bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bose‐Einstein condensation of dipolar excitons in double and single quantum wells
Authors: Timofeev V. B. , Gorbunov A. V. 
Published: March 2008

AbstractExperiments connected with dipolar exciton Bose‐Einstein condensation in ring lateral traps in GaAs/AlGaAs Schottky‐ diode heterostructures with double and single quantum wells are presented. The observed behaviour of luminescence spectra and patterned luminescence structure in circular ring traps, as well as linear polarization of luminescence and long‐range spatial coherence of Bose condensate are discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Plasma assisted molecular beam epitaxy of AlGaN/GaN high electron mobility transistors
Authors: Aidam R. , Kirste L. , Kunzer M. , Müller S. , Waltereit P. 
Published: March 2008

AbstractWe report on the plasma‐assisted molecular beam epitaxy (PAMBE) of AlGaN/GaN high electron mobility transistors (HEMTS). Growth was performed on MOCVD grown GaN Templates and 4H‐SiC(0001) wafers with 3” diameter. In a detailed study of GaN growth conditions the growth rate was varied between 0.28 and 0.5 µm/h. Under optimized conditions, the surface root mean square roughness was less than 0.6 nm. Low temperature PL measurements in the range 1.9 to 3.8 eV showed only the exciton‐emission with a FWHM of 12 meV. AlGaN‐HEMT structures on GaN‐templates exhibited room temperature Hall mobilities of 1600 cm2/Vs and sheet electron concentration of 8 × 1012/cm2. On SiC mobilities of 1220 cm2/Vs were achieved. Current‐voltage output characteristics of PAMBE grown AlGaN/GaN HEMTs on SiC showed a drain current density about 0.8 A/mm for a gate bias of +1V and only small dispersion. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Is Auger recombination responsible for the efficiency rollover in III‐nitride light‐emitting diodes?
Authors: Bulashevich K. A. , Karpov S. Yu. 
Published: March 2008

AbstractPractically all III‐nitride light emitting diodes (LEDs) suffer from the efficiency rollover that occurs at high electric currents in the devices and limits their performance. At the moment, the mechanisms responsible for the rollover are not yet confidently identified despite the crucial importance of this problem for the LED production. On the basis of simulation, we suggest that the Auger recombination is a likely mechanism, producing the efficiency reduction at high currents. Using an empirically estimated Auger recombination coefficient, we argue for significance of this mechanism under practical operation conditions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Reliable nitride‐based near‐ultraviolet light‐emitting diodes with meshed p‐GaN
Authors: Kuo C. W. , Chen C. M. , Feng H. C. , Kuo C. H. 
Published: March 2008

AbstractThis investigation presents nitride‐based near ultraviolet (n‐UV) light emitting diodes (LEDs) with a meshed p‐GaN layer. With 20 mA injection current, it was found that forward voltages were 3.29, 3.31 and 3.39 V while output powers were 7.5, 9.0 and 10.6 mW for the planar indium‐tinoxide (ITO) LED, mesh ITO LED and meshed p‐GaN LED, respectively. The larger LED output power is attributed to increased light extraction efficiency. It was also found that we could use such a meshed p‐GaN layer to achieve reliable nitride‐based n‐UV LEDs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Improvement of hydrogen generation efficiency using GaN photoelectrochemical reaction in electrolytes with alcohol
Authors: Fujii Katsushi , Nakayama Hitoshi , Sato Keiichi , Kato Takashi , Cho Meoung‐Whan , Yao Takafumi 
Published: March 2008

AbstractPhotoelectrochemical water reduction using n‐type GaN in electrolytes with/without alcohol was investigated. For both cases, hydrogen evolution from counterelectrode was observed without bias. Hydrogen gas amount using 1.0 mol/L NaOH electrolyte with alcohol was approximately double compared to that without alcohol where the total current flow charges are similar at 300 min. The amount of hydrogen evolution was almost coincidence with the amount calculated from the total charge flow. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation on conductivity at the GaN/AlN/SiC substrate interface for vertical nitride power FETs
Authors: Wakamiya Y. , Hasegawa F. , Kawanishi H. 
Published: March 2008

