bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and properties of polyimides derived from 1,4‐bis(4‐aminophenoxy)‐2‐(6‐oxido‐6H‐dibenz[c,e] [1,2]oxaphosphorin‐6‐yl) phenylene
Authors: Lin Ching Hsuan , Lin Chun Hung 
Published: June 2007

AbstractA new phosphorus‐containing aromatic diamine, 1,4‐bis(4‐aminophenoxy)‐2‐(6‐oxido‐6H‐dibenz[c,e] [1,2]oxaphosphorin‐6‐yl) phenylene (3) was synthesized by the nucleophilic aromatic substitution of 2‐(6‐oxido‐6H‐dibenz[c,e] [1,2]oxaphosphorin‐6‐yl)‐1,4‐dihydroxy phenylene (1) with 4‐fluoronitrobenzene, followed by catalytic hydrogenation. Light color, flexible, and creasable polyimides with high molecular weight, high glass transition, high thermal stability, improved organosolubility, and good oxygen plasma resistance were synthesized from the condensation of (3) with various aromatic dianhydrides in N,N‐dimethylacetamide, followed by thermal imidization. The number‐average molecular weights of polyimides are in the range of 7.0–8.3 × 104 g/mol, and the weight‐average molecular weights are in the range of 12.5–16.5 × 104 g/mol. The Tgs of these polyimides range from 230 to 304 °C by differential scanning calorimetry and from 228 to 305 °C by DMA. These polyimides are tough and flexible, with tensile strength at around 100 MPa. The degradation temperatures (Td 5%) and char yields at 800 °C in nitrogen range from 544 to 597 °C and 59–65 wt %, respectively. Polyimides 5c and 5e, derived from OPDA and 6FDA, respectively, with the cutoff wavelength of 347 and 342 μm, respectively, show very light color. These polyimides also exhibit good oxygen plasma resistance. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2897–2912, 2007
Public safety aspects of pyrethroid insecticides used in West Nile virus‐carrying mosquito control
Authors: Gammon Derek W 
Published: June 2007

AbstractWest Nile virus is becoming increasingly prevalent in the USA, causing fever, encephalitis, meningitis and many fatalities. Spread of the disease is reduced by controlling the mosquito vectors by a variety of means, including the use of pyrethroid insecticides, which are currently under scrutiny for potential carcinogenic effects in humans. Pyrethrins and resmethrin, a pyrethroid, have been shown to cause tumours in rat and mouse models respectively. However, the tumours appear to be caused by liver enzyme induction and hypertrophy rather than genotoxicity, and the results are therefore unlikely to be applicable to humans. Nonetheless, for resmethrin, the US Environmental Protection Agency (EPA) has concluded that there is a likely risk of carcinogenicity in humans, requiring the manufacturers to provide more detailed data to prove that it can be used safely in vector control. Reproductive toxicity of resmethrin in the rat is also discussed. Copyright © 2007 Society of Chemical Industry
Pressure‐ and temperature‐induced structural changes in simulated amorphous Al2O3·2SiO2
Authors: Van Hoang Vo , Linh Nguyen Ngoc , Hung Nguyen Hoang 
Published: June 2007

AbstractWe investigated the pressure‐ and temperature‐induced structural changes in amorphous Al2O3·2SiO2 by a molecular dynamics method. Simulations were done in a basic cube under periodic boundary conditions containing 3025 ions with the Born–Mayer type pair potentials. In order to study the structural changes, nine models of amorphous Al2O3·2SiO2 at 350 K and at densities ranging from 2.6 g/cm–3 to 4.2 g/cm–3 have been built. The microstructure of the amorphous Al2O3·2SiO2 has been analyzed through the pair radial distribution functions, coordination number, bond‐angle distributions, and interatomic distances. Moreover, we found clear evidence of structural changes from a tetrahedral to an octahedral network structure in the system upon compression. We also found that the changes reverse from an octahedral to a tetrahedral network structure by subsequent heating of an octahedral structure model from 350 K to 1610 K at constant external pressure P = 0 GPa. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of temperature on elastic properties of caesium cyanide
Authors: Singh Preeti , Gaur N. K. , Singh R. K. 
Published: June 2007

