Nitrogen and vacancy clusters in ZnO

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Understanding the interaction of group V impurities with intrinsic defects in ZnO is important for developing p-type material. We have studied N-doped ZnO thin films and N-doped bulk ZnO crystals, with positron annihilation spectroscopy, in contrast to earlier studies that have concentrated on N-implanted ZnO crystals. We show that the introduction of N impurities into ZnO, irrespective of whether it is done during the growth of thin films or bulk crystals or through implantation and subsequent thermal treatments, leads to the formation of stable vacancy clusters and negative ion-type defects. Interestingly, the stability of these vacancy clusters is found almost exclusively for N introduction, whereas single Zn vacancy defects or easily removable vacancy clusters are more typically found for ZnO doped with other impurities.DFG, SFB 787, Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Current and sea level control the demise of shallow carbonate production on a tropical bank (Saya de Malha Bank, Indian Ocean)

Carbonate platforms are built mainly by corals living in shallow light-saturated tropical waters. The Saya de Malha Bank (Indian Ocean), one of the world's largest carbonate platforms, lies in the path of the South Equatorial Current. Its reefs do not reach sea level, and all carbonate production is mesophotic to oligophotic. New geological and oceanographic data unravel the evolution and environment of the bank, elucidating the factors determining this exceptional state. There are no nutrient-related limitations for coral growth. A switch from a rimmed atoll to a current-exposed system with only mesophotic coral growth is proposed to have followed the South Equatorial Current development during the late Neogene. Combined current activity and sea-level fluctuations are likely controlling factors of modern platform configuration

Carbonate chemistry of SONNE cruise SO270

The main objective of the RV Sonne cruise SO270 was to test the hypothesis that Saya de Malha Bank (SMB) is a carbonate platform controlled by water mass boundaries and currents which exert a strong control on sedimentation, ecosystems and biogeochemistry. The proposed project 'Saya de Malha Bank Carbonate Geochemistry – MASCARA Geochemie' contributes to the overarching goal by characterizing the biogeochemical properties of water masses in order to estimate the impact of water masses on the aragonite and calcite saturation state. To achieve the project aims, carbonate chemistry was determined in surface waters by using an underway system (SUNDANS and VINDTA 2C, both instruments are from Marianda, Kiel, Germany). Furthermore, a CTD/Rosette sampler and a multi-corer (MUC ) was used to sample the water column and pore water whereas in addition pore water also the MUC-supernatant was sampled. The underway data include: salinity, sea water temperature, fugacity of CO2 (fCO2) concentrations of dissolved oxygen, chlorophyll (fluorescence) and total alkalinity (TA). Concentrations of nutrients (PO43- and SiOH4-), total dissolved inorganic carbon (DIC) and TA were determined in water samples obtained from CTD/Rosette sampler and within the MUC-supernatant, by using a SKALAR SAN plus System/08529 and a VINDTA 3C system (#29, Marianda, Kiel, Germany). Pore water nutrient concentrations (NOx, NO2-, NH4+, PO43- and SiOH4-) were measured by using a TECANinfiniteF200pro