bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature distribution analysis of AlGaN/GaN HFETs operated around breakdown voltage using micro‐Raman spectroscopy and device simulation
Authors: Kosaka Kenichi , Fujishima Tatsuya , Inoue Kaoru , Hinoki Akihiro , Yamada Tomoaki , Tsuchiya Tadayoshi , Kikawa Junjiroh , Kamiya Shinichi , Suzuki Akira , Araki Tsutomu , Nanishi Yasushi 
Published: June 2007

AbstractImprovement in performance and reliability of high power RF devices is a key issue for AlGaN/GaN HFETs (Hetero‐junction Field Effect Transistors). In this work, we have measured the temperature distribution in AlGaN/GaN HFETs on SiC substrates actually operated around breakdown voltage. Temperature distribution of the HFET was determined by micro‐Raman spectroscopy and was estimated from Raman shift of GaN E2(High) phonon mode. We observed temperature distribution of the HFETs operated at Vg = ‐3 V (DC) and Vds = 50, 65, 80 V (Pulse). The highest temperature position was shifted to the drain side at Vds > 60 V. The results were compared with simulation. It was indicated that the shift was due to high electric field region and virtual gate effects. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of structural perfection of InN layers and InN nanorods grown on the c‐ and r‐planes of Al2O3
Authors: Liliental‐Weber Z. , Lu H. , Schaff W. J. , Kryliouk O. , Park H. J. , Mangum J. , Anderson T. 
Published: June 2007

AbstractTransmission Electron microscopy was applied to determine similarities and difference in structural perfection between InN epi‐layers grown by MBE on c‐ and r‐plane Al2O3 and InN nanocrystals grown on similar substrates using non catalytic, template‐free hydride metal‐organic vapor phase epitaxy. The study showed that nanocrystals had more perfect crystallinity compared to the layers. While the InN layer growth direction followed the crystallographically required epitaxial growth orientation, the nanorod growth was randomly oriented. The opposite growth polarity has been determined for the InN layers grown along c‐direction (In‐polarity) in comparison to nanocrystals grown along same direction (N‐polarity). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Defect structure of a‐plane GaN grown by hydride and metal‐organic vapor phase epitaxy on r‐plane sapphire
Authors: Kröger R. , Paskova T. , Monemar B. , Figge S. , Hommel D. , Rosenauer A. 
Published: June 2007

AbstractTo obtain a deeper insight into the mechanism of defect formation in a‐plane GaN the defect nature in such films grown by metal‐organic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE) was investigated by means of transmission electron microscopy. The films showed, beside the frequently found basal plane stacking faults and threading dislocations, prismatic stacking faults originating at the film/substrate interface and facetted voids. The density of basal plane stacking fault was about 105 cm–1 and the density of partial dislocations was in the range of 1010 cm–2, accordingly. Using selected area diffraction the epitaxial relationship between film and layer was determined. Based on these findings the impact of lattice mismatch on the observed defect characteristic is discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polarity dependence of In‐rich InGaN ternary alloys grown by RF‐MBE
Authors: Shinada T. , Che S. B. , Mizuno T. , Ishitani Y. , Yoshikawa A. 
Published: June 2007

AbstractIn‐rich (XIn > 0.5) InGaN ternary alloys were grown on N‐ and Ga‐polarity GaN templates by radio‐frequency plasma assisted molecular beam epitaxy (RF‐MBE) and their polarity dependence was investigated. In‐rich InGaN alloys with In‐content ranging from 0.5 to 1.0 could be grown without phase separation and sharp single diffraction peak was observed for these samples in X‐ray diffraction (XRD) 2θ–ω scan. Compared to N‐polarity samples, In‐polarity InGaN showed better crystalline quality in spite of about 100 °C lower growth temperature. Moreover, the dependence of crystalline quality on V/III ratio was investigated for In‐polarity samples. It was found that the phase separation in the InGaN tends to occur under metal‐rich condition but this can be prevented in N‐rich and around unity stoichiometry conditions as well. Precise control of V/III ratio to around unity stoichiometry was realized by using a shutter control method, which resulted in improvement of crystalline quality and surface morphology of In‐rich InGaN films. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
MBE growth of cubic AlxIn1–xN and AlxGayIn1–x–yN lattice matched to GaN
Authors: As D. J. , Schnietz M. , Schörmann J. , Potthast S. , Gerlach J. W. , Vogt J. , Lischka K. 
Published: June 2007

