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  • American Institute of Physics (AIP)  (3)
  • American Chemical Society
  • 2000-2004  (3)
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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 5288-5295 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Dielectric LaAlO3 and SrTiO3 thin films and LaAlO3/SrTiO3 multilayers were grown epitaxially by pulsed laser deposition on (001) oriented (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates. Their structural characterization was carried out by x-ray diffraction and cross section transmission electron microscopy, which allowed us to determine the degree of strain in the dielectric material. For a film thickness of 200 nm we observed significant structural relaxation of the LaAlO3 and SrTiO3 single layers toward their single crystal lattice parameters in contrast to LaAlO3/SrTiO3 multilayer structures, where the dielectric material remained coherently strained. The influence of strain on the dielectric properties was studied by impedance spectroscopy in the frequency range of 40 Hz–10 MHz at room temperature. The measurements were performed on parallel plate capacitors, using epitaxial La0.4Sr0.6CoO3 films as bottom and top electrodes. The dielectric constant ε of partially relaxed and coherently strained material was nearly the same. However, the dielectric tunability, i.e., the influence of a direct current bias voltage on ε, was found to be significantly larger for coherently strained dielectrics. For [LaAlO3(30 Å)/SrTiO3(60 Å)]20 multilayers we observed a tunability of nearly 20% at room temperature for a bias voltage of only 1 V, corresponding to an electric field strength of 50 kV/cm. The total dielectric loss of the multilayer capacitors is below 1% for frequencies above 1 MHz and depends only slightly on the bias voltage. © 2002 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 88 (2000), S. 1844-1850 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ti-deficient SrTixO3−δ films, x〈1, were grown on 〈100〉 oriented SrTiO3 single crystal substrates by radio frequency magnetron sputtering from stoichiometric targets. The Ti-deficiency was adjusted by the sputtering gas pressure. The Ti/Sr cation ratio, x, was determined by Rutherford backscattering and energy dispersive x-ray analysis in a scanning electron microscope. To obtain information on the Ti/O ratio, x-ray absorption spectroscopy was carried out as well. We investigated SrTixO3−δ films with x=0.98, 0.95, and 0.89. The epitaxial growth and lattice imperfections were characterized by x-ray diffraction, electron diffraction, and high resolution transmission electron microscopy. The films crystallized in a tetragonal structure with a maximum mosaic spread of about 0.1°. The c axis was oriented perpendicular to the substrate surface where the c-lattice parameter was increasing with decreasing x. For x〉0.89, the Ti deficiency was primarily compensated by a change of the site occupation on the cation sublattices in combination with oxygen vacancies, i.e., the formation of SrTi and VO point defects, whereas for x〈0.95 the intergrowth of homologs series of the Ruddlesden–Popper phases, Srn+1TinO3n+1, was observed. The dielectric properties of the films are briefly discussed in terms of (SrTiVO) defect complexes. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 733-735 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transverse spin lifetimes of spin-polarized photogenerated carriers in InAs self-assembled quantum dots are extracted from the depolarization of their photoluminescence in a magnetic field perpendicular to the spin (the Hanle effect). Hanle measurements on a series of samples reveal that the dot dimensions influence the spin lifetime and its dependence on temperature. The spin lifetime as a function of excitation intensity is qualitatively distinct for carrier spins created in the GaAs host as compared to in the InAs wetting layer. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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