bluuebunny/crossref_metadata_2025 huggingface dataset:
Generalized scalar Preisach model for grain oriented materials excited along arbitrary directions
Authors: Dupré L. , Van Keer R. , Melkebeek J.
Published: July 2002

In this article a generalized dynamic Preisach model is proposed in order to describe in a proper way the excess losses in grain oriented SiFe alloys. The magnetization rate dφ/dt for each Preisach dipole is defined as a function of the effective field, the switching fields α or β together with three material parameters, i.e., kd, kn, and s. Here, kn and s are material parameters introduced, while kd is the classical material parameter in the usual dynamic Preisach model. The correlation between this switching rule and the (n,Hexc) characteristic in the statistical loss theory is discussed. The model has been verified considering unidirectional measurements on grain oriented SiFe Epstein strips.
In situ investigation of ultrathin Fe/Cu(110) films by Brillouin light scattering
Authors: Albini L. , Carlotti G. , Gubbiotti G. , Madami M. , Tacchi S.
Published: July 2002

A compact ultrahigh-vacuum chamber, specially designed to allow in situ Brillouin light-scattering (BLS) and surface magneto-optical Kerr-effect measurements has been set up. Experimental results relative to both the structure and the magnetic properties of ultrathin Fe films grown by e-beam evaporation on a Cu(110) single crystal are presented. Low-energy electron diffraction patterns account for epitaxial growth of fcc Fe(110) up to 4–6 Å, followed by a transition to a more disordered state, consisting of bcc Fe domains. The BLS analysis enabled us to study the dependence of the spin-wave frequency on the angle of incidence of light, on the intensity of the magnetic field, and on its direction on the surface plane.
Large spontaneous spin splitting in gate-controlled two-dimensional electron gases at normal In0.75Ga0.25As/In0.75Al0.25As heterojunctions
Authors: Sato Y. , Kita T. , Gozu S. , Yamada S.
Published: July 2002

Amounts of spontaneous spin splittings were estimated from low-temperature magnetoresistances in two-dimensional electron gases created at In0.75Ga0.25As/In0.75Al0.25As heterojunctions under a gate bias. Typical sheet electron densities and mobilities in the raw wafers were ∼1.0×1012/cm2 and 2–5×105 cm2/V s at 1.5 K, respectively. A maximum spin-orbit coupling constant αzero of ∼30(×10−12 eV m) was obtained for the van der Pauw sample. In gated Hall-bar samples, a decrease in the αzero value with decreasing gate voltage (Vg) was first confirmed in a normal heterojunction. The main origin for such a large αzero, which is a few times larger than any previously reported, was found to be a structure-dependent so-called interface contribution in the Rashba term.
Influence of La defect on the magnetoresistance and magnetic properties of La1−xMnO3
Authors: Kim Sam Jin , Kim Chul Sung , Park Seung-Iel , Lee Bo Wha
Published: July 2002

Influence of the effect of lanthanum deficiency on the structural, magnetoresistance, and magnetic properties have been studied on a series of La1−xMnO3 (x=0, 0.05, 0.1, 0.2, and 0.33) powder samples. The powder samples were prepared by the sol–gel method. The x-ray diffraction analyses of the samples revealed a single phase of rhombohedral symmetry. Magnetization curves showed a weak ferromagnetic ordering for the sample x=0.0 with its Curie TC=138 K, but for the other samples showed ferromagnetic phase. The Curie temperature TC, with increasing deficiency from x=0.05 to x=0.33, was found to be increased from 272 to 279 K, respectively. The saturation magnetic moments per Mn atom at 80 K for x=0.0 and 0.10 are 2.30, 3.21 μB, respectively. A small increasing La defects resulted in changes of their magnetic structures thoroughly. In all the La defect samples, the temperature dependence of resistance shows that metal to insulator transition occurs near the TC and is closely related to the magnetization. The magnetoresistance value of 30% [Δρ/ρ(0)] has been obtained at 272 K under H=1.5 T for the sample x=0.1. The evidence for the formation of double exchange is also shown in x-ray measurements.
Cooperative nucleation and evolution in InGaAs quantum dots in multiply stacked structures
Authors: Xie Qianghua , Brown J. L. , Van Nostrand J. E.
Published: July 2002

We report a type of vertical self-organization of In0.6Ga0.4As quantum dots (QDs) wherein the dot density for the top layer (NT) doubles that of the seed layer (NS). The experimental observation fits well with a scheme of QD vertical self-organization accompanied by additional cooperative dot nucleation at the face centers of an approximate two-dimensional array defined by the embedded seed dots. The dots in the top layer undergo a shape transition from {023} to {011} and a simultaneous shape stabilization and size equalization.
In search of theoretically predicted magic clusters: Lithium-doped aluminum cluster anions
Authors: Thomas O. C. , Zheng W.-J. , Lippa T. P. , Xu S.-J. , Lyapustina S. A. , Bowen K. H.
Published: July 2002

Lithium-doped aluminum cluster anions, LiAln− were generated in a laser vaporization source and examined via mass spectrometry and anion photoelectron spectroscopy (n=3–15). The mass spectrum of the LiAln− series exhibits a local minimum in intensity at n=13. The electron affinity vs cluster size trend also shows a dip at n=13. Agreement is quite good between our measured electron affinity values and those calculated by Rao, Khanna, and Jena, suggesting that their predictions about the structure and bonding of LiAl13 and other clusters in this series are also largely valid.
Effects of β and Te/Ti on the ion temperature gradient modes in anisothermal plasmas
Authors: Gao Zhe , Dong J. Q. , Liu G. J. , Ying C. T.
Published: July 2002

