bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced ferroelectricity in orthorhombic manganites Gd1−xHoxMnO3
Authors: Zhang G. Q. , Luo S. J. , Dong S. , Gao Y. J. , Wang K. F. , Liu J.-M.
Published: March 2011

A series of orthorhombic manganites Gd1−xHoxMnO3 (0 ≤ x ≤ 0.5) are synthesized. The Ho doping leads to a transition of paraelectric phase into ferroelectric one, making Gd1−xHoxMnO3 multiferroic. It is argued that the enhanced electric polarization originates from the transition of the A-type Mn3+ antiferromagnetic state into the spiral spin order driven by the reduction of Mn-O-Mn bond angle due to the doping. The noncollinear spin order of the A-site Ho3+ spins at high doping level may also make contribution to the polarization.
Magnetic phase transition and Mössbauer spectroscopy of ErNi2Mnx compounds
Authors: Wang J. L. , Campbell S. J. , Zeng R. , Dou S. X. , Kennedy S. J.
Published: March 2011

Investigation of ErNi2Mnx with 0.90 ≤ x ≤ 1.10 indicates that the MgCu2-type structure (with space group Fd-3m) is formed within x = 0.97−1.10. Curie temperature TC = 50 K of ErNi2Mn is significantly higher than those of the corresponding ErNi2 (TC = 7 K) and ErMn2 (TC = 15 K) compounds. Detailed analyses of DC magnetization data demonstrate that the magnetic phase transition at the Curie temperature is second order. The magnetic entropy change around TC has been found to be 4.8 J/kg K for a magnetic field change of 0 to 5 T with its relative cooling power ∼283 J/kg. 57Fe Mössbauer spectra below TC have been fitted with three sub-spectra representing three inequivalent local magnetic environments while the paramagnetic spectra are fitted using two sub-spectra for two inequivalent crystal sites (8a and 16d), which supports the conclusion based on Rietveld refinement that Mn atoms occupy at both 8a and 16d sites.
Spin torque switching in triple-quantum dot device with ferromagnetic contacts for memory applications
Authors: Xing M.-J. , Jalil M. B. A. , Tan S. G. , Jiang Y.
Published: March 2011

We investigate the applicability of a triple quantum dot (TQD) device for memory operation, in which information is coded by the magnetization of a ferromagnetic (FM) electrode. In the presence of Rashba spin-orbit coupling, a high spin polarization of current can be generated in the TQD device to induce spin transfer switching of the FM electrode. We evaluate the spin current and spin torque via the Keldysh nonequilibrium Green’s function method. The calculated spin torque can be reversed symmetrically by applying an opposite bias voltage, thus enabling current-induced magnetization switching to be applied for data writing. Additionally, the charge current shows a large modulation when the magnetization of the FM electrode is switched, a feature which can be utilized for reading data. The ability to write and read data demonstrates the applicability of the TQD device for spin transfer torque-based memory.
Competition of perpendicular magnetic anisotropy and exchange magnetic anisotropy in a Pt/Co/α-Cr2O3(0001) thin film
Authors: Shiratsuchi Yu , Noutomi Hayato , Oikawa Hiroto , Fujita Toshiaki , Nakatani Ryoichi
Published: March 2011

We investigated perpendicular magnetic anisotropy and exchange magnetic anisotropy in a Pt/Co/α-Cr2O3(0001) thin film grown on an α-Al2O3(0001) substrate. The film exhibits perpendicular magnetic anisotropy below a Co thickness of 1.2 nm at room temperature. Independent of the magnetic easy direction of the Co layer, the perpendicular exchange bias (PEB) appears in a direction perpendicular to the film below 80 K. The maximum unidirectional magnetic anisotropy energy estimated from the exchange bias field is 0.33 erg/cm2, which is higher than the reported PEB strength. The perpendicular exchange bias is accompanied by the in-plane remanent magnetization and an increase in the in-plane coercivity. We speculate that the increases in the in-plane remanent magnetization and the in-plane coercivity are caused by the spin canting of Cr3+ in the α-Cr2O3(0001) layer.
Development of micromagnetostrictive wireless controllable actuator
Authors: Lee Heung-Shik , Cho Chongdu , Zehnder Alan T. , Choi Kyu-won
Published: March 2011

This paper reports the design, fabrication, and performance characterization of a magnetostrictive microworm actuator. The suggested worm actuator is partially coated with NiFe film of 10 μm thickness. This actuator consists of a body plate of 50 μm thickness and four legs fabricated using SU-8 spin coating together with development and bonding process. Three square sections of NiFe film of 10 μm thickness are in turn electroplated on the top and bottom sides of the SU-8 body. The external magnetic fields are controlled for sinusoidal form of 3 Hz frequency. For the magnetomechanical characterization of the film, the magnetic moment is examined using a vibrating sample magnetometer. For assaying the movement of the actuator, the curvatures of each section under the applied external magnetic field are measured using a microscope measurement system with electromagnet set. The results show wave shape movement and maximum contractile distance between the end tips of legs is 0.777 mm.
Microwave complex permeability and permittivity of nanoferrites
Authors: Sharma Anjali , Afsar Mohammed N.
Published: March 2011

