bluuebunny/crossref_metadata_2025 huggingface dataset:
Room-temperature ferromagnetism in Co doped La2O3
Authors: Wen Qi-Ye , Zhang Huai-Wu , Song Yuan-Qiang , Yang Qing-Hui , Zhu Hao , Wang Wei-Gang , Xiao John Q.
Published: February 2008

Single-phase La2(1−x)Co2xO3−δ polycrystalline samples with x=0%–8% were synthesized by the conventional ceramic method, and the effect of Co content on the magnetic behaviors has been systemically investigated. X-ray diffraction and x-ray photoelectron spectroscopy studies indicate no Co metal clusters or secondary magnetic phases in any samples in this study. It is found that the undoped or slightly doped samples show no ferromagnetic signal, while samples with x in the range of 0.5%–2% exhibit an exponential increase of saturation magnetization (Ms) as a function of Co concentration. When x increases beyond 2%, an inverse correlation between the magnetization and Co content was observed. We reported an Ms as large as 0.05emu∕g and a Curie temperature above RT in our samples, rendering Co:La2O3 a candidate diluted magnetic oxide for RT applications. Our results also strongly support the oxygen vacancy (F-center) mediated mechanism for RT ferromagnetism in transition-metal doped high-k oxides
Magnetic property improvement of Pt-lean FePt∕Fe–B-type nanocomposites by Co substitution
Authors: Chang C. W. , Chang H. W. , Chiu C. H. , Hsieh C. C. , Fang Y. K. , Chang W. C.
Published: February 2008

Effects of Co content on the magnetic properties and microstructure of melt-spun [(Fe1−xCox)0.675Pt0.325]84B16 (x=0–0.5) and [(Fe1−yCoy)0.725Pt0.275]85B15 (y=0 and 0.3) nanocomposite ribbons have been investigated. The substitution of Co for Fe in [(Fe1−xCox)0.675Pt0.325]84B16 ribbons enhances the coercivity (Hci) from 7.5kOe for x=0to10kOe for x=0.3, due to the formation of ordered L10-(Fe,Co)Pt phase with higher anisotropy field. The effect of Co substitution for Fe in [(Fe1−yCoy)0.725Pt0.275]85B15 series ribbons is similar to that in [(Fe1−xCox)0.675Pt0.325]84B16 system. Interestingly, larger magnetization could be obtained by decreasing the boron and Pt content simultaneously. Moreover, L10-(Fe,Co)Pt phase provides [(Fe0.7Co0.3)0.725Pt0.275]85B15 ribbons sufficient high coercivity Hci=5.4kOe, resulting in a remarkable enhancement of energy product from 10.0MGOe for Co-free ribbons to 15.7MGOe for ribbons with y=0.3.
Net Mn moment due to canted spins at SrRuO3∕SrMnO3 interfaces
Authors: Choi Y. , Yoo Y. Z. , Chmaissem O. , Ullah A. , Kolesnik S. , Kimball C. W. , Haskel D. , Jiang J. S. , Bader S. D.
Published: February 2008

A net moment was observed from Mn in a SrRuO3∕SrMnO3 (SRO/SMO) superlattice film via element-specific x-ray resonant magnetic techniques. The collective magnetic behavior of the SRO and SMO layers is significantly modified by their exchange interaction. Bulk magnetometry shows a two-step, easy-axis magnetization reversal process, and x-ray measurements reveal that the reversal with higher coercivity involves the magnetization in the SMO layers. The results provide strong evidence for the presence of pinned SRO magnetization at the SRO/SMO interface. X-ray measurements and micromagnetic simulations reveal that the net Mn moment is due to a canted antiferromagnetic spin configuration in the SMO layers.
Temperature dependence of magnetic anisotropy of Ga-substituted cobalt ferrite
Authors: Ranvah N. , Melikhov Y. , Jiles D. C. , Snyder J. E. , Moses A. J. , Williams P. I. , Song S. H.
Published: February 2008

The temperature dependence of magnetization, magnetic anisotropy, and coercive field of gallium-substituted cobalt ferrite was investigated for a series of compositions of CoGaxFe2−xO4 (0⩽x⩽0.8). Hysteresis loops were measured for each sample over the range of −5T⩽μ0H⩽5T for selected temperatures between 10 and 400K. The magnetization at 5T and low temperatures was found to increase for the lower Ga contents (x=0.2 and 0.4) compared to pure CoFe2O4, indicating that at least initially, Ga3+ substitutes predominantly into the tetrahedral sites of the spinel structure. The high field regions of these loops were modeled using the law of approach to saturation, which represents the rotational process, together with an additional linear forced magnetization term. The first order cubic magnetocrystalline anisotropy coefficient K1 was calculated from curve fitting to these data. It was found that K1 decreased with increasing Ga content at all temperatures. Both anisotropy and coercivity increased substantially as temperature decreased. Below 150K, for certain compositions (x=0, 0.2, 0.4), the maximum applied field of μ0H=5T was less than the anisotropy field and, therefore, insufficient to saturate the magnetization. In these cases, the use of the law of approach method can lead to calculated values of K1 which are lower than the correct value.
Sensitivity dependence of Hall biosensor arrays with the position of superparamagnetic beads on their active regions
Authors: Kumagai Yoshimichi , Imai Yasuharu , Abe Masanori , Sakamoto Satoshi , Handa Hiroshi , Sandhu Adarsh
Published: February 2008

