bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diapause disruption with tebufenozide for early‐instar control of the spruce budworm, Choristoneura fumiferana
Authors: Doucet Daniel , Frisco Caroline , Cusson Michel , Bauce Éric , Palli Subba Reddy , Tomkins Bill , Arif Basil , Retnakaran Arthur 
Published: June 2007

AbstractIn North America, the eastern spruce budworm, Choristoneura fumiferana Clem., is an important coniferous pest against which tebufenozide has proven effective as a control product. By acting as an ecdysone agonist, tebufenozide can induce precocious moulting in late (fifth–sixth) instars but can also be carried over to the next generation owing to its persistence on foliage. The authors conducted laboratory experiments on first‐instar larvae treated with tebufenozide dissolved in acetone. Larvae exposed to doses equal to or above 0.1 µg cm−2 displayed precocious moulting in the second instar after hibernaculum spinning, which effectively disrupted diapause. Larger doses induced moulting in first instars. Evidence is provided that this dose–response difference is related to whether or not an effective dose of tebufenozide is ingested by the first instar prior to the peak of moulting hormone (20‐hydroxyecdysone) in first instars. Doses ineffective to kill first instars are carried over to the second instar, where they induce a precocious moult. This type of response to tebufenozide is dependent on the presence of a moulting machinery (the EcR–USP receptor complex) that is ready for ecdysone transduction. Interestingly, ecdysone levels are low in second instars, as measured by a radioimmunoassay, which suggests that diapause in spruce budworm is maintained by a suppression of ecdysone production. Thus, diapause disruption by tebufenozide may well provide an alternative control strategy for this important pest. Copyright © 2007 Society of Chemical Industry
Crystal field parameters of praseodymium in oxides
Authors: Novák P. , Diviš M. 
Published: June 2007

AbstractThe crystal field parameters of the Pr4+ ion in PrO2 and PrBaO3 are calculated using the density of states projected on the 4f states of the Pr4+ ion. The orbital‐dependent potential is used and the procedure involves an adjustable parameter Δf that determines the relative position of the center of the 4f levels. Δf can be estimated using the LDA + U method. For reasonable values of Δf the calculated crystal field parameters give a splitting close to the one observed. It is shown that the hybridization of the 4f states is important. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Tricritical behavior of Ising metamagnet in both external longitudinal and transverse fields
Authors: Liu Jing , Wei Guozhu , Miao Hailing , Du An 
Published: June 2007

AbstractA two‐sublattice Ising metamagnet in both external longitudinal and transverse fields is studied within the mean‐field approach based on Bogoliubov's inequality for the Gibbs free energy. The phase diagrams in the longitudinal field‐temperature plane and in the transverse field‐temperature plane are determined, respectively. The results show that the tricritical points can occur in a certain region of the external longitudinal and transverse fields, the temperature of the tricritical point monotonically increases with decreasing the transverse magnetic field Ω and increasing the longitudinal magnetic field h. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electronic and optical properties of Ir3Si5
Authors: Migas D. B. , Shaposhnikov V. L. , Rodin V. N. , Dorozhkin N. N. , Borisenko V. E. 
Published: June 2007

AbstractFirst‐principles calculations of the band structure and the dielectric function of Ir3Si5are presented. We find this compound to be characterized by an indirect band gap of 0.97 eV. A number of direct transitions of about 1 eV have been also determined. Features in the dependence of the imaginary and real parts of the dielectric function on photon energy are discussed in comparison with data for some other semiconducting silicides. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin‐polarized transport through two coupled quantum dots
Authors: Trocha P. , Barnaś J. 
Published: June 2007

AbstractSpin‐dependent transport through two coupled single‐level quantum dots attached to ferromagnetic leads with collinear (parallel and antiparallel) magnetizations is analyzed theoretically. Generally, the intra‐ and inter‐dot Coulomb correlations are taken into account. Transport characteristics, including conductance and tunnel magnetoresistance associated with the magnetization rotation from the parallel to antiparallel configurations, are calculated by the noneqiulibrium Green function technique. The relevant Green functions are derived by the equation of motion method. To close the set of equations we employ the Hartree–Fock decoupling scheme. The dot occupation numbers and the Green functions are calculated self‐consistently. We focus on the interplay of interference (Fano resonance) and Coulomb interaction effects. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Construction of superconducting pairs in the two‐dimensional electron gas for the model of itinerant electrons
Authors: Inglot Michał , Wal Andrzej , Lulek Tadeusz 
Published: June 2007

