Physico-chemical investigations on selected gallium doped lanthanum chromites

Investigations on lanthanum gallium chromium mixed oxides of the compositions La_1.0Ga_0.2Cr_0.8O_3−d and La_0.9Ga_0.2Cr_0.8O_3-d are presented regarding their structure, redox stability, conductivity and catalytic activity for the oxidation of propene. The mixed oxide has perovskite-type structure, high redox stability, an electronic p-type conductivity and low catalytic activity. If the perovskite-type compound has a deficiency of lanthanum, the electronic conductivity, surface area and catalytic activity are significantly higher. The catalytic activity is likely comparable to that of gold. Similar to gold electrodes of solid electrolytes, oxygen electrodes formed with gallium doped lanthanum chromite show a relatively high sensitivity to hydrocarbons such as propene at temperatures of about 700 °C. The mixed oxide is possibly suitable as electrode material for exhaust gas sensors using oxide-ion conducting solid electrolytes. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, September 13–20, 1998.     

A tunable,frequency-doubled cw dye laser using an RDP crystal

We report a c.w. intracavity, frequency doubled, rhodamine B dye laser using an RDP crystal 5 cm long. Generated uv powers up to 15 mW are obtained in a single direction with a linewidth of 2 GHz over the range 314–318 nm. A conversion efficiency of about 1.25 × 10^-3 W^-1 is measured.     

Diaryl-disulfimide als Urtitersubstanzen

Ohne ZusammenfassungDiplomarbeit A. Ernst, Halle 1956.     

Search for exotic mesons produced by baryon exchange in the reaction π+p → Λ + x++ at 12 GeV/c

A search for exotic mesons has been carried out at the CERN Omega spectrometer. The baryon-exchange reaction π⁺p → Λ + x⁺⁺ was studied at 12 GeV/c incident beam momentum. No evidence was found for the existence of doubly-charged strange mesons. The upper limit (95% confidence level) for this reaction is 60 nb for exotic mesons with squared masses from 1 to 7 (GeV/c²)² and 150 nb for 7 to 13 (GeV/c²)². These limits are of the same order of magnitude as the exotic cross-sections expected from two-component duality arguments.     

Quantum mechanical repulsion of exciton levels in a disordered quantum well

Spatially resolved photoluminescence spectra of a single quantum well are recorded by near-field spectroscopy. A set of over four hundred spectra displaying sharp emission lines from localized excitons is subject to a statistical analysis of the two-energy autocorrelation function. An accurate comparison with a quantum theory of the exciton center-of-mass motion in a two-dimensional spatially correlated disordered potential reveals clear signatures of quantum mechanical energy level repulsion, giving the spatial and energetic correlations of excitons in disordered quantum systems.     

Umarbeitung 18O-markierter organischer Verbindungen zur massenspektrometrischen Analyse durch Pyrolyse über Gasruß

Zur Isotopenanalyse am Sauerstoff eignen sich entweder elementarer Sauerstoff oder Kohlendiosxid. Kohlenmonxid ist weniger geeignt, da es im Massenspektrum die gleiche Masse wie Stickstoff belegt.     

Metalorganic vapor phase epitaxy of III–V-on-silicon: Experiment and theory

The integration of III–V semiconductors with Si has been pursued for more than 25 years since it is strongly desired in various high-efficiency applications ranging from microelectronics to energy conversion. In the last decade, there have been tremendous advances in Si preparation in hydrogen-based metalorganic vapor phase epitaxy (MOVPE) environment, III–V nucleation and subsequent heteroepitaxial layer growth. Simultaneously, MOVPE itself took off in its triumphal course in solid state lighting production demonstrating its power as industrially relevant growth technique. Here, we review the recent progress in MOVPE growth of III–V-on-silicon heterostructures, preparation of the involved interfaces and fabrication of devices structures. We focus on a broad range of in situ, in system and ex situ characterization techniques. We highlight important contributions of density functional theory and kinetic growth simulations to a deeper understanding of growth phenomena and support of the experimental analysis. Besides new device concepts for planar heterostructures and the specific challenges of (001) interfaces, we also cover nano-dimensioned III–V structures, which are preferentially prepared on (111) surfaces and which emerged as veritable candidates for future optoelectronic devices.