The Outer Hebrides Fault Zone is a major ESE-dipping reactivated structure within Lewisian basement gneisses of the Laurentian craton, northwest Scotland. Detailed mapping in South Uist reveals important new evidence that contributes to a better understanding of the kinematic evolution of the fault zone. Large quantities of pseudotachylite which characterize the fault zone on South Uist may in part be lithologically controlled, and therefore of little value in determining areas of greatest deformation and displacement. Only limited evidence is preserved for ductile and brittle thrust-sense movements along this portion of the fault zone. The tectonics of the fault zone on South Uist are dominated by structures associated with several episodes of pervasive top-down-to-the-SE to -ENE brittle extensional deformation, which are progressively overprinted by protophyllonitic and phyllonitic fabrics associated with top-down-to-the-E to -ENE extension. A series of late-stage high-angle normal faults record top-down-to-the-ESE to -ENE extension and cut the phyllonites. Fluid inclusion studies from syntectonic quartz veins constrain the conditions of phyllonite formation at 370 ± 20 °C. Field evidence suggests that this section of the Outer Hebrides Fault Zone may have been largely unaffected by sinistral strike-slip reactivation as reported along-strike to the north, suggesting both a varied and compartmentalized tectonic and evolutionary history along the length of the Outer Hebrides Fault Zone.

We report temporal measurements of bandgap photoluminescence (PL) from GaAs surfaces under low-intensity CW laser excitation. We have observed slow PL degradation in n-type, p-type and semi-insulating (Cr-doped and LEC-grown) samples, and have fit the data to a simple power law. Calculations indicate a significant contribution from the bulk material, possibly via recombination-enhanced generation or migration of non-radiative centers. The effectiveness of various methods of surface treatment (photowashing, deposition of epitaxial AlGaAs, spin-coating with organic and inorganic sulfide films) has been assessed. One specific technique, involving coating with sodium sulfide, is effective in enhancing the PL efficiency and suppressing the degradation, but these effects are not permanent.