bluuebunny/crossref_metadata_2025 huggingface dataset:
High temperature magnetic properties of Fe81−xCoxGa19/Si(100) films
Authors: Tsai T. L. , Jen S. U. , Kuo P. C.
Published: April 2011

Fe81−xCoxGa19 (with x ranging from 0 to 19 at.% Co) films with thicknesses of about 110 nm were deposited on Si(100) substrates by the dc magnetron sputtering method. The structures of these films at room temperature (RT) were analyzed by x-ray diffraction. Magnetic hysteresis loops of each film were measured from room temperature (RT) to 800 °C, and their saturation magnetization (4πMS) and coercivity (HC) were plotted as a function of temperature (T). Saturation magnetostriction (λS) at RT was also measured. The substitution of Co for Fe would give rise to increases in HC and λS. In terms of high temperature magnetic properties, (A) we find that for each film, there is one low-temperature-phase Curie point (TC1) and one high-temperature-phase Curie point (TC2); (B) based on the temperature dependence of 4πMS, we calculated the reduced hyperbolic Bessel function I∧5/2(T); from the relationship λS(T)=I∧5/2(T)×λS(RT), we can compare the performances of λS(T) at higher temperatures; and (C) HC decreases slightly as T increases initially, but it reaches a maximum when either TC1 or TC2 is approached. It is concluded that the Fe62Co19Ga19 film has the optimal high-temperature magnetic properties, including a larger λS(T), higher TC1, and moderate HC(T).
Evolution of magnetic properties and crystallographic texture in electrical steel with large plastic deformation
Authors: Fukuhara M. , Yonamine T. , Landgraf F. J. G. , Missell F. P.
Published: April 2011

Deformation leads to a hardening of steel due to an increase in the density of dislocations and a reduction in their mobility, giving rise to a state of elevated residual stresses in the crystal lattice. In the microstructure, one observes an increase in the contribution of crystalline orientations which are unfavorable to the magnetization, as seen, for example, by a decrease in B50, the magnetic flux density at a field of 50 A/cm. The present study was carried out with longitudinal strips of fully processed non-oriented (NO) electrical steel, with deformations up to 70% resulting from cold rolling in the longitudinal direction. With increasing plastic deformation, the value of B50 gradually decreases until it reaches a minimum value, where it remains even for larger deformations. On the other hand, the coercive field Hc continually increases. Magnetometry results and electron backscatter diffraction results are compared and discussed.
Magnetic property-texture relationships in galfenol rolled sheet stacks
Authors: Meloy Rob , Summers Eric
Published: April 2011

Recent results in the area of galfenol (iron-gallium) alloy rolled sheet have yielded significant Goss ({110}<001>∥ rolling direction [RD]) texture development and large strain values, > 250 ppm. Goss-textured grain growth is promoted by the use of a grain boundary pinning second-phase particle. After multistage rolling and subsequent heat treatment, Goss grain areas as large as 125 cm2 develop in the RD–transverse direction (TD) plane. Goss grain <100> directions are typically within 15° of the RD inside these grains. Fully processed sheets were sectioned and bonded together to produce laminated stacks. Grain oriented and nongrain oriented stacks were characterized magnetically. Plotting strain data against H-field for both an Oriented Stack (OS) and a Nonoriented Stack (NonOS) yielded saturation stain values of 215 ppm and 70 ppm, at 48.3 MPa prestress, respectively. Magnetostrictive strain coefficient, d33, values of 20 nm/A and 4 nm/A were calculated for the OS and NonOS, respectively. Saturation magnetization values were found to be 1.3 T and 1.2 T for the OS and NonOS. Electron Backscatter Diffraction (EBSD) analysis was performed on cross sections of each laminated stack. EBSD mapping showed a large relative disparity in average grain size, taken from cross sections, of 470 μm and 84 μm for the OS and NonOS. Pole figures, contoured at a half-width of 10°, were analyzed and clearly show a high degree of Goss texture in the OS and a lack of any strong texture in the NonOS. The OS generated a maximum Multiple of Mean Uniform Density value > 16 while the NonOS produced a value < 2.
Magnetocaloric effect and magnetic phase transition in Ho3Co
Authors: Shen Jun , Wu Jian-Feng
Published: April 2011

Magnetocaloric effect (MCE) and magnetic phase transition of Ho3Co compound have been investigated. The two successive magnetic transitions: spin–reorientation transition at TSR = 8.5 K and antiferromagnetic (AFM)–paramagnetic transition at the Néel temperature TN = 21 K are observed. The Ho3Co compound undergoes a field-induced metamagnetic transition from AFM to ferromagnetic states below TN, which leads to a large MCE. The maximal value of magnetic entropy change (ΔSM) is found to be −14.5 J/kg K with a refrigerant capacity (RC) value of 440 J/kg around TN for a field change of 0–5 T. The large ΔSM as well as considerable RC in Ho3Co is very useful for applying it to the magnetic refrigeration in low-temperature ranges.
Simultaneous magnetic force microscopy imaging of perpendicular and in-plane magnetic field gradient on La0.7Sr0.3MnO3 granular film with in-plane magnetization
Authors: Li Zhenghua , Egawa Genta , Yoshimura Satoru , Li Guoqing , Asano Hidefumi , Saito Hitoshi
Published: April 2011

