bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transmission electron microscopy and theoretical analysis of AuCu nanoparticles: Atomic distribution and dynamic behavior
Authors: Ascencio J.A. , Liu H.B. , Pal U. , Medina A. , Wang Z.L. 
Published: May 2006

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

AbstractSummary: Salicylic acid‐doped hollow polyaniline and rhodamine B composite spheres (1.9–3.3 µm in average diameter) with a high conductivity (≈10−1 S · cm−1) and a strong fluorescence were synthesized by a template‐free method. The morphologies, electrical and fluorescent properties of the hollow composite microspheres can be adjusted by changing the content of RhB in the composites opening a simple route to preparing multi‐functionalized micro/nanostructures.SEM and TEM images of PANI‐SA/RhB synthesized under concentration of 1 × 10−3 MRhB.imageSEM and TEM images of PANI‐SA/RhB synthesized under concentration of 1 × 10−3 MRhB.
Protein Sequences as Literature Text
Authors: Vasilevskaya Valentina V. , Gusev Leonid V. , Khokhlov Alexei R. 
Published: May 2006

AbstractSummary:We have performed analysis of protein sequences treating them as texts written in a “protein” language. We have shown that repeating patterns (words) of various lengths can be identified in these sequences. It was found that the maximum word lengths are different for proteins belonging to different classes; therefore, the corresponding values can be used to characterize the protein type. The suggested technique was first applied to analyze (decompose into words) normal (literature) texts written as a gapless symbolic sequence without spaces and punctuation marks. The tests using fiction, scientific, and popular scientific English texts proved the relative efficiency of the technique.Maximum word length for various proteins:—fibrillar proteins,—globular proteins,—membrane proteins.magnified imageMaximum word length for various proteins:—fibrillar proteins,—globular proteins,—membrane proteins.
Molecular theory of field‐dependent proton spin‐lattice relaxation in tissue
Authors: Halle Bertil 
Published: May 2006

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

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

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

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

AbstractAlyGaxIn1–x–yN epilayers with diverse Al and In mole fractions have been grown by plasma‐assisted molecular‐beam epitaxy on GaN‐on‐sapphire. Conventional transmission electron microscopy characterization reveals threading dislocations behavior as commonly observed in such heterostructures, arising from the Al2O3/GaN interface. As an outstanding result, electron diffraction technique reveals ordering along the [0001] direction in quaternary AlGaInN epilayers grown at 650 ºC. This structural ordering is enhanced by high Al concentration. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Orientation‐dependent properties of aluminum nitride single crystals
Authors: Bickermann M. , Heimann P. , Epelbaum B. M. 
Published: May 2006

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

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

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

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

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

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

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

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

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

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

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

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

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

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