bluuebunny/crossref_metadata_2025 huggingface dataset:
Ferroelectric-relaxor behavior of Ba(Ti0.7Zr0.3)O3 ceramics
Authors: Yu Zhi , Ang Chen , Guo Ruyan , Bhalla A. S.
Published: September 2002

Ferroelectric-relaxor behavior of Ba(Ti0.7Zr0.3)O3 ceramics is studied in the temperature range from 150 to 450 K. A broad dielectric peak with a high-dielectric maximum exhibits frequency dispersion. The dielectric relaxation rate follows the Vogel–Fulcher relation with E=0.21 eV and TVF=199.6 K. The polarization hysteresis loops were observed with a remnant polarization of 10 μC/cm2 at 175 K. The high-dielectric constant and high-polarization properties are expected to find practical applications at low temperatures.
Compatibility of state assignments
Authors: Mermin N. David
Published: September 2002

Rudolf Peierls raised the question of when different density matrices can characterize the knowledge available to different people about one and the same physical system. I describe counterexamples to the condition he imposed on such state assignments, and suggest what the correct condition ought to be.
Electromechanical instability of microscale structures
Authors: Yang Fuqian
Published: September 2002

Electrical pull-in instability of microscale structures is an important failure mechanism in microelectromechanical systems (MEMS), in which there is no equilibrium state for the MEMS structures. Using the elastic membrane theory, the electromechanical interaction of a suspended MEMS structure in an electric field is presented. The statically mechanical deformation of the microscale membrane under electrostatic loading is examined. The critical value of electric voltage needed to pull the membrane into the contact with the substrate is determined analytically. The critical pull-in electric voltage is proportional to the square root of the residual tensile force and inversely proportional to the length of the membrane if the residual line tensile force is much larger than the line force due to the stretch of the membrane, while it is inversely proportional to the square of the membrane length if the membrane is initially stress free. The contact problem after the occurrence of the pull-in collapse phenomenon is studied. It turns out that the contact length between the membrane and the substrate increases with the increase of the membrane length and the electric voltage, and decreases with the tensile force in the membrane. A closed-form solution on the release–electric voltage is obtained, which depends on the membrane length and the tensile force.
Theory of the thermal conductivity of molecular liquids: Nitrogen and carbon dioxide
Authors: Rah Kyunil , Eu Byung Chan
Published: September 2002

A statistical mechanical formula of the thermal conductivity of molecular liquids is developed as a generalization to molecular fluids of the theory of thermal conductivity of simple liquids reported recently. The theoretical expression presented for the thermal conductivity of molecular liquids consists of the kinetic part independent of the density and the density-dependent potential part. The latter is given in terms of the intermolecular forces, pair correlation function, and self-diffusion coefficient, in a form similar to the shear and bulk viscosities of the molecular liquids. A generalized Eucken relation is also derived for molecular liquids that relates thermal conductivity to shear viscosity, and used for the calculation of thermal conductivities. The theoretical result obtained for thermal conductivity is successfully tested against experimental data on nitrogen and carbon dioxide available in the literature.
Shadowgraphic imaging of the sub-ps laser-induced forward transfer process
Authors: Papazoglou D. G. , Karaiskou A. , Zergioti I. , Fotakis C.
Published: September 2002

The subpicosecond laser-induced forward transfer process (LIFT) was investigated by means of time-resolved shadowgraphic imaging. The dynamics of the subpicosecond LIFT process of InOx was investigated for time delays between 0.01 and 10 μs following laser irradiation pulse. Measured values of the velocities of the ejected material were to 400±10 m/s, depending on the laser fluence. The fraction of the material ejected by the subpicosecond LIFT process, which is visible to the shadowgraphic technique was measured to be highly directional with narrow angular divergence (3°). Such direct dynamic transfer of the material opens up application possibilities for the fabrication of high-spatial-resolution microstructures.
Multi-diagnostic comparison of femtosecond and nanosecond pulsed laser plasmas
Authors: Zhang Z. , VanRompay P. A. , Nees J. A. , Pronko P. P.
Published: September 2002

Understanding and fully characterizing highly dynamic and rapidly streaming laser ablation plasmas requires multiple techniques for monitoring effects at different stages. By combining multiple diagnostic methods, it is possible to analyze the broad time window over which these ablation plasmas develop and to learn more about the related physical processes that occur. Two laser sources, an 80 fs Ti:Sapphire laser (780 nm) and a 6 ns Nd:YAG laser (1.06 μm), are used in this work in order to compare pulse duration effects at similar wavelengths. Characteristics of the plasma produced by these two lasers are compared under conditions of comparable ablation flux. Results are presented involving correlation of time-resolved Langmuir probe data and electrostatic energy analysis for aluminum plasmas as a representative investigation for metallic systems. In addition, continuous-wave refractive index laser beam deflection is used to characterize the plasma and hot gas generated from boron nitride targets in terms of their ion and neutral atom densities. A self-similarity plasma expansion model is used to analyze the plumes under various conditions. Fundamental data obtained in this way can be relevant to laser micro-machining, laser induced breakdown spectroscopy, and pulsed laser deposition.
Morphologic and magnetic properties of Pd100−xFex nanoparticles prepared by ultrasound assisted electrochemistry
Authors: Guzman Maribel , Delplancke Jean-Luc , Long Gary J. , Delwiche Jacques , Hubin-Franskin Marie-Jeanne , Grandjean Fernande
Published: September 2002