AbstractPower FETs are the next promising application of AlGaN/GaN hetero‐structures. In order to reduce the device size and thermal conductivity, power nitride FETs should be a vertical structure on a conductive SiC or Si substrate. An AlN or/and AlN/GaN multi‐buffer layer is inevitable to grow GaN on a SiC or Si substrate by MOVPE, therefore, current flow at the GaN/AlN/SiC interface is one of the important issues to be investigated. 17 to 350 nm AlN layers were grown on 8o off n–‐epitaxial 4H‐SiC substrates and on a GaN/AlGaN/AlN/SiC structure by alternate‐source‐feeding MOVPE. Ni/AlN/n‐‐epi‐4H‐SiC sample showed Schottky characteristics except 350nm thick AlN sample, indicating that the AlN was not working as an insulator. On the other hand, Ni/AlN/GaN/n–‐epi‐4H‐SiC sample turned out MIS characteristics for the same AlN thickness. This difference can be explained by the heterovalent atomic structure at the interface between AlN(III‐V) and SiC(IV‐IV). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Deep centers in semi‐insulating Fe‐doped native GaN substrates grown by hydride vapour phase epitaxy
Authors: Fang Z.‐Q. , Claflin B. , Look D. C. , Elhamri S. , Smith H. E. , Mitchel W. C. , Hanser D. , Preble E. A. , Evans K. R. 
Published: March 2008

AbstractElectrical properties, Fe concentration, and deep centers in semi‐insulating Fe‐doped GaN substrates grown by hydride vapor phase epitaxy (HVPE) were characterized by temperature‐dependent Hall‐effect measurements, secondary ion mass spectroscopy, and thermally stimulated current (TSC) spectroscopy. Five adjacent samples from a low‐[Fe] wafer displayed very high resistivity, dominated by a center at 0.94 eV. At least six traps were observed in the samples by TSC, with trap B (0.56‐0.60 eV) being dominant. A metastable trap A1 at ∼0.82 eV appeared after white‐light illumination at 300 K. A sample from a high‐[Fe] wafer displayed a lower resistivity, dominated by a center at 0.58 eV. The largest TSC peak in this sample was trap A1, although trap B also appeared. These TSC traps are compared with deep‐level‐transient‐spectroscopy traps reported in conductive epitaxial and bulk HVPE‐GaN. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of thin protective AlN layers on sapphire substrates at 1065 °C for hydride vapor phase epitaxy of AlN above 1300 °C
Authors: Tajima J. , Kubota Y. , Togashi R. , Murakami H. , Kumagai Y. , Koukitu A. 
Published: March 2008

AbstractA thin protective AlN layer was grown on a (0001) sapphire substrate at 1065 °C for main AlN layer growth at high temperature (> 1300 °C) by hydride vapor phase epitaxy (HVPE). The formation of surface pits on the surface of the epitaxial AlN layer, grown directly on the sapphire substrate at 1320 °C, could be prevented by growing the protective layer. The full‐width at half‐maximum (FWHM) of X‐ray diffraction (XRD) rocking curves of asymmetric (10 $\bar 1$ 0) and symmetric (0002) AlN decreased to 19.8 and 9.6 min, respectively. The concentration of oxygen impurities in the layer grown at 1320 °C was also reduced from 3 × 1019 to 4 × 1018 cm−3 by protecting sapphire substrate at 1065 °C. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermal analysis of GaN powder formation via reaction of gallium ethylenediamine tetraacetic acid complexes with ammonia
Authors: Liu Yu‐Huai , Koide Shinya , Miyake Hideto , Hiramatsu Kazumasa , Nakamura Atsushi , Nambu Nobuyoshi 
Published: March 2008

