Universität Stuttgart
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Item Open Access Quantum generation and detection of incoherent phonons in superconductors(1967) Eisenmenger, Wolfgang; Dayem, Aly H.The energy gaps in the quasiparticle excitation spectrum of superconductors cover a corresponding frequency range from about 1 to 1000 GHz. The relaxation and recombination of excited quasiparticles occur mostly via electron-phonon interaction. Thus a superconductor may be utilized as a quantum phonon generator and detector in a frequency range where conventional means of generation become prohibitively difficult. We report on experiments designed to investigate the possibility of using super conducting tunnel diodes for phonon generation and detection.Item Open Access Piezo and pyroelectricity in electrets : caused by charges, dipoles, or both?(1992) Sessler, Gerhard M.; Das-Gupta, Dilip K.; deReggi, Aimé S.; Eisenmenger, Wolfgang; Furukawa, Takeo; Giacometti, José A.; Gerhard-Multhaupt, ReimundIn a homogeneous medium space charges cannot cause piezo or pyroeiectricity. If stressed, there will be affine geometrical changes throughout the medium, and therefore the induction charges on the electrodes will remain the same, and piezoelectricity cannot be generated. However, if dipoles are present in such a homogeneous dielectric, then piezoelectricity is possible. In an inhomogeneous medium such as a semicrystalline polymer, charges and dipoles can cause piezoelectricity. If you have, for instance, a semicrystalline polymer then the crystalline and the amorphous parts are, upon compression, subjected to different degrees of deformation; and for this reason, a piezoelectric effect can be generated.Item Open Access Phonon absorption-spectroscopy in the presence of strong elastic phonon scattering(1986) Mebert, Joachim; Koblinger, Otto; Döttinger, Siegfried; Eisenmenger, WolfgangIn this work we show that in the presence of a strong phonon scattering background absorption structures can only be well resolved by reducing sample thickness to the phonon mean free path. This mean free path can be determined by analyzing the pulse shape of 285 GHz phonons. By reducing sample thickness to the appropriate value of 0,3mm the 21,2 cm -1 crystalline field transition in CaF 2:Er 3+ could be evaluated with the very high resolution of 5 GHz. In experiments performed on a 1mm thick LaF 3 Er 3+ sample we observed an absoption line at 14,2 cm -1 not visible in FIR absorption measurements.Item Open Access Down-conversion of high-frequency acoustic phonons(1987) Galkina, Tatjana I.; Blinov, A. Y.; Bonch-Osmolovskii, M. M.; Koblinger, Otto; Lassmann, Kurt; Eisenmenger, WolfgangMeasurements of phonon transport in amorphous media can give valuable information on the structural properties of these materials and may be of practical interest for its own concerning the question of thermalization in electronic devices. The existence of two-level systems in a-Si:H as one of these technically important materials has been concluded from measurements of dispersion and attenuation of acoustic surface waves.Item Open Access Phonon emission by quasiparticle decay in superconducting tunnel junctions(1970) Kinder, Helmut; Lassmann, Kurt; Eisenmenger, WolfgangImproved measurements on phonon emission and detection by tunnel junctions show qualitative agreement with a numerical evaluation of Tewordt's theory on quasiparticle lifetime.Item Open Access 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, WolfgangCharge 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.Item Open Access Polarization profiles of polyvinylidene fluoride films polarized by a focused electron beam(1989) Schilling, Doris; Dransfeld, Klaus; Bihler, Eckardt; Holdik, Karl; Eisenmenger, WolfgangThe depth profiles of the polarization in films of polyvinylidene fluoride (PVDF) as well as in vinylidene‐fluoride–trifluoroethylene (VDF‐TrFE) copolymer films polarized by a focused electron beam were investigated using the piezoelectrically generated pressure step method. The dominant polarization exhibits a broad maximum inside the film. The position of this maximum depends not only on the energy of the incident electrons but also on the material parameters of the sample. Close to the surface exposed to the electron beam we have in addition observed a small secondary maximum of opposite polarization (amounting to about 1 mC/m2). A qualitative model is presented for the poling of films of PVDF and its copolymers with TrFE by focused electron beam accounting for most of the observed features. The application of electron beams for the poling of ferroelectric films allows the production of piezoelectric bimorphs. By using a well‐focused electron beam also ferroelectric domains of very small lateral dimensions can be created which could become important for ferroelectric data storage.Item Open Access Phonon generation and detection by single particle tunneling in superconductors(1969) Eisenmenger, WolfgangIn reviewing the experiments we should summarize the arguments indicating that the observed phonon signals are due to non thermal phonon radiation emitted in the decay and recombination of injected quasiparticles. It appears very difficult to explain the observed structure in the dependence of the signal amplitude as a function of the generator voltage in terms of heat pulses, e.g., phonons with Planck's distribution. An estimate of the possible heat effect arrives at much smaller signal amplitudes than observed. In addition, only little temperature dependence of the signal amplitude is to be expected. In contrast to this, quantum processes provide a straightforward understanding of the experimental findings.Item Open Access Messung der Hyperschalldämpfung in Quarz(1965) Eisenmenger, Wolfgang; Kinder, Helmut; Lassmann, KurtZur Bestimmung der Hyperschalldämpfung in zylindrischen Quarzstäben für Longitudinalwellen in x-Richtung werden zwei Meßanordnungen für den Frequenzbereich 0,5 GHz bis 2.5GHz sowie für die Frequenz von 1O GHz bei Temperaturen von 4° K bis 273° K beschrieben. Im niedrigeren Frequenzbereich erfolgte eine Rauschbefreiung des Empfangssignals durch elektronische Abtastung und Summation. Neben der Temperatur- und Frequenzabhängigkeit der Dämpfung wurden Geometrieeinflüsse bei der Hyperschallanregung und Ausbreitung näher untersucht. Dabei traten Modeninterferenz und Keilwinkelfehler (Parallelitätsabweichungen der Stabendflächen) besonders deutlich in Erscheinung.Item Open Access Polarization profiles of electron-beam polarized VDF-TrFE copolymer films(1990) Schilling, Doris; Glatz-Reichenbach, Joachim; Dransfeld, Klaus; Bihler, Eckardt; Eisenmenger, WolfgangIn order to understand more clearly the poling mechanism in ferroelectric polymers, the PPS-technique was applied to copolymer films of vinylidenefluoride with trifluoroethylene P(VDF-TrFE), poled by a focused monoenergetic electron beam. Charges were injected in a well-defined way into the polymer films and thus provided information on the influence of externally introduced electrical charges on the poling process in ferroelectric polymers. The electron beam poling of P(VDF-TrFE) films is shown to produce very high values of polarization up to 180 mC/m2, which exceeds those produced in β-PVDF by electron irradiation by a factor of three. The distribution of the polarization across the film thickness is rather asymmetric, especially for samples irradiated with 20- and 30-KeV electrons. This may be caused by the rising electrical conductivity in samples with increasing electron energy. The annealing of the copolymer films before the poling procedure leads to a systematic increase of the polarization, with T a having its steepest rise around Tc.