bluuebunny/crossref_metadata_2025_split huggingface dataset:
Buffer free MOCVD growth of GaN on 4H‐SiC: Effect of substrate treatments and UV‐photoirradiation
Authors: Losurdo Maria , Giangregorio Maria M. , Bruno Giovanni , Kim Tong‐Ho , Choi Soojeong , Brown April 
Published: May 2006

AbstractGaN has been grown directly on the Si‐face 4H‐SiC(0001) substrates using remote plasma‐assisted metalorganic chemical vapour deposition (RP‐MOCVD) with UV‐light irradiation. The effects of substrate pre‐treatments and UV‐photoirradiation of the growth surface on GaN nucleation and film morphology are investigated. Optical data from spectroscopic ellipsometry measurements and morphological data show an improvement in nucleation and material quality with UV‐light irradiation. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nanocrystalline AlN:Si field emission arrays for vacuum electronics
Authors: Lebedev V. , Morales F. M. , Fischer M. , Himmerlich M. , Krischok S. , Schäfer J. A. , Ambacher O. 
Published: May 2006

AbstractNano‐crystalline AlN:Si cold cathodes were grown by molecular beam epitaxy on prefabricated silicon μ ‐tip field emission arrays (FEAs). The investigated FEAs showed an uniform tip distribution and reproducible emission properties. Current densities of up to 0.7 mA for a 4 × 106 tips array (1 tip/μm2) have been achieved at a relatively modest voltage of ∼ 60 V. The emitters revealed a good current stability with fluctuations of about 4% at constant voltage. The FEAs demonstrated a 40‐fold decrease in operating voltage for a given current following the “activation” of the surface by high field conditioning. The corresponding changes in slope of the Fowler–Nordheim plot and UV photoemission spectra confirm that the surface cleaning causes a reduction of the surface emission barrier at least by factor of 3. The observed large electron affinity of the as loaded surface is presumed to be caused by the adsorption of oxygen and carbon containing species. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Time resolved charge profiling of polarization dipoles in high power 525 nm green GaInN/GaN light emitting structures
Authors: Xia Y. , Li Y. , Ou Y. , Zhao W. , Zhu M. , Yilmaz I. , Detchprohm T. , Schubert E. F. , Wetzel C. 
Published: May 2006

AbstractA charge profiling of GaInN/GaN hetero‐polarization structures typical for high power 525 nm green light emitting diodes is presented. We identify three individual charge maxima of some 1.17 × 1012 cm–2 electrons with a line width as narrow as 17 nm corresponding to three individual but widely separated quantum wells. The sheet charge density indicates negligible screening of the polarization charges. The voltage required to deplete each well is found to be ΔU = –0.4 ± 0.1 V and approximates the voltage drop across the polarization dipole of the quantum well. The modulation frequency dependence reveals a characteristic time constant of 1 μs for the dominant trapping and ionization process. Such analysis of high performance green light emitters proves a suitable tool for further device optimization. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New method for the in situ determination of AlxGa1–xN composition in MOVPE by real‐time optical reflectance
Authors: Hardtdegen H. , Kaluza N. , Sofer Z. , Cho Y. S. , Steins R. , Bay H. L. , Dikme Y. , Kalisch H. , Jansen R. H , Heuken M. , Strittmatter A. , Reißmann L. , Bimberg D. , Zettler J.‐T. 
Published: May 2006

AbstractThis paper reports on the in situ determination of the Al‐content in Alx Ga1–x N layers deposited by MOVPE on sapphire and silicon substrates by means of optical reflectance. The accuracy of the conventional in situ method which utilizes the dependence of the refractive index and the extinction coefficient on Al‐content is compared to that of the new dispersion approach. The limits and possibilities of the new approach will be discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Progress in MOVPE growth of crack‐free AlGaN based Bragg reflectors on Si(111)
Authors: Charles M. B. , Zhang Y. , Kappers M. J. , Humphreys C. J. 
Published: May 2006

