Hot Upper Mantle Beneath the Tristan da Cunha Hotspot From Probabilistic Rayleigh-Wave Inversion and Petrological Modeling

Understanding the enigmatic intraplate volcanism in the Tristan da Cunha region requires knowledge of the temperature of the lithosphere and asthenosphere beneath it. We measured phase-velocity curves of Rayleigh waves using cross-correlation of teleseismic seismograms from an array of ocean-bottom seismometers around Tristan, constrained a region-average, shear-velocity structure, and inferred the temperature of the lithosphere and asthenosphere beneath the hotspot. The ocean-bottom data set presented some challenges, which required data-processing and measurement approaches different from those tuned for land-based arrays of stations. Having derived a robust, phase-velocity curve for the Tristan area, we inverted it for a shear wave velocity profile using a probabilistic (Markov chain Monte Carlo) approach. The model shows a pronounced low-velocity anomaly from 70 to at least 120 km depth. VS in the low velocity zone is 4.1-4.2 km/s, not as low as reported for Hawaii (∼4.0 km/s), which probably indicates a less pronounced thermal anomaly and, possibly, less partial melting. Petrological modeling shows that the seismic and bathymetry data are consistent with a moderately hot mantle (mantle potential temperature of 1,410-1,430°C, an excess of about 50-120°C compared to the global average) and a melt fraction smaller than 1%. Both purely seismic inversions and petrological modeling indicate a lithospheric thickness of 65-70 km, consistent with recent estimates from receiver functions. The presence of warmer-than-average asthenosphere beneath Tristan is consistent with a hot upwelling (plume) from the deep mantle. However, the excess temperature we determine is smaller than that reported for some other major hotspots, in particular Hawaii

Sputter deposition of silicon oxynitride gradient and multilayer coatings

The optical properties of silicon oxynitride films deposited by reactive d.c. magnetron sputtered films have been investigated. In particular the absorption characteristics of silicon nitride thin films in the visible spectrum (VIS) and their optical bandgap were analyzed regarding their composition and deposition properties. It could be shown that there is a significant difference between the absorption in the visible spectrum and the optical bandgap for these layers. Furthermore the influence of the unipolar and the bipolar pulse mode on the optical layer properties is presented. The extinction coefficient for silicon nitride single layers could be reduced to a value of 2E-4 at 500 nm without external heating. There is also a dependency of the absorption of silicon oxynitride layers on the discharge voltage. Moreover the resulting spectra of rugate and edge filters consisting of these layers are shown, offering lower absorption than single layers

Reactive pulse magnetron sputtered SiOxNy coatings on polymers

Amorphous SiO2, Si3N4 and SiOxNy single layers have been deposited on silicon, glass and glycol modified polyethylene terephthalate substrates by reactive pulse magnetron sputtering. Apart from the expected correlation between refractive index, coating density and nitrogen content in the reactive gas mixture further results have been found regarding mechanical stress and the humidity barrier property of these thin films. The lowest compressive stress was observed in the coatings deposited with nitrogen contents of around 30% to 50% in the reactive gas mixture. The humidity barrier effect of the thin films already begins to increase significantly at low nitrogen contents of below 20% in the reactive gas. Additional investigations regarding chemical composition, coating adhesion and environmental stability complement this work with the main focus on optimizing these materials for optical multilayer systems on polymer substrates

The double ring magnetron process module - a tool for stationary deposition of metals, insulators and reactive sputtered compounds

The double ring magnetron module has become a powerful tool for solving a great variety of thin film deposition tasks in the field of stationary sputter deposition of substrates in the diameter range of 200 mm at high deposition rates. Different variants of powering - DC, MF (50kHz) and RF (13.56 MHz) - that allow to sputter conductive and insulating materials will be compared. In reactive sputtering new solutions for magnetron design, reactive gas inlet, power input and control systems will be reported, that guarantee during the target life time the stable, reproducible and uniform deposition of materials like SiO2 or Al2O3