bluuebunny/crossref_metadata_2025 huggingface dataset:
Diagnostic accuracy of subcutaneous abdominal fat tissue aspiration for detecting systemic amyloidosis and its utility in clinical practice
Authors: Gameren Ingrid I. Van , Hazenberg Bouke P. C. , Bijzet Johan , Rijswijk Martin H. Van
Published: May 2006

Objective

Aspiration of subcutaneous abdominal fat is a simple and fast method for detecting systemic amyloidosis; however, the sensitivity of this approach remains undetermined. The aim of this study was to assess the accuracy of fat tissue aspiration for detecting systemic amyloidosis and the utility of this method in clinical practice.

Methods

All consecutive patients with established and suspected systemic amyloidosis who attended our tertiary referral hospital between 1994 and 2004 underwent aspiration of subcutaneous abdominal fat. Congo red–stained tissue was assessed quickly in a single smear in a routine manner by a single observer, and was also assessed thoroughly in 3 smears by 2 independent observers.

Results

One hundred twenty patients with established systemic amyloidosis were studied (38 with AA amyloidosis, 70 with AL amyloidosis, and 12 with ATTR amyloidosis). Routine (quick) assessment was associated with a sensitivity of 80% (95% confidence interval [95% CI] 72–87%). Sensitivity increased to 93% (95% CI 87–97%) when 3 smears were thoroughly examined. The specificity of fat aspiration in 45 control subjects was 100% (95% CI 92–100%). One hundred sixty‐two patients for whom there was a clinical suspicion of systemic amyloidosis were screened for amyloidosis by fat tissue aspiration and biopsy of at least 1 other tissue. In 69 (43%) of these 162 patients, a diagnosis of amyloidosis was established, and in 66 (96%) of these patients, the results of fat tissue aspiration were positive. The clinical utility of fat tissue aspiration was greater than that of biopsy of the rectum.

Conclusion

Subcutaneous abdominal fat aspiration is the preferred method for detecting systemic amyloidosis, with sensitivity of 80% associated with use of a routine approach. The use of a thorough assessment (3 fat smears, 2 observers) increased sensitivity to >90%. If the results of fat tissue aspiration are negative, the additional value of a subsequent biopsy of the rectum is negligible.
A simple model‐based control for Pichia pastoris allows a more efficient heterologous protein production bioprocess
Authors: Cos Oriol , Ramon Ramon , Montesinos José Luis , Valero Francisco
Published: May 2006

A predictive control algorithm coupled with a PI feedback controller has been satisfactorily implemented in the heterologous Rhizopus oryzae lipase production by Pichia pastoris methanol utilization slow (Muts) phenotype. This control algorithm has allowed the study of the effect of methanol concentration, ranging from 0.5 to 1.75 g/L, on heterologous protein production. The maximal lipolytic activity (490 UA/mL), specific yield (11,236 UA/gbiomass), productivity (4,901 UA/L · h), and specific productivity (112 UA/gbiomassh were reached for a methanol concentration of 1 g/L. These parameters are almost double than those obtained with a manual control at a similar methanol set‐point. The study of the specific growth, consumption, and production rates showed different patterns for these rates depending on the methanol concentration set‐point. Results obtained have shown the need of implementing a robust control scheme when reproducible quality and productivity are sought. It has been demonstrated that the model‐based control proposed here is a very efficient, robust, and easy‐to‐implement strategy from an industrial application point of view. © 2006 Wiley Periodicals, Inc.
Efficient Sequence‐Specific Purification of Listeria innocua mRNA Species by Triplex Affinity Capture with Parallel Tail‐Clamps
Authors: Nadal Anna , Coll Anna , Aviñó Anna , Esteve Teresa , Eritja Ramon , Pla Maria
Published: May 2006

Parallel clamps can interact in a sequence‐specific manner with homopyrimidine DNA and RNA oligonucleotides to form triplexes. For longer nucleic acids, we have previously demonstrated the inhibitory effect of DNA‐target secondary structures on triplex formation. We further designed a modification of these molecules—that is, tail‐clamps formed by addition of a tail sequence to the parallel clamp—and proved efficient binding of the molecules with structured single‐stranded DNA targets. Here we explore the possible application of the tail‐clamp strategy for triplex formation with RNA targets, which are typically found as strongly folded single‐stranded molecules. Efficient and specific binding of a tail‐clamp designed to form a parallel triplex with Listeria innocua iap mRNA sequences has been verified by UV melting curves and triplex affinity capture techniques. Furthermore, we show for the first time the formation of stable complexes of mRNA with tail‐clamps not only under acidic but also under neutral and slightly basic pH conditions. These results signify a further step towards the possible applications of triplexes with mRNA molecules; research, analytical, and therapeutic uses can be envisaged. As an example, our tail‐clamp‐based triplex affinity capture assay allowed the specific capture and recovery of iap mRNA molecules from an L. innocua total RNA solution with 45 % yield.
Bis‐ortho‐Substitution by Methyl Groups Dramatically Increases the Racemization Barrier of Tröger Bases
Authors: Lenev Denis A. , Lyssenko Konstantin A. , Golovanov Denis G. , Buss Volker , Kostyanovsky Remir G.
Published: May 2006

