bluuebunny/crossref_metadata_2025 huggingface dataset:
Integration of thin film giant magnetoimpedance sensor and surface acoustic wave transponder
Authors: Li Bodong , Salem Nedime Pelin M. H. , Giouroudi Ioanna , Kosel Jürgen
Published: March 2012

Passive and remote sensing technology has many potential applications in implantable devices, automation, or structural monitoring. In this paper, a tri-layer thin film giant magnetoimpedance (GMI) sensor with the maximum sensitivity of 16%/Oe and GMI ratio of 44% was combined with a two-port surface acoustic wave (SAW) transponder on a common substrate using standard microfabrication technology resulting in a fully integrated sensor for passive and remote operation. The implementation of the two devices has been optimized by on-chip matching circuits. The measurement results clearly show a magnetic field response at the input port of the SAW transponder that reflects the impedance change of the GMI sensor.
Effects of magnetomechanical vibrations and bending stresses on three-phase three-leg transformers with amorphous cores
Authors: Hsu Chang-Hung , Chang Yeong-Hwa , Lee Chun-Yao , Yao Chia-Shiang , He Yan-Lou , Chu Huei-Lung , Chang Chia-Wen , Chan Wei-Shou
Published: March 2012

This paper explores the influence of bending stresses on the magnetic characteristics of three-phase transformers with amorphous cores. Different types of core structures, including C-cores and toroidal cores, and their magnetic properties are compared using VSM and XRD. The losses in the magnetic core of the three-phase transformer are analyzed using the finite element analysis for both design and measurement. In addition, experimental results indicated that amorphous-core transformers with rectangular corners had higher audible noise and vibration intensities. This is because the condensed distribution of magnetic flux lines in the corners of the core may create high magnetic inductions associated with high magnetostriction. Finally, experiments with three-phase amorphous-core transformers were performed to study the effects of magnetism and magnetostriction on their performance in terms of core loss, vibration, and audible noise.
Optimization of sputter deposition parameters for magnetostrictive Fe62Co19Ga19/Si(100) films
Authors: Jen S. U. , Tsai T. L.
Published: March 2012

A good magnetostrictive material should have large saturation magnetostriction (λS) and low saturation (or anisotropy) field (HS), such that its magnetostriction susceptibility (SH) can be as large as possible. In this study, we have made Fe62Co19Ga19/Si(100) nano-crystalline films by using the dc magnetron sputtering technique under various deposition conditions: Ar working gas pressure (pAr) was varied from 1 to 15 mTorr; sputtering power (Pw) was from 10 to 120 W; deposition temperature (TS) was from room temperature (RT) to 300 °C, The film thickness (tf) was fixed at 175 nm. Each magnetic domain looked like a long leaf, with a long-axis of about 12–15 μm and a short-axis of about 1.5 μm. The optimal magnetic and electrical properties were found from the Fe62Co19Ga19 film made with the sputter deposition parameters of pAr = 5 mTorr, Pw = 80 W, and TS = RT. Those optimal properties include λS = 80 ppm, HS = 19.8 Oe, SH = 6.1 ppm/Oe, and electrical resistivity ρ = 57.0 μΩ cm. Note that SH for the conventional magnetostrictive Terfenol-D film is, in general, equal to 1.5 ppm/Oe only.
Spin-orbit force in graphene with Rashba spin-orbit coupling
Authors: Chen Chien-Liang , Su Yu-Hsin , Chang Ching-Ray
Published: March 2012

The observation of Rashba spin splitting in graphene on the Ni (111) substrate, motivates the studies to manipulate electron spin via Rashba spin-orbit coupling in graphene. We derive the effective spin-orbit force in Rashba coupled graphene from the Heisenberg equation of motion. The spin-orbit force, different from that in conventional semiconductors, can provide us a physical picture of unusual spin separation due to Rashba spin-orbit coupling in graphene. Finally, we numerically calculate spin Hall conductance and qualitatively explain the result by the spin-orbit force picture in graphene.
Electrical input structures for nanomagnetic logic devices
Authors: Kiermaier J. , Breitkreutz S. , Csaba G. , Schmitt-Landsiedel D. , Becherer M.
Published: March 2012

Co/Pt nanomagnets close to a current driven wire are proposed as an electrical input interface for nanomagnetic logic. Their switching field shows a significant dependence of the external magnetic field sweep rate and the temperature, which can be modeled by the calibrated Sharrock formula, realizing coercivity extrapolations in the µs time scale. The influence of the current pulse in the wire is modeled as a generated Oersted field and an additional temperature rise in the structure. The models are used to simulate the current pulse characteristics sufficient to control the input magnet. Oersted switching experiments verify the proposed modeling, visualize controlled nanomagnets in close vicinity of the wire and thereby demonstrate the functionality of the input device.
Magneto-electric effects on Sr Z-type hexaferrite at room temperature
Authors: Ebnabbasi Khabat , Chen Yajie , Geiler Anton , Harris Vincent , Vittoria Carmine
Published: March 2012

In this paper, magnetoelectric effects of Sr Z-type hexaferrite, Sr3Fe24Co2O41, at room temperature is measured. The change in remanence magnetization was measured by applying a DC voltage or electric field across a slab of hexaferrite. Changes of ∼18% in remanence was observed in an electric field of 10 000 V/cm implying a similar change in the microwave permeability at frequencies below 3 GHz. Also, a change in dielectric constant at 1 GHz of ∼16% in a magnetic field of only 320 Oe was measured. In these types of measurements high resistivity is critical in order to reduce current flow in the hexaferrite. The resistivity of the hexaferrite was raised to 4.28 × 108 Ω-cm by annealing under oxygen pressure. The measurements indicate that indeed electric polarization and magnetization changes were induced by the application of magnetic and electric fields, respectively. The implications for microwave applications appear to be very promising at room temperature.
The effect of dry friction on domain wall dynamics: A micromagnetic study
Authors: Consolo G. , Martinez E.
Published: March 2012

