bluuebunny/crossref_metadata_2025 huggingface dataset:
The equilibration of intrachain and interchain excitations in aggregates of a cyano‐substituted phenylene vinylene polymer
Authors: Miller Paul F , de Souza Melanie M , Moratti Stephen C , Holmes Andrew B , Samuel Ifor DW , Rumbles Garry
Published: June 2006

Aggregates formed in dilute solutions of poly[2,2′‐dimethoxy‐5,5′‐di‐(2″,7″‐dimethyloctyloxy)‐dicyano‐di‐p‐phenylene vinylene], OC1C10‐CNPPV, in toluene exhibit emission from both an intrachain and an interchain excitation that equilibrate on the timescale of the excited states. The position of the equilibrium can be adjusted with temperature, and a binding energy of 130 meV for the interchain species has been determined. A repulsion energy of 350 meV demonstrates that the interchain excitation is not bound in the ground state, indicative of an excited dimer or complex. At ambient temperatures the equilibrated state exhibits a mean photoluminescence quantum yield of 19% that actually decreases with a reduction in temperature, but a mean photoluminescence lifetime of 4.2 ns that shows a moderate increase. These counterintuitive observations, which imply a strong dependence upon temperature of the mean natural radiative lifetime, arise from the relative weighting factors of the two individual natural radiative lifetimes of the interacting species and the dependence upon the position of equilibrium. Copyright © 2006 Society of Chemical Industry
Viscoelastic properties of silica‐grafted poly(styrene–acrylonitrile) nanocomposites
Authors: Goel Vivek , Chatterjee Tirtha , Bombalski Lindsay , Yurekli Koray , Matyjaszewski Krzysztof , Krishnamoorti Ramanan
Published: June 2006

The melt state viscoelastic properties of styrene–acrylonitrile random copolymers grafted to silica nanoparticles and prepared by in situ atom transfer radical polymerization are examined. Linear dynamic oscillatory viscoelastic measurements indicate that nanocomposites with silica contents as low as 1.2 vol % exhibit solid‐like response. Steady shear results in considerable alteration to the mesoscale structure and results in the failure of the Cox‐Merz rule. Flow reversal studies confirm the elastic nature of the mesoscale structure and demonstrate that the relaxation of the flow altered structure is slow, non‐Brownian, and possibly cooperative. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2014–2023, 2006
Decomposition and Ignition of the High‐Nitrogen Compound Triaminoguanidinium Azotetrazolate (TAGzT)
Authors: Tappan Bryce C. , Ali Arif N. , Son Steven F. , Brill Thomas B.
Published: June 2006

The high‐nitrogen compound triaminoguanidinium azotetrazolate (TAGzT) belongs to a class of C, H and N compounds that are free of both oxygen and metal, but retain energetic material properties as a result of their high heat of formation. Its decomposition thus lacks secondary oxidation reactions of carbon and hydrogen. The fact that TAGzT is over 80% nitrogen makes it potentially useful as a gas generant and energetic material with a low flame temperature to increase the impulse in gun or rocket propellants. The burning rate, laser ignition and flash pyrolysis (T‐jump/FTIR spectroscopy) characteristics were determined. It was found that TAGzT exhibits one of the fastest low‐pressure burning rates yet measured for an organic compound. Both the decomposition and ignition behavior of TAGzT are dominated by condensed phase reactions. T‐Jump/FTIR spectroscopy indicates that condensed phase reactions release about 65% of the energy, which helps to explain the high burning rate at low pressure.
Stress and density of defects in Si‐doped GaN
Authors: Chine Z. , Rebey A. , Touati H. , Goovaerts E. , Oueslati M. , Jani B. El , Laugt S.
Published: June 2006

We report a study by photoluminescence (PL), Raman scattering, and highly resolved X‐ray diffraction (HRXRD) of a series of Si‐doped n‐type GaN layers grown by metalorganic vapor phase epitaxy (MOVPE) on sapphire (0001) with the carrier concentration of 2.3 × 1017 – 9 × 1018 cm–3. We found that the band gap reduction deduced from the PL spectra analysis is due to both band gap narrowing (BGN) effect and change of the nature of stress in the GaN:Si layers. The HRXRD spectra show that at high Si‐doping levels (>1.6 × 1018 cm–3) the GaN films become under tensile stress. Progressive decreases of the E2 Raman mode frequency with Si concentration confirm this observation. The stress induced E2 mode frequency shift is estimated to 1.6 cm–1/GPa. Additionally, dislocation densities are determined by HRXRD by employing a model that uses the line width of X‐ray rocking curves. Atomic force microscopy (AFM) is also used to investigate the defect surface structures of GaN:Si layers which are dominated by pinned steps and surface depressions related to threading dislocations. We find that dislocation densities given by AFM measurements are in agreement with those obtained from rocking curve line widths. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulation of impedance and admittance of OLEDs
Authors: Nguyen N. D. , Schmeits M.
Published: June 2006

In this issue's Editor's Choice [1], the electrical characteristics of organic light‐emitting diodes (OLEDs) are calculated for the dc and ac regimes by numerically solving the basic semiconductor equations. The cover picture is taken from a diagram showing the steady‐state electron concentration n0 and the hole concentration p0 for an applied voltage V0 = 3 V as well as the real part of the electron amplitude $ \tilde n $
and the hole amplitude $ \tilde p $ for frequencies of 1 Hz and 105 Hz. α‐NPD and Alq3 molecules being used as active hole‐ and electron‐transporting materials, respectively, are inserted.

