bluuebunny/crossref_metadata_2025 huggingface dataset:
X-ray absorption spectroscopy elucidates the impact of structural disorder on electron mobility in amorphous zinc-tin-oxide thin films
Authors: Siah Sin Cheng , Lee Sang Woon , Lee Yun Seog , Heo Jaeyeong , Shibata Tomohiro , Segre Carlo U. , Gordon Roy G. , Buonassisi Tonio
Published: June 2014

We investigate the correlation between the atomic structures of amorphous zinc-tin-oxide (a-ZTO) thin films grown by atomic layer deposition (ALD) and their electronic transport properties. We perform synchrotron-based X-ray absorption spectroscopy at the K-edges of Zn and Sn with varying [Zn]/[Sn] compositions in a-ZTO thin films. In extended X-ray absorption fine structure (EXAFS) measurements, signal attenuation from higher-order shells confirms the amorphous structure of a-ZTO thin films. Both quantitative EXAFS modeling and X-ray absorption near edge spectroscopy (XANES) reveal that structural disorder around Zn atoms increases with increasing [Sn]. Field- and Hall-effect mobilities are observed to decrease with increasing structural disorder around Zn atoms, suggesting that the degradation in electron mobility may be correlated with structural changes.
How does a shear boundary layer affect the stability of a capillary jet?
Authors: Gañán-Calvo A. M. , Herrada M. A. , Montanero J. M.
Published: June 2014

The stability of a capillary jet with a shear boundary layer growing over its free surface is studied theoretically. The effect of an infinitely thin boundary layer is first examined from the corresponding singularly perturbed eigenvalue problem. Then, a linear stability analysis of the Navier-Stokes equations for a finite boundary layer thickness verifies the consistency of the previous asymptotic study. We show that, for sufficiently long distances from the boundary layer origin, Rayleigh's dispersion relation is recovered, which means that the layer does not affect the jet's stability in that case. However, for distances on the order of the jet's radius, the perturbation growth factor, the most unstable wave number, and the range of unstable wave numbers increase, while the convective-to-absolute instability transition delays drastically. These results establish a general framework to explain a variety of capillary jet phenomena, from the extended jetting regime of capillary jets in gas co-flows to fundamental features of the dripping faucet.
A new hybrid control method for controlling back-to-back converter in permanent magnet synchronous generator wind turbines
Authors: Namjoo N. , Abbasi F. , Hassanzadeh F. , Asrari H. , Hajizadeh A.
Published: June 2014

The increasing environmental concerns during the 20th century have moved the research focus from conventional electricity sources to the renewable ones. In renewable power generation, wind energy has been noted as the most rapidly growing technology; it attracts interest as one of the most cost-effective ways to generate electricity from renewable resources. Moreover, using of power electronic devices to regulate and control of the generated power and transfuse to the grid is essential. In wind power systems, by using different control methods on the power electronic converter, synchronization of these resources to power grid is obtained. Studded wind turbine consists of a permanent magnet synchronous generator which is connected to the grid by a back to back (B2B) converter. In this paper, the main purposes are maximum point power tracking of wind turbine and transfusion to grid, control of reactive power by B2B converter and also fixing DC-link voltage in DC-link reference voltage. Proposed control method consists of vector control, combined tilt-integral-derivative compensator, and fuzzy controller. In order to verify the proposed method, a 1.5 MW wind turbine system is simulated in MATLAB/SIMULINK.
Computational study of heterojunction graphene nanoribbon tunneling transistors with p-d orbital tight-binding method
Authors: Kim SungGeun , Luisier Mathieu , Boykin Timothy B. , Klimeck Gerhard
Published: June 2014

The graphene nanoribbon (GNR) tunneling field effect transistor (TFET) has been a promising candidate for a future low power logic device due to its sub-60 mV/dec subthreshold characteristic and its superior gate control on the channel electrons due to its one-dimensional nature. Even though many theoretical studies have been carried out, it is not clear that GNR TFETs would outperform conventional silicon metal oxide semiconductor field effect transistors (MOSFETs). With rigorous atomistic simulations using the p/d orbital tight-binding model, this study focuses on the optimization of GNR TFETs by tuning the doping density and the size of GNRs. It is found that the optimized GNR TFET can operate at a half of the supply voltage of silicon nanowire MOSFETs in the ballistic limit. However, a study on the effects of edge roughness on the performance of the optimized GNR TFET structure reveals that experimentally feasible edge roughness can deteriorates the on-current performance if the off-current is normalized with the low power requirement specified in the international technology roadmap for semiconductors.
Anomalous effect due to oxygen vacancy accumulation below the electrode in bipolar resistance switching Pt/Nb:SrTiO3 cells
Authors: Lee Shinbuhm , Lee Jae Sung , Park Jong-Bong , Koo Kyoung Yong , Lee Myoung-Jae , Won Noh Tae
Published: June 2014

In conventional semiconductor theory, greater doping decreases the electronic resistance of a semiconductor. For the bipolar resistance switching (BRS) phenomena in oxides, the same doping principle has been used commonly to explain the relationship between the density variation of oxygen vacancies (Vo¨) and the electronic resistance. We find that the Vo¨ density can change at a depth of ∼10 nm below the Pt electrodes in Pt/Nb:SrTiO3 cells, depending on the resistance state. Using electron energy loss spectroscopy and secondary ion mass spectrometry, we found that greater Vo¨ density underneath the electrode resulted in higher resistance, contrary to the conventional doping principle of semiconductors. To explain this seemingly anomalous experimental behavior, we provide quantitative explanations on the anomalous BRS behavior by simulating the mobile Vo¨ [J. S. Lee et al., Appl. Phys. Lett. 102, 253503 (2013)] near the Schottky barrier interface.
Significantly enhanced magnetic properties of a powder of amorphous Fe70MnxMo3Cr4-6W8-10Si4-5B3-5 particles achieved by annealing treatments below the crystallization temperature
Authors: Zhang Jiliang , Zheng Zhigang , Shek Chan Hung
Published: June 2014

