bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of substrate crystalline morphology on the adhesion of plasma enhanced chemical vapor deposited thin silicon oxide coatings on polyamide
Authors: Rochat G. , Leterrier Y. , Plummer C. J. G. , Månson J.-A. E. , Szoszkiewicz R. , Kulik A. J. , Fayet P.
Published: April 2004

The influence of the surface morphology of semicrystalline polyamide 12 (PA12) on the adhesion of thin silicon oxide coatings is analyzed by means of uniaxial fragmentation tests and scanning local-acceleration microscopy (SLAM). Two types of PA12 substrates are investigated, namely, as-received PA12, which contains large spherulites, and quenched PA12, which has a relatively smooth, homogeneous surface structure. The adhesion of the coating is found to be identical for the two types of PA12. This indicates that plasma deposition of the oxide leads to an equivalent functionalization of the two types of surfaces. Nonetheless, localized delamination is observed at spherulite boundaries, and is argued to result from strain concentrations in the corresponding soft zones, revealed by SLAM measurements.
Separation of the first- and second-order contributions in magneto-optic Kerr effect magnetometry of epitaxial FeMn/NiFe bilayers
Authors: Mewes T. , Nembach H. , Rickart M. , Hillebrands B.
Published: April 2004

The influence of second-order magneto-optic effects on Kerr effect magnetometry of epitaxial exchange coupled Fe50Mn50/Ni81Fe19-bilayers is investigated. A procedure for separation of the first-and second-order contributions is presented. The full angular dependence of both contributions during the magnetization reversal is extracted from the experimental data and presented using gray scaled magnetization reversal diagrams. The theoretical description of the investigated system is based on an extended Stoner–Wohlfarth model, which includes an induced unidirectional and fourfold anisotropy in the ferromagnet, caused by the coupling to the antiferromagnet. The agreement between the experimental data and the theoretical model for both the first- and second-order contributions are good, although a coherent reversal of the magnetization is assumed in the model.
Spin wave contributions to the high-frequency magnetic response of thin films obtained with inductive methods
Authors: Counil G. , Kim Joo-Von , Devolder T. , Chappert C. , Shigeto K. , Otani Y.
Published: April 2004

The high-frequency magnetic response of Permalloy thin films have been measured using network-analyzer ferromagnetic resonance. We demonstrate that the excitation of spin waves by the coplanar wave-guide modify the magnetic response appreciably, in particular, by causing a frequency shift and broadening of the resonance peak. An analytic theory is presented to account for the experimental observations and provides a quantitative tool to accurately determine the Gilbert damping constant.
Stray fields of domains in permalloy microstructures—Measurements and simulations
Authors: Barthelmess M. , Pels C. , Thieme A. , Meier G.
Published: April 2004

We have measured the stray fields of thin permalloy (Ni83Fe17) microstructures with different geometries and several thicknesses by magnetic-force microscopy (MFM). The MFM images are compared to corresponding images calculated from micromagnetic simulations. In particular, the type of 180° domain walls is discussed. We observe a transition from cross-tie to asymmetric Bloch walls between 70 and 100 nm film thickness. Good agreement between measurement and simulation is obtained.
Universal tunneling behavior in technologically relevant P/N junction diodes
Authors: Solomon Paul M. , Jopling Jason , Frank David J. , D’Emic Chris , Dokumaci O. , Ronsheim P. , Haensch W. E.
Published: April 2004

Band-to-band tunneling was studied in ion-implanted P/N junction diodes with profiles representative of present and future silicon complementary metal–oxide–silicon (CMOS) field effect transistors. Measurements were done over a wide range of temperatures and implant parameters. Profile parameters were derived from analysis of capacitance versus voltage characteristics, and compared to secondary-ion mass spectroscopy analysis. When the tunneling current was plotted against the effective tunneling distance (tunneling distance corrected for band curvature) a quasi-universal exponential reduction of tunneling current versus, tunneling distance was found with an attenuation length of 0.38 nm, corresponding to a tunneling effective mass of 0.29 times the free electron mass (m0), and an extrapolated tunneling current at zero tunnel distance of 5.3×107 A/cm2 at 300 K. These results are directly applicable for predicting drain to substrate currents in CMOS transistors on bulk silicon, and body currents in CMOS transistors in silicon-on-insulator.
Static high-pressure structural studies on Dy to 119 GPa
Authors: Patterson Reed , Saw Cheng K. , Akella Jagannadham
Published: April 2004

Structural phase transitions in the rare-earth metal dysprosium have been studied in a diamond anvil cell to 119 GPa by x-ray diffraction. Four transformations following the sequence hcp→Sm-type→dhcp→hR24 (hexagonal)→bcm (monoclinic) are observed at 6, 15, 43, and 73 GPa, respectively. The hexagonal to monoclinic transformation is accompanied by a 6% reduction in volume, which is attributed to delocalization of the 4f electrons, similar to that seen in Ce, Pr, and Gd.
Fabry–Pérot cavities based on two-dimensional photonic crystals fabricated in InP membranes
Authors: Mulot M. , Swillo M. , Qiu M. , Strassner M. , Hede M. , Anand S.
Published: April 2004

