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  • 1995-1999  (470)
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  • 1
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7703-7707 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Under chemical reduction at 620 K in an atmosphere of methanol vapor in a nitrogen carrier gas, bismuth iron molybdate [Bi3FeO4(MoO4)2] will give up lattice oxygen and form highly mobile vacancies. These vacancies act as donors and sit about 0.4 eV below the conduction band edge: The band gap is 2.7 eV. Because of the ability to remove up to 1% of the lattice oxygen and still maintain crystallographic stability, it is relatively easy to produce high donor carrier densities (up to 1020 cm−3). Under these conditions, and taking into account that this is a wide gap semiconductor with well compensated deep donor levels, it is possible to measure an electrical conductivity dominated by carrier movement through the impurity band. Both phonon assisted hopping and the transition to metallic impurity conduction have been observed. The crossover temperature from conduction dominated by the impurity band to conduction dominated by the conduction band was seen to increase from 125 to 380 K with increasing oxygen depletion. © 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 77 (1995), S. 6695-6702 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Switchable polarization can be suppressed in Pb(Zr,Ti)O3 thin films by optical, thermal, electrical, and reducing processes. The optical suppression effect occurs by biasing the ferroelectric near the switching threshold and illuminating the material with band gap light; the thermal suppression effect occurs by biasing the ferroelectric near the switching threshold and heating the material to ≈100 °C. The electrically induced suppression effect, known as electrical fatigue, occurs by subjecting the ferroelectric capacitor to repeated polarization reversals. We find that the suppressed polarization in these three cases can be restored to essentially its initial polarization value by creating electronic charge carriers in the ferroelectric. This strongly suggests that all three forms of degradation largely involve locking domains by electronic charge trapping at domain boundaries. The fourth form of polarization suppression, a reducing treatment, was obtained by annealing the crystallized PZT films at 400 °C in nitrogen. The suppressed polarization could not be restored by injecting electronic charge into the reduced films, indicating that the mechanism for polarization suppression is different. In this case, it appears as though ionic defects, such as oxygen vacancies, are responsible for locking the domains, and hence, suppressing the polarization. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This work summarizes results of a simple procedure to incorporate dopants into the near surface region of single-crystal sapphire. We demonstrate the formation of iron-doped and chromium-doped sapphire thin films by solid-phase epitaxial growth. Amorphous alumina films of about 200–350 nm thickness were deposited onto single-crystal sapphire substrates. Fe or Cr ions were introduced into the films during deposition. A post-deposition thermal process was performed in oxidizing ambients at 800–1400 °C to induce epitaxial growth and to incorporate dopants. The epitaxial relationship of the grown film with the substrate was confirmed by both ion channeling and cross-sectional transmission electron microscopy. The growth kinetics were determined by time-resolved reflectivity measurements for different dopant concentrations. Ion channeling angular scans revealed that the Fe or Cr ions are incorporated onto octahedral sites (Al3+ sites) in the corundum structure as expected in equilibrium. External optical transmittance measurements exhibited absorption in the near ultraviolet range associated with the Fe3+ state. The substitution of Cr for Al3+ was also confirmed by the observation of R1 and R2 luminescence lines characteristic of ruby. The doping procedure has potential applications in the fabrication of thin film planar optical waveguides and thin film stress sensors. © 1995 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 6201-6204 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Orientation selection in platinum films of ∼20 nm thickness deposited onto (001) MgO substrates by e-beam evaporation was investigated through ion beam channeling and x-ray diffraction. A mixture of crystallites having (111) and (001) orientation was observed in Pt films deposited over a range of substrate temperatures from 25 to 700 °C, with the (111) orientation dominant at low temperatures. The (111) orientation was present in these evaporated films at significantly higher substrate temperatures than reported for Pt films deposited by sputtering or pulsed laser deposition. Both orientations had strongly preferred in-plane orientations: [110] Pt//[110] MgO for the (001)-oriented crystallites and [110]Pt//[110] MgO for the (111). The orientation selection process was rationalized based on the expected relative interfacial energies for these two orientations. © 1995 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5263-5272 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nucleation and growth kinetics of epitaxial Ba2YCu3O7−x thin films prepared on (001) SrTiO3 by postdeposition annealing of a chemically derived intermediate layer were investigated in specimens quenched from the growth anneal. The films were produced by spin-on deposition of a metal-organic precursor solution at room temperature and ambient pressure, and subsequent postdeposition