AbstractHaving previously reported growth of uncracked AlN/GaN distributed Bragg reflectors (DBRs), this paper reports use of superlattices as a replacement for AlN layers to produce high quality crack free DBRs. In addition an InGaN LED structure grown above the DBR has been studied and showed improved uniformity in comparison with a standard LED structure. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Development of native, single crystal AlN substrates for device applications
Authors: Schowalter L. J. , Schujman S. B. , Liu W. , Goorsky M. , Wood M. C. , Grandusky J. , Shahedipour‐Sandvik F. 
Published: May 2006

AbstractUltra‐low dislocation density aluminum nitride is a very promising substrate for many device structures based on the III–V nitride system. A better lattice and thermal expansion match than foreign substrates such as SiC or sapphire make AlN the substrate of choice for heteroepitaxial growth of AlGaN alloys, especially those with high aluminum concentration. In this paper, we show crystalline and chemical characterization of native aluminum nitride substrates, as well as characterization of AlGaN epilayers with 40 and 50% concentration of aluminum. The observation of atomic steps in atomic force microscope scans of the bare substrates and epilayers, as well as the narrow Full Width at Half Maximum (FWHM) measured on X‐ray diffraction, are an indication of both the good surface preparation of the substrates and quality of the epilayers. An estimation of defect density on epilayers grown by Migration Enhanced Metal Organic Chemical Vapour Deposition (MEMOCVD) resulted in mid 106/cm2. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural analysis of (Ga,Mn)N epilayers and self‐organized dots using MeV ion channeling
Authors: Kuroda S. , Marcet S. , Bellet‐Amalric E. , Cibert J. , Mariette H. , Yamamoto S. , Sakai T. , Ohshima T. , Itoh H. 
Published: May 2006

AbstractRutherford backscattering (RBS) and particle‐induced X‐ray emission (PIXE) experiments were performed on (Ga,Mn)N epilayers and self‐organized dots grown by plasma‐assisted MBE. The combined channeling RBS and Mn PIXE experiments were performed on Ga0.949Mn0.051N epilayer, which was confirmed to be of pure diluted phase by X‐ray diffraction (XRD) in our previous study, in order to check the presence of Mn atoms in the interstitial site in wurtzite crystal. The axis scan around 〈0001〉 and 〈$ 10 \bar 1 2$〉 axes and the plane scan around ($ 10 \bar 1 0$) plane revealed that almost all the Mn atoms were in the substitutional site of wurtzite GaN crystal. For self‐organized dots of (Ga,Mn)N grown on AlN by MBE, the PIXE spectra were measured and the Mn composition in the dot layer was estimated from the ratio of emission intensity of Mn and Ga Kα lines. At a result, it was found that the Mn composition in the dots was higher by two or three times than that in thick epilayers grown with the addition of the same amount of Mn flux. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microstructure of thick AlN grown on sapphire by high‐temperature MOVPE
Authors: Imura M. , Nakano K. , Kitano T. , Fujimoto N. , Okada N. , Balakrishnan K. , Iwaya M. , Kamiyama S. , Amano H. , Akasaki I. , Shimono K. , Noro T. , Takagi T. , Bandoh A. 
Published: May 2006

AbstractThick AlN layers with atomically flat surfaces were successfully grown directly on sapphire substrates by metal‐organic vapor phase epitaxy at high temperatures between 1300 °C and 1600 °C. Dislocations such as those of the edge, screw and mixed types exhibited different behaviors in the AlN epilayers. The dislocation density of AlN was less than 2 × 109 cm–2. Free and bound excitons of AlN were observed with peak energies of 6.084 eV and 6.063 eV, respectively. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
N‐type doping of HVPE‐grown GaN using dichlorosilane
Authors: Richter E. , Hennig Ch. , Zeimer U. , Wang L. , Weyers M. , Tränkle G. 
Published: May 2006

AbstractN‐type doping of GaN in hydride vapour phase epitaxy (HVPE) has been studied. While silane was found to be not suitable, doping from solid silicon was found to be feasible but difficult to handle. Dichlorosilane was found to be a convenient Si doping source for HVPE growth of GaN. High electron mobilities as well as good optical and structural properties are obtained in the doping range of 6 × 1017 cm–3 to 8 × 1018 cm–3 using dichlorosilane. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐catalyst growth and characterization of a ‐plane AlGaN nanorods
Authors: Gaevski Mikhail E. , Sun Wenhong , Yang Jinwei , Adivarahan Vinod , Sattu Ajay , Mokina Irina , Shatalov Maxim , Simin Grigory , Asif Khan M. 
Published: May 2006