Complex permittivity and permeability of nanosized magnetic powders are studied for eight different bands to cover the frequency range from 2–40 GHz. A precise transmission-reflection based waveguide technique has been used to carry out measurements across the frequency bands. The algorithm for transmission and reflection calculations has been modified to account for variable sample thickness in the in-waveguide measurement setup. Diluted nanopowder sample has also been studied. The ferromagnetic resonance in nanoferrites has been observed to be sharper compared to microsized ferrites. Detailed analysis of measurement uncertainties and instrumentation errors has been performed.
Multiple diffraction in two-dimensional magnetophotonic crystals fabricated by the autocloning method
Authors: Baek Seungmin , Baryshev Alexander V. , Inoue Mitsuteru
Published: March 2011

Quasi-2D magnetophotonic crystals (MPCs) comprising bismuth-substituted yttrium iron garnet/silicon dioxide multilayers were fabricated on top of 1D structured substrates and evaluated. Optical and magneto-optical (MO) spectra showed that light coupling to the structure of these MPCs happened in multiple Bragg diffraction regimes, where a mixing of modes with resonant wavelengths occurred within MPCs and a demultiplexing phenomenon was observed. Responses from the crystals were studied in transmission and diffraction geometries. We show that nano-scale tailoring of MPCs’ structure allows one to increase significantly the MO efficiency of magnetic materials and invert their natural MO responses.
Dosimetric evaluation for exposure of patient to a z-gradient coil in magnetic resonance imaging
Authors: Lu Mai , Ueno Shoogo
Published: March 2011

In magnetic resonance imaging, time-varied gradient magnetic fields may stimulate nerves and muscles by inducing electric fields and currents in patients, which may potentially cause health problems. In this paper, a realistic z-gradient coil was numerically designed and the exposure level in a 3D real human man model was calculated by using the impedance method. It was found that the z-gradient coil produces a magnetic flux density (B-field) with two regions of good homogeneity along the coil length, separated by a very weak B-field in the middle of the coil. The spatially averaged B-field is 281 times greater than that of the International Commission on Non-Ionizing Radiation Protection’s (ICNIRP) reference level. The 1-cm2-averaged induced current density in the central nervous system is 87 times greater than that of the ICNIRP’s basic restriction. The maximum current density in all of the body tissues is above the nerve stimulation threshold.
‘Griffiths phase’ versus chemical disorder in low-doped manganites: La0.9Sr0.1MnO3 crystal revisited
Authors: Rozenberg E. , Auslender M. , Shames A.I. , Felner I. , Mogilyansky D. , Mukovskii Ya. M.
Published: March 2011

Magnetic properties, electron paramagnetic and ferromagnetic resonance were studied in the vicinity and above ferromagnetic-paramagnetic (FM-PM) phase transition of the La0.9Sr0.1MnO3 crystal. It appears that complex chemical/structural disorder inherent to manganites influences strongly on both magnetic and resonance properties of this crystal. In particular, it changes the nature of a FM–PM transition to the first- or mixed-order one and induces FM clustering in their PM state. The latter effect results in coexistence of resonance signals, and non-linearity of the PM inverse magnetic susceptibility versus temperature. This model seems to be much more realistic for description of the PM state in La0.9Sr0.1MnO3 than an idealized Griffiths phase approach.
Recent advances in the microstructure design of materials for near room temperature magnetic cooling (invited)
Authors: Lyubina Julia
Published: March 2011

Successful operation of a magnetic cooling device depends crucially on the performance of active magnetic refrigerant material. Extensive research activity has been concentrated on optimizing the magnetic properties of these materials by chemical composition modification. Here, it is shown how the design of appropriate microstructure can be used to control the magnetic properties as well as mechanical stability of refrigerant materials experiencing a first-order magnetic phase transition. In particular, introducing porosity in LaFe13−xSix alloys provides long-term stability by sacrificing only a small fraction of the magnetocaloric effect and results in the desired reduction of the magnetic and thermal hysteresis by a factor of 5, as compared to bulk alloys. Reducing crystallite size down to the nanometer range is shown to substantially lower magnetic hysteresis. On the other hand, the magnetocaloric effect is weakened by about 40% and 60% in alloys with grain size of 70 and 44 nm, respectively.
Oxide phosphors for light upconversion; Yb3+ and Tm3+ co-doped Y2BaZnO5
Authors: Etchart Isabelle , Hernández Ignacio , Huignard Arnaud , Bérard Mathieu , Laroche Marine , Gillin William P. , Curry Richard J. , Cheetham Anthony K.
Published: March 2011

The optical properties of Yb3+ and Tm3+ co-doped Y2BaZnO5, synthesized by solid-state reaction, are investigated in detail. Three main emission bands centered around 479 nm (blue), 654 nm (red), and 796 nm (near-infrared) are observed under near-infrared laser excitation via an upconversion process. Detailed studies of the upconversion properties as a function of dopant concentrations are described and upconversion efficiencies quantified precisely. Maximum efficiencies of ∼ 1.53% in the 730-870 nm near-infrared emission range and of ∼ 0.09% in the 420-530 nm blue range are obtained. The results of power dependence studies and concentration dependent lifetime measurements are presented. This in-depth spectroscopic study allows us, for the first time, to identify the dominant processes involved in the upconversion mechanism of Yb3+, Tm3+ co-doped Y2BaZnO5 oxides.
Liquid crystal alignment on polymer line gratings
Authors: Schenck Walter , Ko Doo-Hyun , Samulski Edward
Published: March 2011