We have shown through racemization kinetics studies that the enantiomerization barriers of the bis‐ortho‐methyl substituted Tröger bases 2 and 3 in acidic media are raised by 30 kJ mol−1 relative to the parent compound 1, that is 130.4(4) and 131.6(4) kJ mol−1, respectively (105 °C, pH 1, ethylene glycol). The enantiomerization barrier of para‐methoxy‐para‐nitro substituted Tröger base 4 was determined by dynamic capillary electrophoresis to 96.3(2) kJ mol−1 (25 °C, pH 2.2, H2O), which is lower by 5 kJ mol−1 relative to 1. The influence of deutero‐substitution on the racemization rates was also studied. The influence of steric and electronic factors on the enantiomerization barrier was investigated by quantum‐mechanical (DFT) calculations. It is shown that enantiomerization takes place in two steps: ring‐opening and further interconversion of the monocyclic intermediate. For the interconversion to occur a transition state has to be passed which is sensitive to steric effects. Ortho‐substitution by methyl groups significantly increases the energy of this state. Thus, compounds 2 and 3 are the simplest Tröger bases which are configurationally stable in acidic media.
A Highly Practical RCM Approach towards a Molecular Building Kit of Spirocyclic Reverse Turn Mimics
Authors: Bittermann Holger , Böckler Frank , Einsiedel Jürgen , Gmeiner Peter
Published: May 2006

The development of privileged molecular scaffolds efficiently mimicking reverse turn motifs and thus increasing both binding and selectivity and enabling the elucidation of the bioactive conformation of a natural peptide has attracted remarkable interest. The frequent occurrence of proline in various turn patterns initiated the design of proline‐based reverse turn mimetics. As a structural hybridization of a highly potent type VI β‐turn inducer 1 with saturated spirocyclic lactams 3 efficiently mimicking type II β turns, we developed a versatile synthetic route towards unsaturated spirocyclic lactams of type 2, when Seebach's self‐reproduction of chirality methodology was combined with a peptide coupling reaction and Grubbs' ring‐closing metathesis. By this means, a variety of model peptides with six‐ up to nine‐membered lactam rings were accessible following a uniform pathway. Introduction of suitably protected templates into solid‐phase peptide synthesis gave rise to unsaturated spirocyclic analogues of the naturally occurring neuropeptide neurotensin. Spectroscopic investigations as well as DFT calculations on a high level of theory revealed a remarkable dependence of the reverse‐turn inducing potency on the ring size. While the secondary structure of the unsaturated spirocyclic ε‐lactam 12 closely agrees with the reference γ‐lactam 3 a, the unsaturated δ‐lactam 11 serves as an extraordinarily potent β‐turn inducer which is even superior to β‐lactams of type 3 b. The eight‐membered unsaturated spirocyclic lactam 13 adopts a conformation almost ideally matching the prerequisites for a canonical type II β turn with the highest stability of the whole series. In contrast, the nine‐membered spirolactam 14 represents a scaffold with a high conformational flexibility.
Internal Noise Coherent Resonance for Mesoscopic Chemical Oscillations: A Fundamental Study
Authors: Hou Zhonghuai , Xiao Tie Jun , Xin Houwen
Published: May 2006

The effect of internal noise for a mesoscopic chemical oscillator is studied analytically in a parameter region outside, but close to, the supercritical Hopf bifurcation. By normal form calculation and a stochastic averaging procedure, we obtain stochastic differential equations for the oscillation amplitude r and phase θ that is solvable. Noise‐induced oscillation and internal noise coherent resonance, which has been observed in many numerical experiments, are reproduced well by the theory.
how functions in leg development during Drosophila metamorphosis
Authors: Fortier Tina M. , Chatterjee Runa , Klinedinst Susan , Baehrecke Eric H. , Woodard Craig T.
Published: May 2006

The Drosophila how gene encodes a KH RNA binding protein with strong similarity to GLD‐1 from nematodes and QK1 from mice. Here, we investigate the function of how during metamorphosis. We show that how RNA and protein are present in a variety of tissues, and phenotypic analyses of how mutants reveal multiple lethal phases and defects during metamorphosis. In addition to previously reported abnormalities in muscle and wing development, how mutants exhibit defects in leg development. how mutant leg imaginal discs undergo cell shape changes associated with elongation, but are oriented improperly, do not evert normally, and often remain incased in peripodial epithelium longer than normal. Consequently, how mutants exhibit short, crooked legs. Our findings suggest that how functions in interactions between imaginal epithelium, peripodial epithelium, and larval epidermal cells during imaginal disc eversion. Developmental Dynamics 235:2248–2259, 2006. © 2006 Wiley‐Liss, Inc.
Coordination and Reduction of HMPA in the Lithiation of (S)‐N‐(α‐Methylbenzyl)allylamine: Crystal Structures of {(S)‐α‐[PhC(H)CH3](CH2CH=CH2)NLi·HMPA}2 and [(Me2N)2POLi]6
Authors: Andrews Philip C. , Minopoulos Magdaline , Roberston Evan G.
Published: May 2006

Monolithiation of the chiral amine (S)‐N‐(α‐methylbenzyl)allylamine, in the presence of the strong Lewis donor solvent hexamethylphoshoramide (HMPA), results in pale yellow crystals which have been crystallographically analysed revealing the structure of the complex to be an asymmetriccisoid dimer {(S)‐α‐[PhC(H)CH3](CH2CH=CH2)NLi·HMPA}2. Variable‐temperature NMR studies show this complex can undergo a thermally induced rearrangement to a 1‐azaallyl complex at ca. 90 °C. Attempted dilithiation of the chiral amine at the N and vinylic C centres with nBuLi and HMPA results in competitive reduction of HMPA to give crystals of the lithium dimethylamidophosphite, structurally authenticated as the hexamer [(Me2N)2POLi]6, in which the Li cation is bonded preferentially to the O centre and not P. The effect is a reduction in the oxidation state of the P centre from (V) to (III), which is supported by ab initio calculations showing the crystal structure to represent the most thermodynamically stable of the possible isomers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Intra–Intermolecular Criss‐cross Cycloaddition of Nonsymmetrical Allenylazines with Fluorinated Enones as an Initial Step in the Synthesis of4H‐Pyrrolo[1,2‐b]pyrazoles
Authors: Man Stanislav , Nečas Marek , Bouillon Jean‐Philippe , Portella Charles , Potáček Milan
Published: May 2006