Nanopowdered alloys of Pd100−xFex, with x=4, 6, 8, and 12, have been prepared by ultrasound assisted electrochemistry. The composition of the individual particles, as determined by x-ray fluorescence, and the bulk composition, as determined by atomic absorption, are in agreement within experimental error. Transmission electron microscopy indicates that the nanopowders consist of agglomerates of small grains with a radius of approximately 5 nm, a radius which is confirmed by the broadening of the reflections in the x-ray powder diffraction patterns. X-ray fluorescence analysis of individual grains indicates a homogeneous distribution of palladium and iron throughout the grains. The x-ray diffraction patterns indicate that solid solutions of iron in palladium show no evidence of any pure palladium, any pure iron, or any other PdFe compound. The 78 K iron-57 Mössbauer spectra of these nanopowders reveal the presence of one magnetic sextet assigned to slowly relaxing superparamagnetic particles of Pd100−xFex and one weak doublet, which is assigned to rapidly relaxing superparamagnetic particles of Pd100−xFex. The hyperfine fields of 29.0 to 31.0 T are typical of iron in a metallic alloy and correspond to a magnetic moment of approximately 2 μB per iron atom. The hysteresis curves obtained at 4.2, 100, and 295 K with a vibrating sample magnetometer are typical of superparamagnetic particles with saturation magnetization values which are substantially smaller than those observed for the bulk. The fit of the magnetization curves with a Langevin function yields estimates of the particle radii which are in good agreement with those obtained both by transmission electron microscopy and by the broadening of the x-ray diffraction peaks.
Rotational effects in the study of the phase lag in the coherent control of HI
Authors: Lefebvre-Brion Hélène
Published: September 2002

A method which introduces the rotation in the calculation of both the dissociation and the autoionization cross sections by the unified multichannel quantum theory is developed. This is applied to the study of the ionization and dissociation phases observed in the coherent control of the 5sσ resonance of HI and DI. It is shown that the absolute value of the dissociation phase is maximum in the vicinity of this resonance.
Nanoscale observation of photoinduced domain pinning and investigation of imprint behavior in ferroelectric thin films
Authors: Gruverman A. , Rodriguez B. J. , Nemanich R. J. , Kingon A. I.
Published: September 2002

Piezoresponse force microscopy has been used to investigate the nanoscale mechanism of imprint behavior of ferroelectric PbTiO3 thin films by studying the photoinduced changes in the hysteresis loops of individual grains. Illumination of the film with UV light resulted in a voltage shift opposite to that observed in ferroelectric thin film capacitors. This effect is attributed to the generation of an electric field within the surface dielectric layer as a result of the interaction between photoinduced charges and polarization charges. Application of a small nonswitching bias to the film with simultaneous UV illumination resulted in domain pinning in the grains where the polarization direction coincided with the direction of the applied field, in agreement with the proposed model. Domain pinning was also observed in grains with polydomain structure suggesting that charge entrapment at the existing domain boundaries in the bulk of the film contributes to the suppression of switchable polarization. However, a symmetric character of hysteresis loops observed in such grains implies that charge entrapment in the bulk of the film does not cause the voltage shift. It has been suggested that a thin high-dielectric interfacial layer can improve the imprint behavior of ferroelectric capacitors.
Comparison of models of electroluminescence in organic double-layer light-emitting diodes
Authors: Nikitenko V. R. , Salata O. V. , Bässler H.
Published: September 2002

A theoretical model of leakage and barrier-limited recombination of charge carriers at the interface separating two disordered organic materials in organic light-emitting diodes is formulated. Spatial disorder of molecular materials is reflected in the model by differentiating the hopping distances associated with jumps leading to recombination from those leading to leakage. The former and the latter are determined by the mean intersite distance and by the shortest hopping distance, respectively. It is shown that the effect of the difference between the two hopping distances on the current and recombination efficiencies depends on a barrier height and electric field strength at the organic–organic interface. The results of the models with barrier-limited recombination and Langevin recombination are compared. It is shown that both models yield comparable results for the steady-state recombination efficiency and current, if at least one of the interfacial energy barriers is small enough and the leakage is modeled in the same way. Thus broad applicability of the Langevin model is shown, when a suggested leakage model is used. The importance of microscopic correlations in the relative positions of electrons and holes at the organic–organic interface is discussed.
High-responsivity, normal-incidence long-wave infrared (λ∼7.2 μm) InAs/In0.15Ga0.85As dots-in-a-well detector
Authors: Raghavan S. , Rotella P. , Stintz A. , Fuchs B. , Krishna S. , Morath C. , Cardimona D. A. , Kennerly S. W.
Published: September 2002

Normal incidence InAs/In0.15Ga0.85As dots-in-a-well detectors operating at T=78 K with λp∼7.2 μm and a spectral width (Δλ/λ) of 35% are reported. The peak at 7.2 μm is attributed to the bound-to-bound transitions between the ground state of the dot and the states within the InGaAs well. A broad shoulder around 5 μm, which is attributed to the bound-to-continuum transition, is also observed. Calibrated blackbody measurements at a device temperature of 78 K yield a peak responsivity of 3.58 A/W (Vb=−1 V), peak detectivity=2.7×109 cm Hz1/2/W (Vb=−0.3 V), conversion efficiency of 57% and a gain ∼25.
Rotational spectroscopy of 3d transition-metal cyanides: Millimeter-wave studies of ZnCN (X 2Σ+)
Authors: Brewster M. A. , Ziurys L. M.
Published: September 2002