Liquid crystal alignment on polymer line gratings fabricated by a soft lithography embossing process derived from PRINTTM (Pattern Replication In Nonwetting Template) is influenced by mold removal (peel-off direction). This indicates the existence of two competing alignment mechanisms: (1) topography (i.e., the Beremann mechanism) and (2) surface modification during peel-off. The degree to which mold removal influenced liquid crystal alignment was found to be dependent on the primary structures of the embossed polymer, and the chemical composition of the mold. These findings suggest alternate ways to affect liquid crystal alignment in roll-to-roll manufacturing.
X-ray photoelectron spectroscopy study on Fe and Co catalysts during the first stages of ethanol chemical vapor deposition for single-walled carbon nanotube growth
Authors: Oida Satoshi , McFeely Fenton R. , Bol Ageeth A.
Published: March 2011

Optimized chemical vapor deposition processes for single-walled carbon nanotube (SWCNT) can lead to the growth of dense, vertically aligned, mm-long forests of SWCNTs. Precise control of the growth process is however still difficult, mainly because of poor understanding of the interplay between catalyst, substrate and reaction gas. In this paper we use x-ray photoelectron spectroscopy (XPS) to study the interplay between Fe or Co catalysts, SiO2 and Al2O3 substrates and ethanol during the first stages of SWCNT forest growth. With XPS we observe that ethanol oxidizes Fe catalysts at carbon nanotube (CNT) growth temperatures, which leads to reduced carbon nanotube growth. Ethanol needs to be decomposed by a hot filament or other technique to create a reducing atmosphere and reactive carbon species in order to grow vertically aligned single-walled carbon nanotubes from Fe catalysts. Furthermore, we show that Al2O3, unlike SiO2, plays an active role in CNT growth using ethanol CVD. From our study we conclude that metallic Fe on Al2O3 is the most optimal catalyst/substrate combination for high-yield SWCNT forest growth, using hot filament CVD with ethanol as the carbon containing gas.
Switching surface polarization of atomic force microscopy probe utilizing photoisomerization of photochromic molecules
Authors: Aburaya Yoshihiro , Nomura Hikaru , Kageshima Masami , Naitoh Yoshitaka , Li Yan Jun , Sugawara Yasuhiro
Published: March 2011

An attempt to develop an atomic force microscopy (AFM) probe with optically switchable polarization is described. Modification with a single molecular layer of photochromic molecules was attempted onto a Si substrate that is a prototype for a probe surface. Polarization switching caused by alternate irradiation of UV and visible lights were detected using the electrostatic force?>spectroscopy (EFS) technique. Si substrates modified with spiropyran and azobenzene exhibited reversible polarization switching that caused changes in CPD of about 100 and 50 mV, respectively. Modification with spiropyran was also attempted onto a Si probe and resulted in a CPD change of about 100 mV. It was confirmed that modification of an AFM probe or substrate with a single molecular layer of photochromic molecules can generate surface polarization switching of a mechanically detectable level.
Note: The weak-correlation limit of the three-electron harmonium atom
Authors: Cioslowski Jerzy , Matito Eduard
Published: March 2011

Asymptotic energy expressions for the weak-correlation limits of the two lowest energy states of the three-electron harmonium atom are obtained in closed forms. When combined with the known results for the strong-correlation limit, these expressions, which are correct through the second order of perturbation theory, yield robust Padé approximants that allow accurate estimation of energies in question for all magnitudes of the confinement strength.
Generation of an amorphous graphite substrate by cumulative deuterium bombardment using molecular dynamics with full nonbonded interactions
Authors: Marian Jaime
Published: March 2011

A deuterated amorphous carbon target is generated from a fresh graphite layer via hyperthermal irradiation with deuterium ions using molecular dynamics (MD) simulations. We use interatomic potentials that include nonbonded (long-range) interactions for maximum accuracy and simulate cumulative bombardment up to doses of 5.80 × 1016 ions cm−2 at 1000 K. The graphite target goes through several stages of erosion and swelling, leading to complete amorphization and significant density loss. The calculations show a transition from graphitelike hybridization to a mixture of diamondlike and linear hybridizations with dose. It is concluded that the current sample sizes obtained directly by cumulative irradiation affordable with MD are not sufficiently large to be used for sputtering calculations under steady-state conditions.
Mesogenic linear azobenzene polymer-stabilized nematic liquid crystals
Authors: Bagramyan Arutyun , Thibault-Maheu Olivier , Galstian Tigran , Bessette André , Zhao Yue
Published: March 2011

We describe the detailed study of a polymer stabilized liquid crystal compound, which was created by using a reactive (monofunctional) azobenzene mesogenic guest and a nematic liquid crystal host. The resonant interaction of light with the azobenzene segment of the guest and the mesogenic nature of the latter enable the optical alignment of host molecules and the permanent fixing of that orientation by means of UV polymerization of the guest. We use dynamic spectral, polarimetric, and scattering techniques to study the orientational ordering and interaction of the guest–host system. We show that the uniform UV polymerization of this compound results in a low scattering material system with dielectric and elastic properties that are relatively close to those of the host, while still providing the capacity for optical configuration of its morphology.
Atomic layer deposited beryllium oxide: Effective passivation layer for III-V metal/oxide/semiconductor devices
Authors: Yum J. H. , Akyol T. , Lei M. , Hudnall T. , Bersuker G. , Downer M. , Bielawski C. W. , Lee J. C. , Banerjee S. K.
Published: March 2011

