Bibliothek

Notizen: Boron nitride films prepared by reactive ion plating from a boron evaporation source were characterized structurally using three independent electron optical techniques: energy filtered electron diffraction with radial distribution function analysis; electron energy-loss spectroscopy of the near-edge structure of the boron K edge; and spectroscopy of the plasmon region of the energy-loss spectrum. Both specimens had a graded BNx layer between the BN layer and the silicon substrate and in addition one specimen had a titanium bonding layer underneath the BNx layer. The presence of c-BN in both specimens was confirmed by all techniques. The specimen with the titanium bonding layer was examined in cross section and showed essentially pure c-BN on the surface. A model for the formation of c-BN assisted by the compressive stress generated during deposition is proposed.

Notizen: Co/Ru hcp (0001) superlattices were grown by UHV evaporation onto mica substrates. We demonstrate the growth of epitaxially ordered Co/Ru superlattices–despite the large lattice mismatch ((approximately-equal-to)8%)–consisting of hcp (0001) Co and Ru sublayers initialized on 150-A(ring)-thick single-crystalline Ru buffer layer by using RHEED and x-ray diffraction. The magnetic properties were studied by magnetization and ferromagnetic resonance (FMR) measurements. For uncoupled Co layers, the resultant anisotropy switch from planar to axial direction (perpendicular to the film plane) with decreasing Co sublayers thickness. For Co sublayer thickness smaller than a critical one tco(approximately-equal-to)14 A(ring), the magnetization is directed perpendicular to the film plane. For small Ru interlayer thickness, large antiferromagnetic exchange coupling between the Co sublayers is observed in agreement with precious results. For a certain range of Co and Ru thicknesses, superlattices with unique magnetic parameters are obtained. Indeed, in the absence of an applied field, the magnetization is oriented along the film normal while the adjacent Co layers are coupled antiferromagnetically. For this magnetic structure, the magnetization process exhibits a hysteresis and the FMR spectra an irreversible behavior when the applied field is along the film normal.As shown by SQUID measurements, when the field is decreased from a quasi-saturated state, the layers are essentially coupled ferromagnetically, the antiferromagnetic state appearing following a spin-flip process (staircaselike on the magnetization curve) for a field smaller than a critical one. However, with increasing field, the antiferromagnetic state disappears by progressive steps suggesting that the spin reorientation process occurs by coherent rotation of the magnetization combined with spin-flip process. The occurrence of this effect is particularly spectacular on the FMR spectra. With decreasing field, a classical FMR absorption is observed due to the basical ferromagnetic state while with increasing field, this absorption is largely reduced or disappears completely due to the antiferromagnetic one. The magnitude of the hysteresis and its evolution with the direction of the applied field, the values of the critical field corresponding to the spin flip and to the field above which the magnetic state is reversible, are very well correlated on the FMR spectra and the magnetization curves.

Notizen: Abstract: Rats were fed a control or vitamin E (all-rac-α-tocopheryl acetate)-deficient diet for 3 or 12 weeks. Serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), tryptophan, and α-tocopherol concentrations were determined in the frontal cortex using HPLC. α-Tocopherol concentrations fell significantly to 27% of control values at 12 weeks. Tissue 5-HT, 5-HIAA, and tryptophan concentrations were not significantly altered by the vitamin E-deficient diet at either time point. In vivo microdialysis revealed normal basal and K+-stimulated concentrations of 5-HT and 5-HIAA, but extracellular concentrations of tryptophan were significantly decreased after 3 weeks on the vitamin E-deficient diet, which resulted in an increase in the tissue/extracellular ratio and suggested a change in compartmentation. However, after 12 weeks on the deficient diet these values had returned to normal. Results in general indicate that a prolonged and substantial depletion of brain vitamin E can occur without major disturbance of serotonergic function.

