bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic coercivity and adjacent track erasure in longitudinal magnetic recording media
Authors: Abarra E. N. , Gill P. , Acharya B. R. , Choe G.
Published: May 2005

Adjacent track erasure (ATE) is investigated for longitudinal recording media with different remanent magnetization and thickness product. The dynamic switching field Hcrp for moment fraction p is found to be a good indicator of signal erasure due to ATE. Given the head fringing field, Hcrp curves can be used to predict ATE for long exposures. Conversely, from the signal degradation of neighboring tracks due to ATE, the average fringing fields at a particular distance from the write head can be estimated.
Effect of boron on the magnetic properties and exchange-coupling effect of FePtB-type nanocomposite ribbons
Authors: Chang C. W. , Chang H. W. , Chiu C. H. , Chang W. C.
Published: May 2005

Phase evolution and magnetic properties of melt-spun (Fe0.675Pt0.325)100−xBx (x=12–20) nanocomposite ribbons are investigated. For those ribbons spun at 45m∕s, followed with a 500°C isothermal annealing for 1–6h, the boron addition not only promotes disorder to order (γ→γ1) transformation but also leads to the formation of different kinds of Fe-borides. Pt exhibits a strong affinity to Fe during thermal processes in forming magnetically hard γ1(FePt) phase, leaving excess Fe to interact with B in forming Fe2B, Fe3B, or FeB. For x=12–18, all ribbons are composed of one hard phase, γ1-FePt, and three soft phases, γ-FePt, Fe2B, and Fe3B. But FeB also coexists for x=20. Through the exchange-coupling interaction between nanoscale γ1-FePt and multiple soft phases, record of magnetic properties of Br=9.4kG, Hci=7.5kOe, and (BH)max=14.0MGOe has been successfully developed in isotropic (Fe0.675Pt0.325)84B16 ribbons, where the reduced remanence ratio (σr∕σ12kOe) is as high as 0.86.
Practical parameter estimation through space harmonic method and experiment of permanent magnet linear synchronous motor for high accuracy field orient control
Authors: Jang Seok-Myeong , You Dae-Joon , Jang Won-Bum , Park Ji-Hoon
Published: May 2005

This paper presents the practical parameter estimation for a slotless air-cored permanent magnet linear synchronous motor (PMLSM) using an analytical method and experiment. In the analytical method, the linkage flux is calculated through the generalized magnetic vector potential obtained by the space harmonics and transfer relation with each region of permanent magnet (PM) mover, air gap, and winding stator. This linkage flux is used to estimate the dynamic parameters such as magnetization inductance, backemf, and thrust constant. Also, the resistance and self-inductance with one phase are obtained by the experiment. Therefore, dynamic simulation of a linear synchronous motor composed of dynamic parameters is performed by the nonrotating (d-q) voltage equation. In good agreement with the estimated parameter values, the experimental results confirm the validity of the analysis method and simulation.
Effects of Ag pinning layers on the magnetic properties of Fe∕Pt multilayer films
Authors: Wei D. H. , Chou S. C. , Chin T. S. , Yu C. C. , Liou Y. , Yao Y. D.
Published: May 2005

Tetragonal L10 ordered Fe∕Pt multilayers were prepared by molecular-beam epitaxy on Pt-buffered MgO(001) substrates at 500°C. An ultrathin Ag (0.5nm) layer was symmetrically inserted into [Fe∕Pt] bilayers with different periods to introduce defects or pinning sites at the interfaces of Ag and Fe∕Pt bilayers. The effects of Ag pinning layers in the Fe∕Pt multilayers have been studied. The insertion of Ag pinning layers effectively reduced the size of magnetic domains. The distribution of angular dependent coercivity of Fe∕Pt multilayers with inserted Ag pinning layers between zero and ten periods, indicates a tendency of the domain-wall motion behavior to be weakened but nucleation mode enhanced.
Effects of an ultrathin MgO inserted layer on the magnetic properties of FePt films
Authors: Wei D. H. , Chou S. C. , Chin T. S. , Yu C. C. , Liou Y. , Yao Y. D.
Published: May 2005

Face-centered-tetragonal L10 Fe∕Pt multilayers have been prepared by molecular-beam epitaxy on MgO (001) substrates at 500°C. An ultrathin MgO layer, 1, 3, and 5nm in thickness, respectively, was inserted into the middle of Fe∕Pt multilayers by using an e-beam evaporation without introducing any oxygen source. The insertion of MgO layer effectively reduced the average grain size and the size of magnetic domains. Out-of-plane coercivity of the FePt films decreased with increasing thickness of the MgO insert layer. It was found through the studies of angular dependent coercivity that upon MgO insertion the decrease in coercivity is originated from the weakening of domain-wall motion, while domain rotation is enhanced depicting a decoupling of intergrain interaction.
Numerical simulation of write-operation in a magnetic random access memory cell array with a magnetostatic interaction
Authors: Nozaki Y. , Terada H. , Matsuyama K.
Published: May 2005

The margin for selective write-operation in a current coincident scheme has been numerically evaluated by considering a magnetostatic interaction in a magnetic random access memory cell array. For a conventional method, the margin over 20% cannot be achieved as the cell size is smaller than 0.2×0.4μm2. This is mainly attributed to the degradation of field localization created by a conductor current. The minimum cell size ensuring the practical margin can be decreased to 0.16×0.24μm2 by using an opposing current flowing through neighboring conductors. The margin is found to be remarkably decreased as a current pulse width becomes less than 0.4 ns because of a gyromagnetic effect.
MRAM array with coupled soft-adjacent magnetic layer
Authors: Guo Yimin , Wang P. , Chen M.-M. , Horng C. , Min T. , Hong L. , Voegeli O. , Tong R. , Chen P. , Le S. , Chen J. , Zhong T. , Yang L. , Liu G. , Chen Y. , Shi S. , Yang K. , Tsang D.
Published: May 2005

