Cathodoluminescence imaging for the determination of dislocation density in differently doped HVPE GaN

In this study we report the potential and limitations of the cathodoluminescence dark spot (DS) counting as a method for the determination of dislocation density and distribution in GaN, produced by the hydride vapour phase epitaxy (HVPE). Different GaN sample series (s.i. GaN:Fe and n-type GaN:Si) were used, in order to study the dependence of the results of the DS-counting on the dopant type and concentration. By the direct comparison of these results to classical defect selective etching, the DS-measurements were validated. It could be shown that each of the both methods have their particular restrictions, which must be considered in their application.     

New leading electrolyte for the direct determination of chloride and other anions in analytical isotachophoresis.

In a number of experiments it was shown that the dithionate ion possesses a higher effective mobility than the chloride ion in aqueous solution, thus enabling the direct and simultaneous isotachophoretic determination of chloride and other anions. Using an acid-base titration, we found only one pKa value for dithionic acid, which is in contrast to the two pKa values stated in the literature. Based on this pKa value, theoretical calculations and the experimentally observed effective mobility of the dithionate ion indicate a higher effective mobility compared to the chloride ion from pH 3. Taking into account the physico-chemical properties of the dithionate, its unrestricted use as isotachophoretic leading ion was confirmed. Based on the dithionate ion, new electrolyte systems for the determination of chloride were used. One system was optimised for the determination of chloride and other low-molecular-mass anions and applied to the analysis of waste water and drinking water. The water samples were analysed in parallel by ion chromatography and compared with the isotachophoretic results.     

Effects of bag surface motion with relativistic kinematics

Radial surface motion of the baryon bag is carried out in a model with relativistic kinematics, with confinement the result of volume energy and surface tension and the pion field coupled to the bag surface. We calculate radial wave functions for the nucleon, the Δ(1233) and the Roper resonance N^*(1450), which is identified as the first radial excitation of the nucleon.

Results are used to calculate form factors and pionic decay widths of the baryons examined. The approximations made in these calculations are discussed in extensio.     

Coherent Generation and Detection of Continuous Terahertz Waves Using Two Photomixers Driven by Laser Diodes

We report on a completely coherent, tunable, continuous-wave THz system where, for the first-time, both the transmitter and receiver are log-periodic-antenna coupled LTG-GaAs based finger-photomixers. This compact room-temperature system exhibits signal-to-noise ratios (> 10³) comparable to or better than what is reported in the literature, and has potential applications in high-resolution spectroscopy and imaging. For the purpose of demonstration, we also present results of spectroscopy measurements carried out on fused silica, which are in agreement with previously published THz-TDS measurements.     

Baryon chiral perturbation theory A.D. 1994

In these lectures, the status of baryon chiral perturbation theory is reviewed. Particular emphasis is put on the two-flavor sector and the physics related to electromagnetic probes. I discuss in some detail the structure of the effective Lagrangian at next-to-leading order, the meaning of low-energy theorems in Compton scattering and pion photoproduction, and confront the chiral predictions with the existing data. Some remaining problems and challenges are outlined.Lectures given at the Indian-Summer School on Electron Scattering from Nucleons and Nuclei, Prague, Czech Republic, September 1994.First, I would like to thank the organizers for their kind invitation and hospitality. I am also grateful to Véronique Bernard and Norbert Kaiser for fruitful collaborations and allowing me to present some material before publication. I would like to thank Gerhard Ecker and Jürg Gasser for sharing with me their insight into the chiral dynamics.