bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modelling the growth of nitrides in ammonia‐rich environment
Authors: Krukowski S. , Kempisty P. , Strąk P. , Nowak G. , Czernecki R. , Leszczynski M. , Suski T. , Bockowski M. , Grzegory I. 
Published: November 2007

AbstractSurface properties and the principal processes at the growth of gallium nitride on GaN (0001) face in ammonia‐based are modeled using DFT (density functional theory – SIESTA code) ab initio calculations and 2‐d diffusion analysis. The GaN growth methods are: ammonia‐source MBE, MOVPE, and also HVPE. The adiabatic trajectories, calculated for hydrogen‐rich and hydrogen‐free state of the GaN(0001) surface, include the adsorption of NH3, GaCl and HCl molecules and the desorption of Ga atoms. The adsorption of ammonia and GaCl has no energy barrier. Thus, in contrast to the results concerning Plasma‐Assisted Molecular Beam Epitaxy (PA MBE), proving that the GaN(0001) surface remains in metal‐rich state, these results indicate that, in the ammonia‐rich environment, typical for HVPE and MOVP growth, the GaN(0001) surface remains in the nitrogen‐rich state. In the case of HCl adsorption, the energy barrier depends on the surface coverage, and could reach 2.0 eV. The direct desorption of single Ga atom has the energy barrier, close to 7 eV. This indicates that Ga surface diffusion (growth controlling process) length is very large, leading to strong interaction of the step kinetics and the diffusion on the terraces. This interaction leads to double–step intertwined structures both in the case of dislocation‐mediated spiral growth and in the step flow growth mode. These morphologies, proposed by the geometric arguments, are observed in the atomic force microscopy (AFM) scans of the GaN(0001) surface. Additionally we have compared the interaction energy of two hydrogen atoms obtained in the DFT SIESTA and the high precision Gaussian in coupled cluster singles, double and perturbation triples CCSD(T) approximation. Both approaches yielded virtually identical interaction energy confirming the validity of DFT analysis of ammonia‐rich growth of GaN. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
TEM investigations of GaN layers grown on silicon and sintered GaN nano‐ceramic substrates
Authors: Borysiuk J. , Caban P. , Strupiński W. , Gierlotka S. , Stelmakh S. , Janik J. F. 
Published: November 2007

AbstractGaN nano‐ceramics were analyzed using transmission electron microscopy (TEM), showing that these ceramics are characterized by highly disoriented grains of the linear size of 100–150 nm. These GaN ceramics were used as substrates for GaN epitaxy in standard MOVPE conditions. For the comparison, MOVPE GaN layers on silicon substrates were grown using similar conditions. It is shown that MOVPE growth of GaN layers is highly anisotropic for both cases. However, the disorientation of the highly mismatched GaN layer on silicon is different from that characterizing GaN layer deposited on the ceramic substrate. In the latter case the disorientation is much higher, and three dimensional in nature, causing creation of polycrystalline structure having large number of the dislocations. In the case of the GaN layer grown on the silicon substrate the principal disorientation is due to rotation around c‐axis, causing creation of mosaic structure of edge dislocations. Additionally, it is shown that the typical grain size in AlN nucleation layer on Si is smaller, of order of 20 nm. These two factors contribute to pronounced differences in later stage of the growth of GaN layer on the ceramic. Due to high growth anisotropy an appropriately thick GaN layer can, eventually, develop flat surfaces suitable for construction of optoelectronic and electronic structures. As shown by the TEM data, this can be achieved only at the cost of creation of the relatively large density of dislocations and stacking faults. The latter defects were not observed for the GaN growth on Si substrates. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thick GaN layers on sapphire with various buffer layers
Authors: Korbutowicz R. , Dumiszewska E. , Prażmowska J. 
Published: November 2007

AbstractThick GaN layers deposited in HVPE system on composite substrates made on sapphire substrates in Metalorganic Vapour Phase Epitaxy (MOVPE) system have been investigated. The following substrates were used: (00.1) sapphire substrates with AlN, AlN/GaN and GaN thin layers. The crystallographic structure and the quality of the epitaxial thick GaN layers were determined. Comparison of the three types of thick layers was performed. Significant differences were observed. It was found that thick GaN deposited on the simplest MOVPE‐GaN/sapphire composite substrate has comparable structure's properties as the other, more complicated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of post treatment on the photorefractive properties of Ru‐doped lithium niobate
Authors: Chiang Chang‐Hung , Chen Jyh‐Chen , Chang Jenq‐Yang , Lu Chung‐Wei 
Published: November 2007