This paper describes a numerical and experimental analysis on the variation of the magnetic sensitivity of the active surface region of AlGaAs∕InGaAs two dimensional electron gas Hall effect biosensors with location and number of superparamagnetic beads. Experiments were conducted using linear arrays of devices consisting of ten sensors each with an area of 5×5μm2. The edges and corners of the Hall sensors were most sensitive and exhibited a linear response. These results are important for commercialization of high sensitivity Hall effect biosensors with a wide dynamic range.
Evolution of charge and spin state of transition metals in the LaMn1−xCoxO3 perovskite series
Authors: Sikora M. , Knizek K. , Kapusta Cz. , Glatzel P.
Published: February 2008

Charge and spin state evolution of the transition metals in the LaMn1−xCoxO3 perovskite series was studied by means of high resolution x-ray absorption and emission spectroscopy. The gradual charge transfer from Mn to Co sites was observed upon increasing Co doping. The high spin of the Mn3+∕4+ and Co2+ ions is preserved in the entire solid solution. Co3+ ions reveal low spin state at low doping, while the gradual increase of the average Co3+ spin state is observed at higher cobalt concentrations. The results plausibly explain the observed magnetization anomalies.
Fabrication of a high temperature superconductor micro-superconducting-quantum-interference-device magnetometer for magnetic hysteresis measurements
Authors: Takeda Keiji , Mori Hatsumi , Yamaguchi Akira , Ishimoto Hidehiko , Nakamura Takayoshi , Kuriki Shinya , Hozumi Toshiya , Ohkoshi Shin-ichi
Published: February 2008

A high-temperature-superconductor-type micrometer-sized dc-SQUID (SQUID denotes superconducting quantum interference divice) magnetometer with much higher sensitivity than a commercial system has been developed. Several kinds of YBa2Cu3O7−δ micro-SQUIDs were fabricated with photolithography techniques to have a hole of 4×9μm2 and 2-μm-wide grain boundary Josephson junctions. Combined with a three dimensional magnetic field coil system, the voltage modulation was observed for three different field directions.
Ultrafast photoinduced ferromagnetism in the perovskite manganite Gd0.55Sr0.45MnO3
Authors: Matsubara M. , Okimoto Y. , Ogasawara T. , Tomioka Y. , Okamoto H. , Tokura Y.
Published: February 2008

We report the ultrafast switching of the magnetic state in the course of photoinduced phase transition from an insulator with short-range charge and orbital order (CO/OO) to a ferromagnetic metal in perovskite-type Gd0.55Sr0.45MnO3. The femtosecond Kerr rotation and reflectivity measurements, which detect the spin and charge dynamics, respectively, have revealed that the metallic state is formed within the time resolution (∼200fs); however, magnetization increases with the time constant of 0.5ps. The relatively slow increase of the magnetization is attributable to the magnetic-field-induced alignment of ferromagnetic domains in the initially produced metallic state.
Magnetic response of YbMnO3 single crystal
Authors: Fontcuberta Josep , Gospodinov Marin , Skumryev Vassil
Published: February 2008

The low ac- and dc-field magnetic susceptibilities of hexagonal YbMnO3 single crystal have been measured along the ab plane and along the c axis (χab,χc). The antiferromagnetic Néel temperature TN is well signaled by a cusp in the temperature dependence of χc but no features are visible in χab. A remarkable anisotropy of paramagnetic susceptibility and the extrapolated Curie–Weiss temperature are observed and related to the quasibidimensional magnetic structure of YbMnO3. Below TN magnetic irreversibility sets, reflecting the presence of a weak ferromagnetic response. Possible scenarios for the origin of the weak ferromagnetism are discussed.
Annealing effects on surface structure and magnetic properties of ultrathin films Co on Pt(111)
Authors: Chen Y. J. , Hwang E. J. , Shern C. S.
Published: February 2008

Annealing effects on magnetic properties, surface structure, and alloy formation for 1 and 2 ML of Co∕Pt(111) were studied. The tools used in the study were in situ magneto-optical Kerr effect, low energy electron diffraction, and Auger electron spectroscopy. The Curie temperatures of both samples decrease with increase of the annealing temperature, which is associated with concentration change of Co–Pt surface alloy. A structural phase transition from CoPt to CoPt3 of an ordered surface alloy was observed when the annealing temperature was between 780 and 810K. The value of critical exponent β near the Curie point turns from a two-dimensional-like to a three-dimensional-like magnetic phase. The curves of coercivity versus sample temperature reveal thermal hysteresis with two plateaus during the cooling process. The mechanism of the thermal hysteresis was discussed. The Curie temperature and the coercivity of the Co∕Pt(111) system can be adjusted by controlling the annealing temperature, which alters the concentrations of the alloy formation.
Detection of 130nm magnetic particles by a portable electronic platform using spin valve and magnetic tunnel junction sensors
Authors: Cardoso F. A. , Germano J. , Ferreira R. , Cardoso S. , Martins V. C. , Freitas P. P. , Piedade M. S. , Sousa L.
Published: February 2008

An integrated biosensor with magnetic tunnel juntions (MTJs) and spin valve (SV) sensor was used for 130nm particle detection. A platform drives an external magnet generating an in-plane dc+ac magnetic field on the sensor at frequencies up to 375Hz, provides a current to bias the sensor, and performs the signal acquisition and treatment. The signal-to-noise ratio of the SV and MTJ was characterized. Bead detection (130nm in diameter) was performed using both sensors leading to a detection limit of 3×108particles∕ml for SV and 3×1010particles∕ml for MTJ.
Study on multiferroic properties in Ni80Fe20∕BaTiO3 bilayer films
Authors: Chen Yi-Chun , Hong Tsung-Hsuan , Jiang Zhen-Xi , Lin Qi-Rui
Published: February 2008