AbstractThe reaction mechanism of gallium ethylenediamine tetraacetic acid (Ga[(OOCCH2)2–N–CH2–CH2–N–(CH2COO)2]NH4) (Ga‐EDTA)with ammonia was investigated. The Ga‐EDTA·NH4 complex powders were analyzed by thermogravimetric and differential thermal analysis (TG/DTA) under flow of ammonia gas and nitrogen gas. From the TG/DTA results, it is shown that the precursors undergo a sharp mass loss at about 296 °C (step I) due to the release of organic groups, followed by further releasing of organic groups (297∼ 552 °C, step II), elimination of carbon and formation of GaN (552 ∼ 650 °C, step III), GaN crystallization and further elimination of carbon (650 ∼ 850 °C, step IV), the improvement of GaN crystal quality (600 ∼ 1100 °C, step‐IV) and the initial decomposition of GaN powders. The X‐ray diffraction analysis of the powders indicates that proper sintering temperature for GaN powders should be approximate to 1100 °C. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
GaInN light emitting diodes with AlInN/GaN distributed Bragg reflector on Si
Authors: Ishikawa H. , Jimbo T. , Egawa T. 
Published: March 2008

AbstractWe report the effect of inserting a lattice‐matched AlInN/GaN distributed Bragg reflector (DBR) on the performance of GaInN light emitting diodes (LEDs) on Si substrates. The lattice‐matched AlInN/GaN DBR is superior to the previously used AlGaN/AlN DBR with respect to the suppression of cracking and the interface smooth ness. The light output power (PEL) of the LED increases with increasing number of pairs in the DBR and agrees well with the calculated one. The PEL of the 14.5‐pair AlInN/GaN DBR LED is about 3.6‐fold higher than that of the non‐DBR LED. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High quantum efficiency of semipolar GaInN/GaN quantum wells
Authors: Feneberg Martin , Lipski Frank , Schirra Martin , Sauer Rolf , Thonke Klaus , Wunderer Thomas , Brückner Peter , Scholz Ferdinand 
Published: March 2008

AbstractThe development of efficient GaInN/GaN based light emitting devices is hampered by built‐in electric fields. These fields, arising from piezoelectric and spontaneous polarization, separate electron and hole wavefunctions and reduce their spatial overlap. Therefore, the internal quantum efficiency is drastically reduced in the presence of built‐in fields.To decrease the detrimental influence of the polarization fields on quantum efficiency, growth on non‐ or semipolar crystal facets is conducted. We investigate samples containing quantum wells grown on the {1$\bar 1$01} facet (tilt angle from (0001) is θ = 62°) of selectively grown GaN stripes and compare them to samples grown on the commonly used c plane. We experimentally determine direction and strength of built‐in polarization fields. These fields are used to compute overlap integrals and to estimate the internal quantum efficiency of semipolar quantum wells in comparison to polar and nonpolar ones. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Normally‐off AlGaN/GaN MOSHFETs with HfO2 gate oxide
Authors: Sugiura S. , Kishimoto S. , Mizutani T. , Kuroda M. , Ueda T. , Tanaka T. 
Published: March 2008

AbstractNormally‐off AlGaN/GaN MOSHFETs with a thick HfO2 as a gate oxide have been fabricated. The HfO2 with a thickness of 100 nm was deposited by pulsed‐laser deposition. The threshold voltage was 3 V and the maximum drain current was 730 mA/mm at a gate voltage of 10 V. The maximum transconductance was 185 mS/mm, which was about 8 times larger than that of the GaN MOSFETs. The field effect mobility was 900–1500 cm2/Vs, which is also higher than that of the GaN MOSFETs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Silanization of inner surfaces of nanoelectrospray ionization emitters for reduced analyte adsorption
Authors: Choi Yong Seok , Wood Troy D. 
Published: March 2008

