bluuebunny/crossref_metadata_2025 huggingface dataset:
Equilibrium analysis of a flowing two-fluid plasma
Authors: Yamada Hideaki , Katano Takayuki , Kanai Kazumi , Ishida Akio , Steinhauer Loren C.
Published: October 2002

An improved formalism for a flowing two-fluid equilibrium with constant density is developed. This extends the usual single-fluid model. In this generalization, the magnetic field is replaced by two quantities, the generalized vorticities of each species. Criteria are found for when the single-fluid model is adequate and when the more general two-fluid model is necessary. The two-dimensional equilibria with purely azimuthal ion flow are studied analytically and numerically. Spherical torus and compact toroid equilibria are found that are relevant to the current experiment. The ion flow and plasma beta as well as the size parameter are found to play a major role in the question of whether two-fluid corrections are needed.
Structural and magnetic characterization of Fe nanoparticles synthesized by chemical vapor condensation process
Authors: Dong X. L. , Choi C. J. , Kim B. K.
Published: October 2002

The structural and magnetic characteristics of iron nanoparticles synthesized by a chemical vapor condensation (CVC) process were investigated systematically by an x-ray diffraction method, high-resolution transmission electron microscopy, Mössbauer spectroscopy, magnetometry and thermogravimetric analysis. Typical particle sizes were found to be in the range of 5–13 nm with uniform dispersion. The resulting microstructure of the nanoparticles correlated with parameters of the CVC process. In particular, a CVC technique was derived to fabricate Fe nanoparticles with different magnetic states, e.g., superparamagnetic, ferromagnetic, or a mixture of these two states.
Comparison of crystal structure and electrical properties of tetragonal and rhombohedral Pb(Zr,Ti)O3 films prepared at low temperature by pulsed-metalorganic chemical vapor deposition
Authors: Funakubo Hiroshi , Tokita Kouji , Oikawa Takahiro , Aratani Masanori , Saito Keisuke
Published: October 2002

The crystal structure and the electrical properties were systematically compared for tetragonal and rhombohedral Pb(Zr,Ti)O3 [PZT] films prepared at various deposition temperatures from 580 °C to 395 °C on (111)Pt/Ti/SiO2/Si substrates by pulsed-metalorganic chemical vapor deposition (pulsed MOCVD). Film orientation changed from (111) to (100) and/or (001) with the decrease in the deposition temperature, but the well-crystallized PZT phase was obtained down to 395 °C. The lattice parameter was almost constant with decreasing deposition temperature, suggesting that the Zr and Ti elements in the films were incorporated into the PZT phase. When the deposition temperature decreased, the leakage current density decreased together with a decrease in surface roughness, especially for tetragonal PZT films. Remanent polarization (Pr) continuously decreased with decreasing deposition temperature down to 395 °C, but was above 20 μC/cm2 even at 395 °C. Specifically, the tetragonal film shows good squareness down to 415 °C. These results show that PZT films with low leakage current density and a large Pr were obtained even at 395 °C by pulsed MOCVD irrespective of the film composition.
Functionalization of graphite, glassy carbon, and polymer surfaces with highly oxidized sulfur species by plasma treatments
Authors: Collaud Coen M. , Keller B. , Groening P. , Schlapbach L.
Published: October 2002

SO 2 and SO2+H2O plasma treatments have been performed on highly oriented pyrolytic graphite, glassy carbon and several polymers in order to functionalize their surface with sulfur in different oxidation states. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy measurements prove that highly oxidized sulfur species (SO3, SO3H, SO4, and SO4H) as well as covalently bound sulfur and low oxidized sulphur species (SO and SO2) are formed and chemisorbed at the surface by plasma treatment. The oxidation state of the adsorbed sulfur species depends on the bias potential applied to the sample. The greater the bias, the lower the oxidation state. The same behavior as a function of the plasma parameters is found for all substrates. The maximal coverage of the surface with sulfur functionalities has been estimated to be about one monolayer. The modifications of the surface topography have also been measured with atomic force microscopy.
Effects of segmented electrode in Hall current plasma thrusters
Authors: Raitses Y. , Keidar M. , Staack D. , Fisch N. J.
Published: October 2002

Segmented electrodes placed along a ceramic channel in a Hall thruster are shown to influence significantly the plasma potential distribution. Both the radial potential and the axial acceleration region are sensitive to the location of the segmented electrodes. The measured and theoretical potential profiles appear to be affected in detail by the electrode material (graphite) having lower secondary electron emission than the ceramic channel walls. The measured plasma potential profile is shown as well to correlate with the observed and desirable narrowing of the plasma plume emanating from the thruster.
Model for assessing the melting on Hugoniots of metals: Al, Pb, Cu, Mo, Fe, and U
Authors: Dai Chengda , Tan Hua , Geng Huayun
Published: October 2002

A shock-release model is proposed to calculate shock temperatures along the principal Hugoniot, and to relate initial shock (Hugoniot) to release melting (off-Hugoniot). Thus a melting point crossing the Hugoniot can be defined. For the shock-release model, an assumed configuration of baseplate(metal-sample)/window is modeled to formulate the initial shock and interfacial release processes, the Lindemann law is used to describe the melting behavior of metals at high pressure, and the Grüneisen equation of state is applied to express the relation between pressure and specific internal energy. The effect of melting on the Hugoniot temperature is considered in this model, so the pressure–temperature regime of solid–liquid mixed phase region can be outlined. Aluminum, lead, copper, molybdenum, iron, and uranium were chosen for modeling calculations. It was found from the comparison of calculated results with their high-pressure melting data from experimental measurements that for most investigated metals γ=γ0(ρ0/ρ) (where γ and ρ are Grüneisen parameter and density, respectively, and subscript 0 denotes ambient conditions) is a good approximation to γ at high pressure, and the melting latent heat (ΔHM) at high pressure is better estimated using ΔHM=RTM (where TM is the melting temperature, and R is the gas constant) than using ΔHM=TM⋅ΔSM0 (where ΔSM0 is the melting entropy at ambient pressure).
Multilayer nanogranular magnetic thin films for GHz applications
Authors: Ikeda Kenji , Kobayashi Kazuyoshi , Fujimoto Masayuki
Published: October 2002