Annealing treatments below crystallization temperature were conducted on commercial Fe70MnxMo3Cr4-6W8-10Si4-5B3-5 (x = balance) amorphous powder. It was found that such treatment could significantly improve the soft magnetic properties of the powder especially at a higher frequency. Saturation magnetization increased to a maximum and hysteresis loop decreased to a minimum after the powder was annealed at 800 K for 30 min. Magnetic force microscopy observation indicated that the size of domain structure was not changed but the phase contrast became obvious after annealing. The enhancements of soft magnetic properties were explained in terms of structural relaxation and nanocrystallization as well as the Bethe-Slater curve. Moreover, a characteristic frequency at which the a.c. susceptibility exhibits a drastic change is found and that frequency changes with the annealing treatment.
Real-time sawtooth control and neoclassical tearing mode preemption in ITER
Authors: Kim D. , Goodman T. P. , Sauter O.
Published: June 2014

Real-time control of multiple plasma actuators is a requirement in advanced tokamaks; for example, for burn control, plasma current profile control and MHD stabilization—electron cyclotron (EC) wave absorption is ideally suited especially for the latter. On ITER, 24 EC sources can be switched between 56 inputs at the torus. In the torus, 5 launchers direct the power to various locations across the plasma profile via 11 steerable mirrors. For optimal usage of the available power, the aiming and polarization of the beams must be adapted to the plasma configuration and the needs of the scenario. Since the EC system performs many competing tasks, present day systems should demonstrate the ability of an EC plant to deal with several targets in parallel and/or to switch smoothly between goals to attain overall satisfaction. Based on pacing and locking experiments performed on TCV (Tokamak à Configuration Variable), the real-time sawtooth control of ITER with this complex set of actuators is analyzed, as an example. It is shown that sawtooth locking and pacing are possible with various levels of powers, leading to different time delays between the end of the EC power phase and the next sawtooth crash. This timing is important since it allows use of the same launchers for neoclassical tearing mode (NTM) preemption at the q = 1.5 or 2 surface, avoiding the need to switch power between launchers. These options are presented. It is also demonstrated that increasing the total EC power does not necessarily increase the range of control because of the geometry of the launchers.
Development of steady-state operation using ion cyclotron heating in the Large Helical Device
Authors: Kasahara H. , Seki T. , Saito K. , Seki R. , Kumazawa R. , Yoshimura Y. , Kubo S. , Shimozuma T. , Igami H. , Takahashi H. , Nagasaki K. , Ueda Y. , Tokitani M. , Ashikawa N. , Shoji M. , Wakatsuki T. , Kamio S. , Tsuchiya H. , Yoshimura S. , Tamura N. , Suzuki C. , Yamada H. , Mutoh T. ,   LHD Experiment Group
Published: June 2014

Using a handshake shape (HAS) antenna phasing dipole for ion cyclotron heating (ICH), the heating efficiency was higher than that using a previous poloidal array antenna in the Large Helical Device. In order to sustain the dipole operation, real-time feedback for impedance matching and maintaining the same phase and power was adopted during long-pulse discharge. The HAS antenna was designed to reduce parasitic losses associated with energetic particle and radio-frequency (RF) sheath effects by field-aligned current concentration on the midplane. Local hot spots and the inhomogeneity of the diverter heat profile in the toroidal direction were reduced. The long-pulse discharge with an electron density (ne0) of 1 × 1019 m−3, center electron temperature (Te0) of 2.5 keV, a plasma duration time (td) of 19 min, and RF heating power (PRF) of 1 MW was achieved by ICH and electron cyclotron heating.
Extension of high Te regime with upgraded electron cyclotron resonance heating system in the Large Helical Device
Authors: Takahashi H. , Shimozuma T. , Kubo S. , Yoshimura Y. , Igami H. , Ito S. , Kobayashi S. , Mizuno Y. , Okada K. , Mutoh T. , Nagaoka K. , Murakami S. , Osakabe M. , Yamada I. , Nakano H. , Yokoyama M. , Ido T. , Shimizu A. , Seki R. , Ida K. , Yoshinuma M. , Kariya T. , Minami R. , Imai T. , Marushchenko N. B. , Turkin Y. ,   LHD Experiment Group
Published: June 2014

Enhancement of the output power per gyrotron has been planned in the Large Helical Device (LHD). Three 77-GHz gyrotrons with an output power of more than 1 MW have been operated. In addition, a high power gyrotron with the frequency of 154 GHz (1 MW/5 s, 0.5 MW/CW) was newly installed in 2012, and the total injection power of Electron cyclotron resonance heating (ECRH) reached 4.6 MW. The operational regime of ECRH plasma on the LHD has been extended due to the upgraded ECRH system such as the central electron temperature of 13.5 keV with the line-averaged electron density ne_fir = 1 × 1019 m−3. The electron thermal confinement clearly improved inside the electron internal transport barrier, and the electron thermal diffusivity reached neoclassical level. The global energy confinement time increased with increase of ne_fir. The plasma stored energy of 530 kJ with ne_fir = 3.2 × 1019 m−3, which is 1.7 times larger than the previous record in the ECRH plasma in the LHD, has been successfully achieved.
A revolutionary concept to improve the efficiency of ion cyclotron antennas
Authors: Milanesio D. , Maggiora R.
Published: June 2014