Nonsymmetrical allenylazines undergo, in boiling xylene, intramolecular cycloaddition by forming an unstable 1,3‐dipole that reacts with an added dipolarophile. In this paper we report the first intra–intermolecular criss‐cross cycloaddition with a fluorinated enone. Although the expected products with three fused heterocycles were not isolated, new bicyclic products were found and characterized. These compounds are formed by a spontaneous transformation involving fluorine atom migration and hydrogen fluoride elimination. A mechanism of the reaction is discussed to explain the formation of these new heterocycles. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
A New Synthetic Route to Polyalkoxypyrimidines Based on the Reaction of Esters and Methyl Thiocyanate
Authors: Herrera Antonio , Martínez‐Alvarez Roberto , Ramiro Pedro , Almy John , Molero Dolores , Sánchez Angel
Published: May 2006

The reaction of aliphatic esters with methyl thiocyanate and triflic anhydride affords substituted 4‐alkoxy‐2,6‐bis(methylthio)pyrimidines with minor amounts of substituted S‐methyl N‐alkanoylthiocarbamates. The structure of the starting ester appears to determine the ratio of final products. Methylthio groups on the pyrimidine ring can be easily converted into methylsulfonyl groups by oxidation. Controlled substitution of one or both methylsulfonyl groups leads to the formation of aminodialkoxy‐ and trialkoxypyrimidines. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
A universal and rapid protocol for protein extraction from recalcitrant plant tissues for proteomic analysis
Authors: Wang Wei , Vignani Rita , Scali Monica , Cresti Mauro
Published: May 2006

A simple and universally applicable protocol for extracting high‐quality proteins from recalcitrant plant tissues is described. We have used the protocol with no modification, for a wide range of leaves and fruits. In all cases, this protocol allows to obtain good electrophoretic separation of proteins. As the protocol is rapid, universal, and compatible with silver staining, it could be used for routine protein extraction from recalcitrant plant tissues for proteomic analysis.
Chiral MEKC‐LIF of amino acids in foods: Analysis of vinegars
Authors: Carlavilla Davinia , Moreno‐Arribas M. Victoria , Fanali Salvatore , Cifuentes Alejandro
Published: May 2006

The formation of D‐amino acids (D‐aa's) in many fermented foods depends, among other factors, on the particular fermentation conditions, the action and autolysis of the microorganisms involved. In this sense, the analysis of chiral amino acids is an interesting analytical strategy for food scientists, since these compounds can be used as bacterial markers and can help, e.g., to detect adulterations, microbiological contaminations, etc. In this work, a fast and sensitive method based on MEKC‐LIF has been developed to analyze and quantitate L‐amino acid (L‐aa) and D‐aa in vinegars. The chiral MEKC‐LIF procedure uses 100 mM sodium tetraborate, 30 mM SDS, and 20 mM β‐CD at pH 9.7 as running buffer, obtaining a good separation of the main vinegar L‐/D‐aa previously derivatized with fluorescein isothiocianate. Namely, L/D proline, alanine, arginine, glutamic, and aspartic acid, plus the nonchiral amino acid γ‐aminobutyric acid are separated in less than 20 min with high efficiency (up to 720 000 plates/m) and good sensitivity (LODs lower than 16.6 nM were achieved). Several D‐aa's were detected and quantified in balsamic, sherry, white wine, and cider vinegars using this MEKC‐LIF procedure, observing interesting differences in their L‐aa and D‐aa profiles and contents.
Intraspecific chemical variability and highlighting of chemotypes of leaf essential oils from Ravensara aromatica Sonnerat, a tree endemic to Madagascar
Authors: Andrianoelisoa Hanitriniaina Sahondra , Menut Chantal , de Chatelperron Philippe Collas , Saracco Jérôme , Ramanoelina Panja , Danthu Pascal
Published: May 2006

Ravensara aromatica Sonnerat is a tree endemic to Madagascar. The essential oil extracted from the leaves is used in aromatherapy. Previous chemical studies have generated some confusion with regard to the chemical composition of this essential oil. In order to eliminate this uncertainty, we undertook a systematic evaluation of the chemical composition of essential oils from leaves of this species. The study focused on 28 individual samples formally identified as R. aromatica. The essential oils were obtained by hydrodistillation and analysed by GC and GC–MS. It was possible to distinguish four groups of trees through principal components analysis and agglomerative hierarchical clustering analysis of the seven chief molecules identified in their essential oils. Two groups were characterized by a prevalence of compounds with an aromatic structure: methyl chavicol (representing more than 90% of the essential oil) in the first group and methyl eugenol (74–82%) in the second group. The predominant compounds of the other two groups proved to be of the monoterpenic type: α‐terpinene (25–28%) and limonene (15–22%) in the third group, while sabinene (25–34%), linalool (7–21%) and terpinen‐4‐ol (6–12%) were the primary constituents of the essential oils in the fourth group. The importance of these results for the commercial production of the essential oils from this species is discussed. Copyright © 2006 John Wiley & Sons, Ltd.
Molecular diagnostic methods in the diagnosis and follow‐up of well‐differentiated thyroid carcinoma
Authors: Rodrigo Juan Pablo , Rinaldo Alessandra , Devaney Kenneth O. , Shaha Ashok R. , Ferlito Alfio
Published: May 2006

