bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simulation insights on the structure of nanoscopically confined poly(ethylene oxide)
Authors: Kuppa V. , Menakanit S. , Krishnamoorti R. , Manias E. 
Published: November 2003

AbstractWe employ atomistic computer modeling to investigate the structure and morphology of poly(ethylene oxide) (PEO) chains confined in 1‐nm slit pores defined by montmorillonite silicate layers. Molecular dynamics computer simulations reveal the Li+ cations to be located in the immediate vicinity of the silicate surfaces and PEO to adopt highly amorphous conformations in a liquidlike bilayer across the slit pores. Despite the orienting influence of the parallel stacked silicate walls, PEO shows no indication of crystallinity or periodic ordering; in fact, for all temperatures simulated, it is less ordered than the most disordered bulk PEO system. These amorphous PEO film configurations are attributed to the combination of severe spatial confinement and the strong coordination of ether oxygens with the alkali cations present in the interlayer gallery. These conclusions challenge the picture traditionally proposed for intercalated PEO, but they agree with a plethora of experimental observations. Indicatively, the simulation predictions are confirmed by wide‐angle neutron scattering and differential scanning calorimetry experiments on PEO/montmorillonite intercalates. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3285–3298, 2003
Deintercalation of a chemically switchable polymer from a layered silicate nanocomposite
Authors: Vohra Vaishali R. , Schmidt Daniel F. , Ober Christopher K. , Giannelis Emmanuel P. 
Published: November 2003

AbstractThe phenomenon of intercalation is widely known as a key process in the area of polymer/layered silicate nanocomposites. In the formation of such nanocomposites, a polymer chain is intercalated between the layers of a layered (silicate) host, typically giving a well‐ordered multilayered stack with a repeat distance of only a few nanometers. Intercalated systems are excellent models for studies of confined geometries, and they often display enhanced material properties as well. In this study, we examined a series of polymers in which it was possible to reverse the intercalation process (i.e., to achieve deintercalation). Homopolymers and copolymers of poly(methyl methacrylate) and poly(tetrahydropyranyl methacrylate) (PTHPMA) were intercalated into an organically modified synthetic fluoromica. Thermally induced deprotection of the tetrahydropyranyl group resulted in the transformation of PTHPMA into poly(methacrylic acid), which was then observed to deintercalate from the silicate host. X‐ray diffraction and thermogravimetric analysis were used to study the deintercalation process. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3151–3159, 2003
11th International Conference on II–VI Compounds (II–VI 2003), Niagara Falls, USA, 22–26 September 2003
Authors: Gutowski J. 
Published: November 2003

AbstractConference Reports are meant to offer an authoritative view on a recently held scientific meeting rather than a comprehensive list of the conference presentations. Authors are invited to describe what they feel were the most interesting contributions.The full Proceedings of the 11th International Conference on II–VI Compounds (II–VI 2003) will be published in phys. stat. sol. (c) in early Spring 2004. Conference papers will also be published in phys. stat. sol. (b). (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exciton–exciton correlation effects on FWM in GaN
Authors: Adachi Satoru , Sasakura Hirotaka , Muto Shunichi , Hazu Kouji , Sota Takayuki , Chichibu Shigefusa F. , Mukai Takashi 
Published: November 2003

AbstractBound and unbound biexcitons in a free‐standing bulk GaN are investigated by time‐integrated and spectrally‐resolved four‐wave mixing measurements, where the formation of hetero‐biexcitons that consist of A and B excitons (XXAB) as well as A biexcitons and their unbound biexciton are clearly observed. Through the FWM spectra and delay‐time dependence, it is found that the interaction between A and B excitons gives rise to the phase shifts of the quantum beating and the energy shifts of the spectra, which is considered as the effect of the unbound state of XXAB (i.e. XX*AB). This interaction is found to play an important role in the FWM signals for all polarizations. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polarity dependent properties of GaN layers grown by hydride vapor phase epitaxy on GaN bulk crystals
Authors: Tuomisto F. , Suski T. , Teisseyre H. , Krysko M. , Leszczynski M. , Lucznik B. , Grzegory I. , Porowski S. , Wasik D. , Witowski A. , Gebicki W. , Hageman P. , Saarinen K. 
Published: November 2003