AbstractAn extended three body force shell model (ETSM), which incorporates the effects of translational–rotational (TR) coupling, three body interactions (TBI) and anharmonicity, has been applied to investigate the temperature dependence of the second order elastic constants (cij, i, j = 1, 2) of CsCN. The elastic constant c44 obtained by us shows an anomalous behaviour with the variation of temperature. The variations of elastic constants (c11, c12, c44) with temperature are almost in excellent agreement with Brillouin scattering measured data. We have also evaluated the temperature variations of the third order elastic constants (cijk) and the pressure derivatives of the cij in the CsCN material. However, their values could not be compared due to lack of experimental data. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Theoretical investigation of intersubband nonlinear optical rectification in Alx lGa1–xlAs/GaAs/Alx rGa1–xrAs asymmetric rectangular quantum wells
Authors: Karabulut İbrahim , Atav Ülfet , Şafak Haluk , Tomak Mehmet 
Published: June 2007

AbstractIn this study, a theoretical investigation of intersubband nonlinear optical rectification in Alx lGa1–x lAs/ GaAs/Alx rGa1–x rAs asymmetric rectangular quantum wells is presented. The electronic states in the asymmetric rectangular quantum well are described within the framework of the envelope function approach including the effects of band nonparabolicity and the effective mass mismatch. The nonlinear optical rectification is calculated using the density matrix formalism. It is found that the nonlinear optical rectification in the asymmetric rectangular quantum well depends sensitively on the parameters such as the width and the asymmetry of the potential well. The adjustable parameters allow for tuning of the asymmetric rectangular quantum well system to the desired wavelength while retaining a large optical rectification coefficient. This gives a new degree of freedom in various device applications based on nonlinear optical properties. Band nonparabolicity is found to significantly influence both electronic states and nonlinear optical rectification. Moreover the resulting optical rectification coefficient is much larger than the ones for bulk GaAs and some other theoretical studies in literature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Is the smallest carbon nanotube (2,2) a metal or a semiconductor?
Authors: Scipioni R. 
Published: June 2007

AbstractWe perform a first principles study of the smallest carbon nanotube ever discovered namely the (2,2) tube with diameter 0.27 nm. Contrary to what recently stated in the literature, the curvature effects are not enough to convert the (2,2) nanotube into a semiconductor and the (2,2) nanotube is metallic in agreement with the simple folding model of graphite. However, as a result of the distortion, the band structure is only converged if a full relaxation and a fine mesh of K points are used to sample the Brillouin zone. We then consider the (2,2) tube in the DWNT (7,7)–(13,13). This system is also found to be metallic. We infer that the recently observed (2,2)@MWNT is a metallic material. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Eta‐pairing and s‐wave pairing in the Penson–Kolb model with next‐nearest neighbour hopping
Authors: Czart W. R. , Robaszkiewicz S. , Tobijaszewska B. 
Published: June 2007

AbstractWe study the two‐dimensional Penson–Kolb model, i.e the tight‐binding model with the pair‐hopping interaction J, and analyze the effects of next‐nearest neighbour hopping t2 on the superconductivity in this system. In the analysis we focus on the properties of the superconducting state with Cooper‐pair center‐of‐mass momentum q = Q (eta‐phase), which can develop in this model for the case of repulsive J (J < 0) and q = 0 (s‐wave phase), which develops for the case of attractive J (J > 0). The evolutions of the phase diagrams, ground state characteristics and the transition temperatures with particle concentration and pairing strength are determined for square lattice. Within the Kosterlitz–Thouless scenario the Uemura‐type plots (Tc vs. 1/λ2(0)) are also derived. The results for t2 ≠ 0 are compared with those found for the case with nn hopping only. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Luminescence of K1–xRbx CaF3 upon the outermost 3p K+ and 4p Rb+ core ionization
Authors: Stryganyuk G. B. , Chornodolskyy Ya. M. , Voloshinovskii A. S. , Ivanov M. P. , Vasylechko L. O. 
Published: June 2007