AbstractWe report on growth of Al0.22Ga0.78N/Al0.06Ga0.94N nanorods over a ‐plane GaN template using low pressure metal‐organic chemical vapor deposition. Nanorods with average diameter of 100 nm were up to 30 µm long. They grew preferentially along the 〈11$ \bar 2 $0〉 crystal direction and possessed excellent optical and mechanical properties. It was shown using monochromatic cathodoluminescence that nanorods emit light both at 320 nm and 350 nm over entire length proving uniform coating of the Al0.06Ga0.94N rod core by an Al0.22Ga0.78N shield. The elastic modulus of nanorod material was found to be 185 GPa. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Strain in a ‐plane GaN layers grown on r ‐plane sapphire substrates
Authors: Roder C. , Einfeldt S. , Figge S. , Hommel D. , Paskova T. , Monemar B. , Haskell B. A. , Fini P. T. , Speck J. S. , Nakamura S. 
Published: May 2006

AbstractThe strain in a ‐plane GaN layers of different thickness grown on r ‐plane sapphire substrates by hydride vapor phase epitaxy was studied by X‐ray diffraction. The layers are found to be under compression in the growth plane and under tension in the growth direction. Therefore, the symmetry of the GaN unit cell is no longer hexagonal but orthorhombic. With increasing layer thickness the strain relaxes and the curvature of the wafer increases. Wafer bending is proposed to be the major strain relaxation mechanism. The anisotropic in‐plane strain relaxation is attributed to the elastic and thermal anisotropy of GaN and sapphire. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of reaction mechanisms by electrospray ionization mass spectrometry: characterization of intermediates in the degradation of phenol by a novel iron/magnetite/hydrogen peroxide heterogeneous oxidation system
Authors: Moura Flávia C. C. , Araujo Maria H. , Dalmázio Ilza , Alves Tânia M. A. , Santos Leonardo S. , Eberlin Marcos N. , Augusti Rodinei , Lago Rochel M. 
Published: May 2006

AbstractElectrospray ionization (ESI) mass spectrometry (MS) and tandem mass spectrometry (MS/MS) were used to monitor the oxidation of phenol by a novel heterogeneous Fenton system based on a Fe0/Fe3O4 composite and H2O2. On‐line ESI‐MS(/MS) shows that this heterogeneous system promotes prompt oxidation of phenol to hydroquinone, which is subsequently oxidized to quinone, other cyclic poly‐hydroxylated intermediates and an acyclic carboxylic acid. A peroxide‐type intermediate, probably formed via an electrophilic attack of HOO. on the phenol ring, was also intercepted and characterized. ESI‐MS(/MS) monitoring of the oxidation of two other model aromatic compounds, benzene and chlorobenzene, indicates the participation of analogous intermediates. These results suggest that oxidation by the heterogeneous system is promoted by highly reactive HO. and HOO. radicals generated from H2O2 on the surface of the Fe0/Fe3O4 composite via a classical Fenton‐like mechanism. Copyright © 2006 John Wiley & Sons, Ltd.
Simultaneous determination of low levels of methotrexate and cyclophosphamide in human urine by micro liquid chromatography/electrospray ionization tandem mass spectrometry
Authors: Barbieri Anna , Sabatini Laura , Indiveri Paolo , Bonfiglioli Roberta , Lodi Vittorio , Violante Francesco S. 
Published: May 2006

AbstractThe aim of this study was to develop and validate a novel solid‐phase extraction (SPE) liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for the simultaneous determination of two antineoplastic drugs, cyclophosphamide (CP) and methotrexate (MTX), in human urine using trophosphamide as internal standard. The method showed good precision and accuracy (mean RSD 2.8% and 0.9%; bias 2.7% and 2.4% for MTX and CP, respectively). The lower limits of detection obtained, 0.2 µg/Lurine for MTX and 0.04 µg/Lurine for CP, were lower than the best previously reported values. The use of a 96‐well SPE plate for matrix purification ensures a high throughput (50 samples/day), allowing the routine biological monitoring of CP and MTX as measures of occupational exposure at very low levels. Copyright © 2006 John Wiley & Sons, Ltd.
Determination of phenylalanine in human serum by isotope dilution liquid chromatography/tandem mass spectrometry
Authors: Lee Hwashim , Park Sangryoul , Lee Gaeho 
Published: May 2006

