pd was detected for all the films. For nominal film thicknesses 〈2.5 nm, the lateral Pd d020 plane distance was expanded as much as ∼0.8%, whereas thicker films had bulk Pd lattice spacing. The average Pd particle size, estimated from the peak broadening, was found to increase from 4 to 100 nm as the film thickness increased from 0.5 to 20 nm. For 2.5 and 10 nm thick films, four 111-oriented Pd domains rotated 90° with respect to each other were also detected. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 170-172 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial AlN thin films have been grown on 6H–SiC substrates by ultra-high-vacuum (UHV) ion-assisted reactive dc magnetron sputtering. The low-energy ion-assisted growth (Ei=17–27 eV) results in an increasing surface mobility, promoting domain-boundary annihilation and epitaxial growth. Domain widths increased from 42 to 135 nm and strained-layer epitaxy was observed in this energy range. For Ei〉52 eV, an amorphous interfacial layer of AlN was formed on the SiC, which inhibited epitaxial growth. Using UHV condition and very pure nitrogen sputtering gas yielded reduced impurity levels in the films (O: 3.5×1018 cm−3). Analysis techniques used in this study are in situ reflection high-energy electron diffraction, secondary-ion-mass spectroscopy, atomic-force microscopy, x-ray diffraction, and cross-section high-resolution electron microscopy. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1365-2559
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Anaplastic choroid plexus carcinoma is a tumour with a predilection for the posterior fossa of infants and can be difficult to distinguish histologically from medulloblastoma without the aid of immunocytochemistry using a panel of antibodies. Of a series of 17 choroid plexus carcinomas (five of which were classed as moderately differentiated and 12 as anaplastic) 17 expressed antigens to transthyretin, transferrin and cathepsin and 16 expressed carbonic anhydrase II. Eleven expressed at least one epithelial marker (cytokeratin or epithelial membrane antigen). In contrast, none of six medulloblastomas expressed epithelial markers, transrythetin, carbonic anhydrase II or transferrin, though three were positive with antibodies to cathepsin.
    Type of Medium: Electronic Resource
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