ALBERT

Notes: We have obtained x-ray phase-contrast images with high spatial resolution by using extremely asymmetric Si 111 Bragg diffractions near the critical angle of the total reflection. The x-ray image could be magnified to 294 times in both vertical and horizontal directions. By using this x-ray microscopy system, we have observed clear phase-contrast images of a 0.7-μm-wide gold-line pattern. © 2001 American Institute of Physics.

Notes: We measure the diffraction peaks of InGaAsP selective metal-organic vapor-phase epitaxial layers on 1.7-μm-wide InP stripe regions between a pair of SiO2 mask stripes. This is achieved by using an x-ray microbeam with low angular divergence and a narrow energy bandwidth that was produced through two-dimensional condensation of undulator radiation x rays from a synchrotron light source using successive asymmetric diffraction. The lattice strain is investigated by changing the SiO2 mask width from 4 to 40 μm. The rocking curves reveal clear peak shifts in the InGaAsP layers from the higher angle side to the lower angle side of the InP substrate peaks as the mask width increases. © 2000 American Institute of Physics.

Notes: The excitation spectra of the 15V 31 344.9 band of the CS2 V 1B2←X 1Σg+ transition and the changes in these spectra with the application of a magnetic field of up to 12 kG have been measured with sub-Doppler resolution. The radiative lifetimes of rotationally resolved single lines and single Zeeman components were measured under collision-free conditions. All of the fluorescence decays were observed to be of a single exponential. Large Zeeman splittings were observed for many lines. The only symmetry allowed spin–orbit interaction is that of the 3A2(B2) component with the 1B2 state. The 3A2(B2) component has no magnetic moment, but a magnetic moment is induced when it is mixed with the 3A2(A1,B1) components. The mixing of the 3A2(B2) and 3A2(A1,B1) components is facilitated by spin–rotation interaction and the Zeeman interaction. From analysis of the observed Zeeman splittings of the perturbed levels, the 3A2(B2) component was determined to lie 14 cm−1 below the nearly degenerate 3A2(A1) and 3A2(B1) components in the energy region where the 15V band is observed. Irregular energy shifts and splittings of rotational lines were observed, and these were attributed to (a) Coriolis interaction between the V1B2(v′(a1);K=0JM) and V 1B2(v(b2);K=1JM) levels and (b) resonant spin–orbit interaction between the rotational levels V 1B2(v′(a1);KJM) and R 3A2(v(a1);KJM). These interactions become appreciable when two levels lie close in energy. Large Zeeman splittings were observed in case (b). Many vibrational lines with irregular intensity and spacing were observed in each band. These were attributed to (c) Fermi resonance between the vibrational levels in the V 1B2 state and (d) resonant spin–orbit interaction between vibrational levels in the V 1B2 and R 3A2 states. In case (d), large Zeeman splittings were observed for a series of rotational lines in a vibrational band. The background lines were identified from observed Zeeman splittings as the transitions to levels of the R 3A2 state, which are induced by resonant spin–orbit interaction with the levels of the V 1B2 state. The intensity of the excitation spectrum of the V 1B2←X1Σg+ transition was observed to decrease as the magnetic field increases. This was attributed to a mixing of the 3A2 state with the V 1B2 state and the resulting triplet–triplet emission, which was not detected in this experiment. It was possible to evaluate the lifetime of the radiative triplet–triplet emission via deperturbation analysis of the perturbed lines. © 2000 American Institute of Physics.

Notes: Vibrational excitation to the symmetric stretching, bending and asymmetric stretching modes of OCS molecules by electron and positron impacts is investigated for impact energy from 2 to 6 eV theoretically and experimentally. Because the OCS molecule is a polar molecule, interactions that induce the vibrational excitation for the three modes are primarily long-range permanent dipole interactions. And hence, all excitation cross sections for three modes thus obtained are found to be similar in size both for electron and positron impacts, although for positron, the magnitude is generally slightly smaller by 25% than that of electron. This situation is markedly different from that of the CO2, where for the symmetric stretching mode, the difference between positron and electron impacts is a few orders of magnitude at 5 eV. Therefore, a comparative discussion of CO2 is useful for further understanding. © 2000 American Institute of Physics.

Notes: We have measured the vibrational energy relaxation of azulene in the S2 state in ethane, carbon dioxide, and xenon over a wide density region by the time-resolved fluorescence spectroscopy. The reduced density of the solvent (the density divided by the critical density) has been changed from the gaslike one (lower than 0.05) to the liquidlike one (2.8 for ethane, 2.7 for carbon dioxide, and 2.0 for xenon). The density dependence of the relaxation rate is compared with that of azulene in the S0 state [D. Schwarzer, J. Troe, M. Votsmeier, and M. Zerezke, J. Chem. Phys. 105, 3121 (1996)]. Although the absolute rate largely depends on the electronic state, the density dependence of the relaxation rates is roughly the same for both electronic states, which can be considered as a side-proof of the isolated binary collision model. Possible origins for the validity of the isolated binary collision model are discussed. © 2000 American Institute of Physics.

