bluuebunny/crossref_metadata_2025_split huggingface dataset:
Epitaxial growth of Fe on GaN(0001): structural and magnetic properties
Authors: Calarco R. , Meijers R. , Kaluza N. , Guzenko V. A. , Thillosen N. , Schäpers Th. , Lüth H. , Fonin M. , Krzyk S. , Ghadimi R. , Beschoten B. , Güntherodt G. 
Published: March 2005

AbstractWe report results on growth studies of Fe on GaN, in particular with respect to structural and magnetic properties. The growth of GaN has been carried out by molecular beam epitaxy (MBE) and metal organic vapour phase epitaxy (MOVPE) on Si(111) and Al2O3 substrates, respectively. Fe depositions of different thicknesses were performed in ultra high vacuum (UHV) at room temperature using an electron‐beam evaporation set‐up. X‐ray diffraction analysis shows that the iron films are crystalline and indications of a (110) bcc orientation of the film are observed. By means of scanning tunneling microscopy (STM) epitaxial islands of Fe on the GaN(0001) surface, on a scale of 500 × 500 nm2, have been observed. The experimentally determined magnetic hysteresis loops, with the magnetic field applied parallel to the sample surface, show a coercive field that decreases as the temperature increases; at 300 K and 50 K we measure a coercive field of 12 G and 36 G, respectively. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Extraction of temperature and number dependent scattering rates for an AlGaN/GaN 2DEG
Authors: Wells A. , Uren M. J. , Balmer R. S. , Nash K. J. , Martin T. , Missous M. 
Published: March 2005

AbstractThe alloy, polar optical and acoustic phonon scattering terms in the mobility in a GaN HFET have been extracted as a function of temperature and number density. It was found that roughness and Coulomb scattering are insignificant at room temperature. Samples with and without an AlN layer at the AlGaN/GaN interface were compared and used to extract the alloy scattering. At room temperature the mobility was dominated by intrinsic scattering terms. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
White X‐ray microbeam analysis of strain and crystallographic tilt in GaN layers grown by maskless pendeoepitaxy
Authors: Barabash R. I. , Ice G. E. , Liu W. , Einfeldt S. , Hommel D. , Roskowski A. M. , Davis R. F. 
Published: March 2005

AbstractWe describe X‐ray and finite element analysis of dislocations, strain and crystallographic tilt in uncoalesced GaN layers grown by maskless pendeoepitaxy. The experimental results reveal that the GaN wings are tilted upward at room temperature. The distribution of strain and tilt depends on the width‐to‐height ratio of the GaN column. As the width‐to‐height ratio increases the wing tilt increases and changes more abruptly at the column/wing interface. Broadening of the GaN Laue reflections is more pronounced in the column region then in the wing region; this is in line with the inhomogeneity of both the strain and the defect density. A split in the Laue reflections from GaN films at the column/wing interface indicates the development of a low‐angle tilt boundary for samples with a large width‐to‐height ratio of the column. Spacing between the dislocations in the tilt boundary at the column/wing interface for GaN grown with maskless pendeoepitaxy is an order of magnitude larger than the dislocation spacing observed for masked lateral epitaxial growth. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hot‐wall MOCVD grown homoepitaxial GaN layers with intense intrinsic excitonic structure
Authors: Kakanakova‐Georgieva A. , Ivanov I. G. , Hallin C. , Janzén E. 
Published: March 2005

AbstractWe report on a new approach to MOCVD growth of GaN, i.e. hot‐wall MOCVD, and its application to homoepitaxy on GaN substrates. The quality of the epilayers is examined by photoluminescence (PL). Homoepitaxially hot‐wall MOCVD grown GaN layers show (1) intense PL free‐exciton emissions relative to the intensity of the principal bound‐exciton emission and (2) homogeneous cathodoluminescence emission within the terraces developed during the step‐flow growth. Impurity concentrations in the material are measured by secondary ion mass spectrometry (SIMS). (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of the low temperature buffer and annealing on the properties of InN layers grown by MOVPE
Authors: Ruterana P. , Morales M. , Gourbilleau F. , Singh P. , Drago M. , Schmidtling T. , Pohl U. W. , Richter W. 
Published: March 2005