Our recently developed magnetic force microscopy for simultaneous imaging of perpendicular and in-plane magnetic field gradients was applied to polycrystalline La0.7Sr0.3MnO3 granular films with in-plane magnetization. The present method clearly imaged the gradient of the perpendicular and the in-plane magnetic field from the boundary phase, which behaved as a magnetic double layer with two separate planes of magnetic charges. Especially after magnetizing the film in one direction, the perpendicular and in-plane magnetic field gradients of a magnetic double layer with opposite-sign magnetic charges were clearly observed by this method. Calculated magnetic field gradients are consistent with those of the magnetic force microscopy images. The present method seems to be effective in evaluating the magnetic isolation between neighboring magnetic grains having the component of in-plane magnetization.
Conduction band offset and quantum states probed by capacitance–voltage measurements for InP/GaAs type-II ultrathin quantum wells
Authors: Singh S. D. , Dixit V. K. , Khamari Shailesh K. , Kumar Ravi , Srivastava A. K. , Ganguli Tapas , Oak S. M.
Published: April 2011

Quantum states in InP/GaAs type-II ultrathin quantum wells (QWs) are investigated through temperature dependent capacitance–voltage (C–V) measurements. We observe a well-defined peak in the apparent carrier density (ACD) profile for the ultrathin QWs at low temperatures in the vicinity of QWs. ACD peak value is found to decrease with the reduction in QW thickness, indicating quantum confinement effect. Decrease in the ACD peak value and increase in its width with increasing temperature confirms that the observed peak in the ACD profiles is related to the two dimensional electrons occupying the quantum states formed in the ultrathin QWs. We do not observe appreciable peak shift in ACD profiles with temperature, which is attributed to the less temperature dependence of the Debye length because of the high doping density used in the barrier region of InP/GaAs ultrathin QWs. We determine a strained value of 180 ± 30 meV for the conduction band discontinuity by simulating the C–V profile through the self-consistent solution of Schrodinger and Poisson equations for InP/GaAs ultrathin QW.
Influence of the type of surfactant and hot compaction on the magnetic properties of SmCo5 nanoflakes
Authors: Zheng Liyun , Gabay Alexander M. , Li Wanfeng , Cui Baozhi , Hadjipanayis George C.
Published: April 2011

In this study, we discuss the effects of a type of surfactant (oleylamine, oleic acid, and trioctylamine) and hot pressing on the hard magnetic properties of crystallographically anisotropic SmCo5 nanoflakes prepared by surfactant-assisted high energy ball milling. The phase, microstructure, and magnetic properties of the hot-pressed SmCo5 were investigated by using x-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. The coercivities of the precursor flakes prepared using oleylamine, oleic acid, and trioctylamine were 14.9, 15.8, and 15 kOe, respectively. Hot-compacted SmCo5 magnets prepared from the nanoflakes milled with oleic acid had the lowest coercivity of 8.1 kOe. It is believed that even after repeated washing in an ultrasonic bath with different solvents, the remaining oleic acid in the SmCo5 nanoflakes led to oxidation of SmCo5 at the surface/interface of nanoflakes during the hot-pressing process. The compacted SmCo5 magnets prepared from the nanoflakes milled with trioctylamine and oleylamine had higher coercivity values of 14.8 and 12.8 kOe, respectively. Unlike oleic acid, oleylamine and trioctylamine contain no oxygen atoms, and therefore there was less oxidation during the process. The compaction temperature also influences the coercivity. The SmCo5 magnets hot pressed at 550 °C had the highest coercivity, whereas those hot pressed at 650 °C had the lowest coercivity; this is attributed to the change of phases and composition of SmCo5 alloys during the hot-pressing process.
Magnetic anisotropy and magnetization reversal of (Ga,Mn)As dot-array
Authors: Kimura H. , Kobayashi S. , Yamaguchi T. , Kitamoto Y. , Munekata H.
Published: April 2011

The present article describes the magnetic anisotropy and magnetization reversal of (Ga,Mn)As dot-arrays with 1 μm and 200 nm in diameter fabricated by electron-beam lithography and Ar ion etching. The magnetization reversal mode is due to the magnetization rotation in the dot-arrays fabricated in the present study; they probably have a single-domain structure. The microfabrication of the (Ga,Mn)As dot-arrays modifies magnetic anisotropy through the relaxation of strain in the dots as previously reported; the 200-nm-dot-array exhibits magnetically isotropic features. The cubic anisotropy constant of the 200-nm-dot-array is estimated to be reduced by approximately a tenth of that of the (Ga,Mn)As epitaxial film by the calculation from the measured M-H loops based on a phenomenological model related to magnetic energy.
Crack-mechanics based brittle damage model including nonlinear equation of state and porosity growth
Authors: Deganis L. E. , Zuo Q. H.
Published: April 2011

A three-dimensional rate-dependent model has been developed for damage and failure of brittle materials under impact. The model extends a recently developed, crack-mechanics based damage model [Zuo et al., Int. J. Solids Struct. 43, 3350 (2006)] to high rate problems by incorporating a nonlinear equation of state (EOS) and porosity growth. The pressure-volume response developed by Addessio and Johnson for ceramics under impact [J. Appl. Phys. 67, 3275 (1990)] was adapted to the current model. The model has been numerically implemented and the responses of a ceramic (silicon carbide) under various loading paths are shown. These responses are compared with those predicted by the existing model (having a linear equation of state) to illustrate the effects of nonlinear EOS and porosity.
Conductance modulation in graphene nanoribbon under transverse asymmetric electric potential
Authors: Bala Kumar S. , Fujita T. , Liang Gengchiau
Published: April 2011