Soft-adjacent magnetic layer (SAL) coupled MRAM arrays have been developed for high density, low current applications. Instead of using shape anisotropies, free layer elements have been used strongly coupled with their adjacent-soft magnetic bit lines, forming coupling anisotropies (perpendicular to bit line directions) on free layer elements to hold stored data. MRAM array test data show that the use of the coupling anisotropies is more stable, less dependent upon free element shape distortions, and give smaller switching variation at very low switching bit line currents. It is revealed that flux closure with SAL prevents free element from middle resistance state caused by vortex.
Magnetic properties of electroplated nano/microgranular NiFe thin films for rf application
Authors: Zhuang Y. , Vroubel M. , Rejaei B. , Burghartz J. N. , Attenborough K.
Published: May 2005

A granular NiFe thin film with large in-plane magnetic anisotropy and high ferromagnetic-resonance frequency developed for radio-frequency integrated circuit (IC) applications is presented. During the deposition, three-dimensional (3D) growth occurs, yielding NiFe grains (ϕ∼1.0μm). Nanonuclei (ϕ∼30–50nm) are observed in single NiFe grains by atomic-force microscopy (AFM). The in-plane magnetic anisotropy is estimated to be ∼50mT. The frequency-dependent complex permeability is extracted. By taking the NiFe film as a magnetic core, solenoid-type inductors are fabricated and demonstrated and show a high operating frequency (∼5.5GHz) with a maximum quality factor (∼3).
Bit yield improvement by precise control of stray fields from SAF pinned layers for high-density MRAMs
Authors: Yoshikawa M. , Kai T. , Amano M. , Kitagawa E. , Nagase T. , Nakayama M. , Takahashi S. , Ueda T. , Kishi T. , Tsuchida K. , Ikegawa S. , Asao Y. , Yoda H. , Fukuzumi Y. , Nagahara K. , Numata H. , Hada H. , Ishiwata N. , Tahara S.
Published: May 2005

A write-operating window with a 100% functional bit yield was successfully obtained by the control of stray fields from synthetic antiferromagnetic (SAF) pinned layers in conventional magnetic random access memories with rectangular magnetic tunneling junction bits. The stray fields were controlled by a newly developed ion-beam etching technique without causing damage and by a precise setting of the SAF pinned layer thickness, and are balanced with Néel coupling fields. As a result, it was found that symmetric switching astroid curves with no offset were obtained and switching distributions were minimized at the zero offset field.
Magnetomechanical properties of nanogranular Co–Fe–Al–O films
Authors: Pasquale M. , Sasso C. P. , Magni A. , Celegato F. , Sohn J. C. , Lim S. H.
Published: May 2005

Using different experimental techniques we analyze the interplay between the structure and the magnetomechanical behavior of soft nanogranular CoFeAlO films with thickness ranging from 125to550nm. The sputtered film is characterized by 40-nm FeCo grains and a saturation magnetization of 16kG. The results show that, due to the role of the mechanically stiff and insulating Al–O matrix, an increase of the resistivity leads to an increase of the anisotropy field and also of the ferromagnetic resonance frequency. The 125-nm-thick films possess the best combination of anisotropy field and resistivity leading to an estimated ferromagnetic resonance frequency around 1.9GHz.
Nanocluster deposition for high density magnetic recording tape media
Authors: Qiu Jiao-Ming , Xu Yun-Hao , Judy Jack H. , Wang Jian-Ping
Published: May 2005

A technique for the fabrication of ultra-high density magnetic recording tape media with no risk of heating polymer substrate is reported. In this approach magnetic nanoparticles were generated by combining gas-phase nanocluster deposition and on-line heating techniques and deposited onto polymer substrate. Magnetic properties of the nanoparticles were optimized during their flight in vacuum prior to deposition. This technique is materials independent and it can fabricate nanocomposite films with high coercivity and very small film thickness. The fabricated magnetic nanoparticles have a uniform size distribution [for CoPt, 8.4% (standard deviation)] and well-defined spherical shape.
Improvement of writing margin in MRAM with novel shape
Authors: Oh S. C. , Lee J. E. , Kim H.-J. , Ha Y. K. , Bae J. S. , Nam K. T. , Kim E. S. , Park S. O. , Kim H. S. , Chung U-In , Moon J. T.
Published: May 2005

We suggest a type of “goggle” cell shape and discuss its switching mechanism in comparison with conventional shapes such as rectangular and elliptical shapes. For the goggle shapes, the dependence of the switching characteristics on the saturation magnetization, the free layer thickness, and the aspect ratio was studied. We found that the “L”-like astroid curve with an enlarged writing margin could be obtained from a goggle shape, especially when the aspect ratio is smaller than 2. This seems to be closely related with the kink formation. We also found that the writing margin could be improved further as the saturation magnetization and thickness of the free layer was optimized.
Galvanomagnetic phenomena in layered organic conductors (Review)
Authors: Kartsovnı̆k M. V. , Peschansky V. G.
Published: May 2005