Electrical and physical characteristics of the atomic layer deposited beryllium oxide (BeO) grown on the Si and GaAs substrates were evaluated as a barrier/passivation layer in the III-V devices. Compared to Al2O3, BeO exhibits lower interface defect density and hysteresis, and smaller frequency dispersion and leakage current density at the same effective oxide thickness, as well as an excellent self-cleaning effect. These dielectric characteristics combined with its advantageous intrinsic properties, such as high thermal stability, large energy band-gap(10.6 eV), effective diffusion barrier, and low intrinsic structural defects, make BeO an excellent candidate for the interfacial passivation layer applications in the channel III-V devices.
First principles study on the local magnetic anisotropy near surfaces of Dy2Fe14B and Nd2Fe14B magnets
Authors: Tanaka Susumu , Moriya Hiroshi , Tsuchiura Hiroki , Sakuma Akimasa , Diviš Martin , Novák Pavel
Published: March 2011

The electronic structures of a (001) surface of crystalline Dy2Fe14B and Nd2Fe14B have been studied and the crystal field parameters at the rare-earth sites have been estimated by using first principles calculations. It is shown that Dy or Nd ions at the surface exhibit an in-plane magnetic anisotropy and can be nucleation sites of magnetization reversal.
Tracking the dynamics of translation and absolute orientation of a sphere in a turbulent flow
Authors: Zimmermann Robert , Gasteuil Yoann , Bourgoin Mickael , Volk Romain , Pumir Alain , Pinton Jean-François ,   International Collaboration for Turbulence
Published: March 2011

We study the six-dimensional dynamics—position and orientation—of a large sphere advected by a turbulent flow. The movement of the sphere is recorded with two high-speed cameras. Its orientation is tracked using a novel, efficient algorithm; it is based on the identification of possible orientation “candidates” at each time step, with the dynamics later obtained from maximization of a likelihood function. Analysis of the resulting linear and angular velocities and accelerations reveal a surprising intermittency for an object whose size lies in the inertial range, close to the integral scale of the underlying turbulent flow.
Improvement of four anode rods ion source
Authors: Abdel Salam F. W. , El-Khabeary H. , Ahmed M. M. , Abdel Reheem A. M.
Published: March 2011

In this work, an improved form of a saddle field ion source has been designed and constructed. It consists of four anode rods made from copper and two copper cathode discs. The two cathode discs are placed symmetrically on both sides of the four anode rods. The electrical discharge and output ion beam characteristics were measured at different pressures using argon gas. The optimum distance between each two anode rods was determined. Also the optimum distance between the four anode rods and any cathode disc was obtained. It was found that the optimum distance between each two anode rods equal to 6 mm, while the optimum distance between the four anode rods and any cathode disc equal to 16 mm, where a stable discharge current and maximum output ion beam current can be obtained. The effect of negative extraction voltage applied to both the extractor electrode and Faraday cup on the output ion beam current was studied. The sputter yield of copper and aluminum targets using argon ions of different energies was determined.
The dynamic effects on dissociation probability of H2–Pt(111) system by embedded atom method
Authors: Tokumasu Takashi , Ito Daigo
Published: March 2011

The effects of the motion of atoms or molecules on the dissociation probability of the H2–Pt(111) system were analyzed by molecular dynamics. The embedded atom method (EAM) was used to model the interaction between a Pt(111) surface and an H2 molecule to consider the dependence of electron density. Initially, the EAM potential was constructed to express the characteristics of the system, such as the electron density or dissociation barrier at certain sites and orientations, as obtained by density functional theory (DFT). Using this potential, simulations of an H2 molecule impinging on a Pt(111) surface were performed, and the characteristics of the collision were observed. These simulations were performed many times, changing the orientation of the H2 molecule, and a dynamic dissociation probability at each site against impinging energy was obtained. On the other hand, a static dissociation probability was defined from the dissociation barrier of a hydrogen molecule obtained by the EAM potential. These results were compared to one another, and the effects of the motion of atoms or molecules, which were called dynamic effects, on the dissociation probability were analyzed. The dynamic effects on the dissociation phenomena were very large at the top site, but were small at bridge or fcc sites.
Fast soliton-like charge pulses in insulating polymers
Authors: Dissado L. A. , Montanari G. C. , Fabiani D.
Published: March 2011

A previously unknown mode of conduction is identified in insulating polymers at moderate fields (40–50 MV/m). This takes the form of coherent charged pulses with a mobility (∼10−10 m2V−1s−1) several orders of magnitude larger than that traditionally associated with independent charge carriers (∼10−14 m2V−1s−1). It is shown that this phenomenon is consistent with a mechanism in which a charged compression boundary is formed electro-mechanically during injection and thereafter travels as a coherent solitary wave (soliton) through the polymer.
Study of the relative performance of silicon and germanium nanoparticles embedded gate oxide in metal–oxide–semiconductor memory devices
Authors: Chakraborty G. , Sengupta A. , Requejo F. G. , Sarkar C. K.
Published: March 2011

In the present work, we have investigated a comparative performance of the silicon (Si) and germanium (Ge) nanoparticles embedded SiO2 floating gate MOS memory devices. In such devices for low applied fields, the tunneling current is dominated by the direct tunneling mechanism, whereas for higher electric fields, the Fowler–Nordheim tunneling mechanism dominates. As the device dimensions get smaller, problem arises in the conventional MOS memory devices due to the leakage through the thin tunnel oxide. This leakage can be reduced via charge trapping by embedding nanoparticles in the gate dielectric of such devices. Here one objective is to prevent the leakage due to the direct tunneling mechanism and the other objective is to reduce the write voltage, by lowering the onset voltage of the Fowler–Nordheim tunneling mechanism. Our simulations for the current voltage characteristics covered both the low and the high applied field regions. Simulations showed that both the Si and the Ge nanoparticles embedded gate dielectrics offer reduction of the leakage current and a significant lowering of the writing or programming onset voltage, compared to the pure SiO2 gate dielectric. In terms of the comparative performance, the Germanium nanoparticles embedded gate dielectric showed better results compared to the silicon nanoparticles embedded one. The results of the simulations are discussed in the light of recent experimental results.
Heating of ions by low-frequency Alfvén waves in partially ionized plasmas
Authors: Dong Chuanfei , Paty Carol S.
Published: March 2011

