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Notes: A modified conductorlike screening continuum solvation model, implemented in the quantum chemistry program GAMESS, has been extended to second order perturbation theory (MP2). Two possible schemes have been considered: (a) the calculation of the MP2 energy using the solvated Hartree–Fock (HF) orbitals, and (b) the implementation of a double-iterative procedure where the HF density is updated with respect to the MP2 surface charges. The influence of the self-consistency of the surface charge distribution with respect to the MP2 density has been analyzed for a small dataset of 21 neutral molecules and 13 ions. In addition, the details of the distribution of surface charge density (σ profiles) and the effects of electron correlation on the accuracy of such distributions is analyzed in terms of the overall concept of deviation of continuum models from dielectric theory, leading to insights into higher order models. © 2000 American Institute of Physics.

Notes: The conductorlike continuum solvation model, modified for ab initio in the quantum chemistry program GAMESS, implemented at the Møller–Plesset Order 2 (MP2) level of theory has been applied to a group of push–pull pyrrole systems to illustrate the effects of donor/acceptor and solvation on the stability and energetics of such systems. The most accurate theoretical gas and solution phase data to date has been presented for the parent furan-2-carbaldehyde (furfural) system, and predictions made for three additional analogues, thiophene-2-carbaldehyde, pyrrole2-carbaldehyde, and, cyclopentadiene-1-carbaldehyde. Solvent effects on internal rotational barriers in all systems were evaluated over six different values of dielectric, using the new method. Calculated electrostatic energies are shown to be highly sensitive to level of theory incorporated. © 2000 American Institute of Physics.

Notes: The properties of nanoscale spheres and tubes are of recent interest due to the discovery of the fullerene molecule and the carbon nanotube. These carbon structures can be modeled as nanoscale spherical or cylindrical shells. In this article, these nanostructures are treated in the thin shell approximation with the elastic properties taken to be those of the graphene sheet. A quantization prescription is applied to the classical elastic modes to facilitate the first calculations of the quantum-mechanical normalizations of selected modes. These modes are shown to be amenable to the study of electron-phonon interactions. Indeed, electron-phonon interaction Hamiltonians are derived. Moreover, it is shown for such a tube of finite length that the electron-phonon interaction strength depends on the axial position. As a special case it is shown that the dispersion relation for the clamped tube depends on the length of the tube. In this article we consider both the vibrational frequencies and the mode quantization for both spherical shell and the nanotube using realistic material parameters. © 2001 American Institute of Physics.

Notes: Top synthetic spin valves with structure Ta/NiFe/CoFe/Cu/CoFe(P1)/Ru/CoFe(P2)/FeMn/Ta on Si (100) substrate with natural oxide were prepared by dc magnetron sputtering system. We have changed only the thickness of the free layer and the thickness difference (P1−P2) in the two ferromagnetic layers separated by Ru, and investigated the effect of magnetic film thickness on the interlayer coupling field in a spin valve with a synthetic antiferromagnet. As the free layer thickness decreased from 70 to 20 Å, the interlayer coupling field was increased due to the magnetostatic coupling (orange peel coupling). In the case of the thickness difference in the pinned layers, the interlayer coupling field agreed with the modified Néel model suggested in the top synthetic spin valve structures. However, in the case of tP1=tP2, and tP1=tP2+5 Å, it was found that the interlayer coupling field could not be explained by the modified Néel model. The deviation of the modified Néel model at the dip zone could be due to the large canting of the pinned layers, which depend on applied field and different thickness in synthetic antiferromagnetic structure. The dependence of Cu thickness on the interlayer coupling field was investigated and 10 Oe of the interlayer coupling field was obtained when the Cu thickness is 32 Å. © 2001 American Institute of Physics.

Notes: The discharge characteristics of a prototype ion source for the Korea Superconducting Tokamak Advanced Research neutral beam system, which has been developed to meet the specification of 120 keV and 65 A beam during 300 s, were investigated. The relationships between the operation conditions, such as the filament current, the arc current (up to 1200 A), the pressure of the ion source, and the measured plasma parameters were studied, and the possibility of steady-state operation was checked. Langmuir probes were used in measuring the plasma parameters and the density distributions. The hydrogen ion density was 2.0×1011 cm−3, the electron temperature was lower than 5 eV, and the plasma uniformity around the bucket was within 30% in the optimum operation conditions. © 2000 American Institute of Physics.