This paper presents a theoretical study of the effect of transverse electric potentials on the transport properties of armchair graphene nanoribbons (AGNRs), formed by pairs of asymmetric gates placed along the side of the ribbon. Single-pair and dual-pair configurations are considered. The effect of hollows (spatial regions void of carbon atoms) in the AGNR channels is also examined. The use of hollowed AGNRs in the dual-pair configuration allows for significant modulation of the transport gap when the two pairs have opposite gate bias polarity. Furthermore, for the dual-gate system, hollowed AGNR channels exhibit the optimal ratio of on-state to off-state conductance, due to the smaller off-state conductance compared with spatially homogenous AGNR channels. Our results indicate that transverse gate technology coupled with careful engineering of hollow geometry may lead to possible applications in graphene-based electronic devices.
Visible luminescence properties of (Ga1−xZnx)(N1−xOx) solid solution (x = 0.22)
Authors: Lee Yueh-Chien , Lin Tai-Yuan , Wu Chih-Wen , Teng Hsisheng , Hu Che-Chia , Hu Sheng-Yao , Yang Min-De
Published: April 2011

Temperature-dependent photoluminescence (PL) and time-resolved photoluminescence (TRPL) are measured for the (Ga1−xZnx)(N1−xOx) solid solution with x = 0.22 to study its luminescence properties. PL result shows that the material exhibits visible luminescence at around 1.87 eV (663 nm) with a broad emission band even at room temperature. The origin of luminescence mechanism can be attributed to the radiative recombination of the electrons bound to donors and the holes bound to acceptors. The investigation from the integrated PL intensity and TRPL as a function of temperature indicates that the activation energy for thermalizing the electrons bound to a donor dominates the luminescence behavior in the (Ga1−xZnx)(N1−xOx) solid solution.
Applicability of nanofluids in high flux solar collectors
Authors: Taylor Robert A. , Phelan Patrick E. , Otanicar Todd P. , Walker Chad A. , Nguyen Monica , Trimble Steven , Prasher Ravi
Published: April 2011

Concentrated solar energy has become the input for an increasing number of experimental and commercial thermal systems over the past 10–15 years [M. Thirugnanasambandam et al., Renewable Sustainable Energy Rev. 14 (2010)]. Recent papers have indicated that the addition of nanoparticles to conventional working fluids (i.e., nanofluids) can improve heat transfer and solar collection [H. Tyagi et al., J. Sol. Energy Eng. 131, 4 (2009); P. E. Phelan et al., Annu. Rev. Heat Transfer 14 (2005)]. This work indicates that power tower solar collectors could benefit from the potential efficiency improvements that arise from using a nanofluid working fluid. A notional design of this type of nanofluid receiver is presented. Using this design, we show a theoretical nanofluid enhancement in efficiency of up to 10% as compared to surface-based collectors when solar concentration ratios are in the range of 100–1000. Furthermore, our analysis shows that graphite nanofluids with volume fractions on the order of 0.001% or less are suitable for 10–100 MWe power plants. Experiments on a laboratory-scale nanofluid dish receiver suggest that up to 10% increase in efficiency is possible (relative to a conventional fluid)—if operating conditions are chosen carefully. Lastly, we use these findings to compare the energy and revenue generated in a conventional solar thermal plant to a nanofluid-based one. It is found that a 100 MWe capacity solar thermal power tower operating in a solar resource similar to Tucson, AZ, could generate ∼$3.5 million more per year by incorporating a nanofluid receiver.
Residual and nitrogen doping of homoepitaxial nonpolar m-plane ZnO films grown by molecular beam epitaxy
Authors: Taïnoff D. , Al-Khalfioui M. , Deparis C. , Vinter B. , Teisseire M. , Morhain C. , Chauveau J.-M.
Published: April 2011

We report the homoepitaxial growth by molecular beam epitaxy of high quality nonpolar m-plane ZnO and ZnO:N films over a large temperature range. The nonintentionally doped ZnO layers exhibit a residual doping as low as ∼1014 cm−3. Despite an effective incorporation of nitrogen, p-type doping was not achieved, ZnO:N films becoming insulating. The high purity of the layers and their low residual n-type doping evidence compensation mechanisms in ZnO:N films.
Effects of poling over the orthorhombic-tetragonal phase transition temperature in compositionally homogeneous (K,Na)NbO3-based ceramics
Authors: Morozov M. I. , Kungl H. , Hoffmann M. J.
Published: April 2011

Li-, Ta-, and Mn-modified (K,Na)NbO3 ceramics with various compositional homogeneity have been prepared by conventional and precursor methods. The homogeneous ceramic has demonstrated a sharper peak in temperature dependent piezoelectric response. The dielectric and piezoelectric properties of the homogeneous ceramics have been characterized at the experimental subcoercive electric fields near the temperature of the orthorhombic–tetragonal phase transition with respect to poling in both phases. Poling in the tetragonal phase is shown to enhance the low-signal dielectric and piezoelectric properties in the orthorhombic phase.
Raman-active wurtzite CdO nanophase and phonon signatures in CdO/ZnO heterostructures fabricated by nonequilibrium laser plasma ablation and stress control
Authors: Ashrafi Almamun , (Ken) Ostrikov Kostya
Published: April 2011

A combination of laser plasma ablation and strain control in CdO/ZnO heterostructures is used to produce and stabilize a metastable wurtzite CdO nanophase. According to the Raman selection rules, this nanophase is Raman-active whereas the thermodynamically preferred rocksalt phase is inactive. The wurtzite-specific and thickness/strain-dependent Raman fingerprints and phonon modes are identified and can be used for reliable and inexpensive nanophase detection. The wurtzite nanophase formation is also confirmed by x-ray diffractometry. The demonstrated ability of the metastable phase and phonon mode control in CdO/ZnO heterostructures is promising for the development of next-generation light emitting sources and exciton-based laser diodes.
Nanosized hexagonal Mn- and Ga-doped BaTiO3 with reduced structural phase transition temperature
Authors: Natsui Hidesada , Moriyoshi Chikako , Yoshida Fumiko , Kuroiwa Yoshihiro , Ishii Tatsuya , Odawara Osamu , Yu Jianding , Yoda Shinichi
Published: April 2011