In this study, we investigated the magnetoelectric coupling effect in Ni80Fe20∕BaTiO3 (NiFe/BTO) bilayer films. Two different samples with interface roughnesses of about 5 and 20nm were synthesized by controlling the BTO deposition rates. The electrostatic force microscope scanning shows an intrinsic surface potential about 0.2V existing in both NiFe/BTO bilayer films. This phenomenon is due to the bond charge induced by interface dipole moments as the interface-bonding model predicted. The films show good ferroelectric properties, but the hysteresis shows bias asymmetry due to the interface effect. The magnetic coercive fields of NiFe/BTO system increase with the interface roughness. The large magnetoelectric coupling is observed from an irregular change of magnetization near the ferroelectric Curie temperature. The multiferroic properties were enhanced by the interface geometry.
Neutral depletion in inductively coupled plasmas using hybrid-type direct simulation Monte Carlo
Authors: Shimada Masashi , Tynan George R. , Cattolica Robert
Published: February 2008

Neutral and ion transport phenomena were simulated by a hybrid-type direct simulation Monte Carlo (DSMC) method for a one-dimensional (1D) electrostatic plasma in Ar/N2 mixtures to identify the mechanism of neutral depletion. The results show that gas heating and pressure balance are the main mechanisms of neutral depletion in an inductively coupled plasma. When plasma pressure becomes comparable to neutral pressure in high density plasma sources (Te∼2−5 eV, ne∼1011−1012 cm−3), the total pressure (neutral pressure and plasma pressure) is conserved. Therefore, the finite plasma pressure (mainly electron pressure) reduces the neutral pressure. Neutrals collide with ions that have been accelerated by the ambipolar electric field and with Franck-Condon dissociated atoms, resulting in gas heating. Significant neutral depletion (up to 90%) is found at the typical condition of inductively coupled plasma process reactors. The resulting neutral depletion enhances the plasma transport to the surrounding wall, increases the particle loss, and decreases the plasma density.
Strain at the surface of GaN epilayers and at GaN/sapphire interface before and after laser lift-off (LLO) from the sapphire substrate
Authors: Elgawadi Amal , Krasinski Jerzy
Published: February 2008

Four GaN epilayers were grown on sapphire by hydride vapor phase epitaxy. The lattice and thermal expansion coefficient mismatches between the epilayers and the sapphire produce a strain in the structure. The strain at the surface of the epilayers was estimated using photoluminescence. By analyzing the variation of the surface strain with thickness, the minimum thickness required to obtain low surface strain was estimated to be approximately 45 μm. Furthermore, the strain at the interface of the sapphire and the epilayers was estimated after laser lift-off of GaN epilayers. The analysis showed that a low and almost constant strain at the surface of the interface for the separated samples can be obtained for an epilayer thickness greater than 18 μm.
Simulation of beams or plasmas crossing at relativistic velocity
Authors: Vay J.-L.
Published: February 2008

This paper addresses the numerical issues related to the modeling of beams or plasmas crossing at relativistic velocity using the particle-in-cell method. Issues related to the use of the standard Boris particle pusher are identified and a novel pusher which circumvents them is proposed, whose effectiveness is demonstrated on single particle tests. A procedure for solving the fields is proposed, which retains electrostatic, magnetostatic, and inductive field effects in the direction of the mean velocity of the species, is fully explicit and simpler than the full Darwin approximation. Finally, results are given, from a calculation using the novel features, of an ultrarelativistic beam interacting with a background of electrons.
Improved confinement and current drive of high temperature field reversed configurations in the new translation, confinement, and sustainment upgrade device
Authors: Guo H. Y. , Hoffman A. L. , Milroy R. D. , Steinhauer L. C. , Brooks R. D. , Deards C. L. , Grossnickle J. A. , Melnik P. , Miller K. E. , Vlases G. C.
Published: February 2008

Previous work in the translation, confinement, and sustainment (TCS) device [Hoffman, Guo, Slough et al., Fusion Sci. Technol. 41, 92 (2002)] demonstrated formation and steady-state sustainment of field reversed configurations (FRC) by rotating magnetic fields (RMF). However, in TCS the plasma temperature was limited to several 10s of eV due to high impurity content. These impurities are greatly reduced in the new TCS upgrade device (TCSU), which was built with a bakable, ultrahigh vacuum chamber, and advanced wall conditioning capabilities. This led to dramatic improvements in TCSU with temperatures well over 200eV, using simple even-parity RMF drive. The higher temperatures, coupled with reduced recycling, allowed plasma to enter into a collisionless, high-ζ (ratio of average electron rotation frequency to RMF frequency) regime. These new FRC states exhibit the following key features: (1) Dramatic improvement in current drive efficiency with ζ approaching 100%, for the first time in TCSU; (2) up to threefold increase in global energy confinement time; and (3) significant reduction in transport rates, accompanied by a striking transition from a Bohm-type transport to a lower hybrid driftlike transport that scales better than gyro-Bohm and is very favorable for the next step FRC development.
Terahertz transmission in subwavelength holes of asymmetric metal-dielectric interfaces: The effect of a dielectric layer
Authors: Han Jiaguang , Lu Xinchao , Zhang Weili
Published: February 2008