In the solar atmosphere, the chromospheric and coronal plasmas are much hotter than the visible photosphere. The heating of the solar atmosphere, including the partially ionized chromosphere and corona, remains largely unknown. In this letter, we demonstrate that the ions can be substantially heated by Alfvén waves with very low frequencies in partially ionized low-beta plasmas. This differs from other Alfvén wave related heating mechanisms such as ion-neutral collisional damping of Alfvén waves and heating described by previous work on resonant Alfvén wave heating. We find that the nonresonant Alfvén wave heating is less efficient in partially ionized plasmas than when there are no ion-neutral collisions, and the heating efficiency depends on the ratio of the ion-neutral collision frequency to the ion gyrofrequency.
Late stage spreading of stratified liquids: Theory
Authors: Ausserré D. , Buraud J.-L.
Published: March 2011

Spreading of a liquid crystal droplet on a solid surface resembles the collapse of a zigguratlike structure and ends up with only two molecular terraces. A model is proposed to describe the time evolution of this late stage structure. It differs from the previous de Gennes–Cazabat theory by several aspects: (1) it avoids previous approximations and gives exact solutions of the kinetic equations; (2) it covers strongly layered liquids such as smectic liquid crystals; (3) it introduces the twodimensional Laplace pressure as an essential motor for spreading; (4) it takes into account the liquid/gas transition in the surface layer that was consistently reported in experiments with 8CB.
An orbital-invariant internally contracted multireference coupled cluster approach
Authors: Evangelista Francesco A. , Gauss Jürgen
Published: March 2011

We have formulated and implemented an internally contracted multireference coupled cluster (ic-MRCC) approach aimed at solving two of the problems encountered in methods based on the Jeziorski–Monkhorst ansatz: (i) the scaling of the computational and memory costs with respect to the number of references, and (ii) the lack of invariance of the energy with respect to rotations among active orbitals. The ic-MRCC approach is based on a straightforward generalization of the single-reference coupled cluster ansatz in which an exponential operator is applied to a multiconfigurational wave function. The ic-MRCC method truncated to single and double excitations (ic-MRCCSD) yields very accurate potential energy curves in benchmark computations on the Be + H2 insertion reaction, the dissociation of hydrogen fluoride, and the symmetric double dissociation of water. Approximations of the ic-MRCC theory in which the Baker–Campbell–Hausdorff expansion is truncated up to a given number of commutators are found to converge quickly to the full theory. In our tests, two commutators are sufficient to recover a total energy within 0.5 mEh of the full ic-MRCCSD method along the entire potential energy curve. A formal analysis shows that the ic-MRCC method is invariant with respect to rotation among active orbitals, and that the orthogonalization procedure used to produce the set of linearly independent excitation operators plays a crucial role in guaranteeing the invariance properties. The orbital invariance was confirmed in numerical tests. Moreover, approximated versions of the ic-MRCC theory based on a truncated Baker–Campbell–Hausdorff expansion, preserve the orbital invariance properties of the full theory.
Monopole antenna arrays for optical trapping, spectroscopy, and sensing
Authors: Çetin A. E. , Yanik Ahmet Ali , Yilmaz Cihan , Somu Sivasubramanian , Busnaina Ahmed , Altug Hatice
Published: March 2011

We introduce a nanoplasmonic platform merging multiple modalities for optical trapping, nanospectroscopy, and biosensing applications. Our platform is based on surface plasmon polariton driven monopole antenna arrays combining complementary strengths of localized and extended surface plasmons. Tailoring of spectrally narrow resonances lead to large index sensitivities (S∼675 nm/RIU) with record high figure of merits (FOM∼112.5). These monopole antennas supporting strong light localization with easily accessible near-field enhanced hotspots are suitable for vibrational nanospectroscopy and optical trapping. Strong optical forces (350 pN/W/μm2) are shown at these hotspots enabling directional control with incident light polarization.
Single molecule actuation and detection on a lab-on-a-chip magnetoresistive platform
Authors: Chaves R. C. , Bensimon D. , Freitas P. P.
Published: March 2011

On-chip magnetic tweezers based on current loops were integrated with magnetoresistive sensors. Magnetic forces up to 1.0±0.3pN are produced to actuate on DNA anchored to the surface of a flow cell and labeled with micrometer-sized magnetic beads. The levitation of the beads stretches the immobilized DNA. The relative position of the magnetic beads is monitored using spin-valve sensors. A bead vertical displacement resolution of 60nm is derived for DNA molecular motor activity in a tweezer steady current regime.
Neutron Compton scattering investigation of sodium hydride: From bulk material to encapsulated nanoparticulates in amorphous silica gel
Authors: Seel A. G. , Sartbaeva A. , Mayers J. , Ramirez-Cuesta A. J. , Edwards P. P.
Published: March 2011