Notizen: We report a woman who had a moderate elevation of serum triglycerides with a type III pattern of hyperlipoproteinaemia when taking a normal diet. She developed eruptive xanthomata with a grossly raised serum triglyceride concentration and chylomicronaemia when pregnant and also when taking a combined oral contraceptive pill containing 50 μg of oestrogen. The xanthomata cleared and the triglyceride level fell when the combined oral contraceptive pill was changed to one with a lower oestrogen content, clofibrate was prescribed and the diet was restricted in carbohydrate and fat. Persistent chylomicronaemia is a serious complication of pregnancy because of the risk of pancreatitis and the potential risk of fetal malnutrition. Treatment with diet and clofibrate is indicated. High oestrogen-containing contraceptive pills appear to be contraindicated in patients with type III or other hypertriglyceridaemic states.

Notizen: A wedge-shaped target was implanted with nitrogen ions using the plasma source ion implantation process, in order to understand the effects of the target edges on the energy and fluence distribution of incident ions. Experimental measurements and analysis of retained dose on silicon samples affixed on the surface of the target, showed results consistent with those predicted by theoretical models. Higher retained dose and greater implantation depths were observed in the vicinity of the edge contained by the normal angle as compared to the edges contained by the acute angles. The target face with smaller area accumulated, on the average, higher dose compared to the face with the larger area. © 1995 American Institute of Physics.

Notizen: We present the materials growth and properties of both epitaxial and amorphous films of Gd2O3 (κ=14) and Y2O3 (κ=18) as the alternative gate dielectrics for Si. The rare earth oxide films were prepared by ultrahigh vacuum vapor deposition from an oxide source. The use of vicinal Si (100) substrates is key to the growth of (110) oriented, single domain films in the Mn2O3 structure. Compared to SiO2 gate oxide, the crystalline Gd2O3 and Y2O3 oxide films show a reduction of electrical leakage at 1 V by four orders of magnitude over an equivalent oxide thickness range of 10–20 Å. The leakage of amorphous Y2O3 films is about six orders of magnitude better than SiO2 due to a smooth morphology and abrupt interface with Si. The absence of SiO2 segregation at the dielectric/Si interface is established from infrared absorption spectroscopy and scanning transmission electron microscopy. The amorphous Gd2O3 and Y2O3 films withstand the high temperature anneals to 850 °C and remain electrically and chemically intact. © 2001 American Institute of Physics.

Notizen: Formation of epitaxial Si1−yCy substitutional alloy layers on monocrystalline silicon surfaces with y≈1 at. % is reported. The preparation method was carbon ion implantation, followed by KrF excimer laser annealing. Results of Rutherford backscattering (RBS), secondary ion mass spectrometry (SIMS) and infrared absorption analyses are compared. The authors concluded that, up to ∼1 at. % carbon content, the dominant process is nonequilibrium trapping of carbon in substitutional lattice sites upon fast resolidification. Above this concentration the complex carbon redistribution processes are influenced by silicon carbide precipitation in the melt and segregation effects in the near-surface region. © 1996 American Institute of Physics.

Notizen: Abstract. PEP-carboxylase was extracted and partially purified from nine species of the genus Sedum and three species of the genus Kalanchoe, all performing CAM. Immunological and molecular properties of these enzymes were compared. Molecular weight estimation with gradient slab gels showed identical molecular weights of about 232,000 for all PEP-carboxylases. Ouchlerlony double-diffusion analysis, immunotitralion and SDS polyacrylamide clectrophoresis indicated the presence of PEP-c dimers consisting of monomers of MW 105,000 and 115,000. A model of PEP-c substructure is proposed. The results are discussed in the context of CAM performance in the genus Sedum

Notizen: Abstract From Sedum morganianum, which is a plant species known to have constitutive crassulacean acid metabolism (CAM), phosphoenolpyruvate (PEP) carboxylase (E.C.4.1.1.31) has been extracted and purified by (NH4)2SC4 precipitation, ion exchange chromatography and gel electrophoresis. A specific antibody to this purified enzyme was obtained by immunization of a rabbit. This antibody was used to compare the antigen–antibody reaction of PEP-carboxylases prepared from other Sedum species including constitutive, facultative and non-CAM plants. The experiments revealed partial immunological indentity of PEP-carboxylases obtained from the different sources.