Effects of β (plasma pressure/magnetic pressure) and Te/Ti (ratio of electron temperature to ion temperature) on the slab ion temperature gradient modes are studied locally for any β value in anisothermal hydrogenic plasmas with no impurities or fast ions. The stabilizing mechanism of finite β on the modes is investigated in detail. It is shown that increasing Te/Ti destabilizes the modes and that βi stabilizes the modes mainly by decreasing Te/Ti, while βe does so directly. βe is the dominant stabilizing factor for a fixed Te/Ti. The numerical results also indicate that the critical β(βc) for mode stabilization decreases as Te/Ti decreases. Ion heating favors the suppression of the ion temperature gradient modes in anisothermal plasmas for any β value.
Mechanical deformation of InP and GaAs by spherical indentation
Authors: Bradby J. E. , Williams J. S. , Wong-Leung J. , Swain M. V. , Munroe P.
Published: July 2002

The mechanical deformation by spherical indentation of both crystalline InP and GaAs was characterized using cross-sectional transmission electron microscopy (XTEM) and atomic force microscopy. All load–unload curves show a discontinuity (or “pop in”) during loading. Slip bands oriented along {111} planes are visible in XTEM micrographs from residual indentations in both materials and no evidence of any phase transformations was found. Higher load indentations (35 mN for InP and 50 mN for GaAs) also revealed subsurface cracking. In contrast no cracking was found beneath a 25 mN InP indent although the hardness and modulus data are almost identical to those of the cracked sample. The subsurface cracks are thought to be nucleated by high stress concentrations caused by dislocation pileup.
General trends in CO dissociation on transition metal surfaces
Authors: Liu Zhi-Pan , Hu P.
Published: July 2002

Dissociative adsorption is one of the most important reactions in catalysis. In this communication we propose a model aiming to generalize the important factors that affect dissociation reactions. Specifically, for a dissociation reaction, say AB→A+B, the model connects the dissociation barrier with the association barrier, the chemisorption energies of A and B at the final state and the bonding energy of AB in the gas phase. To apply this model, we have calculated CO dissociation on Ru(0001), Rh(111), Pd(111) (4d transition metals), Os(0001), Ir(111), and Pt(111) (5d transition metals) using density function theory (DFT). All the barriers are determined. We find that the DFT results can be rationalized within the model. The model can also be used to explain many experimental observations.
Comment on “Role of quasineutrality in drift waves” [Phys. Plasmas 8, 368 (2001)]
Authors: Shukla P. K. , Stenflo L. , Pokhotelov O. A.
Published: July 2002

The physics of various low-frequency electrostatic and electromagnetic waves in a nonuniform magnetoplasma is revisited. It is shown that the approach of Saleem and Haque [Phys. Plasmas 8, 368 (2001)] is misleading with regard to the electrostatic limit and the role of the quasineutrality approximation.
Perpendicular electron trapping associated with nonlinear whistlers
Authors: Jovanović D. , Pegoraro F. , Califano F.
Published: July 2002

Kinetic effects leading to the particle trapping are studied in a magnetized, inhomogeneous plasma configuration within the framework of the gyrokinetic theory in the frequency and spatial scale range that corresponds to the whistler waves. This treatment accounts for finite electron Larmor radius and polarization effects. A coherent nonlinear structure is found, which is identified as a magnetic vortex coupled with an electron hole. This novel electron hole is characterized by a strong magnetic field, and has a typical perpendicular size somewhat shorter than the electron collisionless skin depth. Electrons are trapped in the perpendicular direction by the combination of the electrostatic field, arising from the charge separation, and of the Lorentz force resulting from the propagation of the structure relative to the perturbed magnetic field lines. The trapping effects are restricted to the region at the center of the vortex. The size of this region is related to the electron Larmor-radius and to the Debye length.
Calculation of transmission coefficients at nonideal semiconductor interfaces characterized by a spatial distribution of barrier heights
Authors: Lonergan Mark C. , Jones Frank E.
Published: July 2002

The use of temperature-dependent current–voltage and capacitance–voltage measurements in the determination of transmission coefficients, which can be related to various other heterogeneous charge-transfer rate constants, is analyzed for semiconductor interfaces characterized by a spatial distribution of barrier heights. The level of error introduced by the unknowing neglect of heterogeneity is analyzed using a discrete parallel network of regions with potentially voltage and temperature dependent effective areas and potential barriers. In general, the unknowing neglect of heterogeneity results in an overestimation of the transmission coefficient calculated from barrier heights based on capacitance–voltage measurements and an underestimation when based on barrier heights from temperature dependent current–voltage measurements (Richardson plots). Of particular focus is the calculation of transmission coefficients at semiconductor interfaces that exhibit anomalous behavior, most notably ideality or quality factors greater than unity, due to small-scale, “pinched-off,” barrier inhomogeneities characterized by voltage-dependent effective barriers. In general, the meanings of various empirical treatments of current–voltage data in light of a voltage-dependent barrier height distribution are clarified with a particular focus on the extraction of equilibrium exchange current densities and the meaning of Richardson plots. To be specific, the model of Tung for pinched-off barrier inhomogeneities is used to demonstrate that multiple orders-of-magnitude errors in the calculation of transmission coefficients are possible with systems exhibiting only mildly anomalous behavior (ideality factors less than 1.3) if heterogeneity is neglected. The conditions of applied bias, dopant density, and temperature where the error is minimized are discussed along with the criteria for the rigorous extraction of transmission coefficients. The greatest confidence in the transmission coefficients occurs when the ideality factor is unity and the capacitance–voltage barrier agrees with the Richardson plot barrier.
Triple-sheath structures in a plasma having trapped dust grains
Authors: Nejoh Y. N.
Published: July 2002