(CoFe)–Si–O/Si–O multilayer nanogranular magnetic thin films for GHz rf circuits were designed and fabricated on SiO2/Si substrates using inductively coupled rf sputtering. A multilayer structure consisting of a CoFe ferromagnetic mononanogranular layer covered with an atomic-order SiO2 amorphous phase and a nanometer-order insulative SiO2 amorphous layer was fabricated by repeatedly cosputtering CoFe alloy and SiO2 glass targets and the subsequent single sputtering SiO2 target. The optimized multilayer structured film (appropriate grain size of CoFe and Si–O layer thickness, i.e., CoFe mononanogranular layer: Si–O layer=6 nm: 1 nm) shows superb soft magnetism performance in high-frequency regions, such as a constant 200 of real permeability with 2.2 mΩ cm resistivity and 2.86 GHz self-resonant frequency.
Plasma and ablation dynamics in ultrafast laser processing of crystalline silicon
Authors: Choi Tae Y. , Grigoropoulos Costas P.
Published: October 2002

Mechanisms of ultrafast (femtosecond) laser-induced ablation on crystalline silicon are investigated by time-resolved pump-and-probe microscopy in normal imaging and shadowgraph arrangements. A one-dimensional model of the energy transport is utilized to predict the carrier temperature and lattice temperature as well as the electron and vapor flux emitted from the surface. The temporal delay between the pump and probe pulses is set by a precision translation stage up to about 500 ps and then extended to the nanosecond regime by an optical fiber assembly. The ejection of material is observed at several picoseconds to tens of nanoseconds after the main (pump) pulse by high-resolution, ultrafast shadowgraphs.
Optimization of the silicon oxide layer thicknesses inserted in the Mo/Si multilayer interfaces for high heat stability and high reflectivity
Authors: Ishino M. , Yoda O.
Published: October 2002

We previously demonstrated that the introduction of silicon oxide (SiO2) layers into the interfaces of the Mo/Si multilayer was quite effective in improving the heat stability of the multilayer [M. Ishino et al., Surf. Coat Technol. (to be published)]. However, the soft x-ray reflectivity of the Mo/Si multilayer with SiO2 layers decreased with the thickness of the SiO2 layer because of the large absorption of x rays by oxygen. In this article, an optimization of the thicknesses of the SiO2 layers inserted in the Mo/Si multilayer has been performed so as to minimize the decrease in the soft x-ray reflectivity with the high heat stability maintained. An asymmetric SiO2 layer thicknesses of 0.5 and 1.5 nm are found to be most favorable at the Si-on-Mo interface and at the Mo-on-Si interface, respectively.
Hyper-Rapid thermal defect annealing during grinding of ZnO powders
Authors: Kakazey M. G. , Vlasova M. , Dominguez-Patiño M. , Dominguez-Patiño G. , Gonzalez-Rodriguez G. , Salazar-Hernandez B.
Published: October 2002

We report on the changes in the defect structure of ZnO particles that take place during the grinding of pure ZnO powders and mixtures ZnO–SnO2 and ZnO–TiO2 powders. The qualitative differences in the electron paramagnetic resonance spectra for different specimens were discussed in the context of the hyper-rapid high-temperature spikes created in ZnO particles during mechanical treatment. The thermal spikes cause the defect structure to undergo annealing. The spike duration of the hyper-rapid thermal defects annealing was dependent on the heat conductivity of the ZnO particle environment.
Ferroelectric and ferrimagnetic iron-doped thin-film BaTiO3: Influence of iron on physical properties
Authors: Maier R. , Cohn J. L.
Published: October 2002

Structural and physical properties of ferroelectric and ferrimagnetic pulsed-laser deposition-grown thin-film BaFexTi1−xO3 with 0.5⩽x⩽0.75 (BFTO) are compared with those of BaTiO3 (BTO) films deposited under identical conditions. Fe leads to lattice expansion and deterioration of the crystalline quality in the as-prepared films. Signatures of the paraelectric–ferroelectric phase transition in lattice parameters, resistivity, and capacitance tend to be suppressed in BTO films, but are clearly distinguished in the presence of Fe. While strain elevates TC above bulk values in thin-film BTO to ∼200 °C, Fe doping entails further increases of TC up to ∼320 °C. Current versus voltage measurements demonstrate that Fe converts n-type BTO into p-type BFTO. Fe doping brings about ferrimagnetic ordering with a Néel temperature above 450 °C.
Elemental distribution at the interfaces of NiMn/Co multilayers by x-ray anomalous scattering
Authors: Luo G. M. , Jiang H. W. , Cai J. W. , Liu C. X. , Mai Z. H. , Lai W. Y. , Wang J. , Ding Y. F.
Published: October 2002