In this study we utilize neutron Compton scattering (NCS) to determine differences in nuclear momentum distributions in NaH, both as bulk material and encapsulated as nanoscale particles (from 20 to 50 nm in diameter) within an amorphous silica-gel matrix (SiGNaH). In addition, elemental Na dispersed in such a matrix is also studied (SiGNa). Data treatment and fitting of experimental spectra yields comparison of the nuclear Compton profiles and radial momentum distributions for the proton in both bulk NaH and nanoscale SiGNaH, with resultant proton kinetic energies being in agreement with previous inelastic neutron studies of bulk NaH. Slight differences in proton radial momentum distributions for bulk and nanoscale systems are witnessed and discussed. The technique of stoichiometric-fixing is applied to the backscattering spectra of each system in order to examine changes in the Na profile width, and NCS is shown to be sensitive to the chemical environment change of this heavier nucleus. Examination of the Si and O profile widths in the gel samples also supports this method.
Temperature and composition dependence of the Soret coefficient in Lennard-Jones mixtures presenting evaporation/condensation phase transition
Authors: Leonardi Erminia , D'Aguanno Bruno , Angeli Celestino
Published: March 2011

The thermodiffusive behavior of a Lennard-Jones binary mixture has been studied by using nonequilibrium molecular dynamics. In particular, the dependence of the Soret coefficient, ST, on the temperature and composition has been investigated, exploring a wide range of temperatures from 1000 K to the condensation temperature of the mixture. In a previous paper the dependence of ST on the temperature and the composition was studied for Lennard-Jones binary mixtures presenting mixing/demixing (consolute) phase transition, and the results allowed the formulation of a very simple expression with the computed values of ST in the one phase region outside the critical region closely fitted by the function [T − Tc(x1)]−1, with Tc(x1) the demixing temperature of the mixture under study. The results of the present work show that the same expression of ST can be found for the one phase region outside the evaporation/condensation region but now with Tc representing the condensation temperature of the mixture under study.
Relativistic Bursian diode equilibria
Authors: Ender A. Y. , Kuznetsov V. I. , Schamel H.
Published: March 2011

A comprehensive study of steady-states of a planar vacuum diode driven by a cold relativistic electron beam is presented. The emitter electric field as a characteristic function for their existence is evaluated in dependence of the diode length, the applied potential V, and the relativistic beam factor at injection γ0. It is used to classify the different branches of possible solutions, which encompass electron flows that are (i) transmitted through the diode completely, (ii) partially reflected from a virtual cathode (VC) either within the diode region or at the collector side, and (iii) reflected totally. As a byproduct, the V and γ0 dependences of both bifurcation points of the minimum potential and of the transmitted current are obtained and the ultrarelativistic limit, γ0⪢1, is performed. In this highly relativistic regime, the density of electrons appears to be constant across the diode region except for a small area around the VC.
Catalytic conversion reactions mediated by single-file diffusion in linear nanopores: Hydrodynamic versus stochastic behavior
Authors: Ackerman David M. , Wang Jing , Wendel Joseph H. , Liu Da-Jiang , Pruski Marek , Evans James W.
Published: March 2011

We analyze the spatiotemporal behavior of species concentrations in a diffusion-mediated conversion reaction which occurs at catalytic sites within linear pores of nanometer diameter. Diffusion within the pores is subject to a strict single-file (no passing) constraint. Both transient and steady-state behavior is precisely characterized by kinetic Monte Carlo simulations of a spatially discrete lattice–gas model for this reaction–diffusion process considering various distributions of catalytic sites. Exact hierarchical master equations can also be developed for this model. Their analysis, after application of mean-field type truncation approximations, produces discrete reaction–diffusion type equations (mf-RDE). For slowly varying concentrations, we further develop coarse-grained continuum hydrodynamic reaction–diffusion equations (h-RDE) incorporating a precise treatment of single-file diffusion in this multispecies system. The h-RDE successfully describe nontrivial aspects of transient behavior, in contrast to the mf-RDE, and also correctly capture unreactive steady-state behavior in the pore interior. However, steady-state reactivity, which is localized near the pore ends when those regions are catalytic, is controlled by fluctuations not incorporated into the hydrodynamic treatment. The mf-RDE partly capture these fluctuation effects, but cannot describe scaling behavior of the reactivity.
Electronic transmission selectivity in multiterminal graphitic nanorings
Authors: Girão Eduardo C. , Gomes Souza Filho Antônio , Meunier Vincent
Published: March 2011

Graphene based toroidal carbon nanostructures possess unique electronic properties induced by quantum confinement and cyclic boundary conditions imposed to the wave-functions along the circumference. We used a tight-binding approach to demonstrate that nanoribbon and nanotube based ring structures have energy-dependent selection rules for electron transmission, especially when they are connected to a large number of terminals.
A spintronic source of circularly polarized single photons
Authors: Asshoff Pablo , Merz Andreas , Kalt Heinz , Hetterich Michael
Published: March 2011

We present a spintronic single photon source which emits circularly polarized light, where the helicity is determined by an applied magnetic field. Photons are emitted from an InGaAs quantum dot inside an electrically operated spin light-emitting diode, which comprises the diluted magnetic semiconductor ZnMnSe. The circular polarization degree of the emitted light is high, reaching 83% at an applied magnetic field of 2 T and 96% at 6 T. Autocorrelation traces recorded in pulsed operation mode prove the emitted light to be antibunched. The two circular polarization states could be used for representing quantum states |0⟩ and |1⟩ in quantum cryptography implementations.
Improved electron injection in poly(9,9′-dioctylfluorene)- co-benzothiodiazole via cesium carbonate by means of coannealing
Authors: Vaynzof Yana , Kabra Dinesh , Chua Lay Lay , Friend Richard H.
Published: March 2011

