bluuebunny/crossref_metadata_2025 huggingface dataset:
Lattice-Boltzmann simulations of the drag force on a sphere approaching a superhydrophobic striped plane
Authors: Dubov Alexander L. , Schmieschek Sebastian , Asmolov Evgeny S. , Harting Jens , Vinogradova Olga I.
Published: February 2014

By means of lattice-Boltzmann simulations the drag force on a sphere of radius R approaching a superhydrophobic striped wall has been investigated as a function of arbitrary separation h. Superhydrophobic (perfect-slip vs. no-slip) stripes are characterized by a texture period L and a fraction of the gas area ϕ. For very large values of h/R, we recover the macroscopic formulae for a sphere moving towards a hydrophilic no-slip plane. For h/R = O(1), the drag force is smaller than predicted by classical theories for hydrophilic no-slip surfaces, but larger than expected for a sphere interacting with a uniform perfectly slipping wall. At a thinner gap, h ≪ R the force reduction compared to a classical result becomes more pronounced, and is maximized by increasing ϕ. In the limit of very small separations, our simulation data are in quantitative agreement with an asymptotic equation, which relates a correction to a force for superhydrophobic slip to texture parameters. In addition, we examine the flow and pressure field and observe their oscillatory character in the transverse direction in the vicinity of the wall, which reflects the influence of the heterogeneity and anisotropy of the striped texture. Finally, we investigate the lateral force on the sphere, which is detectable in case of very small separations and is maximized by stripes with ϕ = 0.5.
An experiment on the dynamics of ion implantation and sputtering of surfaces
Authors: Wright G. M. , Barnard H. A. , Kesler L. A. , Peterson E. E. , Stahle P. W. , Sullivan R. M. , Whyte D. G. , Woller K. B.
Published: February 2014

A major impediment towards a better understanding of the complex plasma-surface interaction is the limited diagnostic access to the material surface while it is undergoing plasma exposure. The Dynamics of ION Implantation and Sputtering Of Surfaces (DIONISOS) experiment overcomes this limitation by uniquely combining powerful, non-perturbing ion beam analysis techniques with a steady-state helicon plasma exposure chamber, allowing for real-time, depth-resolved in situ measurements of material compositions during plasma exposure. Design solutions are described that provide compatibility between the ion beam analysis requirements in the presence of a high-intensity helicon plasma. The three primary ion beam analysis techniques, Rutherford backscattering spectroscopy, elastic recoil detection, and nuclear reaction analysis, are successfully implemented on targets during plasma exposure in DIONISOS. These techniques measure parameters of interest for plasma-material interactions such as erosion/deposition rates of materials and the concentration of plasma fuel species in the material surface.
Microwave spectroscopy of the allenyloxy radical (CH2=CCHO)
Authors: Umeki Hiroya , Nakajima Masakazu , Endo Yasuki
Published: February 2014

Pure rotational spectra of the allenyloxy radical (CH2=CCHO) were observed by Fourier transform microwave (FTMW) and FTMW-millimeter wave double-resonance spectroscopy. Molecular constants including the hyperfine interaction constants of CH2=CCHO in the 2A″ ground electronic state were precisely determined. Ab initio calculations indicate that CH2=CCHO has a linear C−C−C backbone with Cs symmetry, where the formyl group is in the Cs plane and perpendicular to the methylene group. The determined rotational constants and the inertial defect agree well with those derived from the calculations, implying that the calculated molecular structure is reasonable. The fine and hyperfine constants also agree with those derived from the calculated spin density, where the unpaired electron is located mainly on the central carbon atom. The ground state CH2=CCHO can, thus, be described as taking the formylvinyl (CH2=Ċ−CH=O) form rather than as the allenyloxy (CH2=C=CH−$\dot{\rm O}$Ȯ) form.
Temperature dependent electronic structure of Pr0.67Sr0.33MnO3 film probed by X-ray absorption near edge structure
Authors: Zhang Bangmin , Sun Cheng-Jun , Chen Jing-Sheng , Venkatesan T. , Heald Steve M. , Moog Chow Gan
Published: February 2014

The Mn K edge X-ray absorption near edge structures (XANES) of Pr0.67Sr0.33MnO3 film (100 nm) on (001) LaAlO3 substrate was measured at different temperatures to probe the MnO6 octahedron distortion and corresponding electronic structure. The absorption of high temperature paramagnetic-insulator phase differed from that of the low temperature ferromagnetic-metal phase. The temperature-dependent absorption intensity of Mn K edge XANES was correlated with the relaxation of distorted MnO6 octahedron, which changed the crystal field acting on the Mn site and the related electronic structure and properties. At low temperature, the splitting of Mn majority eg orbitals decreased and the density of states above the Fermi level increased in the relaxed MnO6 octahedron, as reflected by a wider separation between two sub-peaks in the pre-edge XANES spectra.
Barkhausen spectroscopy: Non-destructive characterization of magnetic materials as a function of depth
Authors: Kypris O. , Nlebedim I. C. , Jiles D. C.
Published: February 2014

In this study, we conceptually divided a ferromagnetic specimen into layers along its depth. For each layer, we derived a non-linear integral equation that describes the attenuation with frequency and distance of magnetic Barkhausen emissions coming from that layer. We postulate that the Barkhausen spectrum measured at the surface by an induction coil can be expressed as the sum of the individual layer spectra. We show how a non-linear least squares algorithm can be used to recover the properties in individual layers. These are related to stress using an extension to the theory of ferromagnetic hysteresis. We found that the quality of the fit is influenced by the sensitivity of the ferromagnetic material to strain, as well as by the sensor-specimen coupling. The proposed method can be used for the non-destructive characterization of stress as a function of depth in magnetic materials.
Magnetic hardening mechanism of SmCo6.6Nb0.4 nanoflakes prepared by surfactant-assisted ball milling method
Authors: Li Y. Q. , Yue M. , Wu Q. , Liu W. Q. , Liu Y. Q. , Zhang D. T. , Zhang J. X. , Hadjipanayis G. C.
Published: February 2014