AbstractThe effect of post treatment on the photorefractive properties of Ru‐doped lithium niobate was studied. The absorption spectra examination of Ru‐doped LiNbO3 crystals with different post treatments showed that the absorption coefficient at 530 nm increased after the reduced treatment was employed and the absorption edge of the reduced crystal shifted towards the infrared band. On the contrary, the trend reversed after the oxidized treatment was employed. In addition, the photorefractive properties were investigated with the two‐beam coupling method conducted via a 532 nm solid state laser. It was found that the oxidized Ru:LiNbO3 had smaller exponential gain coefficient and diffraction efficiency because the charges in the shallow level were exchanged to the deep level. On the other hand, the reduced Ru:LiNbO3 crystals had larger exponential gain coefficient and diffraction efficiency due to the increase of the Ru3+ which existed in the shallow level. The response times of both oxidized and reduced Ru:LiNbO3 were longer than those of the as‐grown ones. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Luminescence characteristics of undoped and Eu‐doped GdCa4O(BO3)3 single crystals and nanopowders
Authors: Solarz P. , Nikl M. , Kłos A. , Lisiecki R. , Ryba‐Romanowski W. , Rzepka A. , Ganschow S. , Pajączkowska A. 
Published: November 2007

AbstractSingle crystals of GdCa4O(BO3)3 (GdCOB) pure and doped with Eu concentration of 1 and 4 at% were grown by the Czochralski and micropulling‐down methods. The distribution of Eu ions in GdCOB crystals was uniform. The substitutions of Eu3+ in Gd, Ca(1) and Ca(2) cation sites and eventually formation Eu2+ have been investigated. The spectroscopic properties of crystals are compared with the properties of nanopowders obtained by sol‐gel method. Radioluminescence spectra of undoped GdCOB crystal show the characteristic emission of Gd3+ at about 312 nm, whereas this emission dramatically decreases in Eu‐doped crystals upon X‐ray excitation, as well as in Eu‐doped nanopowders excited in vacuum ultraviolet (VUV) region. The VUV excitation in the range 125‐333 nm for Eu‐doped samples leads to strong emission in red coming from the 5D0 multiplet of Eu3+, only. In the photoluminescence decay kinetics of 312 nm emissions substantial shortening and departure for single exponential decay in Eu‐doped samples is clearly observed. Higher Eu doping results in further acceleration of the decay. In undoped GdCOB crystal, the lifetime of the Gd3+ 6P7/2 multiplet is 2.79 ms. The Eu3+ 5D0 decay kinetics monitored at 613 nm are rather constant. Numerical fitting of fully exponential curves, reveals lifetimes 2.7 ms for nanopowder and 2.5 ms for single crystal. The results suggest that this material may be used as a red phosphor in plasma display panels in nanopowder form because of strong excitation band of Eu3+ luminescence in the 160‐200 nm regions. Contrary to nanopowder sample, such an excitation band, attributed to the Gd3+–O2– charge transfer was not observed in crystal obtained by the micropulling‐down method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and characterization of Nd, Yb – yttrium oxide nanopowders obtained by sol‐gel method
Authors: Rzepka A. , Ryba‐Romanowski W. , Diduszko R. , Lipińska L. , Pajączkowska A. 
Published: November 2007

AbstractNanopowders of Y2O3 pure, doped and codoped by Nd3+, Yb3+ were obtained by sol‐gel method. Solution with ethylene glycol was choosed as the proper solution where crystallites of powder with Nd and Yb dopants had the same size. Finally the one‐phased compounds of Y2O3 doped 0.5 at% Nd and 1, 2 or 4 at% Yb were obtained. Grain growth and their morphology were investigated in various temperature and time of heating. The changes of crystallite sizes and lattice constants in relation to the heating time and temperature for the composition Y2O3 doped 0.5 at% Nd and 2 at% Yb are presented. Y2O3 containing 0,5 at% of Nd exhibits intense luminescence bands centered at 920 nm, 1100 nm and 1360 nm whereas a single band at about 1020 nm appears in samples co‐doped with neodymium and ytterbium. Luminescence spectra recorded did not depend on the sample preparation procedure and size of grains. OH impurity affects critically the relaxation dynamics of luminescent ion in nanopowders. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Crystal growth and scintillating properties of (Pr,Si)‐doped YAlO3
Authors: Zhuravleva M. , Novoselov A. , Mihokova E. , Mares J. A. , Vedda A. , Nikl M. , Yoshikawa A. 
Published: November 2007