In this paper a numerical investigation of the effects of disorder on the domain wall propagation along magnetic nanostrips induced by fields or currents is carried out. Such effects are included in the extended Landau-Lifshitz-Gilbert equation of motion by generalizing the classical viscous-type dissipation function through the addition of a nonlinear dry friction contribution. The key dynamical features observed by using this approach are: (i) the existence of a propagation threshold for both fields and currents; (ii) the reduction (increase) of the domain wall velocity in the steady-state (precessional) regime; (iii) the independence (dependence) of the velocity achieved at the Walker-type breakdown of (on) the dry-friction coefficient in the case of a field- (current-) driven motion. Our results qualitatively agree with previous numerical models of disorder which make use of different assumptions, mainly based on the spatial fluctuation of the material properties.
Magnetoelectric effect in AlN/CoFe bi-layer thin film composites
Authors: Narendra Babu S. , Min Seong-Gi , Yourdkhani Amin , Caruntu Gabriel , Malkinski Leszek
Published: March 2012

The present work is aimed at fabricating bi-layer aluminum nitride (AlN)/cobalt iron (CoFe) magnetoelectric (ME) thin films using reactive rf/dc magnetron sputtering. A systematic study on structural, morphological, piezoelectric, magnetic and magnetoelectric properties is undertaken. Except for AlN and CoFe, no other phases were detected with the layer thicknesses measured at 160 and 130 nm, respectively. The rms roughness measured was around 2.096 nm for AlN and 1.806 nm for CoFe. The bi-layer thin film exhibited both good piezoelectricity and ferromagnetism, as well as ME effect. A 52% change observed in the piezoelectric signal, measured using magnetic field assisted piezoresponse force microscopy, can be ascribed to the existence of a stress-mediated magnetoelectric coupling between AlN and CoFe.
A model of a linear synchronous motor based on distribution theory
Authors: Trapanese Marco
Published: March 2012

The fundamental idea of this paper is to use the distribution theory to analyze linear machines in order to include in the mathematical model both ideal and non ideal features. This paper shows how distribution theory can be used to establish a mathematical model able to describe both the ordinary working condition of a Linear Synchronous Motor (LSM) as well the role of the unavoidable irregularities and non ideal features.
Characteristics of magnetic force microscopy magnetics on high moment perpendicular magnetic recording writers with high coercivity probes
Authors: Liu Feng , Li Shaoping , Bai Daniel , Wang James , Li Zhanjie , Han Dehua , Pan Tao , Mao Sining
Published: March 2012

High resolution magnetic force microscopy (MFM) imaging with high coercivity probes on perpendicular magnetic recording (PMR) writers directly characterizes magnetic field contour for the writer main pole as well as its shields’ magnetic state. Evolution of write bubble and return field was analyzed by MFM imaging in dynamic phase detection scheme. Different write field components and their out of plane second order derivatives were calculated via finite element modeling. The MFM imaged write field distribution correlates well with the PMR writer out of plane write field component. Magnetic responses of the PMR writer main pole, trailing and side shields are quantified. The trailing and side shields exhibit complicated magnetic saturation behaviors comparing with the PMR writer pole. The side shield’s magnetic response is dependent upon its initial equilibrium state.
Magnetic properties of antidots in conventional and spin-reoriented antiferromagnetically coupled layers
Authors: Ranjbar M. , Piramanayagam S. N. , Sbiaa R. , Chong T. C.
Published: March 2012

Antiferromagnetically coupled (AFC) patterned media technology is one approach to reduce dipolar interactions and thus minimize the switching field distribution (SFD) in bit-patterned media. Achieving anti-parallel alignment of magnetic moments at remanence requires a large exchange coupling field (Hex), especially in patterned nanostructures, which exhibit a large enhancement in coercivity after patterning. In our work, we observed a very high Hex of more than 15 kOe in Co thin film antiferromagnetically coupled to (Co/Pd) multilayers with a high perpendicular magnetic anisotropy (PMA). In contrast, an Hex of only 380 Oe was measured in the case of (Co/Pd) multilayers of the type [Co (0.4 nm)/Pd (0.8 nm)]3 antiferromagnetically coupled with (Co/Pd) multilayers with a high PMA. The effect of Hex on SFD of patterned structures was investigated, and it was found that SFD can be reduced in AFC patterned films with a high Hex.
Post-synthesis heat treatments of γ-Fe2O3 nanoparticles embedded in a refractory matrix: From annealing of structural defects to doping
Authors: Vichery C. , Maurin I. , Boilot J.-P. , Gacoin T.
Published: March 2012

Magnetic nanoparticles (NPs) synthesized by low-temperature routes often present structural disorder, from extended defects to local rearrangements related to vacancy order or inversion in spinel ferrites. Post-synthesis heat treatments of preformed particles embedded in a refractory matrix are shown to modify magnetic anisotropy, either by annealing of crystal defects or by doping, while preserving the mean size and size distribution of the initial colloid. Such protected annealing of γ-Fe2O3 NPs allows a large and tunable increase of the anisotropy constant upon cobalt doping, using a two-step protocol that may involve adsorption of Co(II) ions at the surface of γ-Fe2O3 NPs followed by their dispersion in a silica matrix and heat treatments up to 600 °C.
In vitro cytotoxicity of Selol-loaded magnetic nanocapsules against neoplastic cell lines under AC magnetic field activation
Authors: Falqueiro A. M. , Siqueira-Moura M. P. , Jardim D. R. , Primo F. L. , Morais P. C. , Mosiniewicz-Szablewska E. , Suchocki P. , Tedesco A. C.
Published: March 2012