AbstractInN thin films grown by MOVPE with a thickness of about 100 nm are investigated. Growth was carried out in either two or three steps: deposition of a low temperature nucleation layer at 400 °C and subse‐ quent growth of a thicker InN layer at 530 °C, or use of a GaN buffer layer which was annealed at 1050 °C prior to deposition of the low temperature InN buffer layer. The structural evolution of the layers during a 20 min annealing step at 540 °C under nitrogen was investigated using AFM and XRD. We analyzed the orientation distribution function of the layers by XRD reciprocal space maps applying ψ and χ scans. The results show that the crystalline layer quality is improved by use of a GaN buffer, as also assessed from higher photoluminescence intensity. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Reduction of threading dislocations in GaN overgrowth by MOCVD on TiN porous network templates
Authors: Yun F. , Fu Y. , Moon Y. T. , Özgür Ü. , Xie J. Q. , Doğan S. , Morkoç H. , Inoki C. K. , Kuan T. S. , Zhou L. , Smith D. J. 
Published: March 2005

AbstractGaN overlayers for the purpose of reducing extended defects have been grown by MOCVD on porous network of TiN thin layers which in turn were achieved by in situ nitridation of thin Ti layers (20 nm and 10 nm) on a GaN template. TEM analyses performed for the GaN layer with 20 nm TiN porous netowrk indicate the effectiveness of TiN porous structure in blocking the threading dislocation from penetrating into the upper layer. Plan‐view TEM indicated a reduction in the dislocation density by a factor of 10, compared to the GaN template without TiN network. Subsurface voids were formed during the TiN formation, which act as defect concentrators, and termination sites for dislocations. The reduction in defect density through the use of TiN porous networks is also confimed by X‐ray diffraction data and time‐resolved photoluminescence measurements at room temperature. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Epitaxial Al/GaN and Au/GaN junctions on as‐grown GaN(0001)1 × 1 surfaces
Authors: Orani D. , Piccin M. , Rubini S. , Pelucchi E. , Bonanni B. , Franciosi A. , Passaseo A. , Cingolani R. , Khan A. 
Published: March 2005

AbstractGaN(0001) epilayers were fabricated by rf‐plasma enhanced molecular beam epitaxy on GaN templates. The templates were grown by metalorganic chemical vapor deposition on sapphire. The layers exhibited the 2 × 2 reconstruction of the Ga‐face during growth and the 1 × 1 reconstruction upon cooling. On such surfaces, Al/n‐GaN and Au/n‐GaN junctions were fabricated in‐situ by molecular beam epitaxy. X‐ray photoemission spectroscopy studies allowed us to determine n‐type Schottky barrier heights of 0.61 ± 0.06 and 0.98 ± 0.06 eV, respectively, for the two types of epitaxial junctions. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Chemical Vapor Synthesis of Size‐Selected Zinc Oxide Nanoparticles
Authors: Polarz Sebastian , Roy Abhijit , Merz Michael , Halm Simon , Schröder Detlef , Schneider Lars , Bacher Gerd , Kruis Frank E. , Driess Matthias 
Published: March 2005

AbstractZnO can be regarded as one of the most important metal oxide semiconductors for future applications. Similar to silicon in microelectronics, it is not only important to obtain nanoscale building blocks of ZnO, but also extraordinary purity has to be ensured. A new gas‐phase approach to obtain size‐selected, nanocrystalline ZnO particles is presented. The tetrameric alkyl‐alkoxy zinc compound [CH3ZnOCH(CH3)2]4 is chemically transformed into ZnO, and the mechanism of gas‐phase transformation is studied in detail. Furthermore, the morphological genesis of particles via gas‐phase sintering is investigated, and for the first time a detailed model of the gas‐phase sintering processes of ZnO is presented. Various analytical techniques (powder XRD, TEM/energy‐dispersive X‐ray spectroscopy, magic‐angle spinning NMR spectroscopy, FTIR spectroscopy, etc.) are used to investigate the structure and purity of the samples. In particular, the defect structure of the ZnO was studied by photoluminescence spectroscopy.
Symmetric and Asymmetric Ostwald Ripening in the Fabrication of Homogeneous Core–Shell Semiconductors
Authors: Liu Bin , Zeng Hua Chun 
Published: March 2005