The experimental research on galvanomagnetic phenomena in layered organic conductors at high magnetic fields is discussed in terms of the theoretical ideas about charge transfer phenomena in conductors with a metallic type of conductivity and a quasi-two-dimensional electron energy spectrum of arbitrary form. Attention is devoted mainly to the problem of recovering the dispersion relation of the conduction electrons in layered organic charge-transfer complexes from experimental studies of their magnetoresistance and quantum oscillation phenomena at low temperatures.
Simulation of the adsorption of simple gases on transition metals (Review)
Authors: Petrova N. V. , Yakovkin I. N. , Ptushinskiĭ Yu. G.
Published: May 2005

Results from simulations of the adsorption of gases on transition metal surfaces are presented. Attention is devoted mainly to the adsorption of hydrogen on the (110) surfaces of W and Mo, the structures and adsorption kinetics of oxygen and CO on the Pt(111) surface, and the catalytic reaction of CO oxidation. The choice of these systems is motivated not only by their practical importance and fundamental interest but also by the fact that substantial progress has been made toward understanding the processes of adsorption and the formation of film structures for them with the use of the Monte Carlo method. One of the main requisites for simulation of the adsorbed film structures is to adequately incorporate the lateral interaction between adsorbed molecules, which includes both a direct interaction (electrostatic and exchange) and indirect (via electrons of the substrate). The correct description of the lateral interaction in the simulation has permitted explanation of the mechanisms of formation of the structures of CO films on platinum. At the same time, the complexity of the interaction between adsorbed atoms has at yet precluded the development of a consistent model for the formation of the structure of adsorbed oxygen on the platinum surface. It can be hoped that this problem will soon be solved, making it possible to refine the model of the catalytic reaction of CO oxidation.
Commensurate vortex lattices and oscillation effects in superconducting Mo/Si and W/Si multilayers
Authors: Mikhailov M. Yu. , Yuzephovich O. I. , Bomze Yu. V. , Buchstab E. I. , Fogel N. Ya.
Published: May 2005

We report experimental results of a vortex lattice structure investigation in artificial superconducting Mo/Si and W/Si superlattices. Resistance R and critical current Ic measurements in parallel magnetic fields are performed as well as measurements in tilted magnetic fields. At temperatures where the condition of strong layering is satisfied the dependences Ic(H∥) and R(H∥) exhibit oscillatory behavior. It is shown that the appearance of oscillations and of reentrant behavior (vanishing of the resistivity in definite ranges of H∥) are due to the strong intrinsic pinning and to the effect of commensurability between the vortex lattice period and multilayer wavelength. The locations of Ic(H∥) and R(H∥) extrema correspond to the stable states of a commensurate vortex lattice. Our experimental data are in good quantitative agreement with the Ivlev, Kopnin, and Pokrovsky (IKP) theory. It is shown that the values of the commensurability fields depend exclusively on the superlattice period s and anisotropy coefficient γ and do not depend on the type of materials used for multilayer preparation. A memory effect, i.e., dependence of the oscillation pattern on the magnetic history of the sample, is observed. It is shown experimentally that the state of the vortex matter in the layered superconductors is essentially different from that of type-II superconductors with a random distribution of the pinning centers. Investigation of oscillation and reentrance behavior may be used as a new tool for the study of the vortex lattice arrangement in layered superconductors. The essential advantage of this method is connected with its simplicity and with the possibility of using it in arbitrary large fields. Investigations of the commensurate states may be used for rather precise determination of the anisotropy coefficient γ.
Microwave impedance of YBa2Cu3O7−δ high-temperature superconductor films in a magnetic field
Authors: Pan V. M. , Luzhbin D. A. , Kalenyuk A. A. , Kasatkin A. L. , Komashko V. A. , Velichko A. V. , Lancaster M.
Published: May 2005

The temperature, field, and intensity (amplitude) dependences of the surface impedance of magnetron-sputtered YBa2Cu3O7−δ quasi-single-crystal films on a sapphire substrate with a CeO2 buffer layer were measured. The measurements were performed with a coplanar resonator at 5.25 GHz in a weak constant magnetic field 0<B<12 mT in the temperature range 13 K <T<80 K. They made it possible to obtain the surface resistance and penetration depth versus the temperature and the magnetic field strength and to determine the contribution of Abrikosov vortices to the impedance. The cases with a frozen magnetic field and zero-field cooling with the field subsequently switched on at temperatures below the critical value were investigated separately. A substantial difference in the behavior of the high-frequency response of the vortices in these two cases was found. The Coffey-Clem and Brandt theories were used to study the linear response and the critical state model the nonlinear response of the vortices.
Negative thermal expansion of HTSC-type structures: low temperature structure measurements on Eu1+x(Ba1−yRy)2−xCu3O7−d compounds and theoretical treatment
Authors: Eremenko V. V. , Feodosyev S. B. , Gospodarev I. A. , Sirenko V. A. , Shvedun M. Yu. , McCallum W. , Tovar M.
Published: May 2005

The temperature dependences of the lattice parameters are investigated on the perovskite-like structures Eu1+x(Ba1−yRy)2−xCu3O7−d with Ba substitution by light rare earth, using x-ray diffraction techniques. A negative thermal expansion effect is observed and explained in detail.
Hexagonal ferrite: from macro- to nanocrystal
Authors: Mamluı̆ Yu. A. , Ol’khovik L. P.
Published: May 2005

The directions and most important results of studies of the fundamental magnetic properties of hexagonal ferrites performed at Kharkov National University over the last 50 years are reviewed. The influence of the basic factors (size, surface, and collective) specific to small particles and ensembles of small particles on the evolution of the magnetic properties under a transition from a macro- to a nanocrystal is analyzed in a section devoted to the topical subjects “Nanophysics and nanotechnology of barium ferrite.”
Level statistics for quantum Hall systems
Authors: Kagalovsky V. , Horovitz B. , Avishai Y.
Published: May 2005