AbstractThis paper deals with Pr‐doped and Pr, Si‐codoped YAlO3 single crystal growth by the micro‐pulling‐down method and investigation of their spectroscopic and scintillating properties. The Pr3+ 5d ‐4f radioluminescence intensity is more than 10 times higher than that of Bi4Ge3O12 standard sample, but the Si‐codoping decreases it. Absorption spectra of as‐grown and air‐annealed Si,Pr‐codoped YAlO3 samples show along with an onset of 4f ‐5d transition round 230 nm the induced absorption band at 400 nm which possibly related to a hole center absorption (Pr4+ or O‐). Thermoluminescence measurements above the room temperature were performed in order to monitor deep electron traps. Strong concentration dependence of thermoluminescence was observed for Pr:YAlO3 glow curves. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and characterization of pure and Co2+‐doped Li2B4O7 single crystals
Authors: Piwowarska D. , Kaczmarek S. , Berkowski M. 
Published: November 2007

AbstractPure and Co‐doped Li2B4O7 (LBO) single crystals were grown by the Czochralski method. Starting concentrations of Co2O3 in the melt were: 0.5, 0.85 and 1 mol% relative to Li2CO3. Technological factors affecting the quality of both crystals were discussed. Optical absorption and EPR spectra were analyzed to define the oxidation states and lattice sites of cobalt ions. It was shown that Co2+ ions enter LBO crystal at octahedral Li+ site positions. Low‐temperature EPR measurements revealed that two types of Co2+ complexes can be distinguished in the Li2B4O7:Co crystals. Additional absorption calculated for γ‐irradiated crystals showed Vk type defects suggesting the creation of cation vacancies during growth. The concentration of the defects decreases with an increase of intentional Co concentration. Introduction of cobalt ions to LBO crystal is limited probably by the formation of cobalt ion pairs or by the entrance of cobalt as Co+. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoelectric and photothermal investigations of Zn1‐x‐yBexMnySe solid solutions
Authors: Firszt F. , Strzałkowski K. , Zakrzewski A. J. , Łęgowski S. , Męczyńska H. , Marasek A. 
Published: November 2007

AbstractZn1‐x‐yBexMnySe solid solutions were grown from the melt by the high pressure Bridgman method. Optical, luminescence, photoelectric and photothermal properties of this material were investigated. Interpretation of the piezoelectrically detected photoacoustic spectra was performed using Jackson and Amer theory. From the spectral dependence of the amplitude and phase of photoacoustic signal as well as from photoluminescence spectra the variation of energy gap with composition was determined. The values of thermal diffusivity were derived from the dependence of photoacoustic signal on modulation frequency of the laser radiation illuminating the sample. The photoluminescence‐excitation spectra and photoconductivity spectra were measured. The origin of luminescence in Zn1‐x‐yBexMnySe was discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Observation of individual dislocations in 6H and 4H SiC by means of back‐reflection methods of X‐ray diffraction topography
Authors: Wierzchowski W. , Wieteska K. , Balcer T. , Malinowska A. , Graeff W. , Hofman W. 
Published: November 2007

AbstractSiC crystals of high structural perfection were investigated with several methods of X‐ray diffraction topography in Bragg‐case geometry. The methods included section and projection synchrotron white beam topography and monochromatic beam topography. The investigated 6H and 4H samples contained in large regions dislocations of density not exceeding 103 cm‐2. Most of them cannot be interpreted as hollow core dislocations (micro‐ or nano‐pipes). The concentration of the latter was lower than 102 cm‐2. The present investigation confirmed the possibility of revealing dislocations with all used methods. The quality of presently obtained Bragg‐case multi‐crystal and section images of dislocation enabled analysis based on comparison with numerically simulated images. The analysis confirmed the domination of screw‐type dislocations in the investigated crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Elastic properties of zinc tris(thiourea) sulphate in a wide temperature range studied by Brillouin spectroscopy
Authors: Mielcarek S. , Trzaskowska A. , Mroz B. , Komorowski K. 
Published: November 2007