AbstractTwo methodic concepts, symmetric and asymmetric Ostwald ripening, are elucidated by solution‐route syntheses of oxide and sulfide semiconductors. While the original shape of a crystallite aggregate forms the exterior appearance, the preorganization of the crystallites determines the ultimate interior space structure of the aggregate upon Ostwald ripening. Further investigations on the design of crystallite preorganization and control of the solution process will allow the construction of complex architectures, including nonspherical configurations.
Fragment shape and tree species composition in tropical forests: a landscape level investigation
Authors: Hill J. L. , Curran P. J. 
Published: March 2005

AbstractFragmentation of tropical forest alters community composition as a result of changes in forest shape. This paper uses 22 hypotheses to test the effect of fragment shape on tree species composition in Ghana, West Africa, within biological categories of regeneration guild, rarity, phenology and dispersal. For both regenerating and mature trees, relationships between species composition and the shape of forest fragments were complex; almost half were significant but many failed to support the established hypotheses. Irregular shaped fragments had high proportions of regenerating, light‐demanding pioneers and mature, animal‐dispersed species. Species common to Ghana formed the foundation of communities in fragments of all shapes. Investigation at the landscape level indicated broad patterns of species change. Rigorous hypothesis testing is needed, following extensive demographic work on the ground, before population dynamics within tropical forest fragments can be comprehended fully and applied to conservation management.
Temporal patterns of crop raiding by elephants: a response to changes in forage quality or crop availability?
Authors: Chiyo Patrick I. , Cochrane Erica P. , Naughton Lisa , Basuta Gilbert I. 
Published: March 2005

AbstractTemporal patterns of crop raiding by elephants were studied for 13 months in 1996/1997 at Kibale Forest National Park, Uganda. To determine the influence of environmental factors on the timing of raiding, we tested for correlations between crop raiding patterns and the quality of natural forage within the forest as well as crop availability beyond park boundaries. Crop raiding occurred throughout the year with peaks in dry seasons when crop availability was high. Bananas and maize were the main crops raided. Variations in forage quality were moderate with small seasonal fluctuations and peaks in dry seasons. Monthly crop raiding incidences were not influenced by forage quality but by ripening of maize. Comparison of forage quality and temporal distribution of crop raiding between savanna and forest habitats suggests that crop availability is more important in forest habitats, whereas in savanna habitats large seasonal fluctuations in forage quality have a greater influence on temporal patterns of crop raiding.
The world's biogeographical regions: cluster analyses based on bat distributions
Authors: Procheş Şerban 
Published: March 2005

AbstractAim  Both floral kingdoms and faunal regions have so far been intuitively defined. This study was conducted to compare these with an analytical regionalization based on cluster analyses in a fairly homogeneous, globally distributed group of organisms: the bats (order Chiroptera). This comparison was used to discuss the possibilities of employing clustering techniques in global biogeography.Location  The study considered bat distributions world‐wide.Methods  Analyses were conducted both for presence/absence of genera and species, and for the number of species in each genus. Clusters distinguished at selected dissimilarity values were mapped.Results  A set of c. 10 regional clusters recurred in the analyses, broadly corresponding not only to the world's accepted faunal regions and subregions, but also to the floral kingdoms and subkingdoms.Main conclusions  This study is an analytical confirmation of the fact that similar global distribution patterns are to be found in different groups of organisms. Cluster analyses can be used to refine global regionalization schemes, and, with the accumulation of such data for different taxa and ecologically defined groups, shared patterns can be used to draft one common global biogeographical regionalization. At the same time, differences between the regionalization schemes derived for different groups can be used to partial out the role of dispersal abilities, body size, evolutionary age, etc., in determining global distribution patterns.
Characterization of moorland vegetation and the prediction of bird abundance using remote sensing
Authors: Buchanan Graeme , Pearce‐Higgins James , Grant Murray , Robertson Duncan , Waterhouse Tony 
Published: March 2005

