| 1. |
- Kohler, L, et al.
(författare)
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High-coverage oxygen structures on Rh(111): Adsorbate repulsion and site preference is not enough
- 2004
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Ingår i: Physical Review Letters. - 1079-7114. ; 93:26
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Tidskriftsartikel (refereegranskat)abstract
- A new O induced structure on Rh(111) displaying a (2root3 x 2root3)R30degrees periodicity with an oxygen coverage of 2/3 has been studied by high resolution core level spectroscopy, scanning tunneling microscopy, and density functional theory. Although O favors fcc hollow sites in all other known phases, it occupies both fcc and hcp sites in this structure, which cannot be explained by pairwise adsorbate repulsion only. Both the (22root3 x 2root3)R30degrees and (2x2)-3O structures also exemplify that density-of-states contrast can lead to oxygen adatoms appearing as protrusions in scanning tunneling microscopy images.
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| 2. |
- Gustafson, Johan, et al.
(författare)
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Self-limited growth of a thin oxide layer on Rh(111)
- 2004
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Ingår i: Physical Review Letters. - 1079-7114. ; 92:12
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of the Rh(111) surface at oxygen pressures from 10(-10) mbar to 0.5 bar and temperatures between 300 and 900 K has been studied on the atomic scale using a multimethod approach of experimental and theoretical techniques. Oxidation starts at the steps, resulting in a trilayer O-Rh-O surface oxide which, although not thermodynamically stable, prevents further oxidation at intermediate pressures. A thick corundum like Rh2O3 bulk oxide is formed only at significantly higher pressures and temperatures.
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| 3. |
- Pettersson, A, et al.
(författare)
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Sm-Nd data for granitoids across the Namaqua sector of the Namaqua-Natal Province, South Africa.
- 2009
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Ingår i: Geological Society London, Special Publications. ; 323, s. 219-230
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Tidskriftsartikel (refereegranskat)abstract
- Sm–Nd data for rocks of granitic composition in an east–west traverse across the Namaqua Sector of the Mesoproterozoic c. 1.2 Ga Namaqua–Natal Province of southern Africa provide new evidence about the timing of crustal extraction from the mantle. Recent ion probe zircon dating has shown that, contrary to previous indications that pre-Namaqua basement had been preserved in parts of the Namaqua Sector, the majority of the magmatic rocks were emplaced during the 1.4–1.0 Ga Namaqua tectogenesis and very little U–Pb evidence of older precursors remains. Sm–Nd model ages show that Mesoproterozoic crustal extraction did occur, but was also strong in the Palaeoproterozoic, with local evidence for the existence of Archaean crust. The distribution of model ages generally corresponds with the established terranes, subdivided using lithostratigraphic and structural criteria. The northern part of the Bushmanland Terrane shows early Palaeoproterozoic to Archaean model ages and is clearly different from the southern part, which has Mesoproterozoic model ages. This supports the previously published results of a north–south traverse and justifies the separation of the Garies Terrane from the Bushmanland Terrane, though further subdivisions are not supported. The continuation of the Richtersveld Province east of Pofadder is supported by one sample, and the terrane boundary between the Bushmanland and Kakamas terranes is marked by an abrupt change from Palaeoproterozoic to Mesoproterozoic model ages. Model ages for the Kakamas and Areachap terranes do not distinguish them well. They suggest a Mesoproterozoic to late Palaeoproterozoic origin for both terranes, neither of which has a purely juvenile character. The influence of Palaeoproterozoic crust-forming events is clear in the Kaaien Terrane to the east, possibly reflecting reworking of the Kaapvaal Craton. The Namaqua Sector of the Province thus has a history of crustal extraction and evolution which reaches back locally to the Archaean, with major Palaeoproterozoic and Mesoproterozoic crust-forming events. This differs from the Natal Sector, which has a largely juvenile character related to a Mesoproterozoic Wilson cycle. Attempts to reconstruct the Mesoproterozoic Supercontinent Rodinia will have to take into account the extensive Nd-isotopic evidence for older crustal events in the Namaqua sector.
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| 4. |
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