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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4404-4408 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have explored the effects of various processing parameters on the dielectric and electronic integrity of sol-gel-derived silicate thin films and have identified several factors that strongly affect the thin-film electronic properties. We find that sol-gel dielectrics can exhibit excellent dielectric integrity: viz., low interface trap densities and fairly good insulating properties approaching those of a thermally grown silicon dioxide film on silicon.
    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 70 (1991), S. 2220-2225 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the effects of different post-deposition temperature anneals and N-H concentrations, on the generation of ultraviolet (UV)-induced two-coordinated nitrogen dangling bonds in plasma-enhanced chemical vapor deposited (PECVD) silicon nitride films using electron spin resonance (ESR). It is shown that the nitrogen dangling bond is activated by post-deposition anneals with temperatures as low as 500 °C in N-rich PECVD nitride films followed by subsequent UV broadband illumination. It also appears that there is a possible correlation between the initial N-H concentration in the films and the concentration of generated nitrogen dangling bonds following the anneal/UV sequence. We also report the charge state associated with the nitrogen dangling bond using a combination of ESR and capacitance versus voltage measurements; these measurements suggest that this two-coordinated defect is electrically neutral when paramagnetic.
    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 73 (1993), S. 7720-7729 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron paramagnetic resonance (EPR) and photothermal deflection spectroscopy (PDS) have been utilized to characterize samples of lead lanthanum zirconate titanate (PLZT) ceramics before and after ultraviolet (uv) irradiation. We find a variety of EPR resonances in the unirradiated samples, including those attributable to Cu+2, Fe+3, Pb+3, and Ti+3 ions. The dark optical absorption spectra show broad, exponential subgap absorption tails which increase in magnitude with decreasing grain size. In addition, some of the larger grain ceramics show a prominent absorption enhancement which seems to correlate well with the density of Ti+3 centers. During and after uv illumination with light near the PLZT band gap, substantial increases are seen in the density of paramagnetic Ti+3 and Pb+3 ions, and a broad absorption peak appears at ∼2.6 eV. The spatial distribution of the induced absorption correlates well with the location of the absorbed uv, suggesting that photoproduced carrier pairs are trapped at Ti+4 and Pb+2 ions producing the observed paramagnetism. The Ti+3 EPR spectra can be successfully fit using the crystal-field-splitting parameters derived from the PDS data. We also observe that both the paramagnetism and the induced absorption are readily bleached by light absorbed in the spectral region where the photoinduced peak is located. We suggest that this effect is due to photoionization of the localized charges.
    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 80 (1996), S. 4573-4577 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that voltage shifts in the hysteresis response of SrBi2Ta2O9 (SBT) thin-film capacitors can be induced using both thermal and optical methods. These voltage shifts are important since they can lead to imprint failure in ferroelectric memory devices. It is suggested that the voltage shifts in the hysteresis curve of SBT are caused by trapping of electronic charge carriers near the film/electrode interfaces, as has been previously reported for the Pb(Zr,Ti)O3 (PZT) system. In addition, a direct correlation is established between the magnitude and sign of remanent polarization (Pr) and the thermally induced voltage shifts (Vi), where Vi=αPr+β. It is also found that, unlike the PZT system, the thermally induced voltage shifts in SBT are smaller than those optically induced. One possible implication of this result is that the contribution of defect–dipole complexes to the voltage shifts in SBT is negligible. We suggest that the smaller contribution of defect-dipole complexes to the voltage shifts in SBT may be related to a smaller oxygen vacancy concentration in the perovskite sublattice of SBT as compared to that of PZT. © 1996 American Institute of Physics.
    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 77 (1995), S. 3975-3980 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Band structure calculations and electron paramagnetic resonance measurements are used to show that Pb states determine many of the electronic properties of Pb(Zr,Ti)O3 ferroelectric materials. The valence-band edge consists of hybridized Pb s and O p states at all compositions. The conduction-band minimum changes from a Ti d-like Γ25' state to a Pb p-like X1 state with increasing Zr content. The Pb p character accounts for the relatively small 0.2 eV increase in band gap in the Pb(Ti,Zr)O3 alloys with Zr content compared to the large 2 eV increase in band gap in Ba(Ti,Zr)O3 alloys. The paramagnetic Pb3+ hole center is found to become deeper and acquire some p character as the Zr content is raised. This is attributed to the change in conduction-band character combined with a local off-center displacement of the Pb3+ ion. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4305-4315 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pb(Zr,Ti)O3 and (Pb,La)(Zr,Ti)O3 thin films and bulk ceramics are shown to exhibit two distinct, but related types of photoinduced changes in their hysteresis behavior: (1) a photoinduced suppression of the switchable polarization and (2) a photoinduced voltage shift. Both effects give rise to stable and reproducible hysteresis changes and, thus, either could be the basis of an optical memory. Both phenomena can be explained by trapping of photogenerated charge at domain boundaries to minimize internal depolarizing fields. The space-charge field that causes the voltage-shift effect is primarily due to the migration and subsequent trapping of electrons. However, the thickness dependence of the voltage shift implies that the trapped charge is not confined to the interface. The voltage-shift kinetics exhibit a stretched-exponential dependence, whereas the polarization-suppression effect follows an exponential time dependence. However, both effects exhibit similar relaxation times. In addition, the relaxation time for the voltage-shift effect decreases with increasing light intensity according to a power-law relationship, τ∝I−n, where 0.67〈n〈0.75.
    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 80 (1996), S. 5028-5034 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ultraviolet light induced changes in polyimide liquid-crystal alignment films were investigated. Infrared, UV-visible, x-ray photoelectron spectroscopy, and electron-spin-resonance measure- ments indicated that bond breaking and subsequent oxidation reactions occur in polyimide films (SE7210, OCG284, DuPont 2555 and 2540) during the broadband UV illumination in air. Mechanical rubbing has no effect on the optical and magnetic properties but it causes the removal of the UV-exposed film. Capacitance–voltage measurements indicate that there is a slight decrease in dielectric constant and creation of net negative charges in the film after UV exposure. Sur- face tension of polyimide films before and after UV illumination and changes in the pretilt angle of the polyimide surface following UV exposure have also been studied. The decrease in pretilt angle following UV illumination is attributed to an increase in surface tension. Our results indicate that a simple UV technique can be used to achieve domain divided liquid-crystal pixel electrode design with improved viewing characteristics. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7983-7990 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We explore the interrelationships between the green 510 nm emission, the free-carrier concentration, and the paramagnetic oxygen-vacancy density in commercial ZnO phosphors by combining photoluminescence, optical-absorption, and electron-paramagnetic-resonance spectroscopies. We find that the green emission intensity is strongly influenced by free-carrier depletion at the particle surface, particularly for small particles and/or low doping. Our data suggest that the singly ionized oxygen vacancy is responsible for the green emission in ZnO; this emission results from the recombination of a photogenerated hole with the singly ionized charge state of this defect. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 7036-7040 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this study, we use electron paramagnetic resonance (EPR), optical absorption, and photoluminescence (PL) spectroscopies to determine the various Ce environments in SrS phosphor materials and how these affect absorption and emission properties. As the Ce concentration is increased from 450 to 7500 ppm, the total EPR-active Ce3+ and optical absorption signals increase linearly with Ce concentration; by contrast, the PL intensity saturates at fairly low Ce concentrations (1000 ppm Ce). We suggest that the nonlinear behavior of the PL arises from the presence of nonradiative deexcitation pathways such as defects associated with Ce sites, or Ce–Ce pairs. © 1996 American Institute of Physics.
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