bluuebunny/crossref_metadata_2025_split huggingface dataset:
UV/VUV photodetectors using group III‐nitride semiconductors
Authors: Saito Terubumi , Hitora Toshimi , Hitora Hisako , Kawai Hiroji , Saito Ichiro , Yamaguchi Eiichi 
Published: March 2009

AbstractSchottky barrier photodiodes based on AlN, AlxGa1–xN, GaN, and InyGa1–yN were fabricated with different compositions. In addition, novel types of UV detectors with narrow spectral bandwidths were developed by combining AlxGa1–xN Schottky barrier photodiodes and optical entrance windows made of AlyGa1–yN having exactly or nearly the same composition (y ≥ x). Their spectral responsivities were measured in the spectral range including the vacuum ultraviolet region. The results showed that the devices having a wide variety of cut‐off wavelengths and narrow spectral bandwidths were successfully fabricated and achieved a high out‐of‐band rejection ratio. In addition, satisfactory performances of low noise current, low temperature coefficient, and high stability to UV photons were confirmed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties of InN nanocolumns: Electron accumulation at InN non‐polar surfaces and dependence on the growth conditions
Authors: Segura‐Ruiz J. , Garro N. , Cantarero A. , Iikawa F. , Denker C. , Malindretos J. , Rizzi A. 
Published: March 2009

AbstractInN nanocolumns grown by plasma‐assisted molecular beam epitaxy have been studied by photoluminescence (PL) and photoluminescence excitation (PLE). The PL peak energy was red‐shifted with respect to the PLE onset and both energies were higher than the low temperature band‐gap reported for InN. PL and PLE experiments for different excitation and detection energies indicated that the PL peaks were homogeneously broadened. This overall phenomenology has been attributed to the effects of an electron accumulation layer present atthe non‐polar surfaces of the InN nanocolumns. Variations in the growth conditions modify the edge of the PLE spectra and the PL peak energies evidencing that the density of free electrons can be somehow controlled by the growth parameters. It was observed that In‐BEP and substrate temperature leading to shorter In diffusion lengths diminished the effects of the electron accumulation layer on the optical properties. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Processing approaches of AlGaN/GaN Metal Insulator Semiconductor Hetero Field Effect Transistors (MISHFET) on Si (111) substrates
Authors: Eickelkamp Martin , Ketteniß Nico , Lautensack Christian , Noculak Achim , Kalisch Holger , Jansen Rolf H. , Vescan Andrei 
Published: March 2009

AbstractWe report on the fabrication of AlGaN/GaN MISHFETs using SiO2 and SiN as gate dielectrics. In particular, two different passivation procedures are investigated with respect to the resulting electrical properties. A fluorine based ICP etch step, as used here to remove the gate dielectric prior to passivation layer deposition, is shown to deteriorate the sheet carrier concentration and mobility. Depositing the passivation layer upon the gate dielectric, on the other hand, slightly decreases the sheet resistance as compared to a conventional HFET. Gate diode characteristics reveal significant reduction of gate leakage currents in both, reverse and forward biasing regions, of 1‐2 and up to 6 orders of magnitude, respectively. All devices exhibit more pronounced current collapse compared to a conventional passivated HFET. In addition, a clear depencency on the processing scheme is observed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
222 nm single‐peaked deep‐UV LED with thin AlGaN quantum well layers
Authors: Norimichi Noguchi , Hirayama Hideki , Yatabe Tohru , Kamata Norihiko 
Published: March 2009

AbstractWe fabricated 222 nm AlGaN multi‐quantum well (MQW) deep‐ultraviolet (DUV) light emitting diode (LED) on high quality AlN buffers grown by ammonia (NH3) pulse‐flow multilayer growth method on sapphire substrate. We obtained remarkable enhancement of emission intensity of 220 nm‐band DUV LED by introducing thin (<1.6 nm) quantum well. We realized a single peaked operation of a 222 nm DUV AlGaN MQW LED under pulsed current injection, which is the shortest wavelength of AlGaN LED on sapphire substrate. The maximum output power and external quantum efficiency of 222 nm AlGaN MQW LED were 14 μW and 0.003%, respectively. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Improvement of device characteristics in MIS AlGaN/GaN heterostructure field‐effect transistors by designing insulator/AlGaN structures
Authors: Maeda Narihiko , Hiroki Masanobu , Makimoto Toshiki , Enoki Takatomo , Kobayashi Takashi 
Published: March 2009