The pure rotational spectrum of the ZnCN radical in its X 2Σ+ ground electronic state has been recorded using millimeter/sub-mm direct absorption techniques in the range 339–543 GHz. This work is the first spectroscopic observation of this molecule, which was created by the reaction of zinc vapor and cyanogen gas in a dc discharge. Twenty-one rotational transitions were recorded for the main zinc isotopomer, ZnCN64, in its ground vibrational state, as well as 8–16 transitions for the Zn66, Zn68, and C13 isotopomers. Data was also obtained for ZnCN in several quanta of its bending mode and in the (100) stretching vibration. These measurements indicate that the most stable form of zinc and the cyanide moiety is the linear cyanide structure, as has also been found for copper and nickel. In contrast, the linear isocyanide geometry is lowest in energy for gallium and aluminum. A spectroscopic analysis has been carried out of the (000) and excited vibrational data, establishing rotational, spin-rotation, and l-type doubling parameters. Several structures (r0, rs, and rm(1)) have been determined for ZnCN as well, along with estimates of the heavy-atom stretch (ω1), and bending (ω2) frequencies. These calculations suggest that the metal–carbon bond in ZnCN is weaker than in CuCN or NiCN. The tendency of these metals to form the linear cyanide geometry, as opposed to the linear isocyanide or T-shaped structures, is additionally discussed.
The interfaces of poly(p-phenylene vinylene) and fullerene derivatives with Al, LiF, and Al/LiF studied by secondary ion mass spectroscopy and x-ray photoelectron spectroscopy: Formation of AlF3 disproved
Authors: van Gennip W. J. H. , van Duren J. K. J. , Thüne P. C. , Janssen R. A. J. , Niemantsverdriet J. W.
Published: September 2002

Two mutually exclusive mechanisms have been proposed to explain the improved electron injection by the insertion of a LiF layer between the metal cathode and the active organic layer of organic photoelectronic devices: the dipole and the doping mechanism. The possibility of the doping mechanism was studied by investigating the interface of poly[2-methoxy-5-(3′,7′dimethyl-octyloxyl)-1,4-phenylenevinylene] (MDMO-PPV) or 1-(3-(methoxycarbonyl)propyl)-1-phenyl[6,6]C61 (PCBM) with Al, LiF, or Al/LiF. In this mechanism, Li dopes the organic layer, after liberation via the reaction Al+3LiF→AlF3+3Li. If this reaction takes place, AlF3 should be detectable at the surface. However, SIMS measurements showed that AlF3 is not present at the Al/LiF/MDMO-PPV and Al/LiF/PCBM interfaces. This is evidence that the proposed reaction does not occur. Other evidence that the doping mechanism cannot be the general mechanism to explain the enhanced electron injection comes from the presence of LiF on both organic surfaces. XPS measurements indicate that there is a reaction of Al with the carboxylic oxygen of PCBM, and that a LiF layer between PCBM and Al prevents this reaction.
Sintering, oxidation, and chemical properties of size-selected nickel clusters on TiO2(110)
Authors: Aizawa Masato , Lee Sungsik , Anderson Scott L.
Published: September 2002

We report a study of Nin/TiO2 samples prepared by size-selected deposition of Nin+ (n=1,2,5,10,15) on rutile TiO2(110). The effects of deposition energy and support preparation conditions on the oxidation state of the clusters are examined by x-ray photoelectron spectroscopy (XPS). On the stoichiometric surface, Nin is stable, but oxidation can be driven by increased impact energy. For TiO2 surfaces with chemisorbed oxygen, deposited Nin are oxidized even at low impact energies. Low energy ion scattering spectroscopy was used to characterize the dispersion of Ni on the support, and provide some insight into binding morphology. Small clusters bind preferentially to oxygen sites. Large clusters bind in compact geometries and appear to retain some three dimensional character on the surface. The data suggest that the clusters neither fragment, nor agglomerate, in room temperature deposition. Temperature programmed desorption (TPD) of CO was used to characterize deposited clusters. For these small clusters, no strong desorption features are observed in the temperature range above 140 K, where CO desorbs from TiO2. The lack of CO binding is discussed in terms of strong Ni–TiO2 binding. The ion scattering data indicate that there is significant sintering, and possibly partial encapsulation, of the Ni clusters during the TPD experiments. XPS reveals little change in oxidation state. This is the first study where the oxidation state and morphology of size-selected deposited clusters has been studied, before and after TPD.
Singlet-triplet gaps in diradicals by the spin-flip approach: A benchmark study
Authors: Slipchenko Lyudmila V. , Krylov Anna I.
Published: September 2002

The spin-flip approach has been applied to calculate vertical and adiabatic energy separations between low-lying singlet and triplet states in diradicals. The spin-flip model describes both closed- and open-shell singlet and (low-spin) triplet states within a single reference formalism as spin-flipping, e.g., α→β, excitations from a high-spin triplet (Ms=1) reference state. Since both dynamical and nondynamical correlation effects are much smaller for the high-spin triplet states than for the corresponding singlet states, the spin-flip models yield systematically more accurate results than their traditional (non-spin-flip) counterparts. For all the diradicals studied in this work, the spin-flip variant of the coupled-cluster model with double excitations yields energy separations which are within less than 3 kcal/mol of the experimental or the highly accurate multireference values. In most cases the errors are about 1 kcal/mol.
Analysis of leakage current in GaAs/AlGaAs buried-heterostructure lasers with a semi-insulating GaInP:Fe burying layer
Authors: Barrios C. Angulo , Lourdudoss S. , Martinsson H.
Published: September 2002

