Interaction of atomic hydrogen with the graphite single-crystal surface

The reaction of atomic hydrogen (or atomic deuterium) with highly orientated pyrolytic graphite surfaces has been studied by means of thermal desorption spectroscopy. In some cases atomic deuterium instead of atomic hydrogen, was used solely to assign the desorbed masses unambiguously to the different hydrocarbons. The desorption of D₂ and fourteen hydrocarbons was observed. D₂ desorbed at higher temperatures than the CH-(CD) compounds, the desorption spectra of the hydrocarbons contained two peaks. The dependence of the desorption spectra of several hydrocarbons on the heating rate, the atomic hydrogen exposure and the composition of the desorption products was investigated in detail. The kinetic parameters of the desorption process were determined for CH, C₂H₂, and CD₄. The spectra showed that there must be a first order desorption process for all the hydrocarbons, the values for the activation energy and the frequency factor were the same within experimental errors. The results were discussed by means of a simple model.     

Large third-order nonlinear optical properties of C70 fullerene in the infrared regime

The nonlinear third-order optical susceptibility of C₇₀ in a toluene solution is measured for the first time by the method of degenerate four-wave mixing using 10 ns laser pulses at 1.06 m. The third-order susceptibility X _in ⁽³⁾ is 5.6×10^–12 esu for a C₇₀ toluene solution at a concentration of 0.476 g/l. The correspondent magnitude of the hyperpolarizability ₁₁₁₁ of the C₇₀ molecule is 1.2×10^–30 esu which is in a good agreement with the prediction given by the model of a free electron in a spherical box.     

Hypernuclear interactions and multi-Λ matter

Infinite nuclear matter composed of nucleons and hyperons in various mixture ratios is considered with the Skyrme-like phenomenological potentials. Basic characteristics (energy, density, incompressibility, symmetry energy, chemical potentials) are calculated and their link with the potentials properties is studied. Conditions of stability with respect to baryon emission are analyzed and it is shown that neutron-rich systems are preferable for binding the highest possible number of hyperons.     

Neutrino oscillations in the sun and the205Tl solar neutrino experiment

Neutrino induced transition rates from²⁰⁵Tl to excited states in²⁰⁵Pb were calculated for neutrino fluxes from the different hydrogen burning reactions in the sun. Suppression factors for electron neutrinos due to flavor oscillations in the sun were obtained. The influence of neutrino oscillations on the neutrino capture rate of²⁰⁵Tl in dependence of the mixing angle and neutrino mass difference is discussed.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday     

An optical bridge reflectometer for sensitive measurement of ion implantation dose

An instrument is described that can be used to monitor, with unprecedented sensitivity, changes in the optical reflectivity due to crystailine damage incurred during ion implantation. It is shown that at the shot-noise limit, changes in the optical reflectivity of silicon as small as 5·10^–7 can be measured in a 10 Hz bandwidth with a signal-to-noise ratio of 100, corresponding to an extrapolated uniform implantation dose of 5·10⁸ cm^–2 for ¹¹B⁺ at 50 keV in silicon.     

Dynamical exchange corrections to the dielectric function in a two-dimensional electron gas

The effect of dynamical exchange interactions on the dielectric function of a two-dimensional electron gas is studied using a variational approach. Exchange effects are introduced via the local-field correction. The variationally obtained local-field factor is compared to the earlier perturbative result to first order in the electron-electron interaction.     

Phase coexistence in annealed CaMn7O12

The structural phase transition in annealed CaMn₇O₁₂ has been investigated by using high resolution synchrotron radiation powder diffraction. There is a phase coexistence phenomenon: two different crystallographic phases coexist in the material between 410 and 458 K. The first one is trigonal and it has a charge ordering (CO) of the Mn³⁺ and Mn⁴⁺ ions, while the second one is cubic and charge delocalized (CD). The volume fraction of the CD phase increases with temperature from 22% at 418 K up to 100% at 468 K. Both phases have domains of at least 150 nm at each temperature. The annealing of CaMn₇O₁₂ relaxed a part of the strains in the lattice, but did not influence the phase coexistence phenomenon.     

Numerical simulation for the flow inside V-shapes using grid generation

In this paper, we determined a numerical solution of the Navier-Stokes equations for the flow of incompressible fluid inside the contraction geometry. The governing equations are written in the vorticity-stream function formulations. The numerical solution is based on a technique of automatic numerical generation of a curvilinear coordinate system by transforming the governing equation into the computational plane. The transformed equations are approximated using central differences and solved simultaneously by the alternating direction implicit method and successive over relaxation iteration method.     

Integer quantum Hall effect in graphite

We present Hall effect measurements on highly oriented pyrolytic graphite that indicate the occurrence of the integer quantum-Hall-effect. The evidence is given by the observation of regular plateau-like structures in the field dependence of the transverse conductivity obtained in van der Pauw configuration. Measurements with the Corbino-disk configuration support this result and indicate that the quasi-linear and non-saturating longitudinal magnetoresistance in graphite is governed by the Hall effect in agreement with a recent theoretical model for disordered semiconductors.     

Enhanced ferromagnetic properties of diluted Fe doped ZnO with hydrogen treatment

The single-phase diluted magnetic Fe-ion (5%) doped ZnO powders were prepared by solid-state reaction method. The powders were annealed in Ar or Ar/H₂(5%) atmosphere at 1200 °C. The crystal structure, electric and magnetic properties for the Zn_0.95Fe_0.05O powders have been studied with X-ray diffraction (XRD) vibrating sample magnetometer, resistance and Hall measurement. All the peaks for the XRD pattern of samples belong to the hexagonal (P6₃mc) lattice of ZnO, and no indication of a secondary phase. The lattice parameters for the Zn_0.95Fe_0.05O with an annealing in Ar/H₂(5%) atmosphere were a₀=3.256 Å and c₀=5.206 Å at room temperature. The hysteresis curve for the Zn_0.95Fe_0.05O at room temperature was enhanced ferromagnetic behaviour with an annealing in Ar/H₂(5%) atmosphere. We give an explanation for enhanced ferromagnetic behaviour with H₂ treatment by electric properties.