AbstractThe luminescence and reflection spectra of K1–x Rbx CaF3 crystals have been studied using synchrotron radiation. Luminescence of self‐trapped exciton and core‐valence luminescence are revealed for KCaF3 crystals in UV and VUV spectral range, respectively. The core‐valence VUV luminescence of KCaF3 appears after 3p K+ core ionization and originates from the radiative recombination of 3p K2+ core holes with 2p F– valence electrons. The fast UV luminescence of K1–x Rbx CaF3 crystals has been attributed to the radiative recombination of the holes in 4p Rb2+ impurity core states with 2p F– valence electrons. The impurity core‐valence luminescence of K1–x Rbx CaF3 reveals the excitation threshold corresponding to the ionization of impurity 4p Rb+ core states. Efficient excitation of 4p Rb+ related luminescence of K1–x Rbx CaF3 within the energy range of 3p K+ core ionization is considered as an evidence for the hole migration from the host 3p K+ core band to the impurity 4p Rb+ core states. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of buffer‐related lag phenomena and current collapse in GaN FETs
Authors: Itagaki K. , Kobayashi N. , Horio K. 
Published: June 2007

AbstractDrain‐current responses of GaN MESFETs with a semi‐insulating buffer layer are calculated when the drain voltage and/or the gate voltage are changed abruptly, and pulsed I‐V curves are derived from them. It is shown that so‐called current collapse or current slump is not so dependent on the gate length LG (0.3 μm – 1 μm), and this is essentially determined by a deep‐acceptor density NDA in the buffer layer. LG and NDA dependence of gate lag is also studied, indicating that the gate lag is weaker for longer LG and the lag rate becomes high with NDA, although it may show a saturation behaviour. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phonon dispersion in GaN/AlN non‐polar quantum wells: confinement and anisotropy
Authors: Cros A. , Pomer F. 
Published: June 2007

AbstractWe have calculated the phonon dispersion relations in a non‐polar GaN/AlN quantum well within the dielectric continuum model and making use of Loudon's model of uniaxial crystals. Due to the strong in‐plane anisotropy of this orientation, we have found that in general ordinary and extraordinary phonons are not decoupled. In this work we analyze the conditions for the occurrence of interface modes. In these novel heterostructures there is an added dependence of the phonon dispersion on the orientation of the in‐plane phonon wavevector, which allows the existence of interface phonons at energies forbidden in the better known polar structures. Under particular circumstances the vibrations excited in the wurtzite heterostructure have the characteristics of those found in cubic crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Material and optical properties of Trenched Epitaxial Lateral Overgrowth of a‐plane GaN
Authors: Wang Te‐Chung , Lu Tien‐Chang , Ko Tsung‐Shine , Kuo Hao‐Chung , Chen Hou‐Guang , Yu Min , Chuo Chang‐Cheng , Lee Zheng‐Hong , Wang Sing‐Chung 
Published: June 2007

AbstractThe crystal quality of a‐plane GaN film was successfully improved by using trenched epitaxial lateral overgrowth (TELOG) of a‐plane GaN. Not only the threading dislocation density but also the difference of anisotropic in‐plane strain between orthogonal crystal axes can be mitigated by using TELOG. The low threading dislocation density investigated by transmission electron microscopy was estimated to be 3×107 cm–2 on the N‐face GaN wing. According the results of μ‐PL and CL, the threading dislocations are the strongly non‐radiative center in a‐plane GaN film. Finally, we concluded that a narrower stripped GaN seeds and deeper stripped trenches etched into the surface of sapphire could derive a better quality a‐plane GaN film. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Wide spectral responses InxGa1–xN deep UV photomultiplier tube
Authors: Uchiyama Shoichi , Takagi Yasufumi , Kondoh Haruyasu , Takatsuka Hiroyuki , Suzuki Hideaki , Ohishi Yasuo , Suzuki Nobuharu , Okano Kazuyoshi , Niigaki Minoru , Kan Hirofumi 
Published: June 2007

AbstractWe have designed and fabricated new photo‐tubes and photomultiplier tubes (PMTs) using InxGa1‐xN films as photocathodes. Longer spectral cutoffs were controlled with Indium compositions x, from 365 nm to 430 nm. The calibrated maximum quantum efficiency (QE) of 56% at 200 nm was achieved for x = 0.11 Indium composition in the photo‐tubes. Sharp cutoffs at around 160 nms were determined by window materials and those at around 400 nms were determined by the band gaps of the photocathodes. Gain and input/output linearity properties were confirmed to be very good for the PMTs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Temperature measurement of GaN‐based blue‐violet laser diodes in operation by Raman microprobe
Authors: Takahashi Kenji , Matsuoka Daisuke , Harima Hiroshi , Kisoda Kenji , Tsuda Yuhzoh , Yuasa Takayuki , Taneya Mototaka 
Published: June 2007