The influence of a dielectric thin film on resonant transmission of terahertz pulses in a plasmonic array of subwavelength holes of asymmetric dielectric-metal interfaces is presented. A giant tuning of up to 0.80 THz at the surface plasmon metal-air [±1,0] mode at 1.95 THz and a further enhanced transmission at the metal-Si [±1,0] mode at 0.5 THz are achieved by modifying the film thickness. The experimental results are characterized by numerical simulation based on finite element method and angle-dependent measurements. The sensitive nature in the plasmonic hole array of asymmetric interfaces is promising in applications of biochemical sensing and tunable integrated plasmonic devices.
Synthesis and abnormal photoluminescence of core/shell structured Fe∕ZnO nanoparticles
Authors: Jin C. Q. , Zhong W. , Qi X. S. , Song H. A. , Au C. T. , Tang S. L. , Du Y. W.
Published: February 2008

Core/shell Fe∕ZnO nanocomposite with average diameter of 200nm has been synthesized successfully by means of a combined sol-gel/reduction method. The saturation magnetization of the Fe∕ZnO samples is relatively high due to the core α-Fe particles. According to the transmission electron microscopy image, the Fe nanoparticles are coated with a thin shell of ZnO. Being encapsulated, the nanoparticles are stable in ambient environment. The photoluminescence spectrum recorded at room temperature display ultraviolet band at 390nm as well as three broader bands at 522, 635, and 700nm in the region of green to infrared. Such phenomena differ from those reported in previous publications.
Bulk and near-surface magnetic properties of FeRh thin films
Authors: Ding Y. , Arena D. A. , Dvorak J. , Ali M. , Kinane C. J. , Marrows C. H. , Hickey B. J. , Lewis L. H.
Published: February 2008

Epitaxial Fe48Rh52 thin films of nominal thickness 500Å were grown on MgO (001) substrates via molecular beam epitaxy and capped with 20Å of either Au or MgO. The presence of the anticipated magnetostructural phase transition from antiferromagnetism to ferromagnetism at ∼350K was confirmed by superconducting quantum interference device and magneto-optic Kerr effect magnetometry. X-ray magnetic circular dichroism (XMCD) experiments were carried out at the L2,3 edges; measurements were done in both total electron yield (TEY) mode and indirect transmission mode. At room temperature, the indirect transmission XMCD data show no detectable dichroism, consistent with bulk antiferromagnetic behavior. However, room-temperature TEY data originating from the films’ surface reveal an appreciable dichroic signal indicating the presence of ferromagnetism. This near-surface/interfacial magnetism may be modified by choice of capping layer; the MgO-capped sample exhibited a considerably smaller ferromagnetic XMCD signal. The results have potential impact on the application of FeRh thin films as temperature-variable pinning layers in exchanged-biased systems.
Useful entanglement can be extracted from all nonseparable states
Authors: Masanes Lluís
Published: February 2008

We consider entanglement distillation from a single copy of multipartite quantum states, and instead of rates we analyze the “quality” of the distilled entanglement. This quality is quantified by the fidelity with the gigahertz state. We show that each not fully separable state σ can increase the quality of the entanglement distilled from other states, no matter how weakly entangled is σ. We also generalize this to the case where the goal is distilling states different from the gigahertz. These results provide new insights on the geometry of the set of separable states and its dual (the set of entanglement witnesses).
Increase of thermal resistance between a nanostructure and a surface due to phonon multireflections
Authors: Volz Sebastian , Chapuis Pierre-Olivier
Published: February 2008

The thermal resistance between a nanostructure and a half-body is calculated in the framework of particle-phonons physics. The current models approximate the nanostructure as a thermal bath. We prove that the multireflections of heat carriers in the nanostructure significantly increase resistance, in contradiction with former predictions. This increase depends on the shape of the nanostructure and the heat carrier’s mean-free path only. We provide a general and simple expression for the contact resistance and examine the specific cases of nanowires and nanoparticles.
Etching characteristics of LiNbO3 in reactive ion etching and inductively coupled plasma
Authors: Ren Z. , Heard P. J. , Marshall J. M. , Thomas P. A. , Yu S.
Published: February 2008

The etching characteristics of congruent LiNbO3 single crystals including doped LiNbO3 and proton-changed LiNbO3 have been studied in reactive ion etching (RIE) and inductively coupled plasma (ICP) etching tools, using different recipes of gas mixtures. The effects of parameters including working pressure, RIE power, and ICP power are investigated and analyzed by measurement of etching depth, selectivity, uniformity, etched surface state, and sidewall profile by means of focused ion beam etching, energy-dispersive x-ray analysis, secondary ion mass spectroscopy, scanning electron microscopy, and surface profilometry. The effects of a sample carrier wafer coating have also been investigated. Optimized processes with high etching rates, good mask selectivity, and a near-vertical profile have been achieved. Ridge waveguides on proton-exchanged LiNbO3 have been fabricated and optically measured.
Phase effects for the addition of many coherent sources
Authors: Hammond Richard
Published: February 2008

A phase quality, ϕ, is defined for the addition of N coherent, but out of phase sources. If the phases can be partially controlled to within the phase β, it is shown that the peak output of the laser radiation is ϕN2, where for large N, ϕ=sinc2(β)+(1/N)[1−sinc2(β)].
Lead-free piezoceramics with giant strain in the system Bi0.5Na0.5TiO3–BaTiO3–K0.5Na0.5NbO3. I. Structure and room temperature properties
Authors: Zhang Shan-Tao , Kounga Alain Brice , Aulbach Emil , Granzow Torsten , Jo Wook , Kleebe Hans-Joachim , Rödel Jürgen
Published: February 2008

