Transition Current Density Research Articles

Vibrational transition current density in (2S,3S)-oxirane-d2: visualizing electronic and nuclear contributions to IR absorption and vibrational circular dichroism intensities

Vibrational transition current density (TCD) plots and charge-weighted nuclear displacement vectors for selected vibrational modes of A and B symmetry in (2S,3S)-oxirane-d2 are used to visualize the electronic and nuclear contributions to infrared absorption and vibrational circular dichroism intensities. Vibrational TCD provides a vector field map of the integrand of the electronic contribution to the velocity-form electric dipole transition moment. Linear nuclear and electronic charge flow in planes parallel to the electric dipole transition moment vector provides visualization of contributions to IR intensity, while angular and circular charge flow perpendicular to this vector provide visualization of the magnetic dipole transition moment content of vibrational circular dichroism intensity. Four vibrational modes with several types of nuclear motion and the effect of basis set size on vibrational TCD are examined.

Vibrational Transition Current Density in (S)-Methyl Lactate: Visualizing the Origin of the Methine-Stretching Vibrational Circular Dichroism Intensity

Vibrational transition current density (TCD) plots for the methine stretch of (S)-methyl-d3 lactate-Cd3 in four conformations are presented. A vibrational TCD map is a vector-field plot over a grid of points of the integrand of the electronic contribution to the velocity-form electric dipole transition moment. TCD plots allow visualization of the flow of electron density produced by nuclear motion, which can be used to identify angular and circular charge flow leading to the electronic magnetic dipole transition moment contribution to vibrational circular dichroism (VCD). For the methine stretch in (S)-methyl-d3 lactate-Cd3, nuclear motion is largely confined to the two atoms of the methine bond, but the electron current density is distributed throughout the molecule. The methine-stretching VCD intensity calculated for the (S)-methyl-d3 lactate-Cd3 conformers is interpreted in terms of the relative contributions from the nuclear electric- and magnetic-dipole transition moments, and from linear electron ch...

Microscopic Description of g Factors and M1 Properties in Platinum Isotopes**The project supported by National Natural Science Foundation of China

Starting from the shell model configurations, valence nucleon effective interactions and fermion M1 transition current density operator, the counterparts in the proton-neutron interacting boson model (sdIBM-2) of the fermion Hamiltonian and M1 transition current density operator are derived microscopically with the help of Dyson expansion technique. The boson g factors are abstracted from the boson M1 transition current density operator. Spectra, g factors of states and M1 matrix elements between and are calculated for the even 192-198Pt isotopes in the sdIBM-2. The theoretical results fit experimental data quite well.

Promotion of phase transformation and single-phase formation in silver-doped Tl–Ba–Ca–Cu–O superconducting thin films

Phase transformation and physical characteristics of the spray-pyrolyzed Tl–Ba–Ca–Cu–O superconducting films with 3 mol% silver dopant have been studied using electrical resistivity, x-ray diffraction, and scanning electron microscopy. The major phase formed in the resultant film, annealed at a temperature of 885 °C for 3 min, was found to be the nearly single-phase, high-Tc Tl2Ba2Ca2Cu3Oy (Tl-2223). The multiple phase of Tl2Ba2Ca2Cu3Oy and TlBa2Ca2Cu3Oy (Tl-1223) appeared at annealing temperatures lower and higher than 885 °C. It was also observed that Ag dopant effectively reduces normal resistivity at 300 K and enhances the phase transformation of single-Tl-layer Tl-1223 to double-Tl-layer Tl-2223 phases and further helps to form the nearly single-phase Tl-2223 within a short duration. Critical transition temperature (Tc,zero) and current density (Jc, 77 K, 0 Tesla) of the best resultant film were shown to be 123 K and 5.7 × 104 A/cm2, respectively.

