Dynamical measurements with quartz resonators

Dynamische Messungen mit Quarzresonatoren Die Resonanzfrequenz von Quarzoszillatoren liegt im MHz-Bereich. Die Resonanzen haben hohe Gueten und sind somit empfindlich auf kleine Aenderungen an der Resonatoroberflaeche. 1. Es wurde ein Aufbau entwickelt, um Reibung bei hohen Oberflaechengeschwindigkeiten zu messen (v = 1 m/s). Bei Annaeherung einer Kugel steigen Resonanzfrequenz sowie -breite des Schwingquarzes an. Für groeßere Normalkraefte entsteht ein elastischer Kontakt, der die Frequenzerhoehung erklaert. Kurz vor Eintreten dieses Kontaktes durchlaeuft die Daempfung ein Maximum, das charakteristisch ist für das Auftreten von Reibung. Bei Erhoehung der Schichtdicke (0,4-2,5 nm) einer Schmiermittelbeschichtung (Perfluoropolyether) verringern sich sowohl die Hoehe als auch die Breite dieses Maximums. Es verschwindet mit vollstaendiger Belegung mit einer Monolage (ca. 2 nm). Dies wird durch einen intermittierenden Kontakt der beiden Oberflaechen erklaert. 2. Die Schwingquarzoberfläche wurde mit Polymerbuersten verschiedener Schichtdicken (12-230 nm) beschichtet. Der Loesungsmittelgehalt in diesen Filmen variiert mit dem Dampfdruck der umgebenden Toluolatmosphaere. Bei Trocknung durchlaufen die Filme einen loesungsmittelinduzierten Glasuebergang. Die Sorptionskurven (Loesungsmittelgehalt gegen Dampfdruck) zeigen eine Knick beim Glasuebergang, ihre Ableitungen dagegen eine Stufe. Fuer duenner werdende Schichten verschiebt sich diese Stufe zu niedrigerem Dampfdruck sowie geringerem Loesungsmittelgehalt. Außerdem wird sie breiter und ihre Hoehe nimmt ab.

Vortex dynamics in the high-temperature superconductors YBa 2 Cu 3 O 7 and Bi 2 Sr 2 CaCu 2 O 8 + delta in low- and high-dissipative transport measurements

This thesis investigates phenomena of vortex dynamics in type II superconductors depending on the dimensionality of the flux-line system and the strength of the driving force. In the low dissipative regime of Bi_2Sr_2CaCu_2O_{8+delta} (BSCCO) the influence of oxygen stoichiometry on flux-line tension was examined. An entanglement crossover of the vortex system at low magnetic fields was identified and a comprehensive B-T phase diagram of solid and fluid phases derived.In YBa_2Cu_3O_7 (YBCO) extremely long (>100 mm) high-quality measurement bridges allowed to extend the electric-field window in transport measurements by up to three orders of magnitude. Complementing analyses of the data conclusively produced dynamic exponents of the glass transition z~9 considerably higher than theoretically predicted and previously reported. In high-dissipative measurements a voltage instability appearing in the current-voltage characteristics of type II superconductors was observed for the first time in BSCCO and shown to result from a Larkin-Ovchinnikov flux-flow vortex instability under the influence of quasi-particle heating. However, in an analogous investigation of YBCO the instability was found to appear only in the temperature and magnetic-field regime of the vortex-glass state. Rapid-pulse measurements fully confirmed this correlation of vortex glass and instability in YBCO and revealed a constant rise time (~µs).

Mode coupling for precise measurements of the electronic g-factor of hydrogen-like ions in Penning traps