Level statistics for two classes of disordered systems at criticality are analyzed in terms of different realizations of the Chalker-Coddington network model. These include: 1) Re-examination of the standard U(1) model describing dynamics of electrons on the lowest Landau level in the quantum Hall effect, where it is shown that after proper local unfolding the nearest-neighbor spacing distribution (NNSD) at the critical energy follows the Wigner surmise for Gaussian unitary ensembles (GUE). 2) Quasi-particles in disordered superconductors with broken time reversal and spin rotation invariance (in the language of random matrix theory this system is a representative of symmetry class D in the classification scheme of Altland and Zirnbauer). Here again the NNSD obeys the Wigner surmise for GUE, reflecting therefore only “basic” discrete symmetries of the system (time reversal violation) and ignoring particle-hole symmetries and other finer details (criticality). In the localized regime level repulsion is suppressed.
Contribution to the theory of galvanomagnetic phenomena in polycrystalline metals
Authors: Kaganova I. M. , Kaganov M. I.
Published: May 2005

An algorithm is constructed for calculating the effective conductivity tensor of polycrystals in a magnetic field from the values of the galvanomagnetic characteristics of crystallites. The algorithm is based on a series expansion in powers of the deviations of the tensors from their average values. The effective conductivity tensor is calculated in two limiting cases: in a weak magnetic field for metals with any electronic energy spectrum and in a strong magnetic field for metals with a closed Fermi surface (in this case the initial equations come from the theory of galvanomagnetic phenomena which employs the solution of the classical Boltzmann equation for the distribution function of electrons with an arbitrary dispersion law). The formulas obtained for polycrystals of cubic metals in a weak magnetic field and metals with closed Fermi surfaces in strong fields have the same accuracy as the initial expressions.
New type of topological electronic transition in metals with a change in the Fermi energy
Authors: Makarov V. I. , Bolotov D. V. , Gor’kavyı̆ V. A. , Yatsenko A. A.
Published: May 2005

A new type of electronic topological transition due to an abrupt change in the differential-geometric characteristics of the Fermi surface, whose topology remains unchanged, at some critical energy εd is predicted. This type of electronic topological transition differs from known electronic topological transitions due to a change in the topology of the Fermi surface in that the isoenergy surface ε(p)=εd does not contain any singular points where the velocity of the electrons vanishes. It is shown that a feature common to both types of electronic topological transitions associated with an abrupt change in the topology of the Fermi surface and its differential-geometric characteristics with no change in topology is that a qualitative change occurs in the spherical image of the Fermi surface as a result of the abrupt change in the number of pre-images of a point under a spherical mapping.
Noninteracting electrons in one-dimensional systems
Authors: Gantmakher V. F.
Published: May 2005

The theoretical fundamentals for describing the behavior of noninteracting electrons in one-dimensional systems are presented: the transport characteristics of an ideal wire connecting two thermostats; a description of elastic scattering by a chaotic sequence of barriers using Landauer’s formula; gigantic chaotic oscillations of the resistance; localization; and, the influence of correlations in a random potential on the localization.
Transmission of electrons through a linear molecule: role of delocalized and localized electronic states in current formation
Authors: Petrov É. G.
Published: May 2005

Exact formulas are obtained for the electronic current in the presence of quasielastic and elastic transmission of an electron through a molecule. The elastic transmission mechanism is analyzed in detail. It is shown that “metallization” of a molecule occurs in the presence of electron delocalization, so that all energy levels of the molecule undergo the same shift when a potential difference is established between the electrodes. This explains the appearance of resonance peaks in the conductivity of the molecule. When an electron in the molecule is strongly localized the appearance of conductivity peaks is due to resonance hopping of the electron between the Fermi levels of the electrodes and localized levels of the molecule, with which the appearance of negative conductivity of the molecule is also associated.
Pressure effect on the Fermi surface and electronic structure of LuGa3 and TmGa3
Authors: Pluzhnikov V. B. , Grechnev G. E. , Czopnik A. , Eriksson O.
Published: May 2005

The Fermi surfaces and cyclotron masses of LuGa3 and TmGa3 compounds are studied by means of the de Haas-van Alphen effect technique under pressure. Highly anisotropic pressure dependences of the de Haas-van Alphen frequencies and cyclotron masses are observed in both compounds. Concurrently, ab initio calculations of the volume-dependent band structures are been carried out for these compounds, including the ferromagnetic-configuration phase of TmGa3, by employing a relativistic version of the full-potential linear muffin-tin orbital method within the local spin-density approximation. The experimental data are analyzed on the basis of the calculated volume-dependent band structures and compared with the corresponding pressure effects in the isostructural compound ErGa3.
Magnetic resonance and magnetic anisotropy oscillations in Co/Cu (111) superlattices
Authors: Kaplienko A. I. , Nikolova É. P. , Kut’ko K. V. , Anders A. G. , Zorchenko V. V. , Stetsenko A. N.
Published: May 2005