In this paper, we studied the magnetic hardening mechanism of SmCo6.6Nb0.4 nanoflakes prepared by surfactant-assisted high energy ball milling. The hysteresis loop with the initial magnetization curve and the corresponding differential susceptibility curve of thermally demagnetized SmCo6.6Nb0.4 nanoflakes were studied. It is concluded that the magnetization reversal process of the specimen is determined by domain wall motion, i.e., the magnetic hardening mechanism of the magnetic powders is dominated by domain wall pinning. Moreover, the dependence of coercive field of the nanoflakes on the maximum applied field derived from minor hysteresis loops also confirms the pinning effect in the magnetization reversal.
Effect of diamagnetic barium substitution on magnetic and photovoltaic properties in multiferroic BiFeO3
Authors: Hung C.-M. , Tu C. S. , Xu Z.-R. , Chang L.-Y. , Schmidt V. H. , Chien R. R. , Chang W. C.
Published: February 2014

Spontaneous magnetization and photovoltaic (PV) effects have been measured in (Bi1-xBax)FeO3-δ ceramics for x = 0.05, 0.10, and 0.15. The substitution of Ba2+ ion in the A site of the perovskite unit cell can effectively enhance the ferromagnetic magnetization. The heterostructure of indium tin oxide (ITO) film/(Bi1-xBax)FeO3-δ ceramic/Au film exhibits significant PV effects under illumination of λ = 405 nm. The PV responses decrease with increasing Ba concentration. The maximum power-conversion efficiency in the ITO/(Bi0.95Ba0.5)FeO2.95/Au can reach 0.006%. A theoretical model based on optically excited current in the depletion region between ITO film and (Bi1-xBax)FeO3-δ ceramics is used to describe the I-V characteristic, open-circuit voltage (Voc), and short-circuit current density (Jsc) as a function of light intensity.
Oxide shell reduction and magnetic property changes in core-shell Fe nanoclusters under ion irradiation
Authors: Sundararajan Jennifer A. , Kaur Maninder , Jiang Weilin , McCloy John S. , Qiang You
Published: February 2014

Ion irradiation effects are studied on the Fe-based core-shell nanocluster (NC) films with core as Fe and shell as Fe3O4/Fe3N. These NC films were deposited on Si substrates to thickness of ∼0.5 μm using a NC deposition system. The films were irradiated at room temperature with 5.5 MeV Si2+ ions to ion fluences of 1015 and 1016 ions/cm2. It is found that the irradiation induces grain growth, Fe valence reduction in the shell, and crystallization or growth of Fe3N. The film retained its Fe-core and its ferromagnetic properties after irradiation. The nature and mechanism of oxide shell reduction and composition dependence after irradiation were studied by synthesizing additional NC films of Fe3O4 and FeO + Fe3N and irradiating them under the same conditions. The presence of nanocrystalline Fe is found to be a major factor for the oxide shell reduction. The surface morphologies of these films show dramatic changes in the microstructures due to cluster growth and agglomeration as a result of ion irradiation.
Growth and characterization of nonpolar, heavily Mn-substituted ZnO films
Authors: Shao Q. , Ku P. S. , Wang X. L. , Cheng W. F. , Leung C. W. , Ruotolo A.
Published: February 2014

Eight percent of Mn was successfully diluted into nonpolar ZnO films deposited by pulsed laser deposition on single crystal (100) SrTiO3 substrates. X-ray diffraction patterns and energy-dispersive X-ray spectroscopy confirmed high crystallinity of the films and excluded unintentional magnetic doping. A unique surface domain structure was observed by scanning electron microscope and atomic force microscope, which might play a vital role to strain release induced by lattice mismatch between nonpolar (11–20) ZnO film and (100) SrTiO3 substrate. In addition, the films showed strong ferromagnetism with a large coercivity HC ∼ 180 Oe at room temperature. The large magnetic moment is ascribed to carrier-mediated exchange interaction between the Mn ions, where the majority of the carriers are oxygen vacancies.
Improved texture of polycrystalline hexaferrites using gluconic acid dispersant
Authors: Obi O. , Burns L. , Andalib P. , Chang H. , Chen Y. , Harris V. G.
Published: February 2014

In this work, gluconic acid (GA), a low molecular weight, inexpensive and environmentally friendly solvent, was systematically investigated to determine its viability in enhancing the orientation of ferrite particles. Submicron-scale barium hexaferrite (BaM) powders were thoroughly dispersed via sonication for 30 min in various concentrations of GA (0, 2, 2.5, 5, 10, and 25 vol. %) in deionized water. An increase of ∼18% in squareness (SQ) and ∼69% in energy product ((BH)max) was observed with increase in GA concentration from 0 to 5 vol. %. However, further increase in GA concentration led to a decrease in SQ and (BH)max confirming that the effect of GA stems from an improved viscosity of the dispersant, which balances the freely rotating and stationary particles under dynamic compaction within a magnetic field.
Single crystal structure analysis of a single Sm2Fe17N3 particle
Authors: Inami Nobuhito , Takeichi Yasuo , Ueno Tetsuro , Saito Kotaro , Sagayama Ryoko , Kumai Reiji , Ono Kanta
Published: February 2014