The first author is working as a postdoctoral fellow for an European project on OLEDs. His current research interests are the transport properties of organic semiconductors, where the conduction mechanisms and the role of traps are studied.

This issue also contains a second Editor's Choice entitled “AlGaN/AlN distributed bragg reflectors for deep ultraviolet wavelengths” by Craig G. Moe et al. [2] as well as the Feature Article “p‐type transparent conducting oxides” by Su Sheng, Guojia Fang et al. [3].
Spatially resolved cathodoluminescence, photoluminescence, electroluminescence, and reflectance study of GaInN quantum wells on non‐(0001) GaN facets
Authors: Feneberg M. , Schirra M. , Neubert B. , Brückner P. , Scholz F. , Sauer R. , Thonke K.
Published: June 2006

GaInN light emitting diodes have been grown on the {1$ \bar 1 $01} and the {11$ \bar 2 $2} facet of selectively overgrown GaN. Different luminescence measurements with high spectral and spatial resolution have been performed which show strong indications that the piezoelectric fields in the processed devices are diminished increasing the overall efficiency and reducing the carrier lifetime. Furthermore, the growth conditions on such facets different from {0001} result in altered In incorporation as analyzed by spatially resolved cathodoluminescence. The spectral features found by different measurement techniques are correlated and yield important information on the material quality. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dissociation of VGa–ON complexes in HVPE GaN by high pressure and high temperature annealing
Authors: Tuomisto F. , Hautakangas S. , Makkonen I. , Ranki V. , Puska M. J. , Saarinen K. , Bockowski M. , Suski T. , Paskova T. , Monemar B. , Xu X. , Look D. C.
Published: June 2006

We have used positron annihilation spectroscopy to study the high‐pressure annealing induced thermal recovery of vacancy defects in free‐standing GaN grown by hydride vapor phase epitaxy (HVPE). The results show that the in‐grown Ga vacancy complexes recover after annealing at 1500–1700 K. Comparison of the experimental positron data with ab‐initio calculations indicates that the Doppler broadening measurement of the electron momentum distribution is sensitive enough to distinguish between the N and O atoms surrounding the Ga vacancy. We show that the difference between the isolated VGa in electron irradiated GaN and the VGa–ON complexes in highly O‐doped GaN is clear, and the Ga vacancy related defect complexes that start dissociating at 1500 K can be identified as VGa–ON pairs. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The surface diffusion of Ga on an AlGaN/GaN stripe structure in the selective MOVPE
Authors: Narita Tetsuo , Honda Yoshio , Yamaguchi Masahito , Sawaki Nobuhiko
Published: June 2006

The growth of GaN with an AlGaN/GaN heterostructure was attempted on a (111) Si substrate by selective area metal organic vapor phase epitaxy. The GaN obtained was a trapezoidal stripe with (1$ \bar 1 $01) facets on the sides and a (0001) facet on the top. The distribution of the Al composition on the facets was investigated by cathodeluminescence analyses as a function of the position. The surface diffusion of Ga on the (0001) AlGaN facet was studied under various growth conditions. It was found that the diffu‐ sion length is enhanced by elevating the growth temperature or lowering the Al composition. By the temperature dependence of the diffusion length, the activation energy of the Ga species was estimated. The results depended on the Al composition x; 1.23 ± 0.44 eV (x = 0.05), 1.84 ± 0.58 eV (x = 0.10) and 2.72 ± 0.73 eV (x = 0.15). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical and theoretical study of strong electron coupling in double GaN/AlN quantum wells
Authors: Tchernycheva M. , Nevou L. , Doyennette L. , Julien F. H. , Guillot F. , Monroy E. , Remmele T. , Albrecht M.
Published: June 2006

The electronic confinement in GaN quantum wells coupled by an ultra‐thin AlN barrier is investigated both experimentally and theoretically. The strong coupling between the wells is evidenced by the observation of two pronounced intersubband absorptions peaked at around 0.6 and 0.95 eV for 2 monolayer thick AlN coupling barrier. In agreement with calculations, these absorptions are attributed respectively to the transitions between the ground states of the two coupled wells and between the ground state and the excited state delocalized between the two wells. The experimental results provide clear evidence that the potential drop at the GaN/AlN interfaces is not abrupt, but spread over 1 monolayer. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Resonant Raman characterization of InAlGaN/GaN heterostructures
Authors: Cros A. , Cantarero A. , Pelekanos N. T. , Georgakilas A. , Pomeroy J. , Kuball M.
Published: June 2006

InAlGaN/GaN heterostructures and thin films with In composition ranging from 0.03 to 0.1 are characterized by means of Raman scattering excited at various energies in the ultra violet range, tuning the laser excitation energy through the band gap of InxAlyGa1–x–yN. It is shown that the addition of In to the AlyGa1–yN alloy diminishes considerably the vibration energy of the A1(LO) phonon mode. The phonon line is asymmetric on the low energy side, and the asymmetry increases with In content, while the main peak shifts to lower energies. A shift of the phonon energy has also been observed when the excitation energy is close to the absorption edge of the InxAlyGa1–x–yN layer. The nature of this shift is discussed in relation with intrinsic and extrinsic inhomogeneities in the quaternary alloy. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Temperature‐dependent growth and characterization of N‐polar InN films by molecular beam epitaxy
Authors: Wang Xinqiang , Che Song‐Bek , Ishitani Yoshihiro , Yoshikawa Akihiko
Published: June 2006