The goals of this study are to evaluate invitro compatibility of magnetic nanomaterials and their therapeutic potential against cancer cells. Highly stable ionic magnetic fluid sample (maghemite, γ-Fe2O3) and Selol were incorporated into polymeric nanocapsules by nanoprecipitation method. The cytotoxic effect of Selol-loaded magnetic nanocapsules was assessed on murine melanoma (B16-F10) and oral squamous cell carcinoma (OSCC) cell lines following AC magnetic field application. The influence of different nanocapsules on cell viability was investigated by colorimetric MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. In the absence of AC magnetic field Selol-loaded magnetic nanocapsules, containing 100 µg/mL Selol plus 5 × 1012 particle/mL, showed antitumoral activity of about 50% on B16-F10 melanoma cells while OSCC carcinoma cells demonstrated drug resistance at all concentrations of Selol and magnetic fluid (range of 100–500 µg/mL Selol and 5 × 1012−2.5 × 1013 particle/mL). On the other hand, under AC applied fields (1 MHz and 40 Oe amplitude) B16-F10 cell viability was reduced down to 40.5% (±3.33) at the highest concentration of nanoencapsulated Selol. The major effect, however, was observed on OSCC cells since the cell viability drops down to about 33.3% (±0.38) under application of AC magnetic field. These findings clearly indicate that the Selol-loaded magnetic nanocapsules present different toxic effects on neoplastic cell lines. Further, the cytotoxic effect was maximized under AC magnetic field application on OSCC, which emphasizes the effectiveness of the magnetohyperthermia approach.
A formalism for scattering of complex composite structures. I. Applications to branched structures of asymmetric sub-units
Authors: Svaneborg Carsten , Pedersen Jan Skov
Published: March 2012

We present a formalism for the scattering of an arbitrary linear or acyclic branched structure build by joining mutually non-interacting arbitrary functional sub-units. The formalism consists of three equations expressing the structural scattering in terms of three equations expressing the sub-unit scattering. The structural scattering expressions allow composite structures to be used as sub-units within the formalism itself. This allows the scattering expressions for complex hierarchical structures to be derived with great ease. The formalism is generic in the sense that the scattering due to structural connectivity is completely decoupled from internal structure of the sub-units. This allows sub-units to be replaced by more complex structures. We illustrate the physical interpretation of the formalism diagrammatically. By applying a self-consistency requirement, we derive the pair distributions of an ideal flexible polymer sub-unit. We illustrate the formalism by deriving generic scattering expressions for branched structures such as stars, pom-poms, bottle-brushes, and dendrimers build out of asymmetric two-functional sub-units.
Evaluation of electrical conductivity of Cu and Al through sub microsecond underwater electrical wire explosion
Authors: Sheftman D. , Shafer D. , Efimov S. , Krasik Ya. E.
Published: March 2012

Sub-microsecond timescale underwater electrical wire explosions using Cu and Al materials have been conducted. Current and voltage waveforms and time-resolved streak images of the discharge channel, coupled to 1D magneto-hydrodynamic simulations, have been used to determine the electrical conductivity of the metals for the range of conditions between hot liquid metal and strongly coupled non-ideal plasma, in the temperature range of 10–60 KK. The results of these studies showed that the conductivity values obtained are typically lower than those corresponding to modern theoretical electrical conductivity models and provide a transition between the conductivity values obtained in microsecond time scale explosions and those obtained in nanosecond time scale wire explosions. In addition, the measured wire expansion shows good agreement with equation of state tables.
Kinetic versus ideal magnetohydrodynamic modelling of the resistive wall mode in a reversed field pinch plasma
Authors: Mulec M. , Ivanov I. B. , Heyn M. F. , Kernbichler W.
Published: March 2012

Resistive wall modes (RWMs) are studied within the kinetic model proposed by Heyn et al. [Nucl. Fusion 46, S159 (2006); Phys. Plasmas 18, 022501 (2011)], which accounts for Landau damping, transit-time magnetic pumping, and Coulomb collisions in cylindrical geometry. Results for the reversed field pinch plasma are compared to the magnetohydrodynamic results obtained by Guo et al., [Phys. Plasmas 6, 3868 (1999)]. Stabilization of the external kink mode by an ideal wall as well as stabilization of the resistive wall mode by toroidal plasma rotation is obtained. In contrast to MHD modelling, which predicts a stability window for the resistive wall position, kinetic modelling predicts a one sided window only, i.e., the resistive wall must be sufficiently close to plasma to achieve rotational stabilization of the mode but there is no lower limit on the wall position. Stabilizing rotation speeds are found somewhat smaller when compared to MHD results. In addition, for the present plasma configuration, the kinetic model predicts resistive wall mode stabilization only in one direction of toroidal rotation. In the opposite direction, a destabilizing effect is observed. This is in contrast to MHD where mode stabilization is symmetric with respect to the direction of the toroidal plasma rotation.
Ponderomotive ion acceleration in dense magnetized laser-irradiated thick target plasmas
Authors: Sinha Ujjwal , Kaw Predhiman
Published: March 2012