Triple-sheath structures and temporal evolution of the dust grain-charge in a dusty plasma with the trapped dust grains are investigated by numerical calculation. Trapped dust grains modify the shape of the sheath and give rise to the triple-electric field structures. The sheath width becomes narrower than that of the Boltzmann distributed dust grains due to the existence of trapped dust grains. It is found that trapped dust grains play an important role in the formation of the new sheath structure and shorten the charging time.
Precision alignment of the LIGO 4 km arms using the dual-frequency differential global positioning system
Authors: Althouse W. E. , Hand S. D. , Jones L. K. , Lazzarini A. , Weiss R.
Published: July 2002

The alignment of the Laser Interferometer Gravitational-Wave Observatory (LIGO) using the global positioning system (GPS) is described. The LIGO project is designed to detect gravitational waves from astrophysical sources by laser interferometry. There are two sites separated by 3002 km that will be operated in coincidence. At each site, laser beams propagate in two orthogonal 4 km long evacuated beam lines 1.2 m in diameter. The subject of this article is the alignment of the 16 km of beam tubes using dual-frequency differential GPS. A maximum deviation from straightness in inertial space of 5 mm root mean square and an orthogonality between arm pairs of better than 5 μrad is reported. Analysis of the as-built alignment data allows determination of the geodetic coordinates for the vertices and the arm orientations at both sites. From this information, the baseline distance between the vertices of the Hanford, Washington and Livingston, Louisiana sites was determined to be 3001.8 km.
Transient and quasisteady behavior with rotating magnetic field current drive
Authors: Steinhauer Loren C.
Published: July 2002

The time-dependent behavior of rotating magnetic field (RMF) current drive is investigated using a two-fluid model. The important new factor is the addition of transverse ion mobility in contrast to rigid-ion models of the past. The equations simplify conveniently, allowing the behavior on each surface (r=const) to be isolated, which permits a quadrature solution for the ion fluid rotation. A rapid transient phase leads to quasisteady behavior that evolves on the relatively slow diffusion timescale. The fast transient timescale is set by the ion inertia. Unless there is an ion momentum source to balance the electron drag on the ion fluid, there is no quasisteady current drive effect. Collisions with neutrals offer such a momentum source in some experiments, notably rotamaks and the Star Thrust Experiment. Other sources of ion momentum are essential for RMF current drive in hotter, fusion-relevant plasmas. The properties of the quasisteady state are found, including the self-consistent ion fluid rotation rate and radial electric field, and RMF corrections on the pressure balance.
Large area dense nanoscale patterning of arbitrary surfaces
Authors: Park Miri , Chaikin P. M. , Register Richard A. , Adamson Douglas H.
Published: July 2002

We demonstrate a large-area fabrication of hexagonally ordered metal dot arrays with an area density of ∼1011/cm2. We produced 20 nm dots with a 40 nm period by combining block copolymer nanolithography and a trilayer resist technique. A self-assembled spherical-phase block copolymer top layer spontaneously generated the pattern, acting as a template. The pattern was first transferred to a silicon nitride middle layer by reactive ion etch, producing holes. The nitride layer was then used as a mask to further etch into a polyimide bottom layer. The metal dots were produced by an electron beam evaporation followed by a lift-off process. Our method provides a viable route for highly dense nanoscale patterning of different materials on arbitrary surfaces.
A new mass-detecting capillary viscometer
Authors: Shin S. , Lee S. W. , Keum D. Y.
Published: July 2002

The mass-detecting technique has been applied to design a capillary viscometer for viscosity measurements of both Newtonian and non-Newtonian fluids over a range of shear rates. Flow-rate and pressure-drop measurements are replaced with a measurement of liquid-mass variation with time. Using a precision balance, one can measure the variation of fluid mass collected in the receptacle, m(t), from which the test fluid viscosity and shear rate are mathematically calculated. The feasibility and accuracy of the mass-detecting technique have been demonstrated for water and non-Newtonian fluids by comparing results against established viscosity measurement techniques. The advantages of this design are simplicity (i.e., ease of operation and no moving parts), low cost, and the ability to measure viscosity over a relatively broad range of shear rates.
New method for the calibration of three-dimensional atom-probe mass spectra
Authors: Sebastian Jason T. , Hellman Olof C. , Seidman David N.
Published: July 2002