N‐polar InN films were grown as a function of temperature (∼440–620 °C) on 500 nm thick GaN template by plasma‐assisted molecular beam epitaxy. InN films grown at different temperatures showed different morphologies that could be roughly divided into two regions. Dendritic morphologies could be observed at temperatures lower than 540 °C while step‐flow‐like morphology could be obtained at temperatures higher than 540 °C. Crystalline quality became better with the increase of growth temperature at temperatures lower than 540 °C and almost saturated at higher temperatures. Strong photoluminescence was observed at room temperature and 13 K with the emission peaks at 0.67 and 0.7 eV, respectively. Based on our results, the growth temperature above 540 °C was recommended for N‐polar InN epitaxy. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermodynamics on hydride vapor phase epitaxy of AlN using AlCl3 and NH3
Authors: Kumagai Y. , Takemoto K. , Kikuchi J. , Hasegawa T. , Murakami H. , Koukitu A.
Published: June 2006

A thermodynamic analysis on hydride vapor phase epitaxy (HVPE) of AlN using AlCl3 and NH3 was performed. Regardless of the carrier gas used, partial pressures of Al‐containing gaseous species [AlCl3, AlCl2, AlCl and (AlCl3)2] in equilibrium with AlN are significantly low in the temperature range of 500–1500 °C when the input V/III ratio is above 1. This means that the driving force for AlN growth (ΔPAl) becomes almost equal to the input partial pressure of AlCl3, which is quite different from HVPE of GaN. The good agreement between the calculated and experimental growth rates shows that HVPE of AlN is thermodynamically controlled. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Role of band potential roughness on the luminescence properties of InGaN quantum wells grown by MBE on bulk GaN substrates
Authors: Žukauskas A. , Kazlauskas K. , Tamulaitis G. , Pobedinskas P. , Juršėnas S. , Miasojedovas S. , Ivanov V. Yu. , Godlewski M. , Skierbiszewski C. , Siekacz M. , Franssen G. , Perlin P. , Suski T. , Grzegory I.
Published: June 2006

Role of band potential roughness on luminescence decay time and stimulated emission in InGaN quantum wells (QWs) grown by rf plasma‐assisted molecular beam epitaxy (MBE) on bulk GaN substrates was studied. A high‐photoexcitation regime used ensured conditions similar to those in operating laser diodes. Standard deviation of the potential fluctuations in different thickness InGaN QWs was found to vary in the range of 13–22 meV as revealed by Monte Carlo simulation of localized exciton hopping. A negligible influence of this variation on the luminescence decay time (∼700 ps) and stimulated emission threshold (∼30 kW/cm2) was observed. We attribute this insensitivity to the low density of localized states (∼1 × 1018 cm–3) estimated in our high‐quality QWs grown by MBE, and therefore, assign extended states to be mainly responsible for the properties of highly‐excited luminescence. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transient pump–probe measurements for polarized excitons in strained GaN epitaxial layers
Authors: Ishiguro T. , Toda Y. , Adachi S. , Arita M. , Arakawa Y.
Published: June 2006

We have studied exciton spin relaxation in strained GaN epilayers on various sapphire substrates using spindependent transient reflectivity and three‐pulse four‐wave mixing measurements. Strikingly fast exciton spin relaxation (<1 ps) at 10 K was observed in the lowest exciton level (A‐exciton) both in bulk and GaN layer on c‐sapphire. In contrast, the transient signals in the GaN layer on a‐sapphire show the break down of the spin polarization caused by the exchange interaction. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
In situ and ex situ grazing incidence diffraction anomalous fine structure study of GaN/AlN quantum dots
Authors: Coraux J. , Renevier H. , Proietti M. G. , Favre‐Nicolin V. , Daudin B. , Renaud G.
Published: June 2006

We report on a general method that takes advantage of the full capability of anomalous diffraction and can be applied to the challenging case of small size embedded nanostructures. We study in situ and ex situ GaN Quantum Dots (QDs) grown by Plasma Assisted Molecular Beam Epitaxy (PAMBE), and encapsulated by an AlN epilayer. We investigate the QD strain and composition that are related to size, morphology, and cap layer thickness by means of anomalous diffraction in grazing incidence. The X‐ray energy is tuned across the Ga K‐edge where the Ga atoms scattering power is strongly modified and diffraction becomes chemically selective, giving direct information on composition. Quantitative analysis of the oscillatory extended region above the edge gives information on composition and out‐of‐plane strain of the dots. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New semiconductor alloy GaNAsBi with temperature‐insensitive bandgap
Authors: Yoshimoto Masahiro , Huang Wei , Feng Gan , Oe Kunishige
Published: June 2006

GaNyAs1–x–yBix alloys were grown by molecular beam epitaxy (MBE). Successful incorporation of N and Bi atoms was confirmed and their concentration was evaluated by Rutherford backscattering spectroscopy (RBS) and secondary ion mass spectroscopy (SIMS). Single‐peak photoluminescence (PL) spectra were observed in the temperature range of 10–300 K. The PL peak energy of GaNyAs1–x–yBix alloy decreased with increasing GaBi and GaN molar fractions with redshift coefficients of ∼62 meV/%Bi and ∼130 meV/%N, respectively, at room temperature. The temperature dependence of the PL peak energy in the temperature range of 150–300 K is much smaller than the temperature dependence of the bandgap for InGaAsP. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural evaluation of GaN/sapphire grown by epitaxial lateral overgrowth by X‐ray microdiffraction
Authors: Drakopoulos M. , Laügt M. , Riemann T. , Beaumont B. , Gibart P.
Published: June 2006