The successful design of an ion cyclotron (IC) antenna mainly relies on the capability of coupling high power to the plasma (MW), feature that is currently reached by allowing rather high voltages (tens of kV) on the unavoidable unmatched part of the feeding lines. This requirement is often responsible of arcs along the transmission lines and other unwanted phenomena, such as rectification discharges or hotspots, that considerably limit the usage of IC launchers. In this work, we suggest and describe a revolutionary approach based on high impedance surfaces, which allows to increase the antenna radiation efficiency and, hence, to highly reduce the imposed voltages to couple the same level of power to the plasma. High-impedance surfaces are periodic metallic structures (patches) displaced usually on top of a dielectric substrate and grounded by means of vertical posts usually embedded inside a dielectric, in a mushroom-like shape. In terms of working properties, high impedance surfaces are electrically thin in-phase reflectors, i.e., they present a high impedance, within a given frequency band, such that the image currents are in-phase with the currents of the antenna itself, thus determining a significant efficiency increase. While the usual design of a high impedance surface requires the presence of a dielectric layer, some alternative solutions can be realised in vacuum, taking advantage of double layers of metallic patches. After an introductory part on the properties of high impedance surfaces, this work documents both their design by means of numerical codes and their implementation on a scaled mock-up.
Spontaneous polarization driven Mg concentration profile reconstruction in MgZnO/ZnO heterostructures
Authors: Imasaka K. , Falson J. , Kozuka Y. , Tsukazaki A. , Kawasaki M.
Published: June 2014

Atomic reconstruction at the interface of MgZnO and ZnO in molecular beam epitaxy grown heterostructures is investigated. Using secondary ion mass spectroscopy, we experimentally find that Mg atomic reconstruction depends on the polarity of the interface; it is not observed in n-type interfaces (MgZnO on Zn-polar ZnO) owing to electron accumulation, while in p-type interfaces (ZnO on Zn-polar MgZnO), Mg drastically redistributes into the ZnO layer. Combined with self-consistent calculation of band profiles and carrier distributions, we reveal that the observed Mg reconstruction is not due to thermal diffusion but consequences in order to avoid hole accumulation. This tendency implies inherent significant asymmetry of energy scales of atomic and electronic reconstructions between n-type and p-type interfaces.
Communication: Ultrafast homonuclear correlation spectroscopy with diagonal suppression
Authors: Banerjee Abhishek , Chandrakumar N.
Published: June 2014

A novel ultrafast 2D NMR experiment is introduced for homonuclear correlation spectroscopy in solution state, with diagonal peak suppression in each scan of a two scan procedure. This experiment permits clear visualization of cross peaks between spins whose chemical shifts are very close, which could otherwise be masked by diagonal peaks. The present report describes the principles of its design and illustrates actual performance.
Raising gradient limitations in 2.1 GHz superconducting photonic band gap accelerator cavities
Authors: Simakov Evgenya I. , Arsenyev Sergey A. , Haynes W. Brian , Shchegolkov Dmitry Yu. , Suvorova Natalya A. , Tajima Tsuyoshi , Boulware Chase H. , Grimm Terry L.
Published: June 2014

We report results from recent 2.1 GHz superconducting radio frequency (SRF) photonic band gap (PBG) resonator experiments at Los Alamos. Two 2.1 GHz PBG cells with elliptical rods were fabricated and tested at high power in a liquid helium bath at the temperatures of 4 K and below 2 K. The described SRF PBG cells were designed with a particular emphasis on changing the shape of the PBG rods to reduce peak surface magnetic fields and at the same time to preserve its effectiveness at damping higher-order-modes. The superconducting PBG cavities have great potential for damping long-range wakefields in SRF accelerator structures without affecting the fundamental accelerating mode. The cells performed in accordance with simulation's predictions and the maximum achieved accelerating gradient was 18.3 MV/m. This represents a 30% increase over gradients previously demonstrated in superconducting PBG cavities with round rods.
Suppression of the metal-insulator transition by magnetic field in (Pr1−yYy)0.7Ca0.3CoO3 (y = 0.0625)
Authors: Naito Tomoyuki , Fujishiro Hiroyuki , Nishizaki Terukazu , Kobayashi Norio , Hejtmánek Jiří , Knížek Karel , Jirák Zdeněk
Published: June 2014

The (Pr1−yYy)0.7Ca0.3CoO3 compound (y = 0.0625, TMI-SS=40 K), at the lower limit for occurrence of the first-order metal-insulator (MI) and simultaneous spin-state (SS) transitions, has been studied using electrical resistivity and magnetization measurements in magnetic fields up to 17 T. The isothermal experiments demonstrate that the low-temperature insulating phase can be destabilized by an applied field and the metallic phase returns well below the transition temperature TMI-SS. The reverse process with decreasing field occurs with a significant hysteresis. The temperature scans taken at fixed magnetic fields reveal a parabolic-like decrease in TMI-SS with increasing field strength and a complete suppression of the MI-SS transition in fields above 9 T.
Reinvestigation of high pressure polymorphism in hafnium metal
Authors: Pandey K. K. , Gyanchandani Jyoti , Somayazulu M. , Dey G. K. , Sharma Surinder M. , Sikka S. K.
Published: June 2014