Thyroid cancers are the most common endocrine malignancies and are being diagnosed with increased frequency in modern clinical practice. Among other diagnostic modalities, fine‐needle aspiration (FNA) biopsy of clinically suspicious thyroid nodules is becoming increasingly popular. Preliminary investigations have suggested that molecular diagnostic assays using tumor‐specific markers may improve the sensitivity and accuracy of FNA and so may be expected to reduce the frequency of open surgical procedures by identifying those patients with demonstrably benign lesions who do not require definitive surgical excision of their lesions for diagnosis. At the same time, thyroid‐specific mRNA assays (especially thyroglobulin mRNA testing) have been used by investigators in the postoperative follow‐up of patients with thyroid cancer as a potential means of detecting tumor recurrence in the peripheral blood. Although these studies have not all reported unqualified successes—indeed, some problems based on both technical and biologic limitations have been identified—these assays still hold out the possibility that potentially important new advances in the management of patients with well‐differentiated thyroid cancer may be offered by these and other molecular diagnostic methods. © 2006 Wiley Periodicals, Inc. Head Neck, 2006
Cost analysis for the degradation of highly concentrated textile dye wastewater with chemical oxidation H2O2/UV and biological treatment
Authors: El‐Dein Abdalla Mohey , Libra Judy , Wiesmann Udo
Published: May 2006

The efficiency and cost‐effectiveness of H2O2/UV for the complete decolorization and mineralization of wastewater containing high concentrations of the textile dye Reactive Black 5 was examined. Oxidation until decolorization removed 200–300 mg g−1 of the dissolved organic carbon (DOC). The specific energy consumption was dependent on the initial dye concentration: the higher concentration required a lower specific energy input on a weight basis (160 W h g−1 RB5 for 2.1 g L−1 versus 354 W h g−1 RB5 for 0.5 g L−1). Biodegradable compounds were formed, so that DOC removal could be increased by 30% in a following biological stage. However, in order to attain 800 mg g−1 overall mineralization, 500 mg g−1 of the DOC had to be oxidized in the H2O2/UV stage. A cost analysis showed that although the capital costs are much less for a H2O2/UV stage compared to ozonation, the operating costs are almost double those of ozonation. Thus, while H2O2/UV can compete with ozonation when the treatment goal only requires decolorization, ozonation is more cost‐effective in this case when mineralization is desired. Copyright © 2006 Society of Chemical Industry
Transmission electron microscopy and theoretical analysis of AuCu nanoparticles: Atomic distribution and dynamic behavior
Authors: Ascencio J.A. , Liu H.B. , Pal U. , Medina A. , Wang Z.L.
Published: May 2006

Though the application of bimetallic nanoparticles is becoming increasingly important, the local atomistic structure of such alloyed particles, which is critical for tailoring their properties, is not yet very clearly understood. In this work, we present detailed study on the atomistic structure of Au–Cu nanoparticles so as to determine their most stable configurations and the conditions for obtaining clusters of different structural variants. The dynamic behavior of these nanoparticles upon local heating is investigated. AuCu nanoparticles are characterized by high resolution transmission electron microscopy (HRTEM) and energy filtering elemental composition mapping (EFECM), which allowed us to study the internal structure and the elemental distribution in the particles. Quantum mechanical approaches and classic molecular dynamics methods are applied to model the structure and to determine the lowest energy configurations, the corresponding electronic structures, and understand structural transition of clusters upon heating, supported by experimental evidences. Our theoretical results demonstrate only the core/shell bimetallic structure have negative heat of formation, both for decahedra and octahedral, and energetically favoring core/shell structure is with Au covering the core of Cu, whose reverse core/shell structure is not stable and may transform back at a certain temperature. Experimental evidences corroborate these structures and their structural changes upon heating, demonstrating the possibility to manipulate the structure of such bimetallic nanoparticles using extra stimulating energy, which is in accordance with the calculated coherence energy proportions between the different configurations. Microsc. Res. Tech., 2006. © 2006 Wiley‐Liss, Inc.
Hollow Polyaniline Microspheres with Conductive and Fluorescent Function
Authors: Zhang Lijuan , Wan Meixiang , Wei Yen
Published: May 2006

Summary: Salicylic acid‐doped hollow polyaniline and rhodamine B composite spheres (1.9–3.3 µm in average diameter) with a high conductivity (≈10−1 S · cm−1) and a strong fluorescence were synthesized by a template‐free method. The morphologies, electrical and fluorescent properties of the hollow composite microspheres can be adjusted by changing the content of RhB in the composites opening a simple route to preparing multi‐functionalized micro/nanostructures.

SEM and TEM images of PANI‐SA/RhB synthesized under concentration of 1 × 10−3 MRhB.

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SEM and TEM images of PANI‐SA/RhB synthesized under concentration of 1 × 10−3 MRhB.
Protein Sequences as Literature Text
Authors: Vasilevskaya Valentina V. , Gusev Leonid V. , Khokhlov Alexei R.
Published: May 2006

Summary:We have performed analysis of protein sequences treating them as texts written in a “protein” language. We have shown that repeating patterns (words) of various lengths can be identified in these sequences. It was found that the maximum word lengths are different for proteins belonging to different classes; therefore, the corresponding values can be used to characterize the protein type. The suggested technique was first applied to analyze (decompose into words) normal (literature) texts written as a gapless symbolic sequence without spaces and punctuation marks. The tests using fiction, scientific, and popular scientific English texts proved the relative efficiency of the technique.

Maximum word length for various proteins:—fibrillar proteins,—globular proteins,—membrane proteins.