We performed single crystal structure analysis of Sm2Fe17N3 using X-ray diffraction. A pick-up system combined with a micromanipulation tool driven by piezoelectric actuators and a microgripper was used. A single Sm2Fe17Nx particle with the diameter of about 20 μm was picked up, and X-ray diffraction was measured using an X-ray diffractometer at the synchrotron radiation beamline at the Photon Factory, KEK. Single crystal structure analysis of a Sm2Fe17N3 particle was performed and the structure was successfully determined from X-ray diffraction patterns. The space group and the lattice constants were determined to be R-3m (#166) a = b = 8.7206 Å and c = 12.6345 Å, respectively. Atomic positions of Sm and Fe atoms were accurately determined by single crystal structure analysis of only one particle.
Magnetic marker based homogeneous bioassays utilizing rotating magnetic fields
Authors: Dieckhoff Jan , Schilling Meinhard , Ludwig Frank
Published: February 2014

Magnetic nanoparticles (MNPs) as markers in bioassays utilizing rotating instead of alternating magnetic fields predict an improved sensitivity regarding quantitative protein detection. This finding is based on numerical solutions of the Fokker-Planck equation and pronounced for increasing field amplitudes. In order to verify this prediction, the phase lag change of MNPs in rotating magnetic fields up to 5 mT is measured. The magnetic markers are functionalized single core iron oxide nanoparticles with different sizes. Antibodies which specifically bind to the MNPs cause the phase lag change. The increase of the phase lag change strongly depends on the particle parameters. MNPs with a core diameter of 30 nm show for 5 mT, a significant difference between the two field types. This difference is less pronounced for the 25 nm MNPs due to the increasing influence of Néel relaxation processes and for the 40 nm particles, due to the reduced saturation magnetization. A further improvement for the 30 nm MNPs with field amplitudes over 5 mT is simulated based on the determined particle parameters.
Dirac cones in artificial structures of 3d transitional-metals doped Mg-Al spinels
Authors: Lu Yuan , Feng Min , Shao Bin , Zuo Xu
Published: February 2014

Motivated by recent theoretical predications for Dirac cone in two-dimensional (2D) triangular lattice [H. Ishizuka, Phys. Rev. Lett. 109, 237207 (2012)], first-principles studies are performed to predict Dirac cones in artificial structures of 3d transitional-metals (TM = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) doped Mg-Al spinels. In investigated artificial structures, TM dopants substitute specific positions of the B sub-lattice in Mg-Al spinel, and form a quasi-2D triangular lattice in the a-b plane. Calculated results illustrate the existence of the spin-polarized Dirac cones formed in d-wave bands at (around) the K-point in the momentum space. The study provides a promising route for engineering Dirac physics in condensed matters.
Magnetism of perovskite cobaltites with Kramers rare-earth ions
Authors: Jirák Z. , Hejtmánek J. , Knížek K. , Novák P. , Šantavá E. , Fujishiro H.
Published: February 2014

The band-gap insulators RECoO3 (RE = Nd3+, Sm3+, and Dy3+) with Co3+ ions stabilized in the non-magnetic low-spin state have been investigated by specific heat measurements. The experiments evidence an antiferromagnetic ordering of the rare earths with Néel temperature of TN = 1.25, 1.50, and 3.60 K for NdCoO3, SmCoO3, and DyCoO3, respectively. With increasing external field, the lambda peak in specific heat, indicative of the transition, shifts to lower temperatures and vanishes for field of about 3 T. Starting from this point, a broader Schottky peak is formed, centered in 1 K range, and its position is moved to higher temperatures proportionally to applied field. The origin of the peak is in Zeeman splitting of the ground Kramers doublet, and the gradual shift with field defines effective g-factors for the rare-earth pseudospins in studied compounds. The results obtained are confronted with the calculations of crystal field splitting of the rare-earth multiplets.
Writing magnetic patterns with surface acoustic waves
Authors: Li Weiyang , Buford Benjamin , Jander Albrecht , Dhagat Pallavi
Published: February 2014

A novel patterning technique that creates magnetization patterns in a continuous magnetostrictive film with surface acoustic waves is demonstrated. Patterns of 10 μm wide stripes of alternating magnetization and a 3 μm dot of reversed magnetization are written using standing and focusing acoustic waves, respectively. The magnetization pattern is size-tunable, erasable, and rewritable by changing the magnetic field and acoustic power. This versatility, along with its solid-state implementation (no moving parts) and electronic control, renders it as a promising technique for application in magnetic recording, magnonic signal processing, magnetic particle manipulation, and spatial magneto-optical modulation.
Giant electric-field-induced magnetic anisotropy reorientation with patterned electrodes on a Ni thin film/lead zirconate titanate heterostructure
Authors: Cui Jizhai , Hockel Joshua L. , Nordeen Paul K. , Pisani David M. , Carman Gregory P. , Lynch Christopher S.
Published: February 2014

This study reports a method of using patterned electrodes on a piezoelectric substrate to generate local strain to control magnetic properties of individual magnetic units. By operating different effective electrode pairs on a piezoelectric substrate, a local bi-axial strain is generated. This rotates the magnetic anisotropy of a 35 nm thick and 0.5 mm diameter Ni island through the magnetoelastic effect. The electric-field-induced magnetic anisotropy exhibits an anisotropy field up to 600 Oe and a 75% change in magnetic remanence.
Dependence of Kambersky damping on Fermi level and spin orientation
Authors: Qu T. , Victora R. H.
Published: February 2014