A new method for the calibration of three-dimensional atom-probe (3DAP) microscopy mass spectra has been developed. This method is based on a linear regression procedure that takes full advantage of the large number of data points collected during a typical 3DAP analysis. The data analysis procedures involved in the method are direct, relying only on simple scripting routines written in a spreadsheet program. When performed properly, the calibration ensures that all of the peaks in a mass spectrum lie at their expected positions, making subsequent peak identification and mass window determination procedures relatively unambiguous. One of the distinct advantages of the method is that mass windows determined for one 3DAP spectrum can be applied directly to subsequent spectra from similar specimens, avoiding the need to re-examine the individual peaks in each spectrum. The example of the calibration of a tungsten 3DAP mass spectrum is presented. With minor modifications, the method can be applied to the calibration of spectra from other techniques that utilize time-of-flight mass spectrometry.
Ponderomotive force in a collisional warm two-fluid plasma
Authors: Lee Nam C.
Published: July 2002

An expression for the ponderomotive force of high frequency electromagnetic waves in a warm two-fluid collisional plasma in an ambient magnetic field is obtained by a microscopic method. In addition to the previously known results of collisionless plasmas, the expression contains a term that explicitly reflects the resistive dissipation caused by collision between electrons and ions. This term is similar to the one obtained for an isotropic plasma by using the Vlasov equations, taking the dissipation by the resonant interaction of particles with the waves into account. It is also similar to those obtained by macroscopic methods. The range of the collision frequency for the validity of the result is presented along with other parameters, and compared with other results.
Effects of liquid metal walls on equilibrium and stability in tokamaks
Authors: Aydemir A. Y.
Published: July 2002

The liquid metal wall concept has received a great deal of attention recently because of its perceived advantages in addressing high heat flux, magnetohydrodynamic (MHD) stability, and other related issues in advanced confinement schemes. Despite its inherent and clear benefits, this concept also poses potentially serious problems from the MHD equilibrium and stability point of view. In particular, a liquid metal flow fast enough to stabilize resistive wall modes can also have adverse effects on the MHD equilibrium through its interaction with the background poloidal and toroidal fields. These deleterious effects can be large enough to effectively prevent any expected stabilization of the unstable MHD modes.
Investigation and modeling of the electrical properties of metal–oxide–metal structures formed from chemical vapor deposited Ta2O5 films
Authors: Blonkowski S. , Regache M. , Halimaoui A.
Published: July 2002

Amorphous Ta2O5 films were deposited by low pressure chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD) at temperatures below 450 °C. These films were used to fabricate metal–oxide–metal (MOM) structures with titanium nitride (TiN) electrodes. The electrical properties of the MOM capacitance were investigated by the means of current–voltage and capacitance–voltage characteristics in the 100 Hz–1 MHz frequency range. It is shown that the conduction mechanism changed from Schottky emission, for the LPCVD material, to Poole–Frenkel current for the PECVD material. The roughness of the bottom electrode, as determined by atomic force microscopy measurements, is found to impact the leakage current. For the LPCVD material the capacitance exhibits a strong dependency on the applied bias and the frequency. For the PECVD material, only a small variation of the capacitance is observed when the bias is increased, with almost no frequency dependency. A clear correlation between the capacitance variation and the current density is demonstrated. As far as the current density is lower than 0.1 A/cm2, the capacitance is almost constant. For a higher current density the capacitance increases exponentially. Transmission electron microscope observations have shown that the Ta2O5 films are homogeneous in-depth. Consequently, the capacitance variations could not be explained by interfacial polarization (Maxwell–Wagner mechanism). We suggest a model that well explains the observed capacitance variations. This model is based on the relaxation of the free carriers and the nonlinear Kerr effect (dipolar relaxation). A good fit of the experimental results is obtained by summing both contributions (free carrier relaxation and Kerr effect). For the LPCVD material, the carrier relaxation is found to be the predominant process. For the PECVD material, which exhibits lower leakage current than the LPCVD material, the Kerr effect is the predominant mechanism.
Nonlinearly coupled inertial Alfvén and dust acoustic waves in complex plasmas
Authors: Shukla P. K. , Stenflo L.
Published: July 2002

The nonlinear coupling between finite amplitude inertial Alfvén (IA) and dust acoustic (DA) waves in a complex plasma is considered. By employing a multi-fluid dusty plasma model, which includes the effects of the ponderomotive force on the DA waves, a system of coupled equations is derived and used to study modulational instabilities of a constant amplitude IA wave. The results may have relevance to nonlinear phenomena involving IA and DA waves in low-temperature laboratory and space plasmas.
Shock layer instability near the Newtonian limit of hypervelocity flows
Authors: Hornung H. G. , Lemieux P.
Published: July 2002

The curved bow shock in hypersonic flow over a blunt body generates a shear layer with smoothly distributed vorticity. The vorticity magnitude is approximately proportional to the density ratio across the shock, which may be very large in hypervelocity flow, making the shear layer unstable. A computational study of the instability reveals that two distinct nonlinear growth mechanisms occur in such flows: First, the vortical structures formed in the layer move supersonically with respect to the flow beneath them and form shock waves that reflect from the body and reinforce the structures. Second, the structures deform the bow shock, forming triple points from which shear layers issue that feed the main shear layer. Significant differences exist between plane and axisymmetric flow. Particularly rapid growth is observed for free-stream disturbances with the wavelength approximately equal to the nose radius. The computational study indicates that the critical normal shock density ratio for which disturbances grow to large amplitudes within a few nose radii is approximately 14. This served as a guide to the design of a physical experiment in which a spherical projectile moves at high speed through propane or carbon dioxide gas. The experiment confirms the approximate value of the critical density ratio, as well as the features of the computed flows. Comparisons of calculations of perfect gas flows over a sphere with shadowgraphs of the projectile show very good agreement. The Newtonian theory of hypersonic flow, which applies at high density ratio, makes the assumption that the flow remains smooth. The results show that high density ratio also causes this assumption to fail.
Direct numerical simulation of particle-laden rotating turbulent channel flow
Authors: Pan Yingkang , Tanaka Toshitsugu , Tsuji Yutaka
Published: July 2002