Epitaxial Lateral Overgrowth (ELO) has proven to be an efficient technology to significantly decrease the density of extended defects in the 107 cm–2 ranges. In the present work, called the two‐step‐ELO (2S‐ELO) process, only the coalescence boundaries are defective. In addition in this 2S‐ELO modification, the tilt angle between the two laterally overgrowing wings was found to be negligible. The thickness dependence of the crystal quality of an ELO GaN/sapphire was investigated using a 50 × 0.5 µm X‐ray focused beam of the ESRF synchrotron storage ring. Micro diffraction allows following the mechanism of reduction of the density of extended defects. It is evidenced that no tilt occurs during the 2S‐ELO process. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Epitaxial growth and characterization of InN nanorods and compact layers on silicon substrates
Authors: Sánchez‐García M. A. , Grandal J. , Calleja E. , Lazic S. , Calleja J. M. , Trampert A.
Published: June 2006

This work reports on the morphology and optical properties of wurtzite InN layers grown by plasma assisted molecular beam epitaxy (PA‐MBE) on Si(111) substrates. The layer morphology can be controlled by the effective indium to nitrogen molecular flux ratio, from N‐rich conditions that lead to InN nanorods, to stoichiometric conditions leading to compact InN layers. The nanorods deliver a much higher intensity of the photoluminescence emission than compact layers, with a full width at half maximum down to 34 meV, indicative of a high crystal quality. Raman and X‐ray measurements on the InN nanorods and compact layers confirm the practical full relaxation of both types of materials. TEM measurements reveal a perfect epitaxial alignment of Si substrate‐AlN buffer and InN epilayer with clean AlN‐InN interfaces when growth conditions are optimized. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoemission and X‐ray absorption studies of the electronic structure of GaN‐based diluted magnetic semiconductors
Authors: Hwang J. I. , Ishida Y. , Kobayashi M. , Osafune Y. , Mizokawa T. , Fujimori A. , Takeda Y. , Terai K. , Fujimori S‐I. , Saitoh Y. , Muramatsu Y. , Tanaka A. , Kondo T. , Munekata H. , Hashimoto M. , Tanaka H. , Hasegawa S. , Asahi H.
Published: June 2006

We have investigated the electronic structure of Cr‐ and Mn‐doped GaN using photoemission spectroscopy (PES) and X‐ray absorption spectroscopy (XAS). Cr and Mn XAS at the L‐edge have indicated that the Cr and Mn ions are in the tetrahedral crystal field and that their valences are trivalent and divalent, respectively. Upon Cr and Mn doping into GaN, new states were found to form in the band‐gap region of GaN. Resonant photoemission spectroscopy (RPES) has revealed that the main structure of the Cr 3d partial density of states (PDOS) appears within the band gap of GaN while that of the Mn 3d PDOS appears within the valence band of GaN and as a shoulder above the valence‐band maximum of GaN, indicating that the character of the doping‐induced states is different between Ga1–xCrxN and Ga1–xMnxN. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Meta‐GGA calculation of the electronic structure of group III–V nitrides
Authors: Litimein F. , Bouhafs B. , Nouet G. , Ruterana P.
Published: June 2006

The ground state electronic structure of wurtzite AlN, GaN, and InN has been calculated using full‐relativistic all‐electron full‐potential linearized‐augmented plane‐wave method. Several DFT exchange‐correlation functionals, including the recently proposed non‐empirical meta‐generalised gradient approximation (Meta‐GGA) have been used. The role played by relativistic effects and meta‐GGA functional on the band structures and the density of states is discussed. We find that the meta‐GGA improves the accuracy of the structural properties as well as the energies of the semicore d states in both GaN and InN. This new functional slightly outperforms the local density approximation (LDA) and the generalized gradient approximation (GGA) overall as to lattice parameters, bulk modulus, and valence band widths. We find also that the meta‐GGA induced modifications of the band structure are significant, but limited to the valence band states, while leaving all other features identical to LDA and GGA calculations. Finally, our results show that GaN and InN present anomalous dependence of the valence band splitting versus pressure. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
MOVPE growth of InAsN films on GaAs(001) substrates with an InAs buffer layer
Authors: Kuboya S. , Nakajima F. , Katayama R. , Onabe K.
Published: June 2006

InAsN films of N content up to 3.5% without phase separation were grown on GaAs(001) substrates with a 1.9 μm‐thick InAs buffer layer by metalorganic vapor phase epitaxy (MOVPE). In order to grow the InAsN films with a high N content at low temperature that assures a non‐equilibrium growth environment, 1,1‐dimetylhydrazine (DMHy) and tertiarybutylarsine (TBAs), which can be efficiently decomposed at low temperatures, were adopted as the N and As precursors, respectively. The electron concentration evaluated by the Hall measurement increased with increasing N content and the electrons were degenerated, while the fundamental absorption edge which was determined by the FT‐IR absorption spectroscopy showed a blue‐shift with increasing N content. These results indicate that the Burstein–Moss effect (or band filling effect) is dominant over the bandgap reduction expected from the bandgap bowing. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
RF‐MBE growth and structural characterization of cubic InN films on GaAs
Authors: Nakamura T. , Iida K. , Katayama R. , Yamamoto T. , Onabe K.
Published: June 2006

c‐InN (zincblende structure) films have been successfully grown on GaAs(001) substrates by rf‐plasma‐assisted molecular beam epitaxy. The X‐ray diffraction analysis has confirmed the growth of c‐InN films whose growth temperature was 400–550 °C. The structural properties (i.e. surface flatness and crystal quality) of the InN films are obviously improved for the growth condition of the near surface‐stoichiometry at the In‐rich side. By high resolution transmission electron microscopy images and 2θ/ω X‐ray reciprocal space mapping measurements, hexagonal‐phase InN (h‐InN) is found to be generated from c‐InN{111} facets. The volume content of c‐InN is estimated to be ∼82% at maximum based on an analysis of the X‐ray diffraction intensity. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Assessment of phonon mode characteristics via infrared spectroscopic ellipsometry on a‐plane GaN
Authors: Darakchieva V. , Paskova T. , Paskov P. P. , Arwin H. , Schubert M. , Monemar B. , Figge S. , Hommel D. , Haskell B. A. , Fini P. T. , Nakamura S.
Published: June 2006

