Studying electronic properties in GaN without electrical contacts using γ-γ vs e--γ Perturbed Angular Correlations.

The potential use of combined e--γ vs γ-γ Perturbed Angular Correlations (PAC) experiments as a possible alternative to study electronic properties of materials and/or samples where Hall effect measurements are difficult to perform due to low-quality ohmic contacts is here demonstrated using Si- and Zn-doped GaN samples as a showcase example. To do so, the lattice site of implanted 181Hf/181Ta and the recombination of Ta ionized and excited electronic states were studied as a function of temperature and sample doping in GaN. By combining the γ-γ and e--γ PAC results with Density Functional Theory simulations, it was possible to assign a single stable site with a double-donor character for Ta in GaN. A metastable charge state was also identified at particular temperatures using e--γ PAC. A thermally activated process was observed for the electronic recombination at high temperatures with activation energies of 15(2) meV and 12(1) meV for the Si- and Zn-doped samples, respectively, and attributed to Si shallow donors present in both samples. A reduced number of available electrons was observed in the Zn-doped sample due to donor compensation by the Zn acceptors. At low temperatures, it is suggested that the recombination process occurs via Variable Range Hopping. The doping characteristics of both samples were successfully distinguished.

Production of 83Rb for the KATRIN experiment.

For the neutrino mass determination experiment KATRIN, the long-term stability of the spectrometer voltage is of crucial importance. Therefore, it is planned to control the voltage continuously in a smaller spectrometer, which monitors the position of the conversion electron line emitted in the 32 keV transition in the decay of (83m)Kr. Due to the short half-life of (83m)Kr (t(1/2)=1.83h), it has to be supplied by a long-lived (83m)Kr((83)Rb) generator (t(1/2)=86d). Here, a hitherto unexploited method for the efficient production of (83)Rb and its suitability for its application in the KATRIN monitor spectrometer is described.

Asperfuran, a novel antifungal metabolite from Aspergillus oryzae.

Asperfuran is a novel antifungal dihydrobenzofuran derivative produced by a strain of Aspergillus oryzae. Asperfuran weakly inhibited chitin synthase from Coprinus cinereus. This inhibition could be abolished by the addition of egg lecithin. In the agar diffusion assay asperfuran induced morphological changes in Mucor miehei at very low concentrations (20 ng/disc) while growth was only partly inhibited. In HeLa S3 and L1210 cells it showed weak cytotoxicity, the IC50 was 25 micrograms/ml.