The leakage current in recently demonstrated GaAs/AlGaAs buried heterostructure (BH) lasers with a semi-insulating (SI) GaInP:Fe burying layer has been theoretically and experimentally analyzed. Calculated current–voltage characteristics of n-GaAs/SI-GaInP/n-GaAs and p-GaAs/SI-GaInP/p-GaAs planar configurations have been studied specially to assess the behavior of SI-GaInP:Fe under electron and hole injection. Two-dimensional potential profiles have been used to explain the leakage current mechanism in the SI-GaInP-buried lasers. Simulations reveal that the total leakage current decreases as the active trap concentration in the SI-GaInP:Fe burying layer is increased as expected, but the leakage current is strongly confined in the vicinity of the active region where the local leakage current density increases significantly as the trap density increases. It is found that the insertion of a n-GaInP hole blocking layer between the p-metal and the SI-GaInP layer decreases the total leakage current. Experimental light–current and current–voltage characteristics of fabricated lasers with and without an additional n-GaInP layer, and electroluminescence (EL) emitted from the burying GaInP:Fe layers corroborate qualitatively the simulations and demonstrate the benefits of using a n-GaInP layer for reducing leakage current in these type of lasers.
Anode modification of polyfluorene-based polymer light-emitting devices
Authors: Fung M. K. , Lai S. L. , Tong S. W. , Chan M. Y. , Lee C. S. , Lee S. T. , Wu W. W. , Inbasekaran M. , O’Brien J. J.
Published: September 2002

A glycerol-modified poly(3,4-ethylene dioxythiophene) (PEDOT): poly(styrene sulfonate) (PSS) layer was used as an anode buffer layer in polymer light-emitting devices using poly(9,9-dioctylfluorene) (F8) as the emitter. Devices with a configuration of indium tin oxide/PEDOT:PSS (with or without glycerol)/F8/CsF/Al were fabricated. It was found that the glycerol-modified device showed a much larger current density than the unmodified device. At an operating voltage of 6 V, the glycerol-modified device showed a luminance of 1300 Cd/m2 and a current efficiency of 1.7 Cd/A compared to the corresponding values of 500 Cd/m2 and 1.3 Cd/A in the unmodified device. Analysis by ultraviolet spectroscopy suggests that the two devices have the same energy level structure and the performance improvement should not be due to change in the PEDOT/polymer interface. It was further found that incorporating a suitable amount of glycerol into the PEDOT:PSS layer can increase its conductivity by six times. This leads to a better balance in the hole and electron currents and thus improved device efficiency.
Noise processes in nanomechanical resonators
Authors: Cleland A. N. , Roukes M. L.
Published: September 2002

Nanomechanical resonators can be fabricated to achieve high natural resonance frequencies, approaching 1 GHz, with quality factors in excess of 104. These resonators are candidates for use as highly selective rf filters and as precision on-chip clocks. Some fundamental and some nonfundamental noise processes will present limits to the performance of such resonators. These include thermomechanical noise, Nyquist–Johnson noise, and adsorption–desorption noise; other important noise sources include those due to thermal fluctuations and defect motion-induced noise. In this article, we develop a self-contained formalism for treating these noise sources, and use it to estimate the impact that these noise processes will have on the noise of a model nanoscale resonator, consisting of a doubly clamped beam of single-crystal Si with a natural resonance frequency of 1 GHz.
Thermally induced transmission variations in ZnSe/MgF2 photonic band gap structures
Authors: Larciprete M. C. , Sibilia C. , Paoloni S. , Leahu G. , Li Voti R. , Bertolotti M. , Scalora M. , Panajotov K.
Published: September 2002

We investigate thermally induced transmission variations in a 3.6-μm-thick ZnSe/MgF2 photonic band gap structure by means of a pump–probe setup, in the 600–700 nm range, under cw pump conditions. An induced temperature increase is responsible for the thermal expansion of the layers, as well as changes in the index of refraction. As a result, the band gap structure is redshifted by several nanometers. The initial transmission of the probe beam was restored following the removal of the pump laser, thus indicating the reversible nature of the process.
Characterization of quality of BaxSr1−xTiO3 thin film by the commutation quality factor measured at microwaves
Authors: Razumov S. V. , Tumarkin A. V. , Gaidukov M. M. , Gagarin A. G. , Kozyrev A. B. , Vendik O. G. , Ivanov A. V. , Buslov O. U. , Keys V. N. , Sengupta L. C. , Zhang X.
Published: September 2002