We measured the transmission and analyzed out-of-plane loss in Fabry–Pérot filters based on photonic crystals etched in a suspended InP membrane. The resonant cavity of the Fabry–Pérot filter is based on a single row line defect introduced in a triangular lattice of air holes. The transmission spectrum of these structures is measured by using the end-fire method. We measured a cavity quality factor of 3200 for a resonance wavelength in the 1.5 μm wavelength range. We identify that radiation through the holes at both extremities of the resonant cavity largely contributes to the loss in the device.
Effects of grain boundaries on performance and hot-carrier reliability of excimer-laser annealed polycrystalline silicon thin film transistors
Authors: Chen Tien-Fu , Yeh Ching-Fa , Lou Jen-Chung
Published: April 2004

This work examines the effects of grain boundaries on the performance and hot-carrier reliability of excimer-laser-annealed polycrystalline silicon thin film transistors (poly-Si TFTs) before and after NH3 plasma treatment. Self-aligned poly-Si TFTs, whose channel regions include a 150 nm thick laser-crystallized poly-Si layer with small grains and a 100 nm thick layer with large grains, are fabricated. Other TFTs, with large grains throughout their channels, are fabricated nearby for comparison. The trapping of electrons at grain boundaries in the drain junction creates strong local electric fields that boost the leakage current, cause the threshold voltage to decline as the drain bias increases, enhance the kink effect in the output characteristics, and degrade the hot-carrier reliability of devices. When static hot-carrier stress is applied to nonhydrogenated poly-Si TFTs for less than 104 s at VGS=10 V and VDS=20 V, hot holes are injected into the gate oxide at the same time trap states are created in the drain junction. The screening effect is observed when the same stress is applied to devices that have many grain boundaries in their drain junctions. NH3 plasma treatment prevents the trapping of electrons at grain boundaries. The performance of hydrogenated poly-Si TFTs improves, but the hot-carrier reliability of those TFTs with large grains in their drain junctions degrades. The hydrogenation causes a trade-off between the electrical characteristics and the hot-carrier reliability, and introduces irregular humps in the subthreshold region.
Low-field microwave response and electron paramagnetic resonance identification of valence states of manganese including octahedral Mn5+ in YAlO3 and CaYAlO4
Authors: Rakhimov Rakhim R. , Jackson Enrique M. , Jones David E. , Loutts George B.
Published: April 2004

Microwave response near zero magnetic field has been observed in YAlO3 and CaYAlO4 crystals dilutely doped with Mn in concentration ranging from 0.005 to 0.2 at. %. The response is due to magnetic-field-dependent nonresonant microwave losses, which co-exist with normal electron paramagnetic resonance (EPR) absorption due to Mn2+, Mn4+, and Mn5+ ions in YAlO3 and CaYAlO4. The valence states of manganese have been identified using a dual mode EPR cavity that allowed spectrum recording with polarization of the magnetic vector B1 of the microwave perpendicular or parallel to the static magnetic field B0. The Mn2+ ion, electron spin S=52, and Mn4+, S=32 have been identified using normal B1⊥B0 polarization, while Mn5+, S=1, in unusual octahedral position, has been identified using B1∥B0 polarization. The low-field response did not depend on mutual orientation of the vectors B1 and B0 and had the opposite phase with respect to the paramagnetic absorption. This shows that Mn-doped YAlO3 and CaYAlO4 exhibit magnetically induced microwave absorption, which has a minimum at zero magnetic field and increases with the applied magnetic field. The response in Mn-doped YAlO3 increases with the introduction of Ca2+ ions. The existence of manganese in different valence states, particularly metastable Mn5+ in octahedral position, and the effect of calcium co-doping suggest the formation of relatively free charge carriers that can migrate in the vicinity of paramagnetic manganese ions. The spin-dependent mechanism of the charge migration is discussed to explain magnetoinduced microwave losses.
Influence of H on the composition and atomic concentrations of “N-rich” plasma deposited SiOxNyHz films
Authors: del Prado A. , San Andrés E. , Mártil I. , González-Dı́az G. , Bohne W. , Röhrich J. , Selle B.
Published: April 2004

The influence of H on the composition and atomic concentrations of Si, O, and N of plasma deposited SiOxNyHz films was investigated. The bonding scheme of H was analyzed by Fourier-transform infrared spectroscopy. The composition and absolute concentrations of all the species present in the SiOxNyHz, including H, was measured by heavy-ion elastic recoil detection analysis (HI–ERDA). Samples were deposited from SiH4, O2, and N2 gas mixtures, with different gas flow ratios in order to obtain compositions ranging from SiNyHz to SiO2. Those samples deposited at higher SiH4 partial pressures show both Si–H and N–H bonds, while those deposited at lower SiH4 partial pressures show N–H bonds only. The Si–H and N–H bond concentrations were found to be proportional to the N concentration. The concentration of H was evaluated from the Si–H and N–H stretching absorption bands and compared to the HI–ERDA results, finding good agreement between both measurements. The deviation from H-free stoichiometric SiOxNy composition due to the presence of N–H bonds results in an effective coordination number of N to produce Si–N bonds lower than 3. By fitting the experimental composition data to a theoretical model taking into account the influence of N–H bonds, the actual concentration of N–H bonds was obtained, making evident the presence of nonbonded H. The presence of Si–H and Si–Si bonds was found to partially compensate the effect of N–H bonds, from the point of view of the relative N and Si contents. Finally, the presence of N–H bonds results in a lower Si atom concentration with respect to the stoichiometric film, due to a replacement of Si atoms by H atoms. This decrease of the Si concentration is lower in those films containing Si–H and Si–Si bonds. A model was developed to calculate the Si, O, and N atom concentrations taking into account the influence of N–H, Si–H, and Si–Si bonds, and was found to be in perfect agreement with the experimental data measured by HI–ERDA.
First measurement of backscatter dependence on ion acoustic damping in a high density helium/hydrogen laser-plasma
Authors: Moody J. D. , Williams E. A. , Lours L. , Sanchez J. J. , Berger R. L. , Collins G. A. , Decker C. B. , Divol L. , Glenzer S. H. , Hammel B. A. , Jones R. , Kirkwood R. K. , Kruer W. L. , MacGowan B. J. , Pipes J. , Suter L. J. , Thoe R. , Unites W. , Young P. E.
Published: April 2004