Direct numerical simulations (DNS) of particle-laden rotating turbulent channel flows at the Reynolds number 194 and the rotation number 0.075 (both based on the friction velocity and the channel half width) on a 1283 grid were performed. Particles were traced using the deterministic method combined with the direct particle interactions via hard-sphere collisions and two-way coupling. The particle gravity parallel to the spanwise direction and the particle volume fractions from O(10−6) to O(10−5) were considered. It is found that the presence of the heavier particles (Stokes number Stτ>0.1) and their interparticle collisions near the pressure surface significantly changes the turbulence properties, particularly in the near-wall regions. The DNS results showed that the interparticle collisions make the lighter particle distribution more even and then attenuate the turbulence intensity of the fluid, and make the heavier particle distribution more uneven and then enhance the turbulence intensity of the fluid. It is also found that the slightly heavier particles (Stτ=0.126) form strong streaky structures added “hooks” with a certain skew angle to the streamwise direction near the pressure surface. When the particles become larger and heavier, and the particle volume fraction becomes higher O(10−5), the well-known low/high speed streaks near the pressure surface are destroyed by the particles due to rotation.
Optical spectroscopy on individual CdSe/ZnMnSe quantum dots
Authors: Bacher G. , Schömig H. , Welsch M. K. , Zaitsev S. , Kulakovskii V. D. , Forchel A. , Lee S. , Dobrowolska M. , Furdyna J. K. , König B. , Ossau W.
Published: July 2002

Optical single dot studies in wide-band gap diluted magnetic CdSe/ZnMnSe quantum dots have been performed. Due to the sample design, the photoluminescence energy of the quantum dot signal is energetically below the internal Mn2+ transition, resulting in high quantum efficiencies comparable to nonmagnetic CdSe/ZnSe quantum dots. Magnetic-field- and temperature-dependent measurements on individual dots clearly demonstrate the exchange interaction between single excitons and individual Mn2+ ions, resulting in a giant Zeeman effect and a formation of quasi-zero-dimensional magnetic polarons.
Cathodoluminescence of electron irradiated opal-based nanocomposites
Authors: Dı́az-Guerra C. , Piqueras J. , Golubev V. G. , Kurdyukov D. A. , Pevtsov A. B.
Published: July 2002

Synthetic opals infilled with silicon (opal-Si) and with Si and Pt (opal-Pt-Si) have been irradiated in a scanning electron microscope under high excitation conditions. Electron irradiation-induced changes in the morphology and luminescent defect structure of both types of nanocomposites were assessed by scanning electron microscopy and by cathodoluminescence (CL) microscopy and spectroscopy. Irradiation causes strong morphological changes in the ordered structure of the matrix and quenching of the nanocrystals-related CL emission in the opal-Si samples. On the contrary, such effects are not observed in the opal-Pt-Si nanocomposites. In both types of samples, electron irradiation induces the appearance of a CL band centered at 2.95 eV, attributed to complex centers involving oxygen vacancies in the silica spheres forming the matrix.
Defect modes in coaxial photonic crystals
Authors: Schneider Garrett J. , Hanna Stefan , Davis Joshua L. , Watson George H.
Published: July 2002

One-dimensional (1D) photonic crystals have been constructed by connecting segments of coaxial cable of differing characteristic impedance. Impurities have been introduced into these crystals by inserting cable segments to break the crystal symmetry. This system provides a simple way to study 1D photonic band structure effects with complete control over impurities in the lattice. We have studied the effects of the size, number, and location of defects in the lattice. We have also measured directly the concentration of energy in the steady-state electromagnetic fields within doped crystals, and observed the influence of the defects on the phase (dispersion). A modified dielectric stack model was developed to describe this system, with the results in excellent agreement with our measurements. Our findings compare favorably to previously published measurements of transmission and phase change in three-dimensional photonic crystals.
On the effects of spin–orbit coupling on conical intersection seams in molecules with an odd number of electrons. II. Characterizing the local topography of the seam
Authors: Matsika Spiridoula , Yarkony David R.
Published: July 2002

Characteristic of conical intersections of Born–Oppenheimer potential energy surfaces is η, the dimension of the branching space, the space in which the degeneracy is lifted linearly. In molecules with an odd number of electrons, η=2 for the nonrelativistic Coulomb Hamiltonian, while η=3(5) when the spin–orbit interaction is included and the molecule has (does not have) Cs symmetry. In the η=2 case, the branching space is defined by two vectors: the energy difference gradient vector, g, and the interstate coupling vector, h. g and h can, without loss of generality, be chosen orthogonal. g×h is invariant under the unitary wave function transformation that orthogonalizes g and h. The orthogonal g and h can be used to define an optimal set of coordinates for describing the vicinity of the conical intersection. Here these ideas are generalized to η=3 intersections. In particular, it is shown that g, the energy difference gradient vector, and hr and hi, the real and imaginary parts of the interstate coupling vector, which define the η=3 space, can without loss of generality be chosen orthogonal. It is also shown that g×hr⋅hi is invariant under the unitary wave function transformation that orthogonalizes these vectors. These ideas are illustrated using a portion of the OH(A 2Σ1/2+,X 2Π3/2,1/2)+H2 seam of conical intersection.
Fatigue-free lead zirconate titanate-based capacitors for nonvolatile memories
Authors: Shannigrahi S. R. , Jang Hyun M.
Published: July 2002

