bluuebunny/crossref_metadata_2025 huggingface dataset:
Predictive modeling of the current density and radiative recombination in blue polymer-based light-emitting diodes
Authors: van Mensfoort S. L. M. , Billen J. , Carvelli M. , Vulto S. I. E. , Janssen R. A. J. , Coehoorn R.
Published: March 2011

The results of a combined experimental and modeling study of charge transport, recombination and light emission in blue organic light-emitting diodes (OLEDs) based on a polyfluorene derivative are presented. It is shown that the measured temperature-dependent current-voltage curves and the voltage-dependent current efficiency are accurately described using an OLED device model that is based on the separately determined unipolar electron and hole mobility functions. The recombination rate is calculated using the Langevin formula, including recombination of holes with free as well as trapped electrons. The light emission is obtained from the exciton formation profile using independently determined values of the exciton radiative decay probability, the average dipole orientation, and assuming a fraction of singlet excitons ηS  =​(22±3)%, close to the quantum-statistical value. No additional free parameter is used. This shows that predictive one-dimensional device modeling of OLEDs is feasible.
Local model for magnet–superconductor mechanical interaction: Experimental verification
Authors: Diez-Jimenez Efren , Perez-Diaz Jose-Luis , Garcia-Prada Juan Carlos
Published: March 2011

Several models exist for calculating superconducting repulsion forces in the Meissner state that are based on the method of images. The method of images, however, is limited to a small number of geometrical configurations that can be solved exactly, and the physical interpretation of the method is under discussion. A general local model based on the London equations and Maxwell’s equations has been developed to describe the mechanics of the superconductor-permanent magnet system. Due to its differential form, this expression can be easily implemented in a finite elements analysis and, consequently, is easily applicable to any shape of superconductor in the Meissner state. It can solve both forces and torques. This paper reports different experiments undertaken in order to test the model’s validity. The vertical forces and the angle of equilibrium between a magnet and a superconductor were measured, and a positive agreement between the experiments and theoretical calculations was found.
Rapidly solidified amorphous nanowires
Authors: Chiriac H. , Corodeanu S. , Lostun M. , Stoian G. , Ababei G. , Óvári T.-A.
Published: March 2011

Results on the preparation and magnetic characterization of rapidly solidified amorphous glass-coated nanowires are reported. Rapidly solidified nanowires have been investigated by means of bulk and surface hysteresis loop measurements, scanning electron microscopy, and ferromagnetic resonance. Domain wall velocity has been measured to demonstrate the suitability of the new nanowires for spintronic applications. Changes in composition, in the thickness of the glass coating, and nanowire dimensions allow extensive tailoring of the domain wall mobility.
Sequential bond energies and barrier heights for the water loss and charge separation dissociation pathways of Cd2+(H2O)n, n = 3–11
Authors: Cooper Theresa E. , Armentrout P. B.
Published: March 2011

The bond dissociation energies for losing one water from Cd2+(H2O)n complexes, n = 3–11, are measured using threshold collision-induced dissociation in a guided ion beam tandem mass spectrometer coupled with a thermal electrospray ionization source. Kinetic energy dependent cross sections are obtained for n = 4–11 complexes and analyzed to yield 0 K threshold measurements for loss of one, two, and three water ligands after accounting for multiple collisions, kinetic shifts, and energy distributions. The threshold measurements are converted from 0 to 298 K values to give the hydration enthalpies and free energies for sequentially losing one water from each complex. Theoretical geometry optimizations and single point energy calculations are performed on reactant and product complexes using several levels of theory and basis sets to obtain thermochemistry for comparison to experiment. The charge separation process, Cd2+(H2O)n → CdOH+(H2O)m + H+(H2O)n−m−1, is also observed for n = 4 and 5 and the competition between this process and water loss is analyzed. Rate-limiting transition states for the charge separation process at n = 3–6 are calculated and compared to experimental threshold measurements resulting in the conclusion that the critical size for this dissociation pathway of hydrated cadmium is ncrit = 4.
X-ray absorption fine structure and x-ray diffraction studies of crystallographic grains in nanocrystalline FePd:Cu thin films
Authors: Krupinski M. , Perzanowski M. , Polit A. , Zabila Y. , Zarzycki A. , Dobrowolska A. , Marszalek M.
Published: March 2011

FePd alloys have recently attracted considerable attention as candidates for ultrahigh density magnetic storage media. In this paper we investigate FePd thin alloy film with a copper admixture composed of nanometer-sized grains. [Fe(0.9 nm)/Pd(1.1 nm)/Cu(d nm)]×5 multilayers were prepared by thermal deposition at room temperature in UHV conditions on Si(100) substrates covered by 100 nm SiO2. The thickness of the copper layer has been changed from 0 to 0.4 nm. After deposition, the multilayers were rapidly annealed at 600 °C in a nitrogen atmosphere, which resulted in the creation of the FePd:Cu alloy. The structure of alloy films obtained this way was determined by x-ray diffraction (XRD), glancing angle x-ray diffraction, and x-ray absorption fine structure (EXAFS). The measurements clearly showed that the L10 FePd:Cu nanocrystalline phase has been formed during the annealing process for all investigated copper compositions. This paper concentrates on the crystallographic grain features of FePd:Cu alloys and illustrates that the EXAFS technique, supported by XRD measurements, can help to extend the information about grain size and grain shape of poorly crystallized materials. We show that, using an appropriate model of the FePd:Cu grains, the comparison of EXAFS and XRD results gives a reasonable agreement.
A highly modular beamline electrostatic levitation facility, optimized for in situ high-energy x-ray scattering studies of equilibrium and supercooled liquids
Authors: Mauro N. A. , Kelton K. F.
Published: March 2011