AbstractThe elastic properties of the zinc tris (thiourea) sulphate crystal were studied by Brillouin spectroscopy in the range 80 – 300 K. The measurements were made on single crystals obtained by the isothermal method. The temperature dependences of the Brillouin shift were determined for the crystal in the principal directions and in a few mixed directions on a tandem type spectrometer. The results revealed anomalies in the bulk wave propagation rate and in a few elastic constants at about 138 K. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Elastic properties of KGd(WO4)2:Ho3+ single crystals studied by Brillouin spectroscopy
Authors: Kasprowicz D. , Mielcarek S. , Trzaskowska A. , Majchrowski A. , Michalski E. , Drozdowski M. 
Published: November 2007

AbstractThe analysis some of the acoustic phonons propagating in pure and Ho3+‐doped KGd(WO4)2 single crystals in the GHz frequency range by Brillouin scattering method has been presented. For investigated crystals the velocities of the longitudinal and transverse acoustic phonons [100], [010], [001], [101], [101] and [110] have been determined. Moreover, the value of elastic constants C22, C44 and C66 of pure and Ho3+‐doped KGd(WO4)2 single crystals have been estimated. It was revealed that the presence of the Ho3+‐ions in KGd(WO4)2 crystals, for the used doping concentration 1 at% and 8 at%, does not influence their elastic properties. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of 50 MeV Si ion irradiation on nonlinear optical benzimidazole single crystals
Authors: Kanagasekaran T. , Mythili P. , Srinivasan P. , Vijayan N. , Bhagavannarayana G. , Kulriya P. K. , Kanjilal D. , Gopalakrishnan R. , Ramasamy P. 
Published: November 2007

AbstractThe 50 MeV Si7+ ion irradiation induced modifications on structural, dielectric, optical and mechanical properties of Vertical Bridgman grown benzimidazole (BMZ) crystals were studied. The high resolution X‐ray diffraction studies show the quality of as grown BMZ and irradiated BMZ crystals. The dielectric constant and dielectric loss as a function of frequency and temperature was studied in detail. The ion induced mechanical behaviour of both as grown BMZ and irradiated BMZ crystals has been explained with the indentation effects using Vickers microhardness tester. UV‐VIS. studies reveal the decrease in bandgap values and defects on irradiation. The above results are discussed in detail. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Risk factors in V‐shaped risk associations with all‐cause mortality in type 2 diabetes—The Hong Kong Diabetes Registry
Authors: So Wing Yee , Yang Xilin , Ma Ronald C. W. , Kong Alice P. S. , Lam Christopher W. K. , Ho Chung Shun , Cockram Clive S. , Ko Gary T. C. , Chow Chun‐Chung , Wong Vivian , Tong Peter C. Y. , Chan Juliana C. N. 
Published: November 2007

AbstractBackgroundBody mass index (BMI) is associated with death in a V‐shaped manner in general populations but it is unknown whether BMI or other risk factors also exhibit V‐shaped relationships with death in type 2 diabetic patients.MethodsA prospective cohort of 7534 Chinese, type 2 diabetic patients enrolled since 1995 were censored on 30 July 2005. Spline Cox regression analysis with a stepwise algorithm (p < 0.05) was used to select predictors. Hazard ratio (HR) curves were used to explore the relationships, which were confirmed by standard Cox models.Results763 patients died during the 5.5 years of follow‐up. BMI, high‐density lipoprotein cholesterol (HDL‐C) and white blood cell (WBC) count were related to all‐cause mortality in a V‐shaped manner. The nadirs of the risk curves were at 26 kg/m2 for BMI, 1.15 mmol/L for HDL‐C and 6.25 × 109 counts/L for WBC. The multivariate hazard ratio of BMI away from 26.0 kg/m2 was 1.08; HDL‐C, 1.06 per mmol/L for values less than the nadir and 6.97 per mmol/L for greater than the nadir; and WBC, 1.16 per 109 count/L for less than 6.25 × 109 and 1.47 for greater than the nadir. Respiratory and neoplastic deaths were the major contributors to the increased death in patients with low or high BMI. Neoplastic death was the major contributor to the increased death in those with low WBC. Genitourinary death was the major contributor to the increased death in those with low and high HDL‐C.ConclusionBMI, HDL‐C and WBC are associated with death in a V‐shaped manner in type 2 diabetic patients. Copyright © 2007 John Wiley & Sons, Ltd.
Regulation and function of Dbx genes in the zebrafish spinal cord
Authors: Gribble Suzanna L. , Nikolaus O. Brant , Dorsky Richard I. 
Published: November 2007