The dependence of stimulated backward and forward scattered light on ion acoustic damping (νi) is measured for the first time in a long scale length He/H2 composition plasma at a density of 0.08 critical for 351-nm laser light. Both the stimulated Raman and Brillouin backscattering decrease with increasing ion acoustic damping. Modeling of the backward scattering agrees with the measurements when the Langmuir and ion acoustic fluctuations saturate at δn/n=0.01 and 0.001, respectively. These low saturation levels cannot be explained using standard nonlinear wave decay saturation mechanisms and may indicate that other saturation mechanisms are active in this plasma. Modeling of the forward scattering agrees qualitatively with the measurements and provides an estimate of the density fluctuations in the plasma.
Different current conduction mechanisms through thin high-k HfxTiySizO films due to the varying Hf to Ti ratio
Authors: Paskaleva A. , Bauer A. J. , Lemberger M. , Zürcher S.
Published: April 2004

We have investigated the electrical behavior of high permittivity (high-k) hafnium–titanium–silicate (HfxTiySizO) layers with different Hf:Ti ratios in the films. The films are prepared by metalorganic chemical vapor deposition using a mixture of two single source precursors. Oxide and interface charges, leakage currents and conduction mechanisms are found to be a strong function of the film composition. The films with Hf content less than 10 at. % show lower levels of oxide and interface charges and higher dielectric constant whereas those with Hf content higher than 15 at. % have better leakage current properties. A strong evidence is presented that in films with Hf content lower than 10 at. % the conduction process is governed by a phonon-assisted tunneling, i.e., it is defined rather by the intrinsic properties of the material than by its defect structure.
Surface morphology evolution during Si capping of Ge islands grown on Si(001)-c(4×4)
Authors: Aı̈t-Mansour K. , Dentel D. , Bischoff J. L. , Kubler L.
Published: April 2004

The Si capping of small Ge dots nucleated on a C-precovered Si(001) surface has been investigated by means of reflection high-energy electron diffraction and atomic force microscopy. The growth at 500 °C of three Ge monolayers on the C-induced c(4×4) reconstruction leads to the nucleation of isolated dots, without any wetting layer. Up to a nominal thickness of 5 nm, the surface evolution during the Si cap layer deposition reveals island preservation. A mean size enhancement is even observed for these covered islands. Contrary to the Si capping situation of Ge islands on bare Si surfaces (without C seeding), where a surface smoothing is observed after few monolayers, the modified C-induced surface strain promotes a final Si adatom adsorption on the top of the Ge islands. A rough morphology is therefore maintained during the cap layer growth by this selective Si coverage. The general surface smoothing and the in-plane lattice parameter recovery toward Si bulk values are also strongly delayed.
Cluster size and composition variations in yellow and red light-emitting InGaN thin films upon thermal annealing
Authors: Feng Shih-Wei , Tang Tsung-Yi , Lu Yen-Cheng , Liu Shi-Jiun , Lin En-Chiang , Yang C. C. , Ma Kung-Jen , Shen Ching-Hsing , Chen L. C. , Kim K. H. , Lin J. Y. , Jiang H. X.
Published: April 2004

We study thermal annealing effects on the size and composition variations of indium-aggregated clusters in two InGaN thin films with photoluminescence (PL) in the yellow and red ranges. The methods of investigation include optical measurement, nanoscale material analysis, and theoretical calculation. Such a study is important for determining the relation between the band gap and the average indium content of InGaN. In one of the samples, the major part of the PL spectrum is shifted from the yellow band into the blue range upon thermal annealing. In the other sample, after thermal annealing, a broad spectrum covering the whole visible range is observed. Cathodo-luminescence (CL) spectra show that the spectral changes occur essentially in the photons emitted from the shallow layers of the InGaN films. Photon emission spectra from the deeper layers are essentially unaffected by thermal annealing. The spectral changes upon thermal annealing are mainly attributed to the general trend of cluster size reduction. This interpretation is supported by the CL, x-ray diffraction, and high-resolution transmission electron microscopy results. To obtain a basic physics picture behind the spectral blue shift upon thermal annealing in the yellow emission sample, we theoretically study the quantum-confinement effects of InGaN clusters based on a quantum box model. The theoretical results can generally explain the large blue shift of PL spectral peak position.
Direct piezoelectric effect in relaxor-ferroelectric single crystals
Authors: Davis Matthew , Damjanovic Dragan , Setter Nava
Published: April 2004