We investigate the electron-injecting properties of a ZnO substrate modified by a thin layer of solution-processed Cs2CO3 into poly(9,9′-dioctylfluorene)-co-benzothiodiazole (F8BT). Ultraviolet photoemission spectroscopy studies reveal that in the case of coannealed F8BT/Cs2CO3 films, the Fermi level is pinned at the lowest unoccupied molecular orbital of the F8BT, indicating significant n-doping of the polymer. X-ray photoemission spectroscopy measurements reveal the presence of Cs2CO3 in the coannealed F8BT/Cs2CO3 films. I-V measurements in single carrier devices show a significant improvement in the electron injection of the coannealed F8BT/Cs2CO3, in agreement with the observed n-doping of the polymer upon coannealing.
Scaling of the hysteresis in the glass transition of glycerol with the temperature scanning rate
Authors: Wang Yi-Zhen , Li Ying , Zhang Jin-Xiu
Published: March 2011

By measuring the dependences of the temperature-dependent primary (“alpha”) dielectric relaxation time behavior on the temperature scanning rate for the glass-forming glycerol, we study the scaling of hysteresis at the glass transition in glycerol. Based on the Vogel–Fulcher–Tammann (VFT) expression and the Angell's fragility concept, notable correlations of the systematic kinetic fragility, and of the hysteresis effect in the vitrification/fusion “alpha”-relaxation process of glycerol, with the temperature scanning rate, were reasonably analyzed and discussed. It was observed that the kinetic fragility m and the apparent glass-transition temperature hysteresis width $\Delta T_g^a$ΔTga, respectively, scaled the temperature scanning rate q as m ≈ αmq−γ and $\Delta T_g^a$ΔTga ≈ A0 + αqβ, at which the exponents, γ and β, were suggested to be characteristic of the resistance to the structure change or fragility change of the system during the glass transition. The observed scaling laws are quite similar to the scaling power law for the thermal hysteresis in the first-order phase transition (FOPT) of solids, providing a significant insight into the hysteresis effect in the glass transition of the glass-forming liquids.
Circular polariscopic analysis of strains in a semi-insulating SiC wafer: Its high potential to complement the information obtained from monochromatic x-ray topography
Authors: Takeuchi Hideo
Published: March 2011

We demonstrate that circular polariscopy is highly sensitive to strains in SiC wafers. In the monochromatic x-ray topographic analysis, which is regarded as a fundamental characterization method, the image information is disappeared in various areas: x-ray topography is not always suitable to evaluate wafer-size regions. Using circular polarizer plates, we apply the polariscopic analysis, which reveals the inhomogeneous strain distributed in the whole wafer region; namely, the circular polariscopic map has the high potential to complement the conventional monochromatic x-ray topograph. From the phonon-frequency shift observed in the Raman scattering spectra, the maximum stress is estimated to be ∼490 MPa. The crystal-plane distortion causing the strains is confirmed from the appearance of the forbidden reflections in the θ−2θ x-ray diffraction pattern.
Measurement of volume resistivity/conductivity of metallic alloy in inhibited seawater by optical interferometry techniques
Authors: Habib K.
Published: March 2011

Optical interferometry techniques were used for the first time to measure the volume resistivity/conductivity of carbon steel samples in seawater with different concentrations of a corrosion inhibitor. In this investigation, the real-time holographic interferometry was carried out to measure the thickness of anodic dissolved layer or the total thickness, Utotal, of formed oxide layer of carbon steel samples during the alternating current (ac) impedance of the samples in blank seawater and in 5–20 ppm TROS C-70 inhibited seawater, respectively. In addition, a mathematical model was derived in order to correlate between the ac impedance (resistance) and the surface (orthogonal) displacement of the surface of the samples in solutions. In other words, a proportionality constant [resistivity (ρ) or conductivity (σ) = 1/ρ] between the determined ac impedance [by electrochemical impedance spectroscopy (EIS) technique] and the orthogonal displacement (by the optical interferometry techniques) was obtained. The value of the resistivity of the carbon steel sample in the blank seawater was found similar to the value of the resistivity of the carbon steel sample air, around 1 × 10−5 Ω cm. On the contrary, the measured values of the resistivity of the carbon steel samples were 1.85 × 107, 3.35 × 107, and 1.7 × 107 Ω cm in 5, 10, and 20 ppm TROS C-70 inhibited seawater solutions, respectively. Furthermore, the determined value range of ρ of the formed oxide layers, from 1.7 × 107 to 3.35 × 107 Ω cm, is found in a reasonable agreement with the one found in literature for the Fe oxide–hydroxides, i.e., goethite (α-FeOOH) and for the lepidocrocite (γ-FeOOH), 1 × 109 Ω cm. The ρ value of the Fe oxide–hydroxides, 1 × 109 Ω cm, was found slightly higher than the ρ value range of the formed oxide layer of the present study. This is because the former value was determined by a dc method rather than by an electromagnetic method, i.e., holographic interferometry with applications of EIS, i.e., ac method. As a result, erroneous measurements were recorded due to the introduction of heat to Fe oxide–hydroxides.
An experimental study on discharge mechanism of pulsed atmospheric pressure glow discharges
Authors: Huang Xiaojiang , Sun Liqun , Bao Yun , Zhang Jing , Shi J. J.
Published: March 2011