AbstractHydride vapor phase epitaxy (HVPE) was used to grow nominally undoped 30–160 μm thick GaN layers on both the Ga and N polar sides of high pressure grown single crystal GaN substrates. Measurements of photoluminescence, infrared reflectivity, μ‐Raman scattering and positron annihilation were performed on the samples. The obtained characteristics are strongly dependent on the growth polarity. The material grown on the N polar side has identical properties with the substrate bulk GaN crystals, i.e. high free electron, impurity and point defect concentrations. In the layers grown on the Ga polar side, these concentrations are very low. The results show that the structural and optical properties of homoepitaxial GaN layers grown by HVPE are homogeneous across the layer thickness, which is in contrast to the heteroepitaxial HVPE GaN layers. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of InGaN/GaN single quantum wells by X‐ray scattering and transmission electron microscopy
Authors: Smeeton T. M. , Kappers M. J. , Barnard J. S. , Vickers M. E. , Humphreys C. J. 
Published: November 2003

AbstractA set of InxGa1−xN/GaN single quantum wells (SQWs) were analysed using X‐ray reflectivity (XRR), high resolution X‐ray diffraction (HRXRD) and high resolution transmission electron microscopy (HRTEM). A method for determining the thickness and composition of the single quantum well layers using only X‐ray scattering measurements is described – the results agree very closely with those determined from HRTEM analysis of the same samples. HRTEM lattice fringe images obtained from InGaN subjected to minimal exposure to the electron beam were used to determine local lattice parameter maps. These show the indium to be distributed uniformly within the alloy. The electron beam very rapidly caused damage to the InGaN which could be falsely interpreted as an inhomogeneous indium distribution. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characteristics of AlN growth on vicinal SiC(0001) substrates by molecular beam epitaxy
Authors: Brault J. , Bellet‐Amalric E. , Tanaka S. , Enjalbert F. , Le Si Dang D. , Sarigiannidou E. , Rouviere J.‐L. , Feuillet G. , Daudin B. 
Published: November 2003

AbstractWe present the growth of AlN films on vicinal substrates of SiC(0001). The layers were grown by plasma‐assisted molecular beam epitaxy (PAMBE) and examined in‐situ using reflection high‐energy electron diffraction (RHEED). Morphological and structural properties were characterized by atomic force microscopy (AFM) and High Resolution X‐Ray Diffraction (HRXRD), respectively. The obtained results by AFM show two main differences with AlN films grown on nominally flat SiC substrates: a) the absence of spiral growth hillocks, and b) the formation of predominantly straight steps. HRXRD measurements on misoriented substrate rocking curves have revealed good structural quality of AlN films (tilt and twist), as well as a disorientation of the c‐planes of the AlN with respect to the substrate. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of oxygen on luminescence and vibrational spectra of Mg‐doped GaN
Authors: Koide Yasuo , Walker D. E. , White B. D. , Brillson L. J. , Itoh T. , McCreery R. L. , Murakami Masanori , Kamiyama S. , Amano H. , Akasaki I. 
Published: November 2003

AbstractMg‐doped GaN epilayers are analyzed by Raman and low‐energy electron‐excited nanoluminescence (LEEN) spectroscopies before and after oxygen ambient annealing at temperatures from 450 to 550 °C. Annealing as low as 450 °C shows the appearance of a local vibrational mode of the MgGa acceptor. Correspondingly, LEEN emission at 2.8 eV increases and that at 3.27 eV decreases after annealing in oxygen ambient. On the other hand, electron beam treatment decreases 2.8 eV emission and increases 3.27 eV emission. These luminescence properties are explained by a donor‐acceptor pairs transition model due to hydrogen‐related deep and shallow donors and MgGa acceptor. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The effect of Gallium gallium adsorbate on SiC(0001) surface for GaN by MBE
Authors: Jeganathan K. , Shimizu M. , Ide T. , Okumura H. 
Published: November 2003

AbstractThe adsorption of Gallium gallium (Ga) (Ga) on SiC(0001) reveals a well‐ordered $\sqrt 3 \times \sqrt 3$ − R30° and 3 × 3 surface reconstructions with respect to different Ga adatom coverage. The GaN nucleation behaviours on $\sqrt 3 \times \sqrt 3$ R30° and 3 × 3 surfaces are significantly different. The GaN nucleates randomly in three‐dimensional 3D islands on the $\sqrt 3 \times \sqrt 3$ R30° surface due to unoccupied surface states of dangling bonds. In contrast the 3 × 3 surface was found to be highly suitable for two‐dimensional (2D) GaN nuclei which promotes a step‐flow growth subsequently. The GaN growth kinetics is found to depend on the Ga atomistic process of SiC (0001). (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Impact of exciton localization on the optical properties of non‐polar M‐plane In0.1Ga0.9N/GaN multiple quantum wells
Authors: Jun Sun Yue , Brandt Oliver , Cronenberg Sven , Grahn Holger T. , Ploog Klaus H. 
Published: November 2003