Lead-free piezoelectric ceramics, (1−x−y)Bi0.5Na0.5TiO3–xBaTiO3–yK0.5Na0.5NbO3 (0.05⩽x⩽0.07 and 0.01⩽y⩽0.03), have been synthesized by a conventional solid state sintering method. The room temperature ferroelectric and piezoelectric properties of these ceramics were studied. Based on the measured properties, the ceramics were categorized into two groups: group I compositions having dominant ferroelectric order and group II compositions displaying mixed ferroelectric and antiferroelectric properties at room temperature. A composition from group II near the boundary between these two groups exhibited a strain as large as ∼0.45% at an electric field of 8kV∕mm. Polarization in this composition was not stable in that the piezoelectric coefficient d33 at zero electric field was only about 30pm∕V. The converse piezoelectric response becomes weaker when the composition deviated from the boundary between the groups toward either the ferroelectric or antiferroelectric compositions. These results were rationalized based on a field induced antiferroelectric-ferroelectric phase transition.
Lead-free piezoceramics with giant strain in the system Bi0.5Na0.5TiO3–BaTiO3–K0.5Na0.5NbO3. II. Temperature dependent properties
Authors: Zhang Shan-Tao , Kounga Alain Brice , Aulbach Emil , Jo Wook , Granzow Torsten , Ehrenberg Helmut , Rödel Jürgen
Published: February 2008

The temperature dependence of the dielectric and ferroelectric properties of lead-free piezoceramics of the composition (1−x−y)Bi0.5Na0.5TiO3–xBaTiO3–yK0.5Na0.5NbO3 (0.05⩽x⩽0.07, 0.01⩽y⩽0.03) was investigated. Measurements of the polarization and strain hystereses indicate a transition to predominantly antiferroelectric order when heating from room temperature to 150°C, while for 150<T<200°C both remnant polarization and coercive field increase. Frequency-dependent susceptibility measurements show that the transition is relaxorlike. For some samples, the transition temperature Td is high enough to allow mostly ferroelectric ordering at room temperature. These samples show a drastic increase of the usable strain under an external electric field just after the transition into the antiferroelectric state at high temperatures. For the other samples, Td is so low that they display significant antiferroelectric ordering already at room temperature. In these samples, the usable strain is relatively stable over a wide temperature range. In contrast to Td, the temperature Tm of the transition into the paraelectric high-temperature phase depends far less on the sample composition. These results confirm that the high strain in this lead-free system is due to a field-induced antiferroelectric-ferroelectric phase transition and that this effect can be utilized in a wide temperature range.
Dielectric properties and relaxor behavior of a new (1−x)BaTiO3–xBiAlO3 solid solution
Authors: Yu Huichun , Ye Zuo-Guang
Published: February 2008

A new lead-free perovskite solid solution of (1−x)BaTiO3–xBiAlO3 (x=0.02, 0.05, 0.10, and 0.15) that exhibits ferroelectric properties and relaxor behavior has been synthesized by solid state reactions. X-ray diffraction patterns show a transformation from the tetragonal symmetry into a rhombohedral symmetry as a result of the substitutions of Bi3+ on the A site and Al3+ on the B site in the crystal lattice of BaTiO3. The temperature and frequency dependences of the dielectric constant indicate a crossover from a normal ferroelectric to relaxor behavior. The degree of deviation from the Curie–Weiss law is found to increase with the increasing amount of BiAlO3. The high-temperature slope of the dielectric peak for x=0.05, 0.1 and, 0.15 can be well described by a Lorenz-type relation. Typical relaxor behavior is observed for x=0.15 with the temperature of the dielectric peak Tm=360K at 1kHz, while ferroelectric hysteresis loop is displayed at room temperature. This suggests that the long-range polar order from the end member BaTiO3 persists and coexists with polar nanoregions induced by the chemical disorder following the coupled substitutions in the solid solution.
Impact of incomplete set programing on the performance of phase change memory cell
Authors: Chao Der-Sheng , Lien Chenhsin , Lee Chain-Ming , Chen Yi-Chan , Yeh Jyi-Tyan , Chen Fred , Chen Ming-Jung , Yen Philip H. , Kao Ming-Jer , Tsai Ming-Jinn
Published: February 2008

Phase change memory (PCM) cells with T-shaped structure using tungsten heater were fabricated and the cell characteristics concerning the programing pulse width were also investigated in this work. The numerical modeling shows the thermal nonuniformity over the active region due to the considerable thermal sink of tungsten heater results in the amorphous-phase residues and the incomplete set programing. The experimental results reveal the existence of residual amorphous phase and indicate that the incomplete set programing is the dominant factor to degrade the PCM cell performances, such as the sensing margin and the endurance. The strategies to eliminate the incomplete set programing are the optimization in programing pulse width and the replacement of the tungsten heater with higher resistivity metal such as TiAlN.
Sensitivity analysis of laterally resolved free carrier absorption determination of electronic transport properties of silicon wafers
Authors: Zhang Xiren , Li Bincheng , Gao Chunming
Published: February 2008

Simulations are performed to investigate the uniqueness of simultaneous determination of electronic transport properties (the carrier lifetime, the carrier diffusivity, and the front surface recombination velocity) of silicon wafers by laterally resolved modulated free carrier absorption (MFCA) and multiparameter fitting. The dependences of MFCA amplitude and phase on these transport properties at different pump-probe-beam separations and modulation frequencies are analyzed. The uncertainties of the fitted parameter values are analyzed by investigating the dependences of a mean square variance including both the amplitude error and phase error on corresponding electronic transport parameters. Simulation results show that the electronic transport parameters can be determined accurately through fitting experimental MFCA data carrying both frequency- and space-domain information of carrier diffusion to a rigorous MFCA model. Among the three transport parameters, the carrier diffusivity can be determined most precisely, with an uncertainty of less than ±5%, due to the highest sensitivity of the laterally resolved MFCA signal to the diffusivity. The highly accurate determination of the diffusivity further improves the precision of the carrier lifetime and the front surface recombination velocity values simultaneously determined via multiparameter fitting. Experiments were performed with a silicon wafer and the results were in good agreement with the theoretical simulations.
Thermodynamic analysis of stress effect on Bi4Ti3O12 films
Authors: Li Li-Ben , Lu Xia-Mei , Chen Qing-Dong , Wu Xiu-Mei , Zhu Jin-Song
Published: February 2008

