Universität Stuttgart
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Item Open Access Excited electronic states of flavin-containing coenzyme models(1988) Gückel, Friedemann; Schweitzer, Dieter; Becker, Katja; Schirmer, Rolf Heiner; Zipplies, Matthias F.; Staab, Heinz A.In order to gain further insight into the physical basis of flavin-catalyzed reactions, the interactions of a flavin with a second flavin and with other aromatic ring systems were studied. For this purpose compounds through 1 were synthesized These compounds contain the interacting units in defined geometric orientation. A monomeric flavin and glutathione reductase a flavoenzyme of known active-site chemistry, were included as reference molecules. The present report deals with excited triplet states of the flavin compounds as studied by optical spectroscopy and optically detected magnetic resonances (ODMR) at 1.3K.Item Open Access Metallic coordination polymers using CS2 as starting material(1987) Keller, Heimo J.; Klutz, Thomas; Münstedt, Helmut; Renner, Gerd; Schweitzer, DieterOrganic polymers with "metallic" properties have found widespread interest during the last few years. Acetylene and aniline as well as different nitrogen and sulfur heterocycles have been used as starting materials. One main problem hampering the technical application of these solids up to now is their environmental and thermal instability. Therefore, we introduced metal ions to stabilize polymeric backbones with high electrical conductivity. Because of the enormous coordination ability of sulfur to many transition metal ions we decided to use a polymeric carbon-sulfur backbone.Item Open Access Application of interferometry and holography for precision measurements(1984) Tiziani, Hans J.Phase measurement techniques are becoming a useful tool for precision measurements. Spatial as well as temporal phase shift methods can be used. Optical testing, where computer analysis of interference fringes is becoming increasing important, will be discussed in connection with testing optical components, microprofiles as well as for testing aspheric surfaces. In addition, methods using heterodyne techniques and real time holography will be described.Item Open Access ODMR of triplet states of organic electron donors(1986) Grimm, Hans; Schweitzer, Dieter; Hausser, Karl H.; Keller, Heimo J.Energies of the first excited triplet states and triplet zero field splitting parameters /D/ and /E/ of several organic donors - usually used for the preparation of organic metals and superconductors - are reported.Item Open Access Influence of defects on the splitting of the acceptor ground state in silicon(1984) Ambrosy, Anton; Lassmann, Kurt; Goer, Anne M. de; Salce, Bernard; Zeile, Heinrich-Item Open Access Testing of aspheric surfaces with computer generated holograms(1988) Tiziani, Hans J.; Packroß, Bernd; Schmidt, GerhardAspherical surfaces are becoming more important and can even be mass producted. There is a need for flexible test methods of high accuracy. The paper describes the combination of a computer generated holograms with a partially compensating lens as a powerful tool. An example for testing a steep aspheric surface will be given.Item Open Access Neuartige PVDF-Dünnschichtwandler für Ultraschallmessungen im GHz-Bereich(1985) Ambrosy, Anton; Holdik, Karl; Eisenmenger, WolfgangWegen seines hohen Piezoeffekts wird auch das Pol:ymer Polyvinylidenfluorid (PVDP) als Ultraschallwandler benutzt. Bisher war es jedoch nicht möglich PVDP-Wandler im GHz-Bereich zu verwenden, da für hochfrequente Anwendungen dünnere und ebenere Folien. als sie kommerziell angeboten werden, notwendig sind. Mit der nun folgenden Methode wurden nun erstmals PVDF-Dünnschichtwandler, die noch bei 24 GHz funktionieren, aus der Lösung hergestellt.Item Open Access Satellite phonon absorption lines above the 875 GHz resonance of interstitial oxygen in silicon(1987) Dittrich, Ehrenfried; Scheitler, Wolfgang; Eisenmenger, WolfgangAcoustic phonon spectroscopy with superconducting tunneling junctions as phonon generator and detector revealed a large number of sharp absorption lines between 875 GHz (oxygen resonance) and 1.35 THz for silicon doped with interstitial oxygen (Si:0i). The strength of these lines scales with the square of the oxygen concentration ranging from 1017 to 1018 cm-3. Under mechanical stress the lines show a frequency shift almost identical to the main oxygen resonance at 875 GHz as well as to the also observable isotope resonance. These satellite absorption lines are therefore discussed as 0i–0i neighbour interaction. This is supported by the influence of annealing.Item Open Access Polarization distributions in isotropic, stretched or annealed PVDF films(1988) Bihler, Eckardt; Holdik, Karl; Eisenmenger, WolfgangThe spatial distribution of the polarization in polyvinylidene fluoride (PVDF) films was measured at room temperature with the PPS (piezoelectric pressure step) method. In order to investigate the time development under external fields, a thin insulation polyethylene terephthalate (PET) film covering an evaporated aluminium electrode was inserted between the sample and the measuring electrode. The observed development of inhomogeneous and internal polarization zones is attributed to charge injection and charge trapping at the polarization zone boundaries. The polarization zone develops at a position where the critical field strength for dipole orientation in the crystallites is exceeded by the approach of injected homocharges (or without injection by the depletion of internal homocharges and the excess of heterocharges). The critical field for α-crystallites corresponds to an electric field phase transition at 1.2 MV/cm. The development of central polarization zones in PVDF containing β-crystallites indicates injection of charges with both signs and almost equal mobility. The results indicate that the β-crystallites determine the charge injection rate or the mobility or both.Item Open Access BEDT-TTF radical salts: organic metals and superconductors(1987) Schweitzer, DieterA review of the structural, electronic and superconducting properties of some BEDT-TTF-radical salts is given.