Generalized infrared spectroscopic ellipsometry was applied to study the vibrational properties of anisotropically strained a‐plane GaN films with different thicknesses. We have established a correlation between the phonon mode parameters and the strain, which allows the determination of the deformation potentials and strain‐free frequency of the GaN A1(TO) mode. These results are compared with previous theoretical and experimental findings and discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micro‐photoluminescence studies of InGaN/GaN quantum dots up to 150 K
Authors: Sebald K. , Lohmeyer H. , Gutowski J. , Yamaguchi T. , Hommel D.
Published: June 2006

We present photoluminescence measurements on single InGaN quantum dots grown by metalorganic vapor phase epitaxy. The spatially and spectrally resolved luminescence properties of the single quantum dots were measured using low‐temperature micro‐photoluminescence spectroscopy. The observed sharp emission lines of the quantum dots were characterized by excitation density dependent measurements. They can easily be observed at temperatures up to 150 K. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analytical model for the quantum‐confined Stark effect including electric field screening by non‐equilibrium carriers
Authors: Bulashevich K. A. , Karpov S. Yu. , Suris R. A.
Published: June 2006

We have derived an analytical approximation for the energy levels in a symmetric quantum well applicable in a wide range of the electric field variation. Suppression of the quantum‐confined Stark effect due to the electric field screening by non‐equilibrium carriers is considered self‐consistently within the perturbation theory. Theoretical predictions are compared with available observations. Specific features of the quantum‐confined Stark effect in light‐emitting diode heterostructures are discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
N‐plasma assisted MBE grown GaN films on Si(111)
Authors: Gangopadhyay Subhashis , Schmidt Thomas , Falta Jens
Published: June 2006

GaN films were grown by rf‐plasma assisted molecular beam epitaxy on nitrified Si(111) surfaces. Scanning tunneling microscopy (STM), low energy electron diffraction (LEED), and X‐ray photoelectron spectroscopy (XPS) have been used to characterize the structural and chemical properties of the GaN films. The XPS results show that GaN growth can be initiated only at temperatures below 650 °C. LEED indicates an improvement of the crystalline quality after introduction of a crystalline Si3N4 interface layer. This is confirmed by STM, where an atomically resolved 3 × 3 reconstruction for thin GaN films is observed as well as a smooth growth morphology. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mapping misorientation and crystallographic tilt in GaN layers via polychromatic microdiffraction
Authors: Barabash R. I. , Ice G. E. , Liu W. , Roder C. , Figge S. , Einfeldt S. , Hommel D. , Katona T. M. , Speck J. S. , DenBaars S. P. , Davis R. F.
Published: June 2006

The spatial distribution of strain, dislocations, and crystallographic orientation in uncoalesced and coalesced GaN layers grown on striped Si or SiC substrates was studied by polychromatic X‐ray microdiffraction and high resolution monochromatic X‐ray diffraction. Tilt boundaries formed at the column/wing interface depending on the growth conditions and geometry of the striped substrate. The measurements revealed that the free‐hanging wings are tilted upward at room temperature. A misorientation between the GaN(0001) and the Si(111) or SiC(0001) surface normal is observed. Distinct structural properties of the pendeo and cantilever epitaxially grown samples are discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Unintentionally doped InN grown onto an atomically flat AlN intermediate layer using plasma‐assisted molecular beam epitaxy
Authors: Wang K. R. , Tu L. W. , Lin S. J. , Chen Y. L. , Jiang Z. W. , Chen M. , Hsiao C. L. , Cheng K. H. , Yeh J. W. , Chen S. K.
Published: June 2006

Unintentionally doped InN has been grown onto an atomically flat AlN intermediate layer on top of the Si(111) substrate using plasma‐assisted molecular beam epitaxy (PA‐MBE). Though there are lots of micrometer‐size indium droplets randomly distributed on the top of the surface, the highest electron mobility of this InN thin film measured at room temperature by van der Pauw method is still higher than 1000 cm2/V s with a carrier concentration of 5–8.9 × 1018 cm–3. A symmetrical X‐ray rocking curve is measured and the full‐width‐at‐half‐maximum (FWHM) of this sample is 1089 arcsec. In the meantime, the threading dislocation (TD) density of this material is estimated to around 9.8 × 108 cm–2 – 7.5 × 109 cm–2 depending on the probing regions that are studied by the etching technique and field‐emission scanning electron microscopy (FE‐SEM). (2 × 1) in situ reflection high‐energy electron diffraction (RHEED) patterns show that this sample is grown under In‐rich environment with possible In‐terminated surface. From the FE‐SEM pictures which were taken from the samples after 10 minutes etching in hydrochloride, the surface morphology shows In‐polarity‐like patterns that coincide with those procured in RHEED. To select and grow a high‐quality laminated AlN as intermediate layer is believed to be the major step in obtaining this high electron mobility InN thin film on Si substrate. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
N‐polarity GaN on sapphire substrate grown by MOVPE
Authors: Matsuoka Takashi , Kobayashi Yasuyuki , Takahata Hiroko , Mitate Toshitugu , Mizuno Seiichiro , Sasaki Atsushi , Yoshimoto Mamoru , Ohnishi Tuyoshi , Sumiya Masatomo
Published: June 2006

