María Teresa Alberdi Alonso

Vertebrate taphonomy in circum-lake environments: three cases in the Guadix-Baza Basin (Granada, Spain)

Abstract This work analyses the origin and taphonomy of three Plio-Pleistocene mammal assemblages from the Guadix-Baza basin (Granada, Spain): Huelago; Huescar-1; and Cullar de Baza-1. Similarities and differences in the taphonomic features are evaluated with regard to marginal lacustrine sedimentary processes involved in the accumulation of these mammal assemblages. Selective preservation of skeletal-part and taxa in relation to facies have been explored to determine their suitability for palaeoecological analysis. The mortality in Cullar de Baza-1 and Huelago-1 corresponds to a catastrophic pattern, but other taphonomic features of the bones indicate that accumulation processes were diachronic as occurred in Huescar-1. This could be explained by selective-predation and/or seasonal accumulation of bones. Hydraulic sorting and transportation greatly controlled the size and shape of accumulated skeletal elements, and the different preservational circumstances of each environment largely constrained the taxonomic composition of the fossil bone assemblages. Autochthonous fauna only occurs in Huescar-1 corresponding to subaquatic environments. The absence of carnivores among the identifiable remains from Huelago-1 has no plausible taphonomic or sedimentological explanation. Nevertheless, after taking into account the taphonomic factors, the differences in taxonomic composition between these three mammal assemblages reflect differences in the surrounding habitats. The great diversity of ruminant artiodactyls, in particular browsers, is indicative of wooded or bushy areas in the surroundings of Huelago-1 although not in the immediate area of the lake margin. This diversity coincides with that observed in other Villafranchian localities and represents the greatest diversity of artiodactyls known from the Neogene and Quaternary record of Western Europe. In turn, the high diversity of sub-aquatic forms and a smaller variety of artiodactyl species in Huescar-1, reflects an open, sparsely forested environment susceptible to seasonal drought. A similar sparse forested environment has been deduced for Cullar de Baza-1. The climate and environmental conditions in Huescar-1 and Cullar de Baza-1 are consistent with a climatic deterioration at the beginning of the Middle Pleistocene (‘Glacial Pleistocene’).

Photoemission results on intralayer insertion at III-V/III-V junctions: A critical appraisal of the different interpretations

Several researchers have proposed that band discontinuities at semiconductor heterojunctions may be “tuned” by inserting very thin layers of foreign atoms at the interface which are thought to induce an “interface dipole.” Modifications of the apparent valence-band offset, as measured by photoelectron spectroscopy (PES), have been indeed observed upon Si insertion at GaAs–AlAs interfaces, and they have been generally interpreted as real band-offset changes. However, there is an alternative explanation of the photoemission results in terms of band-bending effects. Here, we present results of PES experiments designed to test the two opposing interpretations. We have examined the effect of Si insertion at polar (100) and nonpolar (110) interfaces, and we have studied the insertion of Si (n-type) and Be (p-type) intralayers. Similar results are obtained for polar and nonpolar interfaces, and effects of opposite sign are observed for Si and Be intralayers. These results can be readily interpreted in terms of a...

Influence of the substrate surface on the self-assembly of ferroelectric PbTiO3 nanostructures obtained by microemulsion assisted Chemical Solution Deposition

The achievement of long range periodicity of ferroelectric nanostructures on substrates remains as a challenge in the processing of devices by the relatively inexpensive self-assembly methods. To this aim, here we make the proposal of processing strategies involving commercial single-crystal SrTiO 3 (100) substrate surface treatment. The topography, global ordering and crystal symmetry of the surface of the treated substrates as well as the near surface layer composition were analysed by Scanning Force Microscopy, Low Energy Electron Diffraction and Auger Electron Spectroscopy, respectively. The study shows that a combination of chemical etching and thermal annealing in air produces smooth and well terraced surfaces which have steps of few unit cells height and a nearly complete TiO 2 termination, while keeping the 1× 1 bulk structure. Preliminary results shows that PbTiO 3 nanostructures, obtained by a novel microemulsion assisted Chemical Solution Deposition method onto such substrates, grow at regular distances and preferentially located at the edges of the substrate surface terraces. Thus, long range order of these nanostructures is envisaged when deposited onto substrates that are treated by the procedure here studied.

Morphology Analysis of Si Island Arrays on Si(001).

The formation of nanometer-scale islands is an important issue for bottom-up-based schemes in novel electronic, optoelectronic and magnetoelectronic devices technology. In this work, we present a detailed atomic force microscopy analysis of Si island arrays grown by molecular beam epitaxy. Recent reports have shown that self-assembled distributions of fourfold pyramid-like islands develop in 5-nm thick Si layers grown at substrate temperatures of 650 and 750°C on HF-prepared Si(001) substrates. Looking for wielding control and understanding the phenomena involved in this surface nanostructuring, we develop and apply a formalism that allows for processing large area AFM topographic images in a shot, obtaining surface orientation maps with specific information on facets population. The procedure reveals some noticeable features of these Si island arrays, e.g. a clear anisotropy of the in-plane local slope distributions. Total island volume analysis also indicates mass transport from the substrate surface to the 3D islands, a process presumably related to the presence of trenches around some of the pyramids. Results are discussed within the framework of similar island arrays in homoepitaxial and heteroepitaxial semiconductor systems.