The loss factor (tan δ) of ferroelectric material at microwaves and the tunability (n) defined as a ratio of the dielectric permittivity at zero dc field to the dielectric permittivity at the given field are strongly connected with the softness of so-called ferroelectric soft mode. The loss factor and the tunability are generalized by the commutation quality factor (CQF). The dielectric response of a ferroelectric material allows one to determine the CQF and to compare it to the theoretical CQF obtained for a perfect ferroelectric sample. In order to compare the theoretical prediction and experimental data, the influence of deposition parameters on microwave properties of BaxSr1−xTiO3 (BSTO) films deposited on sapphire and alumina substrate has been investigated in a wide frequency range (1–30 GHz). The highest CQF at room temperature was obtained for the 30% Ba content target and the deposition temperature 905 °C. The best BSTO films exhibited CQF≅1.6×104 with n=2.1 and tan δ=0.012 at 1 GHz and zero bias. This result is among the best reported for sputtered BSTO films both on sapphire and alumina substrates. Nevertheless the obtained CQF is 3–5 times lower than the upper theoretical limit.
Fabrication of niobium superconductor–insulator–superconductor junctions with a magnetic tunneling barrier NiOx for millimeter and submillimeter mixer applications
Authors: Seko Kazuyuki , Ichikawa Yoshiko , Terajima Ryo , Sakai Joe , Imai Syozo
Published: September 2002

A thin-film superconductor-insulator-superconductor junction with a magnetic barrier, NiOx, and superconducting electrode, Nb, was fabricated. It is shown that the Josephson current was strongly suppressed without external magnetic field. The tunneling barrier was formed by plasma oxidation and or thermal oxidation. The junction with thermal oxidation showed low specific resistance and current–voltage characteristics with a clear energy gap structure. It is shown that this junction has the potential for quasiparticle mixer working at higher submillimeter wave frequency region above ∼700 GHz, especially suited for making an imaging array.
Spin-dependent transmission of holes through periodically modulated diluted magnetic semiconductor waveguides
Authors: Wang X. F. , Vasilopoulos P.
Published: September 2002

We study spin transport of holes through stubless or stubbed waveguides modulated periodically by diluted magnetic semiconductor (DMS) sections of width b1. Injected holes of up (down) spin feel a periodically modulated barrier (well) potential in the DMS sections and have different transmission (T) coefficients. T oscillates with b1 for spin-down and decreases fast for spin-up holes while the relative polarization Pr depends nearly periodically on the stub height. Using asymmetric stubs leads to a nearly square-wave pattern in T and to wide plateaus in Pr. T oscillates with the length between the DMS sections. With two DMS sections per unit, T shows periodically wide gaps for spin-down holes when a DMS width is varied. The results can be used to create efficient spin filters.
Shrinkage- and refractive-index shift-corrected volume holograms for optical interconnects
Authors: Chen Jing-Heng , Su Der-Chin , Su Jung-Chieh
Published: September 2002

The Bragg mismatching condition for volume holograms occurs because of the changes in the thickness and the refractive index of holographic recording materials during the recording and reconstruction procedures. We propose an improved compensation method to physically correct these effects in the fabrications of volume holograms for optical interconnects. In order to show the validity of this method, Slavich photographic plate VRP-M is used to fabricate optical interconnects. The correction of the Bragg diffraction angle shift of about 2.10°, which is induced by 6.14% film shrinkage and 0.06 refractive index shift, is successfully demonstrated with the surface-normal configuration. A shrinkage- and refractive-index shift-corrected volume hologram with 23% diffraction efficiency is experimentally confirmed. The methodology proposed is applicable to other phase media when the associated film shrinkage and refractive-index shift data are experimentally determined.
Modulation of x-ray line intensity emitted by a periodic structure under electron excitation
Authors: Jonnard P. , Ândré J.-M. , Bonnelle C. , Bridou F. , Pardo B.
Published: September 2002

We report on the intensity modulation of a characteristic x-ray line emitted by a periodic structure, as a function of the observation angle. This intensity variation takes place around the Bragg direction corresponding to the diffraction of the x-ray line by the emitting structure. An enhancement of the emitted radiation is observed and interpreted on the basis of the reciprocity theorem. The enhancement remains unchanged by varying the number of emitting periods. Following Yariv and Yeh [J. Opt. Soc. Am. 67, 438 (1977)], a possible application as x-ray resonator to achieve a distributed feedback soft x-ray laser is envisaged.
Healing kinetics of interfacial voids in GaAs wafer bonding
Authors: Wu YewChung Sermon , Hu Guo-Zen
Published: September 2002

A periodic structure of bonded GaAs wafers has been proposed for quasi-phase-matched second-harmonic generation. After bonding, voids were formed at the interface due to the natural topographical irregularities and contamination on the wafer surface. Within the voids, crystallites with diamond-shaped and dendritic geometries were found, which corresponded to the bonded regions. In this study, artificial voids were introduced at the bonded interface to study the growth kinetics of these crystallites, that is the healing kinetics of these voids. It was found that the crystallite geometries and the growth rates are controlled by the nucleation of new surface layers on the bonded planes, which was the slowest stage during the healing process.
Bright blue to orange photoluminescence emission from high-quality InGaN/GaN multiple-quantum-wells on Si(111) substrates
Authors: Poschenrieder M. , Schulze F. , Bläsing J. , Dadgar A. , Diez A. , Christen J. , Krost A.
Published: September 2002