Magnetic resonance was studied in magnetic fields parallel or perpendicular to the film plane in magnetron-sputtered [Co(8 Å)/Cu(dCu)(111)]20 multilayers. Oscillations of the magnetic anisotropy KA and the width ΔHres of the resonance line as a function of the thickness of the copper interlayers were found in the interval dCu=7–19 Å. Extrema of KA and ΔHres were observed at dCu=nd(111), where n is an integer or half-integer, and d(111)=2.087 Å—the distance between the (111) planes in Cu. In addition, the distances between the neighboring maxima or minima were 1, 1.5, and 2d(111). The KA and ΔHres oscillations occurred synchronously with oscillations of the resistivity at saturation (in the field H=15 kOe) and oscillations of the magnetoresistance. An interlayer antiferromagnetic exhange interaction was found in the ranges dCu=8–11 Å and dCu⩾18 Å. The effects observed were due to nonmonotonic variation of the interlayer interface roughness with increasing dCu.
Global optimization of bimetallic cluster structures. I. Size-mismatched Ag–Cu, Ag–Ni, and Au–Cu systems
Authors: Rapallo Arnaldo , Rossi Giulia , Ferrando Riccardo , Fortunelli Alessandro , Curley Benjamin C. , Lloyd Lesley D. , Tarbuck Gary M. , Johnston Roy L.
Published: May 2005

A genetic algorithm approach is applied to the optimization of the potential energy of a wide range of binary metallic nanoclusters, Ag–Cu, Ag–Ni, Au–Cu, Ag–Pd, Ag–Au, and Pd–Pt, modeled by a semiempirical potential. The aim of this work is to single out the driving forces that make different structural motifs the most favorable at different sizes and chemical compositions. Paper I is devoted to the analysis of size-mismatched systems, namely, Ag–Cu, Ag–Ni, and Au–Cu clusters. In Ag–Cu and Ag–Ni clusters, the large size mismatch and the tendency of Ag to segregate at the surface of Cu and Ni lead to the location of core-shell polyicosahedral minimum structures. Particularly stable polyicosahedral clusters are located at size N=34 (at the composition with 27 Ag atoms) and N=38 (at the composition with 32 and 30 Ag atoms). In Ag–Ni clusters, Ag32Ni13 is also shown to be a good energetic configuration. For Au–Cu clusters, these core-shell polyicosahedra are less common, because size mismatch is not reinforced by a strong tendency to segregation of Au at the surface of Cu, and Au atoms are not well accommodated upon the strained polyicosahedral surface.
Global optimization of bimetallic cluster structures. II. Size-matched Ag-Pd, Ag-Au, and Pd-Pt systems
Authors: Rossi Giulia , Ferrando Riccardo , Rapallo Arnaldo , Fortunelli Alessandro , Curley Benjamin C. , Lloyd Lesley D. , Johnston Roy L.
Published: May 2005

Genetic algorithm global optimization of Ag-Pd, Ag-Au, and Pd-Pt clusters is performed. The 34- and 38-atom clusters are optimized for all compositions. The atom-atom interactions are modeled by a semiempirical potential. All three systems are characterized by a small size mismatch and a weak tendency of the larger atoms to segregate at the surface of the smaller ones. As a result, the global minimum structures exhibit a larger mixing than in Ag-Cu and Ag-Ni clusters. Polyicosahedral structures present generally favorable energetic configurations, even though they are less favorable than in the case of the size-mismatched systems. A comparison between all the systems studied here and in the previous paper (on size-mismatched systems) is presented.
The spectroscopic signature of the “all-surface” to “internally solvated” structural transition in water clusters in the n=17–21 size regime
Authors: Lagutschenkov Anita , Fanourgakis George S. , Niedner-Schatteburg Gereon , Xantheas Sotiris S.
Published: May 2005

The existence of a transitional size regime where preferential stabilization alternates between “all-surface” (all atoms on the surface of a cluster) and “internally solvated” (one water molecule at the center of the cluster, fully solvated) configurations with the addition or the removal of a single water molecule, predicted earlier with the flexible, polarizable (many-body) Thole-type model interaction potential (TTM2-F), has been confirmed from electronic structure calculations for (H2O)n, n=17–21. The onset of the appearance of the first “interior” configuration in water clusters occurs for n=17. The observed structural alternation between interior (n=17, 19, 21) and all-surface (n=18, 20) global minima in the n=17–21 cluster regime is accompanied by a corresponding spectroscopic signature, namely, the undulation in the position of the most redshifted OH stretching vibrations according to the trend: interior configurations exhibit more redshifted OH stretching vibrations than all-surface ones. These most redshifted OH stretching vibrations form distinct groups in the intramolecular region of the spectra and correspond to localized vibrations of donor OH stretches that are connected to neighbors via “strong” (water dimer-like) hydrogen bonds and belong to a water molecule with a “free” OH stretch.
Interaction potentials of the RG–I anions, neutrals, and cations (RG=He, Ne, Ar)
Authors: Buchachenko A. A. , Tscherbul T. V. , Kłos J. , Szczȩśniak M. M. , Chałasiński G. , Webb R. , Viehland L. A.
Published: May 2005

Interaction potentials of the iodine atom, atomic cation, and anion with light rare-gas atoms from He to Ar are calculated within the unified ab initio approach using the unrestricted coupled-cluster with singles and doubles and perturbative treatment of triples correlation treatment, relativistic small-core pseudopotential, and an extended basis set. Ab initio points are fit to a flexible analytical function. The calculated potentials are compared with available literature data, assessed in the I−-and I+-ion mobility calculations and the Ar–I−-anion zero electron kinetic-energy spectra simulations, and analyzed using the correlation rules. The results indicate a high precision of the reported potentials.
Time reversal and n-qubit canonical decompositions
Authors: Bullock Stephen S. , Brennen Gavin K. , O’Leary Dianne P.
Published: May 2005

