TY - JOUR A1 - Reith, F. A1 - Fairbrother, L. A1 - Nolze, Gert A1 - Wilhelmi, O. A1 - Clode, P. L. A1 - Gregg, A. O. A1 - Parsons, J. E. A1 - Wakelin, S. A. A1 - Pring, A. A1 - Hough, R. A1 - Southam, G. A1 - Brugger, J. T1 - Nanoparticle factories: Biofilms hold the key to gold dispersion and nugget formation JF - Geology N2 - Biofilms living on gold (Au) grains play a key role in the biogeochemical cycle of Au by promoting the dispersion of Au via the formation of Au nanoparticles as well as the formation of secondary biomorphic Au. Gold grains from Queensland, Australia, are covered by a polymorphic, organic-inorganic layer that is up to 40 μm thick. It consists of a bacterial biofilm containing Au nanoparticles associated with extracellular polymeric substances as well as bacterioform Au. Focused ion beam (FIB) sectioning through the biofilm revealed that aggregates of nanoparticulate Au line open spaces beneath the active biofilm layer. These aggregates (bacterioform Au type 1) resulted from the reprecipitation of dissolved Au, and their internal growth structures provide direct evidence for coarsening of the Au grains. At the contact between the polymorphic layer and the primary Au, bacterioform Au type 2 is present. It consists of solid rounded forms into which crystal boundaries of underlying primary Au extend, and is the result of dealloying and Ag dissolution from the primary Au. This study demonstrates that (1) microbially driven dissolution, precipitation, and aggregation lead to the formation of bacterioform Au and contribute to the growth of Au grains under supergene conditions, and (2) the microbially driven mobilization of coarse Au into nanoparticles plays a key role in mediating the mobility of Au in surface environments, because the release of nanoparticulate Au upon biofilm disintegration greatly enhances environmental mobility compared to Au complexes only. KW - Nanomaterial KW - Gold KW - Electron backscatter diffraction PY - 2010 DO - https://doi.org/10.1130/G31052.1 VL - 38 IS - 9 SP - 843 EP - 846 PB - Geological Society of America AN - OPUS4-37995 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Sitzman, S. D. A1 - Nolze, Gert A1 - Nowell, M. M. T1 - EBSD Pattern Quality and its Use in Evaluating Sample Surface Condition JF - Microscopy and Microanalysis N2 - Modern EBSD systems perform diffraction pattern “quality” (PQ) calculations, essentially measurements of the contrast of the brighter bands in the pattern above background, for every pattern analyzed. Since the calculations are independent of EBSD indexing, data are generated from all points on the analyzed sample surface, regardless of indexability or the state of the material beneath. EBSD maps generated from PQ data are like microstructurally sensitive SEM images, collected at EBSD speeds and grid resolutions, with contrast arising from phase density, crystal structure, crystallographic orientation, grain boundary location, near-surface plastic strain, coating density/thickness, and to some extent topography. Grain boundaries and other aspects of sample microstructure are readily revealed, so the PQ map is a very useful characterization tool in its own right, and serves as a reference for EBSD maps generated from indexing-derived data, such as orientation, grain boundary character, phase distribution and strain maps. KW - Electron backscatter diffraction KW - Sample preparation KW - Pattern quality PY - 2010 DO - https://doi.org/10.1017/S143192761005467X VL - 16 IS - Suppl. 2 SP - 698 EP - 699 PB - Microscopy Society of America AN - OPUS4-37997 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Nolze, Gert A1 - Winkelmann, Aimo T1 - Progress in dynamic EBSD pattern simulation JF - Microscopy and Microanalysis N2 - EBSD is nowadays a common technique for the characterization of crystalline microstructures in scanning electron microscopy. The diffraction patterns are often interpreted by superimposing individual Kikuchi bands which are geometrically described by band edges derived from Braggs law. For the typically very simple crystal structures of technically applied materials, such a simplification of the Kikuchi pattern interpretation works sufficiently well, especially for orientation determinations as a main application of EBSD. The more complex crystal structures, however, are a challenge for EBSD indexing routines which in such cases often fail unpredictably. The use of only the intensities of single reflectors for a description of the Kikuchi band intensity and as a cut-off criterion for a pre-selection of the strongest bands are not satisfactory. Often the result will match too many phases, or there are certain deviations in the intensity prediction which must be adapted manually. This is already problematic if one is absolutely sure that the patterns are originating from the expected phase and it becomes a very questionable procedure for an unknown phase. KW - Electron backscatter diffraction KW - Dynamical simulation KW - Geometrical model KW - Kinematic approach KW - Intensity PY - 2010 DO - https://doi.org/10.1017/S1431927610063324 VL - 16 IS - Suppl. 2 SP - 62 EP - 63 PB - Microscopy Society of America AN - OPUS4-38000 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -