Problems and results of diffusion length investigations by energy-dependent EBIC measurements

The fundamentals of the method are described. From applications of this measuring method the following results were obtained: The determination of the diffusion length on glass-plate bevels with evaporated Schottky contacts is frequently quite difficult and sometimes even impossible. Besides a reduction of the diffusion length with increasing microdefect density surprisingly also the opposite behaviour can be found. Comparative PEM and EBIC investigations yield differences between both diffusion lengths (L_EBIC < < L_PEM) depending on the sample pre-history.     

A 15N labelling,FD and FAB study of ammonia loss from protonated arginine molecules

The positive ion field desorption (FD) spectrum of arginine taken at the best anode temperature only contains a peak due to [M+H]⁺ ions. At higher emitter temperatures a considerable amount of fragmentation is induced and the [M+H NH₃]⁺ ions become most abundant. Specific ¹⁵N labelling reveals that the eliminated ammonia molecule, exclusively, contains one of the terminal nitrogen atoms of the guanidyl group. This also applies to the ammonia loss from metastably decomposing [M+H]⁺ ions. The positive ion fast atom bombardment (FAB) spectrum shows more fragmentation than the FD spectrum. In contrast with the FD results, the [M+H]⁺ ions generated upon FAB with ion lifetimes <10⁻⁶ s eliminate both ammonia containing one of the terminal nitrogen atoms of the guanidyl group and ammonia containing the α-amino group in the ratio of 1.35, as found by ¹⁵N labelling. The metastably decomposing [M+H]⁺ ions, however, eliminate only the former ammonia molecule. In the negative ion FD and FAB spectra no other peak than that corresponding to the [M H]⁻ ion is observed. Some attention has been paid to the thermal degradation of arginine on the basis of a few Curie-point pyrolysis experiments.     

The Improvement of Superconductivity in PbxBi2-xSr2CaCu2Oy

In this paper we present the results of recent studies on the improvement of superconductivity in Pb_xBi_2-xSr₂CaCu₂O_y single crystals by preventing impurities incorporation, employing ZrO₂ crucible for crystal growth and post annealing the as-grown crystals in vacuum or argon. It is realized that the superconductivity of as-grown crystals is improved.     

A Mechanism of High-Tc Superconductivity Relating to Perovskite Crystal Structure

A mechanism of high-T_c superconductivity related to the perovskite crystal structure is proposed by a “phonon attenuation model”, which means that in the perovskite-like crystal structure, a number of “ordering” vacancies or holes occur due to the non-stoichiometric structure features. Such a reticular “spongly-like” structure facilitates lattice thermovibration attenuation perovskite (phonon attenuation) during temperature reduction. This leads to an abrupt drop of the resistivity, owing to the conduction electrons transmitted through the media without collision with irregularities in the lattice due to the lattice thermovibration. This probably is the main reason for high-T_c superconductivity of the perovskite cuprates.     

Investigations of a highly crowded phosphino-substituted biphenyl: A precursor for a λ3, λ5-diphosphaphenanthrene

The synthesis of 2,2′-bis(bis(dimethylamino)-phosphino)-3,3′5,5′-tetra-tert-butylbiphennyl ( 5 ) is described. It was extensively studied by ¹H, ¹³C, and ³¹P NMR spectroscopy. Furthermore, the X-ray analysis of 5 is reported. Crystals of 5 are tetragonal, space group P¯42₁c, a = b = 24.770 (3) Å, c = 12.658 (4) Å, Z = 8. The surprising reaction of 5 with proton acids leading to the formation of various phosphorus containing five- and six-membered ring compounds is discussed. On reaction of one of the six-membered ring compounds ( 9 ) with magnesium in THF, a λ³, λ⁵-diphosphaphenanthrene ( 19 ) was obtained.     

Stress,Strain, and Symmetry of Pseudomorphically Grown Epitaxial Layers

The complete stress and strain tensors and the point symmetry of pseudomorphically grown epitaxial layers are calculated from the epitaxial relationship and the elastic constants of the deposit material. The angle misalignment of crystallographic directions in the deposit due to the strain is also calculated and results are given for the epitaxial systems CaF₂/Si(100) and CaF₂/Si(111).     

Micellar and microemulsion electrokinetic chromatography of hop bitter acids

The elution order of the hop α- and β-acids has been studied under different modes of electrokinetic separation. A model is advanced to explain the shorter migration times of the more hydrophobic β-acids compared to the α-acids in micellar electrokinetic chromatography (MEKC). For quality control of the bitter principles in hops, the ruggedness of electrokinetic separation could be improved by replacing MEKC by microemulsion electrokinetic chromatography (MEEKC).