High-energy x-ray diffraction studies of metallic liquids provide valuable information about structural evolution on the atomic length scale, leading to insights into the origin of the nucleation barrier and the processes of supercooling and glass formation. The containerless processing of the beamline electrostatic levitation (BESL) facility allows coordinated thermophysical and structural studies of equilibrium and supercooled liquids to be made in a contamination-free, high-vacuum (∼10−8 Torr) environment. To date, the incorporation of electrostatic levitation facilities into synchrotron beamlines has been difficult due to the large footprint of the apparatus and the difficulties associated with its transportation and implementation. Here, we describe a modular levitation facility that is optimized for diffraction studies of high-temperature liquids at high-energy synchrotron beamlines. The modular approach used in the apparatus design allows it to be easily transported and quickly setup. Unlike most previous electrostatic levitation facilities, BESL can be operated by a single user instead of a user team.
A Freon-filled bubble chamber for neutron detection in inertial confinement fusion experiments
Authors: Ghilea M. C. , Meyerhofer D. D. , Sangster T. C.
Published: March 2011

Neutron imaging is one of the main methods used in inertial confinement fusion experiments to measure the core symmetry of target implosions. Previous studies have shown that bubble chambers have the potential to obtain higher resolution images of the targets for a shorter source-to-target distance than typical scintillator arrays. A bubble chamber for neutron imaging with Freon 115 as the active medium was designed and built for the OMEGA laser system. Bubbles resulting from spontaneous nucleation were recorded. Bubbles resulting from neutron–Freon interactions were observed at neutron yields of 1013 emitted from deuterium–tritium target implosions on OMEGA. The measured column bubble density was too low for neutron imaging on OMEGA but agreed with the model of bubble formation. The recorded data suggest that neutron bubble detectors are a promising technology for the higher neutron yields expected at National Ignition Facility.
Charge carrier trapping at passivated silicon surfaces
Authors: Seiffe Johannes , Hofmann Marc , Rentsch Jochen , Preu Ralf
Published: March 2011

Surface passivation has become an essential factor for translating high-efficiency crystalline silicon solar cell concepts into industrial production schemes. In photovoltaics, a widespread method to determine the surface recombination is to measure the effective charge carrier lifetime from the photoconductance of symmetrically passivated silicon wafers in transient or quasi-static mode. In this work, it is shown how the injection history at the surface influences the transient effective lifetime measurement for several passivation layers. This dependence leads to systematic differences between quasi-static and transient measurements. The influence can be explained by charge trapping in slow surface states at the surface passivation layer. A model including slow surface states is used in a fit procedure to evaluate the capture cross sections of these traps. The observed effect is well-pronounced for silicon-rich passivation layers like a-Si:H, a-SiCx:H or silicon-rich a-SiOxNy:H. For PECVD-AlOx layers and for thermally grown SiO2 layers as well, however, the effective lifetime measurement could be influenced.
The least channel capacity for chaos synchronization
Authors: Wang Mogei , Wang Xingyuan , Liu Zhenzhen , Zhang Huaguang
Published: March 2011

Recently researchers have found that a channel with capacity exceeding the Kolmogorov–Sinai entropy of the drive system (hKS) is theoretically necessary and sufficient to sustain the unidirectional synchronization to arbitrarily high precision. In this study, we use symbolic dynamics and the automaton reset sequence to distinguish the information that is required in identifying the current drive word and obtaining the synchronization. Then, we show that the least channel capacity that is sufficient to transmit the distinguished information and attain the synchronization of arbitrarily high precision is hKS. Numerical simulations provide support for our conclusions.
Geometric confinement effects on the metal-insulator transition temperature and stress relaxation in VO2 thin films grown on silicon
Authors: Viswanath, Changhyun Ko B. , Yang Zheng , Ramanathan Shriram
Published: March 2011

VO2 undergoes a sharp metal-insulator transition at ∼67 °C with several orders of change in conductivity and optical transmittance. Understanding and control of the properties of vanadium oxide layers grown on technologically relevant substrates such as Si (100) single crystals is therefore of great interest. In this work, we show tunability of metal-insulator transition temperature as well as recoverable stress in VO2 thin films grown on Si substrate by introducing nanoscale atomic layer deposited HfO2 interfacial layers with no degradation in the resistance ratio. For a confined VO2 film, the metal-insulator transition temperature is suppressed by ∼16 °C and the recoverable stress is 150 MPa, compared to 400 MPa for a bare film. These observations are further correlated with in situ variable temperature measurement of stress changes occurring during the phase transition. Structural and microstructural studies on the various samples have been carried out by x ray diffraction and cross-sectional transmission electron microscopy. The strategy of tuning the metal-insulator transition characteristics by nanoscale interfacial dielectrics is of broader relevance in design of programmable materials and integration into solid state devices for electronics.
Design of shared instruments to utilize simulated gravities generated by a large-gradient, high-field superconducting magnet
Authors: Wang Y. , Yin D. C. , Liu Y. M. , Shi J. Z. , Lu H. M. , Shi Z. H. , Qian A. R. , Shang P.
Published: March 2011