AbstractTo obtain a guideline for improving the device performance of GaN‐based Metal‐Insulator‐Semiconductor (MIS) heterostructure field‐effect transistors (HFETs), both HFET and MIS HFETs were fabricated and compared, whose gate capacitances are designed to be equal. With an increased insulator thickness and decreased AlGaN thickness, a high transconductance was successfully obtained that was equivalent to that of HFET, in addition to the reduced gate leakage current in MIS HFETs. Moreover, Al2O3‐based MIS HFETs were revealed to exhibit superior DC characteristics over Si3N4 MIS HFETs. Since deposition of insulators changes the electrical properties of heterostructures, considering the insulator/AlGaN structures as the total barrier layers is effective and indispensable in designing the MIS AlGaN/GaN HFETs. On the basis of the device design, MIS HFETs can be fabricated that exhibit superior device characteristics over those in conventional HFETs. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Energy levels of Nd3+ ions in GaN
Authors: Metcalfe Grace D. , Readinger Eric D. , Shen Hongen , Woodward Nathaniel T. , Dierolf Volkmar , Wraback Michael 
Published: March 2009

AbstractWe report the Stark energy sublevels of Nd3+ ions in GaN grown by plasma‐assisted molecular beam epitaxy as determined by luminescence spectra. The photoluminescence spectra is correlated with transitions from the 4F3/2 doublet state to the 4I9/2, 4I11/2, and 4I13/2 multiplets of the Nd3+ ion for above and below bandgap excitation, with the strongest emission occurring at 1.12 eV (1106 nm). A splitting of the 4F3/2 excited state is determined to be 4.1 meV. From photoluminescence excitation spectra, we also identify the Stark sub‐levels of the excited states 4F5/2, 2H9/2, 4F7/2, 4S3/2, 2G7/2, and 4G5/2. Photoluminescence excitation spectra exhibit an optimal excitation energy of 1.48 eV (836 nm). Site‐selective spectroscopy studies using combined excitation‐emission spectroscopy with confocal microscopy imply enhanced substantial doping at the Ga site. In addition, optical loss and gain measurements of a GaN:Nd waveguide excited above bandgap indicate an internal loss coefficient of ∼6.5 +/– 2 cm–1 and a net gain of ∼ –2 +/– 2 cm–1. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties of ion beam synthesized nitrogen‐rich GaN1‐xAsx
Authors: Chen C.‐H. , Yu K. M. , Walukiewicz W. 
Published: March 2009

AbstractWe have synthesized GaN1‐xAsx alloys using implantation of As into GaN followed by rapid thermal annealing. Appearance of a new As‐derived band at about 2.5 eV below the conduction band edge is confirmed by photomodulated transmission (PT) and photoluminescence (PL). Photoluminescence peaks at about 2.37 eV observed at low temperature in As and Ar implanted Mg doped GaN samples are attributed to emission associated with complexes of damage produced donors and Mg acceptors. The results demonstrate a feasibility of using ion beam synthesis to produce N‐rich group III nitride based highly mismatched alloys. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stacking faults and phase changes in Mg‐doped InGaN grown on Si
Authors: Hawkridge Michael E. , Liliental‐Weber Zuzanna , Yu Kin M. , Reichertz Lothar A. , Schaff William J. , Ager Joel W. , Walukiewicz Wladek 
Published: March 2009

AbstractWe report evidence for the role of Mg in the formation of basal stacking faults and a phase transition in InxGa1‐xN layers doped with Mg grown by molecular beam epitaxy on Si (111) substrates with AlN buffer layers. Several samples with varying In content between x ∼ 0.1 and x ∼ 0.3 are examined by transmission electron microscopy and other techniques. High densities of basal stacking faults are observed in the central region of the InGaN layer away from the substrate or layer surface, but at varying depths within this region. Selected area diffraction patterns show that while the InGaN layer is initially in the wurtzite phase (and of good quality) AlN buffer layer, there is a change to the zinc blende phase in the upper part of the InGaN layer. SIMS measurements show that the Mg concentration drops from a maximum to a steady concentration coinciding with the presence of the basal stacking faults. There is little change in In or Ga concentrations in the same area. High‐resolution electron microscopy from the area of the stacking faults confirms that the change to the cubic phase is abrupt across one such fault. These results indicate that Mg plays a role in the formation of stacking faults and the phase change observed in InxGa1‐xN alloys. We also consider the role of In in the formation of these defects. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Low‐temperature growth of InGaN/GaN nano‐islands investigated by grazing‐incidence X‐ray diffraction
Authors: Schmidt Th. , Flege J. I. , Siebert M. , Figge S. , Yamaguchi T. , Hommel D. , Falta J. 
Published: March 2009

