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1990 - 199424

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Publication Type: search.filters.UBSTyp.KonferenzbeitragSubject: search.filters.subject.530Institute: search.filters.UBSInstitut.1. Physikalisches InstitutStart date: 1990End date: 1994

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Now showing 1 - 10 of 24
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    Dynamics of poling PVDF between 25°C and 120°C
    (1991) Eberle, Gernot; Eisenmenger, Wolfgang
    PVDF films with high β-content are poled in an electric field of 60 MV/m at temperatures between 25°C and 120°C. At 25°C the alignment of dipoles takes place in a central poling zone during several hours of poling. When the temperature is increased to 120°C the poling time necessary to align the dipoles in this narrow zone is reduced to several seconds. In addition, at temperatures higher than 90°C and increased poling times the central poling zone first increases but later decreases in its dielectric displacement. Simultaneously in a 10 μm regime adjoining the positive electrode a secondary displacement zone starts to grow. The strong reduction of this peak under short circuit conditions indicates hetero-charge accumulation in front of an anode.
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    Field induced gas emission of polymer films
    (1992) Selle, Michael; Eberle, Gernot; Gompf, Bruno; Eisenmenger, Wolfgang
    Poling polyvinylidene fluoride under vacuum conditions causes strong gas emission, which is analyzed with a quadrupole mass spectrometer. The dominant peak in the mass spectrum is HF, which is produced by electrochemical reactions at the sample surface. After the electric field is switched off, the gas emission unexpectedly increases to a value higher than under the field. This can be explained by ionic charge detrappingand charge migration
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    High frequency phonon transmission through amorphous films
    (1990) Mebert, Joachim; Maile, Bernd; Eisenmenger, Wolfgang
    We now report on phonon spectroscopy measurements in the frequency range from 300 GHz - 1 THz on thin amorphous films of several materials (i.e. e-beam evaporated SiO2., α-Si and α-Ge). Some films were prepared in a residual gas atmosphere as H20 and N2.
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    Polarization distribution in PVDF obtained by poling under constant current condition
    (1990) Neumann, Guido; Bihler, Eckardt; Eberle, Gernot; Eisenmenger, Wolfgang
    Since the resistivity of PVDE films increases when the films are poled, the voltage across the samples must be increased during the poling process in order to keep the current constant. Under these conditions, the formation of a polarization zone in the center of the film depth is observed. The thickness of the polarization-free zone close to the film surfaces is found to decrease with larger current densities. The results are consistent with a model assuming charge trapping in deep traps associated with the orientation of polar crystallites.
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    Phono-conduction spectroscopy of shallow states in semiconductors
    (1990) Lassmann, Kurt; Gienger, Martin; Groß, Peter
    Phonoconduction spectroscopy of shallow states in semiconductors by help of superconduction Al-junctions as phonon sources with high spectral resolution is a sensitive new technique with phonon frequencies well up in the Debye range. The large k-vector of the phonons involved opens new possibilities for the investigation of electron dynamics and states in semiconductors.
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    Phonon physics : acoustics at terahertz frequencies
    (1992) Eisenmenger, Wolfgang
    It is the natural aim of phonon physics at terahertz frequencies to extend the possible range of phonon spectroscopic investigations to the upper limit of 10THz. There are some approaches in this direction. Especially semiconductor physics and microelectronics see the importance of phonon aspects. With respect to the transitions of photons in high energetic phonons in semiconductors as Ga/As very interesting results have been obtained.
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    Binding energies of trapped charges in PVDF and P(VDF/TrFE)
    (1994) Küssner, Bodo; Dehlen, Bernhard; Eberle, Gernot; Eisenmenger, Wolfgang
    The remanent polarization in PVDF and P(VDF/TrFE) is stabilized by trapped charges. We measured the remanent polarization P as function of temperature during heating from room temperature to 180°C. The discharge current is then computed as the first derivative -dP/dT. Assuming a Debye relaxation and a continuous distribution of binding energies g(E) of the trapped charges we can show that the discharge current I(T) is proportional to g(E=mT), with m=const. The constant m can either be calculated numerically or by analytical approximation, With this method the distribution g(E) can be determined. These data are consistent with the extraordinary long life time of the remanent polarisation in PVDF and P(VDF/TrFE) at room temperature.
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    Investigation of A+-states in Si and Ge by phonon-induced conduction under uniaxial stress
    (1993) Groß, Peter; Lassmann, Kurt
    By the analysis of the stress dependence of phonon induced conductivity (PIC) with superconducting Al-tunneling junctions as phonon generators we have now found strong evidence for a split ground state in the cases Si:Ga+, Si:Al+ and Ge:Zn+.
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    Phonon spectroscopy of low energy vibrations of interstitial oxygen in germanium
    (1993) Lassmann, Kurt; Gienger, Martin; Glaser, Markus
    We can summarize our results as follows: Whereas the band of lowest lying mechanical states of interstitial oxygen in Si can be approximated by a two-dimensional oscillator perturbed by a central potential, the corresponding states in Ge can be well understood by a bindered rotator with a large central potential opposing a bending oscillation and with a sixfold modulation of the rotation due to the influence of the 6 neighbours to the Ge-O-Ge molecule
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    Electric-field profiles in corona- or electron-beam-charged and thermally treated Teflon PTFE, FEP, and PFA films
    (1992) Gerhard-Multhaupt, Reimund; Eberle, Gernot; Xia, Zhongfou; Yang, Guomao; Eisenmenger, Wolfgang
    Charge spreading in three different types of Teflon electrets was studied by means of piezoelectrically generated pressure steps, FEP and PFA samples corona-charged at room temperature usually exhibited only a surface charge layer. Uniform charge spreading throughout the bulk was found in FEP charged at or heated to high temperatures. Charge spreading was much less prominent in PFA because of a smaller retrapping efficiency. In PTFE (polytetrafluorethylene), charges from the surface and the rear electrode were injected into the bulk during charging at any temperature. Electron-beam-deposited charge layers broadened significantly upon heating.