A high-field superconducting magnet can provide both high-magnetic fields and large-field gradients, which can be used as a special environment for research or practical applications in materials processing, life science studies, physical and chemical reactions, etc. To make full use of a superconducting magnet, shared instruments (the operating platform, sample holders, temperature controller, and observation system) must be prepared as prerequisites. This paper introduces the design of a set of sample holders and a temperature controller in detail with an emphasis on validating the performance of the force and temperature sensors in the high-magnetic field.
Steady flows of a highly rarefied gas induced by nonuniform wall temperature
Authors: Kosuge Shingo , Aoki Kazuo , Takata Shigeru , Hattori Ryosuke , Sakai Daisuke
Published: March 2011

Steady behavior of a rarefied gas between parallel plates with sinusoidal temperature distribution is investigated on the basis of the Boltzmann equation. The Cercignani–Lampis (CL) model or the Lord model for diffuse scattering with incomplete energy accommodation is adopted as the boundary condition on the plates. Most of the analysis is carried out numerically with special interest in the free-molecular limit. In the case of the CL model, the nonuniform temperature distribution of the plates may induce a steady free-molecular flow, which is in contrast with the earlier results for the Maxwell-type model [Y. Sone, J. Méc. Théor. Appl. 3, 315 (1984); J. Méc. Théor. Appl. 4, 1 (1985)]. This fact is confirmed through an accurate deterministic computation based on an integral equation. In addition, computations for a wide range of parameters by means of the direct simulation Monte Carlo method reveal that the flow field changes according to the accommodation coefficients and is classified into four types. The effect of intermolecular collisions on the flow is also examined. In the case of the Lord model, no steady flow of the free-molecular gas is induced as in the case of the Maxwell-type model. This result is extended to the case of a more general boundary condition that gives the cosine law (Lambert’s law) for the reflected molecular flux.
Sonine approximation for collisional moments of granular gases of inelastic rough spheres
Authors: Santos Andrés , Kremer Gilberto M. , dos Santos Marcelo
Published: March 2011

We consider a dilute granular gas of hard spheres colliding inelastically with coefficients of normal and tangential restitution α and β, respectively. The basic quantities characterizing the distribution function f(v,ω) of linear (v) and angular (ω) velocities are the second-degree moments defining the translational (Ttr) and rotational (Trot) temperatures. The deviation of f from the Maxwellian distribution parameterized by Ttr and Trot can be measured by the cumulants associated with the fourth-degree velocity moments. The main objective of this paper is the evaluation of the collisional rates of change of these second- and fourth-degree moments by means of a Sonine approximation. The results are subsequently applied to the computation of the temperature ratio Trot/Ttr and the cumulants of two paradigmatic states: the homogeneous cooling state and the homogeneous steady state driven by a white-noise stochastic thermostat. It is found in both cases that the Maxwellian approximation for the temperature ratio does not deviate much from the Sonine prediction. On the other hand, non-Maxwellian properties measured by the cumulants cannot be ignored, especially in the homogeneous cooling state for medium and small roughness. In that state, moreover, the cumulant directly related to the translational velocity differs in the quasi-smooth limit β→−1 from that of pure smooth spheres (β=−1). This singular behavior is directly related to the unsteady character of the homogeneous cooling state and thus it is absent in the stochastic thermostat case.
Principles and promise of Fabry–Perot resonators at terahertz frequencies
Authors: Braakman R. , Blake G. A.
Published: March 2011

Fabry–Perot resonators have tremendous potential to enhance the sensitivity of spectroscopic systems at terahertz (THz) frequencies. Increasing sensitivity will be of benefit in compensating for the relatively low power of current high resolution continuous wave THz radiation techniques, and to fully express the potential of THz spectroscopy as source power increases. Improved sensitivities, and thus scanning speeds, will allow detailed studies of the complex vibration-rotation-tunneling dynamics that large molecules show at THz wavelengths, and will be especially important in studying more elusive, transient species such as those present in planetary atmospheres and the interstellar medium. Coupling radiation into the cavity presents unique challenges at THz frequencies, however, meaning that the cavity configurations common in neighboring frequency domains cannot simply be translated. Instead, novel constructions are needed. Here we present a resonator design in which wire-grid polarizers serve as the input and output coupling mirrors. Using this configuration, Q-factors of a few times 105 are achieved near 0.3 THz. To aid future investigations, the parameter space that limits the quality of the cavity is explored and paths to improved performance highlighted. Lastly, the performance of polarizer cavity-based Fourier transform (FT) THz spectrometers is discussed, in particular those design optimizations that should allow for the construction of THz instrumentation that rivals and eventually surpasses the sensitivities achieved with modern FT-microwave cavity spectrometers.
In situdoping of graphene by exfoliation in a nitrogen ambient
Authors: Brenner Kevin , Murali Raghu
Published: March 2011

We present an in situ method of n-doping graphene by exfoliating in an N-ambient. By exfoliating single-layer graphene in a nitrogen-rich environment, the dopant specie plays an active role in minimizing C–C reconstruction that typically occurs at the moment of defect generation. Employing such in situ methods provides an efficient mechanism of passivating defects produced during graphene growth and transfer, as well as a means of controllably incorporating dopant species into the graphene lattice.
Intercomparison of gamma scattering, gammatography, and radiography techniques for mild steel nonuniform corrosion detection
Authors: Priyada P. , Margret M. , Ramar R. , Shivaramu  , Menaka M. , Thilagam L. , Venkataraman B. , Raj Baldev
Published: March 2011