Thermodynamic theory is applied to study the effect of stress on the polarization of Bi4Ti3O12 films with a two-dimensional model. The spontaneous polarizations and free energies are calculated for three possible kinds of orientations of the Bi4Ti3O12 cell and nine ferroelectric phases in the Bi4Ti3O12 films. The stress effect on the spontaneous polarization caused by the lattice distortion is small and can be neglected for all the stable ferroelectric phases, whereas the domain reorientation induced by the competition between the external stress and a gradient intrinsic stress leads to a significant change of spontaneous polarization in Bi4Ti3O12 films. The calculation result agrees well with the experimental result on Nd-doped Bi4Ti3O12 films.
Characterization of sputtered TiO2 gate dielectric on aluminum oxynitride passivated p-GaAs
Authors: Dalapati Goutam Kumar , Sridhara Aaditya , Wong Andrew See Weng , Chia Ching Kean , Lee Sung Joo , Chi Dongzhi
Published: February 2008

Structural and electrical characteristics of sputtered TiO2 gate dielectric on p-GaAs substrates have been investigated. It has been demonstrated that the introduction of thin aluminum oxynitride (AlON) layer between TiO2 and p-GaAs improves the interface quality. X-ray photoelectron spectroscopy and transmission electron microscopy results show that the AlON layer effectively suppresses the interfacial oxide formation during thermal treatment. The effective dielectric constant value is 1.5 times higher for the TiO2∕AlON gate stack compared to directly deposited TiO2 on p-GaAs substrates, with a comparable interface state density. The capacitance-voltage (C-V), current-voltage (I-V) characteristics, and charge trapping behavior of the TiO2∕AlON gate stack under constant voltage stressing exhibit an excellent interface quality and high dielectric reliability, making the films suitable for GaAs based complementary metal-oxide-semiconductor technology.
A new superintegrable Hamiltonian
Authors: Verrier P. E. , Evans N. W.
Published: February 2008

We identify a new superintegrable Hamiltonian in three degrees of freedom, obtained as a reduction of pure Keplerian motion in six dimensions. The new Hamiltonian is a generalization of the Keplerian one, and has the familiar 1∕r potential with three barrier terms preventing the particle crossing the principal planes. In three degrees of freedom, there are five functionally independent integrals of motion, and all bound, classical trajectories are closed and strictly periodic. The generalization of the Laplace–Runge–Lenz vector is identified and shown to provide functionally independent isolating integrals. They are quartic in the momenta and do not arise from separability of the Hamilton–Jacobi equation. A formulation of the system in action-angle variables is presented.
Chaotic, fractal, and coherent solutions for a new integrable system of equations in 2+1 dimensions
Authors: Maccari Attilio
Published: February 2008

A new integrable and nonlinear system of partial differential equations in 2+1 dimensions is obtained by means of an asymptotically exact reduction method based on Fourier expansion and spatio-temporal rescaling. We find interacting coherent excitations such as the soliton, dromion, lump, ring soliton, breather, and instanton solutions. The interaction between the localized solutions are completely elastic because they pass through each other and preserve their shapes and velocities, the only change being a phase shift. Moreover, the arbitrariness of the functions included in the general solution implies that lower dimensional chaotic patterns such as chaotic-chaotic patterns, periodic-chaotic patterns, chaotic-soliton patterns, and chaotic-dromion patterns can appear in the solution. In a similar way, fractal dromion patterns and stochastic fractal excitations also exist for appropriate choices of the initial conditions.
Blue organic light-emitting diodes based on Mes2B [p-4,4′-biphenyl-NPh(1-naphthyl)]
Authors: Li Fenghong , Jia Wenli , Wang Suning , Zhao Yiqun , Lu Zheng-Hong
Published: February 2008

Here, we report highly efficient blue organic light-emitting diodes (OLEDs) with Mes2B [p-4,4′-biphenyl-NPh(1-naphthyl)] (BNPB) as a blue emitter. It is found that both efficiencies and electroluminescent color are very sensitive to the selection of electron transport materials in the devices. For an optimized structure [indium tin oxide/2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (1nm)∕N,N′-di(naphthalen-1-yl)-N,N′-diphenyl-benzidine (45nm)/BNPB (20nm)/1,3,5-tris(2-N-phenylbenzimidazolyl) benzene (30nm)/LiF (1nm)/Al] with BNPB as an undoped blue emitter, a maximum current efficiency can reach 3.5cd∕A. It is found that BNPB emits two distinct peaks, one of around 450nm and the other of 485nm, and their respective emission intensities depend on the nature of majority charge carrier in the emission layer.
Combustion-aided suspension plasma spraying of Y2O3 nanoparticles: Synthesis and modeling
Authors: Sun X. L. , Tok A. I. Y. , Lim S. L. , Boey F. Y. C. , Kang C. W. , Ng H. W.
Published: February 2008