AbstractGrazing‐incidence X‐ray diffraction (GIXRD) has been used to study the structural properties of nanoscale In‐GaN/GaN(0001) islands, and especially the influence of GaN low‐temperature overgrowth of such structures on their strain state, chemical composition and defect structure. Prior to overgrowth, the presence of almost completely relaxed islands with a very high In content is deduced from the diffraction data. After cap layer growth, the In content is found to be significantly reduced and a broad distribution of composition and strain observed. In case of multiple InGaN island layers separated by GaN spacer layers, additional diffraction spots appear, allowing to identify the formation of cubic nitride material due to the low growth temperature (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spontaneous stratification of InGaN layers and its influence on optical properties
Authors: Liliental‐Weber Z. , Yu K.M. , Hawkridge M. , Bedair S. , Berman A.E. , Emara A. , Domagala J. , Bak‐Misiuk J. 
Published: March 2009

AbstractTransmission Electron Microscopy, high resolution X‐ray diffraction and reciprocal space maps, Rutherford Back Scattering and photoluminescence were applied to study InGaN layers grown by MOCVD with increasing layer thickness (100 nm to 1000 nm) and nominally constant In concentration of 10%. Spontaneous stratification of the layer has been found. A strained layer with lower than nominal In content was found in direct contact with the underlying GaN followed by relaxed layers with a nominal or higher In concentration. A high density of randomly distributed stacking faults as well as domains with cubic structure and closely distributed stacking faults (polytype‐like) were present in the thicker layers. Strong corrugation of the thicker sample surface was observed. The appearance of multiple photoluminescence line positions was related not only to the spontaneously formed layers with different In content, but also to the structural planar defects formed in the thicker layers. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Studies of electrical resistance in Ni75Cr7Si7.5Mn10.5 and Ni80.5Cr4.2Si6.5Mn5B3.8 glass‐coated wires
Authors: García C. , Zhukova V. , Val J. J. del , Blanco J. M. , Zhukov A. 
Published: March 2009

AbstractIn this paper we studied thermal stability of Ni75Cr7Si7.5Mn10.5 and Ni80.5Cr4.2Si6.5Mn5B3.8 glass coated microwires with metallic nucleus diameters ranging between 10 μm and 20 μm using electrical resistance measurements, X‐ray diffraction and DSC methods. Electrical resistance was measured during Joule heating of the sample i.e. flowing the DC current. X‐ray diffraction was used to determine the crystalline structure in as‐prepared microwires.It was found that electrical resistance per length, ρ, depends on the sample geometry. Besides this dependence is opposite for Ni75Cr7Si7.5Mn10.5 and Ni80.5Cr4.2Si6.5Mn5B3.8 glass coated microwires. Such dependences have been related with effect of rapid solidification conditions on the grain sizes and consequently on grain growth process during annealing. Temperature coefficient of resistivity in the case of Ni75Cr7Si7.5Mn10.5 microwires is much smaller (about 5 times smaller). Considerable dependence of the current density for beginning of phase transition on metallic nucleus diameter has been attributed to the thermal transfer conditions. Efficiently of joule heating for the case of thinner microwires is smaller and the current density for achieving the phase transition‐higher. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Lipophilicity Studies on Pyrrolyl‐Acetic Acid Derivatives. Experimental Versus Predicted logP Values in Relationship with Aldose Reductase Inhibitory Activity
Authors: Chrysanthakopoulos Marios , Koletsou Antigoni , Nicolaou Ioannis , Demopoulos Vassilis J. , Tsantili‐Kakoulidou Anna 
Published: March 2009