AbstractDbx homeodomain proteins are important for spinal cord dorsal/ventral patterning and the production of multiple spinal cord cell types. We have examined the regulation and function of Dbx genes in the zebrafish. We report that Hedgehog signaling is not required for the induction or maintenance of these genes; in the absence of Hedgehog signaling, dbx1a/1b/2 are expanded ventrally with concomitant increases in postmitotic neurons that differentiate from this domain. Also, we find that retinoic acid signaling is not required for the induction of Dbx expression. Furthermore, we are the first to report that knockdown of Dbx1 function causes a dorsal expansion of nkx6.2, which is thought to be the cross‐repressive partner of Dbx1 in mouse. Our data confirm that the dbx1a/1b/2 domain in zebrafish spinal cord development behaves similarly to amniotes, while extending knowledge of Dbx1 function in spinal cord patterning. Developmental Dynamics 236:3472–3483, 2007. © 2007 Wiley‐Liss, Inc.
The developing embryonic cardiac outflow tract is highly sensitive to oxidant stress
Authors: Fisher Steven A. 
Published: November 2007

AbstractThis study tested the hypothesis that the remodeling of the cardiac outflow tract (OFT) may represent a developmental window of vulnerability to reactive oxygen species (ROS). Chick embryos were exposed in ovo or ex ovo to increasing concentrations of the stable oxidant hydrogen peroxide (H2O2). As assessed by trypan blue staining, H2O2 induced cell injury in the stage 25–30 OFT at concentrations as low as 1 nM. Higher concentrations were required to induce cell injury in the ventricular and atrial myocardium. Using DCFDA as an indicator of oxidant stress, H2O2 also induced a greater fluorescent signal in the OFT myocardium. H2O2 at these low concentrations also induced Caspase activity, indicative of activation of the pathway of PCD. Interestingly, the induction of Caspase‐3 activity was predominately in the OFT cushion mesenchymal cells. Thus, the developing OFT is particularly sensitive to ROS‐mediated injury, suggesting that ROS could play a role in the development of congenital defects of the cardiac OFT. Developmental Dynamics 236:3496–3502, 2007. © 2007 Wiley‐Liss, Inc.
p38α MAP kinase‐deficient mouse embryonic stem cells can differentiate to endothelial cells, smooth muscle cells, and neurons
Authors: Guo Yan‐Lin , Ye Jianming , Huang Faqing 
Published: November 2007

Abstractp38 MAP kinase α (p38α) regulates various cellular processes in adult cells, but little is known about its function in stem cells. We investigated the potential of wild type and p38α deficient mouse embryonic stem cells (ESCs) to differentiate into endothelial cells (ECs), smooth muscle cells (SMCs), and neurons. Our differentiation methods allowed simultaneous development of all these cell types. ECs formed monolayers similar to mature ECs and could assemble into vessel‐like structures. SMCs had well‐organized actin filaments with morphology similar to adult SMCs. Neurons exhibited well‐developed cell bodies and elongated axons. Deletion of the p38α gene did not significantly compromise ESC differentiation since p38α−/− cells could express cell‐specific markers and displayed similar overall morphology to the cells differentiated from p38α+/+ ESCs. Although p38α regulates various cellular activities of adult SMCs, ECs, and neurons, our data demonstrate that p38α is not essential for ESC differentiation to these cell types. Developmental Dynamics 236:3383–3392, 2007. © 2007 Wiley‐Liss, Inc.
Non‐linear seismic analysis and vulnerability evaluation of a masonry building by means of the SAP2000 V.10 code
Authors: Pasticier Laurent , Amadio Claudio , Fragiacomo Massimo 
Published: November 2007

AbstractThe aim of the paper is to explore the possibilities offered by SAP2000® v.10, a software package with user‐friendly interface widely used by practising engineers, for seismic analyses of masonry buildings. The reliability of the code was first investigated by carrying out static push‐over (SPO) analyses of two walls, already analysed by other researchers using advanced programs. The equivalent frame modelling was employed in all analyses carried out. The code was then used to investigate the seismic performance of an existing two‐storey building typical of the north‐east of Italy, with the walls being made of roughly squared stones. An SPO analysis was performed first on the most significant wall, followed by a number of time‐history analyses aimed to evaluate the dynamic push‐over curves. Finally, the seismic fragility curves were derived, considering the seismic input as a random variable. Copyright © 2007 John Wiley & Sons, Ltd.