Elemental distributions of Ni, Mn, and Co nearby the interfaces of sputtered ultrathin NiMn/Co multilayers have been investigated by x-ray anomalous scattering. In the direction normal to the film, the elements Ni, Co, and Mn are observed to vary gradually at the Co/NiMn interface with each element having a different distribution. After the samples were annealed at 300 °C for periods of 3, 10, or 20 h, the elements are observed to vary gradually at the NiMn/Co interface, as well. To obtain information on the in-plane distribution of each element at the interfaces, x-ray diffuse scattering experiments were performed with x-ray energy close to the Ni, Co, and Mn K edges. Different geometrical interfacial correlated roughness is observed with different x-ray energy.
Surface superconductivity and structural analysis of YC2 single crystals encapsulated in carbon nanocages
Authors: Yosida Y.
Published: October 2002

The magnetization measurements in the temperatures between 2 and 10 K and in the applied fields up to 5 T and x-ray powder diffraction measurement at 293 K for YC2 single crystals encapsulated in carbon nanocages are reported. The highest critical field in the magnetization curve near Tc is in excellent agreement with the nucleation field Hc3 for surface superconductivity. Hc3(2 K), increasing with decreasing mean particle diameter, shows an effect of small-particle size of our nanocrystals. No appreciable size dependence of the Ginzburg critical region is found and suggested to be evidence of the partial suppression of surface superconductivity through the contact between YC2 crystals and the innermost nanocages. Structural parameters derived from the Rietveld refinement of the CaC2 model are consistent with those of the bulk YC2.
Transformation of shock compression pulses in glass due to the failure wave phenomena
Authors: Kanel G. I. , Bogatch A. A. , Razorenov S. V. , Chen Zhen
Published: October 2002

A method of observing the compressive failure waves in glass is presented. Its advantages are good reproducibility of the recorded data and capabilities of measuring, the kinematic parameters of the failure wave and determining by one shot the failure threshold. The experiments presented herein confirm that the network of growing cracks in shock-compressed glass may indeed be considered as a failure wave with a small stress increment. Transformation was observed of the elastic compression wave followed by the failure wave in a thick glass plate into a typical two-wave configuration in a pad of thin glass plates.
Full-band Monte Carlo model with screened pseudopotential based phonon scattering rates for a lattice with basis
Authors: Nguyen Phuong Hoa , Hofmann Karl R. , Paasch Gernot
Published: October 2002

In advanced full-band Monte Carlo (MC) models, the Nordheim approximation with a spherical Wigner-Seitz cell for a lattice with two atoms per elementary cell is still common, and in the most detailed work on silicon by Kunikiyo et al. [J. Appl. Phys. 74, 297 (1994)], the atomic positions in the cell have been incorrectly introduced in the phonon scattering rates. In this article the correct expressions for the phonon scattering rates based on the screened pseudopotential are formulated for the case of several atoms per unit cell. Furthermore, the simplest wave number dependent approximation is introduced, which contains an average of the cell structure factor and the acoustic and the optical deformation potentials as two parameters to be fitted. While the band structure is determined by the pseudopotential at the reciprocal lattice vectors, the phonon scattering rates are essentially determined by wave numbers below the smallest reciprocal lattice vector. Thus, in the phonon scattering rates, the pseudopotential form factor is modeled by the simple Ashcroft model potential, in contrast to the full band structure, which is calculated using a nonlocal pseudopotential scheme. The parameter in the Ashcroft model potential is determined using a method based on the equilibrium condition. For the screening of the pseudopotential form factor, the Lindhard dielectric function is used. Compared to the Nordheim approximation with a spherical Wigner–Seitz cell, the approximation results in up to 10% lower phonon scattering rates. Examples from a detailed comparison of the influence of the two deformation potentials on the electron and hole drift velocities are presented for Ge and Si at different temperatures. The results are prerequisite for a well-founded choice of the two deformation potentials as fit parameters and they provide an explanation of the differences between the two materials, the origin of the anisotropy of the drift velocities, and the origin of the dent in the drift velocity–field relation in a certain field range. The validity of the model is demonstrated by means of comparison with experiments on Ge and Si.
Ionic and electronic processes in quartz:Mechanisms of thermoluminescence and optically stimulated luminescence
Authors: Itoh N. , Stoneham D. , Stoneham A. M.
Published: October 2002

We suggest a model of the atomic and electronic processes responsible for the so-called 110 and 325 °C thermoluminescence (TL) peaks, including predose behavior, and for the room temperature optically stimulated luminescence (OSL) of quartz. Our model is based on defects and defect processes typical of those known from many previous studies of quartz. It explains the experimental observations that the two TL peaks and OSL are correlated with respect to the effects of thermal annealing and photoexcitation after irradiation. The model indicates that the energy for the two TL peaks and OSL is all stored by the same defect pairs. These defect pairs comprise [AlO4]− and [X/M+]+ generated by a radiolytic reaction [AlO4/M+]0→[AlO4]−+M+. Here [AlO4]− is an Al impurity center substituting a Si atom, M+ is an alkali ion, [X/M+] is M+ stabilized by a defect denoted by X and [AlO4/M+]0 is an [AlO4]− center charge compensated by M+. Even though the 110 and 325 °C TL peaks and OSL arise from the same defect pairs, they should emit different luminescence because they arise through different mechanisms: the 325 °C TL peak through the migration of M+, and the OSL through the migration of holes. The 110 °C TL peak is ascribed to the electron–hole recombination at the [AlO4]− centers. According to the model, the TL at 110 and 325 °C and OSL luminesce at different wavelengths.
Dopant deactivation in heavily Sb doped Si (001): A high-resolution x-ray diffraction and transmission electron microscopy study
Authors: Takamura Yayoi , Vailionis Arturas , Marshall Ann F. , Griffin Peter B. , Plummer James D.
Published: October 2002