annealing to form Ba2YCu3O7−x (BYC). Integrated x-ray intensities of reflections from the majority, c-axis-normal epitaxial BYC in the films were analyzed as a function of time at annealing temperature. Data collected from specimens annealed at 730 and 750 °C were consistent with upward growth of the BYC from nuclei at the substrate surface with a constant growth rate. The linear transformation kinetics suggest the growth process is controlled by molecular processes at the BYC/intermediate interface, and is not rate limited by diffusion. The activation energy for film growth along its [001] axis was estimated to be ∼5 eV. The microstructure of fully annealed films grown on (001) SrTiO3 was, in general, similar to that of films prepared on (001) LaAlO3 using the same metal-organic deposition technique. The volume fraction of the c-axis in-plane epitaxial orientation in films on (001) SrTiO3 was, however, much smaller than in films prepared identically on (001) LaAlO3. Vicinal polishing of the SrTiO3 by as much as 2.5° off [001] in the direction of [101] increased the volume fraction of c-axis in-plane domains in the films somewhat. These domains were preferentially oriented so that their (001) planes were parallel to the steps in the SrTiO3 surface. The fraction of the films on vicinal SrTiO3 occupied by c-axis in-plane domains was, however, still significantly less than that present in BYC films prepared on nominally on-axis (001) LaAlO3. © 1995 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 711-713 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Oxidation kinetics are reported for thin films of TiN, both directly exposed to a dry oxygen ambient and beneath polycrystalline Pt films of ∼100 nm thickness. Oxygen resonance backscattering spectrometry was used to detect thin oxide layers at the Pt/TiN interface produced by oxidation annealing at 550–650 °C. A linear oxidation rate law was observed for the buried TiN film, indicating the oxidation rate is independent of average titanium oxide thickness. The linear rate constant had an activation enthalpy of 2.4±0.1 eV. © 1997 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 4577-4585 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Oxidation kinetics are reported for TiN thin film diffusion barriers beneath polycrystalline Pt films of 50–200 nm thickness annealed in dry O2/N2 ambients of varying oxygen partial pressure and total pressure near 1 atm. Oxygen resonance backscattering spectrometry was used to detect thin oxide layers at the Pt/TiN interface produced by oxidation annealing at 475–650 °C. Over part of this temperature range, a linear oxidation rate law was observed for the buried TiN film, indicating the oxidation rate was independent of average titanium oxide thickness. Possible rate-controlling oxidation mechanisms are analyzed critically in light of the kinetic data and results from microstructural studies of the Pt/TiN specimens. We conclude that the rate-limiting step in the Pt/TiN oxidation process is diffusion of oxygen through the Pt grain boundaries. © 1997 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2660-2662 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electric field emanating from the surface of a poled ferroelectric (FE) can control the conduction properties of an overlying semiconducting (SC) film; this combination of materials can thus serve as a nondestructive readout (NDRO), nonvolatile memory device. We have characterized prototypes of these devices which utilize semiconducting In2O3 deposited on thin film lead zirconate titanate and bulk BaTiO3 FEs. The remanent state SC resistance in thin film FE NDRO devices is often opposite to that predicted from the known direction of FE polarization. In these cases charge injected from the SC film into the FE and trapped near the interface appears to control the electric field at the SC/FE interface. By contrast, the response of SC films on bulk FEs is largely controlled by just the FE remanent polarization. The measured SC resistance values in the "up'' and "down'' polarization states can be fairly accurately predicted by calculating the accumulation and depletion charge densities from the measured carrier concentrations, mobilities, and FE hysteresis behavior. We also observe a correlation between charge trapping in bulk and thin film of NDRO memory devices and the presence or absence of temperature-bias–stress-induced voltage shifts (imprint) of the FE hysteresis curves. We suggest that the presence of near-interfacial traps in the FE controls both imprint and NDRO memory response. © 1996 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2011-2013 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Germanosilicate glasses exhibit a significant photosensitive response which has been linked to the presence of oxygen-deficient germanium point defects in the glass structure. Based on this correlation, a process which produces highly photosensitive thin films without the use of hydrogen exposures, has been developed. This process, applicable to a wide range of desired xGeO2:bf〉(1−x)SiO2 film composition, uses reactive atmosphere sputtering and allows extensive control of the degree of oxidation of the films during synthesis to produce dramatic demonstrations of photosensitivity. In preliminary tests, our films demonstrated ultraviolet-induced refractive index perturbations (Δn) of up to −4×10−3 in the visible and −0.4×10−3 at 1.5 μm. Since no hydrogen exposure was necessary, this process yielded stable films which retained their predisposition for large photosensitivity for over one year of storage.
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