7 research outputs found
Synergistic gold-copper detoxification at the core of gold biomineralisation in Cupriavidus metallidurans
No full textThe bacterium Cupriavidus metallidurans is capable of reducing toxic Au(i/iii)-complexes into metallic gold (Au) nano-particles, thereby mediating the (trans)formation of Au nuggets in Earth surface environments. In this study we describe a novel detoxification pathway, which prevents synergistic copper (Cu)/Au-toxicity. Gold-complexes and Cu-ions exert cooperative toxicity, because cellular uptake of Au(i/iii)-complexes blocks Cu(i) export from the cytoplasm by the Cu-efflux pump CupA. Using a combination of micro-analytical and biochemical methods we show that inducible resistance to these Cu/Au mixtures is mediated by the periplasmic Cu(i)-oxidase CopA, which functions as an oxygen-consuming Au(i)-oxidase. With high Au-complex loads the enzymatic activity of CopA detoxifies the reduction pathway of Au(iii)-complexes via Au(i)-intermediates to Au(0) nanoparticles in the periplasm. Thereby the concentration of highly toxic Au(i) in the cytoplasm is diminished, while allowing direct reduction of Au(iii) to Au nanoparticles in the periplasm. This permits C. metallidurans to thrive in Au-rich environments and biomineralise metallic Au.L. Bütof, N. Wiesemann, M. Herzberg, M. Altzschner, A. Holleitner, F. Reithc and D. H. Nie
Die Übungssequenz macht den Meister...? Eine experimentelle Studie zu Kontext-Effekten von Übungsstimuli bei Real-Time-Response-Messungen
No full textDie Übungssequenz macht den Meister...? Eine experimentelle Studie zu Kontext-Effekten von Übungsstimuli bei Real-Time-Response Messungen
No full textRobust Valley Polarization of Helium Ion Modified Atomically Thin MoS2
No full textAtomically thin semiconductors have dimensions that are commensurate with critical feature sizes of future optoelectronic devices defined using electron/ion beam lithography. Robustness of their emergent optical and valleytronic properties is essential for typical exposure doses used during fabrication. Here, we explore how focused helium ion bombardement affects the intrinsic vibrational, luminescence and valleytronic properties of atomically thin MoS<sub>2</sub>. By probing the disorder dependent vibrational response we deduce the interdefect distance by applying a phonon confinement model. We show that the increasing interdefect distance correlates with disorder-related luminscence arising 180 meV below the neutral exciton emission. We perform ab-initio density functional theory of a variety of defect related morphologies, which yield first indications on the origin of the observed additional luminescence. Remarkably, no significant reduction of free exciton valley polarization is observed until the interdefect distance approaches a few nanometers, namely the size of the free exciton Bohr radius. Our findings pave the way for direct writing of sub-10 nm nanoscale valleytronic devices and circuits using focused helium ions
Helium ion modified luminescence and valley depolarization of atomically thin MoS2
No full textWe show a systematic study of the impact of disorder on the optical properties and intervalley scattering of atomically thin MoS2. Using a helium ion microscope (HIM) we induce defects in the crystal lattice. Optical analysis reveals significant shifts of both first order Raman modes E’ and A1 which are well explained by phonon confinement due to increasing disorder linking the ion dose to the inter-defect distance. Low-temperature (T=10K) confocal micro-photoluminescence (µ-PL) exhibits additional pronounced defect-related luminescence that can be precisely tailored with the ion dose used for exposure. We attribute the observed luminescence to originate from chemisorbed atoms/molecules at mono-sulfur vacancies in good agreement with DFT calculations. Quasi-resonant polarization resolved µ-PL measurements reveal a robust degree of circular polarization ~ 85% for doses where ion-induced luminescence is observed. This observation is in good agreement with the occurrence of mono-sulfur vacancies that are not contributing to intervalley scattering due to their C3-symmetry as recently theoretically reported [2]. Our results demonstrate the potential of helium ion microscopy applied to 2D layered materials for modifying intrinsic optical properties and fundamental understanding of disorder and its implication on the valley depolarization [3]