AbstractTernary and quaternary cubic c‐AlxIn1–xN/GaN and c‐AlxGayIn1–x–yN/GaN heterostructures lattice‐matched to c‐GaN on freestanding 3C‐SiC substrates were grown by plasma‐assisted molecular beam epitaxy. The c‐AlxGayIn1–x–yN alloy permits the independent control of band gap and lattice parameter. The ternary and quaternary films were grown at 620 °C. Different alloy compositions were obtained by varying the Al and Ga fluxes. The alloy composition was measured by Energy Dispersive X‐ray Spectroscopy (EDX) and Rutherford Backscattering Spectrometry (RBS). X‐ray reciprocal space map of asymmetric (‐1‐13) reflex were used to measure the lattice parameters and to verify the lattice match between the alloy and the c‐GaN buffer. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Wave guide optimization for homoepitaxial laser diodes
Authors: Figge S. , Dennemarck J. , Aschenbrenner T. , Zargham A. , Hommel D. 
Published: June 2007

AbstractGaN‐based high power laser diodes in the violet spectral range are demanding for conductive substrates with a lower thermal resistance than the commonly used sapphire. The only feasible approach to this goal is homoepitaxy on GaN wafers produced from thick GaN layers grown by hydride vapour phase epitaxy. One drawback of GaN substrates is the high refractive index and therefore it acts as an parasitic wave guide. In this paper we will discuss the optimization of the wave guide and the n‐side cladding layer. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of surface morphology of n‐type GaN after photoelectrochemical reaction in various solutions for H2 gas generation
Authors: Fujii Katsushi , Ito Takashi , Ono Masato , Iwaki Yasuhiro , Yao Takafumi , Ohkawa Kazuhiro 
Published: June 2007

AbstractSurface morphology and chemical composition at n‐type GaN surface after photoelectrochemical reactions were investigated. Whisker‐like Ga oxides were observed in the lower pH solutions and hexagonal columns were observed in the higher pH solutions. The results indicate that different reactions occur in the different pH solutions. Dissolution amount was the lowest at a neutral pH solution. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mega‐cone blue LEDs based on ZnO/GaN direct wafer bonding
Authors: Murai A. , Thompson D. B. , Masui H. , Fellows N. , Mishra U. K. , Nakamura S. , DenBaars S. P. 
Published: June 2007

AbstractThe cover picture of this issue of physica status solidi (c) has been taken from the article [1].
Preface: phys. stat. sol. (c) 4/7
Authors: Akimoto Katsuhiro , Chichibu Shigefusa , Suemasu Takashi 
Published: June 2007

AbstractThe International Workshop on Nitride Semiconductors (IWN 2006) was held in Kyoto, Japan from 22 to 27 October 2006. This workshop was part of a continuing series of IWN, first held at Nagaya, Japan (2000), Aachen, Germany (2002), and Pittsburg, USA (2004). The conference was well attended by 841 participants from 33 countries. From over 550 abstracts submitted, the Program Committee accepted 441 abstracts. There were 11 invited talks including 3 plenary presentations for a total of 96 oral presentations, with the remaining papers given as posters. Among them, 228 manuscripts were submitted and reviewed by the usual evaluation process of physica status solidi. Finally 212 papers were accepted and the present special volume contains the collection of those papers.IWN 2006 was organized as a unified meeting of four independent topical workshops: Growth, Optoelectronic Properties, Optical Devices and Electron Devices. The first half of the week, on Monday and Tuesday, the workshops were held together at Kyoto International Conference Hall, whereas on Wednesday and Thursday, the workshops were separately held at Ritsumeikan University and Kyoto University.At the topical workshops, the activities concentrated on discussion and information exchange rather than just the presentation of the research results. The effectiveness of non‐polar substrates for both electronic and optical devices was emphasized. Point defects and dislocations were suggested to play a significant role in optical properties of AlGaN. Light extraction and thermal management were assessed to be important to design high efficiency white LEDs. The ammonothermal method was proposed as a promising growth method for bulk GaN. We can expect that from such discussions made at the topical workshops new research trends will be derived which will yield further amazing results.The Editors would like to thank the members of the Executive Committee and Program Committee, especially H. Miyake and T. Araki, for their support and advice through the organization of the event. We would also like to express our appreciation to the referees for their careful reading and scientific evaluation of the papers in this special issue. Finally, we would like to express our gratitude to Stefan Hildebrandt and Julia Hübner for their assistance in the technical editorial process and to physica status solidi for the rapid publication of the proceedings.
Deriving a mechanistic model for potential energy surface of coordination compounds of nontransition elements
Authors: Tchougréeff A. L. 
Published: June 2007

