Segregation and trapping of erbium during silicon molecular beam epitaxy

3 pages, 4 figures.Erbium surface segregation is observed during growth of Er-doped Si by molecular beam epitaxy on Si(100) at 600 °C. Once a critical Er surface areal density of 2 × 1014 Er/cm2 is reached, enhanced Er trapping is observed, possibly due to the formation of silicide precipitates. Er segregation on Si(100) is fully avoided when growth is performed in an oxygen background pressure of ~ 10 – 10 mbar, due to the formation of Er-O complexes. No Er segregation is observed on Si(111), which is attributed to the formation of epitaxial Er3Si5 precipitates.This work is part of the research program of FOM and was made possible by financial support from NWO, STW, and IOP Electro-Optics. R. Serna acknowledges financial support from CSIC, Spain.Peer reviewe

X-ray reflectivity of an Sb delta-doping layer in silicon

X‐ray reflectivity measurements were made on Si(001) crystals containing a delta‐doping layer of Sb atoms a few nanometers below the surface. The measurements show the Sb doping profile to be abrupt towards the substrate side of the sample and to decay towards the surface with a characteristic decay length of 1.01 nm

‘To the land or to the sea' : diet and mobility in early medieval Frisia

This study investigated palaeodiet and population mobility in early medieval Frisia through the stable isotope analysis of individuals buried in the fifth–eighth century AD cemetery of Oosterbeintum, a terp site on the northern coast of the Netherlands. The results cast new light on the role of the northern Netherlands in trade and migration in the early medieval period, and have significance for the study of interaction and movement throughout the wider North Sea region. Bone collagen and tooth enamel from humans and animals were analyzed using carbon, nitrogen, oxygen, and strontium isotopes. δ13C and δ15N results indicated that the population had a terrestrial, C3-based diet. High δ15N values were observed in humans and fauna, which are probably related to the terp's salt-marsh location. The δ18O and 87Sr/86Sr data revealed a high proportion of non-locals buried at Oosterbeintum, some of whom had probably migrated from regions as distant and varied as Scandinavia and southern England. It is suggested that this immigration may be associated with Frisian maritime trading activities. New data are also presented from a small number of contemporaneous European sites

Survival and long-term maintenance of tertiary trees in the Iberian Peninsula during the Pleistocene. First record of Aesculus L.

The Italian and Balkan peninsulas have been places traditionally highlighted as Pleistocene glacial refuges. The Iberian Peninsula, however, has been a focus of controversy between geobotanists and palaeobotanists as a result of its exclusion from this category on different occasions. In the current paper, we synthesise geological, molecular, palaeobotanical and geobotanical data that show the importance of the Iberian Peninsula in the Western Mediterranean as a refugium area. The presence of Aesculus aff. hippocastanum L. at the Iberian site at Cal Guardiola (Tarrasa, Barcelona, NE Spain) in the Lower– Middle Pleistocene transition helps to consolidate the remarkable role of the Iberian Peninsula in the survival of tertiary species during the Pleistocene. The palaeodistribution of the genus in Europe highlights a model of area abandonment for a widely-distributed species in the Miocene and Pliocene, leading to a diminished and fragmentary presence in the Pleistocene and Holocene on the southern Mediterranean peninsulas. Aesculus fossils are not uncommon within the series of Tertiary taxa. Many appear in the Pliocene and suffer a radical impoverishment in the Lower–Middle Pleistocene transition. Nonetheless some of these tertiary taxa persisted throughout the Pleistocene and Holocene up to the present in the Iberian Peninsula. Locating these refuge areas on the Peninsula is not an easy task, although areas characterised by a sustained level of humidity must have played an predominant role