Kambersky damping represents the loss of magnetic energy from the electrons to the lattice through the spin orbit interaction. It is demonstrated that, for bcc Fe-based transition metal alloys, the logarithm of the energy loss is proportional to the density of states at the Fermi level. Both inter and intraband damping are calculated for spins at arbitrary angle to the previously examined [001] direction. Although the easy axis ⟨100⟩ shows isotropic relaxation and achieves the minimum damping value of 0.002, other directions, such as ⟨110⟩, show substantial anisotropic damping.
Micromagnetic simulations of spin-wave normal modes and the spin-transfer-torque driven magnetization dynamics of a ferromagnetic cross
Authors: Pramanik Tanmoy , Roy Urmimala , Tsoi Maxim , Register Leonard F. , Banerjee Sanjay K.
Published: February 2014

We studied spin-transfer-torque (STT) switching of a cross-shaped magnetic tunnel junction in a recent report [Roy et al., J. Appl. Phys. 113, 223904 (2013)]. In that structure, the free layer is designed to have four stable energy states using the shape anisotropy of a cross. STT switching showed different regions with increasing current density. Here, we employ the micromagnetic spectral mapping technique in an attempt to understand how the asymmetry of cross dimensions and spin polarization direction of the injected current affect the magnetization dynamics. We compute spatially averaged frequency-domain spectrum of the time-domain magnetization dynamics in the presence of the current-induced STT term. At low currents, the asymmetry of polarization direction and that of the arms are observed to cause a splitting of the excited frequency modes. Higher harmonics are also observed, presumably due to spin-wave wells caused by the regions of spatially non-uniform effective magnetic field. The results could be used towards designing a multi-bit-per-cell STT-based random access memory with an improved storage density.
Scalar spectral measures associated with an operator-fractal
Authors: Jorgensen Palle E. T. , Kornelson Keri A. , Shuman Karen L.
Published: February 2014

We study a spectral-theoretic model on a Hilbert space L2(μ) where μ is a fixed Cantor measure. In addition to μ, we also consider an independent scaling operator U acting in L2(μ). To make our model concrete, we focus on explicit formulas: We take μ to be the Bernoulli infinite-convolution measure corresponding to scale number \documentclass[12pt]{minimal}\begin{document}$\frac{1}{4}$\end{document}14. We then define the unitary operator U in L2(μ) from a scale-by-5 operation. The spectral-theoretic and geometric properties we have previously established for U are as follows: (i) U acts as an ergodic operator; (ii) the action of U is not spatial; and finally, (iii) U is fractal in the sense that it is unitarily equivalent to a countable infinite direct sum of (twisted) copies of itself. In this paper, we prove new results about the projection-valued measures and scalar spectral measures associated to U and its constituent parts. Our techniques make use of the representations of the Cuntz algebra \documentclass[12pt]{minimal}\begin{document}$\mathcal {O}_2$\end{document}O2 on L2(μ).
Electrolyte/photoanode engineered performance of TiO2 based dye sensitised solar cells
Authors: Divya S. , Thankappan Aparna , Vallabhan C. P. G. , Nampoori V. P. N. , Radhakrishnan P. , Mujeeb A.
Published: February 2014

The performance of dye sensitized solar cells (DSSCs) depends on the collective contribution from its constituents which include the nanoparticle film, dye, electrolyte, and the counter electrode. In this report, we have tried to elucidate the varying performance of the TiO2 based DSSCs standardised using N719 dye and Platinum as counter electrode with various electrolytes including quasi static electrolytes. We have also evaluated the photovoltaic characteristics of the cells employing different morphological structured TiO2 photoanode. The DSSC based on the hierarchical anatase TiO2 nanotree photoelectrode showed the highest light-to-electricity conversion efficiency of 10.2%.
Magnetism in CaMnO3 thin films
Authors: Flint C. L. , Grutter A. J. , Jenkins C. A. , Arenholz E. , Suzuki Y.
Published: February 2014

Epitaxial CaMnO3 thin films on (001) LaAlO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, and SrTiO3 were synthesized in a range of strain states from coherently strained on LaAlO3 (1.6% strain) to fully relaxed on SrTiO3. We observed a magnetic ordering transition in CaMnO3 thin films suppressed from the Néel temperature of bulk CaMnO3 with the suppression increasing with increasing strain in the thin film. In contrast to bulk studies, our CaMnO3 films do not exhibit any sign of weak ferromagnetism according to field-dependent magnetization and x-ray magnetic circular dichroism measurements. Therefore, to within experimental resolution, all of our CaMnO3 films are antiferromagnetic with negligible oxygen off-stoichiometry.
Note: Electronic damping of microphonics in superconducting resonators of a continuous wave linac
Authors: Joshi Gopal , Sahu Bhuban Kumar , Agarwal Vivek , Kumar Girish
Published: February 2014

The paper presents an implementation technique to damp the microphonics in superconducting resonators utilizing the coupling between the electromagnetic and the mechanical modes of a resonator. In the technique used the resonant frequency variations are fed back to modulate the field amplitude through a suitable transfer function. Of the two transfer functions used in the experiments, one emulates a derivative action and is placed in a negative feedback configuration. The other transfer function is essentially a parallel combination of second order low pass filters and is used in a positive feedback configuration. Experiments with the Quarter Wave resonators of IUAC, New Delhi linac demonstrate that the damping of some of the modes increases significantly with the introduction of this feedback leading to a reduction in power required for field stabilization and quieter operation of the RF control system.
Temperature effects on atomic pair distribution functions of melts
Authors: Ding J. , Xu M. , Guan P. F. , Deng S. W. , Cheng Y. Q. , Ma E.
Published: February 2014