AbstractWe consider a 3 × 3 finite plane lattice with Born–von Karman boundary conditions, threaded by magnetic field perpendicular to it, such that two quanta of flux cover exactly three Bravais cells. The corresponding magnetic translation group is determined, and the single‐electron energy levels of the system are labelled by three‐dimensional irreps of this group. We perform also the Clebsch–Gordan decomposition, and interpret selected irreps as the relevant superconducting pairs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the CTMA for the infinite U Anderson impurity model
Authors: Keiter Hellmut , Baumgartner Klaus , Duffe Sebastian 
Published: June 2007

AbstractIf one wants to deal with strongly correlated electron lattice systems within dynamical mean field theory, one needs an impurity solver, i.e. a solution for the dynamics of the Anderson magnetic impurity problem. The most ambitious approach to that problem has been the consistent t‐matrix approximation (CTMA). The basic integral equations could be solved with a slow variable approximation, which compared well with a direct numerical solution. Fermi‐liquid behavior was not obtained, presumably the normalscattering potential was treated approximately only. We show, how the normal scattering potential can be included exactly. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A study of the optical and EPR spectra for Ni2+ ion at the Cd2+(II) site of CsCdCl3 crystal
Authors: Feng Wen‐Lin , Wu Xiao‐Xuan , Zheng Wen‐Chen 
Published: June 2007

AbstractThe optical absorption bands and spin‐Hamiltonian parameters (g ‐factors g‖, g⊥ and zero‐field splitting D measured by EPR spectra) of Ni2+ ion at the Cd2+ (II) site of CsCdCl3 crystals are calculated by using the method of diagonalizing the complete energy matrix of 3d8 ions in trigonal symmetry. The calculated results are in reasonable agreement with the observed values. The defect structure of this Ni2+ impurity center is also estimated from the calculations. The results are discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Annihilation of threading dislocations in strain relaxed nano‐porous GaN template for high quality GaN growth
Authors: Hartono H. , Soh C. B. , Chua S. J. , Fitzgerald E. A. 
Published: June 2007

AbstractPorous GaN subjected to heat treatment under in‐situ MOCVD chamber annealing at 850 °C for 3 minutes has shown significant annihilation of threading dislocations and improvement of its optical quality. Similar phenomenon is not observed for the porous GaN samples annealed at lower temperatures. The annealing was done in a mixed of N2 and NH3 ambient, which resulted in air‐gap formation. Encounter of threading dislocations with the air‐gap might cause them to bend horizontally and annihilate each other. Dark‐field cross‐section TEM image confirms the annihilation of threading dislocations within the porous/air‐gap region. This dislocation density reduction causes a significant enhancement of the optical quality as shown by doubled Raman intensity of E2 phonon peak after the annealing as compared to the as‐fabricated porous GaN. Because the fabricated porous GaN samples are already relaxed, no further strain relaxation is observed after annealing. Such a template is suitable for use in high quality GaN growth. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Subband structure and transport properties of two‐dimensional electron gas in AlxGa1–xN/GaN heterostructures
Authors: Han Xiuxun , Honda Yoshio , Narita Tetsuo , Yamaguchi Masahito , Sawaki Nobuhiko 
Published: June 2007

AbstractWe report on Hall mobility and Shubnikov‐de Haas (SdH) measurements of the two dimensional electron gas (2DEG) formed in a series of AlxGa1–xN/GaN heterostructures with different Al composition grown on sapphire substrates. In samples of x = 0.15 and 0.20, we found single periodical oscillations. In a sample of x = 0.30 a double periodical one was clearly resolved, which indicates that more than one subband has been occupied by electrons. Fast Fourier transform (FFT) analysis yielded information about the electron density and subband structure of the 2DEGs. The oscillatory part of the SdH signal was analyzed to extract the quantum scattering time at 4.2 K. It was found that as the increase of the Al content, quantum scattering time of the ground subband decreases gradually. We attributed it to the enhanced interface roughness scattering and the onset of the inter‐subband scattering in the sample with higher Al content. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mega‐cone blue LEDs based on ZnO/GaN direct wafer bonding
Authors: Murai A. , Thompson D. B. , Masui H. , Fellows N. , Mishra U. K. , Nakamura S. , DenBaars S. P. 
Published: June 2007