AbstractAims  To characterize and identify upland vegetation composition and height from a satellite image, and assess whether the resulting vegetation maps are accurate enough for predictions of bird abundance.Location  South‐east Scotland, UK.Methods  Fine‐taxa vegetation data collected using point samples were used for a supervised classification of a Landsat 7 image, while linear regression was used to model vegetation height over the same image. Generalized linear models describing bird abundance were developed using field‐collected bird and vegetation data. The satellite‐derived vegetation data were substituted into these models and efficacy was examined.Results  The accuracy of the classification was tested over both the training and a set of test plots, and showed that more common vegetation types could be predicted accurately. Attempts to estimate the heights of both dwarf shrub and graminoid vegetation from satellite data produced significant, but weak, correlations between observed and predicted height. When these outputs were used in bird abundance–habitat models, bird abundance predicted using satellite‐derived vegetation data was very similar to that obtained when the field‐collected data were used for one bird species, but poor estimates of vegetation height produced from the satellite data resulted in a poor abundance prediction for another.Conclusions  This pilot study suggests that it is possible to identify moorland vegetation to a fine‐taxa level using point samples, and that it may be possible to derive information on vegetation height, although more appropriate field‐collected data are needed to examine this further. While remote sensing may have limitations compared with relatively fine‐scale fieldwork, when used at relatively large scales and in conjunction with robust bird abundance–habitat association models, it may facilitate the mapping of moorland bird abundance across large areas.
Spatial variation in species diversity and composition of flea assemblages in small mammalian hosts: geographical distance or faunal similarity?
Authors: Krasnov Boris R. , Shenbrot Georgy I. , Mouillot David , Khokhlova Irina S. , Poulin Robert 
Published: March 2005

AbstractAim  Spatial variation in the diversity of fleas parasitic on small mammals was examined to answer three questions. (1) Is the diversity of flea assemblages repeatable among populations of the same host species? (2) Does similarity in the composition of flea assemblages among populations of the same host species decay with geographical distance, with decreasing similarity in the composition of local host faunas, or with both? (3) Does the diversity of flea assemblages correlate with climatic variables?Location  The study used previously published data on 69 species of small mammals and their fleas from 24 different regions of the Holarctic.Methods The diversity of flea assemblages was measured as both species richness and the average taxonomic distinctness of their component species. Similarity between flea assemblages was measured using both the Jaccard and Morisita–Horn indices, whereas similarity in the composition of host faunas between regions (host ‘faunal’ distance) was quantified using the Jaccard index. Where appropriate, a correction was made for the potentially confounding influence of phylogeny using the independent contrasts method.Results  Flea species richness varied less within than among host species, and is thus a repeatable host species character; the same was not true of the taxonomic distinctness of flea assemblages. In almost all host species found in at least five regions, similarity in flea assemblages decreased with increases in either or both geographical and faunal distance. In most host species, the diversity of flea assemblages correlated with one or more climatic variable, in particular mean winter temperature.Main conclusions  Spatial variation in flea diversity among populations of the same mammal species is constrained by the fact that it appears to be a species character, but is also driven by local climatic conditions. The results highlight how ecological processes interact with co‐evolutionary history to determine local parasite biodiversity.
Historical transoceanic dispersal of a freshwater shrimp: the colonization of the South Pacific by the genus Paratya (Atyidae)
Authors: Page Timothy J. , Baker Andrew M. , Cook Benjamin D. , Hughes Jane M. 
Published: March 2005

AbstractAim  To infer the phylogenetic relationships within the freshwater shrimp genus Paratya Miers, 1882 (Atyidae) and to use these data to answer biogeographical questions about the location, timing and form of evolution of this genus in the South Pacific.Location  Paratya are spread throughout various freshwater habitats in the western Pacific, with a disjunct northern range in the North Pacific (Japan, Korea, Ryukyu Islands, Siberia) and South Pacific (Australia, New Zealand, New Caledonia, Lord Howe, Norfolk Island).Methods  Specimens were obtained from throughout its range. Mitochondrial sequences of cytochrome oxidase subunit I and 16S ribosomal DNA were analysed using phylogenetic techniques to identify whether landmasses are monophyletic and what the relationships are between landmasses. Molecular clock dating methods were used to date divergences between taxa.Results  Each landmass was recovered as monophyletic. Japan/Ryukyu Islands is the most basal group, followed by New Zealand. Australian specimens form a sister group to a clade made up of two groups (New Caledonia and Lord Howe/Norfolk Island). The oldest divergence within the genus (between North and South Pacific) took place 12–19 Ma.Main conclusions  The geographical origin of the genus (either Gondwana or Laurasia) is unclear. Dispersal occurred between the North and South Pacific long after the split up of Gondwana. Dispersal likely explains the presence of Paratya on each landmass in the South Pacific, from continent to isolated oceanic island. This dispersal is conjectured to have taken place through oceanic currents because of the amphidromous life cycle of some taxa of Paratya, given that amphyidromy is plesiomorphic in atyid shrimp.
A modern pollen rain study from the central Andes region of South America
Authors: Reese Carl A. , Liu Kam‐biu 
Published: March 2005