Direct measurements of longitudinal (d33) and transverse (d31) piezoelectric coefficients have been made on cuboid samples of [001]C-poled 0.955Pb[Zn1/3Nb2/3]O3-0.045PbTiO3 (PZN-4.5PT) and 0.68Pb[Mg1/3Nb2/3]O3-0.32PbTiO3 (PMN-32PT) single crystals. The measurements were made in a Berlincourt-type press over a wide range of dynamic and static bias stresses. In the transverse mode, the response was found to be essentially anhysteretic and d31 was independent of the dynamic stress amplitude. In contrast, for the longitudinal mode, the piezoelectric charge-stress behavior is hysteretic. Moreover, the relative hysteresis size and the d33 coefficient are both strong functions of bias stress, dynamic stress amplitude, and frequency; coupling of the dynamic stress dependency of d33 to the charge-stress hysteresis is demonstrated by a quasi-Rayleigh-type relationship. The observed hysteretic response could be due to domain switching in the crystals although this would be unexpected for a [001]C-poled rhombohedral crystal. Instead, following the observed difference between transverse and longitudinal behaviors, it is suggested that polarization rotation away from the poling direction leads to a hysteretic response.
Structural modification of silica glass by laser scanning
Authors: Zhao Jian , Sullivan James , Zayac John , Bennett Ted D.
Published: April 2004

The thermophysical nature of rapid CO2 laser heating of silica glass is explored using a numerical simulation that considers the structural state of the glass, as characterized by the fictive temperature. The fictive temperature reflects the thermodynamic temperature at which the glass structure would be in equilibrium. To demonstrate that the thermophysical model can accurately predict the structural change in the glass, the fictive temperature is measured experimentally utilizing the fact that the fictive temperature change corresponds to a change of glass properties that can be revealed through wet chemical etching. The relationship between the etch rate and the fictive temperature is determined by preparing and etching samples of known fictive temperature. Wet chemical etching is used to measure the fictive temperature over the entire laser affected zone and the results are found to compare favorably with the results of the thermophysical model. The model and experimental measurements demonstrate that rapid laser processing results in an increased fictive temperature near the surface of the glass. The fictive temperature increase is about 1000 K and is uniform to within 5% over the laser affected zone. Near the boundary of this zone, the fictive temperature transitions abruptly to the value of the surrounding untreated glass.
Effect of dye concentration on the charge carrier transport in molecularly doped organic light-emitting diodes
Authors: Chen Jiangshan , Ma Dongge
Published: April 2004

The effect of the concentration of 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7, 7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as dopant in tris(8-quinolinolato) aluminum (Alq3) on the charge carrier transport in Alq3:DCJTB was investigated by measuring the steady current-voltage characteristics and the transient electroluminescence. The dopant concentration dependence of the current-voltage relationship clearly indicates the carrier trapping by the DCJTB molecule. The DCJTB concentration significantly affects the electron mobility in Alq3:DCJTB. The mobility has a nontrivial dependence on the doping level. For relatively low doping levels, less than 1%, the electron mobility of Alq3:DCJTB decreases with the doping level. An increasing mobility is then observed if the dopant concentration is further increased, followed by a decrease for doping levels larger than ∼2%. The change of the electron mobility with the DCJTB concentration in Alq3 is attributed to the additional energetic disorder due to potential fluctuations caused by the dipole–dipole interaction of random distribution dopant at the relatively low doping concentration, and to the phase separation at the high doping concentration.
Dynamics of Tm–Ho energy transfer and deactivation of the F43 low level of thulium in fluorozirconate glasses
Authors: da Vila L. D. , Gomes L. , Tarelho L. V. G. , Ribeiro S. J. L. , Messaddeq Y.
Published: April 2004

The mechanism involved in the Tm3+ (3F4)→Ho3+ (5I7) energy transfer and Tm3+ (3H4, 3H6)→Tm3+ (3F4, 3F4) cross relaxation as a function of the donor and acceptor concentrations was investigated in Tm–Ho-codoped fluorozirconate glasses. The experimental transfer rates were determined for the Tm→Ho energy transfer from the best fit of the acceptor luminescence decay using an expression which takes into account the Inokuti–Hirayama model and localized donor-to-acceptor interaction solution. The original acceptor solution derived from the Inokuti–Hirayama model fits well the acceptor luminescence transient only for low-concentrated systems. The results showed that a fast excitation diffusion that occurs in a very short time (t≪γ−2) reduces the mean distance between an excited donor (D*) and the acceptor (A). A localized donor-to-acceptor interaction takes place, leading to an exponential decay of donors as an average of the microscopic rate equation solution of each D*–A pair separated by distance R that contributes in addition to the Inokuti–Hirayama solution. The observation that the experimental transfer rates were always much bigger than the one predicted by the diffusion model, in which the energy transfer process is assisted by excitation migration among donors state, reinforces the existence of a fast excitation diffusion among donor ions before the energy transfer to acceptor already observed in Yb:Er:ZBLAN. The fast excitation diffusion effect was observed to dominate both the Tm→Tm cross relaxation and Tm→Ho energy transfer ions from H43 and F43 thulium states, respectively.
Fractional Brownian motion of an Al nanosphere in liquid Al–Si alloy under electron-beam irradiation
Authors: Yokota Takeshi , Howe J. M. , Jesser W. A. , Murayama M.
Published: April 2004