The discharge mechanism of pulsed atmospheric pressure glow discharges excited by the unipolar positive voltage pulses between two parallel plate electrodes with or without one dielectric barrier on the ground electrode in flowing helium has been characterized by nanosecond time resolved optical and electrical measurements. The uniform glow discharges can only be achieved when the voltage pulse duration is less than 1 μs with bare electrodes. With introducing a dielectric barrier on the ground electrode, a model of electrons traveling on the background ions between two discharge events is proposed to explain the discharge mechanism and characteristics in terms of discharge ignition, discharge spatial profile and discharge current amplitude.
Fourier transform infrared spectroscopic and theoretical study of water interactions with glycine and its N-methylated derivatives
Authors: Panuszko Aneta , Śmiechowski Maciej , Stangret Janusz
Published: March 2011

In this study we attempt to explain the molecular aspects of amino acids' hydration. Glycine and its N-methylated derivatives: N-methylglycine, N,N-dimethylglycine, and N,N,N-trimethylglycine were used as model solutes in aqueous solution, applying FT-IR spectroscopy as the experimental method. The quantitative version of the difference spectra method enabled us to obtain the solute-affected HDO spectra as probes of influenced water. The spectral results were confronted with density functional theory calculated structures of small hydration complexes of the solutes using the polarizable continuum model. It appears that the hydration of amino acids in the zwitterionic form can be understood allowing a synchronized fluctuation of hydrogen bonding between the solute and the water molecules. This effect is caused by a noncooperative interaction of water molecules with electrophilic groups of amino acid and by intramolecular hydrogen bond, allowing proton transfer from the carboxylic to the amine group, accomplishing by the chain of two to four water molecules. As a result, an instantaneous water-induced asymmetry of the carboxylate and the amino group of amino acid molecule is observed and recorded as HDO band splitting. Water molecules interacting with the carboxylate group give component bands at 2543 ± 11 and 2467 ± 15 cm−1, whereas water molecules interacting with protons of the amine group give rise to the bands at 2611 ± 15 and 2413 ± 12 cm−1. These hydration effects have not been recognized before and there are reasons to expect their validity for other amino acids.
Six-dimensional quasiclassical and quantum dynamics of H2 dissociation on the c(2 × 2)-Ti/Al(100) surface
Authors: Chen Jian-Cheng , Juanes-Marcos Juan Carlos , Woittequand Sylvain , Somers Mark F. , Díaz Cristina , Olsen Roar A. , Kroes Geert-Jan
Published: March 2011

Based on a slab model of H2 dissociation on a c(2 × 2) structure with Ti atoms in the first and third layers of Al(100), a six-dimensional (6D) potential energy surface (PES) has been built. In this PES, a molecular adsorption well with a depth of 0.45 eV is present in front of a barrier of height 0.13 eV. Using this PES, H2 dissociation probabilities are calculated by the classical trajectory (CT), the quasiclassical trajectory (QCT), and the time-dependent wave-packet (TDWP) method. The QCT study shows that trajectories can be trapped by the molecular adsorption well. Higher incident energy can lead to direct H2 dissociation. Vibrational pre-excitation is the most efficient way to promote direct dissociation without trapping. We find that both rotational and vibrational excitation have efficacies close to 1.0 in the entire range of incident energies investigated, which supports the randomization in the initial conditions making the reaction rate solely dependent on the total (internal and translational) energy. The H2 dissociation probabilities from quantum dynamics are in reasonable agreement with the QCT results in the energy range 50–200 meV, except for some fluctuations. However, the TDWP results considerably exceed the QCT results in the energy range 200–850 meV. The CT reaction probabilities are too low compared with the quantum dynamical results.
Nanorod solar cell with an ultrathin a-Si:H absorber layer
Authors: Kuang Yinghuan , van der Werf Karine H. M. , Houweling Z. Silvester , Schropp Ruud E. I.
Published: March 2011

We propose a nanostructured three-dimensional (nano-3D) solar cell design employing an ultrathin hydrogenated amorphous silicon (a-Si:H) n-i-p junction deposited on zinc oxide (ZnO) nanorod arrays. The ZnO nanorods were prepared by aqueous chemical growth at 80 °C. The photovoltaic performance of the nanorod/a-Si:H solar cell with an ultrathin absorber layer of only 25 nm is experimentally demonstrated. An efficiency of 3.6% and a short-circuit current density of 8.3 mA/cm2 were obtained, significantly higher than values achieved for planar or even textured counterparts with three times thicker (∼75 nm) a-Si:H absorber layers.
Direct creation of microdomains with positive and negative surface potential on hydroxyapatite coatings
Authors: Plecenik T. , Tofail S. A. M. , Gregor M. , Zahoran M. , Truchly M. , Laffir F. , Roch T. , Durina P. , Vargova M. , Plesch G. , Kus P. , Plecenik A.
Published: March 2011

A method for the direct patterning of electrostatic potential at the surface of hydroxyapatite is presented here. Microdomains of surface potential have been created on hydroxyapatite coatings by a 20 keV focused electron beam with minimal alterations of surface chemistry. The success of such approach has been confirmed by Kelvin probe force microscopy measurements, which show that this method is capable of creating micron sized positive and negative local electrostatic potential. The shape and potential difference of these domains were found to depend on the dose of total injected charge from the electron beam as well as the speed with which such charge is injected.