Combustion-aided suspension plasma spraying (SPS) was developed for the synthesis of Y2O3 nanoparticles. Numerical models for Ar, Ar∕O2, and combustion-aided plasma fields were built using FLUENT V6.3.2© to compare their different plasma thermophysical properties. Modeling and experimental results both indicate that the plasma field was substantially altered by combustion-aided SPS. The plasma exhibited an elevated volume average temperature and reduced velocity as well as a broadened plasma plume, which resulted in an enhanced vapor supersaturation degree and a faster quenching rate in the radial direction. These can be attributed to the dual effects of oxygen dissociation/recombination and acetone solvent combustion. Consequently, productivity of the obtained nanoparticles increased remarkably and the particles’ morphology was improved, with a smaller mean particle size and a narrower size distribution in comparison with those of powder feeding spraying. Furthermore, plasma-induced cubic→monoclinic phase transformation in the as-sprayed Y2O3 particles was restrained by combustion-aided SPS to some extent.
Lower current operation of phase change memory cell with a thin TiO2 layer
Authors: Xu Cheng , Song Zhitang , Liu Bo , Feng Songlin , Chen Bomy
Published: February 2008

The phase change memory cell with 8nm TiO2 layer inserted between phase change material Ge2Sb2Te5 and bottom heating electrode tungsten was fabricated. It showed an advanced electrical threshold switching characteristics in the dc current-voltage measurement with the much lower value of threshold voltage of 1.5V. The reset current of the device cell decreased 68% compared with that without TiO2 layer. These results will contribute to the lower power consumption of the phase change memory. Besides that, the device cell showed good endurance characteristics, demonstrating the capability of random access memory application.
Large magnetization in high Gd concentration GaGdN and Si-doped GaGdN grown at low temperatures
Authors: Zhou Yi Kai , Choi Sung Woo , Emura Shuichi , Hasegawa Shigehiko , Asahi Hajime
Published: February 2008

GaGdN layers were grown at temperatures below 300°C by radio-frequency plasma-assisted molecular-beam epitaxy on sapphire substrates. GaGdN samples with high Gd concentration as high as 12.5% were obtained. X-ray diffraction results showed no obvious secondary phase, which means that the phase separation can be suppressed by the growth at low temperatures. Local structure around the Gd atom was investigated by extended x-ray absorption fine structure measurement using GdLIII edge. It was shown that Gd atoms were mainly incorporated into the Ga sites in the GaGdN layers. All the samples grown at low temperatures exhibited ferromagnetic characteristics. It is considerable that electrons coming from defects, especially, nitrogen vacancy, stabilize ferromagnetism, and that the carrier-induced ferromagnetism occurs in the low-temperature-grown GaGdN. Furthermore, Si was doped into GaGdN layers during growth in order to increase carrier density, and larger magnetization was observed.
Lack of charge offset drift is a robust property of Si single electron transistors
Authors: Hourdakis Emmanouel , Wahl Jeremy A. , Zimmerman Neil M.
Published: February 2008

One of the challenges that single-electron transistors (SETs) face before they can be considered technologically useful is the charge offset drift. Recently, two different types of Si SETs were shown to have a drift of only 0.01e (the fundamental charge) over several days. Those devices came from one fabrication source. Here, we present the results for Si SETs fabricated by our group (a different source) demonstrating their operation as SETs. We confirm that the charge offset drift is less than 0.01e, demonstrating the lack of charge offset drift is generic to Si devices and not dependent on the fabrication source.
A stable lotus-leaf-like water-repellent copper
Authors: Guo Zhi-Guang , Liu Wei-Min , Su Bao-Lian
Published: February 2008

The stable lotus-leaf-like superhydrophobic copper was fabricated by means of a very simple and industrially up scalable method. Under both the growth of CuO microcrystals on the surface and the chemical modification, the wettability of the copper substrate changed from hydrophilic to water-repellent superhydrophobic, with surface hierarchical structures similar to that of lotus leaf.
Probing a nonuniform two-dimensional electron gas with random telegraph signals
Authors: Chen Ming-Jer , Lee Chien-Chih , Lu Ming-Pei
Published: February 2008

We observe a sequence of two-level random telegraph signals (RTSs) in the drain/source current of a 1.7nm gate oxide silicon metal-oxide-semiconductor field-effect transistor. The RTS magnitude is transformed into the apparent Debye length around a negatively charged oxide trap. We achieve excellent reproduction of the Debye data (40 down to 5nm). This leads to the quantified area spanned by the dominant conductive percolation paths in the underlying two-dimensional electron gas (2DEG). We find that most of the 2DEG in inversion is recovered in a largest threshold voltage sample (∼0.35V), while for the lowest threshold (∼0.15V), a certain conductive filament is likely to occur. The gate direct tunneling current further corroborates the percolation picture.
Left-handed behavior of combined and fishnet structures
Authors: Lam V. D. , Kim J. B. , Lee S. J. , Lee Y. P.
Published: February 2008

The left-handed (LH) behavior of a combined structure of cut wire pair and continuous wire was experimentally studied. It was found that the LH behavior of a combined structure can still be observed as the width of cut wire pair increases until the cut wire joins the continuous wire, the so-called fishnet structure. These structures were designed, fabricated, and measured in the microwave frequency regime. In addition, we report the experimental results of the parametric study on the fishnet structure, which are also compared with the previous theoretical studies.
Estimation of second order phase transition temperature of the orthorhombic phase of Gd5(SixGe1−x)4 using Arrott plots
Authors: Hadimani R. L. , Melikhov Y. , Snyder J. E. , Jiles D. C.
Published: February 2008