AbstractMolecules of coordination compounds (those formed by a central atom—largely by a transition or non‐transition metal ion, but also by non‐transition elements like sulfur, phosphorus, etc., and by atoms or groups surrounding it—the ligands) for decades represent a significant problem for any “classical” description given in terms of empirical force fields of molecular mechanics (MM) due to diversity of coordination polyhedra resulting in the numerosity of the parameters necessary to describe the objects of interest within such a setting. This situation is further toughened by the specific collection of effects known as mutual influence of ligands, of which the trans‐effect in transition metal complexes is the most known. A feature particularly complicating understanding the ligand influence is its qualitative dependence on the nature of the central atom. The real source of these problems is of course the specificity of the electronic structure of the coordination compounds. If compared with usual organic molecules for which the MM in its classical form is rather successful the major distinction characteristic for coordination compounds is the absence of fairly distinguishable two‐center two‐electron bonds incident to its central atom (ion). Using a methodology called deductive molecular mechanics (DMM) we have recently shown that for “organic” molecules it is possible to sequentially derive the form of the MM force field departing from a simple but intuitively transparent model of electronic structure of a single chemical bond. Here we present an analogous derivation for the force fields describing coordination compounds. It is based on the analysis of electronic structure of the closest ligand shell of coordination compounds and on that of its relation with the geometry changes induced by chemical substitution (ligand influence) performed recently by Levin and Dyachkov. By using the elements of the one‐electron density matrix as an economical set of electronic structure variables for the closest ligand shell, the DMM model of coordination compounds is constructed. Next, by excluding the electronic structure variables the effective elastic elements describing the force fields concordant with the mutual ligands' influence in coordination compounds are constructed and their dependence on the state of the central ion is established. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Variational estimates for exchange‐correlation interaction obtained within Super‐CI approach to MCSCF approximation
Authors: Gusarov S. I. , Goidenko I. A. , Dmitriev Yu. Yu. , Labzowsky L. N. 
Published: June 2007

AbstractTwo possible variation approximations for the exchange‐correlation interaction are considered in the one‐particle approach to the electronic structure theories. These approximations appear within the Super‐CI procedure in the MCSCF optimization schemes. The basic formalism shows its close connection to the Green's function theory in the extended Koopmans' approach. An immediate implementation of the corresponding Super‐CI Green's functions is the Møller‐Plesset open‐shell and quasi‐degenerate perturbation expansions, and the density matrix functional theory. The relativistic formulation which is based on the relativistic extended Koopmans' approach can be used to calculate radiation corrections in frames of the conventional Feynman formalism. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Determination of three natural pesticides in processed fruit and vegetables using high‐performance liquid chromatography/tandem mass spectrometry
Authors: Sannino Anna 
Published: June 2007

AbstractThis paper describes a method for the sensitive and selective determination of two macrocyclic lactones (abamectin and spinosad) and azadirachtin in apple purée, concentrated lemon juice, tomato purée and canned peas. The general sample extraction–partitioning method for our gas chromatography and liquid chromatography multiresidue methods has been used. The analytical procedure involves an extraction with acetone and liquid–liquid partitioning with ethyl acetate/cyclohexane combined in one step. The extracts are analyzed by liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI‐MS/MS) without any further clean‐up step. The pesticides are separated on a reversed‐phase C12 column using a gradient elution. Thirteen simultaneous MS/MS transitions of precursor ions were monitored. Studies at fortification levels of 2.5–10 µg/kg and 25–100 µg/kg gave mean recoveries ranging from 70–100% for all compounds with satisfactory precision (relative standard deviation (RSD) from 3–20%). The excellent selectivity and sensitivity allows quantification and identification of low levels of pesticides in canned peas, tomato and apple purées (limits of quantitation (LOQs) 1–5 µg/kg) and in concentrated lemon juice (LOQs 2–10 µg/kg). The quantification of analytes was carried out using the most sensitive transition for every compound and by 'matrix‐matched' standards calibration. Copyright © 2007 John Wiley & Sons, Ltd.
Quantitative detection of metabolites using matrix‐assisted laser desorption/ionization mass spectrometry with 9‐aminoacridine as the matrix
Authors: Vaidyanathan Seetharaman , Goodacre Royston 
Published: June 2007

