15 Fakultätsübergreifend / Sonstige Einrichtung
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/16
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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 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 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 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 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 spectroscopy measurements at amorphous films(1994) Mebert, Joachim; Eisenmenger, WolfgangPhonon spectroscopy measurements were used to examine the scattering of high frequency phonons (300 GHz-1 THz) in amorphous materials. The experiments were done with the use of time and frequency resolved measurements of the phonon transmission behaviour through amorphous single films of different thicknesses. The typical film thicknesses were of the order of 10 nm. In contrast to the pure amorphous semiconductors Si and Ge our experiments show inelastic phonon scattering processes in the case of SiO 2 and Si:H. This inelastic phonon scattering also occurs when the pure semiconductors Si and Ge are prepared in an O 2 or H 2 atmosphere, but is missing when the preparation process is done in an N 2 atmosphere. In films of the pure semiconductors a-Si and a-Ge we only found evidence to elastic scattering processes. In further experiments at heated a-Si:H samples we could examine the atomical bonded hydrogen to be the center of the inelastic phonon scattering.