08 Fakultät Mathematik und Physik

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1984 - 19894

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Publication Type: search.filters.UBSTyp.ZeitschriftenartikelAuthor: search.filters.author.Holdik, Karl

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    Electric field-induced gas emission from PVDF films
    (1987) Bihler, Eckardt; Holdik, Karl; Eisenmenger, Wolfgang
    Charge injection, conduction and trapping are important processes for stabilizing the electric polarization in the piezoelectric polymer PVDF. In order to study the nature of the pertinent charges in PVDF we measured the gas emission from PVDF using a permeable electrode under an applied electric field up to 0.7 MV/ cm. The films were covered on one side with evaporated copper, on the other side a copper wire gauze was used as a permeable electrode. The polymer films were mounted in an UHV-system with a built-in quadrupole mass spectrometer for residual gas analysis. Charging the permeable electrode negatively, gas emission was found mainly consisting of hydrogen, hydrogen fluoride, and fluorine. For comparison FEP-and PET-films were examined.
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    Polarization distributions in isotropic, stretched or annealed PVDF films
    (1989) Bihler, Eckardt; Holdik, Karl; Eisenmenger, Wolfgang
    The time development of the polarization distribution across the film thickness in polyvinylidene fluoride (PVDF) was observed using the pressure step response technique. The crystallite phase composition of the samples was changed by annealing and stretching at elevated temperatures. It is shown that the crystallite phase composition, e.g., the β crystallite content, determines the spatial distribution of the permanent polarization in PVDF.
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    Quasiparticle recombination time of superconducting tin films in a parallel magnetic field
    (1985) Holdik, Karl; Welte, Michael; Eisenmenger, Wolfgang
    The influence of a parallel magnetic field on the quasiparticle recombination time of superconducting tin tunneling junctions has been determined experimentally. The results are compared with the predictions of a theoretical model that takes into account the modification of the quasiparticle density of states by the applied magnetic field.
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    Investigation of piezoelectricity distributions in poly(vinylidene fluoride) by means of quartz- or laser-generated pressure pulses
    (1984) Gerhard-Multhaupt, Reimund; Sessler, Gerhard M.; West, James E.; Holdik, Karl; Haardt, Martin; Eisenmenger, Wolfgang
    The direct determination of charge, polarization, or piezoelectricity profiles in thin dielectrics is now possible if piezoelectrically generated pressure steps or pulses and laser‐induced pressure pulses are employed. These recently developed high‐resolution methods were applied to the same piezoelectric poly(vinylidene fluoride) (PVDF) samples. Comparison of the respective results demonstrates the feasibility, the advantages, and the limitations of the new techniques for the study of piezoelectricity distributions. It is confirmed that, for relatively low poling fields, the piezoelectric activity of thermopoled PVDF foils is often confined to a layer near the positively biased surface. The same effect is found for poling with a positive corona discharge. For high‐field corona poling, the piezoelectric activity extends throughout the PVDF film.