This paper focuses on the mild steel (MS) corrosion detection and intercomparison of results obtained by gamma scattering, gammatography, and radiography techniques. The gamma scattering non-destructive evaluation (NDE) method utilizes scattered gamma radiation for the detection of corrosion, and the scattering experimental setup is an indigenously designed automated personal computer (PC) controlled scanning system consisting of computerized numerical control (CNC) controlled six-axis source detector system and four-axis job positioning system. The system has been successfully used to quantify the magnitude of corrosion and the thickness profile of a MS plate with nonuniform corrosion, and the results are correlated with those obtained from the conventional gammatography and radiography imaging measurements. A simple and straightforward reconstruction algorithm to reconstruct the densities of the objects under investigation and an unambiguous interpretation of the signal as a function of material density at any point of the thick object being inspected is described. In this simple and straightforward method the density of the target need not be known and only the knowledge of the target material's mass attenuation coefficients (composition) for the incident and scattered energies is enough to reconstruct the density of the each voxel of the specimen being studied. The Monte Carlo (MC) numerical simulation of the phenomena is done using the Monte Carlo N-Particle Transport Code (MCNP) and the quantitative estimates of the values of signal-to-noise ratio for different percentages of MS corrosion derived from these simulations are presented and the spectra are compared with the experimental data. The gammatography experiments are carried out using the same PC controlled scanning system in a narrow beam, good geometry setup, and the thickness loss is estimated from the measured transmitted intensity. Radiography of the MS plates is carried out using 160 kV x-ray machine. The digitized radiographs with a resolution of 50 μm are processed for the detection of corrosion damage in five different locations. The thickness losses due to the corrosion of the MS plate obtained by gamma scattering method are compared with those values obtained by gammatography and radiography techniques. The percentage thickness loss estimated at different positions of the corroded MS plate varies from 17.78 to 27.0, from 18.9 to 24.28, and from 18.9 to 24.28 by gamma scattering, gammatography, and radiography techniques, respectively. Overall, these results are consistent and in line with each other.
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noise in MgO double-barrier magnetic tunnel junctions
Authors: Yu G. Q. , Diao Z. , Feng J. F. , Kurt H. , Han X. F. , Coey J. M. D.
Published: March 2011

Low frequency noise has been investigated in MgO double-barrier magnetic tunnel junctions (DMTJs) with tunneling magnetoresistance (TMR) ratios up to 250% at room temperature. The noise shows a 1/f frequency spectrum and the minimum of the noise magnitude parameter is 1.2×10−10 μm2 in the parallel state for DMTJs annealed at 375 °C. The bias dependence of noise and TMR suggests that DMTJs with MgO barriers can be useful for magnetic field sensor applications.
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gate stacks with low interface trap density fabricated by electron cyclotron resonance plasma postoxidation
Authors: Zhang R. , Iwasaki T. , Taoka N. , Takenaka M. , Takagi S.
Published: March 2011

An electron cyclotron resonance (ECR) plasma postoxidation method has been employed for forming Al2O3/GeOx/Ge metal-oxide-semiconductor (MOS) structures. X-ray photoelectron spectroscopy and transmission electron microscope characterizations have revealed that a GeOx layer is formed beneath the Al2O3 capping layer by exposing the Al2O3/Ge structures to ECR oxygen plasma. The interface trap density (Dit) of Au/Al2O3/GeOx/Ge MOS capacitors is found to be significantly suppressed down to lower than 1011 cm−2 eV−1. Especially, a plasma postoxidation time of as short as 10 s is sufficient to reduce Dit with maintaining the equivalent oxide thickness (EOT). As a result, the minimum Dit values and EOT of 5×1010 cm−2 eV−1 and 1.67 nm, and 6×1010 cm−2 eV−1 and 1.83 nm have been realized for Al2O3/GeOx/Ge MOS structures with p- and n-type substrates, respectively.
Semiclassical instanton approach to calculation of reaction rate constants in multidimensional chemical systems
Authors: Kryvohuz Maksym
Published: March 2011

The semiclassical instanton approximation is revisited in the context of its application to the calculation of chemical reaction rate constants. An analytical expression for the quantum canonical reaction rate constants of multidimensional systems is derived for all temperatures from the deep tunneling to high-temperature regimes. The connection of the derived semiclassical instanton theory with several previously developed reaction rate theories is shown and the numerical procedure for the search of instanton trajectories is provided. The theory is tested on seven different collinear symmetric and asymmetric atom transfer reactions including heavy-light-heavy, light-heavy-light and light-light-heavy systems. The obtained thermal rate constants agree within a factor of 1.5–2 with the exact quantum results in the wide range of temperatures from 200 to 1500 K.
Low-lying excited states and nonradiative processes of the adenine analogues 7H- and 9H-2-aminopurine
Authors: Lobsiger Simon , Sinha Rajeev K. , Trachsel Maria , Leutwyler Samuel
Published: March 2011