Laser annealing is being studied as an alternative dopant activation technique to form the ultrashallow, low resistivity junctions required in future generations of integrated circuits. This method benefits from the ability to create uniform, box-shaped dopant profiles with concentrations that can exceed equilibrium solubility values. These supersaturated dopant concentrations, however, exist in a metastable state and deactivate upon subsequent thermal processing. Electrical measurements show that antimony deactivation becomes increasingly severe as the concentration increases. High-resolution x-ray diffraction (HR-XRD), secondary ion mass spectroscopy and transmission electron microscopy were used to study the deactivation process. Under most conditions, Sb deactivation occurs through the precipitate mechanism in which the inactive dopant forms precipitates, leading to a decrease in the substitutional dopant concentration. However, the HR-XRD data reveal that at high concentrations above 6.0×1020 cm−3 during low temperature anneals, the inactive dopant forms a type of inactive structure that resides on a substitutional site within the Si matrix.
Raman measurement and optical properties of Nd:GdCa4O(BO3)3 crystals
Authors: Xia H. R. , Zheng W. Q. , Zhang S. J. , Cheng Z. X. , Cheng X. F. , Yang Z. H.
Published: October 2002

X-ray diffraction measurements on a 0.65 at. % Nd-doped GdCa4O(BO3)3 (Nd:GdCOB) crystal revealed a noncentrosymmetric monoclinic space group Cm with lattice parameters a=8.091±0.001, b=16.023±0.002, c=3.559±0.006 Å, and β=101.30±0.01°. The fitting primitive cell contained two Nd:GdCOB units. Raman data show that the characteristic spectra of Nd:GdCOB are mainly associated with BO3 triangles and partly by Ca(1)O6 octahedra, which implies that the structural rigidity of Nd:GdCOB is mainly associated with the B–O bond stretching and bending modes and partly by the Ca(1)–O bonds. The large distortions of the Gd/NdO6 and Ca(2)O6 octahedra intensify the polar forces and anisotropic lattice forces, which indicates excellent nonlinear properties for Nd:GdCOB. Simultaneously, the large distortions of the Gd/NdO6 octahedra also provide a suitable crystal field for the activated Nd3+ ions, with the site symmetry m lacking inversion symmetry. This condition increases the probability of the parity-forbidden f→f transitions. Also due to the greater number of anion groups in the primitive cell, this crystal would be expected to be excellent as a self-frequency doubled material. The absorption parameters calculated by Judd–Ofelt theory show that the transitions I9/24→F5/24 and I9/24→H9/22 have larger absorption cross sections and enable the laser-diode pumping band around 808 nm to be more than 30 nm in bandwidth. In the calculated luminescence parameters, the radiation F3/24→I11/24 transition at wavelength of 1060 nm has the largest fluorescence branch-ratio and differential stimulated-emission cross section.
What is the ground electronic state of KO?
Authors: Lee Edmond P. F. , Soldán Pavel , Wright Timothy G.
Published: October 2002

High-level, restricted coupled cluster with singles, doubles, and perturbative triples calculations are performed to determine the ground electronic state of KO. In the absence of spin–orbit coupling, we find that the ground state is a Σ2 + state, with a Π2 state lying just over 200 cm−1 higher in energy. We ascertain that basis set extension, higher-order correlation energy, mass-velocity, and Darwin relativistic terms do not change this ordering. We then calculate the low-lying Ω states when spin–orbit coupling is turned on. The Σ21/2+ state undergoes an avoided crossing with the Π21/2 state, and we therefore designate the ground state as X12. This state is essentially Σ21/2+ at short R, but essentially Π21/2 at long R; there is a corresponding A12 state with the opposite behavior. These states have significantly different shapes and so spectroscopy from the adiabatic states. Finally, we calculate the dissociation energy D0, of KO as 66±1 kcal mol−1 and derive ΔHf(KO, 0 K) as 13.6±1 kcal mol−1.
Atomic polarizability, volume and ionization energy
Authors: Politzer Peter , Jin Ping , Murray Jane S.
Published: October 2002

Our primary focus in this work has been upon the relationship between atomic polarizability and volume, although we also looked at the role of ionization energy. For approximating volumes in this context, we tried ten different measures of atomic radii, based upon both empirical and theoretical criteria. Our results confirm that the polarizability can be expressed, to good accuracy, as directly proportional to the volume alone, provided that an appropriate set of radii is used. Most effective for the present purpose are (a) the distances to the outermost maxima of the orbital radial densities and (b) outermost orbital 〈r〉 values. Our data also support an earlier prediction that the correlation would be enhanced by the inclusion of a slowly varying periodic function of the nuclear charge.
Ultraviolet and visible dispersed spectroscopy for the photofragments produced from H2O in the extreme ultraviolet
Authors: Mitsuke Koichiro
Published: October 2002