AbstractWe demonstrate the fabrication of hexagonal pyramid shaped light‐emitting diodes (LEDs), “mega‐cone” LEDs based on ZnO/GaN wafer bonding. Compared with a conventional type LEDs with thin Ni/Au p‐type electrode, external quantum efficiency was 3.1 times higher at 20 mA of current injection condition. We also report on the structural, optical, and electrical characteristics of the mega‐cone LED. The results here indicate the high potential of these mega‐cone LEDs for light sources. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Observations on surface morphologies and dislocations of a‐plane GaN grown by metal organic chemical vapor deposition
Authors: Ko T. S. , Wang T. C. , Chen H. G. , Gao R. C. , Huang G. S. , Lu T. C. , Kuo H. C. , Wang S. C. 
Published: June 2007

AbstractIn this study, we grew non‐polar a‐plane GaN thin films on r‐plane sapphire using a series of growth conditions by metal‐organic chemical vapor deposition. The results showed that high temperature and low‐pressure conditions benefited two‐dimension growth could lead to a fully coalesced a‐plane GaN layer with a very smooth surface. The best surface morphology with an excellent mean roughness of 10.5 Å was obtained. The different thickness AlN as a nucleation layer and the different δ/β ratio were also considered. The results revealed that the surface morphology would get worse when the thickness of nucleation layer and δ/β ratio were away from the values of optimal condition. The observation of transmission electronic microscopy shown the lowest density of threading dislocations was 1.85×1010/cm2. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermal and electrical properties of high‐quality freestanding GaN wafers with high carrier concentration
Authors: Oshima Yuichi , Yoshida Takehiro , Eri Takeshi , Shibata Masatomo , Mishima Tomoyoshi 
Published: June 2007

AbstractThe thermal and electrical properties of GaN were investigated using high‐quality freestanding crystals in the high carrier concentration region between 1.0x1018 and 1.24x1019 cm‐3. The carrier concentration n increased almost linearly with increasing Si doping concentration. A very low electrical resistivity of 2.5 mΩcm was obtained at n = 1.24x1019 cm‐3, combined with its high electron mobility. Thermal expansion coefficients along 〈11$ \bar 2 $0〉 and 〈10$ \bar 1 $0〉 were confirmed to be approximately constant at 5.1x10‐6 K‐1 (298‐573 K) in the measured doping concentration range. Thermal conductivity remained high in the measured carrier concentration range at approximately 2.0 Wcm‐1K‐1 for n = 1.0x1018 cm‐3, and 1.87 Wcm‐1K‐1 for n = 1.24x1019 cm‐3. The compatibility of low electrical resistivity and high thermal conductivity has potential to contribute significantly to the realization of high‐performance high‐power nitride devices. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigations of the growth conditions for GaN‐bulk crystals grown by the sublimation technique
Authors: Rost H.‐J. , Siche D. , Müller R. , Gogova D. , Schulz T. , Albrecht M. , Fornari R. 
Published: June 2007

AbstractSpontaneous nucleation of GaN and the growth of thick polycrystalline layers by the sublimation technique in nitrogen atmosphere have been studied as a function of growth environment and conditions. Average growth rates higher than 10 microns per hour were realised by reaction of gallium, evaporated from an elemental source, with nitrogen from ammonia gas. The growth temperature was in the range of 1000 – 1300 °C; the pressure was varied between 200 ‐ 800 hPa and the ammonia flow between 50‐500 sccm min–1. It was found that the growth rate only moderately decreases during a long‐term experiment when using an optimised set of growth parameters. Furthermore, a strong influence of the growth environment on the growth rate and impurity content was found. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Practical issues in carrier‐contrast imaging of GaN structures
Authors: Sumner J. , Oliver R. A. , Kappers M. J. , Humphreys C. J. 
Published: June 2007

AbstractScanning capacitance microscopy (SCM), scanning spreading resistance microscopy (SSRM) and secondary electron emission within a scanning electron microscope (SEM) were used to image two magnesium‐doped GaN samples, grown under identical conditions. In only one of these samples were the dopants activated by annealing. Under normal imaging conditions for SCM and SSRM, no discernable change in contrast was observed in the unactivated sample, whilst for SEM imaging contrast increased over ca. 40 s of imaging time, indicating some activation of the dopants by the electron beam. In addition, various sample preparation techniques were attempted in order to minimise the roughness of the GaN cross‐section used for SCM imaging. Some techniques which reduce the surface roughness lead to a poor SCM signal‐to‐noise ratio. However, a cleaving technique is described which produces suffi‐ciently large and flat areas within multi‐layered GaN specimens for the extraction of useful SCM data. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Realization of AlGaN/GaN HEMTs on Si‐on‐polySiC substrates
Authors: Cordier Yvon , Chenot Sébastien , Laügt Marguerite , Tottereau Olivier , Joblot Sylvain , Semond Fabrice , Massies Jean , Di Cioccio Léa , Moriceau Hubert 
Published: June 2007