AbstractQuantitative detection of metabolites is a highly desirable feature in metabolome analyses. Recently, the successful detection of multiple metabolites using matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) in the negative ion mode employing 9‐aminoacridine as the organic matrix was reported (Edwards JL, Kennedy RT. Anal. Chem. 2005; 77: 2201–2209). However, there is little information available on quantitative detection of multiple metabolites using MALDI‐MS and in particular the influence changes in metabolite levels have on such detections. We investigated this aspect by spiking a synthetic metabolite cocktail (consisting of 39 metabolites including amino acids, organic acids and phospho‐metabolites) with five representative metabolites at increasing concentrations, one metabolite at a time, and assessed the signals from replicate determinations. It was possible to detect quantitative changes in the spiked metabolites. Although analyte suppression was observed, it was possible to observe scenarios where the spiked metabolite had little or no influence on the quantitative detection of some metabolites. It appears that the mass spectral response of the metabolite is suppressed only when the spiked chemical species are relatively similar in chemical terms. This suggests that quantitation is possible in scenarios where changes in a specific metabolite or a class of metabolites are monitored following appropriate analyte separation strategies, and that careful interpretations must be made when using the technique for quantitative analysis in unbiased metabolomic approaches. Copyright © 2007 John Wiley & Sons, Ltd.
Polyaniline‐coated nanoelectrospray emitters treated with hydrophobic polymers at the tip
Authors: Choi Yong Seok , Wood Troy D. 
Published: June 2007

AbstractIn nanoelectrospray ionization (nanoESI) techniques, the hydrophilic character of the emitters generally produces large bases for the Taylor cones, thereby generating relatively large droplet sizes and consequently reduced sensitivity. In order to minimize this ‘wetting’ effect in nanoESI, a model hydrophobic polymer (an acrylic paint) was coated at the tip of commercial polyaniline (PANI)‐coated emitters, and their performance was compared with that of unmodified PANI emitters using oxytocin and neuropeptide Y (NPY) solutions. In experiments with oxytocin, the hydrophobic emitter produced higher signal intensities (up to 3.6 times) as well as higher signal‐to‐noise ratios (33% increase) than those from the unmodified PANI emitter. In addition, the hydrophobic emitter showed reusability and a slightly wider linear dynamic range (10 nM to 50 µM, r2 = 0.9938) than that from the unmodified PANI emitter (10 nM to 10 µM, r2 = 0.9904). In the case of NPY, the hydrophobic emitter also enabled an approximately 350‐fold overall increase in sensitivity than the unmodified PANI emitter (70 zmol vs. 25 amol). The enhanced performance of the hydrophobic emitter clearly indicates potential for further increases in nanoESI sensitivity using emitters with tailored hydrophobic overcoatings. Copyright © 2007 John Wiley & Sons, Ltd.
Matrix‐assisted laser desorption/ionization mass spectrometry of polysaccharides with 2′,4′,6′‐trihydroxyacetophenone as matrix
Authors: Hsu Nien‐Yeen , Yang Wen‐Bin , Wong Chi‐Huey , Lee Yuan‐Chuan. , Lee Reiko T. , Wang Yi‐Sheng , Chen Chung‐Hsuan 
Published: June 2007

AbstractSo far, there have been only a few matrices reported for detection of polysaccharides with molecular weight higher than 3000 Daltons by matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS). In this work, we found that 2′,4′,6′‐trihydroxyacetophenone (THAP) is a good matrix for MALDI time‐of‐flight MS analysis of polysaccharides with broad mass range. Large polysaccharides, dextrans, glycoproteins and polysialic acids have been successfully detected by MALDI‐MS with THAP as matrix. Copyright © 2007 John Wiley & Sons, Ltd.
A multiplexed post‐translational modification monitoring approach on a matrix‐assisted laser desorption/ionization time‐of‐flight/time‐of‐flight mass spectrometer
Authors: Hoffman Michael D. , Rogalski Jason C. , Sniatynski Matthew J. , Locke Jennifer , Kast Juergen 
Published: June 2007