N‐polar GaN was grown on (0001) sapphire using two‐step growth technique by MOVPE. In the growth, the key points were the controlling of the density of nuclei in a buffer layer and promoting lateral growth at high temperature. The grown GaN films had mirror‐like smooth surfaces and were proved to have N‐polarity using convergent‐beam electron diffraction and coaxial impact‐collision ion spectroscopy. The FWHM of this GaN in the ω‐scan was also much narrower than the previous reports. The density of threading dislocations was much less than for usual Ga‐polar GaN grown with a GaN or AlN buffer layer by MOVPE and MBE. In PL at room temperature, the strong edge emission was observed as Ga‐polarity. The p‐type conduction in Mg‐doped GaN was also realized by the same methods as for Ga‐polarity. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigating the electrical properties of Si donors in AlxGa1–xN alloys
Authors: James G. R. , Omnès F. , Leitch A. W. R.
Published: June 2006

In this paper a study of the electrical properties of Si‐doped AlxGa1–xN is presented. The AlxGa1–xN layers, grown using the metalorganic chemical vapour deposition technique, were studied using variable temperature Hall effect and persistent photoconductivity measurements. High quality conducting AlxGa1–xN layers were obtained for 0 ≤ x ≤ 0.5, with the mobility decreasing from 215 cm2/V s (GaN) to 10 cm2/V s (Al0.51Ga0.49N), at 300 K. The carrier concentration of these layers was typically between 2.5 × 1018 cm–3 and 7 × 1017 cm–3 at 300 K. For AlxGa1–xN layers with 0 ≤ x ≤ 0.41 the temperature dependence of the carrier concentration between 300 and 15 K could be studied, yielding the Si donor activation energy. The carrier concentrations of higher Al content samples (0.5 ≤ x ≤ 0.65) could not be accurately measured below 300 K, and thus the Si activation energy was obtained from the temperature dependence of the resistivity. It was found that the Si activation energy escalated with increasing Al content of the layers, and followed the trend predicted for a shallow hydrogen‐like donor, up to x = 0.65. Illumination of the samples at low temperature with a blue LED showed that the layers exhibit little persistent photoconductivity, further confirmation that Si remains a shallow donor in AlxGa1–xN. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Site selectivity of Fe3+Gaand the formation of Fe3+Ga–Gaipairs in GaN
Authors: Gehlhoff W. , Azamat D. , Hoffmann A.
Published: June 2006

The electron paramagnetic resonance (EPR) spectra of Fe‐related defects in high quality thick freestanding hydride vapor phase (HVPE) grown GaN have been studied in the X‐ and Q‐band. The dominating part of the complex resonance pattern is due to isolated Fe3+(3d5,S= 5/2) on the two equivalent Ga sites A and B with C3Vpoint symmetry in the hexagonal GaN unit cell. These two physically equivalent sites, caused by the ABAB stacking sequence of the wurtzite structure, can be distinguished by EPR for electron spin systemsS≥ 2. We found a preferential incorporation of Fe in one of the two types of Ga sites. Moreover, despite the strong overlap with the intensive Fe3+transitions we could identify the main part of the additional observed very weak lines asERRORpairs. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Identification of catecholamines in the immune system by desorption/ionization on silicon
Authors: Kraj Agnieszka , Jarzebinska Justyna , Gorecka‐Drzazga Anna , Dziuban Jan , Silberring Jerzy
Published: June 2006

Desorption/ionization from porous silicon dioxide (DIOSD), in combination with a standard matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) instrument, was used for the identification of catecholamines in the human peripheral blood lymphocytes. A routine MALDI‐TOF analysis does not allow for sensitive detection of low molecular mass compounds (i.e. below 400 Da) due to the pronounced background ions arising from the matrix. Therefore, we have tested DIOSD methodology for the identification of catecholamines in the immune system. Using DIOSD, catecholamines were unambiguously identified in the cell extract of peripheral blood lymphocytes at the femtomolar level. The DIOSD extends the possible use of MALDI‐TOF mass spectrometry towards small molecules that were previously detected by other methods. Copyright © 2006 John Wiley & Sons, Ltd.
Mass spectrometry techniques for detection of ligand‐dependent changes in the conformational flexibility of cellular retinol‐binding protein type I localized by hydrogen/deuterium exchange
Authors: Careri M. , Elviri L. , Mangia A. , Zagnoni I. , Torta F. , Cavazzini D. , Rossi G. L.
Published: June 2006

Hydrogen/deuterium exchange, measured by electrospray ionization with orthogonal quadrupole time‐of‐flight mass spectrometry (ESI‐Q‐TOFMS) and by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS), was used as a means to probe and map differences in conformational flexibility between the ligand‐free and ligand‐bound forms of cellular retinol‐binding protein type I. Labelled fragments were obtained by digestion of the protein with pepsin. The differences in space‐resolved time courses of deuterium incorporation identified regions that exhibit a remarkably higher degree of flexibility in the apo‐protein than in the holo‐protein. These segments encompass residues that are thought, on the basis of structural homology of the retinol carrier with other members of the intracellular lipid‐binding proteins family, to belong to the dynamic portal through which all‐trans retinol can access its high‐affinity, solvent‐shielded, binding site. Copyright © 2006 John Wiley & Sons, Ltd.
The complexation of two different ammonium ions with resorcarenes in protic solvent medium investigated by electrospray ionisation Fourier transform ion cyclotron resonance mass spectrometry
Authors: Mäkinen Marko , Karjalainen Antti , Vainiotalo Pirjo
Published: June 2006