AbstractLocalized states in M‐plane In0.1Ga0.9N/GaN multiple quantum wells without the influence of internal electrostatic fields along the growth direction are studied. The recombination dynamics originates from simultaneous exciton relaxation towards a band of localized states and radiative recombination. The presence of localized states further manifests itself in the anomalous temperature dependence of the photoluminescence line width. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical and magnetic properties of the DyN/GaN superlattice
Authors: Zhou Y. K. , Kim M. S. , Teraguchi N. , Suzuki A. , Nanishi Y. , Asahi H. 
Published: November 2003

AbstractFerromagnet/semiconductor DyN/GaN superlattice structures were grown on SiC substrate by radio frequency molecular beam epitaxy. Formation of DyN was confirmed by X‐ray diffraction measurements. The temperature dependence of the photoluminescence (PL) spectra for the DyN/GaN superlattice and GaDyN samples was studied. Sharp PL peaks from two samples showed no shift with temperature, indicating the intra‐atomic f–f transition at Dy ions. Comparison of the PL spectra for the DyN/GaN superlattice and GaDyN suggests that GaDyN is formed at the GaN/DyN interface. The DyN/GaN superlattice exhibited two ferromagnetic components; one is major at low temperatures (<50 K) and the other is major at high temperatures (>350 K). The former shows large coercivity Hc of about 1800 Oe at 7 K, which was originated from DyN layers. The latter may come from GaDyN, which was formed at the GaN/DyN interface. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structure analysis of ELO‐GaN using a 2 × 4 μm2 micro‐beam X‐ray of an 8‐GeV storage ring
Authors: Miyajima T. , Takeya M. , Goto S. , Tomiya S. , Takeda S. , Kurihara H. , Watanabe K. , Kato M. , Hara N. , Tsusaka Y. , Matsui J. 
Published: November 2003

AbstractWe investigated the micrometer‐scale structure of epitaxially laterally overgrown GaN (ELO‐GaN) using a 2 × 4 μm2 micro‐beam X‐ray of an 8‐GeV storage ring. The GaN (0 0 0 12) rocking curve of the wing region had a sharp peak with a FWHM of 46 arcsec, but that of the seed region had several broad peaks. This peak‐narrowing corresponds to the reduction of the threading dislocation (TD) density and to the increase of grain size. The grain in the wing region was typically 5 μm × 5 μm and extended along the ELO stripe of GaN 〈100〉. On the other hand, a larger grain with a 10 μm × 10 μm was observed in the wing region of another ELO‐GaN sample which did not coalesce during the growth. We conclude that the homogeneity of the GaN c‐surface tilting can be declined by coalescence of the wing regions. We believe that this inhomogeneity of the GaN c‐surface tilting and the grain size strongly affect the performance of GaN‐based laser diodes grown on ELO‐GaN. Moreover, GaN c‐surface tilting of 81.5 arcsec was observed in the wing region of ELO‐GaN although no SiO2 mask was used. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of heavy nitrogen doping in III–V semiconductors – How well does the conventional wisdom holdfor the dilute nitrogen “III–V‐N alloys”?
Authors: Zhang Yong , Fluegel B. , Hanna M. C. , Geisz J. F. , Wang L.‐W. , Mascarenhas A. 
Published: November 2003