Electrodeposition of Copper-Nickel Alloys from a Citrate Bath Containing Boric Acid

SUMMARYCopper-nickel alloys have been electrodeposited on steel substrates from a bath containing copper sulphate, nickel sulphate, sodium sulphate, sodium citrate and boric acid. Galvanostatic cathodic polarization, cathodic current efficiency and composition of the alloys were studied as influenced by bath composition, current density and temperature.The bath is characterized by high cathodic current efficiency. Current density is found to strongly influence the composition of the deposits. At low current densities (lower than a certain transition current density), a copper-rich alloy is deposited with copper (the more noble metal) being the preferentially deposited metal. At larger current densities, nickel becomes the nobler metal and is deposited preferentially. The magnitude of the transition current density depends upon the bath composition and temperature. The structure and surface morphology of the as-deposited alloys were examined by XRD and SEM. The results reveal the presence of a single solid solution phase with face centred cubic structure. The morphology of the deposits is mainly controlled by the alloy composition.

Electron Transition Current Density in Molecules. 2. Ab Initio Calculations for Electronic Transitions in Ethylene and Formaldehyde

We present the first examples of ab initio calculations of electron transition current density (TCD) maps in molecules. Expressions for TCD, derived previously, are implemented at the ab initio level for the π−π* transition in ethylene and the π−π* and n−π* transitions in formaldehyde, with the CI-singles approximation for the excited states. The vector field calculations of the TCD were carried out utilizing an adaptation of Gaussian 92 and displayed with the AVS software program package. The TCDs can be viewed in various planes to achieve the perspective desired. In the case of the π−π* transitions, large vector-field components can be seen along the direction of the allowed electric dipole transition moment. Minor components perpendicular to the principal direction can also be seen, which integrate to zero over the volume of the molecule and do not contribute to the electric dipole transition moment. For formaldehyde, distinct contributions from π−π* and ny − 3px configurations are observed. For the n−π* transition in formaldehyde, the magnetic dipole character of this transition is apparent from the circulation of TCD about the CO bond axis at both the oxygen and the carbon centers. In addition, the electric quadrupole character of this transition is apparent in the xy-symmetric pattern of the TCD in a region midway along the CO bond. We conclude that TCDs of electronic transitions provide new insight into the spatial character and composition of such transitions, which should prove useful in relating the results of quantum mechanical calculations to molecular electronic structure and dynamics.

Electron Transition Current Density in Molecules. 3. Ab Initio Calculations for Vibrational Transitions in Ethylene and Formaldehyde

Electron Transition Current Density in Molecules. 3. <i>Ab Initio</i> Calculations for Vibrational Transitions in Ethylene and Formaldehyde

Electron Transition Current Density in Molecules. 1. Non-Born−Oppenheimer Theory of Vibronic and Vibrational Transitions

The one-particle electron transition current density (TCD) for vibronic transitions between pairs of stationary states in molecules is defined. Expressions for TCD are developed using the complete adiabatic (CA) formalism in which the electronic wave function carries an explicit dependence on the nuclear momenta, as well as the usual dependence on nuclear positions. In the case of vibronic transitions, the principal non-Born−Oppenheimer (non-BO), nuclear-momentum-dependent contribution to TCD is accompanied by a less important BO, nuclear-position-dependent contribution. For vibrational transitions within a single electronic state, the BO contribution vanishes, leaving only non-BO, nuclear-momentum-driven TCD. In the limit of pure electronic transitions, or vibrational transitions within a single electronic state, it is shown that electron TCD satisfies the continuity equation for the conservation of electron transition probability density (TPD) for any pair of stationary states. TCD is a vector field having a unique representation at each point in the Cartesian space of a molecule. It is shown that TCD is a dynamic representation of the changes in TPD associated with electrons in molecules under the influence of a transition-inducing perturbation and that it provides direct visual information concerning the participation of all spatial regions of the molecule in quantum transitions. The use of TCD provides an opportunity to view uniquely electronic motion associated with quantum mechanical transitions in molecules.