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Maximum word length for various proteins:—fibrillar proteins,—globular proteins,—membrane proteins.
Molecular theory of field‐dependent proton spin‐lattice relaxation in tissue
Authors: Halle Bertil
Published: May 2006

A molecular theory is presented for the field‐dependent spin‐lattice relaxation time of water in tissue. The theory attributes the large relaxation enhancement observed at low frequencies to intermediary protons in labile groups or internal water molecules that act as relaxation sinks for the bulk water protons. Exchange of intermediary protons not only transfers magnetization to bulk water protons, it also drives relaxation by a mechanism of exchange‐mediated orientational randomization (EMOR). An analytical expression for T1 is derived that remains valid outside the motional‐narrowing regime. Cross‐relaxation between intermediary protons and polymer protons plays an important role, whereas spin diffusion among polymer protons can be neglected. For sufficiently slow exchange, the dispersion midpoint is determined by the local dipolar field rather than by molecular motions, which makes the dispersion frequency insensitive to temperature and system composition. The EMOR model differs fundamentally from previous models that identify collective polymer vibrations or hydration water dynamics as the molecular motion responsible for spin relaxation. Unlike previous models, the EMOR model accounts quantitatively for 1H magnetic relaxation dispersion (MRD) profiles from tissue model systems without invoking unrealistic parameter values. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Tb‐doped GaN quantum dots grown by plasma‐assisted molecular beam epitaxy
Authors: Hori Yuji , Andreev Thomas , Jalabert Denis , Tanaka Mitsuhiro , Oda Osamu , Le Si Dang Daniel , Daudin Bruno
Published: May 2006

We report on the growth of Tb‐doped GaN quantum dots deposited by plasma‐assisted molecular beam epitaxy. It was found that Tb ions enhance the desorption process of Ga ad‐atom on the growing surface. This effect becomes more important with increasing growth temperature, and above a certain amount of Tb, the QDs formation is completely inhibited. Transitions from the 5D4 excited state were found intense and temperature stable, while the transitions from 5D3 excited state were only observed at low temperature. A comparative optical study with Tb‐doped AlN thick layer indicates that Tb ions are incorporated in GaN QDs. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
First InGaN/GaN thin film LED using SiCOI engineered substrate
Authors: Dorsaz J. , Faure B. , Carlin J.‐F. , Mosca M. , Gilet P. , Letertre F. , Bressot S. , Larheche H. , Bove P.
Published: May 2006

InGaN / GaN multiple quantum well (MQW) light emitting diodes (LEDs) were deposited by metal‐organic chemical vapor deposition (MOCVD) onto SiCOI engineered substrates. SiCOI substrates are composed of SiC thin film transferred on a silicon substrate through silicon oxide layer by the Smart Cut™ technology. LEDs structures grown on SiCOI were characterized, then transferred onto Si substrates via a metallic bonding process and SiCOI substrates were removed. Three different metallic stacks were used for metallic bonding, including mirror and barrier diffusion. Vertical thin film LED obtained were characterized and showed a 2 to 3 times increase of external quantum efficiency. These results demonstrate the potential of SiCOI engineered substrates as an alternative to laser lift off for thin film LED fabrication. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Wet chemical etching of AlN in KOH solution
Authors: Cimalla I. , Foerster Ch. , Cimalla V. , Lebedev V. , Cengher D. , Ambacher O.
Published: May 2006

In this work we investigated the influence of the AlN material quality on the etching rate in KOH‐based solutions. Thus, AlN layers were deposited by three different methods on sapphire and silicon substrates (i) by metal organic chemical vapor deposition (MOCVD), (ii) by molecular beam epitaxy (MBE), and (iii) by reactive sputter deposition. The etch rate is strongly dependent on crystal quality and etch temperatures. The high quality MBE‐AlN could be etch anisotropic with a preferred lateral component in [11$ \bar 2$0] direction at 60 °C while the polycrystalline AlN layers we etched isotropic and homogenously already at room temperature. The wet chemical etching in KOH solution is mainly an etching along defects and grain boundaries. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of growth temperature on AlGaInN layers: a TEM analysis
Authors: Méndez D. , Albrecht M. , Monroy E. , Jalabert D. , Strunk H. P. , Sanchez A. M. , García R.
Published: May 2006

AlyGaxIn1–x–yN epilayers with diverse Al and In mole fractions have been grown by plasma‐assisted molecular‐beam epitaxy on GaN‐on‐sapphire. Conventional transmission electron microscopy characterization reveals threading dislocations behavior as commonly observed in such heterostructures, arising from the Al2O3/GaN interface. As an outstanding result, electron diffraction technique reveals ordering along the [0001] direction in quaternary AlGaInN epilayers grown at 650 ºC. This structural ordering is enhanced by high Al concentration. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Orientation‐dependent properties of aluminum nitride single crystals
Authors: Bickermann M. , Heimann P. , Epelbaum B. M.
Published: May 2006

We have measured the optical properties of different facets and different growth zones in AlN bulk single crystals grown by physical vapor transport. These crystals have a pronounced zonal structure. The systematic investigation shows that absorption and luminescence properties are similar to AlN crystals and epitaxial layers grown with other techniques. However, the intensity and position of below band‐gap features was found to vary strongly with the zone or facet investigated. We conclude that intrinsic defect formation and impurity concentration strongly depend on the growth direction. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microphotoluminescence of GaN/AlN quantum dots grown by MBE
Authors: Zhuravlev K. S. , Ree D. D. , Mansurov V. G. , Nikitin A. Yu. , Paskov P. P. , Holtz P.‐O.
Published: May 2006