The photofragmentation of H2O has been studied by fluorescence spectroscopy at photon energies between Ehν=16.9–54.5 eV. The primary photon beam was monochromatized undulator radiation supplied from the UVSOR synchrotron radiation facility. The fluorescence in the wavelength range of 280–720 nm was dispersed with an imaging spectrograph. The dispersed spectra exhibit the hydrogen Balmer lines of H*[n2LJ′′→2 2LJ″″(n=3–9)] and the emission band systems of H2O+[Ã 2A1(0,v2′,0)→X̃ 2B1(0,0,0)], OH+(Ã 3ΠΩ,v′→X̃ 3Σ−,v″), and OH(Ã 2Σ+,v′→X̃ 2ΠΩ,v″). The fluorescence cross sections for these transitions have characteristic dependences on Ehν and vibrational quantum numbers. The cross section summed over the Balmer lines takes a minimum value at Ehν=21.7 eV and is very small even at 24.9 eV beyond which it steadily increases with increasing Ehν. This behavior is understood as that the superexcited states correlating with H*(n⩾3)+OH(Ã 2Σ+) are too repulsive to be accessible below Ehν∼30 eV by the Franck–Condon transitions from H2O(X̃ 1A1) and as that the Balmer emission below 30 eV is mainly due to the H*(n⩾3)+H(n=1)+O(3Pg) channel. The appearance energy of the OH+(Ã 3ΠΩ,v′→X̃ 3Σ−,v″) transitions is found to be ca. 25.5±0.3 eV. This value is much higher than the dissociation limit of 21.5 eV for the OH+(Ã 3ΠΩ)+H(n=1) channel, but is consistent with the vertical ionization energy to H2O+[(1b1)−2(4a1)1 2A1] that has been assumed to correlate with the above dissociation limit in the literature. The vibrational distribution of OH+(Ã 3ΠΩ) evaluated from the OH+(Ã 3ΠΩ,v′→X̃ 3Σ−,v″) band intensities is similar to the prior distribution in the rigid-rotor harmonic-oscillator approximation.
The observation and characterization by rotational spectroscopy of the weakly bound trimer Ar2HBr
Authors: Kisiel Z. , Pietrewicz B. A. , Pszczółkowski L.
Published: October 2002

The weakly bound trimer between two argon atoms and a molecule of hydrogen bromide was identified from its rotational spectrum observed at conditions of supersonic expansion. The spectrum was measured with a cavity, Fourier transform microwave spectrometer and the rotational, quartic, and bromine hyperfine coupling constants were determined for the two most abundant isotopomers Ar402H79Br and Ar402H81Br. The various spectroscopic observables dependent on the harmonic force field were successfully reproduced using ab initio force field calculations. Experimental moments of inertia were then used, together with calculated vibration-rotation inertial contributions to derive the rz geometry. The resulting d(ArBr)=4.166 Å, d(ArAr)=3.840 Å, compare with rz distances d(ArBr)=4.155 Å for ArHBr, and d(ArAr)=3.836 Å for Ar2. Angular information derived from the measured nuclear hyperfine splitting constants and from the electric dipole moment was found to be in remarkable agreement. Comparisons of the available information on the interaction energy and geometries for the ArHX and the Ar2HX series of clusters have been made in order to assess the relationship between the experimental ground state based structural parameters and the desired equilibrium geometry.
Electronic spectra of the C2n+1H (n=2–4) radicals in the gas phase
Authors: Ding H. , Pino T. , Güthe F. , Maier J. P.
Published: October 2002

The visible electronic spectra of the linear l-C2n+1H (n=2–4) radicals have been measured in the gas phase. These have been obtained by means of a mass-selective resonant two-color two-photon ionization technique coupled to a supersonic plasma source. The observed spectra are assigned to the A 2Δ←X 2Π, B 2Σ−←X 2Π, and C 2Σ+←X 2Π electronic transitions arising from σ→π electron promotion. The assignments are based on ab initio calculations, wavelength dependence of the 000 transition on size, and isotopic substitution. The lifetime broadening of the bands and effects due to vibronic coupling are associated with the carbon skeleton bending modes. The detection of these carbon chains in the diffuse interstellar medium appears to be more favorable by radio astronomy rather than by electronic spectroscopy.
Photodissociation of 1,1- and 1,2-C2F2Cl2 at 193 nm by product translational spectroscopy
Authors: Lee Ya-Rong , Chen Cheng-Chu , Lin Shen-Maw , Ko Hung-Sheng
Published: October 2002

In this work, we have investigated the photodissociation of 1,1- and 1,2-C2F2Cl2 (DCDFE) at 193 nm using product translational spectroscopy. Results show that both molecules undergo the competing dissociation of the C–Cl and the C=C bond ruptures with a branching ratio of approximately 1:∼0.3. For 1,1-DCDFE, a slow Cl component was detected in addition to the fast Cl product. In contrast, we observed no slow component for 1,2-DCDFE, but a pair of secondary products Cl+C2F2 from the internally excited fragment CF=CFCl. From the measured anisotropy and energy disposal of the products, we conclude that upon excitation to the ππ* state, both molecules dissociate primarily on the excited potential energy surface.
Measurements of fuel and shell areal densities of OMEGA capsule implosions using elastically scattered protons
Authors: Frenje J. A. , Li C. K. , Séguin F. H. , Kurebayashi S. , Petrasso R. D. , Soures J. M. , Delettrez J. , Glebov V. Yu. , Meyerhofer D. D. , Radha P. B. , Roberts S. , Sangster T. C. , Skupsky S. , Stoeckl C.
Published: October 2002