When a circularly polarized laser pulse falls on an overdense plasma, it displaces the electrons via ponderomotive force creating a double layer. The double layer constitutes of an ion and electron sheath with in which the electrostatic field present is responsible for ion acceleration. In this paper, we have analyzed the effect a static longitudinal magnetic field has over the ion acceleration mechanism. The longitudinal magnetic field changes the plasma dielectric constant due to cyclotron effects which in turn enhances or reduces the ponderomotive force exerted by the laser depending on whether the laser is left or right circularly polarized. Also, the analysis of the ion space charge region present behind the ion sheath of the laser piston that undergoes coulomb explosion has been explored for the first time. We have studied the interaction of an incoming ion beam with the laser piston and the ion space charge. It has been found that the exploding ion space charge has the ability to act as an energy amplifier for incoming ion beams.
The long-range non-additive three-body dispersion interactions for the rare gases, alkali, and alkaline-earth atoms
Authors: Tang Li-Yan , Yan Zong-Chao , Shi Ting-Yun , Babb James F. , Mitroy J.
Published: March 2012

The long-range non-additive three-body dispersion interaction coefficients Z111, Z112, Z113, and Z122 are computed for many atomic combinations using standard expressions. The atoms considered include hydrogen, the rare gases, the alkali atoms (up to Rb), and the alkaline-earth atoms (up to Sr). The term Z111 arising from three mutual dipole interactions is known as the Axilrod-Teller-Muto coefficient or the DDD (dipole-dipole-dipole) coefficient. Similarly, the terms Z112, Z113, and Z122 arise from the mutual combinations of dipole (1), quadrupole (2), and octupole (3) interactions between atoms and they are sometimes known, respectively, as dipole-dipole-quadrupole, dipole-dipole-octupole, and dipole-quadrupole-quadrupole coefficients. Results for the four Z coefficients are given for the homonuclear trimers, for the trimers involving two like-rare-gas atoms, and for the trimers with all combinations of the H, He, and Li atoms. An exhaustive compilation of all coefficients between all possible atomic combinations is presented as supplementary data.
Spin accumulation in parallel-coupled quantum dots driven by a symmetric dipolar spin battery
Authors: Jiang Cui , Gong Wei-Jiang , Zheng Yisong
Published: March 2012

By applying a symmetric dipolar spin battery in a parallel-coupled quantum-dot (QD) structure, the spin accumulation in the QDs is investigated. We find that the spin accumulation can be achieved via electrically adjusting the left-right antisymmetry of the QD-lead couplings or introducing different magnetic fluxes through the sub-rings of this system. And, the spin accumulation properties are closely dependent on the number of QDs in this structure. Compared with the electrical method, the magnetic method is more efficient to manipulate the spin accumulation. When the intradot Coulomb interaction is considered, the electrically induced spin accumulation is somewhat suppressed, but in the magnetic method the spin accumulation is efficiently enhanced. We believe that the results can be observed in the experiment of spintronics, which provides an alternative scheme for spin manipulation.
Why edge effects are important on the intrinsic loss mechanisms of graphene nanoresonators
Authors: Jiang Jin-Wu , Wang Jian-Sheng
Published: March 2012

Molecular dynamics simulations are performed to investigate edge effects on the quality factor of graphene nanoresonators with different edge configurations and of various sizes. If the periodic boundary condition is applied, very high quality factors (3 × 105) are obtained for all kinds of graphene nanoresonators. However, if the free boundary condition is applied, quality factors will be greatly reduced by two effects resulting from free edges: the imaginary edge vibration effect and the artificial effect. Imaginary edge vibrations will flip between a pair of doubly degenerate warping states during the mechanical oscillation of nanoresonators. The flipping process breaks the coherence of the mechanical oscillation of the nanoresonator, which is the dominant mechanism for extremely low quality factors. There is an artificial effect if the mechanical oscillation of the graphene nanoresonator is actuated according to an artificial vibration (non-natural vibration of the system), which slightly reduces the quality factor. The artificial effect can be eliminated by actuating the mechanical oscillation according to a natural vibration of the nanoresonator. Our simulations provide an explanation for the recent experiment, where the measured quality factor is low and varies between identical samples with free edges.
Self-diffusion in strongly coupled Yukawa systems (complex plasmas)
Authors: Khrapak Sergey A. , Vaulina Olga S. , Morfill Gregor E.
Published: March 2012

We show that the idea of mapping between the Newtonian and Brownian diffusivities proposed and tested on a class of particle systems interacting via soft and ultra-soft potentials (inverse-power-law, Gaussian core, Hertzian, and effective star-polymer) by Pond et al. [Soft Matter 7, 9859 (2011)] is also applicable to the Yukawa (screened Coulomb) interaction. Some consequences of this result with respect to self-diffusion in strongly coupled complex (dusty) plasmas are discussed.
Effect of variations in diameter and density on the statistics of aligned array carbon-nanotube field effect transistors
Authors: E. Islam Ahmad , Du Frank , Ho Xinning , Hun Jin Sung , Dunham Simon , Rogers John A.
Published: March 2012

This paper describes a systematic experimental and theoretical analysis of performance variations in transistors that use aligned arrays of single-wall carbon nanotubes (SWNTs) grown on quartz substrates. Theoretical models, calibrated using measurements on statistically relevant numbers of transistors that each incorporate an individual aligned semiconducting SWNT, enable separate examination of different contributors to measured variations in transistors that incorporate arrays of SWNTs. Using these models and associated experiments, we study the scaling of the statistics of key performance attributes in transistors with different numbers of incorporated SWNTs and reveal long-range spatial nonuniformities in the distributions of SWNT diameters as the main contributor to observed performance variability.
Phase space analysis of multipactor saturation in rectangular waveguide
Authors: Lingwood C. J. , Burt G. , Dexter A. C. , Smith J. D. A. , Goudket P. , Stoltz P. H.
Published: March 2012