Using molecular dynamics simulations, we investigate the temperature-dependent evolution of the first peak position/shape in pair distribution functions of liquids. For metallic liquids, the peak skews towards the left (shorter distance side) with increasing temperature, similar to the previously reported anomalous peak shift. Making use of constant-volume simulations in the absence of thermal expansion and change in inherent structure, we demonstrate that the apparent shift of the peak maximum can be a result of the asymmetric shape of the peak, as the asymmetry increases with temperature-induced spreading of neighboring atoms to shorter and longer distances due to the anharmonic nature of the interatomic interaction potential. These findings shed light on the first-shell expansion/contraction paradox for metallic liquids, aside from possible changes in local topological or chemical short-range ordering. The melts of covalent materials are found to exhibit an opposite trend of peak shift, which is attributed to an effect of the directionality of the interatomic bonds.
Enhanced giant magnetoimpedance effect in patterned FeNi/FeCo nanostructure
Authors: Zhang Yi , Dong Juan , Liu Qingfang , Wang Jianbo
Published: February 2014

Enhanced giant magnetoimpedance effect has been observed in FeNi/FeCo nanostructure. 50 nm thick patterned FeCo micrometer pillar with in-plane uniaxial anisotropy was deposited on the surface of 100 nm isotropous FeNi magnetic film. The diameter of FeCo pillar is controllable. Before magnetoimpedance measurement, electrodes were fabricated by laser ablation. All samples show a typical giant magnetoimpedance curves at different frequencies. The optimized giant magnetoimpedance ratio is more than 80% at 30 MHz, when the FeCo micro-pillar's diameter is 50 μm. The phenomenon can be explained by the enhanced transverse permeability of FeNi film which was induced by anisotropy FeCo pillars due to exchange-coupling effect at the interface.
Impact of structural disorder on the magnetic ordering and magnetocaloric response of amorphous Gd-based microwires
Authors: Biswas Anis , Yu Y. Y. , Bingham N. S. , Wang H. , Qin F. X. , Sun J. F. , Yu S. C. , Franco V. , Srikanth H. , Phan M. H.
Published: February 2014

We have studied the impact of structural disorder on the magnetic ordering and magnetocaloric response of amorphous Gd68Ni32 and Gd53Al24Co20Zr3 microwires. We find that the presence of structural disorder significantly broadens the paramagnetic to ferromagnetic (PM-FM) transition and the temperature-dependent magnetic entropy change, while the nature of the second-order magnetic transition and long-range ferromagnetic order are not essentially affected by this effect. The large magnetic moment of Gd and the presence of the long-range ferromagnetic order are believed to result in a large magnetic entropy change, which together with the broadening of the PM-FM transition due to structural disorder contribute to a large refrigerant capacity. The excellent magnetocaloric properties of the amorphous microwires make them very promising candidates for active magnetic refrigeration.
Two dimensional growth of ultrathin Fe films on BaTiO3 with sharp chemical interface
Authors: Radaelli G. , Cantoni M. , Lijun Li , Espahbodi M. , Bertacco R.
Published: February 2014

The Fe/BaTiO3 interface is a prototypical artificial multiferroic system displaying purely electronic magnetoelectric effects at room temperature. As magneto-electric coupling is essentially localized at the interface, the properties of the very first Fe layers in contact with BaTiO3 play a major role. In this paper, we investigate, by using X-ray photoemission spectroscopy and photoelectron diffraction, the in-situ growth, by molecular beam epitaxy, of ultrathin Fe films (∼7 monolayers) on a BaTiO3/SrTiO3(001) template. We found that growing the Fe films above room temperature (373 K) is essential in order to avoid island growth and obtain a continuous film. Post-annealing up to 473 K improves the film crystallinity but prevents chemical interdiffusion and roughening. Just an interfacial monolayer of oxidized iron is detected in these conditions, which appears as an unavoidable consequence of the Fe/BaTiO3 chemical interaction. Its active role in magnetoelectric coupling must be carefully taken into account to correlate theoretical predictions and experiments.
Strain relaxation and enhanced perpendicular magnetic anisotropy in BiFeO3:CoFe2O4 vertically aligned nanocomposite thin films
Authors: Zhang Wenrui , Jian Jie , Chen Aiping , Jiao Liang , Khatkhatay Fauzia , Li Leigang , Chu Frank , Jia Quanxi , MacManus-Driscoll Judith L. , Wang Haiyan
Published: February 2014

Self-assembled BiFeO3:CoFe2O4 (BFO:CFO) vertically aligned nanocomposite thin films have been fabricated on SrTiO3 (001) substrates using pulsed laser deposition. The strain relaxation mechanism between BFO and CFO with a large lattice mismatch has been studied by X-ray diffraction and transmission electron microscopy. The as-prepared nanocomposite films exhibit enhanced perpendicular magnetic anisotropy as the BFO composition increases. Different anisotropy sources have been investigated, suggesting that spin-flop coupling between antiferromagnetic BFO and ferrimagnetic CFO plays a dominant role in enhancing the uniaxial magnetic anisotropy.
Theoretical study of optical properties of anti phase domains in GaP
Authors: Tea E. , Vidal J. , Pedesseau L. , Cornet C. , Jancu J.-M. , Even J. , Laribi S. , Guillemoles J.-F. , Durand O.
Published: February 2014