There has been a recent controversy about the high pressure polymorphism of Hafnium (Hf). Unlike, the earlier known α→ω structural transition at 38 ± 8 GPa, at ambient temperature, Hrubiak et al. [J. Appl. Phys. 111, 112612 (2012)] did not observe it till 51 GPa. They observed this transition only at elevated temperatures. We have reinvestigated the room temperature phase diagram of Hf, employing x-ray diffraction (XRD) and DFT based first principles calculations. Experimental investigations have been carried out on several pure and impure Hf samples and also with different pressure transmitting media. Besides demonstrating the significant role of impurity levels on the high pressure phase diagram of Hf, our studies re-establish room temperature α→ω transition at high pressures, even in quasi-hydrostatic environment. We observed this transition in pure Hf with equilibrium transition pressure Po = 44.5 GPa; however, with large hysteresis. The structural sequence, transition pressures, the lattice parameters, the c/a ratio and its variation with compression for the α and ω phases as predicted by our ab-initio scalar relativistic (SR) calculations are found to be in good agreement with our experimental results of pure Hf.
Arrays of membrane isolated yttrium-barium-copper-oxide kinetic inductance bolometers
Authors: Lindeman M. A. , Bonetti J. A. , Bumble B. , Day P. K. , Eom B. H. , Holmes W. A. , Kleinsasser A. W.
Published: June 2014

We are developing of arrays of membrane isolated resonator-bolometers, each with a kinetic inductance device (KID) to measure the temperature of the membrane. The KIDs are fabricated out of the high temperature superconductor YBCO to allow operation at relatively high temperatures. The bolometers are designed to offer higher sensitivity than sensors operating at 300 K, but they require less expensive and lighter weight cooling than even more sensitive conventional superconducting detectors operating at lower temperatures. The bolometer arrays are applicable as focal planes in infrared imaging spectrometers, such as for planetary science missions or earth observing satellites. We describe the devices and present measurements of their sensitivity.
Magnetic skin layer of NiO(100) probed by polarization-dependent spectromicroscopy
Authors: Mandal Suman , Belkhou Rachid , Maccherozzi Francesco , Menon Krishnakumar S. R.
Published: June 2014

Using polarization-dependent x-ray photoemission electron microscopy, we have investigated the surface effects on antiferromagnetic (AFM) domain formation. Depth-resolved information obtained from our study indicates the presence of strain-induced surface AFM domains on some of the cleaved NiO(100) crystals, which are unusually thinner than bulk AFM domain wall widths (∼150 nm). Existence of such magnetic skin layer is substantiated by exchange-coupled ferromagnetic Fe domains in Fe/NiO(100), thereby evidencing the influence of this surface AFM domains on interfacial magnetic coupling. Our observations demonstrate a depth evolution of AFM structure in presence of induced surface strain, while the surface symmetry-breaking in absence of induced strain does not modify the bulk AFM domain structure. Realization of such thin surface AFM layer will provide better microscopic understanding of the exchange bias phenomena.
Inverse spin Hall effect in a closed loop circuit
Authors: Omori Y. , Auvray F. , Wakamura T. , Niimi Y. , Fert A. , Otani Y.
Published: June 2014

We present measurements of inverse spin Hall effects (ISHEs), in which the conversion of a spin current into a charge current via the ISHE is detected not as a voltage in a standard open circuit but directly as the charge current generated in a closed loop. The method is applied to the ISHEs of Bi-doped Cu and Pt. The derived expression of ISHE for the loop structure can relate the charge current flowing into the loop to the spin Hall angle of the SHE material and the resistance of the loop.
Ferroelectricity in wurtzite structure simple chalcogenide
Authors: Moriwake Hiroki , Konishi Ayako , Ogawa Takafumi , Fujimura Koji , Fisher Craig A. J. , Kuwabara Akihide , Shimizu Takao , Yasui Shintaro , Itoh Mitsuru
Published: June 2014

The possibility of the new class ferroelectric materials of wurtzite structure simple chalcogenide was discussed using modern first-principles calculation technique. Ferroelectricity in the wurtzite structure (P63mc) can be understood by structure distortion from centrosymmetric P63/mmc by relative displacement of cation against anion along c-axis. Calculated potential surface of these compounds shows typical double well between two polar variants. The potential barriers for the ferroelectric polarization switching were estimated to be 0.25 eV/f.u. for ZnO. It is slightly higher energy to the common perovskite ferroelectric compound PbTiO3. Epitaxial tensile strain on the ab-plane (0001) is effective to lower the potential barrier. The potential barrier decreased from 0.25 to 0.15 eV/f.u. by 5% ab-plane expansion in wurtzite structure ZnO. Epitaxial ZnO thin film with donor type defect reduction should be a possible candidate to confirm this ferroelectricity in wurtzite structure simple chalcogenide.
Image analysis of jet structure on electrospinning from free liquid surface
Authors: Kula Jiri , Linka Ales , Tunak Maros , Lukas David
Published: June 2014

