[en] In Northern Germany seismicity is reported which occurred close to recent gas production. The goal of the study is better to better understad and constrain underlying geomechanical boundary conditions by addressing the following key questions: a) How critical is the initial state of stress for fault reactivation in Northern Germany) ; c) How and where is the state of stress modified by depletion?; d) Are there observed Coupling Coefficients (Reservoir Stress Path) indicate for the whole field?, e) What effects does the depletion on the earths surface have and can it be differentiated from other causes?, f) Is there differential subsidence across the Soehlingen field?; g) How do the poro-elastic effects resulting from production modify the state of stress at Wustrow, Dehlingen and Havel reservoir levels? and h) Can reservoir management help to reduce the seismicity? The geomechanical interpretation of the processes is based on rock mechanical tests of reservoir analogue rocks to obtain the strength of intact and weakened reservoir rocks, on observations of vertical displacements (Satellite data and leveling) on measured pressure and minimum horizontal stress data in wells. Based on a unique database from borehole data of the considered gas field it was possible to determine initial stress conditions and the evolution of stress and pore pressure within the field and two of its reservoirs over time. Laboratory experiments on 53 cores from 35 blocks of rocks show that neither the intact nor the weakened reservoir rocks fail under initial stress conditions (natural stress field prior to production). During production, the stress field is modified through pore pressure stress coupling. Under certain circumstances (e.g. compartment boundaries, compartments with different properties) stress changes can lead to failure of weakened reservoir rocks (pre-existing faults). Modelled and observed deformation (INSAR and levelling studies) agree well, which can lead to the conclusion that INSAR methods can also be used for monitoring gas fields at great depth even in challenging conditions (salt above). The modelling indicates that seismicity is most likely to be induced at internal or reservoir bounding faults due to stress changes in the reservoir and the still high pore pressures outside the reservoir. Since the reservoirs and thus the internal and bounding faults are of limited size, this limits the maximum magnitude of induced events. If the seismicity would be triggered outside the reservoir, higher magnitudes could become possible. A reservoir management including the consideration of pore pressure stress coupling and natural tectonic stress field can help to reduce risk of large scale fault reactivation inside and at reservoir boundaries.

[en] Epitaxial 4H-SiC structures with heavily boron or aluminium doped layers have been prepared by vapour phase epitaxy. The samples have been annealed in Ar atmosphere in an RF-heated furnace between 1700 and 2000 deg. C for 45 min to 64 h. Secondary ion mass spectrometry has been employed to obtain depth distributions as well as lateral distributions (ion imaging) for boron and aluminium. Transmission electron microscopy has been used to study the crystallinity and determine phase composition. Solubility limits of ∼1x10²⁰ Al/cm³ (1700 deg. C) and <1x10²⁰ B/cm³ (1900 deg. C) have been deduced

[en] The properties of the intrinsic double acceptor with energy levels 78 and 203 meV above valence band in GaAs have been studied using DLTS and Hall measurements in non stoichiometric GaAs (Ga_0.55As_0.45). The defect is most likely associated with the isolated cation antisite Ga_As. (author) 10 refs., 7 figs., 1 tab

[en] The removal of uranium (VI) from zerovalent iron permeable reactive barriers and wetlands can be explained by its association with iron oxides. The long term stability of immobilized U is yet to be addressed. Remobilization of U(VI) from iron oxides via diverse reaction pathways (acidification, reduction, complex formation) is investigated. Prior, uranium coprecipitation experiments were conducted under various conditions. The addition of various amounts of a pH-shifting agents (pyrite), an iron complexing agent (EDTA) or iron (III) reduction agent (TiCl₃) yielded in uranium remobilization, concentrations above the US EPA allowed maximum contaminant level (MCL=30 μg/l). U(VI) release in nature strongly depends on the conditions and the mechanism of its fixation by geological materials. (author)

[en] The effect of phosphorus implantation into a 4H-SiC epitaxial layer immediately before the thermal growth of a gate insulator in an atmosphere of dry oxygen on the reliability of the gate insulator is studied. It is found that, together with passivating surface states, the introduction of phosphorus ions leads to insignificant weakening of the dielectric breakdown field and to a decrease in the height of the energy barrier between silicon carbide and the insulator, which is due to the presence of phosphorus atoms at the 4H-SiC/SiO_2 interface and in the bulk of silicon dioxide

[en] The effectiveness of elemental iron (Fe ) to remove uranium (U) from the aqueous phase has been demonstrated. While the mitigation effect is sure, discrepancies in the removal mechanism have been reported. The objective of this study was to investigate the mechanism of U(VI) removal from aqueous phases by Fe . For this purpose, a systematic sequence of bulk experiments was conducted to characterize the effects of the availability and the abundance of corrosion products on U(VI) removal. Results indicated that U(VI) removal reactions did not primary occur at the surface of the metallic iron. It is determined that U(VI) co-precipitation with aging corrosion products is a plausible explanation for the irreversible fixation under experimental conditions. Results of XRD analyses did no show any U phases, whereas SEM-EDX analyses showed that U tended to associate with rusted areas on the surface of Fe . Recovering U with different leaching solutions varied upon the dissolution capacity of the individual solutions for corrosion products, showing that the irreversibility of the removal depends on the stability of the corrosion products. U(VI) co-precipitation as removal mechanism enables a better discussion of reported discrepancies

[en] Full text: Silicon carbide is a promising semiconductor material for applications in high temperature and high power devices. The successful growth of good quality epilayers in this material has enhanced its potential for device applications. As a novel semiconductor material, there is a need for studying its basic physical properties and the role of dopants in this material. In this study, silicon carbide epilayers were grown on 4H-SiC wafers of (0001) orientation with a miscut angle of 8 deg at a temperature of 1550 deg C. The epilayers contained regions of high aluminium doping well above the solubility of aluminium in silicon carbide. High temperature annealing of this material resulted in the precipitation of aluminium in the wafers. The samples were analysed by secondary ion mass spectrometry and transmission electron microscopy. Selected area diffraction studies show the presence of aluminium carbide and aluminium silicon carbide phases. Copyright (2002) Australian Society for Electron Microscopy Inc

[en] Secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) are utilized to study precipitation and the solubility of B in 4H-SiC epitaxial layers super saturated with B. Heat treatments are performed in Ar atmosphere in an rf-heated furnace at temperatures between 1700 and 2000 deg. C. SIMS ion images, and TEM micrographs reveal the formation of two types of precipitates where the larger, more thermally stable one is suggested to be B₄C. The boron solubility is determined from SIMS depth profiles and is shown to follow the Arrhenius expression: 7.1 x 10²² exp(-1.4 eV/k _B T) cm^-3 over the studied temperature range