Nanosized hexagonal BaTiO3 particles were synthesized at 1373 K, grain growth was prevented by reducing the temperature of the cubic–hexagonal phase transition. Crystal structures of nanosized hexagonal Mn- and Ga-doped BaTiO3 were studied by high-energy synchrotron radiation powder diffraction at BL02B2 of SPring-8. Substituting the trivalent cations of Mn and Ga for Ti weakened the Mn–O and Ga–O bonding forces and stabilized the hexagonal phase, which reduced the phase transition temperature. These nanoparticles can be used in the manufacture of electronic components, owing to the properties of hexagonal BaTiO3.
Enhanced nanoparticle-oligonucleotide conjugates for DNA nanomachine controlled surface-enhanced Raman scattering switch
Authors: Zhang Zhiliang , Wen Yongqiang , Ma Ying , Luo Jia , Zhang Xingye , Jiang Lei , Song Yanlin
Published: April 2011

In this letter, a pH-responsive surface-enhanced Raman scattering (SERS) switching system based on the controlled organization of silver nanoparticles (AgNPs) by DNA nanomachine has been designed. In this system, the polyvalent linkages between AgNPs and cyclic disulfide groups-modified DNA tremendously increased the stability of the AgNP-DNA conjugates. Using this kind of conjugates, the SERS enhancement was demonstrated with good controllability and reproducibility through the controlled formation/deformation of SERS “hotspots” by the adjustment of pH of aqueous media.
Achievement of a high channel strain via dry oxidation of recessed source/drain Si1−xGex structures
Authors: Yoo J.-H. , Kim S.-W. , Koo S.-M. , Ko D.-H. , Lee H.-J.
Published: April 2011

This study proposes a method of acquiring a high channel strain by locally oxidizing recessed Si1−xGex source/drain structures and forming a Ge condensation layer as an effective stressor. Combination of several transmission electron microscopy characterization techniques including nanobeam diffraction allowed us to analyze the thickness and composition of the Ge condensation layer formed upon oxidation, and the evolution of the channel strain. Nanobeam diffraction results demonstrate that this method can be critically used to effectively increase the channel strain.
Analyzing carrier lifetime of double-layer organic solar cells by using optical electric-field-induced second-harmonic generation measurement
Authors: Taguchi Dai , Shino Tatsunori , Chen Xiangyu , Zhang Le , Li Jun , Weis Martin , Manaka Takaaki , Iwamoto Mitsumasa
Published: April 2011

By using optical electric-field-induced second-harmonic generation (SHG) measurement, we directly probed charge accumulation and decay processes in double-layer [copper-phthalocyanine (CuPc)/C60] organic solar cells (OSCs). Results showed that negative excess charges accumulated at the CuPc/C60 interface under photoillumination and the charges decayed in a two-step process in dark. Analysis using the filtering method showed that 24% of the accumulated negative excess charges decayed with a lifetime τL1=5.3×10−5 s and the other 76% of charges decayed with a lifetime τL2=6.2×10−2 s. We conclude that analyzing SHG signal response provides a direct way to investigate carrier lifetime in multilayer OSCs.
Measurements and microscopic model of quantum capacitance in graphene
Authors: Xu Huilong , Zhang Zhiyong , Peng Lian-Mao
Published: April 2011

Metal-oxide-semiconductor (MOS) structures based on graphene were fabricated with ultrathin Y2O3 films as the top gate oxide. While the quantum capacitance of graphene was measured using the MOS structure and shown to agree well with theory for ideal graphene at large channel potential, it deviates significantly from theory near the Dirac point. A general microscopic capacitance model is developed and used to describe the quantum capacitance anomaly near the Dirac point. Excellent agreement with experiment results was achieved using this model and key parameters including potential fluctuation and local carrier density fluctuation were retrieved.
Hypersonic confined eigenvibrations of gold nano-octahedra
Authors: Pan H. H. , Wang Z. K. , Lim H. S. , Ng S. C. , Zhang V. L. , Kuok M. H. , Tran T. T. , Lu X. M.
Published: April 2011

The size-dependence of the vibrational mode frequencies of octahedron-shaped gold nanocrystals has been measured by micro-Brillouin spectroscopy. A finite element analysis reveals that the nine well-resolved peaks observed are due to confined acoustic modes with each peak arising from more than one mode. The elastic constants of the nanocrystals are found to be comparable to those of bulk gold crystals. Findings suggest that the eigenfrequencies of any free regular-shaped homogeneous object always scale with its inverse linear dimension. Additionally, this universal relationship is valid for such objects of any size in the classical regime and is independent of elastic properties.
Where is the Ag in FePt–Ag composite films?
Authors: Chen J. S. , Zhou Y. Z. , Sun C. J. , Han S.-W. , Chow G. M.
Published: April 2011

The miscibility of Ag with FePt composited films was investigated with anomalous x-ray scattering (AXS) and extended x-ray absorption fine structure (EXAFS) at Ag K edge. In the AXS spectra for FePt Bragg peaks, the cusp near Ag K edge was observed, indicating alloying between Ag and FePt in the FePt–Ag thin films. Semiquantitative analysis showed 4.2 at. % and 5.9 at. % Ag were in FePt lattice for the samples with 20 vol % and 30 vol % Ag, respectively. EXAFS studies indicated in the alloyed FePt–Ag phase, Ag replaced the Fe sites in FePt lattice. Most of Ag segregated from FePt and formed fcc phase. This segregated Ag phase only had short range order, which may be due to that segregated Ag had small grain size and/or some disordered Ag phase existed in FePt grain boundaries.
Few-electron quantum dots in InGaAs quantum wells: Role of fluctuations
Authors: Granger G. , Studenikin S. A. , Kam A. , Sachrajda A. S. , Poole P. J.
Published: April 2011

