XPS investigation of a-Si : H thin films after light soaking

Amorphous hydrogenated silicon thin films prepared by homogeneous chemical vapour deposition have been studied. The Si2p, O1s and C1s electron spectra have been recorded after different light soaking times using repeated 100 mW/cm² white light illumination and X-ray photoelectron spectroscopy (XPS) measurements. The change of the position and intensity of the Si2p peak has been observed after light soaking and is explained by the transformation of the Si–H bonds. The correlation between the micropore density in a-Si : H film and the binding energy of Si2p electrons is demonstrated.     

Charge Radii of Argon Isotopes in the f7/2 Shell and Radii Systematics in the Ca-Region

Changes in mean square (ms) nuclear charge radii of Ar isotopes across the 1f_7/2 shell are studied by fast-beam collinear laser spectroscopy using an ultra-sensitive detection method based on optical pumping and state-selective collisional ionization. The new data set on Ar, in combination with the known charge radii of K, Ca and Ti in the ν1f_7/2 shell, offers an opportunity to obtain a more complete overview of nuclear radii trends around the proton shell closure Z = 20 and between the neutron shell closures N = 20 and N = 28.     

Nuclear charge radii changes of uranium and hafnium isotopes determined by laser spectroscopy

The present work reports measurements of isotope shifts and hyperfine structure in the optical spectra of two high-Z elements: Hf and U. The experiments are based on the observation of the resonance fluorescence in a well collimated atomic beam, excited by a tunable dye laser. The chains of the stable Hf isotopes and of^{233–236, 238}U have been investigated and changes in ms nuclear charge radii have been deduced. The results have been discussed from the point of view of nuclear structure in the investigated regions.     

A Fully Coupled Solver for Incompressible Navier–Stokes Equations using Operator Splitting

The steady incompressible Navier–Stokes equations are coupled by a Poisson equation for the pressure from which the continuity equation is subtracted. The equivalence to the original N–S problem is proved. Fictitious time is added and vectorial operator-splitting is employed leaving the system coupled at each fractional-time step which allows satisfaction of the boundary conditions without introducing artificial conditions for the pressure. Conservative second-order approximations for the convective terms are employed on a staggered grid. The splitting algorithm for the 3D case is verified through an analytic solution test. The stability of the method at high values of Reynolds number is illustrated by accurate numerical solutions for the flow in a lid-driven rectangular cavity with aspect ratio 1 and 2, as well as for the flow after a back-facing step.     

Vibrational behavior of matrix‐isolated ions in Tutton compounds IV. Infrared spectroscopic study of NH4+ and SO42‐ ions included in nickel sulfates and selenates

Infrared spectra of K₂Ni(SeO₄)₂·6H₂O and (NH₄)₂Ni(SeO₄)₂·6H₂O containing SO₄^2‐ ions and those of K₂Ni(SO₄)₂·6H₂O and K₂Ni(SeO₄)₂·6H₂O containing NH₄⁺ ions are presented and discussed in the region of ν₃ and ν₁ of the sulfate ions and in the region of ν₄ of the NH₄⁺ ions, respectively. The SO₄^2‐ ions matrix‐isolated in the selenate matrices (approximately 1 mol%) exhibit three bands for ν₃ and one band for ν₁ in agreement with the low site symmetry C₁ of the host selenate ions. The NH₄⁺ guest ions included in the potassium sulfate matrix are characterized also with three bands for ν₄. However, the ammonium ions in (NH₄)₂Ni(SeO₄)₂·6H₂O as well as those included in K₂Ni(SeO₄)₂·6H₂O display four infrared bands corresponding to ν₄ due probably to some kind of disorder of the ammonium ions. The extent of energetic distortion of the isomorphously included sulfate ions as deduced from the values of Δν₃ and Δν_max is commented. The spectroscopic experiments reveal that the SO₄^2‐ guest ions are weaker distorted in the selenate matrices as compared to the same ions in the neat sulfates due to the larger unit‐cell volumes of the selenate compounds. The band positions of the water librations in the host potassium compounds are affected by the included ammonium cations. The formation of hydrogen bonds between the NH₄⁺ guest ions and the XO₄^2‐ host ions leads to a decrease in the proton acceptor capabilities of the anions and as a result the hydrogen bonds weaken on going from the neat potassium compounds to the mixed crystals. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical and holographic properties of Fe+Mn co-doped Bi4Ge3O12 crystals

The effect of iron and manganese co-doping on the light-induced, dark- and photoconductivity and holographic properties of Bi₄Ge₃O₁₂ crystals in comparison with Fe- and Mn-single doping is studied. Fe+Mn co-doped crystals exhibited strong photochromic effect at room temperature, the photochromic effect being fully reversible by thermal annealing. The observed light-induced absorption changes and non-linear dependence of photoconductivity on light intensities indicate deep and shallow photoactive levels contribution to the charge transport mechanism of Fe+Mn co-doped BGO. Holographic gratings are successfully recorded at different wavelengths and a possibility to extend the photorefractive sensitivity into the red spectral range is demonstrated. It is found furthermore that Fe+Mn-doping combination leads to faster response time during holographic recording, especially after a preliminary exposure with ultraviolet light, in comparison with Fe- and Mn-single doping.     

W1{infty}-convergence of the discrete free boundary for obstacle problems

We examine the discrete free boundaries arising from a finiteelement discretization of a variational inequality. We giveL error bounds for the Hausdorff distance of the discrete andtrue free boundary, as well as for the normals. The theoreticalresults are confirmed by numerical experiments in two and threedimensions.     

Optical isotope shifts and changes in nuclear charge radii of stable Ti isotopes

Isotope shifts and hyperfine structures in three optical transitions of TiI have been investigated by using laser induced resonance fluorescence in a collimated atomic beam. From the isotope shifts data, changes of the mean square charge radii of the stable titanium isotopes have been determined for the first time. Using a combined analysis with muonic atom data on root mean square nuclear charge radii, improved model independent r ^21/2 values for the odd-even Ti isotopes have been obtained.