Growth of (11n) oriented Bi–Ca–Sr–Cu–O films by liquid phase epitaxial method

Films of Bi–Ca–Sr–Cu–O (BCSCO) superconductor of the Bi2CaSr2Cu2Ox composition have been grown by the liquid phase epitaxy method (LPE) using a partially closed growth chamber. The films were grown on (110) NdGaO3 substrates by slow cooling under optimized conditions below the peritectic melting point (885 °C) of Bi2CaSr2Cu2O8. Optimization of parameters, such as seed rotation, soak of initial growth temperature, and growth period, results in the formation of the 2122 phase of BCSCO. X-ray diffraction (XRD) measurements show that the films grown on (110) NdGaO3 have a preferred (11n) orientation. The best values of zero resistance transition (Tc0) and critical current density (Jc0) obtained for films grown on (110) NdGaO3 substrates are 87 K and 5.7 × 104 A/cm2 (at 20 K), respectively. The films grown at rotation rates of less than 30 and more than 80 rpm are observed to be associated with a subphase in the Bi2CaSr2Cu2O8 system. Electron microprobe analysis indicates the composition of this subphase to be Bi0.07Ca0.93Sr2Cu5O8. Higher growth temperatures (&gt;860 °C) also encourage the formation of this phase.

硫酸塩浴からのＺｎ―鉄族金属合金電析に及ぼすチオシアン酸イオンの影響

The electrodepositon of Zn-iron-group metal binary alloys, which has been applied in the production of highly corrosion-resistant alloy-plated steel sheet, was conducted in sulfate baths. The current density-dependence of the alloy composition demonstrated a typical feature of an anomalous codeposition in sulfate baths. As the present authors reported previously, the alloy deposition behavior was divided with respect to the current density into four regions. The presence of thiocyanate (SCN-) ions in the baths changed the alloy deposition behavior both in lower current density region I where normal codeposition occurred with extremely poor current efficiency and in the region II where anomalous codeposition occurred with high current efficiency. The partial current efficiency of iron-group metal was found to increase in regions I and II. The boundary current density between these two regions, which was also known as the transition current density, was also found to increase. It was concluded that the catalytic action of SCN- ions served to explain well the changes in the electrodeposition behavior.

Electrodeposition of Zn-Ni alloys in sulfate electrolytes

The electrodeposition of Zn-Ni in sulfate solutions has been investigated by means of polarization curves, morphological analysis and electrochemical impedance using a rotating disc electrode. The polarization curves showed two parts, the first one related to the Zn-Ni normal codeposition and the second one to the Zn-Ni anomalous codeposition. The mass transport influenced only the Zn-Ni normal codeposition and had no influence on the anomalous codeposition. The temperature showed a great influence on the Zn-Ni alloy deposition and affected both parts of polarization curves. The electrolyte composition had no influence on the Zn-Ni anomalous codeposition, but it affected the transition current density between normal codeposition and anomalous codeposition. The impedance diagrams were obtained in sulfate electrolytes and showed four loops at low frequency domain at the beginning of anomalous codeposition : three capacitive loops and one inductive. For the high polarizations, one of the capacitive loops disappears. These results were discussed comparatively to those previously obtained for chloride electrolyte, in view of establishing a kinetic model for the sulfate electrolyte.

Melt processing for obtaining REBa/sub 2/Cu/sub 3/O/sub y/ superconductors (RE=Nd, Sm) with high T/sub c/ and large J/sub c/

An oxygen-controlled melt growth (OCMG) process has been employed for NdBa/sub 2/Cu/sub 3/O/sub y/ (Nd123) and SmBa/sub 2/Cu/sub 3/O/sub y/ (Sm123) superconductors for a comparative study. Both Nd123 and Sm123 samples melt-grown in reduced oxygen atmospheres exhibited an enhanced superconducting transition temperature (T/sub c/) with a sharp transition and large critical current density (J/sub c/) in a high field region at 77 K and for the applied field parallel to the c-axis of samples (H/c). For Nd123, a preferential formation of high T/sub c/ phase in a low oxygen partial pressure (P(O/sub 2/)) could be qualitatively described considering the thermodynamic stability boundaries of the Nd/sub 1+x/Ba/sub 2-x/Cu/sub 3/O/sub y/ solid solutions on the LOG[P(O/sub 2/)] vs. 1/T (K/sup 9/-1) phase diagram. A long-term oxygen annealing study for an OCMG-processed Nd123 sample revealed that the annealing temperature should be as low as 300/spl deg/C. >