The work analyses intra-jet distances during electrospinning from a free surface of water based poly(vinyl alcohol) solution confined by two thin metallic plates employed as a spinning electrode. A unique computer vision system and digital image processing were designed in order to track position of every polymer jet. Here, we show that jet position data are in good compliance with theoretically predicted intra-jet distances by linear stability analysis. Jet density is a critical parameter of electrospinning technology, since it determines the process efficiency and homogeneity of produced nanofibrous layer. Achievements made in this research could be used as essential approach to study jetting from two-dimensional spinning electrodes, or as fundamentals for further development of control system related to Nanospider™ technology.
Effect of microstructure anisotropy on the deformation of MAX polycrystals studied by in-situ compression combined with neutron diffraction
Authors: Guitton A. , Van Petegem S. , Tromas C. , Joulain A. , Van Swygenhoven H. , Thilly L.
Published: June 2014

In situ compression tests combined with neutron diffraction were performed on Ti2AlN MAX polycrystals with lamellar anisotropic microstructure: the diffraction peak evolution (position and profile) with applied stress reveals that lamellar grains parallel to compression axis remain elastic while lamellar grains perpendicular to compression plastify, both families being subjected to strong variations of heterogeneous strains (types II and III). We demonstrate that this behavior originates from the complex response of the very anisotropic lamellar microstructure and explains the observation of reversible hysteretic loops when cycling MAX polycrystals even in the elastic regime.
Operation of resonant-tunneling diodes with strong back injection from the collector at frequencies up to 1.46 THz
Authors: Feiginov Michael , Kanaya Hidetoshi , Suzuki Safumi , Asada Masahiro
Published: June 2014

In search for possibilities to increase the operating frequencies of resonant-tunneling diodes (RTDs), we are studying RTDs working in an unusual regime. The collector side of our diodes is so heavily doped that the collector depletion region is fully eliminated in our RTDs and the ground quantum-well subband stays immersed under (or stays close to) the collector quasi-Fermi level. The electron injection from the collector into the RTD quantum well is very strong in our diodes and stays comparable to that from the emitter in the whole range of RTD operating biases. Our RTDs exhibit well pronounced negative-differential-conductance region and peak-to-valley current ratio around 1.8. We demonstrate operation of our diodes in RTD oscillators up to 1.46 THz. We also observe a fine structure in the emission spectra of our RTD oscillators, when they are working in the regime close to the onset of oscillations.
Deep-level emission in ZnO nanowires and bulk crystals: Excitation-intensity dependence versus crystalline quality
Authors: Hou Dongchao , Voss Tobias , Ronning Carsten , Menzel Andreas , Zacharias Margit
Published: June 2014

The excitation-intensity dependence of the excitonic near-band-edge emission (NBE) and deep-level related emission (DLE) bands in ZnO nanowires and bulk crystals is studied, which show distinctly different power laws. The behavior can be well explained with a rate-equation model taking into account deep donor and acceptor levels with certain capture cross sections for electrons from the conduction band and different radiative lifetimes. In addition, a further crucial ingredient of this model is the background n-type doping concentration inherent in almost all ZnO single crystals. The interplay of the deep defects and the background free-electron concentration in the conduction band at room temperature reproduces the experimental results well over a wide range of excitation intensities (almost five orders of magnitude). The results demonstrate that for many ZnO bulk samples and nanostructures, the relative intensity R = INBE/IDLE can be adjusted over a wide range by varying the excitation intensity, thus, showing that R should not be taken as an indicator for the crystalline quality of ZnO samples unless absolute photoluminescence intensities under calibrated excitation conditions are compared. On the other hand, the results establish an all-optical technique to determine the relative doping levels in different ZnO samples by measuring the excitation-intensity dependence of the UV and visible luminescence bands.
Origin of high piezoelectric activity in perovskite ferroelectric ceramics
Authors: Zeng Weidong , Zhou Xiujuan , Chen Jun , Liao Jiayi , Zhou Changrong , Cen Zhenyong , Yang Tao , Yang Huabin , Zhou Qin , Chen Guohua , Yuan Changlai
Published: June 2014

Dense (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3 (BNT-BTx%, x = 3, 5, 6, and 7) ceramics exhibit large piezoelectricity for electrical poling below coercive fields. In particular, the piezoelectric activity and permittivity frequency dispersion have been found to be closely related. The significantly increased piezoelectric constant and sharply decreased permittivity frequency dispersion are observed to occur for poled ceramics under the critical poling electrical fields. These results suggest that the high piezoelectric response stems from poling electrical fields-induced-ordered nanodomains.
High-order face-shear modes of relaxor-PbTiO3 crystals for piezoelectric motor applications
Authors: Ci Penghong , Liu Guoxi , Chen Zhijiang , Zhang Shujun , Dong Shuxiang
Published: June 2014

The face-shear vibration modes of [011] poled Zt ± 45° cut relaxor-PT crystals and their applications for linear piezoelectric motors were investigated. Unlike piezoelectric ceramics, the rotated crystal was found to exhibit asymmetric face-shear deformations, and its two high-order face-shear modes degraded into two non-isomorphic modes. As an application example, a standing wave ultrasonic linear motor (10 × 10 × 2 mm3) operating in high-order face-shear vibration modes was developed. The motor exhibits a large driving force (1.5 N) under a low driving voltage (22 Vpp). These findings could provide guidance for design of crystal resonance devices.
Electron interactions and Dirac fermions in graphene-Ge2Sb2Te5 superlattices
Authors: Sa Baisheng , Sun Zhimei
Published: June 2014