We performed microphotoluminescence studies of structure with single layered of GaN QDs embedded in an AlN matrix grown by MBE. Distinct UV PL lines have been found and attributed to several subgroups of QDs with different size. Relative intensity of the PL lines depends on the excitation power and temperature, whereas their energy position does not change with the excitation power evidencing in negligible screening of the built‐in electric field in GaN/AlN QDs by free carriers. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic, optical and electrical properties of GaN and AlN doped with rare‐earth element Gd
Authors: Choi S. W. , Zhou Y. K. , Emura S. , Lee X. J. , Teraguchi N. , Suzuki A. , Asahi H.
Published: May 2006

We have investigated magnetic, optical, and electrical properties of rare‐earth element Gd‐doped GaN and AlN layers grown on (0001) Si face of 6H‐SiC substrates by radio‐frequency molecular beam epitaxy. Magnetization versus magnetic field curves for Ga0.94Gd0.06N and Al0.98Gd0.02N showed a ferromagnetic order at room temperature. Photo luminescence spectra for the Ga0.94Gd0.06N showed a sharp peak at around 652 nm. Cathodoluminescence spectra for the Al0.98Gd0.02N showed a strong and sharp emission at 318 nm. Both samples exhibited n‐type conduction with a relatively high carrier concentration of above 5x1019 cm–3 at room temperature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Critical points of the bandstructure of AlN/GaN superlattices investigated by spectroscopic ellipsometry and modulation spectroscopy
Authors: Buchheim C. , Goldhahn R. , Winzer A. T. , Cobet C. , Rakel M. , Esser N. , Rossow U. , Fuhrmann D. , Hangleiter A. , Ambacher O.
Published: May 2006

The ground state transition energies of AlN/GaN superlattices are determined by photoreflectance spectroscopy and spectroscopic ellipsometry. A shift of the transition energies in dependence on the barrier and well widths is found. The results are compared to quantum mechanical calculations at the Brillouin zone centre. Extending the measurements up to 9.8 eV, quantum confinement effects are observed for higher energetic critical points of the bandstructure, too. The complex dielectric functions of the superlattices are reported from 1.2 to 9.8 eV. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An analytical model for GaN MESFET's using new velocity‐field dependence
Authors: Kabra Sneha , Kaur Harsupreet , Haldar Subhasis , Gupta Mridula , Gupta R. S.
Published: May 2006

A physical analytical model is developed for the output current voltage characteristics and for describing the behavior of electrons in sub‐micron GaN MESFET's. A semi‐empirical formula has been proposed to approximate the electron drift velocity versus electric field in GaN by fitting it with the Monte Carlo simulation data. It gives a true physical description and an excellent approximation of the velocity field dependence in GaN revealing the presence of a velocity peak which is substantially higher than the saturation velocity at temperature close to 300 K and at typical doping concentration of 1017/cm3. The resulting I‐V curves are in excellent agreement with the experimental data. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiple defects in GaInN multiple quantum wells grown on ELO GaN layers and on GaN substrates
Authors: Tomiya S. , Goto O. , Hoshina Y. , Tanaka T. , Ikeda M.
Published: May 2006

A new type of structural defects was observed in GaInN multiple quantum well structures with higher In concentrations that were grown on low‐threading‐dislocation‐density templates. The defects were investigated by using various kinds of transmission electron microscopy techniques, and were found to consist of planar defects and associated dislocations. The planar defects nucleate at the interfaces between the quantum well layers and barrier layers. The dislocations are created at the edge boundary of the planar defects and run almost along the c‐axis towards the epi‐surface. The planar defects are revealed to be inversion domains which are thought to be caused by the segregation of excess In‐In bonds at the interface between the quantum well layer and the barrier layer. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fabrication and characterization of indium‐tin‐oxide/GaN visible‐blind UV detectors
Authors: Lui H. F. , Fong W. K. , Surya C. , Cheung C. H. , Djurišić A. B.
Published: May 2006

We report the fabrication and characterization of visible‐blind GaN‐based UV photodetectors with indium‐tin‐oxide (ITO)/GaN Schottky junctions. We have systematically studied the optimal growth conditions for the ITO layers. Responsivity of 0.041 A/W was obtained for the optimised ITO/GaN UV detectors at 350nm. The I‐V characteristics show that the reverse leakage currents of the devices are strongly dependent on the deposition conditions of the ITO. The experimental results indicate that interfacial traps play an important role on the optoelectronic properties of the devices. To improve the ITO/GaN interface, a thin Ni layer was deposited between the ITO and the GaN. Our results show that this leads to significant improvements in the leakage current, low‐frequency excess noise and the UV‐to‐visible rejection ratio. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Infrared reflectance measurement for InN thin film characterization
Authors: Fukui K. , Kugumiya Y. , Nakagawa N. , Yamamoto A.
Published: May 2006

Infrared reflectance measurements of a series of InN thin films have been performed and attempt to derive carrier concentration and other physical constants for InN thin film characterization. Fitting calculations are performed by use of the dielectric function equation based on phonon‐plasmon coupling model. Longitudinal and transverse optical phonon frequencies, plasma frequency and their damping parameters can be derived from fitting. From those results, electrical and phonon properties of InN and characterization of films are discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of AlN films and their characterization
Authors: Jain Rakesh B. , Gao Ying , Zhang Jianping , Qhaleed Fareed R. S. , Gaska Remis , Li Jiawei , Arjunan Arulchakkravarthi , Kuokstis Edmundas , Yang Jinwei , Asif Khan M.
Published: May 2006