The development of lead zirconate titanate (PZT)-based capacitors has been a long time goal of ferroelectric random access memories (FRAM). However, PZT-based perovskites with common platinum (Pt) electrodes have suffered from a significant reduction of the remanent polarization (Pr) after a certain number of read/write cycles (electrical fatigue). We now report the development of fatigue-free lanthanum-modified PZT capacitors using common Pt electrodes. The capacitors fabricated at 580 °C by applying a PZT seed layer exhibited fatigue-free behavior up to 6.5×1010 switching cycles, a quite stable charge retention profile with time, and comparatively high Pr values, all of which assure their suitability for practical FRAM applications.
N
-side illuminated microcrystalline silicon solar cells
Authors: Gross A. , Vetterl O. , Lambertz A. , Finger F. , Wagner H. , Dasgupta A.
Published: July 2002

Thin-film microcrystalline silicon solar cells illuminated through the n layer were studied and compared with classical p-layer illuminated cells. To investigate the corresponding charge carrier extraction properties, variation of the intrinsic absorber layer thickness was carried out. It was found that the J–V characteristic and the quantum efficiency of the n- and p-side illuminated cells are almost identical in the thickness range investigated, up to 7 μm. No differences in the collection of photogenerated electrons or holes are observed. Hence, the illumination side of μc-Si:H single junction solar cells of conventional thickness may be randomly chosen without adverse effect on their performance.
Time-dependent Hartree–Fock schemes for analytical evaluation of the Raman intensities
Authors: Quinet Olivier , Champagne Benoı̂t
Published: July 2002

Using the time-dependent Hartree–Fock method two analytical schemes are elaborated for determining the derivatives of frequency-dependent polarizability with respect to atomic Cartesian coordinates. The first scheme is iterative and consists in determining the mixed derivatives of the density matrix with respect to atomic Cartesian coordinates and dynamic electrical fields. The second takes advantage of the 2n+1 rule to express the polarizability derivatives in terms of first-order derivatives. Both schemes are implemented in the GAMESS program. They enable the fully analytical evaluation of the Raman intensities with inclusion of the frequency dispersion. The potential of these methods is illustrated by determining the polarizability derivatives and Raman intensities of small molecules.
Room-temperature and 50 GHz operation of a functional nanomaterial
Authors: Song A. M. , Omling P. , Samuelson L. , Seifert W. , Shorubalko I. , Zirath H.
Published: July 2002

We demonstrate an artificial electronic nanomaterial, constructed by arrangement of nanometer-sized symmetry-breaking elements into a two-dimensional lattice. The material exhibits intrinsic nonlinear electronic functionality, and therefore functions also as a two-dimensional ratchet. We show that individual devices can be made by simply cutting pieces from the material. We also demonstrate that these devices operate at temperatures up to room temperature and at frequencies at least up to 50 GHz.
Structural properties of ZnSe epilayers on (111) GaAs
Authors: Kontos A. G. , Chrysanthakopoulos N. , Calamiotou M. , Kehagias T. , Komninou P. , Pohl U. W.
Published: July 2002

Structural and optical studies of ZnSe epilayers, which were grown on the B side of (111)-oriented GaAs substrates, indicate the presence of tensile in-plane strains in the epilayers at room temperature. Electron microscopy observations showed that the ZnSe epilayer forms a coherent sharp interface with the GaAs substrate and consists of crystallites which are grown in epitaxial or twin orientation with respect to the substrate, having the (111) planes oriented parallel to the interface. In addition, embedded twins are observed within the epilayer. The twin boundaries are, generally, terminated by Shockley partial dislocations, which are expected to relax the compressive lattice mismatch strain. Plastic or thermal relaxation cannot account for sign and magnitude of the observed strains. Evidence is found that the observed tensile strains are piezoelectrically induced in a depletion layer, due to Fermi level pinning at the ZnSe/GaAs interface.
Characteristics of InGaN laser diodes in the pure blue region
Authors: Nagahama Shin-ichi , Yanamoto Tomoya , Sano Masahiko , Mukai Takashi
Published: July 2002

InGaN multi-quantum-well-structure laser diodes (LDs), whose emission wavelengths are in the pure blue region, were grown on epitaxially laterally overgrown GaN on a free-standing GaN substrate by the metaorganic chemical-vapor deposition method. The wavelength dependence of the InGaN LD characteristics was investigated. These results indicated that there is a strong relationship between the threshold current density and the emission wavelength of LDs. LDs with an emission wavelength of 460 nm were demonstrated. The threshold current density and voltage of these LDs were 3.3 kA/cm2 and 4.6 V, respectively. The estimated lifetime was approximately 3000 h under 50 °C continuous-wave operation at an output power of 5 mW.
Thermal diffusivity measurements in liquids using signal common-mode-rejection demodulation in a thermal-wave cavity
Authors: Balderas-López J. A. , Mandelis Andreas
Published: July 2002