We study the electron transport properties of gated quantum dots formed in InGaAs/InP quantum well structures grown by chemical-beam epitaxy on prepatterned substrates. Quantum dots form directly underneath narrow gates due to potential fluctuations. We measure the Coulomb-blockade diamonds in the few-electron regime of a single dot and observe photon-assisted tunneling peaks under microwave irradiation. A singlet-triplet transition at high magnetic field and Coulomb-blockade in the quantum Hall regime are also observed.
Nonlinear split-ring metamaterial slabs for magnetic resonance imaging
Authors: Lopez Marcos A. , Freire Manuel J. , Algarin Jose M. , Behr Volker C. , Jakob Peter M. , Marqués Ricardo
Published: April 2011

This work analyzes the ability of split-ring metamaterial slabs with zero/high permeability to reject/confine the radiofrequency magnetic field in magnetic resonance imaging systems. Split-ring slabs are designed and fabricated to work in a 1.5 T system. Nonlinear elements consisting of pairs of crossed diodes are inserted in the split-rings, so that the slab permeability can be switched between a value close to unity when interacting with the strong field of the transmitting coil, and zero or high values when interacting with the weak field produced by protons in tissue. Experiments are shown where these slabs locally increase the signal-to-noise-ratio.
Multilayer epitaxial graphene formed by pyrolysis of polycrystalline silicon-carbide grown on c-plane sapphire substrates
Authors: McArdle Timothy J. , Chu Jack O. , Zhu Yu , Liu Zihong , Krishnan Mahadevaiyer , Breslin Christopher M. , Dimitrakopoulos Christos , Wisnieff Robert , Grill Alfred
Published: April 2011

We use ultrahigh vacuum chemical vapor deposition to grow polycrystalline silicon carbide (SiC) on c-plane sapphire wafers, which are then annealed between 1250 and 1450 °C in vacuum to create epitaxial multilayer graphene (MLG). Despite the surface roughness and small domain size of the polycrystalline SiC, a conformal MLG film is formed. By planarizing the SiC prior to graphene growth, a reduction in the Raman defect band is observed in the final MLG. The graphene formed on polished SiC films also demonstrates significantly more ordered layer-by-layer growth and increased carrier mobility for the same carrier density as the nonpolished samples.
High external quantum efficiency and fill-factor InGaN/GaN heterojunction solar cells grown by NH3-based molecular beam epitaxy
Authors: Lang J. R. , Neufeld C. J. , Hurni C. A. , Cruz S. C. , Matioli E. , Mishra U. K. , Speck J. S.
Published: April 2011

High external quantum efficiency (EQE) p-i-n heterojunction solar cells grown by NH3-based molecular beam epitaxy are presented. EQE values including optical losses are greater than 50% with fill-factors over 72% when illuminated with a 1 sun AM0 spectrum. Optical absorption measurements in conjunction with EQE measurements indicate an internal quantum efficiency greater than 90% for the InGaN absorbing layer. By adjusting the thickness of the top p-type GaN window contact layer, it is shown that the short-wavelength (<365 nm) quantum efficiency is limited by the minority carrier diffusion length in highly Mg-doped p-GaN.
Entanglement enhances classical communication
Authors: Miller Johanna L.
Published: April 2011

As a laboratory experiment shows, when Alice and Bob each have one of a pair of entangled photons, they can transmit data more accurately over a noisy channel.
Microfluidic devices streamline fluorescence experiments
Authors: Smart Ashley G.
Published: April 2011

Reactions orchestrated on chips the size of a penny elucidate protein folding and other complex biological processes.
Freedom, fairness, and funds give hope to Egypt's scientists
Authors: Feder Toni
Published: April 2011

Science and technology will figure more strongly in Egypt's future, but the first priorities include urgent needs like feeding the hungry and eradicating illiteracy.
Obama's 2012 budget would freeze total spending, expand science and technology
Authors: Kramer David
Published: April 2011

Clean energy and basic physical sciences research would continue to shine in the president's budget. But House Republicans want cuts in R&D to begin right now.
Shedding new light on light in the ocean
Authors: Dickey Tommy D. , Kattawar George W. , Voss Kenneth J.
Published: April 2011

Recent advances are making it possible for optical oceanographers to solve a host of pressing environmental problems.
The first stars, as seen by supercomputers
Authors: Abel Tom
Published: April 2011

Today's telescopes cannot look far enough into the cosmic past to observe the formation of primordial stars. If you want to see that process, you need sophisticated numerical simulations.
Locating explosions, volcanoes, and more with infrasound
Authors: Szuberla Curt A. L. , Arnoult Kenneth M.
Published: April 2011

Sound with frequencies below the human threshold of hearing has long been used for global monitoring of large acoustic outbursts such as those in nuclear tests. Now infrasound is helping scientists detect much smaller events at close range.
Probing surface tension additivity on chemically heterogeneous surfaces by a molecular approach
Authors: Wang Jihang , Bratko Dusan , Luzar Alenka
Published: April 2011