We have investigated the UV vibronic spectra and excited-state nonradiative processes of the 7H- and 9H-tautomers of jet-cooled 2-aminopurine (2AP) and of the 9H-2AP-d4 and -d5 isotopomers, using two-color resonant two-photon ionization spectroscopy at 0.3 and 0.045 cm−1 resolution. The S1 ← S0 transition of 7H-2AP was observed for the first time. It lies ∼ 1600 cm−1 below that of 9H-2AP, is ∼1000 times weaker and exhibits only in-plane vibronic excitations. In contrast, the S1 ← S0 spectra of 9H-2AP, 9H-2AP-d4, and 9H-2AP-d5 show numerous low-frequency bands that can be systematically assigned to overtone and combinations of the out-of-plane vibrations ν1′, ν2′, and ν3′. The intensity of these out-of-plane bands reflects an out-of-plane deformation in the 1ππ*(La) state. Approximate second-order coupled-cluster theory also predicts that 2-aminopurine undergoes a “butterfly” deformation in its lowest 1ππ* state. The rotational contours of the 9H-2AP, 9H-2AP-d4, and 9H-2AP-d5 \documentclass[12pt]{minimal}\begin{document}$0^0_0$\end{document}000 bands and of eight vibronic bands of 9H-2AP up to \documentclass[12pt]{minimal}\begin{document}$0^0_0+600$\end{document}000+600 cm−1 exhibit 75%–80% in-plane (a/b) polarization, which is characteristic for a 1ππ* excitation. A 20%–25% c-axis (perpendicular) transition dipole moment component may indicate coupling of the 1ππ* bright state to the close-lying 1nπ* dark state. However, no 1nπ* vibronic bands were detected below or up to 500 cm−1 above the 1ππ* \documentclass[12pt]{minimal}\begin{document}$0^0_0$\end{document}000 band. Following 1ππ* excitation, 9H-2AP undergoes a rapid nonradiative transition to a lower-lying long-lived state with a lifetime ⩾5μs. The ionization potential of 9H-2AP was measured via the 1ππ* state (IP = 8.020 eV) and the long-lived state (IP \documentclass[12pt]{minimal}\begin{document}$>$\end{document}> 9.10 eV). The difference shows that the long-lived state lies ⩾1.08 eV below the 1ππ* state. Time-dependent B3LYP calculations predict the 3ππ* (T1) state 1.12 eV below the 1ππ* state, but place the 1nπ* (S1) state close to the 1ππ* state, implying that the long-lived state is the lowest triplet (T1) and not the 1nπ* state.
Syringe-vacuum microfluidics: A portable technique to create monodisperse emulsions
Authors: Abate Adam R. , Weitz David A.
Published: March 2011

We present a simple method for creating monodisperse emulsions with microfluidic devices. Unlike conventional approaches that require bulky pumps, control computers, and expertise with device physics to operate devices, our method requires only the microfluidic device and a hand-operated syringe. The fluids needed for the emulsion are loaded into the device inlets, while the syringe is used to create a vacuum at the device outlet; this sucks the fluids through the channels, generating the drops. By controlling the hydrodynamic resistances of the channels using hydrodynamic resistors and valves, we are able to control the properties of the drops. This provides a simple and highly portable method for creating monodisperse emulsions.
Spontaneous mode-selection in the self-propelled motion of a solid/liquid composite driven by interfacial instability
Authors: Takabatake Fumi , Magome Nobuyuki , Ichikawa Masatoshi , Yoshikawa Kenichi
Published: March 2011

Spontaneous motion of a solid/liquid composite induced by a chemical Marangoni effect, where an oil droplet attached to a solid soap is placed on a water phase, was investigated. The composite exhibits various characteristic motions, such as revolution (orbital motion) and translational motion. The results showed that the mode of this spontaneous motion switches with a change in the size of the solid scrap. The essential features of this mode-switching were reproduced by ordinary differential equations by considering nonlinear friction with proper symmetry.
Transparent, near-infrared organic photovoltaic solar cells for window and energy-scavenging applications
Authors: Lunt Richard R. , Bulovic Vladimir
Published: March 2011

We fabricate near-infrared absorbing organic photovoltaics that are highly transparent to visible light. By optimizing near-infrared optical-interference, we demonstrate power efficiencies of 1.3±0.1% with simultaneous average visible transmission of >65%. Subsequent incorporation of near-infrared distributed-Bragg-reflector mirrors leads to an increase in the efficiency to 1.7±0.1%, approaching the 2.4±0.2% efficiency of the opaque cell, while maintaining high visible-transparency of >55%. Finally, we demonstrate that a series-integrated array of these transparent cells is capable of powering electronic devices under near-ambient lighting. This architecture suggests strategies for high-efficiency power-generating windows and highlights an application uniquely benefiting from excitonic electronics.
Nearly lattice-matched InAlN/GaN high electron mobility transistors grown on SiC substrate by pulsed metal organic chemical vapor deposition
Authors: Xue JunShuai , Hao Yue , Zhang JinCheng , Zhou XiaoWei , Liu ZiYang , Ma JunCai , Lin ZhiYu
Published: March 2011