Gd 5 ( Si x Ge 1 − x ) 4 for 0.41⩽x⩽0.5 is orthorhombic and ferromagnetic at lower temperature, monoclinic and paramagnetic at higher temperature, and shows a first order magnetic-structural phase transition between the two. Magnetic moment versus magnetic field (MH) isotherms were measured just above the first order transition temperature for Gd5Si1.95Ge2.05 and Gd5Si2Ge2 samples and the field-induced coupled phase transition from paramagnetic/monoclinic to ferromagnetic/orthorhombic phase was observed. Using the method developed by Arrott [Phys. Rev. 108, 1394 (1957)], the ferromagnetic portions of the MH isotherms were used to project the second order magnetic phase transition temperature of the orthorhombic phase, a region where the transition does not occur due to the first order transition at a lower temperature. These data points fall on the extrapolated line of the second order phase transition, drawn from the Si-rich region of the phase diagram.
Efficient coupling to W1 photonic crystal waveguide on InP membrane through suspended access guides
Authors: Talneau A. , Lee K. H. , Guilet S. , Sagnes I.
Published: February 2008

Suspended access ridges have been designed and integrated with a single-missing row photonic crystal guide on InP membrane in order to improve the coupling efficiency. This integration provides control of the injection into the photonic crystal (PhC) guide and a deterministic choice of the termination of the PhC. Low propagation losses have been measured for both the photonic crystal guide on InP membrane and the suspended ridges.
Picosecond photoexcitation of acoustic waves in locally canted gold films
Authors: Pezeril T. , Leon F. , Chateigner D. , Kooi S. , Nelson Keith A.
Published: February 2008

The laser photoacoustic technique is used to generate and detect picosecond coherent acoustic vibrations in gold film media deposited on Si substrates. As a consequence of the gold crystallites’ canted orientation, the pump-probe picosecond transient reflectivity shows oscillations at the fundamental shear mode frequency. The shear character of the mode is suggested by its dispersion, by the dependence of the signal on the probe laser wavelength, and by x-ray texture analysis.
Plasma/ion-controlled metal catalyst saturation: Enabling simultaneous growth of carbon nanotube/nanocone arrays
Authors: Levchenko I. , Ostrikov K.
Published: February 2008

It is shown that the simultaneous saturation of Ni nanoparticles used as catalyst for vertically aligned carbon nanotube and nanocone arrays can be improved in low-temperature plasma- or ion-assisted processes compared with neutral gas-based routes. The results of hybrid multiscale numerical simulations of the catalyst nanoarrays (particle sizes of 2 and 10nm) saturation with carbon show the possibility of reducing the difference in catalyst incubation times for smallest and largest catalyst particles by up to a factor of 2. This approach is generic and provides process conditions for simultaneous nucleation and growth of uniform arrays of vertically aligned nanostructures.
Improvement of the vacuum ultraviolet efficiency of low pressure Xe discharge by nitrogen admixture
Authors: Park Ki Wan , Hwang Hyeon Seok , Han Man Hyeop , Baik Hong Koo , Song Kie Moon
Published: February 2008

We investigated Xe–N2 gas discharge primarily as a source of vacuum ultraviolet for florescent lamps. The discharge performances of Xe based nitrogen admixture gas are improved when compared with the results of pure Xe discharge. The experimental results come from investigating the Xe positive column and were determined by measuring the infrared radiation during the discharge operation. These results suggest that the integrated infrared area is increased by about 40% under optimal conditions. This efficiency increase occurs because low energy electrons contribute to the production of exited nitrogen, which can excite Xe gas.
An anticorrosive magnesium/carbon nanotube composite
Authors: Endo M. , Hayashi T. , Itoh I. , Kim Y. A. , Shimamoto D. , Muramatsu H. , Shimizu Y. , Morimoto S. , Terrones M. , Iinou S. , Koide S.
Published: February 2008

Here, we report a drastically improved anticorrosive characteristic of magnesium alloy composites with the introduction of multiwalled carbon nanotubes. Highly depressed corrosion of nanotube-filled magnesium composite in salt water is due to the formation of stable oxide films along the grain boundaries of magnesium. Our results indicate that carbon nanotube acted as effective multifunctional filler to improve both mechanical and anticorrosive performances of magnesium alloy.
Structural and dielectric properties of epitaxial Sm2O3 thin films
Authors: Yang H. , Wang H. , Luo H. M. , Feldmann D. M. , Dowden P. C. , DePaula R. F. , Jia Q. X.
Published: February 2008

Epitaxial Sm2O3 thin films were deposited on (001) SrTiO3 substrates by pulsed laser deposition. The structural and dielectric properties were investigated. Microstructural studies by x-ray diffraction and transmission electron microscopy showed that the Sm2O3 thin films have a cubic structure and an epitaxial relationship of (004)Sm2O3∥(002)SrTiO3 and [440]Sm2O3∥[200]SrTiO3. A high dielectric constant of 30.5 was found, which can be attributed to the cubic structure and the high crystalline quality and shows a potential application of epitaxial Sm2O3 thin film for high-k material.
Enhanced green laser activation by antireflective gate structures in panel transistors
Authors: Shieh Jia-Min , Chen Chih , Lin Yu-Ting , Pan Ci-Ling
Published: February 2008

Antireflective gate structures of polycrystalline silicon (poly-Si) and silicon dioxide films enable postimplantation green continuous-wave laser annealing of all Si regions of green laser-crystallized panel Si transistors. About 40% of the incident laser-energy penetrates to the channels, owing to antireflective gate structures with the absorptive gate poly-Si, while 65% of the incident laser-energy enters the source/drain regions because of Fresnel reflections at the air/source (drain) interfaces. Such inverted laser-energy profiles and ascendant defect distributions along the channels/junctions/contact regions, yielded continuous, improved epilike Si microstructures over the entire active layer. The electron mobility of the transistors, 620cm2∕Vs, approaches that of integrated-circuits transistors.