Surface free energy of a chemically heterogeneous surface is often treated as an approximately additive quantity through the Cassie equation [Cassie ABD (1948)
Discuss Faraday Soc
3:11–16]. However, deviations from additivity are common, and molecular interpretations are still lacking. We use molecular simulations to measure the microscopic analogue of contact angle,
θ

c

, of aqueous nanodrops on heterogeneous synthetic and natural surfaces as a function of surface composition. The synthetic surfaces are layers of graphene functionalized with prototypical nonpolar and polar head group: methyl, amino, and nitrile. We demonstrate positive as well as negative deviations from the linear additivity. We show the deviations reflect the uneven exposure of mixture components to the solvent and the linear relation is recovered if fractions of solvent-accessible surface are used as the measure of composition. As the spatial variations in polarity become of larger amplitude, the linear relation can no longer be obtained. Protein surfaces represent such natural patterned surfaces, also characterized by larger patches and roughness. Our calculations reveal strong deviations from linear additivity on a prototypical surface comprising surface fragments of melittin dimer. The deviations reflect the disproportionately strong influence of isolated polar patches, preferential wetting, and changes in the position of the liquid interface above hydrophobic patches. Because solvent-induced contribution to the free energy of surface association grows as cos 
θ

c

, deviations of cos 
θ

c

from the linear relation directly reflect nonadditive adhesive energies of biosurfaces.
Prostaglandin E2–prostoglandin E receptor subtype 4 (EP4) signaling mediates UV irradiation-induced systemic immunosuppression
Authors: Soontrapa Kitipong , Honda Tetsuya , Sakata Daiji , Yao Chengcan , Hirata Takako , Hori Shohei , Matsuoka Toshiyuki , Kita Yoshihiro , Shimizu Takao , Kabashima Kenji , Narumiya Shuh
Published: April 2011

UV radiation induces systemic immunosuppression. Because nonsteroidal anti-inflammatory drugs suppress UV-induced immunosuppression, prostanoids have been suspected as a crucial mediator of this UV effect. However, the identity of the prostanoid involved and its mechanism of action remain unclear. Here, we addressed this issue by subjecting mice deficient in each prostanoid receptor individually or mice treated with a subtype-specific antagonist to UV irradiation. Mice treated with an antagonist for prostaglandin E receptor subtype 4 (EP4), but not those deficient in other prostanoid receptors, show impaired UV-induced immunosuppression, whereas administration of an EP4 agonist rescues the impairment of the UV-induced immunosuppression in indomethacin-treated mice. The EP4 antagonist treatment suppresses an increase in the number of CD4+/forkhead box P3-positive (Foxp3+) regulatory T cells (Treg cells) in the peripheral lymph nodes (LNs) and dendritic cells expressing DEC205 in the LNs and the skin after UV irradiation. Furthermore, the EP4 antagonist treatment down-regulates UV-induced expression of receptor activator of NF-κB ligand (RANKL) in skin keratinocytes. Finally, administration of anti-RANKL antibody abolishes the restoration of UV-induced immunosuppression by EP4 agonism in indomethacin-treated mice. Thus, prostaglandin E2(PGE2)–EP4 signaling mediates UV-induced immunosuppression by elevating the number of Treg cells through regulation of RANKL expression in the epidermis.
MicroRNA as biomarkers and regulators in B-cell chronic lymphocytic leukemia
Authors: Moussay Etienne , Wang Kai , Cho Ji-Hoon , van Moer Kris , Pierson Sandrine , Paggetti Jérôme , Nazarov Petr V. , Palissot Valérie , Hood Leroy E. , Berchem Guy , Galas David J.
Published: April 2011

Early cancer detection and disease stratification or classification are critical to successful treatment. Accessible, reliable, and informative cancer biomarkers can be medically valuable and can provide some relevant insights into cancer biology. Recent studies have suggested improvements in detecting malignancies by the use of specific extracellular microRNAs (miRNAs) in plasma. In chronic lymphocytic leukemia (CLL), an incurable hematologic disorder, sensitive, early, and noninvasive diagnosis and better disease classification would be very useful for more effective therapies. We show here that circulating miRNAs can be sensitive biomarkers for CLL, because certain extracellular miRNAs are present in CLL patient plasma at levels significantly different from healthy controls and from patients affected by other hematologic malignancies. The levels of several of these circulating miRNAs also displayed significant differences between zeta-associated protein 70 (ZAP-70)
+
and ZAP-70
−
CLL. We also determined that the level of circulating miR-20a correlates reliably with diagnosis-to-treatment time. Network analysis of our data, suggests a regulatory network associated with BCL2 and ZAP-70 expression in CLL. This hypothesis suggests the possibility of using the levels of specific miRNAs in plasma to detect CLL and to determine the ZAP-70 status.
Unveiling the complex electronic structure of amorphous metal oxides
Authors: Århammar C. , Pietzsch Annette , Bock Nicolas , Holmström Erik , Araujo C. Moyses , Gråsjö Johan , Zhao Shuxi , Green Sara , Peery T. , Hennies Franz , Amerioun Shahrad , Föhlisch Alexander , Schlappa Justine , Schmitt Thorsten , Strocov Vladimir N. , Niklasson Gunnar A. , Wallace Duane C. , Rubensson Jan-Erik , Johansson Börje , Ahuja Rajeev
Published: April 2011