Superconductivity and microstructure of epitaxial (Tl,Bi)Sr 1.6Ba 0.4Ca 2Cu 3O 9−δ thin films

Epitaxial (Tl,Bi)Sr 1.6Ba 0.4Ca 2Cu 3O 9−δ ((Tl,Bi)-1223) thin films on (100) single crystal LaAlO 3 substrates were successfully synthesized by a two-step procedure. The (Tl,Bi)-1223 phase development in both air and argon was systematically investigated by X-ray diffraction. The microstructure and epitaxial relationship between films and substrates were measured by X-ray Φ scan, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The DC resistance versus temperature transition, zero-field-cooled (ZFC) and field-cooled (FC) magnetization transition, hysteresis curve, and transport critical current density were measured. The zero-resistance transition temperature was 107 K, and the critical current density at 77 K and zero field was higher than 2 × 10 6 A/cm 2. (Tl,Bi)-1223 films have good flux-pinning properties as shown by the slow decrease of the critical current density in an external magnetic field.

Torsional multipole magnetic response of a heavy spherical nucleus

The predictions of the distorted Fermi-sphere model for magnetic isoscalar resonances are summarized. In this model a heavy spherical nucleus is thought of as a charged piece of spin and isospin saturated nuclear Fermicontinuum possessing properties of an elastic-like matter. The magnetic resonances are described in fluid-dynamical terms and interpreted as manifestations of elastic torsional vibrations of the nucleus. The process of nuclear magnetization induced by inelastically scattered electrons is described as a transition from a currentless ground state to a magnetized excited one which is characterized by a non-zero magnetic multipole moment. We present calculations of a complete set of integral characteristic parameters of Mλ, T = 0 resonances such as position of energy peak, excitation probability and magnetic oscillator strength computed as functions of mass number and multipole degree λ ≥ 2. An analytic form is given for collective transition current density and the PWBA computed form factors that may be used for analysis of measurements with inelastically scattered electrons. Numerical estimates are performed with use of the DWBA code. Theoretical predictions are presented in juxtaposition with the DALINAC data available on M2 giant resonance in spherical nuclei. We briefly discuss the microscopic effects of two-particle correlations between nucleons occupying two different single-particle orbits of shell structured mean field that may, in our opinion, be responsible for the collective torsional magnetic response predicted by the model in question.

Analytic model for the grain structures of near-bamboo interconnects

Scaling of electromigration test results for near-bamboo interconnects from accelerated test conditions to service conditions requires an understanding of the microstructural characteristics of the interconnects. An analytic model has been developed that allows prediction of the average polygranular cluster lengths and the number of clusters in a line, given the linewidth, the line length, and the characteristics of the grain size distribution of the original film. Grain-structure characteristics have also been measured for lines patterned from computer-generated thin-film microstructures. The large-cluster-length tail of the polygranular cluster-length distribution is well fit by an exponential distribution function, which can be accurately predicted using our new analytic model. Polycrystalline clusters shorter than a critical length Lcr cannot fail due to electromigration-induced grain-boundary diffusion alone, so that when all clusters in a line are shorter than Lcr, there is a transition in failure mechanisms. The model can be used to calculate the number of clusters longer than Lcr as a function of the line and grain-structure characteristics, as well as a function of the current density. The current-density dependence of the median time to failure due to polygranular failure mechanisms in near-bamboo lines, as well as the transition current density at which the transition in failure mechanisms occurs are predicted. This transition current density depends on the linewidth and the line length, as well as the grain size and grain size distribution of the film from which the line was patterned.