III-V/Si heterostructures are currently investigated for silicon photonics and solar energy conversion. In particular, dilute nitride alloy GaAsPN grown on a GaP/Si platform exhibits lattice match with Si and an optimal band gap configuration for tandem solar cell devices. However, monolithic “coherent” growth of the GaP thin layer on Si suffers from the nucleation of extended structural defects, which can hamper device operation as well as the GaP/Si interface level and through their propagation inside the overall heterostructure. However, the effect of such structural defects on optical and transport properties is actually not well understood in details. In this letter, we investigate the anti phase domains defect (also called inversion domains) by means of ab initio calculations giving insights into the alteration of optical and transport properties of GaP due to the defective GaP/Si interface.
Nanocrystalline ribbons for energy harvesting applications
Authors: Chiriac H. , Ţibu M. , Lupu N. , Skorvanek I. , Óvári T.-A.
Published: February 2014

An energy harvesting device based on nanocrystalline ribbons, able to convert mechanical vibrations to electrical energy, is presented. Such an energy harvesting device having embedded wireless microsensors can provide continuous monitoring of machines or infrastructure health without using service personnel in different areas with high risks. A multilayer core based on magnetic nanocrystalline ribbons was implemented to build the coil for an electromagnetic energy harvesting device with superior characteristics (voltage and power) compared to piezoelectric or pure magnetostrictive devices. Two different configurations were realized and tested for the energy harvester: vibrating core and vibrating magnets. The highest power density achieved for our harvesters using nanocrystalline ribbons is 45 mW/cm3 at 1 g (resonant frequency 47 Hz) and seems to be among the highest reported in literature.
Optimization of sensor design for Barkhausen noise measurement using finite element analysis
Authors: Prabhu Gaunkar N. , Kypris O. , Nlebedim I. C. , Jiles D. C.
Published: February 2014

The effects of design parameters for optimizing the performance of sensors for magnetic Barkhausen emission measurement are presented. This study was performed using finite element analysis. The design parameters investigated include core material, core-tip curvature, core length, and pole spacing. Considering a combination of permeability and saturation magnetization, iron was selected as the core material among other materials investigated. Although a flat core-tip would result in higher magnetic flux concentration in the test specimen, a curved core-tip is preferred. The sensor-to-specimen coupling is thereby improved especially for materials with different surface geometries. Smaller pole spacing resulted in higher flux concentration.
Highly efficient and electrically robust carbon irradiated semi-insulating GaAs based photoconductive terahertz emitters
Authors: Singh Abhishek , Pal Sanjoy , Surdi Harshad , Prabhu S. S. , Nanal Vandana , Pillay R. G.
Published: February 2014

We demonstrate here an efficient photoconductive THz source with low electrical power consumption. We have increased the maximum THz radiation power emitted from SI-GaAs based photoconductive emitters (PCEs) by two orders of magnitude. By irradiating the SI-GaAs substrate with Carbon-ions up to 2 μm deep, we have created lot of defects and decreased the lifetime of photo-excited carriers inside the substrate. Depending on the irradiation dose, we find 1 to 2 orders of magnitude decrease in total current flowing in the substrate, resulting in subsequent decrease of heat dissipation in the device. This has resulted in increasing maximum cut-off of the applied voltage across PCE electrodes to operate the device without thermal breakdown from ∼35 V to >150 V for the 25 μm electrode gaps. At optimum operating conditions, carbon irradiated (1014 ions/cm2) PCEs give THz pulses with power about 100 times higher in comparison to the usual PCEs on SI-GaAs and electrical to THz power conversion efficiency has improved by a factor of ∼800.
Large grain growth of Ge-rich Ge1−xSnx (x ≈ 0.02) on insulating surfaces using pulsed laser annealing in flowing water
Authors: Kurosawa Masashi , Taoka Noriyuki , Ikenoue Hiroshi , Nakatsuka Osamu , Zaima Shigeaki
Published: February 2014

We investigate Sn incorporation effects on the growth characteristics of Ge-rich Ge1−xSnx (x < 0.02) on SiO2 crystallized by pulsed laser annealing (PLA) in air and water. Despite the very low Sn content of 2%, Sn atoms within the GeSn layers play a role in preventing ablation and aggregation of the layers during these PLA. Raman and electron backscatter diffraction measurements demonstrate achievement of large-grain (∼800 nmϕ) growth of Ge0.98Sn0.02 polycrystals by using PLA in water. These polycrystals also show a tensile-strain of ∼0.68%. This result opens up the possibility for developing GeSn-based devices fabricated on flexible substrates as well as Si platforms.
An approach to achieve significantly faster luminescence decay of thin-film scintillator by surface plasmons
Authors: Liu Bo , Zhu Zhichao , Zhu Jingtao , Wu Shuang , Chen Hong , Gu Mu , Cheng Qian , Chen Hong , Cheng Chuanwei , Wang Zhanshan , Zhao Yuping , Zhang Qingli
Published: February 2014

A fast component of 2.2 ns from the LSO thin-film scintillator was achieved through coupling of scintillator with surface plasmons of silver nanoparticles. From the emission spectra, the observed fast component is from the transition of 5d to 4f level of Ce3+ in LSO. The fast component is attributed to the enhanced spontaneous recombination rate due to the surface plasmons. The present demonstration provides an interesting approach to improve the timing resolution of scintillator, which is distinguished from these conventional methods.
Hole-conductor-free perovskite organic lead iodide heterojunction thin-film solar cells: High efficiency and junction property
Authors: Shi Jiangjian , Dong Juan , Lv Songtao , Xu Yuzhuan , Zhu Lifeng , Xiao Junyan , Xu Xin , Wu Huijue , Li Dongmei , Luo Yanhong , Meng Qingbo
Published: February 2014