AbstractIsotope dilution liquid chromatography/tandem mass spectrometry (ID‐LC/MS/MS) has been developed as a candidate reference method to determine the level of phenylalanine in human serum. The advantages of this method include a simple sample preparation without derivatization, selective detection of analytes, and the use of an isotopic analogue as an internal standard. Phenylalanine and its isotopic analogue, phenylalanine‐ring‐13C6, were monitored at the transitions m/z 166.2/120.2 and 172.2/126.2 in the multiple‐reaction monitoring (MRM) mode, respectively. The expanded uncertainty of the measurement result of phenylalanine in the serum was approximately 1.2% within a 95% confidence level. A standard reference material, with a certified value of phenylalanine, was analyzed in order to verify this method. The result obtained by the ID‐LC/MS/MS method differed somewhat from the certified value, but agreed well with the gravimetric value. The measurement result of phenylalanine in serum by ID‐LC/MS/MS was compared with the results from the commercial HPLC method, which was carried out in clinics. The results from the commercial HPLC method showed inconsistent results with each other. The busted results from the commercial HPLC method suggest that it should be possible to trace the results of the commercial fields to well‐characterized reference materials or methods. Copyright © 2006 John Wiley & Sons, Ltd.
High‐throughput quantification of perindopril in human plasma by liquid chromatography/tandem mass spectrometry: application to a bioequivalence study
Authors: Nirogi Ramakrishna V. S. , Kandikere Vishwottam N. , Shukla Manoj , Mudigonda Koteshwara , Maurya Santosh , Komarneni Prashanth 
Published: May 2006

AbstractA simple, sensitive and rapid high‐performance liquid chromatography/positive ion electrospray tandem mass spectrometry method was developed and validated for the quantification of perindopril in human plasma. Following liquid‐liquid extraction, the analytes were separated using an isocratic mobile phase on a reversed‐phase column and analyzed by mass spectrometry in the multiple reaction monitoring mode using the respective [M+H]+ ions, m/z 369/172 for perindopril and m/z 417/234 for the internal standard. The method exhibited a linear dynamic range of 0.1–100 ng/mL for perindopril in human plasma. The lower limit of quantification was 0.1 ng/mL with a relative standard deviation of less than 6.1%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 2.0 min for each sample made it possible to analyze more than 450 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability and bioequivalence studies. Copyright © 2006 John Wiley & Sons, Ltd.
Hybrid density functional theory study of fragment ions generated during mass spectrometry of 1,3‐dioxane derivatives
Authors: Albu Titus V. 
Published: May 2006

AbstractIt was recently reported that the cis,cis and trans,trans diastereoisomers of four 2(r)‐R‐2,4(R),6(S)‐trimethyl‐1,3‐dioxane derivatives show distinct electron ionization mass spectra. As a possible explanation for this finding, the authors suggested that the ions generated during the mass spectrometry of these compounds could follow different fragmentation patterns that initiate from different ion conformations. In this report, hybrid density functional theory methods have been used to investigate the conformational preference of three ions involved in the mass spectrometry of some 1,3‐dioxane derivatives. We found that there is indeed more than one stable ion conformation for each of the investigated ions. Energy profiles along the torsional coordinates connecting the conformers are presented, and factors influencing the relative stability of ion conformations are discussed. Copyright © 2006 John Wiley & Sons, Ltd.
Precursor ion scanning for the non‐targeted detection of individual arsenosugars in extracts of marine organisms
Authors: Kanaki Katerina , Pergantis Spiros A. 
Published: May 2006