Amorphous materials represent a large and important emerging area of material’s science. Amorphous oxides are key technological oxides in applications such as a gate dielectric in Complementary metal-oxide semiconductor devices and in Silicon-Oxide-Nitride-Oxide-Silicon and TANOS (TaN-Al
2
O
3
-Si
3
N
4
-SiO
2
-Silicon) flash memories. These technologies are required for the high packing density of today’s integrated circuits. Therefore the investigation of defect states in these structures is crucial. In this work we present X-ray synchrotron measurements, with an energy resolution which is about 5–10 times higher than is attainable with standard spectrometers, of amorphous alumina. We demonstrate that our experimental results are in agreement with calculated spectra of amorphous alumina which we have generated by stochastic quenching. This first principles method, which we have recently developed, is found to be superior to molecular dynamics in simulating the rapid gas to solid transition that takes place as this material is deposited for thin film applications. We detect and analyze in detail states in the band gap that originate from oxygen pairs. Similar states were previously found in amorphous alumina by other spectroscopic methods and were assigned to oxygen vacancies claimed to act mutually as electron and hole traps. The oxygen pairs which we probe in this work act as hole traps only and will influence the information retention in electronic devices. In amorphous silica oxygen pairs have already been found, thus they may be a feature which is characteristic also of other amorphous metal oxides.
Measuring the Approximate Number System
Authors: Gilmore Camilla , Attridge Nina , Inglis Matthew
Published: April 2011

Recent theories in numerical cognition propose the existence of an approximate number system (ANS) that supports the representation and processing of quantity information without symbols. It has been claimed that this system is present in infants, children, and adults, that it supports learning of symbolic mathematics, and that correctly harnessing the system during tuition will lead to educational benefits. Various experimental tasks have been used to investigate individuals' ANSs, and it has been assumed that these tasks measure the same system. We tested the relationship across six measures of the ANS. Surprisingly, despite typical performance on each task, adult participants' performances across the tasks were not correlated, and estimates of the acuity of individuals' ANSs from different tasks were unrelated. These results highlight methodological issues with tasks typically used to measure the ANS and call into question claims that individuals use a single system to complete all these tasks.
The Other-Race Effect does not Rely on Memory: Evidence from a Matching Task
Authors: Megreya Ahmed M. , White David , Burton A. Mike
Published: April 2011

Viewers are typically better at remembering faces from their own race than from other races; however, it is not yet established whether this effect is due to memorial or perceptual processes. In this study, UK and Egyptian viewers were given a simultaneous face-matching task, in which the target faces were presented upright or upside down. As with previous research using face memory tasks, participants were worse at matching other-race faces than own-race faces and showed a stronger face inversion effect for own-race faces. However, subjects' performance on own and other-race faces was highly correlated. These data provide strong evidence that difficulty in perceptual encoding of unfamiliar faces contributes substantially to the other-race effect and that accounts based entirely on memory cannot capture the full data. Implications for forensic settings are also discussed.
Study on scalable Coulombic degradation for estimating the lifetime of organic light-emitting devices
Authors: Zhang Wenwen , Wu Zhaoxin , Liang Shixiong , Jiao Bo , Zhang Xinwen , Wang Dawei , Hou Xun , Chen Zhijian , Gong Qihuang
Published: April 2011

The luminance decays of organic light-emitting diodes (OLEDs) are investigated with initial luminance of 1000 to 20 000 cd m−2 through a scalable Coulombic degradation and a stretched exponential decay. We found that the estimated lifetime by scalable Coulombic degradation deviates from the experimental results when the OLEDs work with high initial luminance. By measuring the temperature of the device during degradation, we found that the higher device temperatures will lead to instabilities of organic materials in devices, which is expected to result in the difference between the experimental results and estimation using the scalable Coulombic degradation.
GaAs metal–oxide–semiconductor device with titanium dioxide as dielectric layer: effect of oxide thickness on the device performance
Authors: Kundu Souvik , Roy Sandip Kumar , Banerji P
Published: April 2011

GaAs-based metal–oxide–semiconductor devices were fabricated with titanium dioxide (TiO2) as an oxide layer having three different thicknesses of 33, 54 and 71 nm. The phase purity of TiO2 was confirmed by Raman spectroscopy. Sulfur passivation on GaAs surface prior to TiO2 deposition was proposed to suppress poor native oxide formation on GaAs. Frequency-dependent studies on the capacitance–voltage were made in the frequency range 10 kHz–1 MHz. It was found that within this frequency range dispersion of the oxide capacitance was 4.9% per decade. Electrical measurements exhibited low leakage current, a dielectric constant of ≈27 and an interface trap density (D
it) of ∼1011 cm−2 eV−1. Two orders of magnitude reduction in current density were observed as the temperature went down from 290 to 100 K. Flatband voltage (V
FB), dielectric loss tangent (tan φ) and ac conductivity (σac) were determined from the capacitance–voltage (C–V) and conductance–voltage (G
P/ω–V) characteristics as a function of oxide thickness.
High-speed and low-voltage performance in a charge-trapping flash memory using a NiO tunnel junction
Authors: Seo Yujeong , An Ho-Myoung , Kim Hee-Dong , Hwang In Rok , Hong Sa Hwan , Park Bae Ho , Kim Tae Geun
Published: April 2011

A novel charge-trapping nonvolatile memory using gate injection switching is demonstrated in this paper. This device is composed of metal/NiO/nitride/oxide/silicon in order to make use of the electrical transport phenomenon found in NiO tunnel junctions. Compared with the reference structure of a conventional metal/oxide/nitride/oxide/silicon memory, the proposed device showed a larger memory window, very fast switching speeds of 100 ns/1 µs and a low operation voltage of ±5 V for the program/erase states. In addition, we observed that a large number of interface states in the bottom oxide were reduced using deep-level transient spectroscopy.
He plasma pretreatment effects on oxygen plasma-induced carbon loss and surface roughening in an ultralow-k organosilicate glass film
Authors: Behera Swayambhu P , Wang Qing , Kelber Jeffry A
Published: April 2011