The complexations of two ammonium ions (guests) with two resorcarenes (hosts) were investigated using electrospray ionisation Fourier transform ion cyclotron resonance mass spectrometry. Although the two guests and the two hosts were noticeably similar, the quantity of the corresponding supramolecular complexes formed varied significantly due to the differences in host conformations and guest ability to form non‐covalent interactions. Copyright © 2006 John Wiley & Sons, Ltd.
Simultaneous identification and verification of Bacillus anthracis
Authors: Krishnamurthy Thaiya , Hewel Johannes , Bonzagni Neil J. , Dabbs Jason , Bull Robert L. , Yates John R.
Published: June 2006

Specific identification of Bacillus anthracis (B. anthracis) is vital for the accurate treatment of afflicted personnel during biological warfare situations and civilian terrorist attacks. In order to accomplish this, we have subjected the lysates from B. anthracis to affinity purification using monoclonal antibodies for the selected antigenic protein present in the bacteria. The bound antigenic protein was identified by multi‐dimensional protein identification technology (MudPIT) to be a surface layer protein EA1. The same antigen was identified from the lysates from a few strains of B. anthracis demonstrating the observation to be common for B. anthracis strains. Hence, this presents an effective pathway for the identification of the bacteria present in unknown samples of various origins. Generation of a database containing the EA1 protein has been found to be useful in the database search of unknown samples. Published in 2006 by John Wiley & Sons, Ltd.
The effects of in situ chemical oxidation on microbiological processes: A review
Authors: Sahl Jason , Munakata‐Marr Junko
Published: June 2006

The effects of in situ chemical oxidation (ISCO) on biological processes, as reported in the literature, were researched to determine if coupling ISCO with in situ bioremediation could be achieved in field and laboratory experiments. Literature was compiled concerning the effect of ISCO on microbial communities following addition of a chemical oxidant at a range of concentrations designed to treat a variety of subsurface contaminants. The results indicate that although microbial communities may potentially be adversely affected by chemical oxidation in the short term, a rebound of microbial biomass and/or bioremediation activity can be expected. Successfully coupling ISCO with bioremediation in field applications may be a cost‐effective method of achieving risk‐based site remediation goals. © 2006 Wiley Periodicals, Inc.
Advances in photocatalytic remediation technology
Authors: Kittrell J. R. , Dupre Carl R. , Gerrish David A.
Published: June 2006

The cost of remediation at hazardous waste sites is estimated at billions of dollars annually. It is imperative that more cost‐effective remediation technologies be developed, particularly to address the more complex megasites. Chlorinated hydrocarbons represent the major contaminants at many such sites. It has long been recognized that chlorinated hydrocarbons can be destroyed by photocatalytic oxidation. Traditional photocatalysts, however, have often shown inadequate destruction activity, a loss of activity over time, and poor selectivity, thereby producing substantial amounts of phosgene and chloroform by‐products. This article presents results obtained using novel photocatalyst compositions. The results demonstrate the ability to achieve high photocatalytic destruction activity for chlorinated hydrocarbons with full retention of activity over extended time periods and with complete elimination of phosgene and chloroform by‐products. © 2006 Wiley Periodicals, Inc.
Functional correlates of Doppler flow study of the female urethral vasculature
Authors: Yang J.‐M. , Yang S.‐H. , Huang W.‐C.
Published: June 2006

Objectives

To examine the effect of individual patient factors (age, parity, body mass index, menstrual cycle, menopause, hormone replacement therapy, bladder neck position and urethral mobility) on the appearance of Doppler flow in urethral vessels, to investigate the association between the Doppler flow parameters and intrinsic urethral function, storage and voiding, and to explore differences in the urethral vasculature between subjects with and without urodynamic stress incontinence (USI).

Methods

Over a 4‐year period we prospectively performed imaging studies in 355 women, including 244 who denied any lower urinary tract symptoms within the previous 3 months (Group A) and 111 who had had lower urinary tract symptoms (Group B). Studies included morphologic assessment and Doppler flow investigation of the lower urinary tract. Vascular flow velocity and vessel density in the urethral vasculature were measured. For women in Group B, multichannel urodynamic studies were also performed.

Results

The urethral vasculature has five main branches of vessels. Their appearance was not affected by the menstrual cycle or menopause except for those of the anterior vaginal vessel and anterior branch of the middle urethral vessel. Other than that of the posterior urethral vessel, in which there was a correlation with parity, the resistance index (RI) was not affected by individual patient factors. However, there was a correlation between the vascular index (VI) and individual factors such as age (r = −0.336, P = 0.002), body mass index (r = −0.287, P = 0.028), menopause (r = −0.402, P < 0.001), and hormone replacement therapy (r = 0.392, P = 0.027). Only the VI and RI of the posterior urethral vessel correlated significantly with the urethral pressure profile. In subjects with lower urinary tract symptoms, the appearance of the urethral vasculature on power Doppler imaging and the corresponding RI and VI values were not correlated with objective evidence of USI.