AbstractArsenosugars are a group of arsenic compounds reported to be present in a wide variety of marine organisms. Numerous such compounds have been identified and characterized in marine organisms; however, unknown arsenosugar species may also be present. This indicates the need for an analytical technique suitable for their non‐targeted detection. One such technique is tandem mass spectrometry operated in the precursor ion scanning mode. This technique is based on scanning for precursor ions that give specific product ions, characteristic of the compounds under investigation. In the present study two subgroups of arsenosugar species were examined, the oxo‐ and the thioarsenosugars, the CID behavior of which is well known from previous studies. In the case of the oxoarsenosugars characteristic product ions were observed at m/z 237 and 97, and for the thioarsenosugars at m/z 253 and 97. Validation of this approach was carried out by analyzing extracts of two commercial kelp powders with known contents of arsenosugar species. All arsenosugars reported to exist in these materials were detected successfully using the precursor ion scanning approach. The limits of detection for the oxo‐ and the thioarsenosugar species, and the selectivity and sensitivity of the method, strongly indicate the suitability of this approach for the non‐targeted detection of arsenosugars in extracts of marine origin. Copyright © 2006 John Wiley & Sons, Ltd.
Analysis of isotope ratios in vitamin K1 (phylloquinone) from human plasma by gas chromatography/mass spectrometry
Authors: Jones Kerry S. , Bluck Leslie J. C. , Coward W. Andy 
Published: May 2006

AbstractVitamin K1 is a fat‐soluble vitamin required for the γ‐carboxylation of vitamin K‐dependent proteins. Recent work has suggested an important role for vitamin K1 in bone health beyond its more established function in the control and regulation of blood coagulation. However, current UK recommended intakes do not reflect this recent evidence. The use of stable isotopes provides a powerful tool to investigate vitamin K kinetics, turnover and absorption in man, although published methods have reported difficulties in the extraction and analysis of isotope ratios of vitamin K in human plasma. In this paper, we report a new methodology for the extraction and measurement of isotope ratios in vitamin K1. Sample clean‐up is achieved with liquid‐liquid extraction, enzyme hydrolysis with lipase and cholesterol esterase, and solid‐phase extraction. Isotopic analysis of the pentafluoropropionyl derivative of vitamin K1 is performed by gas chromatography/mass spectrometry (GC/MS). The limit of quantitation is equivalent to at least 0.3 nmol/L and the method is demonstrated to be linear over a range of enrichments. This method provides a robust alternative to previous work requiring the use of semi‐preparative high‐performance liquid chromatography (HPLC). Copyright © 2006 John Wiley & Sons, Ltd.
Human papillomavirus vaccines
Authors: Stanley Margaret A. 
Published: May 2006

AbstractA wealth of epidemiological and molecular evidence has led to the conclusion that virtually all cases of cervical cancer and its precursor intra‐epithelial lesions are a result of infection with one or other of a subset of genital human papillomaviruses (HPVs) suggesting that prevention of infection by prophylactic vaccination would be an effective anti‐cancer strategy. The papillomaviruses cannot be grown in large amounts in culture in vitro, but the ability to generate HPV virus like particles (VLPs) by the synthesis and self‐assembly in vitro of the major virus capsid protein L1 provides for a potentially effective sub unit vaccine. HPV L1 VLP vaccines are immunogenic and have a good safety profile. Published data from proof of principle trials and preliminary reports from large Phase III efficacy trials suggest strongly that they will protect against persistent HPV infection and cervical intra epithelial neoplasia. However, the duration of protection provided by these vaccines is not known, the antibody responses induced are probably HPV type specific and immunisation should occur pre‐exposure to the virus. Second generation vaccines could include an early antigen for protection post‐exposure and alternative delivery systems may be needed for the developing world. Copyright © 2006 John Wiley & Sons, Ltd.
Vaccinia virus proteolysis—a review
Authors: Byrd Chelsea M. , Hruby Dennis E. 
Published: May 2006

AbstractIt is well known that viruses, as obligate intracellular parasites, must use their hosts' metabolic machinery in order to replicate their genomes and form infectious progeny virions. What is less well known are the details of how viruses make sure that once all the necessary proteins are made, that they assume the correct configuration at the proper time in order to catalyse the efficient assembly of infectious virions. One of the methods employed by viruses to regulate this process is the proteolytic cleavage of viral proteins. Over the past several decades, studies in numerous laboratories have demonstrated that morphogenic proteolysis plays a major and essential role during the assembly and maturation of infectious poxvirus virions. In this review we describe the history of vaccinia virus proteolysis as a prototypic viral system. Copyright © 2006 John Wiley & Sons, Ltd.