AbstractDuring the course of nanoelectrospray ionization (nanoESI) of substance P, an unusual type of signal reduction was observed with flow rates <10 nL/min. This reduction in signal appears to be induced by the adsorption of positively charged analytes onto negatively charged free silanol groups on the inner surface of emitters; analytes with higher pI values (such as substance P) exhibit greater tendency for adsorption. Support for this hypothesis is demonstrated by the decrease in signal reduction in the presence of concentrated salts or for emitters whose internal silanols have been covalently silanized. Emitters treated with hexamethyldisilazane or 3‐aminopropyltriethoxysilane showed higher analyte signals for substance P than untreated emitters, suggesting a reduction of analyte adsorption onto the inner walls of silanized emitters. The efficacy of reduced peptide adsorption was demonstrated for emitters silanized with 3‐aminopropyltriethoxysilane using a simple peptide mixture as well as a more complex peptide mixture (a tryptic digest of horse hemoglobin). Copyright © 2008 John Wiley & Sons, Ltd.
Sorting of seeds by hydrochory
Authors: Chambert S. , James C. S. 
Published: March 2008

AbstractThe species composition of riparian vegetation is determined by a variety of processes, including the dispersal of seeds. The seed types that end up at certain locations are determined by their particular characteristics as well as the prevailing hydrology and the physical characteristics of the river channel. A conceptual model is proposed to identify the hydraulic processes involved in the hydrochory pathway that may lead to differential response of different seed types and hence their sorting. The results of a series of laboratory experiments are presented to demonstrate the sorting between seed types by these processes. The behaviour of non‐buoyant seeds during settling and entrainment is shown to be consistent with that of mineral sediments, and their sorting can therefore be described by existing sediment transport theory. Significant sorting of buoyant seed types takes place during transport under the influence of wind and during ingress into marginal emergent vegetation, trapping by vegetation and stranding during receding flows on sloping channel banks. Copyright © 2008 John Wiley & Sons, Ltd.
Behaviour of Ti6Al4V implant alloy in vitro after plastic deformation by bending
Authors: Kierzkowska Agnieszka , Krasicka‐Cydzik Elzbieta 
Published: March 2008

AbstractElectrochemical and biological tests were used to evaluate in vitro the behaviour of anodised Ti6Al4V ELI samples after plastic deformation by bending. The implant rods of 6 mm diameter, anodised in H3PO4 acid solution, were used. Bending of implant rods was performed according to typical intra‐surgical procedure applied during pre‐shaping stage of implantation. The electrochemical properties were evaluated on the corrosion potential Ecorr and the results of the electrochemical impedance spectroscopy tests (EIS) of deformed samples immersed in simulated body fluid (SBF). Biological behaviour was estimated in contact with human osteoblasts. Electrochemical and biological changes demonstrated that mechanically disturbed anodic layer strived to achieve ‘the state of balance’ during immersion in electrolyte. After ∼6 days in SBF the former bi‐layer structure of the anodic surface layer was recovered. Moreover, all samples irrespective of bending angle achieved similar values of Ecorr corresponding to the corrosion potential of the sample deformed at the 20° angle. Biological tests in vitro confirmed that deformation of anodic surface layer on implant titanium alloy also stimulated its bioactivity. The observed higher number of osteoblasts and enzyme level are conducive for the formation of hydroxyapatite crystals (ALP), which stimulate in‐growth of bone tissue and accelerate healing process. Copyright © 2008 John Wiley & Sons, Ltd.
Combined XPS, SIMS, and AFM analyses of silicon nanocrystals embedded in silicon oxide layers
Authors: Vanzetti L. , Barozzi M. , Iacob E. , Bersani M. , Pucker G. , Bellutti P. 
Published: March 2008

AbstractSilicon nanocrystals (Si‐ncs) embedded in a dielectric matrix (e.g. Si3N4, SiO2) attract significant interest for their use in silicon‐based devices such as memories, light amplifiers, and light emitting diodes. Si‐ncs in an SiO2 matrix are generally obtained through thermal annealing of silicon‐rich oxide (SRO) at elevated temperatures (900–1200 °C). In this study, we have investigated the composition of annealed SRO layers close to the interfaces with Si3N4, or c‐Si with XPS, SIMS, and atomic force microscopy (AFM). The analyses indicate an approximately 2‐nm thick Si‐depleted region close to both the Si3N4 and c‐Si interface formed after annealing at 1050 °C. The formation of this Si‐depleted layer is of importance for both electrical transport and charge storage in annealed SRO. Copyright © 2008 John Wiley & Sons, Ltd.
Zero inflation in ordinal data: Incorporating susceptibility to response through the use of a mixture model
Authors: Kelley Mary E. , Anderson Stewart J. 
Published: March 2008