Metalorganic-chemical-vapor-phase-deposition-grown InGaN/GaN multiple-quantum-wells on Si(111) substrates were studied by high-resolution x-ray diffractometry (HRXRD) and photoluminescence (PL). By varying the quantum well deposition parameters, growth time, growth temperature, and In flow rate, systematic changes of the quantum well PL were found. The luminescence peak wavelengths and the corresponding intensities depend monotonically on each of these varied growth parameters. A considerable shift of the PL peak wavelength from blue (442 nm) to orange emission (649 nm) was achieved by decreasing the InGaN deposition temperature from 790 to 720 °C. HRXRD analysis shows changes in structural quality with InGaN growth temperature.
Substituent position-induced color tunability in polymer light-emitting diodes
Authors: Kim Jin Young , Park Sung Heum , Lee Kwanghee , Yum In Suk , Jin Sung Ho
Published: September 2002

We report substituent position-induced color tunability in polymer light-emitting diodes fabricated with poly[2-{2- or 3- or 4-[(3,7-dimethyloctyl)oxy] phenyoxy}-1,4-phenylenevinylene] (DMOPPPV). When the position of the substituent in DMOP-PPV moves to the ortho, meta, and para sites, the corresponding photo- and electroluminescence spectra shift their peaks to a longer wavelength of about 540, 560, and 585 nm, respectively. We ascribe this to the different degree of steric effect in the backbone for each substituent position. As the substituent position is closer to the main chain, the planarity of the backbone is less conserved, thereby reducing the effective conjugated length of the main chain and broadening the π-π* energy gap.
Doping of interfaces in (La0.7Sr0.3MnO3)1−x:(MgO)x composite films
Authors: Köster S. A. , Moshnyaga V. , Samwer K. , Lebedev O. I. , Tendeloo G. van , Shapoval O. , Belenchuk A.
Published: September 2002

Composite thin films of (La0.7Sr0.3MnO3)1−x:(MgO)x (x=0–0.5) were grown on Al2O3 (0001) substrates by a metalorganic aerosol deposition technique. A columnar growth of the films with the predominance of (111)- and (1̄10)-orientation was observed. Pure films (x=0) show a Curie temperature of TC=362 K, a metallic behavior accompanied with a low residual resistivity ρ∼10−4 Ω cm at T=4.2 K and a very small low-field magnetoresistance. Low amounts of MgO doping, x=0.05, result in a totally different electrical transport behavior which is a pronounced low-field magnetoresistance MR=25% at T=4.2 K. The MgO was found to be located at the interfaces between the grains thus building tunneling barriers and enhancing spin polarized tunneling similar to a system with vertical artificial tunnel junctions.
Last but Not Least
Authors: Ninio Jacques
Published: September 2002

In a periodic pattern of horizontally and vertically aligned quadrangles, two sets of illusory lines are seen to pulsate at orthogonal orientations, corresponding to the directions of knight's moves on a chessboard. The illusion seems to be governed by subtle rules of long-range interactions between parallel and non-parallel orientation filters.
The effects of bovine somatotropin on hair follicle activity and cashmere fibre growth in goats
Authors: Villar D. , Rhind S. M. , McMillen S. R. , Dicks P.
Published: September 2002

The aim of this study was to determine the role of circulating growth hormone
(GH) profiles in the cessation of secondary hair follicle activity and
secondary fibre growth in goats during autumn/winter and to determine
whether it is possible to extend the period of growth of this fibre by
artificially increasing circulating concentrations of this hormone. Nine
cashmere goats were each injected, weekly, with 50 mg of bovine somatotropin
(bST; treated) in carrier oil, for a period of 5 months between late August
and late January. Goats of a second group of 9 animals were injected with
sesame oil and served as controls. Treated goats had significantly higher
circulating concentrations of growth hormone (P<
0.001), insulin (P< 0.01), thyroxine
(P< 0.001), and insulin-like growth factor-I (IGF-I;
P< 0.001). Secondary fibre growth rate and liveweight
gains were significantly (P< 0.05) higher in treated
than control goats. The proportion of active secondary follicles was
positively associated with circulating IGF- I concentrations in treated but
not control goats. Follicle activity was not related to the profiles of any of
the other hormones measured. The mean date of cessation of secondary fibre
growth was not affected by treatment. It is concluded that treatment with bST
stimulated the rate of secondary fibre growth but did not delay the time of
cessation of this growth or the decline in follicle activity. It is further
concluded that circulating hormone profiles do not directly control follicle
activity and secondary fibre growth and moult and that their effects probably
involve changes within the skin and/or hair follicle, possibly in hormone
receptor populations, deiodinase enzyme activity, or growth factor synthesis.
Distribution, Ecology and Rarity of the Nationally Vulnerable Species Pultenaea selaginoides (Fabaceae)
Authors: Lynch A. J. J.
Published: September 2002

Pultenaea selaginoides Hook.f. (Fabaceae) is a Tasmanian
endemic shrub classified as nationally vulnerable. Only four populations of
P. selaginoides totalling fewer than 1000 individuals
are known to be extant, and one of these populations consists of only six
individuals. The habitat of P. selaginoides is
restricted to sites in flood-prone, riparian areas or coastal ridgelines
subject to cloud-lie and runoff retention. However, there appears to be
unoccupied habitat available. Pultenaea selaginoides can
resprout or coppice after disturbance or regenerate from the soil stored seed
bank. Most populations are producing seed, and large quantities may be
produced. Germination of the seed can be induced by short-term temperatures of
60–100°C. Only the largest population is formally reserved, but all
sites should be managed for the perpetuation of
P. selaginoides. Because of the narrowness of its
distribution, its low total population size, its innate seed dormancy, the
ageing of most of the populations, and the uncertaintpy about the precise
causes of its rarity, P. selaginoides should continue to
be regarded as vulnerable to extinction.
Vegetation Changes after 10 Years of Grazing Exclusion and Intermittent Burning in a Themeda triandra (Poaceae) Grassland Reserve in South-eastern Australia
Authors: Lunt Ian D. , Morgan John W.
Published: September 2002