On pure states of n quantum bits, the concurrence entanglement monotone returns the norm of the inner product of a pure state with its spin-flip. The monotone vanishes for n odd, but for n even there is an explicit formula for its value on mixed states, i.e., a closed-form expression computes the minimum over all ensemble decompositions of a given density. For n even a matrix decomposition ν=k1ak2 of the unitary group is explicitly computable and allows for study of the monotone’s dynamics. The side factors k1 and k2 of this concurrence canonical decomposition (CCD) are concurrence symmetries, so the dynamics reduce to consideration of the a factor. This unitary a phases a basis of entangled states, and the concurrence dynamics of u are determined by these relative phases. In this work, we provide an explicit numerical algorithm computing ν=k1ak2 for n odd. Further, in the odd case we lift the monotone to a two-argument function. The concurrence capacity of ν according to the double argument lift may be nontrivial for n odd and reduces to the usual concurrence capacity in the literature for n even. The generalization may also be studied using the CCD, leading again to maximal capacity for most unitaries. The capacity of ν⊗I2 is at least that of ν, so odd-qubit capacities have implications for even-qubit entanglement. The generalizations require considering the spin-flip as a time reversal symmetry operator in Wigner’s axiomatization, and the original Lie algebra homomorphism defining the CCD may be restated entirely in terms of this time reversal. The polar decomposition related to the CCD then writes any unitary evolution as the product of a time-symmetric and time-antisymmetric evolution with respect to the spin-flip. En route we observe a Kramers’ nondegeneracy: the existence of a nondegenerate eigenstate of any time reversal symmetric n-qubit Hamiltonian demands (i) n even and (ii) maximal concurrence of said eigenstate. We provide examples of how to apply this work to study the kinematics and dynamics of entanglement in spin chain Hamiltonians.
Infrared spectra of the water-nitrogen complexes (H2O)2–(N2)n(n=1–4) in argon matrices
Authors: Hirabayashi Shinichi , Ohno Kayo , Abe Hisashi , Yamada Koichi M. T.
Published: May 2005

The infrared spectra of the water-nitrogen complexes trapped in argon matrices have been studied with Fourier transform infrared absorption spectroscopy. The absorption lines of the H2O–N21:1,1:2,1:n, and 2:1 complexes have been confirmed on the basis of the concentration effects. In addition, we have observed a few lines and propose the assignments for the 2:2,2:3, and 2:4 complexes in the ν1 symmetric stretching and ν2 bending regions of the proton-acceptor molecule, and in the bonded OH stretching region of the proton-donor molecule. The redshifts in the bonded OH stretching mode and blueshifts in the OH bending mode suggest that the hydrogen bonds in the (H2O)2–(N2)n complexes with n=1–4 are strengthened by the cooperative effects compared to the pure H2O dimer. Two absorption bands due to the 3:n complexes are also observed near the bonded OH stretching region of the H2O trimer.
Fully state-resolved photodissociation of formaldehyde, H2CO→H+HCO: K conservation and a rigorous test of statistical theories
Authors: Yin Hong-Ming , Nauta Klaas , Kable Scott H.
Published: May 2005

The photodissociation dynamics of the reaction H2CO+hν→H+HCO have been investigated in the range 60–400cm−1 above the reaction threshold. Supersonically cooled formaldehyde was excited into 15 specific J, Ka, Kc rotational states in two vibrational levels 214161 and 2241 in the Ã(A21) state. The laser-induced fluorescence spectra of the nascent HCO fragment provided detailed product state distributions (PSDs), resolved by N, Ka, Kc, and J. When just the overall molecular rotation N is considered the PSDs are in remarkable agreement with calculations based on phase space theory (PST). However, when the projection of N onto the molecular frame (Ka,Kc) is included the distributions show consistent deviations from PST. In particular, there is a tendency to preserve the initial parent rotational motion about the a and b axes. The effect is that states with higher initial Ka in H2CO produce higher final Ka in the HCO fragment. There is also a tendency for the upper/lower members of the asymmetry doublets in H2CO to map onto the same upper/lower set of product state asymmetry doublets. Finally, there are oscillations in some of the detailed PSDs that remain unexplained.
Experimental analysis and modified rotor description of the infrared fundamental band of HCl in Ar, Kr, and Xe solutions
Authors: Pérez J. , Padilla A. , Herrebout W. A. , Van der Veken B. J. , Hernández A. Calvo , Bulanin M. O.
Published: May 2005

We report an experimental study of the rotovibrational fundamental PQR-band shapes in the IR absorption spectra of HCl dissolved in condensed rare gases in a wide range of temperatures. The effective vibrational frequencies are determined from analysis of the fine rotational structure partially resolved in the band wings. The central Q-branch components appear redshifted with respect to the effective vibrational frequencies, their shifts in different solvents found to match the HCl stretching mode shifts in binary Rg⋯HCl van der Waals heterodimers. Theoretical quasi-free rotor and modified rotor models are applied to describe evolution of the band profiles at changing thermodynamic conditions. Both models are shown to reproduce equally well the observed spectral density distributions in the band wings. However, the modified rotor formalism that accounts for depopulation of the lower-energy rotational solute states provides better agreement with the experiment in the range of the P- and R-branch maxima. We surmise that the Q branches separated from the measured spectral profiles are formed by transitions between rotationally hindered states of diatomic molecules coupled to the solvent by the local anisotropy of the interaction potential.
An isoperimetric problem for leaky loops and related mean-chord inequalities
Authors: Exner Pavel
Published: May 2005