The g-factor is a constant which connects the magnetic moment $vec{mu}$ of a charged particle, of charge q and mass m, with its angular momentum $vec{J}$. Thus, the magnetic moment can be writen $ vec{mu}_J=g_Jfrac{q}{2m}vec{J}$. The g-factor for a free particle of spin s=1/2 should take the value g=2. But due to quantum electro-dynamical effects it deviates from this value by a small amount, the so called g-factor anomaly $a_e$, which is of the order of $10^{-3}$ for the free electron. This deviation is even bigger if the electron is exposed to high electric fields. Therefore highly charged ions, where electric field strength gets values on the order of $10^{13}-10^{16}$V/cm at the position of the bound electron, are an interesting field of investigations to test QED-calculations. In previous experiments [H"aff00,Ver04] using a single hydrogen-like ion confined in a Penning trap an accuracy of few parts in $10^{-9}$ was obtained. In the present work a new method for precise measurement of magnetic the electronic g-factor of hydrogen-like ions is discussed. Due to the unavoidable magnetic field inhomogeneity in a Penning trap, a very important contribution to the systematic uncertainty in the previous measurements arose from the elevated energy of the ion required for the measurement of its motional frequencies. Then it was necessary to extrapolate the result to vanishing energies. In the new method the energy in the cyclotron degree of freedom is reduced to the minimum attainable energy. This method consist in measuring the reduced cyclotron frequency $nu_{+}$ indirectly by coupling the axial to the reduced cyclotron motion by irradiation of the radio frequency $nu_{coup}=nu_{+}-nu_{ax}+delta$ where $delta$ is, in principle, an unknown detuning that can be obtained from the knowledge of the coupling process. Then the only unknown parameter is the desired value of $nu_+$. As a test, a measurement with, for simplicity, artificially increased axial energy was performed yielding the result $g_{exp}=2.000~047~020~8(24)(44)$. This is in perfect agreement with both the theoretical result $g_{theo}=2.000~047~020~2(6)$ and the previous experimental result $g_{exp1}=2.000~047~025~4(15)(44).$ In the experimental results the second error-bar is due to the uncertainty in the accepted value for the electron's mass. Thus, with the new method a higher accuracy in the g-factor could lead by comparison to the theoretical value to an improved value of the electron's mass. [H"af00] H. H"affner et al., Phys. Rev. Lett. 85 (2000) 5308 [Ver04] J. Verd'u et al., Phys. Rev. Lett. 92 (2004) 093002-1

Application of comprehensive gas chromatography (GCxGC) to measurements of volatile organic species in ambient air

The focus of this thesis was the in-situ application of the new analytical technique "GCxGC" in both the marine and continental boundary layer, as well as in the free troposphere. Biogenic and anthropogenic VOCs were analysed and used to characterise local chemistry at the individual measurement sites. The first part of the thesis work was the characterisation of a new set of columns that was to be used later in the field. To simplify the identification, a time-of-flight mass spectrometer (TOF-MS) detector was coupled to the GCxGC. In the field the TOF-MS was substituted by a more robust and tractable flame ionisation detector (FID), which is more suitable for quantitative measurements. During the process, a variety of volatile organic compounds could be assigned to different environmental sources, e.g. plankton sources, eucalyptus forest or urban centers. In-situ measurements of biogenic and anthropogenic VOCs were conducted at the Meteorological Observatory Hohenpeissenberg (MOHP), Germany, applying a thermodesorption-GCxGC-FID system. The measured VOCs were compared to GC-MS measurements routinely conducted at the MOHP as well as to PTR-MS measurements. Furthermore, a compressed ambient air standard was measured from three different gas chromatographic instruments and the results were compared. With few exceptions, the in-situ, as well as the standard measurements, revealed good agreement between the individual instruments. Diurnal cycles were observed, with differing patterns for the biogenic and the anthropogenic compounds. The variability-lifetime relationship of compounds with atmospheric lifetimes from a few hours to a few days in presence of O3 and OH was examined. It revealed a weak but significant influence of chemistry on these short-lived VOCs at the site. The relationship was also used to estimate the average OH radical concentration during the campaign, which was compared to in-situ OH measurements (1.7 x 10^6 molecules/cm^3, 0.071 ppt) for the first time. The OH concentration ranging from 3.5 to 6.5 x 10^5 molecules/cm^3 (0.015 to 0.027 ppt) obtained with this method represents an approximation of the average OH concentration influencing the discussed VOCs from emission to measurement. Based on these findings, the average concentration of the nighttime NO3 radicals was estimated using the same approach and found to range from 2.2 to 5.0 x 10^8 molecules/cm^3 (9.2 to 21.0 ppt). During the MINATROC field campaign, in-situ ambient air measurements with the GCxGC-FID were conducted at Tenerife, Spain. Although the station is mainly situated in the free troposphere, local influences of anthropogenic and biogenic VOCs were observed. Due to a strong dust event originating from Western Africa it was possible to compare the mixing ratios during normal and elevated dust loading in the atmosphere. The mixing ratios during the dust event were found to be lower. However, this could not be attributed to heterogeneous reactions as there was a change in the wind direction from northwesterly to southeasterly during the dust event.