Notes: Today, many bright photon beams in the ultraviolet and x-ray wavelength range are produced by insertion devices installed in specially designed third-generation storage rings. There is the possibility of producing photon beams that are orders of magnitude brighter than presently achieved at synchrotron sources, by using self-amplified spontaneous emission (SASE). At the Advanced Photon Source (APS), the low-energy undulator test line (LEUTL) free-electron laser (FEL) project was built to explore the SASE process in the visible through vacuum ultraviolet wavelength range. While the understanding gained in these experiments will guide future work to extend SASE FELs to shorter wavelengths, the APS FEL itself will become a continuously tunable, bright light source. Measurements of the SASE process to saturation have been made at 530 and 385 nm. A number of quantities were measured to confirm our understanding of the SASE process and to verify that saturation was reached. The intensity of the FEL light was measured versus distance along the FEL, and was found to flatten out at saturation. The statistical variation of the light intensity was found to be wide in the exponential gain region where the intensity is expected to be noisy, and narrower once saturation was reached. Absolute power measurements compare well with GINGER simulations. The FEL light spectrum at different distances along the undulator line was measured with a high-resolution spectrometer, and the many sharp spectral spikes at the beginning of the SASE process coalesce into a single peak at saturation. The energy spread in the electron beam widens markedly after saturation due to the number of electrons that transfer a significant amount of energy to the photon beam. Coherent transition radiation measurements of the electron beam as it strikes a foil provide additional confirmation of the microbunching of the electron beam. The quantities measured confirm that saturation was indeed reached. Details are given in Milton et al., Science 292, 2037 (2001) (also online at www.sciencexpress.org as 10.1126/science. 1059955, 17 May 2001), and Lewellen et al., "Present Status and Recent Results from the APS SASE FEL," to be published in the Proceedings of the 23rd International Free-Electron Laser Conference, Darmstadt, Germany, 20–24 August 2001. © 2002 American Institute of Physics.

Notes: The voltage dependence of magnetoresistance (MR) and the low-frequency voltage fluctuation were studied in magnetic tunnel junctions with an AlN or an Al2O3 barrier formed by plasma nitridation or oxidation. The junctions consist of free and pinned NiFe layers by a FeMn antiferromagnetic layer. For the Al2O3 junction, the variation of half-reduction voltage of MR is about 50 mV from 401.3 mV in maximum to 351.4 mV in minimum depending upon the oxidation time. For the AlN junction, the less nitrided junction with a nitridation time of 120 s shows the higher-half-reduction voltage by about 100 mV than for optimally nitrided or oxidized ones. From the low-frequency voltage noise data, the less nitrided AlN junction shows larger 1/f noise magnitude compared with other junctions with an optimal condition, implying more defect states in the barrier due to unnitrided Al metals. In order to investigate the influence of nitrogen on ferromagnetic layer, another junction with an Al2O3 barrier was made after the pinned NiFe layer was exposed to N2 plasma for 10 s. This junction reveals a lower MR and worse bias voltage dependence than any junctions studied here. The voltage dependence of MR, therefore, is likely influenced by the interface state rather than the defects in the barrier, although the two factors play an important role in determining MR. © 2002 American Institute of Physics.

Notes: The optical and magneto-optical properties of ordered Fe3Pt have been investigated by spectroscopic ellipsometry and magneto-optical Kerr spectroscopy. The diagonal component of the optical conductivity tensor of the compound exhibits a broad absorption peak at about 2 eV, which is shifted by about 0.5 eV to lower energies from the corresponding one in pure bcc Fe. The Kerr angle spectrum of the compound disperses quite similarly in both spectral trend and magnitude to that of pure Fe below 3.5 eV but differently above it. The lower-energy shift of the 2-eV-absorption structure of the compound is interpreted as due to the shift of the minority-spin Fe-d states toward EF through the hybridization with Pt-d states. The Kerr effect of the compound is attributable to a large spin-orbit coupling in Pt as well as the well-hybridized spin-polarized bands. © 2001 American Institute of Physics.

Notes: We have analyzed amplification of transverse phonons confined in quantum well (QW) heterostructures through piezoelectric electron–phonon interaction with drifting electrons. It was found that this mechanism of interaction couples the low-dimensional electrons and the shear-horizontal (SH) confined phonons. We have studied the electrostatic potential accompanying the SH waves and found that efficient interaction can be achieved for the lowest antisymmetric SH phonon branch in a narrow band of phonon frequencies. For AlGaAs QWs the amplification coefficient was calculated to be on the order of 100 cm−1 in the sub-THz phonon frequency range. These results suggest an electrical method for coherent phonon generation in the technologically well-developed AlGaAs QW heterostructures. © 2001 American Institute of Physics.

Notes: In laser materials processing, localized evaporation caused by focused laser radiation forms a plume of mixed vapor and ambient gas above the material surface. The beam is refracted and absorbed as it traverses the plume, thus modifying its power density on the surface. In this work, plume–beam interaction is studied using an axisymmetric, high-temperature gas-dynamic model of a plume formed by vapor from an iron surface. The beam propagation in the plume is calculated from the paraxial wave equation including absorption and refraction. The simulation results quantify the effects of plasma plume properties on the beam radius and laser power density variations at the material surface. It is shown that absorption and refraction in the plume have significant impacts on the laser–material interaction. Absorption of the beam in the plume has much less direct effect on the power density at the material surface than refraction does. However, absorption is essential for the formation of the plume, without which there is no refraction. Helium gas is more efficient than argon for reducing the beam refraction and absorption effects. Laser energy reflected from the material surface has significant effects on the plume properties. © 2001 American Institute of Physics.