Ex situ Fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) have been used to characterize the effects of He plasma pretreatment on O2 plasma-induced modification of the surface composition and structure of nanoporous ultralow dielectric constant (k) organosilicate glass (OSG) films. Oxygen plasma induces Si–C bond scission and carbon abstraction, and increased k values. Carbon abstraction exhibits diffusion-dominated kinetics. FTIR data, however, indicate that He plasma pretreatment prior to O2 plasma exposure induces pore sealing in the OSG film interior, inhibiting carbon abstraction, but only at longer O2 plasma exposure times (exposure time >5 min). The data are consistent with XPS data showing that OSG exposure to He plasma results in a more SiO2-like surface layer, but that atomic O will diffuse through a continuous SiO2 film. AFM data also indicate that He plasma pretreatment inhibits subsequent OSG surface roughening upon exposure to oxygen plasma.
Facilitating breakdown in noble gases at near-atmospheric pressure using antennas
Authors: Sobota A , Gendre M F , Manders F , van Veldhuizen E M , Haverlag M
Published: April 2011

Electrical breakdown in near-atmospheric pressure noble gases requires voltages that are quite high, which is undesirable for a large number of possible applications. Metallic structures (antennas) were used on the outer side of the lamp burner to enhance the electric field locally while keeping the same potential difference across the electrodes. Optical and electrical measurements were performed in an argon or xenon atmosphere at 0.3 or 0.7 bar, with 4 or 7 mm between the electrode tips. We used rod-shaped tungsten electrodes of 0.6 mm in diameter. We found that both active and passive antennas facilitate breakdown, and we demonstrated the differences between the two types and their effects on the breakdown process.
Imaging gas and plasma interactions in the surface-chemical modification of polymers using micro-plasma jets
Authors: Oh Jun-Seok , Olabanji Olumuyiwa T , Hale Craig , Mariani Raffaello , Kontis Konstantinos , Bradley James W
Published: April 2011

This paper reports on the correlation between gas flow and plasma behaviour in the outflow of a micro-atmospheric pressure plasma jet operating in helium using both 2D optical imaging and Schlieren photography. Schlieren photography shows that the helium outflow changes from laminar to turbulent conditions after distances between 20 and 50 mm from the nozzle. Above a flow rate of 1.4 slm, the length of the laminar region decreases with increasing flow rate. However, by contrast the visible plasma plume increases in length with increasing flow rate until its extension just exceeds that of the laminar region. At this point, the plasma becomes turbulent and its length decreases. Exposing polystyrene (PS) samples to the plasma jet significantly alters the water contact angle in a defined area, with the hydrophobic PS surface becoming more hydrophilic. This modification occurs both with and without direct contact of the visible glow on the surface. The radius of the treated area is much larger than the width of the visible jet but much smaller than the area of the turbulence on the surface. The treated area reduces with increasing nozzle–substrate distance.
Determination of ro-vibrational excitations of N2(B, v′) and N2(C, v′) states in N2 microwave discharges using visible and IR spectroscopy
Authors: Mavadat M , Ricard A , Sarra-Bournet C , Laroche G
Published: April 2011

UV–visible and infrared (IR) emission spectroscopy measurements were performed in a N2 microwave discharge at pressures between 0.1 and 3 Torr and powers of 200 and 300 W. Although emission spectroscopy in the IR region has rarely been investigated, this technique has nevertheless provided numerous key data. The plasma temperature as a function of pressure was measured using the rotational transitions of N2(B, 2–A, 0) in the N2 discharge. In addition, the vibrational distribution of the N2(B, v′ = 0–3) states was measured by means of IR emission spectroscopy. These experiments confirmed that the excitation of these states occurred primarily through electron collisions on the N2(A) metastable molecules.
Slotted cage resonator for high-field magnetic resonance imaging of rodents
Authors: Marrufo O , Vasquez F , Solis S E , Rodriguez A O
Published: April 2011

A variation of the high-frequency cavity resonator coil was experimentally developed according to the theoretical frame proposed by Mansfield in 1990. Circular slots were used instead of cavities to form the coil endplates and it was called the slotted cage resonator coil. The theoretical principles were validated via a coil equivalent circuit and also experimentally with a coil prototype. The radio frequency magnetic field, B1, produced by several coil configurations was numerically simulated using the finite-element approach to investigate their performances. A transceiver coil, 8 cm long and 7.6 cm in diameter, and composed of 4 circular slots with a 15 mm diameter on both endplates, was built to operate at 300 MHz and quadrature driven. Experimental results obtained with the slotted cage resonator coil were presented and showed very good agreement with the theoretical expectations for the resonant frequency as a function of the coil dimensions and slots. A standard birdcage coil was also built for performance comparison purposes. Phantom images were then acquired to compute the signal-to-noise ratio of both coils showing an important improvement of the slotted cage coil over the birdcage coil. The whole-body images of the mouse were also obtained showing high-quality images. Volume resonator coils can be reliably built following the physical principles of the cavity resonator design for high-field magnetic resonance imaging applications of rodents.
Comment on ‘The plasma–sheath transition in low temperature plasmas: on the existence of a collisionally modified Bohm criterion’
Authors: Franklin R N
Published: April 2011

This comment points out that in general for an active plasma it is not sufficient to treat the sheath in isolation.
Reply to the Comment on ‘The plasma–sheath transition in low temperature plasmas: on the existence of a collisionally modified Bohm criterion’
Authors: Brinkmann Ralf Peter
Published: April 2011

The newly found ‘collisionally modified Bohm criterion’ does not result from arbitrary definitions but from a systematic analysis of the sheath dynamics under the assumption λD ≪ l, where λD is the local Debye length and l the local ion gradient length. It is also not related to a point of inflection but to a removable singularity.