Fractional forces and Brownian motion are expected to govern the behavior of nanoscale metallic solids in liquids, but such systems have not been studied. We investigated the motion of a crystalline Al nanosphere inside a partially molten Al–Si alloy particle, using an electron beam to both stimulate and observe the motion of the nanosphere. The irregular motion observed was quantified as antipersistant fractional Brownian motion. Analysis of possible phenomena contributing to the motion demonstrates that the incident electrons provide the fractional force that moves the Al nanosphere and that gravity and the oxide shell on the partially molten particle cause the antipersistant behavior.
Role of hydrogen in molecular beam epitaxy of ZnO
Authors: Sano Michihiro , Miyamoto Kazuhiro , Kato Hiroyuki , Yao Takafumi
Published: April 2004

The role of hydrogen in the growth and material properties of ZnO films grown at temperature as low as 300 °C by plasma-assisted molecular beam epitaxy with and without hydrogen irradiation was investigated. Results showed that during growth, the surface morphology changed from small hemispherical grains (10 nm) to large hexagonal islands (100 nm) by molecular hydrogen irradiation. The observed changes in the surface morphology correlated with the surface migration length of Zn adatoms on the surface with or without H termination. X-ray diffraction and photoluminescence measurements showed that the structural and optical properties of ZnO films were significantly improved by H2 irradiation during growth and that the ZnO films grown here at low temperature (300 °C) by H2 irradiation had crystalline quality as high as that of ZnO grown at higher temperature (600 °C) without H2 irradiation. Secondary ion mass spectrometry and Hall effect measurements indicated that most of hydrogen incorporated in the ZnO films grown here did not act as shallow donors.
Theory of the composition dependence of the band offset and sheet carrier density in the GaN/AlxGa1−xN heterostructure
Authors: Satpathy S. , Popovic Z. S. , Mitchel W. C.
Published: April 2004

We present a systematic study of the sheet carrier density and valence-band offset in the GaN/AlxGa1−xN(0001) heterostructure as a function of x from ab initio density-functional methods. We find that the calculated sheet carrier density increases rapidly with x for x⩽0.3 in good agreement with experiments, but beyond this concentration, it quickly saturates to a value of about 2×1013 cm−2. The band offset shows a small asymmetry between the Ga-face and N-face interfaces and changes more or less linearly with x, although a small bowing is found. The layer-projected densities of states indicate the formation of the two-dimensional electron gas at the Ga-face interface and confirm the absence of interface states in the gap.
Ionization instability by energized electrons in weakly ionized unmagnetized plasmas
Authors: Conde L.
Published: April 2004

A fluid model for an ionization instability in weakly ionized and non magnetized plasmas is presented. The equilibrium state is assumed to exist in a plasma where additional ionizations are produced by an energized electron group Jeb, considered as monoenergetic, with energy exceeding the ionization threshold of the neutral gas. Ionization by thermal electrons and all charge losses are contemplated and the Poisson equation relates the plasma potential fluctuations with electric charge densities. The leading role of elastic collisions between ions and neutral atoms is evidenced and determines the characteristic time and length scales. The instability requires a minimum suprathermal electron current density Jeb within a narrow energy range. According to the magnitude of this current, two different growth modes are possible separated by a bifurcation point. There is aperiodic exponential growth for low wave numbers and an increasing amplitude plasma wave from the bifurcation up to a maximum wave number. This latter feature determines the characteristic length for electric charge fluctuations. The quasineutral approximation recovers the exponential growth modes but fails to predict this maximum wave number for the oscillatory growth rate.
Role of trapped electron mode turbulence in internal transport barrier control in the Alcator C-Mod Tokamak
Authors: Ernst D. R. , Bonoli P. T. , Catto P. J. , Dorland W. , Fiore C. L. , Granetz R. S. , Greenwald M. , Hubbard A. E. , Porkolab M. , Redi M. H. , Rice J. E. , Zhurovich K. , Group Alcator C-Mod
Published: April 2004

Nonlinear gyrokinetic simulations of trapped electron mode (TEM) turbulence, within an internal particle transport barrier, are performed and compared with experimental data. The results provide a mechanism for transport barrier control with on-axis radio frequency heating, as demonstrated in Alcator C-Mod experiments [S. J. Wukitch et al., Phys. Plasmas 9, 2149 (2002)]. Off-axis heating produces an internal particle and energy transport barrier after the transition to enhanced Dα high confinement mode. The barrier foot reaches the half-radius, with a peak density 2.5 times the edge density. While the density profile peaks, the temperature profile remains relatively unaffected. The peaking and concomitant impurity accumulation are controlled by applying modest central heating power late in the discharge. Gyrokinetic turbulence simulations of the barrier formation phase, using the GS2 code [W. Dorland et al., Phys. Rev. Lett. 85, 5579 (2000)] show that toroidal ion temperature gradient driven modes are suppressed inside the barrier foot, but continue to dominate in the outer half-radius. As the density gradient steepens further, trapped electron modes are driven unstable. The onset of TEM turbulence produces an outflow that strongly increases with the density gradient, upon exceeding a new nonlinear critical density gradient, which significantly exceeds the linear critical density gradient. The TEM turbulent outflow ultimately balances the inward Ware pinch, leading to steady state. Moreover, the simulated turbulent particle diffusivity matches that inferred from particle balance using measured density profile data and the calculated Ware pinch. This turbulent diffusivity exhibits a strong unfavorable temperature dependence that allows control with central heating.
Faraday rotation spectra of bismuth-substituted rare-earth iron garnet crystals in optical communication band
Authors: Zhang Guang-Yu , Xu Xue-Wu , Chong Tow-Chong
Published: April 2004