Conclusion

Patient factors may affect specific Doppler flow parameters of the urethral vasculature, which are related to intrinsic resting urethral closure. There is no difference in the appearance of the urethral vasculature in subjects with or without USI. Copyright © 2006 ISUOG. Published by John Wiley & Sons, Ltd.
INPLAS ‐ Das Kompetenznetz Industrielle Plasma‐Oberflächentechnik
Authors: Bräuer G. , Brand C. , Baar A. , Bub O.
Published: June 2006

Deutschland gehört zu den Weltmarktführern in der Plasmatechnik und ihren Anwendungen. Dies hat eine vom BMBF im Jahr 2003 in Auftrag gegebene Studie gezeigt. Um die weltweite Spitzenposition zu sichern und auszubauen, ist neben weiteren Fördermaßnahmen, die bereits eingeleitet sind, eine Vernetzung und Bündelung von Einzelaktivitäten notwendig. Aus diesem Grund wurde im Herbst 2005 das Kompetenznetz Industrielle Plasma‐Oberflächentechnik e.V. (INPLAS) gegründet. Die Auftaktveranstaltung fand am 22. März 2006 in Dresden statt. Der Artikel gibt einen Überblick über Ziele und Leistungen des Netzwerks sowie dessen Aufbau und Struktur.
Elephant importation from range countries: ethical and practical considerations for accredited zoos
Authors: Hutchins Michael , Keele Mike
Published: June 2006

Zoo elephant populations are in serious demographic peril. Advances in elephant management and care are expected to lead to improved reproductive success. The existing cohort of reproductively viable adult females is aging, however, and effective changes may not come fast enough to sustain the population over time. If so, importation of captive, semi‐domesticated, and wild elephants from range countries may be necessary for zoo programs to survive. Yet, due to the high profile elephants now have with animal rights activists, there may be increasing legal and political barriers to elephant importation. This makes it especially important that zoos become more proactive in addressing remaining weaknesses in elephant management and care and building the case for elephants in zoos. This article summarizes the key considerations for AZA‐accredited zoos that are contemplating future importations. These include ethical, legal, practical, public relations, and other considerations. The authors strongly recommend that zoos position themselves for possible future importations immediately instead of waiting until the last minute. It is equally critical that zoos recognize their existing vulnerabilities and attempt to address them proactively; only then, can they take control of their own fate and reduce the potential for later regret. Zoo Biol 25:219–233, 2006. © 2006 Wiley‐Liss, Inc.
Who Will be the Shade of Our Tree When You Leave? Collaborating as Women to Advance Community Emancipation
Authors: Daniels Doria
Published: June 2006

In 1994, out of a population of 45 million people an estimated 7.7 million people lived in informal settlements in South Africa (South African Institute of Race Relations, 1994). This article focuses on one community whose residents' desperation to own housing contributed to community disintegration, typified by infighting among women, and threats to human life. Issues of diversity became more prominent and destabilized community‐building efforts. One effort to collaboratively break down barriers that deterred women from working together is presented to illustrate how these women created bonds based on “discovered similarities.” The participatory and personal‐experience approach described here contributed to their becoming active protagonists of their learning and encouraged tolerance and understanding among community women from differing ethnic, linguistic, and political backgrounds. The article concludes with a discussion of the critical importance of recognizing and working with and through differences within the current South African reality.
Where am I? Locating Myself and its Implications for Collaborative Research
Authors: Langhout Regina Day
Published: June 2006

This paper examines how a younger white female graduate student and an African American female undergraduate viewed the relationship between the graduate student and older African American working class women. This relationship was formed around a community garden project. The graduate student understood the relationship to be based on gender and class background similarities; the undergraduate viewed it based on race differences and unexamined white privilege. Both interpretations are challenged as unidimensional. Through this re‐telling, questions are raised about why situating ourselves via our identities is not practiced more frequently. Possible explanations of this lack of attention to situativity include a Cartesian philosophy of science that separates objectivity and subjectivity, a general unawareness of privilege by those who have it, and a dominant scientific discourse that neglects the role of the researcher. This paper illustrates why reflexivity is crucial for the work of community psychology.
Similarity and structure of the ectoparasite communities of rockfish species from the southern Chilean coast in a temporal scale
Authors: GONZÁLEZ M. T. , OLIVA M. E.
Published: June 2006

The understanding of the patterns and processes underlying the structure of parasite communities has progressed significantly in the last years; however, much of the evidence available to date on parasite community comes from unconfirmed studies. In this study the ectoparasite communities of 2 related rockfishes, Sebastes capensis and Helicolenus lengerichi, from the southern Chilean coast (ca. 40 °S) were examined to determine whether their specific compositions are similar, structured in non-random ways, and repeatable among years. From 2001 to 2004, 189 specimens of S. capensis and 101 of H. lengerichi were examined, 10 and 9 parasite species were recorded in S. capensis and H. lengerichi, respectively. Component ectoparasite communities of these hosts were taxonomically similar (60%), but the abundances and prevalences of their parasites differed significantly among years and between hosts. The most prevalent species were Lepeophtheirus chilensis, and Microcotyle sp. for S. capensis, and Microcotyle sp., Juanetia continentalis, and Interniloculus chilensis for H. lengerichi. Infracommunities of S. capensis showed higher species richness and parasite numbers than those of H. lengerichi. The similarity among infracommunities (measured as parasite abundance) varied significantly among years both within and between hosts. Despite this, temporal nestedness patterns were observed in infracommunities of these hosts, suggesting that their ectoparasite communities are structured and might be predictable in time, at least in the southern Chilean coast where they share the same habitat.