Implosions of capsules filled with small quantities of deuterium–tritium (DT) were studied using up to seven proton spectrometers on the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Simultaneous measurements of elastically scattered protons, i.e., “knock-on” protons generated from DT neutrons were obtained in several directions. The capsules, nominally 945 μm in diameter and with CD shells of ∼20 μm thickness, were filled to about 15 atm and irradiated with 23 kJ of UV light. The high-energy protons from these implosions were used to infer fuel areal density (6.8±0.5 mg/cm2), an average shell areal density (71±3 mg/cm2), and shell asymmetries of up to about 25 mg/cm2. In addition to presenting new results, these measurements verify and significantly improve upon the accuracy of the fuel areal density results obtained utilizing knock-on deuterons from hydrodynamically equivalent, pure DT implosions [C. K. Li et al., Phys. Plasmas 8, 4902 (2001)].
Turbulent generation of large-scale flows and nonlinear dynamics of flute modes
Authors: Andrushchenko Zhanna N. , Pavlenko Vladimir P.
Published: October 2002

Generation of large-scale flows (zonal flows and streamers) by flute mode turbulence is examined. The evolution equations for mean flow generation are obtained by averaging the model equations over fast small scales. For a system containing both drift-type waves and large-scale structures, small scales are modulated by larger scale shear flows so that energy in the small-scale component is not conserved. A WKB-type wave kinetic equation that describes the conservation (along the rays) of an action-like invariant of the flute mode turbulence with slowly varying parameters due to the mean sheared flow is formulated. The relevant action-like integral is shown to correspond to the quantity conserved for the small-scale component alone. The structure of the action integral is determined by the structure of the matrix element describing the interaction of the small-scale and large-scale component. The k-space diffusion coefficient for the zonal flows and streamers are calculated.
Electron holography study of active interfaces in zinc oxide varistor materials
Authors: Elfwing Mattias , Olsson Eva
Published: October 2002

Electron holography measurements on individual interfaces in ZnO varistor material have been performed in the transmission electron microscope and correlated with the interfacial microstructure. The interfacial microstructure, including the local chemistry, has been determined using scanning transmission electron microscopy in combination with energy-dispersive x-ray spectrometry. The grain boundary charge was directly determined from electron holography to be negative, with a positively charged depletion region across it. The phase information has been analyzed to reveal several aspects of the double Schottky barrier, including the barrier height and the depletion region width. Variation in sample thickness was compensated for using a standard electron energy-loss log-ratio method combined with a total-inelastic mean free path calculated from scattering theory. From a potential line trace across the interface the barrier height was measured to be 0.71±0.20 V and the depletion region width estimated to approximately 150 nm. Evaluation of the mean inner potential of a ZnO grain from the phase map yielded a value of |V0|=21±4.2 V. Calculations of the mean inner potential using a nonbinding approximation and the Doyle–Turner scattering amplitudes, yielded, however, a lower value, |V0|=16.1 V. An asymmetric spatial extent of the depletion region was observed. These findings are compared to previously reported results from active interfaces in ZnO varistor materials.
Shock front formation at vacuum arc anodes
Authors: Gidalevich E. , Goldsmith S. , Boxman R. L.
Published: October 2002

A vacuum arc plasma jet between copper electrodes is considered as a supersonic hydrodynamic jet (the primary plasma jet) that bombards the anode and sputters and/or reflects ions (secondary plasma). An initial primary ion jet velocity of v0=1.5×104 m/s is assumed. The time-dependent interaction between primary and secondary ions is considered for primary ion concentrations of n0=1018 and 1019 m−3 and for a Cu-Cu self-sputtering yield coefficient of β=0.2. It is found by numerical calculation that the primary jet is decelerated by the collisions with the secondary ions. In the case where the mean free path in the primary plasma is much less than the interelectrode gap (l11≪L) and the mean free path for the primary-secondary ion collision is much more than the interelectrode gap (l12≫L), the primary jet decelerates, but initially remains supersonic, while at a later time the deceleration is to a subsonic value, and a shock front appears. For a primary ion concentration of n0=1018 m−3 and an initial secondary ion velocity ≈0.1×v0, a shock front appears at time t≈245×L/v0 while for n0=1019 m−3, at t≈135×L/v0.
Cell geometry designs for efficient plasma display panels
Authors: Veronis G. , Inan U. S.
Published: October 2002

We investigate the performance of several nonstandard plasma display panel cell geometry designs involving two-dimensional variations of the standard coplanar-electrode design. A cell design with a modified shape of sustain electrodes is found to have ∼20% larger visible light generation efficiency without substantial increase of the operating voltages. Similar performance improvement is achieved by designs with different shapes of the upper dielectric, or by those involving two different dielectric layers. The dependence of cell performance on the design parameters of these structures is investigated.
Magnetic and electrical properties of Mn-doped p-type β-FeSi2 single crystals
Authors: Arushanov E. , Ivanenko L. , Vinzelberg H. , Eckert D. , Behr G. , Rößler U. K. , Müller K.-H. , Schneider C. M. , Schumann J.
Published: October 2002

We investigated the temperature and magnetic field dependence of the Hall effect, the magnetization and the resistivity of Mn-doped β-FeSi2 single crystals in the temperature range of 4–300 K in magnetic fields up to 5 T. A negative magnetoresistance as well as strong nonlinear magnetic field dependence of the Hall resistivity and magnetization were observed. The anomalous contribution to the Hall resistivity is found to be important. We also observed the value of the anomalous Hall coefficient to increase with decreasing temperature as the square of the resistivity. It was shown that the magnetization of Mn-doped samples cooled in zero-external field and in a field are different. This resembles the properties of spin glasses. The dominant scattering mechanisms are determined by analyzing the Hall mobility data. The value of the valence band deformation potential is estimated. A particularly important role is played by the anomalous Hall effect which is the microscopic mechanism involving the spin dependent scattering on Mn ions and spin–orbit coupling in the Mn-doped β-FeSi2 single crystals.
Preparation and characterization of surface plasmon resonance tunable gold and silver films
Authors: Gupta R. , Dyer M. J. , Weimer W. A.
Published: October 2002