We consider a class of Hamiltonians in L2(R2) with attractive interaction supported by piecewise C2 smooth loops Γ of a fixed length L, formally given by −Δ−αδ(x−Γ) with α>0. It is shown that the ground state of this operator is locally maximized by a circular Γ. We also conjecture that this property holds globally and show that the problem is related to an interesting family of geometric inequalities concerning mean values of chords of Γ.
Simulations of crescent water wave patterns on finite depth
Authors: Kristiansen Ø. , Fructus D. , Clamond D. , Grue J.
Published: May 2005

A numerical study of the instabilities of Stokes waves on finite depth has been carried out using an efficient fully nonlinear method [D. Clamond and J. Grue, “A fast method for fully nonlinear water-wave computations,” J. Fluid Mech. 447, 337 (2001)]. First, attention is given to five-wave instabilities with k0h=O(1), k0 being the wavenumber and h the depth. Both instabilities leading to breaking and instabilities leading to recurrence are studied, yielding considerably different patterns than on infinite depth. Higher-order instabilities are exemplified, for the first time, by simulations of six- and seven-wave instabilities. Simulations of interactions between four- and five-wave instabilities show that a classical modulational instability can destabilize a three-dimensional perturbation causing crescent waves to appear, in accordance with the hypothesis of [M.-Y. Su and A. W. Green, “Coupled two- and three-dimensional instabilities of surface gravity waves,” Phys. Fluids 27, 2595 (1984)]. Also, a recurrent five-wave instability can boost the energy in a four-wave instability.
Where does photocurrent flow in polycrystalline CdS?
Authors: Azulay D. , Millo O. , Silbert S. , Balberg I. , Naghavi N.
Published: May 2005

We have studied the local photoconductance in polycrystalline CdS films using conductance atomic force microscopy under illumination, and found that photoconductivity along the grain boundaries is excited at photon energies significantly smaller than the CdS band gap, Eg, whereas phototransport through the grains is detected only above Eg. In addition, we observed a rather strong persistent photoconductivity effect at both conduction channels. The implications of these findings regarding the band tails in CdS films and photovoltaic applications are discussed.
The triplet channel in the photodissociation of ozone in the Hartley band: Classical trajectory surface hopping analysis
Authors: Qu Z.-W. , Zhu H. , Grebenshchikov S. Yu. , Schinke R.
Published: May 2005

The triplet channel in the photodissociation of ozone in the Hartley band, O3+hν→O(P3)+O2(Σ3), is investigated by means of a classical trajectory surface hopping method using ab initio diabatic potential energy surfaces for the B and the R states. Because of the strong recoil in the R state along the breaking O–O bond, O2(Σ3) is produced with a high rotational energy. The nonadiabatic transition probability depends markedly on the coordinate along the crossing seam. As a consequence a unique correlation is found between the internuclear geometry at the crossing and the final vibrational state of O2(Σ3). The calculated distribution of the translational energy is in good accord with the measured distribution.
Improvement of efficiency of dye-sensitized solar cells by reduction of internal resistance
Authors: Han Liyuan , Koide Naoki , Chiba Yasuo , Islam Ashraful , Komiya Ryoichi , Fuke Nobuhiro , Fukui Atsushi , Yamanaka Ryohsuke
Published: May 2005

With the aim of increasing conversion efficiency, the series-internal resistance of dye-sensitized solar cells (DSCs) was investigated with electrochemical impedance spectroscopy measurement based on an equivalent circuit of DSCs. It was found that series-internal resistance correlates positively with the sheet resistance of the transparent conducting oxide and the thickness of the electrolyte layer and negatively with the roughness factor of the platinum counter electrode. A cell sensitized with a black dye with series-internal resistance of 1.8Ωcm2 was fabricated and showed conversion efficiency of 10.2% when measured with a metal mask under an air mass of 1.5 sunlight.
One-dimensional transport of In2O3 nanowires
Authors: Liu Fei , Bao Mingqiang , Wang Kang L. , Li Chao , Lei Bo , Zhou Chongwu
Published: May 2005

The gate-dependent one-dimensional transport of single-crystal In2O3 nanowire field effect transistors is studied at low temperature by measuring current (I-V) and differential conductance (dIds∕dVds). At a smaller positive gate bias, gaps at near-zero source-drain bias were observed for both current and differential conductance spectra due to the absence of the density of states in the source-drain energy window for a small Vds. The transport can be explained using conventional low-temperature field effect transistor theory. On the other hand, at a large gate bias when the Fermi energy of the nanowire moves up into its conduction band, the differential conductance of the semiconducting In2O3 nanowire exhibits zero-bias anomalies, following a power-law behavior.
Single-mode surface-emitting quantum-cascade lasers
Authors: Pflügl C. , Austerer M. , Schrenk W. , Golka S. , Strasser G. , Green R. P. , Wilson L. R. , Cockburn J. W. , Krysa A. B. , Roberts J. S.
Published: May 2005

We present high-power surface-emitting second-order distributed feedback quantum-cascade lasers in GaAs and InP material systems. The GaAs device, grown by molecular-beam epitaxy, showed single-mode peak output powers of 3 W at 78 K in pulsed operation. With the InP-based devices, which are grown by metalorganic vapor phase epitaxy, we obtained single-mode peak output powers of 1 W at room temperature. These are the highest output powers for surface emission of quantum-cascade lasers reported so far. The InP-based distributed feedback lasers also have very low threshold current densities and are working well above room temperature.
Light-induced order-of-magnitude decrease in the electric field for domain nucleation in MgO-doped lithium niobate crystals
Authors: Sones C. L. , Wengler M. C. , Valdivia C. E. , Mailis S. , Eason R. W. , Buse K.
Published: May 2005