Single crystal AlN layers have been produced by migration enhanced metal organic chemical vapor deposition (MEMOCVD), hydride vapor phase epitaxy (HVPE) and their combination. The growth was carried out on 2” basal plane sapphire substrates. In MEMOCVD, the duration and waveforms of precursors were varied to achieve better surface mobility and thus better atomic incorporation. It resulted in superior layer quality templates with the narrowest (002) X‐ray rocking curve full width half maximum (FWHM). Such high quality AlN templates were used as seeds for subsequent HVPE growth. Thick films with thickness ranging from 1‐25 µm have been grown by HVPE with growth rates as high as 200 µm/min, highest ever reported. Films grown by the two methods have been extensively characterized by Nomarski microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), high‐resolution X‐ray diffractometry (HRXRD), and photoluminescence (PL). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of the local structure of InN with a bandgap energy of 0.8 and 1.9 eV and annealed InN using X‐ray absorption fine structure measurements
Authors: Miyajima Takao , Kudo Yoshihiro , Wakahara Akihiro , Yamaguchi Tomohiro , Araki Tsutomu , Nanishi Yasushi
Published: May 2006

We compared the local structure around In atoms in microwave‐excited MOCVD‐ and MBE‐grown InN film which indicates an absorption edge at 1.9 and 0.8 eV, respectively. The co‐ordination numbers of the 1st‐nearest neighbor N atoms and the 2nd‐nearest neighbor In atoms for MBE‐grown InN were n(N) = 3.9 ± 0.5 and n(In) = 12.4 ± 0.9, which are close to the ideal value of n(N) = 4 and n(In) = 12 for InN without defects, respectively. By thermal annealing, the structure of MBE‐grown InN was changed from InN to In2O3, and the absorption edge was changed from 0.8 to 3.5 eV. However, the microwave‐excited MOCVD‐grown InN had no structure of In2O3, and had the reduced co‐ordination numbers of the 2nd‐nearest neighbor In atoms of n(In) = 10.6‐11.7. From these results, we conclude that the origin of the 1.9‐eV absorption edge of InN is the imperfections (defects) of the In lattice sites of InN, rather than the generation of In2O3, which has a bandgap energy of 3.5 eV. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and morphology of MOVPE grown InGaN/GaN islands
Authors: Gangopadhyay S. , Schmidt Th. , Einfeldt S. , Yamaguchi T. , Hommel D. , Falta J.
Published: May 2006

The dependence of the surface morphology on the growth temperature of InGaN/GaN(0001) samples grown by metal organic vapour phase epitaxy has been investigated using scanning probe microscopy. By lowering the growth temperature, the thermal diffusion of the InGaN is reduced which results in an increase of the island density. For 1.3 nm InGaN deposition at 650 °C, large spiral disc‐like InGaN islands with atomically flat top surfaces are observed which preferentially nucleate at GaN substrate defects. In contrast, InGaN growth at 600 °C leads to a homogeneous nucleation of small islands with a granular appearance. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural investigations of GaN films with X‐ray standing waves
Authors: Siebert Michael , Schmidt Thomas , Flege Jan Ingo , Einfeldt Sven , Figge Stephan , Hommel Detlef , Falta Jens
Published: May 2006

The technique of X‐ray standing waves (XSW) was applied for the first time to thick undoped GaN films grown on (0001) sapphire substrates. The film polarity was determined unambiguously in (006) backscattering geometry, which proves the feasibility of XSW measurements on this system. Reflectivity measurements yielded a significant decrease of the crystal quality already at a Mg dopant concentration as low as 4 × 1018cm–3. For a Mg dopant concentration of (3‐4)×1019cm–3, crystallites with a difference in the lattice constant of Δc/c = 0.51‰ are found, which impedes XSW investigations on thick doped crystals. In order to solve this problem, we propose a modified sample structure, consisting of a thin doped layer on top of a thick undoped GaN film. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Crack‐free AlGaN/GaN Bragg mirrors grown on Si (111) substrates by metalorganic vapor phase epitaxy
Authors: Chiu A. P. , Chen N. C. , Chang P. H. , Shih C. F.
Published: May 2006

Crack‐free distributed Bragg reflectors (DBR) with high reflectance and high Al content were grown over Si (111) substrates by metalorganic vapor phase epitaxy. This is achieved by introducing a set of nine period AlN / GaN short‐period superlattices (SL) with average Al content of 50% instead of the bulk Al0.5Ga0.5N. We found that the AlN / GaN superlattices not only decreased the tensile strain but also improved the reflectance. Moreover, this structure also improves the surface roughness and reduces the dislocation densities. The larger refractive index ratio between high‐Al‐content AlxGa1‐xN and GaN permits one to obtain a spectral stopband width of 25 nm and a reflectance value 62% at 480 nm for 7 mirror periods. We present the experimental and simulation results and the characterization by normal direction reflectance spectrum, high resolution x‐ray diffraction (HRXRD), field emission scanning electron microscopy (SEM) and atomic force microscopy (AFM). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Neue Germanide mit geordneter Ce3Pt4Ge6‐Struktur – Die Verbindungen Ln3Pt4Ge6 (Ln: Pr–Dy)
Authors: Imre Anette , Hellmann Andrea , Mewis Albrecht
Published: May 2006

New Germanides with an Ordered Variant of the Ce3Pt4Ge6 Type of Structure – The Compounds Ln3Pt4Ge6 (Ln: Pr–Dy)