AbstractThe aim of this paper is to produce a methodology that will allow users of ordinal scale data to more accurately model the distribution of ordinal outcomes in which some subjects are susceptible to exhibiting the response and some are not (i.e. the dependent variable exhibits zero inflation). This situation occurs with ordinal scales in which there is an anchor that represents the absence of the symptom or activity, such as ‘none’, ‘never’ or ‘normal,’ and is particularly common when measuring abnormal behavior, symptoms, and side effects. Due to the unusually large number of zeros, traditional statistical tests of association can be non‐informative. We propose a mixture model for ordinal data with a built‐in probability of non‐response, which allows modeling of the range (e.g. severity) of the scale, while simultaneously modeling the presence/absence of the symptom. Simulations show that the model is well behaved and a likelihood ratio test can be used to choose between the zero‐inflated and the traditional proportional odds model. The model, however, does have minor restrictions on the nature of the covariates that must be satisfied in order for the model to be identifiable. The method is particularly relevant for public health research such as large epidemiological surveys where more careful documentation of the reasons for response may be difficult. Copyright © 2008 John Wiley & Sons, Ltd.
Organizational antecedents of second‐order competences
Authors: Danneels Erwin 
Published: March 2008

AbstractAccording to dynamic capability theory, some firms are better able than others at altering their resource base by adding, reconfiguring, and deleting resources or competences. This study focuses on the first form of dynamic capability: the competence to build new competences. Two such second‐order competences are studied: the ability to explore new markets and the ability to explore new technologies—referred to as marketing and R&D second‐order competences, respectively. Using two wave panel data on a sample of U.S. public manufacturing firms, five organizational antecedents of these second‐order competences are examined: willingness to cannibalize, constructive conflict, tolerance for failure, environmental scanning, and resource slack. Willingness to cannibalize, constructive conflict, scanning, and slack have contemporaneous effects, while scanning also has a lagged effect and slack has a U‐shaped lagged effect on marketing and R&D second‐order competences. Copyright © 2008 John Wiley & Sons, Ltd.
Microanalysis of Gothic mural paintings (15th century) in Slovenia: Investigation of the technique used by the Masters
Authors: Kriznar A. , Ruiz‐Conde A. , Sánchez‐Soto P. J. 
Published: March 2008

AbstractThe present article focuses on an interdisciplinary research on cultural heritage concerning the microanalysis of Gothic mural paintings made during the 15th century in Slovenia. The samples were chosen from the churches of Crngrob (1453), Mirna (1463–1465), Mevkuž (1465) and Mače (1467), attributed to two of the most important Gothic painters of that period of time: Master Bolfgang and Master of Mače. The chemical and phase composition of all the mortars, number of their layers and selection of the pigments were of interest. For this purpose, fragments of mural paintings were studied with several instrumental techniques: optical microscopy (OM), SEM‐EDX, x‐ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). In early artworks, the mortar was made using a mixture of lime and more or less clean sand. Later, crushed lime‐rock or marble instead of sand was added to lime. The pigments identified by EDX microanalysis of cross sections previously studied by OM, are of earth or mineral origin. Therefore, they are durable in fresco and lime techniques: lime white, yellow and red natural or burned ochres, green earth and azurite. The results confirmed the high technical quality of both painters and the relationships between the teacher and the disciple. Master Bolfgang and Master of Mače combine three basic techniques of mural painting: fresco, secco and lime techniques. This kind of investigation and methodology allow us to know better the Central European Art and the Slovenian Art in the Adriatic zone, as well as the general map of European Art in the 14–15th centuries. Copyright © 2008 John Wiley & Sons, Ltd.
Syntheses, Structures and Spectroscopic Characterization of Extended Waugh‐Type Polyoxometalates with Metal Ions as Linkers
Authors: Cheng Haiyan , Ren Yuanhang , Liu Shuxia , Xie Linhua 
Published: March 2008