A recently developed signal common-mode rejection demodulation signal methodology [Mandelis et al., Rev. Sci. Instrum. 71, 2440 (2000)] has been used to make direct absolute thermal diffusivity measurements in liquids using a thermal-wave cavity. This methodology combines the precision of the thermal-wave cavity scan and the flexibility of modulation-frequency scan modes, along with baseline suppression, yielding a high-resolution technique for thermal diffusivity measurements in liquids. The thermal diffusivity of two pure liquids (distilled water and ethylene glycol) has been measured and good agreement has been obtained with values reported in the literature.
Inhomogeneous broadening in quantum dots with ternary aluminum alloys
Authors: Allen C. Nì , Finnie P. , Raymond S. , Wasilewski Z. R. , Fafard S.
Published: July 2002

We study how the optical properties of InAs self-assembled quantum dots (QDs) grown on GaAs substrate are affected when using AlGaAs barriers to increase the carrier confinement. The inhomogeneous broadening of the QD ensemble is found to increase when ternary aluminum alloys are used next to or within the QDs. By growing thin GaAs spacers to separate the QDs from the AlGaAs barriers, we obtain QD ensembles which exhibit little photoluminescence quenching and well-defined excited states up to room temperature. Postgrowth rapid thermal annealing is then used to intermix these InAs/GaAs/AlGaAs QDs and diffuse the Al towards the QDs. In contrast with QDs having thick binary GaAs barriers, the inhomogeneous broadening of QDs with nearby AlGaAs barriers is not decreased with intermixing, leading to unresolved excited state peaks when the interdiffusion length becomes comparable to the GaAs spacer thickness.
Nondegenerate monopole-mode two-dimensional photonic band gap laser
Authors: Park Hong-Gyu , Hwang Jeong-Ki , Huh Joon , Ryu Han-Youl , Lee Yong-Hee , Kim Jeong-Soo
Published: July 2002

We propose and demonstrate photonic band gap lasing action from a nondegenerate monopole-mode, high-quality factor cavity. By optical pumping at room temperature, the monopole-mode laser is realized and identified from its mode shape, spectrum, and polarization. The monopole-mode laser shows nondegeneracy and genuine two-dimensional oscillation with incident threshold pump power less than 0.3 mW. This laser mode has a small modal volume of ∼4.5(λ/2nslab)3 and shows a quality factor of larger than 1900, estimated from the spectral linewidth below threshold.
Cross-correlation functions in two-dimensional and three-dimensional colloidal crystals
Authors: Ohshima Yuichi N. , Hatakeyam Koushi E. , Satake Motoi , Homma Yumi , Washidzu Ryosuke , Nishio Izumi
Published: July 2002

We have measured the mean square displacement of a particle (MSD) and mean product of displacement of a particle and that of another particle (x-MSD) in two-dimensional (2d) and three-dimensional (3d) colloidal crystals for the first time using digital video microscopy. These (x-)MSDs have been compared to an overdamped bead-spring lattice model with effective viscous drag γeff (the OBS-γeff model). The observed 3d system contained ordered structures created by sedimentation equilibrium adjacent to the internal cell wall and was regarded as the (1 1 1) surface of a face-centered cubic lattice. The observed 2d system was a single layer of hexagonal-like ordered structures which were generated in a certain region of the space between the flat surface of the internal cell wall and a convex lens. In the observed time region, the MSDs for 2d system and 3d system were in good agreement with the theoretical MSDs for 2d system and 3d system, which were predicted to logarithmically diverge and to converge, respectively. The observed x-MSDs for the 2d system were in disagreement with theoretical ones in short time behavior. For the 3d system, the disagreement between the theory and the experimental results were found in the amplitudes as well as in the short time behavior. It was assumed that these differences were caused by the hydrodynamic coupling which was not fully incorporated in the OBS-γeff, and an improved treatment, the OBS-cutoff model was introduced. The OBS-γeff elongates the relaxation time of each mode with the constant ratio of γeff/γ, while the OBS-cutoff assumes the relaxation time of the modes to be infinity if the wave number of a mode is larger than a certain cutoff wave number. For the 3d system, the MSD and x-MSD for nearest neighbors obtained from the OBS-cutoff were in excellent agreement with the observed ones. In addition, it was found that the hydrodynamic interaction was the dominant factor on the short time behavior of (x-)MSD.
Enhanced photoresponse of carbonaceous film/silicon junctions by doping with bromanil
Authors: Ozaki Jun-ichi , Hiranaka Kaoru , Oya Asao
Published: July 2002

Bromanil (BA) doping of a naphthalene pitch, a kind of soluble carbonaceous material, enhanced the photoresponse of the junction between this material and a p-type silicon substrate by about tenfold. Morphological and spectroscopic studies revealed that the enhancement was partly caused by an increase in the surface roughness of the carbonaceous films, and by the enhanced dissociation of excitons in the carbonaceous films upon the BA doping.
Quantum, intramolecular flexibility, and polarizability effects on the reproduction of the density anomaly of liquid water by simple potential functions
Authors: Mahoney Michael W. , Jorgensen William L.
Published: July 2002