Changes in the vegetation composition of a remnant
Themeda triandra Forsskal grassland in south-eastern
Australia were documented following the replacement of stock grazing with
intermittent burning at 3–11-year intervals. The vegetation was
initially sampled in 1986, 1 year after stock were removed, and then 10 years
later in 1996. Most frequently encountered grassland species were abundant in
both surveys, although there was little correspondence between species
richness at the quadrat scale in 1986 and 1996. Total floristic richness
increased slightly over the 10-year period, owing to the proliferation of tall
forbs with wind-blown seeds, including exotic thistles and colonising native
forbs. Unfortunately, most native ‘increasers’ were
‘weedy’ species which are not typical or common components of
species-rich temperate grassland remnants in southern Victoria. Thus,
replacing grazing with intermittent burning has not resulted in the flora
becoming more similar to that of high-quality, species-rich grassland
remnants, but instead, has promoted a group of ruderal colonisers. The ability
to identify factors contributing to particular botanical changes was
hampered by the design of the management regimes implemented over the past
decade. Suggestions are provided to overcome these difficulties, incorporating
principles from adaptive management.
The occurrence of pregnancy in Merino ewes teased with testosterone- treated wethers before the start of joining
Authors: Johns M. A. , Croker K. P. , Sunderman F. M. , Derbyshire K.
Published: September 2002

Five experiments were conducted to develop simple strategies for using
testosterone-treated wethers to increase the reproductive efficiency of ewe
flocks to which entire rams were joined before the peak of the breeding
season.
In experiments 1–4, a number of strategies involving fewer injections,
single injections of more testosterone with and without wethers left in the
flocks during joining, were compared with the standard technique used for
preparing male behaviour in wethers (3 injections of 150 mg testosterone
enanthate at 7-day intervals starting 28 days before the introduction of
entire rams). In experiment 5, the single dose strategy, either subcutaneous
or intramuscular, was investigated. The treated wethers were joined with ewe
flocks that had been isolated from rams for at least 28 days, 14 days before
the entire rams were joined with the ewes for 6 or 8 weeks.
The weeks of conception in all groups were estimated using real-time
ultrasound imaging. This allowed patterns of conception in the various
treatment groups to be compared. These observations also provided the
information for determining pregnancy status and the percentages of fetuses
present.
In 4 of the experiments, the teased groups had a significantly more
concentrated pattern of conception than did the unteased control groups.
The results of this study have shown that the reproductive efficiency of ewe
flocks is improved by having a more concentrated lambing following the
introduction of wethers treated with a subcutaneous injection of 375 mg
testosterone enanthate before the entire rams are joined with them, even when
the wethers are left in the flock during the joining period. As a result, the
length of the joining period can be reduced to 5–6 weeks compared with
the 8 weeks usually used for unteased flocks.
The relative wool contamination potential of Awassi and black Merino sheep when penned together with white Merinos
Authors: Hatcher S. , Foulds R. A. , Lightfoot R. J. , Purvis I. W.
Published: September 2002

Fleeces, top and finished fabric processed from white Merino (fibre recipient)
ewes, run in close contact for 2 weeks, with either Awassi, black Merino or
white Merino control (fibre donor) ewes, were analysed for the presence of
contaminant fibres (pigmented, urine stained and kemp). Kemp and pigmented
fibres were transferred from Awassi and black Merino sheep into the fleeces of
the recipient ewes. The concentration of kemp and pigmented fibres found in
the fleeces, top and fabric of the black Merino treatment was substantially
greater than the Awassi and Merino control groups which were not different
from each other. Fibres transferred from the black Merino group were darker
than those from Awassi sheep and thus posed a greater potential contamination
threat. Contaminant fibres which are structurally different from the wool bulk
(such as kemp) tend to be removed during worsted processing, while those with
similar dimensions (such as pigmented Merino wool fibres) are more likely to
persist in the system and appear as contaminants in worsted fabric.
Tactical versus continuous stocking for persistence of perennial ryegrass (Lolium perenne L.) in pastures grazed by sheep in south-western Victoria
Authors: Waller R. A. , Quigley P. E. , Saul G. R. , Kearney G. A. , Sale P. W. G.
Published: September 2002