We report on a growth of nearly lattice-matched InAlN/GaN heterostructures on 4H–SiC substrates by pulsed metal organic chemical vapor deposition, and an excellent device characteristic of high electron mobility transistors (HEMTs) fabricated on these InAlN/GaN heterostructures. The electron mobility is 1032 cm2/V s together with a high two-dimensional-electron-gas density of 1.59×1013 cm−2 for the In0.17Al0.83N/AlN heterostructures. HEMTs with gate dimensions of 0.5×50 μm2 and 3 μm source-drain distance exhibits a maximum drain current of 1 A/mm, a maximum extrinsic transconductance of 310 mS/mm, and current gain and maximum oscillation cutoff frequencies of 18 GHz and 39 GHz, respectively.
Phase-field simulation of strain-induced domain switching in magnetic thin films
Authors: Hu Jia-Mian , Sheng G. , Zhang J. X. , Nan C. W. , Chen L. Q.
Published: March 2011

The strain-induced magnetic domain switching in epitaxial CoFe2O4 (CFO) thin films was studied using phase-field method. In particular, we investigated the domain switching from an initial in-plane direction to out-of-plane under the action of in-plane elastic strains. An abrupt switching feature is observed for a single-domain film while the switching of a multidomain CFO thin film is gradual. Typical magnetic domain structures as a result of the biaxial isotropic in-plane strains are presented.
Confinement effects on dipole–dipole interactions in nanofluids: The role of equilibrium fluctuations
Authors: Jeener J.
Published: March 2011

When spin bearing molecules are enclosed in an elongated nanovoid, and each molecule diffuses across the whole volume in times much shorter than the characteristic times of NMR spin dynamics, a time independent average dipolar Hamiltonian emerges which couples the spins in each molecule equally with the spins in any other molecule. Baugh et al. [Science, 134, 1505 (2001)] have observed the remarkable orientation dependent linewidth in such a situation, and offered a convincing interpretation using the techniques of solid state NMR. In the present paper I show that, contrary to previous expectations, the same linewidth can be predicted with liquid NMR techniques, provided that one takes into account equilibrium fluctuations in the estimation of the dipolar field.
Enhanced photoelectrochemical activity for Cu and Ti doped hematite: The first principles calculations
Authors: Meng X. Y. , Qin G. W. , Li S. , Wen X. H. , Ren Y. P. , Pei W. L. , Zuo L.
Published: March 2011

To improve photoelectrochemical (PEC) activity of hematite, the modification of energy band by doping 3d transition metal ions Cu and Ti into α-Fe2O3 were studied via the first-principles calculations with density function theory (DFT)+U method. The results show that the band gap of hematite is ∼2.1 eV and n-type dopant Ti improves the electric conductivity, confirmed by recent experiments. The p-type dopant Cu enhances the utilization ratio of solar energy, shifts both valance, and conduction band edges to a higher energy level, satisfying hydrogen production in the visible light driven PEC water splitting without voltage bias.
Description of the low field nonlinear dielectric properties of ferroelectric and multiferroic materials
Authors: Borderon C. , Renoud R. , Ragheb M. , Gundel H. W.
Published: March 2011

Ferroelectric and multiferroic materials present a nonlinear variation in their permittivity due to domain wall motion. Currently, this variation is described either by the Rayleigh law for fields above a threshold or by a power law for soft ferroelectrics. We propose a hyperbolic law based on the contributions of domain walls and intrinsic lattice which includes the two classic approaches. The threshold field is clearly defined by considering reversible and irreversible components of the permittivity. A good agreement between the hyperbolic law and experimental data is obtained. Moreover, we show that the threshold field obeys to the Volgel–Fulcher law.
Switching current reduction using perpendicular anisotropy in CoFeB–MgO magnetic tunnel junctions
Authors: Khalili Amiri P. , Zeng Z. M. , Langer J. , Zhao H. , Rowlands G. , Chen Y.-J. , Krivorotov I. N. , Wang J.-P. , Jiang H. W. , Katine J. A. , Huai Y. , Galatsis K. , Wang K. L.
Published: March 2011

We present in-plane CoFeB–MgO magnetic tunnel junctions with perpendicular magnetic anisotropy in the free layer to reduce the spin transfer induced switching current. The tunneling magnetoresistance ratio, resistance-area product, and switching current densities are compared in magnetic tunnel junctions with different CoFeB compositions. The effects of CoFeB free layer thickness on its magnetic anisotropy and current-induced switching characteristics are studied by vibrating sample magnetometry and electrical transport measurements on patterned elliptical nanopillar devices. Switching current densities ∼4 MA/cm2 are obtained at 10 ns write times.
Deep-ultraviolet light-emitting diodes with gradually increased barrier thicknesses from n-layers to p-layers
Authors: Tsai Miao-Chan , Yen Sheng-Horng , Kuo Yen-Kuang
Published: March 2011

In this work, the structure with gradually increased barrier thicknesses from the n-layers to p-layers is proposed to replace the traditional structure with equal barrier thickness in deep-ultraviolet AlGaN light-emitting diodes. Simulation approach yields to a result that, when increased barrier thicknesses are used, the distribution of electron and hole carriers inside the active region becomes quite uniform, which leads to efficient recombination of electrons and holes and thereby a significant enhancement in output power.
Synchrotron radiation photoemission study of in situ manganese silicate formation on SiO2 for barrier layer applications
Authors: Casey Patrick , Bogan Justin , Brennan Barry , Hughes Greg
Published: March 2011