The ability of simple potential functions to describe the properties of liquid water at a range of thermodynamic state points has been explored. These simple potential function models represent a water molecule by a set of sites, either rigid or flexible relative to each other, that interact with a simple, generally classical, Hamiltonian, which has parameters that are empirically determined. Calculations on several models that include intramolecular flexibility, electronic polarization or quantum mechanical effects have been performed. The consequences of altering these parameters have been systematically examined to determine factors of importance in reproducing properties of pure liquid water. It is found that simple four-site models that incorporate classical intramolecular flexibility or electronic polarization do not improve the description of the density anomaly of liquid water. Quantum statistical mechanical path integral calculations on the classical rigid nonpolarizable TIP5P model [J. Chem. Phys. 112, 8910 (2000)] and the classical flexible nonpolarizable TIP4F model indicate that although quantum mechanical effects destructure the rigid model, they improve the radial distribution and energy distribution properties of the flexible model. In addition, although quantum effects make the density behavior of the rigid model worse, they improve the density behavior of the flexible model. Path integral calculations have also been performed on quantum D2O TIP5P water; this leads to a temperature of maximum density that is higher and to a more structured liquid than results from calculations on quantum H2O TIP5P water. A similar effect is seen with calculations on a five-site rigid model, TIP5P(PIMC), which was parameterized using path integral rather than classical Monte Carlo calculations.
Microelectromagnets for the control of magnetic nanoparticles
Authors: Lee C. S. , Lee H. , Westervelt R. M.
Published: July 2002

A microelectromagnet matrix and a ring trap that position and control magnetic nanoparticles are demonstrated. They consist of multiple layers of lithographically defined Au wires separated by transparent, insulating polyimide layers on sapphire substrates. Magnetic field patterns produced by these devices allow microscopically precise control and manipulation of magnetic nanoparticles. A microelectromagnet matrix produces single or multiple peaks in the magnetic field magnitude, which trap, move, and rotate magnetic nanoparticles, as well as electromagnetic fields to probe and detect particles. Microelectromagnets are new tools with which to study and manipulate nanoparticles and biological entities.
Evaluated Enthalpies of Formation of the Stable Closed Shell C1 and C2 Chlorinated Hydrocarbons
Authors: Manion Jeffrey A.
Published: July 2002

Experimental data on the enthalpies of formation of chloromethanes, chloroethynes, chloroethenes, and chloroethanes are critically reviewed. Enthalpy of formation values for the C1 and C2 chlorinated hydrocarbons are highly cross-linked by various measured reaction equilibria and currently available sets of values are not internally self-consistent. It is shown that the early static bomb combustion calorimetry studies on highly chlorinated compounds generally give enthalpies of formation that are systematically more positive than later values derivable from rotating bomb combustion or equilibria studies. Those previously recommended values which were based mainly on the early static bomb work therefore need substantial revision. On the basis of more recent literature data obtained with rotating bomb combustion calorimetry, together with analyses of literature data on other reaction enthalpies and equilibria involving chlorinated hydrocarbons, an updated self-consistent set of ΔfHo[298.15 K] values for closed shell chlorinated C1 and C2 hydrocarbons (25 compounds) is recommended. Data on the enthalpies of vaporization are also reviewed and values of ΔvapH[298.15 K] and ΔvapHo[298.15 K] are recommended. The presently suggested enthalpies of formation for highly chlorinated alkenes and alkanes (particularly C2Cl4, C2HCl3, C2HCl5, and C2Cl6) are significantly (8–15 kJ mol−1) more negative than given by most previous evaluators. Values for the chloroethynes are 10–25 kJ mol−1 more positive than given in previous reviews and more limited changes are suggested for other compounds in the series.
Improvement of the pulsed wire method for undulator magnetic-field measurement
Authors: Park K. H. , Jeong S. H. , Kim D. E. , Park I. S. , Chung C. W. , Kang B. K.
Published: July 2002

The U10 undulator for the Pohang Light Source was measured with a pulsed wire measurement (PWM) method. By adjusting the aperture of the slotted optical switch (SOS) for PWM, the sensitivity of SOS output to the wire displacement improved significantly. A calibration table, which translates the output voltage to the displacement of wire, was obtained and the linearity of the PWM was enhanced using this table. The magnetic-field profile of the U10 undulator measured with the PWM method agrees well with that measured with Hall probe mapping. The effect of the wire dispersion on PWM is also discussed.
Euclidean scalar Green function in a higher dimensional global monopole space–time
Authors: Bezerra de Mello E. R.
Published: July 2002

We construct the explicit Euclidean scalar Green function associated with a massless field in a higher dimensional global monopole space–time, i.e., a (1+d)-space–time with d⩾3 which presents a solid angle deficit. Our result is expressed in terms of an infinite sum of products of Legendre functions with Gegenbauer polynomials. Although this Green function cannot be expressed in a closed form, for the specific case where the solid angle deficit is very small, it is possible to develop the sum and obtain the Green function in a more workable expression. Having this expression it is possible to calculate the vacuum expectation value of some relevant operators. As an application of this formalism, we calculate the renormalized vacuum expectation value of the square of the scalar field, 〈Φ2(x)〉Ren, and the energy-momentum tensor, 〈Tμν(x)〉Ren, for the global monopole space–time with spatial dimensions d=4 and d=5.