AbstractAlGaN/GaN High Electron Mobility Transistors have been realized on resistive Si(111)/SiO2/polySiC substrates. The epitaxial structures were grown by Molecular Beam Epitaxy. The structural, optical, and electrical properties of these films are studied and compared with those of reference heterostructures grown on thick Si(111) substrates. Channel mobility of 1470 cm2/Vs at room temperature and sheet carrier density of 6.65x1012 cm–2 have been achieved. Field effect transistors with 3.6 µm x 100 µm gates have been fabricated on these layers and exhibit a drain current superior to 450 mA/mm and a transconductance of 123 mS/mm. Furthermore, to evaluate the influence of heat transfer onto electrical properties, the resistance change with the power dissipated inside Transmission Line Measurement devices has been compared with those in devices realized with layers grown on thick Si(111) and 4H‐SiC substrates. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
GaN/air gap based micro‐opto‐electro‐mechanical (MOEM) Fabry‐Pérot filters
Authors: Cho E. , Pavlidis D. , Sillero E. 
Published: June 2007

AbstractStructural and optical properties of Fabry‐Pérot filters (FPFs) with GaN/air gap based distributed Bragg reflectors (DBRs) were studied. Reflectance of GaN/air gap DBRs on sapphire substrate was calculated from the standard transmission matrix method and results showed that 98% reflectance is achievable with only 3.5 pairs at a center wavelength of 450 nm. The thickness of the GaN layer and the first AlN layer was determined according to the deformation induced by the residual stress. In‐plane strain corresponding to growth conditions and the thickness of the GaN epilayer was considered for this analysis. Optical tuning efficiency and spectral range were found to be 0.27 and 25 nm respectively for FPFs with GaN/air gap (322 nm/113 nm) based DBRs and a λ0/2 air resonant cavity. The calculated pull‐in voltage was 1.5 V. Crack free AlN grown on GaN by in‐house MOCVD showed an etching rate of 0.2 nm/min. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Self‐separated freestanding GaN grown on patterned substrate by Hydride Vapor Phase Epitaxy
Authors: Lai Chih‐Ming , Liu Wen Yu , Tsay Jenq‐Dar , Liu Po Chun , Guo Yih‐Der , Huang Hsin‐Hsiung , Chang Yu Hsiang , Yeh Jul Chin 
Published: June 2007

AbstractA freestanding Gallium Nitride bulk is obtained without using laser lift‐off technology. Two techniques such as mask‐less ELOG and air‐bridge structure are applied on patterned substrate. A self‐separated result is successfully demonstrated by using mask‐less ELOG and air‐bridge structure. Due to the thermal coefficient of expansion (TCE) mismatch between the GaN layer and the non‐native (foreign) substrate, separation happens during cooling down after HVPE growth. Both two structures successfully help to lift GaN off the substrate. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Normally‐off operation in AlGaN/GaN/AlGaN double heterojunction field effect transistors
Authors: Shimizu Mitsuaki , Inada Masaki , Yagi Shuichi , Piao Guanxi , Okumura Hajime , Arai Kazuo , Yano Yoshiki , Akutsu Nakao 
Published: June 2007

AbstractNearly normally‐off operation of the GaN‐based heterojunction field effect transistors was obtained using AlGaN/GaN/AlGaN double heterojunction channel. The aluminum compositions of the AlGaN heterobarriers are designed so as to deplete the electron carrier in the AlGaN/GaN/AlGaN channel, which gives the threshold gate voltage of about 0 V. The maximum drain current density was over 170 mA/mm. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An analysis of the increase in sheet resistance with the lapse of time of Al0.3Ga0.7N/GaN HEMT structure wafers
Authors: Kikawa Junjiroh , Yamada Tomoyuki , Tsuchiya Tadayoshi , Kamiya Shinichi , Kosaka Kenichi , Hinoki Akihiro , Araki Tsutomu , Suzuki Akira , Nanishi Yasushi 
Published: June 2007