AbstractAlthough heavily N doped III–V semiconductors are frequently referred to as dilute nitrogen III–V‐nitride alloys in general, it is important to realize that there are some subtle but important differences among them. In the indirect gap semiconductor GaP, since even a single N impurity can have a bound state, as far as the absorption near the band gap is concerned, it is difficult to describe GaP:N as an alloy. The N induced bound states (a hierarchy of impurity complexes) can in fact give rise to rather strong absorption below the indirect band gap, which effectively reduced the energy of the “absorption edge”, but the position of the absorption edge cannot be defined in a conventional way. In the direct gap semiconductor GaAs, a single N impurity does not form a bound state but instead has a resonant state above the conduction band edge. In this aspect, GaAs:N is similar to the situation in a conventional alloy, say, GaAs:P, except that the perturbation of N to the host is much stronger than that of P. However, because in reality N incorporation is typically in a random manner and a cluster as small as one N pair can generate bound states, the permissible region for GaAs:N to behave as a regular alloy is in fact rather limited, i.e., only when the N concentration is low enough so that the N pair and cluster states do not significantly interact with the host. In this study, a precise tracking of the evolution of the host and N induced impurity states will be offered for the two prototype systems, GaAs:N and GaP:N, with x varying from as low as ∼10−5 to ∼10−2. Such a study gives valuable insight to the underlying physics of the material evolution, sets up a bench‐mark for testing the theoretical modeling of this type of system, and serves to enhance our understanding of the behavior of isoelectronic impurities in semiconductors in general. The dissimilarity between GaP:N and GaAs:N indicates that seeking a unified model for all the isoelectronic doping systems is unrealistic. Our study also indicates that for strongly perturbed systems like GaP:N and GaAs:N, certain materials properties could be less well defined or not uniquely defined, as compared to those in other conventional semiconductor alloys. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermal conductivity of GaN crystals grown by high pressure method
Authors: Jeżowski A. , Stachowiak P. , Plackowski T. , Suski T. , Krukowski S. , Boćkowski M. , Grzegory I. , Danilchenko B. , Paszkiewicz T. 
Published: November 2003

AbstractResults of measurements of thermal conductivity κ of bulk GaN crystals in the temperature interval4.2–300 K are reported. Experiments were performed on three types of GaN material: (i) single, high‐pressure grown GaN crystals showing highly n‐type conductivity, (ii) on bulk Mg doped GaN crystals with slightly p‐type conductivity, (iii) on homoepitaxial GaN layer grown by hydride vapour phase epitaxy (HVPE) on bulk GaN crystal. For the n‐GaN crystals, the record thermal conductivity value κmax is equal to 1600 W/m × K at Tmax = 45 K, and κ ≅ 230 W/m K at 300 K. It is suggested that for this crystal and for T ≥ Tmax the contribution of Umklapp phonon scattering processes dominate in the heat transport processes. A heavily Mg doped crystal and HVPE GaN layer on bulk GaN show much lower thermal conductivity in the whole applied temperature region. The temperature dependence of κ shows the importance of point defects (impurities, vacancies) in determination of the thermal resistance of GaN bulk crystals. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Control of electron density in InN by Si doping and optical properties of Si‐doped InN
Authors: Higashiwaki M. , Inushima T. , Matsui T. 
Published: November 2003

AbstractWe have studied Si‐doping profiles of InN films grown by plasma‐assisted molecular‐beam epitaxy and their photoluminescence (PL) properties. We confirmed experimentally that Si acts as a donor in InN. Undoped and Si‐doped InN films with electron densities (n) of 1.6 × 1018 − 1.4 × 1019 cm−3 showed clear n dependences of PL properties. The PL peak shifted to the higher energy side with increasing n, and the PL intensity decreased with increasing n. These were characteristics of degenerated semiconductors with a large density of defects and/or dislocations. The band‐gap energy of degenerated InN films with n = 1.6 × 1018 − 4.7 × 1018 cm−3 was estimated to be about 0.6 eV by assuming a nonparabolic conduction band and a constant band‐renormalization effect. By taking the band‐gap shrinkage of about 20 meV due to the conduction‐band renormalization into account, we suggest that the band‐gap energy of intrinsic InN is 0.6–0.65 eV. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization of the growth of Ga1− xMnxN epilayers using plasma‐assisted MBE
Authors: Kuroda S. , Bellet‐Amalric E. , Biquard X. , Cibert J. , Giraud R. , Marcet S. , Mariette H. 
Published: November 2003

AbstractA systematic compositional and structural study of GaN : Mn epilayers grown by molecular beam epitaxy (MBE) was performed, with a special attention to the dependence on the growth conditions. The “growth diagram” related to the Ga/N flux ratio for GaN was modified by adding Mn flux. In particular, the stable Ga‐bilayer coverage on the surface for the Ga‐rich condition was reduced in the presence of Mn. The Mn incorporation in the epilayers was found to be strongly dependent on the Ga/N flux ratio. The X‐ray diffraction (XRD) and extended X‐ray absorption fine structure (EXAFS) measurements revealed a clear contrast between the precipitation of a perovskite compound GaMn3N at Mn compositions higher than 1.7%, and the single phase of the wurtzite Ga1−xMnxN at lower Mn compositions. The single‐phase epilayers (x ≤ 1.7%) exhibited intrinsic ferromagnetic behaviors at room temperature. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of GaN on a‐plane sapphire: in‐plane epitaxial relationships and lattice parameters
Authors: Paskova T. , Darakchieva V. , Valcheva E. , Paskov P. P. , Monemar B. , Heuken M. 
Published: November 2003