Efficient hole-conductor-free organic lead iodide thin film solar cells have been fabricated with a sequential deposition method, and a highest efficiency of 10.49% has been achieved. Meanwhile, the ideal current-voltage model for a single heterojunction solar cell is applied to clarify the junction property of the cell. The model confirms that the TiO2/CH3NH3PbI3/Au cell is a typical heterojunction cell and the intrinsic parameters of the cell are comparable to that of the high-efficiency thin-film solar cells.
Towards forming-free resistive switching in oxygen engineered HfO2−x
Authors: Sharath S. U. , Bertaud T. , Kurian J. , Hildebrandt E. , Walczyk C. , Calka P. , Zaumseil P. , Sowinska M. , Walczyk D. , Gloskovskii A. , Schroeder T. , Alff L.
Published: February 2014

We have investigated the resistive switching behavior in stoichiometric HfO2 and oxygen-deficient HfO2−x thin films grown on TiN electrodes using reactive molecular beam epitaxy. Oxygen defect states were controlled by the flow of oxygen radicals during thin film growth. Hard X-ray photoelectron spectroscopy confirmed the presence of sub-stoichiometric hafnium oxide and defect states near the Fermi level. The oxygen deficient HfO2−x thin films show bipolar switching with an electroforming occurring at low voltages and low operating currents, paving the way for almost forming-free devices for low-power applications.
Real time monitoring of superparamagnetic nanoparticle self-assembly on surfaces of magnetic recording media
Authors: Ye L. , Qi B. , Pearson T. , Cordeau Y. , Mefford O. T. , Crawford T. M.
Published: February 2014

Nanoparticle self-assembly dynamics are monitored in real-time by detecting optical diffraction from an all-nanoparticle grating as it self-assembles on a grating pattern recorded on a magnetic medium. The diffraction efficiency strongly depends on concentration, pH, and colloidal stability of nanoparticle suspensions, demonstrating the nanoparticle self-assembly process is highly tunable. This metrology could provide an alternative for detecting nanoparticle properties such as colloidal stability.
Piezoelectric control of magnetic anisotropy in the Ni0.46Zn0.54Fe2O4/Pb(Mg1/3Nb2/3)O3-PbTiO3 composite
Authors: Dong Chunhui , Guo Dangwei , Wu Lei , Wang Fenglong , Jiang Changjun , Jia Chenglong , Xue Desheng
Published: February 2014

A gate-controllable in-plane magnetic anisotropy with C2v symmetry was observed in a Ni0.46Zn0.54Fe2O4/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure. Detailed amplitude analysis reveals a linearly electric modulation in anisotropy energy that arises from a strain-mediated magnetoelectric coupling across the interface. In particular, an electrically-driven rotational in-plane magnetic easy axis and anisotropic-isotropic transition in NiZn ferrite film, respectively, enable possibilities for magnetization control in multiferroic devices.
Improved light extraction from white organic light-emitting devices using a binary random phase array
Authors: Inada Yasuhisa , Nishiwaki Seiji , Matsuzaki Jumpei , Hirasawa Taku , Nakamura Yoshitaka , Hashiya Akira , Wakabayashi Shin-ichi , Suzuki Masa-aki
Published: February 2014

We have developed a binary random phase array (BRPA) to improve the light extraction performance of white organic light-emitting devices (WOLEDs). We demonstrated that the scattering of incoming light can be controlled by employing diffraction optics to modify the structural parameters of the BRPA. Applying a BRPA to the substrate of the WOLED leads to enhanced extraction efficiency and suppression of angle-dependent color changes. Our systematic study clarifies the effect of scattering on the light extraction of WOLEDs.
Raman-Brillouin scattering from a thin Ge layer: Acoustic phonons for probing Ge/GeO2 interfaces
Authors: Yaacoub L. , Schamm-Chardon S. , Ovsyuk N. N. , Zwick A. , Groenen J.
Published: February 2014

We report on Raman–Brillouin scattering by acoustic phonons from a thin Ge layer. The high frequency acoustic phonons involved in this scattering are used to probe the native oxide present on top of the Ge layer. By comparing experiment and photoelastic modelling, a quantitative analysis is performed which shows that an interfacial layer is located in between the Ge and GeO2 oxide layers. The native oxide is found to be composed of a 0.5 nm thick interfacial layer and a 1 nm thick GeO2 layer on top of it. Sensitivity down to the sub-nm scale is evidenced.
Effects of site occupancy and valence state of Fe ions on ferromagnetism in Fe-doped In2O3 diluted magnetic semiconductor
Authors: Yan Shiming , Qiao Wen , Zhong Wei , Au Chak-Tong , Dou Youwei
Published: February 2014

The effects of oxygen vacancies, valence state of Fe ions, and site occupancy of Fe ions on ferromagnetism in Fe-doped In2O3 were investigated both experimentally and theoretically. The Fe3+ ions prefer to occupy the 8b sites and do not contribute to the room temperature (RT) ferromagnetism. It is found that the presence of Fe2+ ions in In2O3 can be induced through the creation of oxygen vacancies. The Fe2+ ions tend to occupy the 24d sites, and the origin of RT ferromagnetism can be related to the strong Fe:4s and Fe:3d hybridization. Our findings not only give a clear picture on the origin of ferromagnetism of Fe-doped In2O3 but also provide a way to tune the magnetic property of Fe-doped In2O3 through the control of valence states of dopant and the control of sites for dopant occupation.
Multicanonical Monte Carlo simulations of a de novo designed protein with end-to-end β-sheet
Authors: Uyaver Sahin , Hansmann Ulrich H. E.
Published: February 2014