Graphene based superlattices have been attracted worldwide interest due to the combined properties of the graphene Dirac cone feature and all kinds of advanced functional materials. In this work, we proposed a novel series of graphene-Ge2Sb2Te5 superlattices based on the density functional theory calculations. We demonstrated the stability in terms of energy and lattice dynamics for such kind of artificial materials. The analysis of the electronic structures unravels the gap opening nature at Dirac cone of the insert graphene layer. The Dirac fermions in the graphene layers are strongly affected by the electron spin orbital coupling in the Ge2Sb2Te5 layers. The present results show the possible application in phase-change data storage of such kind of superlattice materials, where the Ge2Sb2Te5 layers exhibit as the phase-change data storage media and the graphene layer works as the electrode, probe, and heat conductor.
Comment on “Unexpected size effect in the thermopower of thin-film stripes” [J. Appl. Phys. 110, 083709 (2011)]
Authors: Szakmany Gergo P. , Orlov Alexei O. , Bernstein Gary H. , Porod Wolfgang
Published: June 2014

In a recent article, Sun et al. [J. Appl. Phys. 110, 083709 (2011)] claim to measure a size-dependent thermoelectric effect in a micron-scale single-metal thermocouple. In this Comment, we demonstrate that the observed phenomenon is not due to a size-dependent Seebeck effect as claimed, but is rather wire-size-dependent heat transport that causes unequal heating at the bonding pads. As a result, the bonding pads are at two different temperatures, and the observed voltage corresponds to a thermoelectric effect of a parasitic thermocouple formed between their metal structure and the bonding-pad wires. We provide simulations and suggest a control experiment based on their structure that supports our contention that the observation depends on width-dependent heat transport in the wires.
Magnetic field controllable nonvolatile resistive switching effect in silicon device
Authors: Wang Jimin , Zhang Xiaozhong , Piao Hong-Guang , Luo Zhaochu , Xiong Chengyue , Wang Xiaofeng , Yang Fuhua
Published: June 2014

A Si–SiO2–MgO device showing nonvolatile resistive switching effect is fabricated. It is observed the resistance of the device changed from high value to low value at a certain transition voltage after being stimulated by a large current. In addition, the transition voltage shifts reproducibly under a reversed large current. By applying a reading voltage in the range of the transition voltages, nonvolatile resistive switching phenomena with on/off ratio of about 10, endurance of more than 200 cycles and retention of more than 104 s is obtained. More importantly, it is also observed that the magnetic field could shift the transition voltage to higher values, affecting or even suppressing the resistive switching. The magnetic field controllable nonvolatile resistive switching effect in the silicon device suggested by this work may be helpful to the silicon based industry.
Enhanced bipolar fatigue resistance in CaZrO3-modified (K,Na)NbO3 lead-free piezoceramics
Authors: Yao Fang-Zhou , Patterson Eric A. , Wang Ke , Jo Wook , Rödel Jürgen , Li Jing-Feng
Published: June 2014

The bipolar fatigue behavior of (K,Na)NbO3 (KNN)-based lead-free piezoceramics was investigated. A comparative analysis demonstrated that CaZrO3-modified KNN ceramics exhibited highly enhanced bipolar fatigue resistance due to the reduced lattice distortion (c/a ratio) and coexistence of orthorhombic and tetragonal phases. The hypothesis was verified by systematical studies of cycle-dependent large and small signal parameters and micro-morphologies. It was identified that mechanical stress induced microstructure damage beneath the electrodes renders the KNN ceramics to be vulnerable to bipolar cycling; while the mild fatigue behavior for CaZrO3-modified ones mainly originates from a thermally reversible domain wall pinning.
Electrical characteristics and formation mechanism of atmospheric pressure plasma jet
Authors: Liu Lijuan , Zhang Yu , Tian Weijing , Meng Ying , Ouyang Jiting
Published: June 2014

The behavior of atmospheric pressure plasma jet produced by a coplanar dielectric barrier discharge in helium in external electrostatic and magnetic field is investigated. Net negative charges in the plasma jet outside the tube were detected. The deflection of the plume in the external field was observed. The plasma jet is suggested to be formed by the electron beam from the temporal cathode which is accelerated by a longitudinal field induced by the surface charges on the dielectric tube or interface between the helium and ambient air. The helium flow is necessary for the jet formation in the surrounding air.
Ultrafast carrier dynamics in polycrystalline bismuth telluride nanofilm
Authors: Jia Lin , Ma Weigang , Zhang Xing
Published: June 2014

In this study, the dynamics of energy carriers in polycrystalline bismuth telluride nanofilm are investigated by the ultrafast pump-probe method. The energy relaxation processes are quantitatively analyzed by using the numerical fitting models. The extracted hot carrier relaxation times of photon excitation, thermalization, and diffusion are around sub-picosecond. The initial reflectivity recovery is found to be dominantly determined by the carrier diffusion, electron-phonon coupling, and photo-generated carriers trapping processes. High-frequency and low-frequency oscillations are both observed and attributed to coherent optical phonons and coherent acoustic phonons, respectively.
Grain boundary barrier modification due to coupling effect of crystal polar field and water molecular dipole in ZnO-based structures
Authors: Ji Xu , Zhu Yuan , Chen Mingming , Su Longxing , Chen Anqi , Zhao Chengchun , Gui Xuchun , Xiang Rong , Huang Feng , Tang Zikang
Published: June 2014