Precise control of thermal evaporation deposition parameters allows the reproducible production of silver and gold island films on glass substrates with tunable surface plasmon resonance wavelengths. Specific combinations of substrate temperature, deposition rate, and film thickness produce films exhibiting surface plasmon resonance wavelengths that can be adjusted from throughout the visible and into the near infrared regions of the electromagnetic spectrum. The effects of deposition parameters on surface plasmon resonance wavelengths are quantified using a so-called “design of experiment” analysis. The analysis produces reliable predictive models for producing Ag and Au films with predetermined surface plasmon resonance wavelengths.
Electric field effects on electron mobility in n-AlGaAs/GaAs/AlGaAs single asymmetric quantum wells
Authors: Lima F. M. S. , Fonseca A. L. A. , Nunes O. A. C. , Fanyao Q.
Published: October 2002

We calculated low-temperature electron mobility in n-AlGaAs/GaAs/AlGaAs single asymmetric quantum wells in the presence of a uniform electric field directed perpendicularly to the interfaces. The quantum well asymmetry is due to the doping profile (one-side modulation doping). Following a variational scheme, we solved both Schrödinger and Poisson equations simultaneously and the results were used to calculate the low-temperature (quasielastic) scattering rates. Only relevant scattering mechanisms were taken into account, namely ionized impurity, interface roughness, alloy disorder, and acoustic phonons (deformation potential and piezoelectric coupling). Our results show that both interface roughness and alloy disorder scattering rates are strongly dependent upon the electric field strength. We also show that there are interesting changes in the dominance of the mobility among different scattering processes, which leads to the formation of a maximum in the mobility dependence on the electric field strength. In general, this maximum occurs for some positive electric field (antiparallel to growth direction) and it indicates that longitudinal electric fields can be used to dislocate the electron wave function, enhancing in turn the two-dimensional electron mobility in such quantum wells.
Luminescence of pulsed laser deposited Gd2O3:Eu3+ thin film phosphors on quartz glass substrates
Authors: Seo Soo Yeon , Lee Seonghoon , Park Hee Dong , Shin Namsoo , Sohn Kee-Sun
Published: October 2002

Thin film phosphors of Gd2O3:Eu3+ were deposited on quartz glass plates by pulsed laser deposition and compared with typically used thin film phosphors composed of Y2O3:Eu3+ in terms of cathodoluminescence (CL) and photoluminescence (PL). Both the CL and PL of Gd2O3:Eu3+ thin film phosphor were superior to those of corresponding data on currently widely used Y2O3:Eu3+ red thin film phosphor. In particular, the Gd2O3:Eu3+ thin film phosphor showed a much better cathodoluminescence at low excitation energy (less than 1 keV) than a Y2O3:Eu3+ film of the same thickness, indicating that the Gd2O3:Eu3+ thin film phosphor is a much better candidate for use in field emission displays.
Magnetic properties and martensitic transformation in quaternary Heusler alloy of NiMnFeGa
Authors: Liu Z. H. , Zhang M. , Wang W. Q. , Wang W. H. , Chen J. L. , Wu G. H. , Meng F. B. , Liu H. Y. , Liu B. D. , Qu J. P. , Li Y. X.
Published: October 2002

Quaternary Heusler alloy Ni2(Mn,Fe)Ga has been studied systematically for the structure, martensitic transformation, and magnetic properties in two systems of Ni50.5Mn25−xFexGa24.5 and Ni50.4Mn28−xFexGa21.6. Substituting Fe for Mn up to about 70%, the pure L21 phase and the thermoelastic martensitic transformation still can be observed in these quaternary systems. Iron doping dropped the martensitic transformation temperature from 220 to 140 K, increased the Curie temperature from 351 to 429 K, and broadened the thermal hysteresis from about 7 to 18 K. Magnetic analysis revealed that Fe atoms contribute to the net magnetization of the material with a moment lower than that of Mn. The temperature dependence of magnetic-field-induced strains has been improved by this doping method.
Spectra and energy levels of Tb3+(4f 8) in GaN
Authors: Gruber John B. , Zandi Bahram , Lozykowski H. J. , Jadwisienczak W. M.
Published: October 2002

The cathodoluminescence spectra of Tb3+ ions implanted and annealed in GaN epilayers have been analyzed and modeled according to its incorporation into a substitutional Ga lattice site having D2 point group symmetry. High-resolution emission spectra obtained at 11 K between 380 and 750 nm are identified as transitions from the G65,D35 combined manifold and the D45 manifold to individual energy (Stark) levels of the FJ7 multiplet manifolds. All intense peaks and nearly all weaker peaks and bands are associated with emission from Tb3+ ions in a similar site. The observed crystal-field splitting of the F67,F57, and F47 manifolds is much too large for any lattice-sum predictions based on Tb3+ ions in C3v sites. Calculated splittings and relative intensities based on a site symmetry of D2 give the best overall agreement with the observed data.
Topological complexity, contact order, and protein folding rates
Authors: Faisca P. F. N. , Ball R. C.
Published: October 2002