The survival of perennial ryegrass (Lolium perenne L.)
plants was studied in sheep pastures in south-western Victoria during the dry
summer of 1996–97. Recruitment of perennial ryegrass seedlings into the
pasture sward was also monitored in the autumn–winter periods in 1997
and 1998. The objective was to investigate whether a tactical stocking
strategy, consisting of variable length summer, autumn and winter rotations
and continuous stocking in spring, might increase perennial ryegrass tiller
survival and seedling recruitment in the autumn, compared with continuous
stocking all year. The grazing strategies were compared on 2 contrasting
pastures: an upgraded pasture [sown with newer cultivars of perennial
ryegrass and subterranean clover (Trifolium subterraneum
L.) with 26 kg phosphorus/ha.year as applied fertiliser] and a
naturalised perennial ryegrass pasture receiving 6 kg P/ha.year. Paddocks
were grazed by Border Leicester × Merino ewes,
mated to a terminal sire so as to lamb in September.
Perennial ryegrass tiller density was higher on the upgraded pasture with a
mean density of 7750 tillers/m2 in early summer
which declined to zero live tillers by mid summer. Live tillers began to
reappear before the opening rains and then increased after the rain. Mean
tiller density in the upgraded pasture declined over the 2 summers, with only
2050 tillers/m2 being present 2 months after the
opening rains in 1998. There were no effects (P>0.05)
of pasture type or grazing strategy on the number of tagged tillers that
survived the summer period. Only 12% of the vegetative tillers,
randomly tagged in December 1996, survived to May 1997. More than half of the
tillers (56%) that produced a seedhead produced daughter tillers which
survived the dry summer–autumn period.
A significant (P<0.05) interaction between grazing
strategy and pasture type occurred with the number of perennial ryegrass
seedlings that had established 4 weeks after the opening rains in 1997. There
was a 5–11-fold increase in seedling numbers which regenerated in the
tactically stocked, upgraded pasture compared with the other treatments.
Seedling recruitment was considerably lower in the autumn of 1998, due
presumably to an overall decline in perennial ryegrass density relative to
annual grasses in 1997.
A second experiment investigated the effect of excluding sheep from grazing at
anthesis until seedhead maturation or until the opening rains, together with a
mechanical seed dislodgment treatment at seed maturity. All exclusion
treatments increased seedling recruitment 4–7-fold, compared with
continuous stocking. The results suggest a possible mechanism by which
perennial ryegrass density can be increased without expensive reseeding.
Changes in the botanical composition and nutritive characteristics of pasture, and nutrient selection by dairy cows grazing rainfed pastures in western Victoria
Authors: Jacobs J. L. , McKenzie F. R. , Ward G. N.
Published: September 2002

Changes in pasture metabolisable energy (ME), crude protein (CP), neutral
detergent fibre (NDF), phosphorus (P), potassium (K), calcium (Ca), magnesium
(Mg), sulfur (S), sodium (Na) and chlorine (Cl) were measured at each grazing,
in 4 paddocks on 2 farms (farm A and farm B) in western Victoria from May 1995
to March 1997. Selection differentials were calculated from quality parameters
using measures of pre- and post-grazing masses. Changes in botanical
composition and pasture allowance were also measured.
The nutritive characteristics of pasture on both farms followed similar
trends. Metabolisable energy and CP were highest in winter and early spring
with values of over 11 MJ/kg DM and 250 g/kg DM respectively. The
lowest concentrations of ME and CP in pasture on farm A (9.4 MJ/kg DM; 128
g/kg DM) were observed in April and February respectively. On farm B the
corresponding lowest values (8.4 MJ/kg DM; 100 g/kg DM) were in March.
In contrast, NDF values on farm A were lowest in June (466 g/kg DM) and on
farm B (436 g/kg DM) in May, with highest values in February (648 g/kg
DM) and March (692 g/kg DM) respectively. Concentrations of P, K, S and Cl
in pasture followed a similar pattern to that of ME with highest values in
winter and lowest in summer, while changes in Ca concentrations related more
closely to changes in NDF. The concentrations of Mg and Na were highest in
autumn and spring, respectively, with lowest values in late spring and summer.
Selection differentials indicated that the ME of pasture consumed was
4–22% higher than the pasture on offer. For CP the range of
selection differentials was always greater than 1, but varied widely
(1.08–1.83). The selection differentials for NDF were always negative,
with an average value of 0.84. Selection differentials for minerals varied
little over the year, with values generally indicating a positive selection
differential (P 1.12, 1.15; Ca 1.16, 1.16; Mg 1.15, 1.18; K 1.23, 1.27; Na
1.05, 1.07; Cl 1.16, 1.14; S 1.27, 1.28) for farms A and B. Pasture allowances
ranged from 10–60 kg DM/cow.day and there was no relationship
between selection differentials for all nutritive characteristics and pasture
allowance.
The results obtained in this study indicated that although the ME of pasture
consumed throughout the year should be adequate to meet production of 30
L/cow.day in early lactation with minimal liveweight loss, it was
associated with high levels of CP and potentially low concentrations of NDF in
relation to cow requirements. Results therefore indicate a possible need for
supplementing pasture diets in winter and spring to balance the diet for CP
and NDF. In addition, it is likely that both Ca and Mg intake from pasture may
be limiting in early lactation and therefore additional supplements of both
minerals may be required during this period.
Modelling pesticide residues on greasy wool: use of farm records at the time of treatment to predict residues
Authors: Karlsson J. , Horton B. J. , Gillibrand M. , Campbell N. J. , Barr W. , Best D. J.
Published: September 2002

A model has been used to predict expected pesticide residues on wool at
shearing after normal on-farm treatments. If wool producers keep accurate
records of treatments at the time they are carried out, the model can predict
the residue with greater accuracy and precision than if treatment records are
less specific. The expected range is halved and the predicted residue is lower
where wool producers have kept treatment records, compared with wool from
previous surveys where only the usual farm information was available.
If declarations by wool producers are used to assist wool buyers who require
wool with low pesticide residues, these declarations will have more value if
they are supported by documentation of treatments used on the sheep.