The first hominin of Europe

The earliest hominin occupation of Europe is one of the most debated topics in palaeoanthropology. However, the purportedly oldest of the Early Pleistocene sites in Eurasia lack precise age control and contain stone tools rather than human fossil remains(1-5). Here we report the discovery of a human mandible associated with an assemblage of Mode 1 lithic tools and faunal remains bearing traces of hominin processing, in stratigraphic level TE9 at the site of the Sima del Elefante, Atapuerca, Spain(6-8). Level TE9 has been dated to the Early Pleistocene ( approximately 1.2 - 1.1 Myr), based on a combination of palaeomagnetism, cosmogenic nuclides and biostratigraphy. The Sima del Elefante site thus emerges as the oldest, most accurately dated record of human occupation in Europe, to our knowledge. The study of the human mandible suggests that the first settlement of Western Europe could be related to an early demographic expansion out of Africa. The new evidence, with previous findings in other Atapuerca sites ( level TD6 from Gran Dolina(9-13)), also suggests that a speciation event occurred in this extreme area of the Eurasian continent during the Early Pleistocene, initiating the hominin lineage represented by the TE9 and TD6 hominins.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62855/1/nature06815.pd

Segregation and trapping of erbium during silicon molecular beam epitaxy

3 pages, 4 figures.Erbium surface segregation is observed during growth of Er-doped Si by molecular beam epitaxy on Si(100) at 600 °C. Once a critical Er surface areal density of 2 × 1014 Er/cm2 is reached, enhanced Er trapping is observed, possibly due to the formation of silicide precipitates. Er segregation on Si(100) is fully avoided when growth is performed in an oxygen background pressure of ~ 10 – 10 mbar, due to the formation of Er-O complexes. No Er segregation is observed on Si(111), which is attributed to the formation of epitaxial Er3Si5 precipitates.This work is part of the research program of FOM and was made possible by financial support from NWO, STW, and IOP Electro-Optics. R. Serna acknowledges financial support from CSIC, Spain.Peer reviewe

Dataset: Age determination results from site Amersfoort

sediment/rock: 0.000 m * Maximum DEPTH, sediment/rock: 12.170

Structure determination of the NiSi2(111) surface with medium-energy ion backscattering from individual monolayers

The surface structure of the epitaxial NiSi2/Si(111) system has been determined applying new ion scattering methods. By detection of backscattered ions with ultrahigh energy resolution the signals from successive atomic layers are separated. Angular distributions of the yield of ions mainly backscattered from a single Ni monolayer directly provide the (sub)surface atom coordinates. In addition, analysis of the energy losses in the first atomic layer, which depend on the specific ion trajectories, allows an independent structure determination. Using either of the two methods, the NiSi2(111) surface is found to have a bulklike topology, i.e. it is terminated by a SiNiSi triple layer. Other surface structure models, such as termination by a Si double layer, are ruled out. The outermost NiNi and NiSi interlayer spacings are found to be contracted with respect to their bulk values in the strained silicide by 0.05 ± 0.02 and 0.12 ± 0.02 Å, respectively

Structure determination of the NiSi₂(111) surface with medium-energy ion backscattering from individual monolayers

The surface structure of the epitaxial NiSi2/Si(111) system has been determined applying new ion scattering methods. By detection of backscattered ions with ultrahigh energy resolution the signals from successive atomic layers are separated. Angular distributions of the yield of ions mainly backscattered from a single Ni monolayer directly provide the (sub)surface atom coordinates. In addition, analysis of the energy losses in the first atomic layer, which depend on the specific ion trajectories, allows an independent structure determination. Using either of the two methods, the NiSi2(111) surface is found to have a bulklike topology, i.e. it is terminated by a SiNiSi triple layer. Other surface structure models, such as termination by a Si double layer, are ruled out. The outermost NiNi and NiSi interlayer spacings are found to be contracted with respect to their bulk values in the strained silicide by 0.05 ± 0.02 and 0.12 ± 0.02 Å, respectively

Monolayer resolution in medium-energy ion-scattering experiments on the NiSi2(111) surface

The surface structure of the epitaxial NiSi2/Si(111) system has been determined applying a new ion-scattering method. Detecting backscattered ions with ultrahigh energy resolution we resolve the signals from successive atomic layers. From both their intensity and energy, which depends on the specific ion trajectories, we directly deduce the (sub)surface atom coordinates. Applying this new approach, we find that the NiSi2(111) surface has a bulklike topology, i.e., it is terminated by a Si-Ni-Si triple layer. The outermost Ni-Si and Ni-Ni interlayer distances are relaxed from their bulk values