Surface water molecules induced grain boundaries (GBs) barrier modification was investigated in ZnO and ZnMgO/ZnO films. Tunable electronic transport properties of the samples by water were characterized via a field effect transistor (FET) device structure. The FETs fabricated from polar C-plane ZnO and ZnMgO/ZnO films that have lots of GBs exhibited obvious double Schottky-like current-voltage property, whereas that fabricated from nonpolar M-plane samples with GBs and ZnO bulk single-crystal had no obvious conduction modulation effects. Physically, these hallmark properties are supposed to be caused by the electrostatical coupling effect of crystal polar field and molecular dipole on GBs barrier.
A ballistic two-dimensional-electron-gas Andreev interferometer
Authors: Amado M. , Fornieri A. , Biasiol G. , Sorba L. , Giazotto F.
Published: June 2014

We report the realization and investigation of a ballistic Andreev interferometer based on an InAs two dimensional electron gas coupled to a superconducting Nb loop. We observe strong magnetic modulations in the voltage drop across the device due to quasiparticle interference within the weak-link. The interferometer exhibits flux noise down to ∼80 μΦ0/Hz and a robust behavior in temperature with voltage oscillations surviving up to ∼7 K. Besides this remarkable performance, the device represents a crucial first step for the realization of a fully-tunable ballistic superconducting magnetometer and embodies a potential advanced platform for the investigation of Majorana bound states, non-local entanglement of Cooper pairs, as well as the manipulation and control of spin triplet correlations.
Three-dimensional strain state and spacer thickness-dependent properties of epitaxial Pr0.7Sr0.3MnO3/La0.5Ca0.5MnO3/Pr0.7Sr0.3MnO3 trilayer structure
Authors: Wang Haiou , Zhang Jie , Jia Quanjie , Xu Feng , Tan Weishi , Huo Dexuan , Gao Ju
Published: June 2014

Epitaxial colossal magnetoresistive trilayer structures consisting of ferromagnetic metallic Pr0.7Sr0.3MnO3 (PSMO) and antiferromagnetic insulator La0.5Ca0.5MnO3 (LCMO) were fabricated on (001)-oriented single crystal MgO substrates using pulsed laser deposition technique. The evolution of three-dimensional strain states and electrical and magnetic transport properties of PSMO/LCMO/PSMO trilayers have been studied as a function of LCMO spacer thickness and lattice strain. When the thickness of LCMO spacer is 6 nm, lattice strain in the trilayer begins to be relaxed. Furthermore, trilayers with thickness of LCMO spacer up to 36 nm are not fully strain relaxation. The unit cell volume of the films is not conserved and exhibits the variation with LCMO layer thickness. Strain relaxation states are determined by bulk strain (εB) and Jahn–Teller (εJT) strain together. The electrical and magnetic transport properties, including metal-insulator transition temperatures TMI and saturation magnetization MS, also show systematic variations with respect to LCMO layer thickness.
Metallic behavior and negative differential resistance properties of (InAs)n (n = 2 − 4) molecule cluster junctions via a combined non–equilibrium Green's function and density functional theory study
Authors: Wang Qi , Zhang Jianbing , Li Rong , Xu Yuanlan , Miao Xiangshui , Zhang Daoli
Published: June 2014

In this present work, the geometric structures and electronic transport properties of (InAs)n (n = 2, 3, 4) molecule cluster junctions are comparatively investigated using NEGF combined with DFT. Results indicate that all (InAs)n molecule cluster junctions present metallic behavior at the low applied biases ([−2V, 2V]), while NDR appears at a certain high bias range. Our calculation shows that the current of (InAs)4 molecule cluster–based junction is almost the largest at any bias. The mechanisms of the current–voltage characteristics of all the three molecule cluster junctions are proposed.
Analytical estimations for thermal crosstalk, retention, and scaling limits in filamentary resistive memory
Authors: Lohn Andrew J. , Mickel Patrick R. , Marinella Matthew J.
Published: June 2014

We discuss the thermal effects on scaling, retention, and error rate in filamentary resistive memories from a theoretical perspective using an analytical approach. Starting from the heat equation, we derive the temperature profile surrounding a resistive memory device and calculate its effect on neighboring devices. We outline the engineering tradeoffs that are expected with continued scaling, such as retention and power use per device. Based on our calculations, we expect scaling to continue well below 10 nm, but that the effect of heating from neighboring devices needs to be considered for some applications even at current manufacturing capabilities. We discuss possible designs to alleviate some of these effects while further increasing device density.
Binomial distribution-based quantitative measurement of multiple-acceptors fluorescence resonance energy transfer by partially photobleaching acceptor
Authors: Zhang Lili , Yu Huaina , Zhang Jianwei , Chen Tongsheng
Published: June 2014

We report that binomial distribution depending on acceptor photobleaching degree can be used to characterize the proportions of various kinds of FRET (Fluorescence Resonance Energy Transfer) constructs resulted from partial acceptor photobleaching of multiple-acceptors FRET system. On this basis, we set up a rigorous quantitation theory for multiple-acceptors FRET construct named as Mb-PbFRET which is not affected by the imaging conditions and fluorophore properties. We experimentally validate Mb-PbFRET with FRET constructs consisted of one donor and two or three acceptors inside living cells on confocal and wide-field microscopes.
Plasmon resonance mediated enhancement in Fabry-Pérot cavity modes
Authors: Abhilash T. , Balasubrahmaniyam M. , Patra Anuradha , Kasiviswanathan S.
Published: June 2014