AbstractBlue‐violet GaN‐based laser diodes have been characterized by microscopic Raman scattering to obtain temperature distributions in the chip during operation. The local temperature increased steeply in the vicinity of the light‐emitting layer at distance < ∼20 μm. At injection current I = 120 mA with laser output of 150 mW, the local temperature at the light emitting layer was about 50 °C higher than that of the chip mount, 25 °C. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ionization energy of GaN point defects
Authors: Béré A. , Belabbas I. , Nouet G. , Ruterana P. , Chen J. , Segda G. , Koulidiati J. 
Published: June 2007

AbstractThe ionization or transition energies of gallium or nitrogen vacancy in bulk GaN were investigated by density‐functional based tight‐binding calculations. Calculations of the formation energy of neutral configurations are in agreement with previous DFT determination. It is shown that for the defect configurations, the metallic character of gallium atoms needs to adjust the level of the valence band maximum. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Direct growth of a‐plane GaN on r‐plane sapphire substrate by metalorganic vapor phase epitaxy
Authors: Araki Masahiro , Hoshino Katsuyuki , Tadatomo Kazuyuki 
Published: June 2007

AbstractWe have investigated a direct growth of non‐polar a‐plane GaN on r‐plane sapphire substrate by metalorganic vapor‐phase epitaxy (MOVPE). We found that high‐density nucleation of GaN islands was grown on r‐plane sapphire substrate at an initial stage of high temperature growth without a buffer layer, which resulted in a flat surface of the a‐plane GaN. We also studied an effect of growth conditions on surface morphologies and the growth features of the a‐plane GaN. The results showed that inverse‐triangular pits surrounded with facets were formed at a relatively high V/III ratio, and the lateral growth rate along the c‐axis direction was enhanced at a relatively low V/III ratio. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study on the sublimation growth of GaN using different powder sources and investigation on the sublimation behaviour of GaN powder by means of thermogravimetry
Authors: Kallinger B. , Meissner E. , Seng D. , Sun G. , Hussy S. , Friedrich J. , Müller G. 
Published: June 2007

AbstractThe goal of this work is to study the sublimation growth of GaN and the evaporation behaviour of GaN powders. The reactor design and growth parameters, i.e. gas pressure, gas flow, growth temperature and hot zone design together with the RF heating system, were optimized by using numerical simulation and thermogravimetric (TG) studies. Numerical modelling using the software packages CrysVUn and CrysMAS was used to adjust the flow pattern with respect to a maximum species transport towards the growth interface and to find an appropriate pressure range. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of MOVPE InN films grown on 3c‐SiC/Si(111) templates
Authors: Cho M. S. , Sawazaki N. , Sugita K. , Hashimoto A. , Yamamoto A. , Ito Y. 
Published: June 2007

AbstractAn experimental study has been made on the correlation between the fabrication conditions for 3c‐SiC/Si (111) template and electrical and crystallographic properties of InN films grown on the templates. The template has been prepared by C+‐ion implantation into Si (111). Although the 3c‐SiC layers show a large (170 arcmin) FWHM of XRC (111) diffraction, InN films with a considerably small (about 50 arcmin) FWHMs for (0002) and (10‐10) diffraction are grown on the layers. A lower implantation dose brings a smaller XRC FWHMs for 3c‐SiC. The post implantation annealing is found to be effective to improve the quality of the 3c‐SiC layer and, therefore, to improve the quality of InN films. Hall mobility in InN is found to be markedly increased by decreasing FWHM of InN (0002) diffraction. The best data of carrier concentration and Hall mobility are 6.2×1018 cm–3 and 630 cm2/Vs, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of electrical properties of AlGaN/GaN heterostructures grown on vicinal substrates by rf‐MBE
Authors: Shen X. Q. , Furuta K. , Nakamura N. , Okumura H. 
Published: June 2007

