1. Physikalisches Institut
Centre de recherche public Accréditation CIR
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Téléphone : +49-(0)711-685-64947
Mail :
Adresse :
Pfaffenwaldring 57
D-70550 Stuttgart
Allemagne
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Profil scientifique partiel |
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Domaines étudiés partiels
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Quelques documents de 1. Physikalisches Institut
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Polarization dynamics of VDF-TrFE copolymers
Auteurs :
Eckardt Bihler, Gernot Eberle et Wolfgang Eisenmenger
Masquer le résumé
The polymer polyvinylidenefluoride (PVDF) and its copolymers with trifluoroethylene (TrFE) exhibit a strong piezoelectric effect after poling in high electric fields (100 MV/m). HV impulses of definite duration have been applied to the polymer in order to study the dynamics of the poling process. The dielectric displacement during the HV impulse was recorded. After the impulse, the remanent polarization under short-circuit conditions was also measured. It was thus possible to obtain the minimum poling time dependent on the applied field strength necessary to stabilize the remanent polarization. Comparing the time development of the dielectric displacement with the corresponding remanent polarization revealed a time delay between the orientation of the dipoles and their stabilization. It is concluded that the process of orientation of the dipoles itself is not sufficient to lead to a remanent polarization and that an additional interaction between the trapped charges and the oriented dipoles can explain the stability of the remanent polarization and the observed time delay.
Source :
University of Stuttgart
Energy resolved measurements of the phonon ionization of D and A+ centers in silicon with superconducting Al tunnel junctions
Auteurs :
Wilfried Burger et Kurt Lassmann
Masquer le résumé
By means of phonon spectroscopy with superconducting-Al tunnel junctions as tunable phonon generators we show that the threshold energy of the phonon-induced conductivity for Si: B+ and Si: P- agrees well with far-infrared data, proving that the ionization is mainly a one-phonon process. This ionization mechanism allows a sensitive detection of very-high-frequency phonons.
Source :
University of Stuttgart
Investigation of piezoelectricity distributions in poly(vinylidene fluoride) by means of quartz- or laser-generated pressure pulses
Auteurs :
Wolfgang Eisenmenger, Reimund Gerhard-Multhaupt, Martin Haardt, Karl Holdik, Gerhard M. Sessler et James E. West
Masquer le résumé
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.
Source :
University of Stuttgart
Investigation of piezoelectricity distributions in poly(vinylidene fluoride) by means of quartz- or laser-generated pressure pulses
Auteurs :
Wolfgang Eisenmenger, Reimund Gerhard-Multhaupt, Martin Haardt, Karl Holdik, Gerhard M. Sessler et James E. West
Masquer le résumé
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.
Source :
University of Stuttgart
Observation of phonon frequency thresholds in the anomalous Kapitza resistance
Auteurs :
Wolfgang Eisenmenger, Ulrich Heim, Otto Koblinger, Michael Welte et Michael A. Welte
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Phonons emitted by superconducting tunneling junctions into insulator crystal substrates exhibit a sharp amplitude reduction above 85 GHz if the tunneling diodes are covered by 4He. This is attributed to the onset of an enhanced phonon transport into helium.
Source :
University of Stuttgart
Electric field profiles in electron-beam-charged polymer electrets
Auteurs :
Wolfgang Eisenmenger, Reimund Gerhard-Multhaupt, Martin Haardt et Gerhard M. Sessler
Masquer le résumé
A recently developed method, which uses piezoelectrically generated pressure steps for the determination of electric-field profiles in dielectrics, has been applied to electron-beam-charged polyfluoroethylenepropylene (FEP) and polyethyleneterephthalate (PETP) electrets. The results indicate that the technique can be employed to study volume charge effects in thin dielectrics. If properly calibrated, the method provides a quantitative measure of charge-integral functions or electric-field distributions in polymer foils.
Source :
University of Stuttgart
Reflection of high-frequency phonons at silicon-solid interfaces
Auteurs :
Wolfgang Eisenmenger et Dieter Marx
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In reflection experiments with phonons of frequencies above 280 GHz propagating along (110) directions we observed large deviations from the acoustic mismatch theory for silicon-metal, silicon-condensed gas, and silicon-liquid helium interfaces.
Source :
University of Stuttgart
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