AbstractWe have observed the increase in sheet resistance with the lapse of time for some Al0.3Ga0.7N/GaN HEMT structure wafers, and this was due to the decrease in electron mobility rather than the decrease in carrier concentration. In the wafers, a lot of triangular micro‐cracks extending to 〈11$ \bar 2 $0〉 directions were observed by AFM, which were a few tiny lines initially. On the other hand, a wafer that was kept in the nitrogen atmosphere was little increased in sheet resistance. It is plausible that oxygen decreases surface energy of cleaved planes, and micro‐cracks progress. The reciprocal lattice map of XRD showed no lattice relaxation of the AlGaN/GaN system. Monochromatic CL image of 359 nm wavelength showed those micro‐cracks as dark lines, which means that the micro‐cracks work as non‐radiative centers, and the charge of trapped electrons might deplete or scatter 2DEG beneath the micro‐cracks and cause the increase in sheet resistance. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Off‐state drain current and breakdown voltage of AlGaN/GaN MIS‐HEMT with multilayered gate insulator
Authors: Yagi S. , Shimizu M. , Inada M. , Okumura H. , Ohashi H. , Yano Y. , Akutsu N. 
Published: June 2007

AbstractWe report the fabrication of AlGaN/GaN high electron mobility transistors (HEMT) with high‐k /SiN and high‐k /SiO2/SiN gate structures. HfO2, ZrO2, TiO2 and Ta2O5 were used as high‐k materials. Both high‐k /SiN and high‐k /SiO2/SiN metal‐insulator‐semiconductor (MIS) HEMTs showed good operating characteristics. However, in the case of high‐k /SiN MIS‐HEMT, the off‐state drain current was large. On the other hand, in the case of the high‐k /SiO2/SiN MIS‐HEMT, the off state current was significantly reduced due to the presence of the SiO2 layer, and the breakdown voltage characteristics were improved. The breakdown voltages of HfO2/SiO2/SiN MIS‐HEMT and ZrO2/SiO2/SiN at gate‐drain distance Lgd = 28 μm were 1.8 kV and 1.7 kV, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coherent manipulation of A and B excitons in GaN
Authors: Ishiguro T. , Toda Y. , Adachi S. , Hazu K. , Sota T. , Chichibu S. F. 
Published: June 2007

AbstractAn optical coherent manipulation of excitonic polarizations in hexagonal bulk GaN is achieved by means of an interferometric technique combined with spectrally‐resolved degenerate four‐wave‐mixing (FWM). Initial phase of the FWM quantum beats between A and B excitonic polarizations are arbitrarily controlled, in which simultaneous increase (decrease) of the beats in both polarizations are observed. In addition, 80% selective amplification and 40% suppression of one of the excitonic polarizations are realized. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polarity control of InN grown by MOVPE on sapphire (0001)
Authors: Wang W. J. , Sugita K. , Nagai Y. , Houchin Y. , Hashimoto A. , Yamamoto A. 
Published: June 2007

AbstractPolarity control of MOVPE InN on sapphire (0001) was investigated. Two kinds of polarity InN films on sapphire substrate by MOVPE have been prepared by controlling the substrate nitridation process and/or the LT‐GaN buffer annealing process. Surface of the nitrided sapphire is a crucial factor in determining the polarity of InN film. N‐polarity InN film was grown on the 1000 °C‐nitrided substrate without LT‐GaN buffer; while In‐polarity InN film was grown on the 900 °C‐nitrided substrate. In the case of InN growth with a LT‐GaN buffer, buffer annealing is a crucial issue in determining the polarity of InN film. N‐ and In‐polarity InN films were obtained on the long‐time‐annealed buffer and the short‐time‐annealed buffer, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Temperature dependence of the quantum efficiency in green light emitting diode dies
Authors: Li Y. , Zhao W. , Xia Y. , Zhu M. , Senawiratne J. , Detchprohm T. , Schubert E. F. , Wetzel C. 
Published: June 2007

AbstractThe electroluminescence of GaInN/GaN multiple quantum well light‐emitting diode dies is analyzed at variable low temperatures. We compare the external quantum efficiency of three dies of nominally identical structure but strongly different RT performance at 520 nm. For all dies, the external quantum efficiency increases as the temperature is lowered. A maximum is reached for all near 158 K while for lower temperatures as low as 7.7 K, the efficiency continuously drops. The low‐temperature efficiency is the lowest for the highest performing die at RT. The peak energy exhibits a blue shift from RT to 158 K followed by a red shift for lower temperatures. In the same low‐temperature range, a secondary emission peak appears near 390 nm that resembles a donor‐acceptor pair transition. The pronounced efficiency maximum is tentatively assigned to competition of carrier transport properties and the non‐radiative lifetime in the active region. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)