Bismuth-substituted rare-earth iron garnet (REBIG) crystals are used in optical isolators for optical communication. However, the Faraday rotation (FR) spectra of REBIG crystals in the wavelength region of 1.3–1.6 μm have not yet been theoretically studied. To interpret the spectra, we assumed that the FR in this wavelength range was dominated by the contribution of the electric dipole transitions, and calculated the FR spectra. REBIG bulk crystals were grown from the Bi2O3 self-fluxed melt by the top-seeded solution growth method. The experimental results agreed with the theoretical calculation of FR in (HoBi)3Fe5O12, (YbBi)3Fe5O12, (YYbBi)3Fe5O12, and (TbBi)3Fe5O12. The results indicate that the theoretical analysis method of the FR spectra of REBIG in the visible range of wavelengths can be applied in the optical communication band.
Numerical studies on the stabilization of neoclassical tearing modes by radio frequency current drive
Authors: Yu Q. , Zhang X. D. , Günter S.
Published: April 2004

Numerical modeling on the stabilization of neoclassical tearing modes by localized radio frequency (rf) current drive has been carried out to study the effects of various wave and plasma parameters on the stabilization and the associated physics. The change of the rf current profile due to the magnetic island has been taken into account by modeling the two-dimensional transport of the fast electrons induced by the rf wave. It is found that, when the rf deposition width is much larger than the island width, the modulated rf current drive to deposit the rf current around the island’s o point has a stronger stabilizing effect than a nonmodulated one. The slowing down time of the fast electrons and the initial island width when applying the rf wave are also found to be important in determining the stabilizing effect.
Confined electron-confined phonon scattering rates in wurtzite AlN/GaN/AlN heterostructures
Authors: Pokatilov Evgenii P. , Nika Denis L. , Balandin Alexander A.
Published: April 2004

We investigate theoretically confined electron-confined phonon scattering rates in three-layered planar wurtzite AlN/GaN/AlN heterostructures with free-surface boundary conditions. The thicknesses of the core and cladding layers are chosen to be a few nanometers to ensure phonon and electron spectrum modification due to spatial confinement. We have considered electron-phonon interactions via deformation and piezoelectric potentials. The scattering rates are calculated for both intra- and intersubband transitions of confined electrons. The influence of the built-in electric field, characteristic for GaN/AlN interfaces, on polarization and intensity of the electron-acoustic phonon interaction in heterostructures is discussed. Specific features of the deformation and piezoelectric scattering of electrons in wurtzite three-layered heterostructures and their differences from the scattering in homogenous slabs have been established. It has been shown that it is possible to tune the strength of the electron-phonon interaction in a desired way by varying the core and cladding layers thicknesses. The obtained results can be used for optimization of GaN-based heterostructures for electronic and spintronic applications.
Interface steps in field effect devices
Authors: Wehrli Samuel , Helm Christian
Published: April 2004

The charge doped into a semiconductor in a field effect transistor (FET) is generally confined to the interface of the semiconductor. A planar step at the interface causes a potential drop due to the strong electric field of the FET, which in turn is screened by the doped carriers. We analyze the dipolar electronic structure of a single step in the Thomas–Fermi approximation and find that the transmission coefficient through the step is exponentially suppressed by the electric field and the induced carrier density as well as by the step height. In addition, the field enhancement at the step edge can facilitate the electric breakthrough of the insulating layer. We suggest that these two effects may lead to severe problems when engineering FET devices with very high doping. On the other hand, steps can give rise to interesting physics in superconducting FETs by forming weak links and potentially creating atomic size Josephson junctions.
Aspect ratio dependence of the ideal internal kink mode stability in a toroidal plasma with circular cross section
Authors: Wahlberg C.
Published: April 2004

The theory by Bussac et al. [Phys. Rev. Lett. 35, 1638 (1975)] on the stability of the ideal, internal kink mode in a toroidal plasma with circular cross section is extended to finite values of the inverse aspect ratio εa. The aspect ratio dependence comes from the term following the Bussac term in a large aspect ratio expansion of the potential energy δW of the mode. Although formally of higher order in the inverse aspect ratio, this term is of the same order of magnitude as the Bussac term when the safety factor q is close to (but below) unity at the plasma center and εa is finite. The new term is always stabilizing, but affects δW only marginally when the poloidal beta value βp is small and/or εa is small. For values of εa relevant for most tokamaks and βp larger than 0.3–0.5, however, the new term strongly modifies δW and leads to a second stability regime of the ideal, internal kink mode, in agreement with earlier numerical calculations.
Structure of the OH− stretching vibrational band in SrxBa1−xNb2O6
Authors: David C. , Tunyagi A. , Ulex M. , Wöhlecke M. , Betzler K. , Lengyel K. , Kovács L.
Published: April 2004