One of the smallest proteins with end-to-end β-sheet is the designed 36-residue protein DS119. We recently suggested that the rate-limiting step in the folding of the βαβ protein is the formation of the central helix that then provides a scaffold for the parallel β-sheet formed by the two chain ends. In the present report we investigate whether and how this folding mechanism depends on the energy function, and compare the efficiency of molecular dynamics and Monte Carlo implementations of multicanonical sampling. While we find the native structure with similar frequency as in our previous simulations, we observe that the folding mechanism differs for both force fields.
Radio frequency regenerative oscillations in monolithic high-Q/V heterostructured photonic crystal cavities
Authors: Yang Jinghui , Gu Tingyi , Zheng Jiangjun , Yu Mingbin , Lo Guo-Qiang , Kwong Dim-Lee , Wei Wong Chee
Published: February 2014

We report temporal and spectral domain observation of regenerative oscillation in monolithic silicon heterostructured photonic crystals cavities with high quality factor to mode volume ratios (Q/V). The results are interpreted by nonlinear coupled mode theory (CMT) tracking the dynamics of photon, free carrier population, and temperature variations. We experimentally demonstrate effective tuning of the radio frequency tones by laser-cavity detuning and laser power levels, confirmed by the CMT simulations with sensitive input parameters.
Optical demagnetization in defect-mediated ferromagnetic ZnO:Cu films
Authors: Hu L. , Zhu L. P. , He H. P. , Ye Z. Z.
Published: February 2014

Optical demagnetization effect has been observed in a defect-rich ZnO:Cu film. Phenomenally, UV illumination can effectively quench dual-donor oxygen vacancy (VO) and interstitial zinc (Zni) mediated magnetic ordering (90% loss) with carrier recapture in ionized Zni (Zni2+ rather than Zni+) traps. The involvement of carriers by means of metal Zn vapor annealing provides a bound carrier related magnetic scenario, stressing a more significant place of bound carrier rather than free carrier. Using light correlated electron spin resonance and magnetic measurements, the magnetic “on” and “off” state can be continuously manipulated via UV light, which is explained by the reversible process of [Cus+/Cus2+] + Zni2+ ↔ [Cus+, h] + Zni+ (s and h denote the substitutional Cu ions on Zn sites in ZnO lattice and hole carrier, respectively). A slow charge-transfer process (∼15 μs) from Zni+ bound carriers to [Cus+, h] states determines the unexpected optical demagnetization, well corresponding to control experiments.
Effects of Cr doping on the magnetic properties of multiferroic YMnO3
Authors: Han Tai-Chun , Wu I-Chu , Hsu Hsin-Kai
Published: February 2014

We have synthesized a series of YMn1−xCrxO3 (0 ≤ x ≤ 0.1) samples and study the effect of Cr-doping on their magnetic properties. The magnetic characterization indicates that with increasing Cr-content up to 0.1, the antiferromagnetic (AFM) transition temperature increases from 73 to 89 K. Our experiment results also indicate that the Cr-doped samples exhibit the characteristics of spin-glass state at low temperature. Moreover, the magnetic hysteresis curves of the doped samples show a weak ferromagnetic (FM) behavior. It is found that the spin-glass state of the Cr-doped samples is due to the competition between AFM superexchange and FM double-exchange interaction, induced by the Cr doping.
Large voltage modulation in magnetic field sensors from two-dimensional arrays of Y-Ba-Cu-O nano Josephson junctions
Authors: Cybart Shane A. , Cho E. Y. , Wong T. J. , Glyantsev V. N. , Huh J. U. , Yung C. S. , Moeckly B. H. , Beeman J. W. , Ulin-Avila E. , Wu S. M. , Dynes R. C.
Published: February 2014

We have fabricated and tested two-dimensional arrays of YBa2Cu3O7−δ superconducting quantum interference devices. The arrays contain over 36 000 nano Josephson junctions fabricated from ion irradiation of YBa2Cu3O7−δ through narrow slits in a resist-mask that was patterned with electron beam lithography and reactive ion etching. Measurements of current-biased arrays in magnetic field exhibit large voltage modulations as high as 30 mV.
Position-controlled InP nanowires with 10–100 μm pitches using Au-deposited SiO2/InP patterned substrates
Authors: Kawaguchi Kenichi , Sudo Hisao , Matsuda Manabu , Ekawa Mitsuru , Yamamoto Tsuyoshi , Arakawa Yasuhiko
Published: February 2014

Vapor-liquid-solid (VLS) growth of position-controlled InP nanowires (NWs) with 10–100 μm pitches was investigated on SiO2-mask-patterned InP substrates. In addition to the vertical VLS NWs formed by Au catalysts, excess group-III materials that were diffused from the large mask region formed plural inclined NW-like structures from single openings. The introduction of HCl gas during the NW growth was found to remove the excess group-III materials effectively. Vertical InP NWs with minimal tapering were formed by controlling the HCl flow rate while suppressing the formation of tilted NWs. InP NWs having lengths independent of the pattern pitches, which were regulated by the VLS mechanism, were obtained.
Many-body effects on optical gain in GaAsPN/GaPN quantum well lasers for silicon integration
Authors: Park Seoung-Hwan
Published: February 2014

Many-body effects on the optical gain in GaAsPN/GaP QW structures were investigated by using the multiband effective-mass theory and the non-Markovian gain model with many-body effects. The free-carrier model shows that the optical gain peak slightly increases with increasing N composition. In addition, the QW structure with a larger As composition shows a larger optical gain than that with a smaller As composition. On the other hand, in the case of the many-body model, the optical gain peak decreases with increasing N composition. Also, the QW structure with a smaller As composition is observed to have a larger optical gain than that with a larger As composition. This can be explained by the fact that the QW structure with a smaller As or N composition shows a larger Coulomb enhancement effect than that with a larger As or N composition. This means that it is important to consider the many-body effect in obtaining guidelines for device design issues.