Notes: We present a strategy for solvating biomolecules in molecular dynamics or Monte Carlo simulations. The method employs a thin layer (often monomolecular) of explicit water with additional external forces representing the electrostatics, pressure, fluctuations, and dissipations caused by the neglected bulk. Long-range electrostatic corrections are supplied through a set of variable surface charges (polarons) that recreates the mean reaction field (or dielectric properties) of an infinite solvent. We refer to this "fictitious" boundary layer as a "surface of active polarons" (or SOAP). Test simulations of the solvation free energies of 15 amino acid analogs and nine ions are in good agreement with experiment (correlation coefficients: 0.995 and 1.000, respectively) despite the use of unaltered published force-fields with only one adjustable parameter. Dynamical capabilities of SOAP are illustrated by application to a six residue peptide with a stable conformation (SYPFDV), as well as a flexible nine residue HIV-1 gp120 peptide (TLTSCNTSV from PDB 1hhg). Future extensions, calibrations, and applications are discussed briefly. © 2000 American Institute of Physics.

Notes: A global model for electronegative plasma, in which the negative ion distribution is assumed to be a parabolic profile in the axial direction with a flat central region and a similar edge profile in the radial direction in the electronegative region, is applied to study the power and pressure dependences of plasma parameters in low-pressure CF4 discharges. The electron density increases approximately linearly with the power. The electron temperature also increases with the power due to the decrease in neutral number density with increase in power, resulting in the increase in plasma potential. The density of CF3+ is a weak function of the power, while the densities of CF2+, CF+, and F+, which are strongly correlated to the densities of the respective radicals, depend on the power. On the other hand, the decrease in electron temperature with the pressure significantly results in a decrease in the degree of dissociation. The electron density also decreases gradually with the pressure except for the case of pressure lower than 5 mTorr. The densities of CF2+, CF+, and F+ decrease gradually with the pressure at pressures higher than 5 mTorr, while the density of CF3+ increases gradually with the pressure. The electron energy probability function (EEPF) is measured with a Langmuir probe in an inductively coupled rf (13.56 MHz) CF4 discharge over a pressure range from 2 to 30 mTorr, while keeping the power injected into the plasma at about 70 W. The measured EEPFs are approximately Maxwellian at any pressure, although there is a slight deviation from a Maxwellian distribution at pressures higher than 10 mTorr. The results estimated from the measured EEPF are compared to the model and show reasonably good agreement. © 2002 American Institute of Physics.

Notes: The role of the bias pretreatment for the enhanced nucleation of the diamond nuclei in the chemical vapor deposition of diamond is theoretically investigated. We obtain the kinetic energy of ions impinging on the surface of the substrate as a function of bias voltage. The experimentally obtained optimum bias voltage of −100 V for the enhanced nucleation of diamond nuclei corresponds to the C ion energy of ∼5 eV at the surface of the substrate. The reduction of the ion energy is caused by the scattering in the ion sheath region of the plasma. The ion sheath width and the ion energy on the surface of the substrate are given as functions of the gas pressure and the bias voltage. The results are compared with the experimental results. © 2001 American Institute of Physics.

Notes: Surface melting of Si(001) surface has been investigated by x-ray reflectivity up to the bulk melting temperature: Tm;b. An in situ system was designed for measurements of x-ray reflectivity at high temperatures under an atmosphere of He-gas flow. It has been shown that the surface density changes at T=Tm;s*〈Tm;b−110 K. This change was observed at T=Tm;s* both on cooling and heating (a reversible phenomenon). The density of the near-surface at Tm;b〉T〉Tm;s*, which is larger than that of the bulk solid, is 2.5(1)×103 kg/m3 which is almost the same as that of the bulk liquid, though a macroscopic melting does not occur. This reversible phenomenon indicates the surface melting at T=Tm;s*. © 2001 American Institute of Physics.

Notes: The impurity (Cr3+)-doping effect on the stability of charge and orbital ordering has been systematically investigated for Nd1/2Ca1/2Mn1−yCryO3 crystals by measurements of magnetotransport and x-ray diffraction. The random field in terms of eg orbital deficiencies on the Cr sites drives the charge and orbital correlations to dynamical and short range, which is most relevant to the high-resistive state exhibiting colossal magnetoresistance. In the Cr-doped manganite, we can observe the coexistence of ferromagnetic–metallic and charge–orbital ordered phases, their spatial distributions, diffuse x-ray scattering, magnetic-field annealing, and the aging effect on the magnetic and electric properties, etc. These phenomena are reminiscent of those of relaxor ferroelectrics composed of ferroelectric clusters embedded in a paraelectric matrix. We propose that the mixed-valent manganite can be viewed as a "magneto- and electrorelaxor." © 2001 American Institute of Physics.