AbstractPost‐translational modifications (PTMs) of proteins are essential for proper function, as they regulate many aspects of a protein's activity and interaction with substrates. When analyzing modified peptides derived from such proteins by mass spectrometry, these modifications can dissociate, producing either a marker ion or neutral loss characteristic of the modification, which have conventionally been monitored with a precursor ion scan or neutral loss scan, respectively. Although powerful, both precursor ion scans and neutral loss scans can only screen for one particular modification at a time. This has led to the development of multiple neutral loss monitoring (MNM) for neutral losses and multiple precursor ion monitoring (MPM) for marker ions on electrospray instruments. Here, we report their implementation on a matrix‐assisted laser desorption/ionization (MALDI) instrument as well as the inception of a novel scan strategy termed targeted multiple precursor ion monitoring (tMPM). This latter scan strategy has been developed on a MALDI tandem time‐of‐flight (TOF/TOF) mass spectrometer for the identification of multiple PTMs via their associated marker ions by manipulating certain components of the instrument, notably the timed ion selector and the delayed extraction source 2. Targeted MPM combined with a second approach, multiple neutral loss monitoring (MNM), is shown to be a successful approach in the identification of PTMs, identifying multiple modified peptides in a complex sample matrix. Copyright © 2007 John Wiley & Sons, Ltd.
Laser desorption/ionization mass spectrometry on porous silicon for metabolome analyses: influence of surface oxidation
Authors: Vaidyanathan Seetharaman , Jones Dan , Ellis Joanne , Jenkins Tudor , Chong Chin , Anderson Mike , Goodacre Royston 
Published: June 2007

AbstractLaser desorption/ionization mass spectrometry (LDI‐MS) on porous silicon is a promising analytical strategy for the rapid detection of metabolites in biological matrices. We show that both oxidized and unoxidized porous silicon surfaces are useful in detecting protonated/deprotonated molecules from compounds when analyzed in mixtures. We demonstrate the feasibility of using this technique for the simultaneous detection of multiple analytes using a synthetic cocktail of 30 compounds commonly associated with prokaryotic and eukaryotic primary metabolism. The predominantly detected species were the protonated molecules or their sodium/potassium adducts in the positive‐ion mode and the deprotonated molecules in the negative‐ion mode, as opposed to fragments or other adducts. Surface oxidation appears to influence mass spectral responses; in particular, in the mixture we studied, the signal intensities of the hydrophobic amino acids were noticeably reduced. We show that whilst quantitative changes in individual analytes can be detected, ion suppression effects interfere when analyte levels are altered significantly. However, the response of most analytes was relatively unaffected by changes in the concentration of one of the analytes, so long as it was not allowed to dominate the mixture, which may limit the dynamic range of this approach. The differences in the response of the analytes when analyzed in mixtures could not be accounted for by considering their gas‐phase and aqueous basicities alone. The implications of these findings in using the technique for metabolome analyses are discussed. Copyright © 2007 John Wiley & Sons, Ltd.
On the structure of random plane‐oriented recursive trees and their branches
Authors: Mahmoud Hosam M. , Smythe R. T. , Szymański Jerzy 
Published: June 2007

AbstractThis paper is an investigation of the structural properties of random plane‐oriented recursive trees and their branches. We begin by an enumeration of these trees and some general properties related to the outdegrees of nodes. Using generalized Pólya urn models we study the exact and limiting distributions of the size and the number of leaves in the branches of the tree. The exact distribution for the leaves in the branches is given by formulas involving second‐order Eulerian numbers. A martingale central limit theorem for a linear combination of the number of leaves and the number of internal nodes is derived. The distribution of that linear combination is a mixture of normals with a beta distribution as its mixing density. The martingale central limit theorem allows easy determination of the limit laws governing the leaves in the branches. Furthermore, the asymptotic joint distribution of the number of nodes of outdegree 0, 1 and 2 is shown to be trivariate normal. © 1993 John Wiley & Sons, Inc.