AbstractWe have studied GaN films grown on a‐plane sapphire substrates by both hydride vapor phase epitaxy (HVPE) and metalorganic vapor phase epitaxy (MOVPE). The in‐plane orientation relationships between the epitaxial films and the substrate are determined to be [11–20]GaN ∥ [0001]sapphire and [1–100]GaN ∥ [1–100]sapphire in the HVPE growth, while [1–100]GaN ∥ [0001]sapphire and [11–20]GaN ∥ [1–100]sapphire are found in the MOVPE growth. The different orientation preferences are attributed to the atom termination of the sapphire surface determined by the substrate treatment used in the different growth methods. The effect of the lattice matches on the in‐plane lattice parameters and strain anisotropy in the two cases is studied. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Carrier capture times in InGaN/GaN multiple quantum wells
Authors: Fan W. H. , Olaizola S. M. , Wang T. , Parbrook P. J. , Wells J.‐P. R. , Mowbray D. J. , Skolnick M. S. , Fox A. M. 
Published: November 2003

AbstractWe have investigated the temperature and carrier density dependence of the carrier capture time of two optically pumped InGaN/GaN multiple quantum well laser structures by subpicosecond time‐resolved differential transmission spectroscopy. We find that the carrier capture time varies significantly with both the temperature and the carrier density. The carrier density dependence is consistent with screening of piezoelectric fields, in agreement with theoretical predictions. The sample with the lower threshold for stimulated emission has a faster carrier capture rate, which highlights the importance of carrier capture for the lasing process. At room temperature the capture time is less than 1.2 ps in both samples. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Sub‐microscopic transient lens spectroscopy of InGaN/GaN quantum wells
Authors: Okamoto Koichi , Fujita Shigeo , Kawakami Yoichi , Scherer Axel 
Published: November 2003

AbstractTransient lens (TL) spectroscopy was developed with sub‐micrometer spatial resolution to observe the temporal and special behavior of the nonradiative processes of carrier dynamics in InGaN/GaN quantum wells (QW). We have observed the carrier density dynamics and the thermal dynamics in the TL signals with a nanosecond pulsed laser. We have also observed TL and photoluminescence (PL) signals by using near‐field scanning optical microscopy (NSOM), and find that both PL and TL images are correlated and exhibit submicron scale spatial inhomogeneity. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Shallow donors in GaN
Authors: Freitas J. A. , Moore W. J. , Shanabrook B. V. , Braga G. C. B. , Koleske D. D. , Lee S. K. , Park S. S. , Han J. Y. 
Published: November 2003

AbstractHigh‐resolution, variable temperature PL experiments were performed in the spectral region associated with recombination processes involving the ground and excited states of the neutral donor bound excitons. High‐resolution infrared measurements in combination with high‐sensitive SIMS unambiguously identified Si and O shallow donors and yield their ground state binding energies. These binding energies are in excellent agreement with values obtained by the analysis of the two‐electron‐satellite PL spectra considering the participation of ground and excited state donor bound excitons. This work clarifies conflicting aspects existing in donor identification and the binding energies of the impurities and excitons. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of AlN buffer layer on the growth of InN epitaxial film on Si substrate
Authors: Yamaguchi T. , Saito Y. , Morioka C. , Yorozu K. , Araki T. , Suzuki A. , Nanishi Y. 
Published: November 2003

AbstractInN films were grown on Si(111) substrates by RF‐MBE, and an AlN buffer layer was inserted between Si substrates and a low‐temperature InN buffer layer. The AlN buffer layer suppressed the formation of amorphous‐like SiNx layer on the Si substrate surface, which led to the improvement of the crystallinity of the low‐temperature InN buffer layer. High‐quality InN films could then be realized on the low‐temperature InN buffer layer with the AlN buffer layer inserted. The best value of the XRC‐FWHM was 31.3 arcmin for InN films with a thickness of 300 nm. In addition, a surface reconstruction of InN was observed for the first time. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)