In certain high power RF systems multipactor cannot be avoided for all operating points, but its existence places limits on performance, efficiency, lifetime, and reliability. As an example multipactor in the input couplers of superconducting RF cavities can be a major limitation to the maximum RF power. Several studies have concentrated on rectangular waveguide input couplers which are used in many light sources. Most of these studies neglect space charge assuming that the effect of space charge is simply to defocus the electron bunches. Modelling multipactor to saturation is of interest in determining the performance of waveguide under a range of conditions. Particle-in-cell modelling including space charge has been performed for 500 MHz half-height rectangular waveguide. Phase plots of electron trajectories can aid understanding the processes taking place in the multipactor. Results strongly suggest that the multipacting trajectories are strongly perturbed by space charge causing the electrons to transition from two-surface to single-surface trajectories as the multipactor approaches saturation.
Kapitza conductance of symmetric tilt grain boundaries in graphene
Authors: Cao Ajing , Qu Jianmin
Published: March 2012

Non-equilibrium molecular dynamics simulations were employed to study the Kapitza conductance of symmetric tilt grain boundaries in the monolayer graphene sheet. Both armchair and zig-zag oriented bicrystal graphene were investigated. The Kapitza conductance of the interface shows length dependence up to 300 nm, which arises from the fact that long-wavelength phonons allowed in large-size graphene are able to transmit through the interface contributing to the Kapitza conductance. The Kapitza conductance exhibits monotonic increase with temperature, opposite to the trend of thermal conductivity of bulk graphene above room temperature. We found that the Kapitza conductance is inversely proportional to the number of dislocations per length of grain boundaries. The facts that the phonon density of states (DOS) shows no difference between the two crystals separated by the grain boundary and the vibrational DOS of grain boundary region atoms deviates from that of bulk atoms reveal that the interfacial thermal resistance arises from the structure defects, causing additional phonon scattering for the mismatched phonon spectrum of defects. The predicted length-independent Kapitza conductance ranges from 19 to 47 GW/Km2, which is larger than that of any other interfaces reported in the literature. Finally, theoretical analysis was carried out to explain why the thermal resistance scales with the number of defects per unit length.
Role of the Renner-Teller effect after core hole excitation in the dissociation dynamics of carbon dioxide dication
Authors: Laksman J. , Månsson E. P. , Grunewald C. , Sankari A. , Gisselbrecht M. , Céolin D. , Sorensen S. L.
Published: March 2012

The fragmentation of the doubly-charged carbon dioxide molecule is studied after photoexcitation to the C 1s12πu and O 1s12πu states using a multicoincidence ion-imaging technique. The bent component of the Renner-Teller split states populated in the 1s→ π* resonant excitation at both the carbon and oxygen 1s ionization edges opens pathways to potential surfaces in highly bent geometries in the dication. Evidence for a complete deformation of the molecule is found in the coincident detection of C+ and \documentclass[12pt]{minimal}\begin{document}${\rm O}_2^+$\end{document}O2+ ions. The distinct alignment of this fragmentation channel indicates rapid deformation and subsequent fragmentation. Investigation of the complete atomization dynamics in the dication leading to asymmetric charge separation shows that the primary dissociation mechanisms, sequential, concerted, and asynchronous concerted, are correlated to specific fragment kinetic energies. The study shows that the bond angle in fragmentation can extend below 20°.
Anomalous positive flatband voltage shifts in metal gate stacks containing rare-earth oxide capping layers
Authors: Caraveo-Frescas J. A. , Hedhili M. N. , Wang H. , Schwingenschlögl U. , Alshareef H. N.
Published: March 2012

It is shown that the well-known negative flatband voltage (VFB) shift, induced by rare-earth oxide capping in metal gate stacks, can be completely reversed in the absence of the silicon overlayer. Using TaN metal gates and Gd2O3-doped dielectric, we measure a ∼350 mV negative shift with the Si overlayer present and a ∼110 mV positive shift with the Si overlayer removed. This effect is correlated to a positive change in the average electrostatic potential at the TaN/dielectric interface which originates from an interfacial dipole. The dipole is created by the replacement of interfacial oxygen atoms in the HfO2 lattice with nitrogen atoms from TaN.
The extrinsic origins of high permittivity and its temperature and frequency dependence in Y0.5Ca0.5MnO3 and La1.5Sr0.5NiO4 ceramics
Authors: Li Ming , Sinclair Derek C.
Published: March 2012

Recently, many charge-ordered compounds containing mixed-valence transition metal ions have been considered as possible multiferroics. Theoretically it has been proposed that charge (orbital) ordering could generate “electronic ferroelectricity” in some of these compounds. Experimentally, temperature- and frequency-dependent high permittivity is commonly presented as evidence of ferroelectricity in these materials. Here, systematic impedance spectroscopy studies on Y0.5Ca0.5MnO3 and La1.5Sr0.5NiO4 ceramics reveal, however, the high permittivity and its temperature- and frequency-dependence over the ranges of 10–300 K and 10 Hz–1 MHz, respectively, are mainly associated with an extrinsic non-ohmic sample-electrode contact effect, rather than an intrinsic response. A general strategy to distinguish the intrinsic dielectric properties of these charge-ordered compounds from extrinsic contributions using impedance spectroscopy is also demonstrated.
Comment on “Minimum free-energy pathway of nucleation” [J. Chem. Phys. 135, 134508 (2011)]
Authors: Schmelzer Jürn W. P. , Abyzov Alexander S.
Published: March 2012