We report an order-of-magnitude reduction in the electric field required for domain nucleation in 1 mol % MgO-doped near-stoichiometric and 5 mol % MgO-doped congruently grown lithium niobate crystals induced by illumination from a focused continuous wave laser beam at wavelengths of 514, 488, and 457 nm. A smaller decrease of 31% is also observed for undoped congruently grown crystals. The effect is independent of the visible wavelengths explored. Light-controlled domain patterning is also demonstrated.
A different way of performing picosecond ultrasonic measurements in thin transparent films based on laser-wavelength effects
Authors: Devos A. , Côte R. , Caruyer G. , Lefèvre A.
Published: May 2005

We present a way of using picosecond ultrasonics to simultaneously get the thickness and elastic properties of thin dielectric layers. This is based on the use of a blue probe which is shown to improve the detection of acousto-optic oscillations in the dielectric from which the sound velocity can be measured from the refractive index. At the same wavelength a strong response of the silicon is used to detect the arrival of the acoustic pulse. We apply this scheme to various materials deposited on silicon substrates.
Topological instability as a criterion for design and selection of aluminum-based glass-former alloys
Authors: Sá Lisboa R. D. , Bolfarini C. , Botta F. W. J. , Kiminami C. S.
Published: May 2005

This letter proposes a criterion to quantitatively correlate chemical composition with crystallization behaviors of Al-based glass-former alloys. By extending to multicomponent systems the topological instability model of Egami and Waseda [J. Non-Cryst. Solids 64, 113 (1984)], we introduce a “lambda (λ) criterion” according to which amorphous alloys with λ>0.1 exhibit glassy behavior, whereas alloys with λ<0.1 are nanocrystalline. Nanoglassy alloys occur when λ≈0.1. A large number of experimental findings in the literature supports the λ criterion, rendering it a useful tool for the design and selection of glass-former systems and compositions.
Enhanced liquid atomization: From flow-focusing to flow-blurring
Authors: Gañán-Calvo Alfonso M.
Published: May 2005

This letter describes the generation of small turbulence scales in connection with a singular back-flow pattern leading to efficient atomization. A simple pneumatic atomizer configuration results, with a tenfold efficiency increase over available plain-jet air-blast atomizers. Back-flow atomization derives from a global bifurcation of the liquid-gas flow pattern; the bifurcation is triggered by a single geometrical parameter of the atomizer. The extremely simple geometry involved can be implemented down to the micrometric scale, thus opening the door to the improvement of current atomizers and to unprecedented designs.
AlGaN films grown on (0001) sapphire by a two-step method
Authors: Shih C. F. , Chen N. C. , Lin S. Y. , Liu K. S.
Published: May 2005

A two-step growth method, commonly used for GaN on sapphire, was applied to grow high-quality Al0.2Ga0.8N on sapphire. Comparing to the one grown on a low-temperature grown AlN buffer layer, the decomposition, recrystallization, and islands coalescence processes of the two-step growth increased the surface flatness, the crystal quality, the electrical property, suppressed the phase separation, and released the biaxial tensile strain. A 2.0μm thick high-quality crack-free nearly GaN-free Al0.2Ga0.8N epilayer was obtained.
Enhanced stress relaxation in ultrathin SiGe-on-insulator by H+-implantation-assisted oxidation
Authors: Sadoh T. , Matsuura R. , Miyao M. , Ninomiya M. , Nakamae M. , Enokida T.
Published: May 2005

Effects of H+ implantation (⩽5×1016cm−2) on stress relaxation in an oxidation-induced Ge condensation method have been investigated to form stress-relaxed ultrathin (∼30nm) SiGe-on-insulator (SGOI) virtual substrates. High-dose (⩾1015cm−2) implantation enhanced stress relaxation, which was attributed to bond breaking at the SiGe∕buriedSiO2 interface. However, oxidation velocity was also enhanced due to irradiation defects. Two-step annealing (500 °C for 30 min and 850 °C for 60 min) before oxidation was proposed to remove irradiation defects. This achieved enhanced stress relaxation in ultrathin SGOI without changing oxidation velocity.
Propagation properties of guided waves in index-guided two-dimensional optical waveguides
Authors: Kusunoki Fuminori , Yotsuya Tsutom , Takahara Junichi , Kobayashi Tetsuro
Published: May 2005

Index-guided two-dimensional (2D) optical waveguides are numerically studied to investigate propagation properties of guided optical waves. The 2D optical waveguide consists of a dielectric thin film sandwiched between two semi-infinite metals. We demonstrate that vertically localized 2D optical waves can be laterally confined and guided by index guiding when the dielectric film has a high-refractive-index core and claddings of a lower index. The index guiding provides good optical power transmittance, otherwise optical power is rapidly attenuated due to lateral beam divergence.
Catalyst-free growth of GaAs nanowires by selective-area metalorganic vapor-phase epitaxy
Authors: Noborisaka Jinichiro , Motohisa Junichi , Fukui Takashi
Published: May 2005

We report on the fabrication of GaAs hexagonal nanowires surrounded by {110} vertical facets on a GaAs (111) B substrate using selective-area (SA) metalorganic vapor-phase epitaxial (MOVPE) growth. The substrate for SA growth was partially covered with thin SiO2, and a circular mask opening with a diameter d0 of 50–200 nm was defined. After SA-MOVPE, GaAs nanowires with a typical diameter d ranging from 50 to 200 nm and a height from 2 to 9μm were formed vertically on the substrate without any catalysts. The size of the nanowire depends on the growth conditions and the opening size of the masked substrate. A possible growth mechanism is also discussed.