AbstractThe lipophilicity of a series of pyrrolyl‐acetic acid derivatives, inhibitors of the aldose reductase enzyme, was assessed by direct partitioning experiments in the n‐octanol–water system. Distribution coefficients concerning both the neutral and the anionic species were compared to calculated values generated by commonly used software. The reliability of the predictions was evaluated considering the absolute differences, as well as the correlation between experimental and predicted logP or logD values. The inferior performance of the different algorithms for logD7.4 prediction should be attributed to additional sources of errors and in particular to the nonsystematic interference of ion pairing in partitioning. Although the traditional fragmental system of Rekker as modified in PrologP (logPCDR) was quite successful in logP estimation of the pyrrolyl‐acetic acid derivatives, the nonlinear artificial neural network module ANN2005, implemented in the same software was found to be more consistent in reflecting the features involved in partitioning process. Plot of experimental logP versus aldose reductase inhibitory activity values revealed a definite trend in biological activity and adequate quantitative relationships were further established if, besides logP, Hammett electronic constant σ or Abraham's hydrogen bond acceptor term was included in the regression equation. Among the calculated logP, logPANN05 and ABlogP showed an analogous trend with biological activity, although leading to equations of inferior quality, whereas the other calculated logP values failed to show any regular pattern.
Range separation combined with the Overhauser model: Application to the H2 molecule along the dissociation curve
Authors: Gori‐Giorgi Paola , Savin Andreas 
Published: March 2009

AbstractThe combination of density‐functional theory with other approaches to the many‐electron problem through the separation of the electron–electron interaction into a short‐range and a long‐range contribution (range separation) is a successful strategy, which is raising more and more interest in recent years. We focus here on a range‐separated method in which only the short‐range correlation energy needs to be approximated, and we model it within the “extended Overhauser approach.” We consider the paradigmatic case of the H2 molecule along the dissociation curve, finding encouraging results. By means of very accurate variational wavefunctions, we also study how the effective electron–electron interaction appearing in the Overhauser model should be to yield the exact correlation energy for standard Kohn‐Sham density functional theory. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Structural and interaction analysis of helical heparin oligosaccharides with the fragment molecular orbital method
Authors: Sawada Toshihiko , Fedorov Dmitri G. , Kitaura Kazuo 
Published: March 2009

AbstractThe fragment molecular orbital method (FMO) was applied to the geometry optimization of several heparin oligosaccharides at the RHF/6‐31(+)G(d) level combined with the polarizable continuum model (PCM). For comparison, GLYCAM force field optimization in explicit solvent was also conducted. Good accuracy of FMO was demonstrated in comparison to ab initio at the MP2/PCM level. The interaction analysis was conducted using the pair interaction energy decomposition analysis (PIEDA), and the role of hydrogen bonding and solvent was elucidated in the helix formation of heparin in solution. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Recent topics in numerical integration
Authors: Cools Ronald , Huybrechs Daan , Nuyens Dirk 
Published: March 2009

AbstractIn this article, we describe some recent topics in the approximation of univariate and multivariate integrals. We especially pay attention to progress in the area of oscillatory integrals and in quasi‐Monte Carlo methods using lattice rules. Many pointers to the relevant literature are provided. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
New aspects in fragmentation of peptide nucleic acids: comparison of positive and negative ions by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry
Authors: Ziehe Matthias , Grossmann Tom N. , Seitz Oliver , Linscheid Michael W. 
Published: March 2009

AbstractThe use of peptide nucleic acids (PNAs) is steadily increasing in biochemistry and diagnostics. So far, PNAs have mostly been investigated using cationic conditions in mass spectrometry. Furthermore, the use of fragmentation techniques developed for peptides and proteins like infrared multiphoton dissociation (IRMPD) and electron capture dissociation (ECD) has barely been examined. However, especially the fragmentation behavior of PNA oligomers in negative ion mode is of high importance, due to the ability to interact with nucleic acids which are almost exclusively analyzed in the negatively charged state. In the current study PNA fragmentations under cationic and anionic conditions were investigated and different fragmentation techniques like collision‐induced dissociation (CID), IRMPD and ECD were applied. Especially when using CID and IRMPD, amide bonds were broken, whereas ECD resulted in the elimination of nucleobases. Differences were also observed between positive and negative ionization, while the sequence coverage for the negative ions was superior to positive ions. The fragmentation behavior using IRMPD led to almost complete sequence coverage. Additionally, in anions the interesting effect of multiple eliminations of HNCO was found. Copyright © 2009 John Wiley & Sons, Ltd.
Doping control analysis of emerging drugs in human plasma – identification of GW501516, S‐107, JTV‐519, and S‐40503
Authors: Thevis Mario , Beuck Simon , Thomas Andreas , Kortner Birthe , Kohler Maxie , Rodchenkov Grigory , Schänzer Wilhelm 
Published: March 2009