AbstractAim To provide a greater understanding of the modern pollen rain for the central Andes region of South America, thus laying the groundwork for future pollen studies and the derivation of pollen‐climate transfer functions and response surfaces.Location Peru, Bolivia and Chile.Methods Standard palynological techniques for surface soil sampling and discriminant analysis.Results Statistical analysis of the 40 surface samples revealed four palynologically distinct assemblages: (1) the Yungas on the eastern slopes of the Andes; (2) the puna grasslands of the Altiplano; (3) the Coastal Deserts to the west of the Andes; and (4) the Southern Bolivian Highlands.Main conclusions The Yungas group is characterized by high percentages of Urticaceae/Moraceae pollen and fern spores along with trace amounts of pollen from common zoophilous lowland taxa such as Piperaceae, Bignoniaceae and Malpighiaceae. The puna assemblage of the Altiplano is characterized by the dominance of grass (Poaceae) in combination with moderate frequencies of Asteraceae pollen, which tend to increase slightly towards the southern (drier) locations of the Altiplano. Lower percentages of grass pollen and the greater prevalence of Asteraceae, Solanaceae, and the Chenopodiaceae/Amaranthaceae families define the coastal deserts to the west of the Andes. Samples taken from the Southern Bolivian Highlands are characterized by the dominance of Solanaceae in the area, in combination with the pollen of other xerophytic taxa.
Efficience de différentes stratégies de détection de la Trypanosomiase Humaine Africaine àT. b. gambiense
Authors: Lutumba Pascal , Robays Jo , Miaka Constantin , Kande Victor , Simarro Pere P. , Shaw Alexandra P. M. , Dujardin Bruno , Boelaert Marleen 
Published: March 2005

ResumeIntroduction  La détection active de la Trypanosomiase Humaine Africaine (THA) se base souvent sur l'utilisation de deux tests de dépistage: la palpation ganglionnaire (PG) et le card agglutination test for trypanosomiasis (CATT). Cette analyse de décision compare l'efficience de trois stratégies alternatives pour ce dépistage: PG seul, CATT seul ou leur combinaison en parallèle (PG and CATT).Methode  Une stratégie de détection de THA a été définie comme la séquence de l’étape de dépistage suivi par la confirmation parasitologique. L'efficacité de chaque stratégie a étéévaluée en nombre de vies sauvées. Le coût des tests de dépistage et de confirmation a été estimé en US$. Les estimations des différents paramètres proviennent de la littérature et des observations faites par le programme de contrôle de la THA en RD Congo entre 1996 et 2002. Une analyse de sensibilité a été effectuée pour les paramètres sujets à incertitude.Resultats  La stratégie basée sur le CATT revient à US$125 par vie sauvée pour la séquence complète des tests, la PG revient à US$517 et la combinée à US$452. Le coût marginal de l'ajout du PG au CATT est entre 1225 à US$5000 par vie sauvée. L'analyse de sensibilité montre que les résultats sont robustes aux variations plausibles des paramètres.Discussion  La stratégie CATT est la plus efficiente des trois. L'efficacité en terme de vies sauvées d'aucune des stratégies de détection ne dépasse 60% des décès évitables. Cette faiblesse est due à la basse sensibilité des examens parasitologiques de confirmation. Un gain d'efficience dans le contrôle peut être obtenu en recourant à la stratégie CATT et en réinvestissant soit dans de meilleurs examens de confirmation, soit dans une plus grande couverture.