Monte Carlo simulations of protein folding show the emergence of a strong correlation between the relative contact order parameter, CO, and the folding time, t, of two-state folding proteins for longer chains with number of amino acids N⩾54, and higher contact order, CO>0.17. The correlation is particularly strong for N=80 corresponding to slow and more complex folding kinetics. These results are qualitatively compatible with experimental data where a general trend towards increasing t with CO is indeed observed in a set of proteins with chain length ranging from 41 to 154 amino acids.
Numerical determination of pseudorotation constants
Authors: Katzer Gernot , Sax Alexander F.
Published: October 2002

We describe a general numerical method for the calculation of pseudorotation constants at an accuracy suited for thermodynamic applications. The pseudorotation is treated using classical mechanics along a pseudorotational pathway, which is spanned by molecular structures obtained from conventional ab initio geometry optimization. We present numerical results for systems with vertical pseudorotation arising from ring puckering (cyclopentane, cyclopentasilane) and for systems with in-plane pseudorotation arising from Jahn–Teller distortion of planar rings (benzene cation, cyclopentadienyl radical, cyclopropenyl radical).
Front velocity in models with quadratic autocatalysis
Authors: Vanag Vladimir K. , Epstein Irving R.
Published: October 2002

Front propagation is studied in several reaction–diffusion models based on the Oregonator model of the Belousov–Zhabotinsky reaction. Each system involves autocatalysis (X→2X), termination (2X→0) and consumption of the autocatalyst (X→0, X+Y→0), augmented with interconversion (X↔R) between the autocatalyst X and a rapidly diffusing unreactive species R. We investigate the dependence of the front velocity on the diffusion coefficients of X and R, the interconversion rates, and the other kinetic parameters, when the system possesses either one or two stable steady states.
Quaternionic eigenvalue problem
Authors: De Leo Stefano , Scolarici Giuseppe , Solombrino Luigi
Published: October 2002

We discuss the (right) eigenvalue equation for ℍ, ℂ and ↛ linear quaternionic operators. The possibility to introduce an isomorphism between these operators and real/complex matrices allows us to translate the quaternionic problem into an equivalent real or complex counterpart. Interesting applications are found in solving differential equations within quaternionic formulations of quantum mechanics.
Wavefronts, caustic sheets, and caustic surfing in gravitational lensing
Authors: Frittelli Simonetta , Petters A. O.
Published: October 2002

Very little attention has been paid to the properties of optical wavefronts and caustic surfaces due to gravitational lensing. Yet the wavefront-based point of view is natural and provides insights into the nature of the caustic surfaces on a gravitationally lensed lightcone. We derive analytically the basic equations governing the wavefronts, lightcones, caustics on wavefronts, and caustic surfaces on lightcones in the context of weak-field, thin-screen gravitational lensing. These equations are all related to the potential of the lens. In the process, we also show that the standard single-plane gravitational lensing map extends to a new mapping, which we call a wavefront lensing map. Unlike the standard lensing map, the Jacobian matrix of a wavefront lensing map is not symmetric. Our formulas are then applied to caustic “surfing.” By surfing a caustic surface, a space–borne telescope can be fixed on a gravitationally lensed source to obtain an observation of the source at very high magnification over an extended time period, revealing structure about the source that could not otherwise be resolved. Using our analytical expressions for caustic sheets, we present a scheme for surfing a caustic sheet of a lensed source in rectilinear motion. Detailed illustrations are also presented of the possible types of wavefronts and caustic sheets due to nonsingular and singular elliptical potentials, and singular isothermal spheres, including an example of caustic surfing for a singular elliptical potential lens.
Effect of time dependent concentration gradients on electrochemical atomic force microscopy measurements
Authors: Stappers L. , Fransaer J.
Published: October 2002

During electrochemical atomic force microscopy (AFM) measurements that involve metal deposition or dissolution, the photodiode voltage changes when the electrode potential changes. These changes in photodiode voltage are caused by deflection of the laser beam due to concentration gradients near the electrode. In this work, the changes in photodiode voltage versus polarization time were studied using a commercial AFM. For an anodically polarized electrode, the concentration increases near the electrode due to metal dissolution. This causes a steady decrease in photodiode voltage. For a cathodically polarized electrode, oscillations in the photodiode voltage are observed. These oscillations are caused by Rayleigh–Bénard instabilities due to the fact that the concentration, and hence the density of the electrolyte near the electrode, is lower than the bulk electrolyte. A mathematical model was constructed that calculates the changes in photodiode voltage with polarization time.
Precipitation of an icosahedrally symmetric ordered phase in Zr–Ti–Cu–Ni–Al metallic glasses
Authors: Xing L. Q. , Shen Y. T. , Kelton K. F.
Published: October 2002

Results from a study of the precipitation of an icosahedrally symmetric ordered phase in Zr62−xTixCu20Ni8Al10 amorphous alloys are presented. The data indicate the development of icosahedral short-range order (similar to that in the ordered phase) in the undercooled melt during quenching, and in the amorphous phase with annealing in the supercooled liquid region. Precipitation is controlled by long-range diffusion in alloys made with less than 3 at. % Ti. The resulting lower nucleation rates and longer induction times lead to a fine microstructure that contains icosahedral phase (i phase) grains ranging from 50 to 100 nm in diameter. In the glasses made with 5–7.5 at. % Ti, the composition of the precipitating phase is more similar to that of the glass, lowering the kinetic nucleation barrier and leading to an extremely fine nanostructured devitrified material, with i phase grain sizes from 2 to 5 nm. The x-ray diffraction pattern from this phase is similar to that of the i phase. However, because the grain size is nearly the same as the edge length of the unit cell of a high-order crystal approximate phase, no distinction can be made between the i phase and crystal approximate phases in such nanostructured materials.