AbstractAn important aspect of preventive doping research is the rapid implementation of tests for emerging drugs with potential for misuse into routine doping control assays. New therapeutics of different classes such as PPARδ‐agonists (e.g. GW501516), ryanodine‐calstabin‐complex stabilizers (e.g. S‐107 and JTV‐519), and selective androgen receptor modulators (SARMs, e.g. S‐40503) are currently used for the treatment of particular medical conditions such as metabolic syndrome, cardiac arrhythmia, debilitating diseases and osteoporosis, respectively. Due to their being at an early stage of clinical trials and the limited availability of data on the metabolism and possible renal elimination of the active drugs, the development of protocols for doping control analyses of plasma specimens could be an option for the detection of the circulating agents. The mass spectrometric fragmentation of four emerging drug candidates (GW501516, S‐107, JTV‐519, and S‐40503) was elucidated by positive electrospray ionization and collision‐induced dissociation using a high resolution/high accuracy mass spectrometer. A screening and confirmation procedure was established based on liquid chromatography/tandem mass spectrometry requiring a volume of 100 µL of plasma. Proteins were precipitated using acetonitrile, the specimens were centrifuged and the supernatant analyzed using a triple‐quadrupole mass spectrometer employing multiple reaction monitoring of diagnostic ion transitions. The method was validated with regard to specificity, limits of detection (0.4–8.3 ng/mL), recoveries (72–98%), intraday and interday precisions (12–21%), and ion suppression/enhancement effects. Copyright © 2009 John Wiley & Sons, Ltd.
Critical assessment of the applicability of gas chromatography‐combustion‐isotope ratio mass spectrometry to determine amino sugar dynamics in soil
Authors: Decock Charlotte , Denef Karolien , Bodé Samuel , Six Johan , Boeckx Pascal 
Published: March 2009

AbstractAmino sugars in soils have been used as markers of microbial necromass and to determine the relative contribution of bacterial and fungal residues to soil organic matter. However, little is known about the dynamics of amino sugars in soil. This is partly because of a lack of adequate techniques to determine ‘turnover rates’ of amino sugars in soil. We conducted an incubation experiment where 13C‐labeled organic substrates of different quality were added to a sandy soil. The objectives were to evaluate the applicability of compound‐specific stable isotope analysis via gas chromatography‐combustion‐isotope ratio mass spectrometry (GC‐C‐IRMS) for the determination of 13C amino sugars and to demonstrate amino sugar dynamics in soil. We found total analytical errors between 0.8 and 2.6‰ for the δ13C‐values of the soil amino sugars as a result of the required δ13C‐corrections for isotopic alterations due to derivatization, isotopic fractionation and analytical conditions. Furthermore, the δ13C‐values of internal standards in samples determined via GC‐C‐IRMS deviated considerably from the δ13C‐values of the pure compounds determined via elemental analyzer IRMS (with a variation of 9 to 10‰ between the first and third quartile among all samples). This questions the applicability of GC‐C‐IRMS for soil amino sugar analysis. Liquid chromatography‐combustion‐IRMS (LC‐C‐IRMS) might be a promising alternative since derivatization, one of the main sources of error when using GC‐C‐IRMS, is eliminated from the procedure. The high 13C‐enrichment of the substrate allowed for the detection of very high 13C‐labels in soil amino sugars after 1 week of incubation, while no significant differences in amino sugar concentrations over time and across treatments were observed. This suggests steady‐state conditions upon substrate addition, i.e. amino sugar formation equalled amino sugar decomposition. Furthermore, higher quality substrates seemed to favor the production of fungal‐derived amino sugars. Copyright © 2009 John Wiley & Sons, Ltd.