The stretching mode of the hydroxyl ions in SrxBa1−xNb2O6 crystals with x=0.38 to 0.79 has been measured by the Fourier transform infrared spectroscopy technique. The main absorption band at about 3493 cm−1 is accompanied by a shoulder on the low energy side. The shape of the shoulder depends strongly on the Sr/Ba ratio of the crystal which allows a rough estimation of the composition. The main absorption band including the shoulder has been decomposed using Lorentzian and Gaussian curves and the parameters of three components have been determined. The components are attributed to OH− transitions in different cation environments strongly depending on the crystal composition. The temperature dependence of the OH− absorption band is approximately linear in the 20–200 °C range and does not show any peculiarities at the phase transition temperature.
ZnO-channel thin-film transistors: Channel mobility
Authors: Hoffman R. L.
Published: April 2004

ZnO-channel thin-film transistor (TFT) test structures are fabricated using a bottom-gate structure on thermally oxidized Si; ZnO is deposited via RF sputtering from an oxide target, with an unheated substrate. Electrical characteristics are evaluated, with particular attention given to the extraction and interpretation of transistor channel mobility. ZnO-channel TFT mobility exhibits severe deviation from that assumed by ideal TFT models; mobility extraction methodology must accordingly be recast so as to provide useful insight into device operation. Two mobility metrics, μavg and μinc, are developed and proposed as relevant tools in the characterization of nonideal TFTs. These mobility metrics are employed to characterize the ZnO-channel TFTs reported herein; values for μinc as high as 25 cm2/V s are measured, comprising a substantial increase in ZnO-channel TFT mobility as compared to previously reported performance for such devices.
Pressure measurements from Raman spectra of stressed diamond anvils
Authors: Popov M.
Published: April 2004

The problem of pressure measurements in a diamond anvil cell from Raman spectra of stressed diamond anvils have been studied. A splitting of the threefold-degenerate optic mode of diamond into singlet and doublet modes was observed in the Raman spectra from the stressed anvils. On the basis of the splitting effect quantitative relations between Raman spectra from the diamond anvil tip, stresses in the anvil tip and pressure in a sample have been considered. The obtained results demonstrate that Raman spectra from the diamond anvil tip can be widely used for measurements of the normal stress in the sample (or pressure for the quasi-hydrostatic compression). The calibration of the Raman spectra against the sample pressure up to 220 GPa has been proposed.
Sources of variation in fibre diameter attributes of Australian alpacas and implications for fleece evaluation and animal selection
Authors: McGregor B. A. , Butler K. L.
Published: April 2004

Sources of variation in fibre diameter attributes of Australian alpacas and implications for fleece evaluation and animal selection were investigated using data collected in the years 1994–97, from 6 properties in southern Australia. Data were analysed using REML (multiple regression analysis) to determine the effect on mean fibre diameter (MFD) and coefficient of variation of MFD (CV(FD)) of age, origin (property), sex (entire male, female), breed (Huacaya, Suri), liveweight, fibre colour, individual, and interactions of these effects. The mean (n = 100) age (range) was 4.2 years (0.1–11.9), liveweight 72.0 kg (12.0–134 kg), MFD 29.1 μm (17.7–46.6 μm), CV(FD) 24.33% (15.0–36.7%). A number of variables affected MFD and CV(FD). MFD increased to 7.5 years of age, and correlations between MFD at 1.5 and 2 years of age with the MFD at older ages were much higher than correlations at younger ages. Fibre diameter 'blowout' (increase with age) was positively correlated with the actual MFD at ages 2 years and older. There were important effects of farm, and these effects differed with year and shearing age. Suris were coarser than Huacayas with the effect reducing with increased liveweight; there was no effect of sex. Fleeces of light shade were 1 μm finer than dark fleeces. CV(FD) declined rapidly between birth and 2 years of age, reaching a minimum at about 4 years of age and then increasing; however, CV(FD) measurements on young animals were very poor predictors of CV(FD) at older ages, and the response of CV(FD) to age differed with farm and year. Suris had a higher CV(FD) than Huacayas on most properties, and MFD, liveweight, and sex did not affect CV(FD). Fleeces of dark shade had higher CV(FD) than fleeces of light shade in 2 of the years. It is concluded that there are large opportunities to improve the MFD and CV(FD) of alpaca fibre through selection and breeding. The potential benefit is greatest from reducing the MFD and CV(FD) of fibre from older alpacas, through reducing the between-animal variation in MFD and CV(FD). Sampling alpacas at ages <2 years is likely to substantially decrease selection efficiency for lifetime fibre diameter attributes.
Assessment of quality defects in macadamia kernels using NIR spectroscopy
Authors: Guthrie John , Greensill Colin , Bowden Ray , Walsh Kerry
Published: April 2004