In their recent paper [J. Chem. Phys. 135, 134508 (2011)], Philippe and Blavette10.1063/1.3644935 claimed to have found for the first time—based on minimum free energy considerations—that the nucleation pathway in solid solutions involves a universal two-step behavior: nuclei sharply enrich up to near equilibrium values of the concentration and then grow. This claim of priority is not correct. The same scenario was proposed by us long ago [J. W. P. Schmelzer, A. R. Gokhman, and V. M. Fokin, J. Colloid Interface Sci. 272, 109 (2004)]10.1016/j.jcis.2003.08.038 and then applied and further developed. In particular, it was shown by us that only the account of both thermodynamic and kinetic factors allows one to determine correctly the most probable path of evolution in nucleation-growth processes. The two-step scenario is retained, however, also in these generalizations of our original approach.
Transport properties of hybrid graphene/graphane nanoribbons
Authors: Zou Wei , Yu Zhizhou , Zhang C. X. , Zhong J. X. , Sun L. Z.
Published: March 2012

The transport properties of hybrid nanoribbons constructed by substituting zigzag graphane nanoribbons into zigzag graphene nanoribbons are investigated using the first-principles calculations and non-equilibrium Green’s function. The transport properties of the hybrid systems are improved due to the appearance of transport platform with nontrivial conductance around the Fermi level. This enhancement attributes to the extra bands induced by the substituted graphane nanoribbons. Moreover, this enhancement is sensitive to the position and concentration of the substituted graphane nanoribbons in the system. Our results indicate that such hybrid system is an effective approach to modulate the transport properties of zigzag graphene nanoribbons.
Lattice position and thermal stability of diluted As in Ge
Authors: Decoster S. , Wahl U. , Cottenier S. , Correia J. G. , Mendonça T. , Amorim L. M. , Pereira L. M. C. , Vantomme A.
Published: March 2012

We present a lattice location study of the n-type dopant arsenic after ion implantation into germanium. By means of electron emission channeling experiments, we have observed that the implanted As atoms substitute the Ge host atoms and that, in contrast to several implanted metal impurities in Ge, no significant fraction of As is found on interstitial sites. The substitutional As impurities are found to be thermally stable up to 600 °C. After 700 °C annealing a strong reduction of emission channeling effects was observed, in full accordance with the expected diffusion-induced broadening of the As profile.
A “place n play” modular pump for portable microfluidic applications
Authors: Li Gang , Luo Yahui , Chen Qiang , Liao Lingying , Zhao Jianlong
Published: March 2012

This paper presents an easy-to-use, power-free, and modular pump for portable microfluidic applications. The pump module is a degassed particle desorption polydimethylsiloxane (PDMS) slab with an integrated mesh-shaped chamber, which can be attached on the outlet port of microfluidic device to absorb the air in the microfluidic system and then to create a negative pressure for driving fluid. Different from the existing monolithic degassed PDMS pumps that are generally restricted to limited pumping capacity and are only compatible with PDMS-based microfluidic devices, this pump can offer various possible configures of pumping power by varying the geometries of the pump or by combining different pump modules and can also be employed in any material microfluidic devices. The key advantage of this pump is that its operation only requires the user to place the degassed PDMS slab on the outlet ports of microfluidic devices. To help design pumps with a suitable pumping performance, the effect of pump module geometry on its pumping capacity is also investigated. The results indicate that the performance of the degassed PDMS pump is strongly dependent on the surface area of the pump chamber, the exposure area and the volume of the PDMS pump slab. In addition, the initial volume of air in the closed microfluidic system and the cross-linking degree of PDMS also affect the performance of the degassed PDMS pump. Finally, we demonstrated the utility of this modular pumping method by applying it to a glass-based microfluidic device and a PDMS-based protein crystallization microfluidic device.
Band gap control via tuning of inversion degree in CdIn2S4 spinel
Authors: Seminovski Yohanna , Palacios Pablo , Wahnón Perla , Grau-Crespo Ricardo
Published: March 2012

Based on theoretical arguments, we propose a possible route for controlling the band-gap in the promising photovoltaic material CdIn2S4. Our ab initio calculations show that the experimental degree of inversion in this spinel (fraction of tetrahedral sites occupied by In) corresponds approximately to the equilibrium value given by the minimum of the theoretical inversion free energy at a typical synthesis temperature. Modification of this temperature, or of the cooling rate after synthesis, is then expected to change the inversion degree, which in turn sensitively tunes the electronic band-gap of the solid, as shown here by screened hybrid functional calculations.
Multiferroicity in 0.7Pb(Zr0.52Ti0.48)O3-0.3Pb(Ni1/3Nb2/3)O3 ceramics
Authors: Su Jie , Lu Xiaomei , Liu Yaoyang , Zhang Junting , Li Guorong , Ruan Xuezheng , Huang Fengzhen , Du Jun , Zhu Jinsong
Published: March 2012