Synchrotron radiation photoelectron spectroscopy (SRPES) is used to investigate the in situ formation of ultra thin Mn silicate layers on SiO2, which has relevance for copper diffusion barrier layers in microelectronic devices. High temperature vacuum annealing of metallic Mn (∼1.5 nm) deposited on a 4 nm thermally grown SiO2 film results in the self limiting formation of a magnesium silicate layer, the stoichiometry of which is consistent with the formation of MnSiO3. Curve fitted Mn 3p SRPES spectra show no evidence for the presence of a manganese oxide phase at the Mn/SiO2 interface, in contrast to previous reports.
Transport in ferromagnetic GdTiO3/SrTiO3 heterostructures
Authors: Moetakef Pouya , Zhang Jack Y. , Kozhanov Alexander , Jalan Bharat , Seshadri Ram , Allen S. James , Stemmer Susanne
Published: March 2011

Epitaxial GdTiO3/SrTiO3 structures with different SrTiO3 layer thicknesses are grown on (001) (LaAlO3)0.3(Sr2AlTaO6)0.7 substrate surfaces by hybrid molecular beam epitaxy. It is shown that the formation of the pyrochlore (Gd2Ti2O7) phase can be avoided if GdTiO3 is grown by shuttered growth, supplying alternating monolayer doses of Gd and of the metalorganic precursor that supplies both Ti and O. Phase-pure GdTiO3 films grown by this approach exhibit magnetic ordering with a Curie temperature of 30 K. The electrical transport characteristics can be understood as being dominated by a conductive interface layer within the SrTiO3.
High quality, transferrable graphene grown on single crystal Cu(111) thin films on basal-plane sapphire
Authors: Reddy Kongara M. , Gledhill Andrew D. , Chen Chun-Hu , Drexler Julie M. , Padture Nitin P.
Published: March 2011

The current method of growing large-area graphene on polycrystalline Cu surfaces (foils or thin films) and its transfer to arbitrary substrates is technologically attractive. However, the quality of graphene can be improved significantly by growing it on single-crystal Cu surfaces. Here we show that high quality, large-area graphene can be grown on epitaxial single-crystal Cu(111) thin films on reusable basal-plane sapphire [α-Al2O3(0001)] substrates for transfer to another substrate. While enabling graphene growth on Cu single-crystal surfaces, this method has the potential to avoid the high cost and extensive damage to graphene associated with sacrificing bulk single-crystal Cu during graphene transfer.
Ab initio molecular dynamics of Al irradiation-induced processes during Al2O3 growth
Authors: Music Denis , Nahif Farwah , Sarakinos Kostas , Friederichsen Niklas , Schneider Jochen M.
Published: March 2011

Al bombardment induced structural changes in α-Al2O3 (R-3c) and γ-Al2O3 (Fd-3m) were studied using ab initio molecular dynamics. Diffusion and irradiation damage occur for both polymorphs in the kinetic energy range from 3.5 to 40 eV. However, for γ-Al2O3(001) subplantation of impinging Al causes significantly larger irradiation damage and hence larger mobility as compared to α-Al2O3. Consequently, fast diffusion along γ-Al2O3(001) gives rise to preferential α-Al2O3(0001) growth, which is consistent with published structure evolution experiments.
Permittivity and microwave absorption of semi-insulating InP at microwave frequencies
Authors: Krupka Jerzy , Hartnett John G. , Piersa Mirosław
Published: March 2011

Permittivity and dielectric losses of a Fe-doped semi-insulating bulk InP sample were determined at microwave frequencies from 4 to 300 K employing the whispering gallery mode technique. The dielectric loss tangent of the sample at 11 GHz exhibited a local maximum near 12 K. Since the dc conductivity at this temperature was not measurable in our sample the low temperature loss peak is attributed to the local displacement of bound charge carriers.
Practice-based chronic condition care coordination: challenges and opportunities
Authors: Ehrlich Carolyn , Kendall Elizabeth , Muenchberger Heidi
Published: March 2011

This paper explores issues related to the types of support that practice nurses require to engage in care coordination for people with chronic conditions. A sample of practice nurses and general practitioners participated in a focus group discussion to identify their perspectives on the role of practice nurses as providers of care coordination, the specific tasks that might be conducted and the types of support that might be required. The data were analysed using thematic analysis. The findings suggested there was considerable confusion about care coordination and a lack of conceptual clarity. Nevertheless, nurses were committed to engaging in activities that would promote care coordination. Four main themes emerged that indicated the importance of a developmental and well-supported implementation process. These themes included the need for cultural change within the whole practice, increased capacity to develop trusted and tested partnerships, appropriate role definition and a full understanding of the financial models that could support care coordination. Practice nurses clearly have a role in care coordination, but models of care coordination need to be localised and contextualised within specific GP practices. Cultural change will, in many instances, be critical to the development of localised programs. Broad supportive structures, including ongoing mentorship and administrative assistance (particularly with financial and procedural aspects of care coordination) will be required when implementing programs that enhance roles for practice nurses.
Enhancing palliative care in rural Australia: the residential aged care setting
Authors: Mitchell Geoffrey , Nicholson Caroline , McDonald Keith , Bucetti Anne
Published: March 2011