Spectral data were collected of intact and ground kernels using 3 instruments (using Si-PbS, Si, and InGaAs detectors), operating over different areas of the spectrum (between 400 and 2500 nm) and employing transmittance, interactance, and reflectance sample presentation strategies. Kernels were assessed on the basis of oil and water content, and with respect to the defect categories of insect damage, rancidity, discoloration, mould growth, germination, and decomposition. Predictive model performance statistics for oil content models were acceptable on all instruments (R2 > 0.98; RMSECV < 2.5%, which is similar to reference analysis error), although that for the instrument employing reflectance optics was inferior to models developed for the instruments employing transmission optics. The spectral positions for calibration coefficients were consistent with absorbance due to the third overtones of CH2 stretching. Calibration models for moisture content in ground samples were acceptable on all instruments (R2 > 0.97; RMSECV < 0.2%), whereas calibration models for intact kernels were relatively poor. Calibration coefficients were more highly weighted around 1360, 740 and 840 nm, consistent with absorbance due to overtones of O-H stretching and combination. Intact kernels with brown centres or rancidity could be discriminated from each other and from sound kernels using principal component analysis. Part kernels affected by insect damage, discoloration, mould growth, germination, and decomposition could be discriminated from sound kernels. However, discrimination among these defect categories was not distinct and could not be validated on an independent set.It is concluded that there is good potential for a low cost Si photodiode array instrument to be employed to identify some quality defects of intact macadamia kernels and to quantify oil and moisture content of kernels in the process laboratory and for oil content in-line. Further work is required to examine the robustness of predictive models across different populations, including growing districts, cultivars and times of harvest.
Context evaluation: a profile of irrigator climate knowledge, needs and practices in the northern Murray - Darling Basin to aid development of climate-based decision support tools and information and dissemination of research
Authors: Keogh D. U. , Abawi G. Y. , Dutta S. C. , Crane A. J. , Ritchie J. W. , Harris T. R. , Wright C. G.
Published: April 2004

Understanding client needs, knowledge and practices offers a means of ensuring research outputs match intended audience requirements. This paper shows the initial impact of context evaluation on the development of a suite of decision support tools and information to help irrigators better manage their water resources under different climatic conditions. The context evaluation study involved a survey of ~170 irrigators in the northern Murray�Darling Basin in Australia. It sought to clarify how they make cropping area and water management decisions and their levels of understanding and use of climate information. We found irrigators consult widely on cropping decisions and those with large areas commonly apply the Southern Oscillation Index to property decisions. Respondents demonstrated a reasonably good understanding of climate phenomena in an Southern Oscillation Index knowledge test. Two-thirds use seasonal climate outlook information, but only 20% are very confident to apply climate information to decisions. More than half would find a decision support system (comprising tools and information) useful for cropping decisions. Almost 75% would change their crop area, and 43% their crop type, if given advance information about water availability up to 4 months ahead of irrigation season. About 70% have access to a computer and half to the internet, but two-thirds consider their personal computing skill is only nil or basic. Twenty-three percent of respondents expressed interest in working directly with the research team to interact regarding their requirements, indicating the potential for future participative research activities such as collaborative, on-farm research. The context evaluation facilitated formation of a focus group that cooperated to assess research findings and incorporate improvements to the project�s set of decision support tools. The evaluation was a new experience for the researchers and, albeit an arms-length consultation process, it has broadened our knowledge about our target audience and their preferred ways to access research findings.
Social principles for agricultural extension to assist in the promotion of natural resource management
Authors: Vanclay F.
Published: April 2004

An understanding of social issues, the social nature of farming, and the social basis of adoption is needed if agricultural extension is to be effective in addressing natural resource management issues, and in promoting sustainability in its triple bottom line conceptualisation. Twenty-seven principles are presented here, with the key principles being: awareness of farming as a social activity; recognition of the social diversity of farmers and the social drivers in agriculture; and the socio-cultural basis of adoption.
Use of nuclear genes for phylogeny reconstruction in plants
Authors: Small Randall L. , Cronn Richard C. , Wendel Jonathan F.
Published: April 2004

Molecular data have had a profound impact on the field of plant systematics, and the application of DNA-sequence data to phylogenetic problems is now routine. The majority of data used in plant molecular phylogenetic studies derives from chloroplast DNA and nuclear rDNA, while the use of low-copy nuclear genes has not been widely adopted. This is due, at least in part, to the greater difficulty of isolating and characterising low-copy nuclear genes relative to chloroplast and rDNA sequences that are readily amplified with universal primers. The higher level of sequence variation characteristic of low-copy nuclear genes, however, often compensates for the experimental effort required to obtain them. In this review, we briefly discuss the strengths and limitations of chloroplast and rDNA sequences, and then focus our attention on the use of low-copy nuclear sequences. Advantages of low-copy nuclear sequences include a higher rate of evolution than for organellar sequences, the potential to accumulate datasets from multiple unlinked loci, and bi-parental inheritance. Challenges intrinsic to the use of low-copy nuclear sequences include distinguishing orthologous loci from divergent paralogous loci in the same gene family, being mindful of the complications arising from concerted evolution or recombination among paralogous sequences, and the presence of intraspecific, intrapopulational and intraindividual polymorphism. Finally, we provide a detailed protocol for the isolation, characterisation and use of low-copy nuclear sequences for phylogenetic studies.