AbstractElectrical properties of AlGaN/GaN heterostructures grown on vicinal sapphire and 4H‐SiC (0001) substrates by molecular beam epitaxy (MBE) are investigated. It is found that electrical properties of the 2‐dimensional electron gas (2DEG) in the heterostructures grown on vicinal substrates are superior to those grown on conventional on‐axis substrates. Furthermore, samples grown on 2.0°‐off vicinal substrates show better 2DEG mobility than those grown on the 0.5°‐off vicinal substrates both at room‐ and low‐temperature. Anisotropic phenomenon of the 2DEG mobility in the heterostructures grown on 1.0°‐ and 2.0°‐off substrates is demonstrated, which strongly relates to the macro‐step structures on the surface. The 2DEG mobility exceeding 2000 cm2/Vs is obtained at the room temperature from our all‐MBE‐grown sample measured in the direction parallel to the macro‐step. It is suggested that the direction effect should be taken into account when designing the device structure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photo‐catalysis effect of III‐V nitride film
Authors: Sumiya Masatomo , Ohara Keisuke , Ohsawa Takeo , Kawai Yu. , Shirai Masato , Fuke Shunro , Koinuma Hideomi , Matsumoto Yuji 
Published: June 2007

AbstractWe have studied the photo catalysis effect in III‐V nitride film having the potential overall water splitting under UV‐ or visible light irradiation. It was found that the photo catalysis effect was greater on the surface of GaN film with Ga‐face (+c) polarity than that with N‐face (‐c) polarity. This polarity dependence was discussed in term of band profile caused by the spontaneous polarization. Alloying InN mole fraction with GaN made it possible to generate the photo catalysis effect for visible light in III‐V nitride film. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Origins of n‐type residual carriers in RF‐MOMBE grown InN layers
Authors: Iwao Kosuke , Yamamoto Akio , Hashimoto Akihiro 
Published: June 2007

AbstractWe have investigated quantitatively on the origins of residual electrons in InN layers to make clear some roles of oxygen incorporation for band‐gap widening. It has been found out that a linear relation was observed between oxygen and residual electron concentrations for InN layers grown by RF‐MOMBE using TMIn source, although the residual electron concentration is super‐linearly dependent on oxygen concentration for InN layers grown by RF‐MBE using metal In source. The experimental results strongly indicate that oxygen atoms and/or nitrogen vacancies induced by oxygen incorporation are major origins of the residual carrier concentrations. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of Ni/Au, ITO, and ATO‐based current spreading layers for near‐ultraviolet light‐emitting diodes
Authors: Chong Wing Cheung , Lau Kei May 
Published: June 2007

AbstractCurrent‐voltage (I‐V) characteristics, optical transmittance, and light output power measurements were performed to investigate different contact schemes including Ni (5 nm)/Au (5 nm), Ag (0.5 nm)/ITO (100 nm), and Ag (0.5 nm)/ITO (5 nm)/ATO (150 nm) for near‐ultraviolet (∼400 nm) III‐nitride light‐emitting diodes (LEDs). Ag/ITO contacts show the highest transmittance of 98.73% at 406 nm when annealed at a temperature of 700 °C for 5 minutes in air. The lowest forward voltage of LEDs with Ag/ITO contacts is 3.29 V at 20 mA compared to 3.16 V of Ni/Au contacts annealed at 570 °C for 5 minutes in air. E‐beam evaporated Ag/ITO/ATO contacts, on the other hand, give somewhat higher forward voltage at 3.36 V after annealing, but high transmittance of ATO‐based contacts at short wavelength regions shows its potential applicability to very short wavelength UV LEDs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of A‐plane (11‐20) In‐rich InGaN on R‐plane (10‐12) sapphire by RF‐MBE
Authors: Noda M. , Kumagai Y. , Takado S. , Muto D. , Na H. , Naoi H. , Araki T. , Nanishi Y. 
Published: June 2007

AbstractNon‐polar A‐plane (11‐20) high In content (In‐rich) InGaN was grown on R‐plane (10‐12) sapphire with an InN template by radio‐frequency plasma assisted molecular beam epitaxy (RF‐MBE). Nitridation of R‐plane sapphire was carried out at 300 °C for 2 hours by RF‐nitrogen plasma. A template of A‐plane InN was grown at 400 °C. The In‐rich InGaN films were then grown at the same temperature on the InN template. We characterized the films using reflection high‐energy electron diffraction (RHEED), X‐ray diffraction (XRD), scanning electron microscopy (SEM) and photo‐luminescence (PL). These results indicated clearly that non‐polar In0.71Ga0.29N was successfully obtained with a PL emission at approximately 1.1 eV. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)