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Subject: search.filters.subject.530Institute: search.filters.UBSInstitut.1. Physikalisches InstitutStart date: 1980End date: 1989Publication Type: search.filters.UBSTyp.Zeitschriftenartikel

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Now showing 1 - 10 of 28
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    Reflection of high-frequency phonons at silicon-solid interfaces
    (1981) Marx, Dieter; Eisenmenger, Wolfgang
    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.
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    Continuous high resolution phonon spectroscopy up to 12meV : measurement of the A+ binding energies in silicon
    (1986) Burger, Wilfried; Lassmann, Kurt
    We have measured the binding energies of Ga+, Al+, and In+ centers in silicon with energy-resolved phonon-induced electrical conductivity. For Ga+ and Al+ we obtain the value of about 2 meV as earlier found for B+, whereas the binding energy of In+ is 6 meV. Spectral structures attributed to impurity interactions found for higher concentrations of In at energies up to about 12 meV demonstrate that acoustic phonons up to this energy are transmitted from the tunnel junction to the substrate.
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    Diffusive scattering of high-frequency phonons at free silicon surfaces
    (1983) Marx, Dieter; Eisenmenger, Wolfgang
    Comparing measurements of high-frequency phonon reflection at the uncovered and optically polished (100)-silicon surface, with calculations considering phonon focusing, reveal complete diffusive scattering with at most 4% specular reflection contribution. Two possible mechanisms causing diffusive scattering are discussed.
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    Analysis of the phonon spectrum emitted by superconducting Al-tunneling junctions at high quasiparticle injection rates
    (1981) Welte, Michael; Eisenmenger, Wolfgang
    The phonon spectrum emitted by superconducting Al-tunneling junctions is analyzed by experiments, in which two junctions of different energy gaps are used as phonon generator and detector. The energy gap of the Al-films is varied by the evaporation conditions. The experiments show clearly that the phonon spectrum and the quasiparticle distributions in the generator are strongly nonthermal and depend markedly on the primary tunneling injection. At high injection rates also significant consequences of gap reductions and instabilities are observed.
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    Physikalisch-medizinische Aspekte selbstfokussierter elektromagnetisch erzeugter Stoßwellen
    (1988) Eisenmenger, Wolfgang
    Gegenüber schon länger bekannten Methoden der Stoßwellenerzeugung in Flüssigkeiten wie Unterwasserfunkenentladung, chemische Detonation, mechanischer Schlag oder der Fokussierung von piezoelektrisch erzeugten Druckwellen, wurde die elektromagnetische Stoßwellenerzeugung erst im Jahre 1959 eingeführt. Sie diente seinerzeit zur Erzeugung von ebenen Stoßwellen für physikalische Stoßfrontuntersuchungen. Da mit diesem Generator bereits ebene Stoßwellen mit Drucken bis zu 700 bar über einem Querschnitt von 50 mm Durchmesser erzeugt werden konnten, ist verständlich, daß bei geeigneter Fokussierung leicht höhere Fokusdrucke bei wesentlich geringeren Drucken am Stoßwellengenerator selbst zu realisieren sind. Diese Situation führte zur Entwicklung des Stoßwellenlithotriptors "Lithostar" mit Linsenfokussierung sowie zum Vorschlag eines selbstfokussierenden elektromagnetischen Stoßwellengenerators.
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    The influence of the dynamic Jahn-Teller effect on the phonon-scattering mechanism at acceptors in semiconductors with cubic symmetry
    (1982) Sigmund, Ernst; Lassmann, Kurt
    Phonon scattering experiments of various types in cubic semiconductors doped with deep effective mass acceptors indicate an extra resonance scattering at some meV. It is shown, using Green's function and transformation techniques that these resonances are due to a dynamic Jahn-Teller effect of the 8 acceptor ground state.
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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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    The distribution of splittings (Ultrasonic investigation of the acceptor ground state of Si(B) ; 2)
    (1982) Zeile, Heinrich; Lassmann, Kurt
    The splitting distribution of the acceptor ground state of Si(B) is determined from the frequency dependence of the ultrasonic resonance attenuation and from acoustic paramagnetic resonance. In the purest crystals a residual distribution is found of unknown origin. In crystals containing carbon or oxygen at concentrations above about 10 22 m-3 the distribution is broadened in rough accordance with statistical estimates.
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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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    Investigation of the Kapitza anomaly by frequency resolved phonon transport in silicon wafers
    (1987) Klar, Wolfgang; Lassmann, Kurt
    The threshold at 85 GHz for anomalously large transmission of phonons into LHe has been investigated with Si-wafers for various surface treatments and coverages by phonon spectroscopy. With this multiple boundary scattering geometry we observe an increased sensitivity to spectral features. Connected with the threshold there is a phase shift of the signal compatible with a loss of the slower diffuse portion of the phonon signal to the covering liquid helium. This phase shift depends nonlinearly on modulation frequency between 5 kHz and 200 kHz (modulation of the generator to sort out the monochromatic phonons) and in a characteristic manner on the surface treatment. The finite phase shift at 5 kHz is indicative of very long lived 85 GHz phonons up into the 100 µs is range inspite of the multiple Si-LHe-interface scattering involved. Minor differences in polishing quality show up clearly in the phase shift at low modulation frequencies.