0.7Pb(Zr0.52Ti0.48)O3-0.3Pb(Ni1/3Nb2/3)O3 (abbreviated as PZT-PNN) ceramics were prepared using the solid-state reaction method. The results reveal that ferroelectric and anti-ferromagnetic orderings coexist (multiferroicity) in PZT-PNN ceramics. Furthermore, the abnormal behavior of dielectric constant and loss observed at Néel temperature gives an evidence of the coupling between the ferroelectric and anti-ferromagnetic orderings (magnetoelectric coupling). The ferroelectric loops become slimmer with increasing temperature and the remnant polarization persists up to above the temperature of dielectric maximum (Tm), indicates a lead-induced ferroelectric behavior.
Band alignment of TiN/HfO2 interface of TiN/HfO2/SiO2/Si stack
Authors: Wang Xiaolei , Han Kai , Wang Wenwu , Yang Hong , Zhang Jing , Ma Xueli , Xiang Jinjuan , Chen Dapeng , Ye Tianchun
Published: March 2012

Band alignment of TiN/HfO2 interface of TiN/HfO2/SiO2/Si stack is investigated by x-ray photoelectron spectroscopy (XPS). The p-type Schottky barrier height (p-SBH) is found to increase with thicker HfO2 thickness. Since considering only the metal/dielectric interface cannot explain this phenomenon, band alignment of TiN/HfO2 interface of TiN/HfO2/SiO2/Si stack is demonstrated based on band alignment of entire gate stack. Dependence of p-SBH on HfO2 thickness is interpreted and contributed to fixed charges in gate stack, interfacial gap state charges at HfO2/SiO2 interface, and space charges in Si substrate. Electrical measurements of capacitor structures further support XPS results and corresponding explanation.
Effect of annealing under O2 and H2 on the piezoelectric parameters of the Ca12Al14O33 single crystals
Authors: Castel Elias , Ik Shin Tong , Fourcade Sébastien , Decourt Rodolphe , Maglione Mario , García-Víllora Encarnaçión , Shimamura Kiyoshi
Published: March 2012

Piezoelectric single-crystal ingots of Ca12Al14O33 were grown by Czochralski technique. Upon specific chemical reductions, this dielectric material can be turned into an oxygen solid electrolyte, a mixed conductor, or an electride. We followed the thermal evolution of the piezoelectric performances of as-grown samples and compared it with oxygen and hydrogen annealed ones. The structure of Ca12Al14O33 crystal was studied by powder x ray diffraction patterns, and the chemical processing efficiency was checked by optical transmittance measurements. The dielectric permittivity ɛ11 and piezoelectric coefficient d15 were found to be on the orders of 8–12 and 16–20 pC/N, respectively. This material exhibits good bulk shear wave coupling factor k14 about 0.34 and promising surface acoustic wave (SAW) velocities of 3500 m/s that render it suitable for SAW devices as a substrate. The piezoelectric response of crystals before and after annealing under H2 and O2 is maintained. The observed evolutions may be related to the conductivity of the material or the electrical transport properties, which are known to be sensitive to the oxygen and the hydrogen content.
A tunable acoustic diode made by a metal plate with periodical structure
Authors: Sun Hong-xiang , Zhang Shu-yi , Shui Xiu-ji
Published: March 2012

A model of acoustic diodes is realized by a thin brass plate with single-sided periodical grating structure immersed in water and studied both numerically and experimentally. The unidirectional transmission of acoustic waves is identified in two different frequency ranges, which can be systematically controlled by adjusting the sizes of the structural units. The results indicate that the acoustic diodes have the advantages of tunable frequency range, broader bandwidth, and simple structure as well as being easy to be achieved. The remarkable unidirectional transmission effect has great potential applications in ultrasonic devices, such as acoustic rectifiers, acoustic diodes, and related fields.
Equivalence of direct and converse magnetoelectric coefficients in strain-coupled two-phase systems
Authors: Lou Jing , Pellegrini Gerry N. , Liu Ming , Mathur Neil D. , Sun Nian X.
Published: March 2012

We demonstrate an equivalence between direct and converse magnetoelectric effects in two-phase systems comprising piezoelectric and magnetostrictive materials. This was achieved by recasting the Maxwell relation in terms of the effective electrical and magnetic dipole moments for the system and comparing coupling strengths at the same electrical and magnetic d.c. biases. Our findings therefore apply to magnetoelectric systems comprising more than two phases and correct the two widely held but opposing views that are compromised by incorrect parameterization or inconsistent bias conditions.
Bias-dependent oscillatory electron transport of monatomic sulfur chains
Authors: Yu Jing-Xin , Cheng Yan , Sanvito Stefano , Chen Xiang-Rong
Published: March 2012

The bias-dependent oscillatory electron transport of monatomic sulfur chains sandwiched between gold electrodes is investigated with density functional theory and non-equilibrium Green’s function method. At zero bias, in contrast to the typical odd-even oscillations observed in most metallic chains, we find that the conductance oscillates with a period of four atoms. However, as the bias voltage is increased the current displays a two-atom periodicity. This emerges gradually, first for the longer chains and then, at voltages larger than 0.7 V, for lengths. The oscillatory behaviors are analyzed by the density of states and the energy-dependent and bias-dependent transmission coefficients.
Influence of Si Co-doping on electrical transport properties of magnesium-doped boron nanoswords
Authors: Tian Yuan , Lu Hongliang , Tian Jifa , Li Chen , Hui Chao , Shi Xuezhao , Huang Yuan , Shen Chengmin , Gao Hong-jun
Published: March 2012

