Isotope dilution mass spectrometry for micro- and trace-element determination

Isotope dilution mass spectrometry is an important method for accurate and precise determination of trace- and micro-amounts of the elements. Using different ionization techniques in the mass spectrometer most of the elements of the periodic table can be analysed.     

Ab initio calculation of the two lowest excited states of H2S relevant for the photodissociation in the first continuum

We present extensive MRD CI ab initio calculations for the first two excited states of ¹A″ symmetry (¹B₁ and ¹A₂ in the C_2v point group). Full three-dimensional potential energy surfaces are constructed by varying both H---S-bond lengths as well as the HSH bending angle. The lower adiabatic potential is dissociative whereas the upper one is binding. These surfaces, together with the transition dipole moments with the ground electronic state, form the basis for future investigations of the photodissociation of hydrogen sulfide.     

Characterization of high-temperature superconductors by electron microprobe analysis

In order to optimize the physical properties of HTSC small single crystals grown from a melt for basic studies of their physical properties the influence of the environment on their impurity content was investigated by EPMA. This requires quantitative analysis of all elements being present in the crystals. The accuracy of results was affected by problems with the choice and quality of standards, by contamination but also by malfunction of microprobe electronics. The HTSC materials were found to react with mills, milling balls, crucibles and the atmosphere. These problems are being discussed and some reactions being studied for Y₁Ba₂Cu₃O_6+x (0 < x < 1) HTSC in A1₂O₃ and ZrO₂ crucibles. The crystals grown contain reproducible amounts of impurities depending on boundary conditions and exhibit a zone structure in composition particularly for Y and Ba within their range of homogeneity.     

Ultra-trace analysis of U,Th, Ca and selected heavy metals in high purity refractory metals with isotope dilution mass spectrometry

A method for the determination of trace impurities (U, Th, Ca, Fe, Cr, Ni, Cu, and Cd) in the refractory metals molybdenum and tungsten with isotope dilution mass Spectrometry (IDMS) has been developed. This method enables determinations of uranium and thorium down to the lowest pg/g level with high precision and accuracy. Selective chromatographic, extractive and electrolytic methods for the trace-matrix separation were combined with positive thermal ionization mass spectrometry. Different samples of high purity (4N) and of ultra high purity (UHP) materials for advanced technologies were analysed. The detection limits reached are (in ng/g): U 0.006, Th 0.008, Ca 10, Fe 19, Cr 0.5, Ni 0.6, Cu 2.7, and Cd 0.12. A comparison of results with other sensitive analytical methods (ICP-MS, GDMS, SIMS) makes obvious the urgent necessity of a reliable calibration method like IDMS because the analytical results obtained by the other methods often spread over a wide range.     

Microstructure and electrical properties of BaTiO<Subscript>3</Subscript> and (Ba,Sr)TiO<Subscript>3</Subscript> ferroelectric thin films on nickel electrodes

Nickel thin films have been sputtered on standard Si/SiO₂ substrates with TiO₂ as an adhesive layer. The thermal stability of these substrates was analyzed. SEM images show an increase in grain size with annealing temperature. They were found to be stable till 800°C, beyond which the nickel layer disintegrated. These substrates were used for deposition of BaTiO₃ and (Ba,Sr)TiO₃ dielectric thin films under a reducing atmosphere. The dielectric thin films were processed with various pyrolysis and annealing temperatures in order to optimize the dielectric properties. Increased pyrolysis temperatures showed an increase in the grain size. Results on these nickelised substrates were finally compared with dielectric films deposited on platinized silicon substrates under identical conditions but crystallized in an oxygen atmosphere.     

A modular approach toward functionalized three-dimensional macromolecules: from synthetic concepts to practical applications

A new strategy for the preparation of functional, multiarm star polymers via nitroxide-mediated "living" radical polymerization has been explored. The generality of this approach to the synthesis of three-dimensional macromolecular architectures allows for the construction of nanoscopically defined materials from a wide range of different homo, block, and random copolymers combining both apolar and polar vinylic repeat units. Functional groups can also be included along the backbone or as peripheral/chain end groups, thereby modulating the reactivity and polarity of defined portions of the stars. This modular approach to the synthesis of three-dimensional macromolecules permits the application of these tailored materials as multifunctional hosts for hydrogen bonding, nanoparticle formation, and as scaffolds for catalytic groups. Examples of applications of the functional stars in catalysis include their use in a Heck-type coupling as well as an enantioselective addition reaction.