Six new germanides Ln3Pt4Ge6 with Ln = Pr–Dy were synthesized by heating mixtures of the elements at 900 °C, annealing the inhomogeneous powders at 1050‐1100 °C for six days and then cooling down from 700 °C in the course of two months. The crystal structures of Pr3Pt4Ge6 (a = 26.131(5), b = 4.399(1), c = 8.820(2) Å), Sm3Pt4Ge6 (a = 25.974(3), b = 4.356(1), c = 8.748(1) Å), and Dy3Pt4Ge6 (a = 26.079(5), b = 4.311(1), c = 8.729(2) Å) were determined by single crystal X‐ray methods. The compounds are isotypic (Pnma, Z = 4) and crystallize with an ordered variant of the Ce3Pt4Ge6 type of structure (Cmcm, Z = 2) consisting of CaBe2Ge2‐ and YIrGe2‐analogous units. The platinum atoms are located in distorted square pyramids of germanium atoms and build up with them a three‐dimensional network. The coordination polyhedra of the platinum and germanium atoms around the rare‐earth metal atoms are pentagonal and hexagonal prisms. These are completed by some additional atoms resulting in coordination numbers of 14 and 15 respectively. The other germanides were investigated by powder methods resulting in the following lattice constants: a = 26.067(6), b = 4.388(1), c = 8.800(2) Å for Ln = Nd; a = 25.955(7), b = 4.337(1), c = 8.728(2) Å for Ln = Gd; a = 25.944(5), b = 4.322(1), c = 8.698(2) Å for Ln = Tb. The atomic arrangement of Ln3Pt4Ge6 is compared with the well‐known monoclinic structure of Y3Pt4Ge6.
The Stannides AuNiSn2 and AuCuSn2 – Bulk Synthesis and Superstructure Determination
Authors: Lange Stefan , Nilges Tom , Hoffmann Rolf‐Dieter , Pöttgen Rainer
Published: May 2006

The stannides AuNiSn2 and AuCuSn2 were prepared by melting of the elements in silica ampoules at 1300 K followed by slow cooling to room temperature. The structures of both compounds were refined on the basis of single crystal X‐ray data: $P{\bar 3}m{\rm 1}$, a = 412.41(14), c = 529.24(11) pm, wR2 = 0.0268, 159 F2 values, 10 variables for AuNiSn2 and a = 425.97(17), c = 526.88(15) pm, wR2 = 0.0507, 159 F2 values, 11 variables for AuCuSn2 (twinned crystal, BASF = 0.305(4)). These stannides crystallize with a superstructure of the NiAs type with a complete ordering of the transition metal atoms. They derive from a AuSn subcell structure, where every other layer of octahedral voids in the hexagonal closest packing of the tin atoms is filled by nickel in AuNiSn2 and by copper in AuCuSn2. Due to the symmetry reduction smaller NiSn6/6 (CuSn6/6) and larger AuSn6/6 octahedra alternate along the c axis. The crystal chemistry is discussed on the basis of a group‐subgroup scheme.
Condensation of Rare Earth Pyrazolates: The Dimeric, Trimeric and Polymeric Units [Gd2(Pz)6(PzH)4], [Nd3(Pz)9(PzH)2] and $^{1}_{\infty}\rm [Eu(Pz)_{2}(PzH)_{2}]$
Authors: Quitmann Catharina C. , Bezugly Victor , Wagner Frank R. , Müller‐Buschbaum Klaus
Published: May 2006

Solvent free high‐temperature oxidations of rare earth metals with the heterocycle pyrazole as well as in low to non‐coordinating solvents were investigated to isolate intermediate stages between monomeric and polymeric pyrazolates of the lanthanides. Reaction conditions were tuned according to simultaneous DTA/TG and temperature dependent X‐ray powder diffraction experiments on known monomeric and polymeric pyrazolates, that gave rise to the idea that further structure intermediates could be isolated. Reactions in 1,2,3,4‐tetrahydroquinoline gave the dimeric complex [Gd2(Pz)6(PzH)4](PzH)(Tech) (1) as well as the triangular complex [Nd3(Pz)9(PzH)2](PzH)(Tech)2 (2). The solvent free melt synthesis resulted in a new polymeric form of $^{1}_{\infty}\rm [Eu(Pz)_{2}(PzH)_{2}]$ (3) (pyrazole, PzH = C3H3NNH; pyrazolate anion, Pz− = C3H3NN−; 1,2,3,4‐tetrahydroquinoline, Tech = C9H13N). All three compounds contain coordinating pyrazolate amide groups and pyrazole molecules the latter decreasing in numbers upon condensation of the building units. According to simultaneous DTA/TG/MS investigations the condensation process can be identified with the release of pyrazole molecules.1 consists of dimeric molecules containing trivalent gadolinium with a C.N. of eight. The two gadolinium atoms show different coordination polyhedra. Only σ coordination and bridging is found for 1. 2 consists of trimeric molecules containing trivalent neodymium. The neodymium atoms also exhibit different coordination polyhedra with C.N.s of eight and nine. Both π and σ coordination is found for 2, the π coordinating pyrazolate ligands acting as lids of the triangular units. Topological analysis of the electron localization function (ELF) for 2 calculated at the scalar‐relativistic DFT level reveals only weakly covalent π donor η5‐Pz–Nd interactions compared to the stronger covalent σ donor Pz–Nd interactions. The topological analysis of both, the ELF and the electron density reveals no significant differences of the respective charges of the Nd atoms. 3 exhibits a one‐dimensional chain structure with EuII and a C.N of ten. It can thus be addressed the β form of the referring formula with a new arrangement of the coordinating ligands. Like the α form 3 shows σ and π coordination of pyrazole and pyrazolate ligands. Simultaneous DTA/TG analysis reveals that the low‐temperature α form shows a phase transition into the β form between 110 °C and 130 °C. The three compounds were investigated by low‐temperature single crystal X‐ray analysis, Mid IR and Far IR spectroscopy.