Magnesium-doped boron nanoswords were synthesized via a thermoreduction method. The as-prepared nanoswords are single crystalline and β-rhombohedral (β-rh) phase. Electrical transport measurements show that variable range hopping conductivity increases with temperature, and carrier mobility has a greater influence than carrier concentration. These results are consistent with the three dimensional Mott’s model (M. Cutler and N. F. Mott, Phys. Rev. 181, 1336 (1969)) besides a high density of localized states at the Fermi level compared with bulk β-rh boron. Conductivity of Mg-doped boron nanoswords is significantly lower than that of “pure” (free of magnesium) boron nanoswords. Electron energy loss spectroscopy studies confirm that the poorer conductivity arises from silicon against magnesium doping.
Origin of the dielectric response in Ba0.767Ca0.233TiO3
Authors: Shimizu Takao , Fu Desheng , Taniguchi Hiroki , Taniyama Tomoyasu , Itoh Mitsuru
Published: March 2012

We perform a Raman scattering study to elucidate the mechanism of temperature independent dielectric response of Ba0.767Ca0.233TiO3 (BCTO-0.233) from a viewpoint of phonon dynamics. BCTO-0.233 remains tetragonal below Tc down to 3.5 K. Over-damped soft phonon observed in a pure BaTiO3 is found to become underdamped in BCTO-0.233, suggesting that local dipoles induced by Ca2+ off-centering suppress the hopping of Ti ions to reduce damping of the soft-mode. The temperature dependence of the soft-mode frequency agrees qualitatively with the dielectric permittivity through Lyddane-Sachs-Teller relationship, indicating that the dielectric response of BCTO-0.233 is governed by the soft-mode.
Chemical and optical properties of carbon-doped TiO2: A density-functional study
Authors: Lu Jibao , Dai Ying , Guo Meng , Yu Lin , Lai Kangrong , Huang Baibiao
Published: March 2012

The conflict of understandings on experimental results about chemical and optical properties of C-doped TiO2, which has been overlooked for a long time but is essential for studies of the basic properties of this material, is unraveled. It is shown that in anatase TiO2 the doped C and O atoms can easily couple with each other at typical synthesis conditions due to the large binding energy and small energy barrier, while in rutile phase, the coupling can hardly occur. The characteristics of the structures are elaborated in detail, which provides insights into the chemical, optical, and magnetic properties of C-doped TiO2.
A novel surface modification technique for forming porous polymer monoliths in poly(dimethylsiloxane)
Authors: Burke Jeffrey M. , Smela Elisabeth
Published: March 2012

A new method of surface modification is described for enabling the in situ formation of homogenous porous polymer monoliths (PPMs) within poly(dimethylsiloxane) (PDMS) microfluidic channels that uses 365 nm UV illumination for polymerization. Porous polymer monolith formation in PDMS can be challenging because PDMS readily absorbs the monomers and solvents, changing the final monolith morphology, and because PDMS absorbs oxygen, which inhibits free-radical polymerization. The new approach is based on sequentially absorbing a non-hydrogen-abstracting photoinitiator and the monomers methyl methacrylate and ethylene diacrylate within the walls of the microchannel, and then polymerizing the surface treatment polymer within the PDMS, entangled with it but not covalently bound. Four different monolith compositions were tested, all of which yielded monoliths that were securely anchored and could withstand pressures exceeding the bonding strength of PDMS (40 psi) without dislodging. One was a recipe that was optimized to give a larger average pore size, required for low back pressure. This monolith was used to concentrate and subsequently mechanical lyse B lymphocytes.
Optical bistability in a quantum dots/micropillar device with a quality factor exceeding 200 000
Authors: Arnold Christophe , Loo Vivien , Lemaître Aristide , Sagnes Isabelle , Krebs Olivier , Voisin Paul , Senellart Pascale , Lanco Loïc
Published: March 2012

Optical bistability is demonstrated in a micropillar cavity with a record quality factor of 215 000, embedding a few thousand quantum dots. A power threshold of 380μW is obtained, with an on/off response contrast of 5.6 dB. We characterize the saturation of the quantum dots absorption and the cavity mode frequency shift through coherent reflection spectroscopy. We show that a near-unity coupling efficiency is achieved and that the planar quality factor Q0 is around 450 000.
Optical properties for the Mott transition in VO2
Authors: Kang Manil , Kim Sok Won , Ryu Ji-Wook , Noh Taejong
Published: March 2012

The relationship between the first-order metal-insulator transition (MIT) and the structural phase transition (SPT) in VO2 film is analyzed by dielectric function, optical conductivity, plasma energy, and electrical conductivity. The MIT and SPT temperatures in VO2 films were approximately 68 and 75 °C, respectively, with an intermediate phase existing between 68 and 75 °C. The optical and electrical results indicate that the first-order MIT in VO2 films is not driven by the SPT.
Oscillatory exchange bias and training effects in nanocrystalline Pr0.5Ca0.5MnO3
Authors: Jammalamadaka S. Narayana , Rao S. S. , Bhat S. V. , Vanacken J. , Moshchalkov V. V.
Published: March 2012

We report on exchange bias effects in 10 nm particles of Pr0.5Ca0.5MnO3 which appear as a result of competing interactions between the ferromagnetic (FM)/anti-ferromagnetic (AFM) phases. The fascinating new observation is the demonstration of the temperature dependence of oscillatory exchange bias (OEB) and is tunable as a function of cooling field strength below the SG phase, may be attributable to the presence of charge/spin density wave (CDW/SDW) in the AFM core of PCMO10. The pronounced training effect is noticed at 5 K from the variation of the EB field as a function of number of field cycles (n) upon the field cooling (FC) process. For n > 1, power-law behavior describes the experimental data well; however, the breakdown of spin configuration model is noticed at n ≥ 1.