Fabry-Pérot (FP) modes of a dielectric cavity with a planar distribution of metal nanoparticles at one end have been studied numerically. An unusual enhancement in the strength of FP modes is observed close to the strong localized surface plasmon resonance of the metal nanoparticles. Experimental evidence for the numerical results has been provided by studying ZnO thin film cavities with Ag (Au) nanoparticles at one end. The enhancement in FP resonances has been interpreted in terms of a redefined cavity having a strongly dispersive adjacent medium.
Designing food and habitat trees for urban koalas: graft compatibility, survival and height of tall eucalypt species grafted onto shorter rootstocks
Authors: Trueman Stephen J. , McMahon Tracey V. , Grant Elektra L. , Walton David A. , Wallace Helen M.
Published: June 2014

The Corymbia and Eucalyptus species eaten by koalas are generally large trees, but these are often unpopular with urban landowners and councils because of the dangers of limbs falling from a great height. We aimed to develop shorter koala food and habitat trees for urban areas by heterografting tall eucalypt species onto rootstocks of shorter species and comparing their survival and growth with homografted trees and control ungrafted trees. In total, 12 of 14 interspecific scion/rootstock combinations were grafted successfully in the nursery but graft compatibility and field survival depended on taxonomic relatedness. The six interspecific combinations that had multiple surviving trees at 5 years after planting were all between species within the same taxonomic section or between a species and its own interspecific hybrid. Almost all trees died from grafts between species in different taxonomic sections. In most cases, the height of surviving interspecific grafted trees did not differ from control intraspecific grafted trees or from ungrafted trees of their scion species. Grafting elicited a ‘thrive or not survive’ response that diminished its usefulness for producing shorter trees. However, one combination, E. moluccana/E. behriana, had field survival of 40% and reduced height (4.0 m vs 9.9 m). These could be valuable habitat trees for koalas and other fauna in urban areas.
Magnetic Pd/Fe3O4 Composite: Synthesis, Structure, and Catalytic Activity
Authors: Bai Shi-Qiang , Jiang Lu , Huang Sheng-Li , Lin Ming , Zhang Shuang-Yuan , Han Ming-Yong , Xu Jianwei , Lu Yixin , Jin Guo-Xin , Hor T. S. Andy
Published: June 2014

Composite Pd/Fe3O4 (1) was designed and synthesised by immobilization of tridentate pincer ligands with triethoxysilane groups on Fe3O4 nanoparticles, PdII complexation, and in-situ reduction process. The composite was characterised by transmission electron microscopy, scanning electron microscopy energy-dispersive X-ray spectroscopy, powder X-ray diffraction, vibrating sample magnetometer, Fourier transform infrared spectroscopy, thermogravimetric analysis, and Brunauer–Emmett–Teller analysis. The composite featured Pd nanoparticles of ~2–4 nm, exhibited good thermal stability and hydrophilic property as well as excellent catalytic activity towards the reduction of 4-nitrophenol to 4-aminophenol in water.
Chapter 3. The ‘ins and outs’ of a study abroad programme
Authors: Beattie John
Published: June 2014

This chapter looks in detail at all the stages involved in setting up and managing the exchange experience of several cohorts of students from the Faculty of Translation and Interpreting at a Catalan university in Barcelona, Spain. The history of the exchange is briefly presented, followed by the articulation of all the stages of the exchange; prior to departure, monitoring the students during the actual period of Stay Abroad and, finally, follow-up activities. The complex interplay of factors involved in mobilising and monitoring large numbers of exchange students is presented and reference is also made to the degree to which it is possible to undertake successful Stay Abroad initiatives from the planning stage right through to their completion.
Chapter 5. L2 fluency development in formal instruction and study abroad
Authors: Valls-Ferrer Margalida , Mora Joan Carles
Published: June 2014

This chapter examines L2 fluency development across Formal Instruction (FI) and Study Abroad (SA) learning periods, thus investigating one of the research questions in the SALA Project, namely whether a three-month SA after a FI period results in significant benefits. The longitudinal approach in the present study focuses both on the period abroad and on the FI periods before and after SA. In addition, we also examined the impact of onset level and language contact profiles on development. L2 fluency improved significantly over time, with gains being mainly obtained during SA. Lower initial fluency levels and greater language contact were associated with fluency gains during SA, but did not fully explain the differential impact of FI and SA on fluency development.
Chapter 6. Phonological development in L2 speech production during study abroad programmes differing in length of stay
Authors: Avello Pilar , Lara Ann Rebecca
Published: June 2014

The present study addresses the main objectives of the SALA Project regarding the impact of Study Abroad (SA), as well as possible differential effects of Length of Stay (LoS), on second language (L2) phonology. Two groups of undergraduate Spanish/Catalan learners of English following three-month and six-month SA programmes respectively were recorded performing a reading aloud task before and after SA. A group of native speakers of English provided baseline data used to evaluate the learners’ performance. Segmental production accuracy was analysed by conducting acoustic measurements for vowel duration and quality and for voice onset time (VOT) in voiceless plosives. Results suggested no strong effect of SA and no significant differences in the learners’ production as a function of LoS.
Chapter 7. The role of onset level on L2 perceptual phonological development after formal instruction and study abroad
Authors: Mora Joan Carles
Published: June 2014

The present study addresses, focusing on perceptual phonological competence, one of the main research questions within the SALA Project: namely, whether there are differential gains attributable to Formal Instruction (FI) and Study Abroad (SA) contexts, and whether there are different patterns of development associated with learners’ pre-SA onset level. The data analysed comprises a three-year language learning period. The results revealed significant gains in discrimination ability during the FI period and lack of gains during SA, with no significant loss or gain occurring at delayed post-test. Large inter-subject differences indicated that the amount of gains obtained during FI varied as a function of learners’ initial level, the lower learner group obtaining the largest gains in discrimination scores.