AbstractTwo extended Waugh‐type polyoxometalates compounds, (NH4)4Na2[MnMo9O32]·6H2O (1) and (NH4)2Na2[{Cu(H2O)4}(MnMo9O32)]·5H2O (2) have been synthesized and characterized. Both of the left‐handed and right‐handed [MnMo9O32]6− polyanions enantiomers can be observed in compounds 1 and 2. In compound 1, the homochiral [MnMo9O32]6− polyanions enantiomers are linked by sodium ions to form two kinds of alternately arranged 2D polymeric sheets, which are further stacked into a 3D framework. In compound 2, the homochiral [MnMo9O32]6− polyanions enantiomers are linked by [(H2O)2Cu(μ2‐H2O)2Na(H2O)2]3+ bimetal aggregates to form two kinds of alternately arranged zigzag chains, which are further weaved into a 2D polymeric sheet by sodium ions. In addition, the influence of the synthesis conditions has also been studied.
Coordination Mode of the Nickel(II) Cation with N‐Diisopropoxyphosphinyl‐p‐bromothiobenzamide
Authors: Safin Damir A. , Sokolov Felix D. , Baranov Sergey V. , Szyrwiel Łukasz , Babashkina Maria G. , Shakirova Elmira R. , Hahn F. Ekkehardt , Kozlowski Henryk 
Published: March 2008

AbstractReaction of the potassium salt of N‐diisopropoxyphosphinyl‐p‐bromothiobenzamide p‐BrC6H4C(S)NHP(O)(OiPr)2 (HL) with Ni(NO3)2 in aqueous EtOH leads to complex of formula [Ni(HL‐O)2(L‐O,S)2] (1). The structure of 1 was investigated by single crystal X‐ray diffraction analysis, IR, 1H and 31P{1H} NMR spectroscopy, MALDI and microanalysis. The nickel(II) ion in 1 has a tetragonal‐bipyramidal environment, (Oax)2(Oeq)2(Seq)2, with two neutral ligand molecules coordinated in axial positions through the oxygen atoms of the P=O groups. The equatorial plane of bipyramide is formed by two anionic ligands involving 1,5‐O,S‐coordination mode. The chelating ligands are bound in trans configuration.
Synthesis and Spectroscopic Characterization of the Benzaldehyde Schiff Base of S‐Allyldithiocarbazate and its Copper(II) Complex and the X‐ray Crystal Structure of Bis[S‐allyl‐β‐N‐benzylidene)dithiocarbazato]Copper(II)
Authors: Yazdanbakhsh M. , Heravi M. M. , Takjoo R. , Frank W. 
Published: March 2008

AbstractS‐allyl‐β‐N‐(benzylidene)dithiocarbazate (sabdtc, 1), prepared from hydrazine hydrate, carbon disulfide, allyl bromide and benzaldehyde, reacts with copper(II) nitrate in ethanol solution to form the complex Cu(sabdtc)2 (2). 1 function as a single negatively charged bidentate chelating ligand and coordinates via the azomethine nitrogen atom and thioenolate sulfur atom to the metal ion. 1 and 2 were characterized by elemental analyses, 1H NMR, 13C NMR, UV/Vis, IR, and mass spectra. Spectroscopic evidences suggest a four‐coordinate distorted square planar structure for 2. The molecular and crystal structure of 2 was determined by single crystal X‐ray analysis. Crystallographic data for 2 at 291(2) K: space group C2/c, a = 20.340(3), b = 15.503(3), c = 7.659(1) Å, β = 95.96(2)°, Z = 4, R1 = 0.044 and wR2 = 0.0689.