Melt processing for obtaining NdBa2Cu3Oy superconductors with high T c and large J c

A reduced oxygen atmosphere during melt processing turned out to be critical for the fabrication of NdBa2Cu3Oy (Nd123) superconductors possessing high superconducting transition temperature (Tc) with a sharp transition and large critical current density (Jc) at 77 K. In a dc magnetization measurement, Nd123 superconductors melt processed in flowing a mixture gas of 1% O2 in Ar exhibited the Tc of about 95 K and the transition width of 1.5 K with the applied field of 10 Oe. A four-probe measurement showed the zero resistive transition Tc (R=0) of about 95 K. An anomalous peak effect in the magnetization hysteresis (M-H) loops was commonly observed and lead to large magnetic Jc of 2×104 A/cm2 at 77 K and 2 T for the applied field H parallel to the c axis of a sample (H∥c). This achievement is attributable to a preferential formation of high Tc phase (x&amp;lt;0.1) among the Nd1+xBa2−xCu3Oy solid solutions in a reduced oxygen atmosphere.

Dipole torus mode in nuclear fluid-dynamics

The nuclear fluid-dynamics is applied to the study of a dipole electric response related to the transverse poloidal oscillations of a particle flow. This response is associated with excitation in the nucleus volume of the spherical Hill vortex-torus-like current structure harmonically oscillating in time; the nucleus shape remains spherical. The energy evaluated within the distorted Fermi-surface model is predicted to be E(1 torus −) = 65–85A −1 3 MeV , i.e. the torus excitation is expected to be identified experimentally as 2khω isoscalar dipole resonance. An analytic form is derived for the electric form factor and numerical calculations of the transition current density are presented. The contribution to the cross section of photoabsorption computed in the PWBA is estimated to be σ γ(1 torus −)= 10 −3−10 −4Z 2 A MeV·fm 2 . Some hints for further experiments are suggested.

Boson-model M1 form factors for inelastic electron scattering on 130,132,134Ba

The proton-neutron interacting-boson model (IBA-2) is used to predict the (e,e') form factor for collective 1+ excitation in 130,132,134Ba. A simple estimate of the 130Ba transition current density, and thence of the form factor, is obtained from the known form factor of 164Dy by a scaling method built on PWBA and Fourier-Bessel analysis. A weightier prediction is obtained from microscopic boson structure and DWBA. The 1+ excitation should be observable in the bariums. Boson g factors are calculated.

クロムを有する亜鉛合金の電析

Zn-Cr and Zn-Fe-Cr alloys were electrodeposited from sulfate baths. It was found that the Zn-Cr deposits contained extremely small amounts of Cr(III) compound. In Zn-Fe-Cr system, on the other hand, the Cr content in the deposits was considerably higher and the partial current density of Cr increased linearly with that of Fe. Cr(III) compound was present near the surface of the deposits and metallic Cr was co-present with Cr(III) compound in the bulk of the deposits.The increase in the concentration of Cr3+ in the baths brought about an increase in the transition current density or critical current density at which massive Zn deposition began to occur, indicating that Cr3+ behaved as a buffering agent during the deposition of both alloys.

Spatially resolved measurements of the current transport in Y1Ba2Cu3O7 films

The spatial variation of the resistive transition and critical current density jc in Y1Ba2Cu3O7 films, grown on single crystalline and polycrystalline SrTiO3, has been imaged by low temperature scanning electron microscopy (LTSEM) with a spatial resolution of about 1 mu m. In polycrystalline samples the limitation of jc due to the weak link behavior of the grain boundary network has been directly imaged. The studies on epitaxial YBCO films with jc (77 K) above 106 A/cm2 reveal temperature variations in the local resistive transition curves up to 200 mK. Possible mechanisms for the observed spatial variations are discussed.