The delivery of palliative care in residential aged care communities is challenging, even more so in rural areas due to workforce ageing and shortages. The objectives of the present study were to: (i) assess the needs of, and quality of palliative care delivered to residents of 16 residential aged care facilities in rural southern Australia; and (ii) identify the needs of care staff to facilitate the delivery of quality palliative care. A cross-sectional survey of all residents, assessing the degree of functional limitation, stage of palliative care, and the presence of several quality indicators was conducted. Separate focus groups of care staff and relatives of residents sought information on the quality of care delivered, perceived strengths and weaknesses of the care delivered, and education and training needs. Quality palliative care in residential aged care facilities (RACFs) is hampered by workforce shortages, with low ratios of registered nurses, limited access to general practitioners after hours, and some communication difficulties. Some staff reported low confidence in technical and psychosocial aspects of care, especially for relatives. Relatives described mostly appropriate care, while acknowledging workload constraints. Most residents whose condition was unstable, deteriorating or terminal received advance care planning, though family expectations and unwillingness to discuss end-of-life care did tend to delay planning. Unstable residents with a reasonable prognosis were more likely to be transferred to hospital than terminally ill residents. Palliative care in participating RACFs appears to be adequate. Provision of targeted education for health care providers and implementation of protocols for advance care planning and end-of life care pathways will enhance this care.
Physician's assistants: a workforce solution for Australia?
Authors: Kurti Linda , Rudland Susan , Wilkinson Rebecca , DeWitt Dawn , Zhang Catherine
Published: March 2011

Significant medical workforce shortages, particularly in rural and remote locations, have prompted a range of responses in Australia at both state and Commonwealth levels. One such response was a pilot project to test the suitability of the Physician Assistant (PA) role in the Australian context. Five US-trained and accredited PAs were employed by Queensland Health and deployed in urban, rural and remote settings across Queensland. A concurrent mixed-method evaluation was conducted by Urbis, an independent research firm. The evaluation found that the PAs provided quality, safe clinical care under the supervision of local medical officers. The majority of nurses and doctors who worked with the PAs believed that the PAs made a positive contribution to the health care team by increasing capacity to meet patient needs; reducing on-call requirements for doctors; liaising with other clinical team members; streamlining procedures for efficient patient throughput; and providing continuity during periods of doctor changeover. The Pilot demonstrated that a delegated PA role can provide safe, quality health care by augmenting an established healthcare team. The PA role has the potential to benefit the community by increasing the capacity of the health care system, and to improve recruitment and retention by providing an additional professional pathway. The small size of the Pilot limits the ability to generalise regarding the future efficacy of the PA role in Australia. Further research is required to test training and deployment of PAs in a wider range of Australian clinical settings, including general practice and rural health clinics.
Efficient purification of neonatal porcine gonocytes with Nycodenz and differential plating
Authors: Yang Yanfei , Honaramooz Ali
Published: March 2011

Gonocytes are the only type of germ cells present in the postnatal testis and give rise to spermatogonial stem cells. Purification of gonocytes has important implications for the study and manipulation of these cells and may provide insights for the ongoing investigation of the male germline stem cells. To obtain a pure population of gonocytes from piglet testis cells, a wide range of Nycodenz concentrations were investigated for density gradient centrifugation. We also examined differential plating of testis cells for various culture durations with different extracellular matrix (ECM) components (fibronectin, poly-d-lysine, poly-l-lysine, laminin and collagen Types I and IV). Gonocytes were highly enriched in pellets of testis cells after using 17% Nycodenz centrifugation to a purity of 81 ± 9%. After culturing testis cells on plates precoated with different ECM components for 120 min, the proportion of gonocytes increased among non-adherent cells (suspended in the medium), with fibronectin or poly-d-lysine resulting in the greatest (up to 85%) and laminin in the lowest (54%) gonocyte proportion. Combining the most promising ECM coatings (fibronectin and poly-d-lysine) and further extension of their culture duration to 240 min did not improve final gonocyte purity. However, centrifugation with 17% Nycodenz followed by differential plating with fibronectin and poly-d-lysine coating further purified gonocytes among the collected cells to >90%. These results provide a simple, quick and efficient approach for obtaining highly enriched populations of piglet gonocytes for use in the study and manipulation of these germline stem cells.
Evaluation of the developmental potential of metaphase I oocytes from stimulated intracytoplasmic sperm injection cycles
Authors: Li Mei , Li Yuan , Ma Shui-Ying , Feng Huai-Liang , Yang Hui-Jun , Wu Ke-Liang , Zhong Wan-Xia , Che Li , Chen Zi-Jiang
Published: March 2011

The objective of the present study was to evaluate the developmental potential and clinical application value of metaphase I (MI) oocytes obtained from stimulated intracytoplasmic sperm injection (ICSI) cycles. ICSI was performed on MI oocytes immediately after denudation (Group A), or on in vitro-matured (IVM) oocytes following culture; oocytes in culture were further divided into two groups, being cultured for either 3–5 h (Group B) or 24–28 h (Group C). Metaphase II oocytes from the same cycle(s) isolated for ICSI served as the control group (Group D). The rates of normal fertilisation, cleavage and high-quality embryos were compared among the four groups. High-quality embryos were transferred whenever possible, and pregnancy rates were evaluated. Results showed that normal fertilisation rates for Groups B, C and D were significantly higher than that of Group A (68.6%, 57.8%, 74.5% and 30.1%, respectively; P < 0.01). The rate of high-quality embryos in Group B was comparable with Group D; the rate for Group C was significantly lower than that of the other groups (P < 0.05). Two clinical pregnancies were achieved after transfer of embryos from IVM oocytes. In vitro maturation of MI oocytes for a short period of time may increase the number of available embryos; however, overnight in vitro culture of MI oocytes did not improve results.