Laser sintering of perovskite-oxide and metal coatings by the sol gel process

This paper presents a novel laser technique for the formation of metal Ag and perovskite-oxide La_xSr_1-xCoO₃ coatings. Metallic Ag and La_xSr_1-xCoO₃ are conductive materials with applications as resistors and as electrodes in the microelectronics area. Suitable precursors in the form of sol gels are placed on substrates and are subsequently sintered by high-power laser irradiation. The Ag precursor is an aqueous sol of nanosized particles, while for the La_0.8Sr_0.2CoO₃, a sol gel type precursor is used. Substrates (e.g., fused silica) are coated with the precursor solutions by spinning and are dried to stable solid layers. The coatings are cured and sintered to a defined pattern by means of a 3-kW CO₂ laser beam scanned over the whole substrate surface. The microstructure of the coatings was examined by the use of scanning electron microscopy and X-ray diffraction, and the electrical properties were measured by the four-point resistivity method. The La_0.8Sr_0.2CoO₃ coatings had a perovskite cubic structure with a lattice constant of 0.383 nm. The resistivity of the coatings was 30 mQ cm, and the temperature dependence of the resistivity was 1.8 mQ cm/°C. Metallic Ag coatings with a thickness of 100-170 nm were obtained with a resistivity of 20 7Q cm. This new technology is promising for the growth of three-dimensional (3-D) structures and multilayers, especially because it can be introduced in industrial scale production.     

Particle image velocimetry in a foam-like porous structure using refractive index matching: a method to characterize the hydrodynamic performance of porous structures

We present a method to measure two-dimensional velocity fields inside an artificial foam-like porous structure using particle image velocimetry and a refractive index matching technique to avoid optical distortion. The porous structure is manufactured by stereolithography with the epoxy resin WaterShed^? XC 11122 as solid material, and anisole is used as refractive index-matched fluid. It was found that the direction of build-up of the stereolithographic structure plays an important role for the quality of the recorded images. The velocity fields measured in this study and the turbulent statistics derived thereof allow to characterize the hydrodynamic performance of the artificial foam-like structure and clarify the mechanisms of mixing. Results from this study compare well to results from a large eddy simulation reported by Hutter et?al. (Chem Eng Sci 66:519–529, 2011b) and hence reinforce these simulations.     

Al and Ti secondary neutral and secondary ion emission from oxide samples in the high-frequency sputtering mode of HF-plasma SNMS

A strong Al⁺ and a minor Ti⁺ peak without a proportional increase of the O⁺ signal in SNMS high-frequency sputtering mode (HFM) time profiles of an insulating μm-thick oxide layer on Ti-48Al-2Cr-2Nb led us to check for a possible contribution of positive secondary ions (SI⁺). SI⁺ and SI^– (negative secondary ions) can be detected in ion energy spectra. This is shown using Al⁺, O^–, AlO^–, and AlO₂ ^– ions sputtered from massive Al₂O₃. Similarly, and depending on stoichiometry, also Ti⁺ from mixed sintered, microscopically inhomogeneous Al₂O₃-TiO₂-SiO₂ pellets has been identified to be partly SI⁺. The subtraction of an assumed contribution of ionized secondary neutrals (SN⁺) suggests that SI⁺ may form several 10% of the detected ions obtained in the HFM sputtering and plasma processes. However, the positive surface potential of some 10 V being necessary to cause detectable SI⁺ contributions does not build up on μm-thin insulating layers. Therefore, we have to conclude that the Al⁺ and Ti⁺ peaks in the sputter time profiles of the μm-thick oxide layer on Ti-48Al-2Cr-2Nb which are accompanied by an O⁺ deficiency cannot have been caused by SI⁺. Instead, their more probable origin is the inhomogeneous Al₂O₃ interlayer itself. Together with the residues of a topmost TiO₂ layer which has strongly been depleted in O by preferential sputtering, the relative O⁺ deficiency may be explained without assuming SI⁺ contributions. Received: 22 February 1999 / Revised: 1 July 1999 / Accepted: 6 July 1999     

Topochemical characterization of materials using 3D-SIMS

Summary The potential of 3D-SIMS for characterization of high molybdenum powder and sintered high purity molybdenum will be demonstrated. The concentration of the measured trace elements in the sintered molybdenum did not exceed 200 ppb. In the powder the concentration was found to be about 1 ppm. For material scientists it is very important to ascertain if the trace elements are homogeneously distributed or precipitated. Although the concentration of the elements of interest was rather low, qualitative images of the three dimensional distribution can be obtained.     

Imaging surface spectroscopy for two- and three-dimensional characterization of materials

Secondary ion mass spectrometry (SIMS) exhibits a unique potential for the measurement of two-and three-dimensional distributions of trace elements in advanced materials, which is demonstrated on relevant technological problems. One example is the characterization of high purity iron. With this material segregation experiments have been performed and the initial and final distribution of the trace elements have been measured. Another example is the investigation of the corrosion behaviour of high purity chromium. Samples oxidized with (16)O and (18)O have been measured to explain the growing and adhesion of the oxide layer. All imaging techniques generate a vast quantitiy of data. In order to extract the important information the assistance of chemometric tools is essential. Detection of chemical phases by classification using neural networks or de-noising of scanning-SIMS images by wavelet-filtering demonstrates the increase of the performance of analytical imaging techniques.     

A photochemical activation scheme of inert dinitrogen by dinuclear Ru(II) and Fe(II) complexes

A general photochemical activation process of inert dinitrogen coordinated to two metal centers is presented on the basis of high-level DFT and ab initio calculations. The central feature of this activation process is the occupation of an antibonding pi* orbital upon electronic excitation from the singlet ground state S0 to the first excited singlet state S1. Populating the antibonding LUMO weakens the triple bond of dinitrogen. After a vertical excitation, the excited complex may structurally relax in the S1 state and approaches its minimum structure in the S1 state. This excited-state minimum structure features the dinitrogen bound in a diazenoid form, which exhibits a double bond and two lone pairs localized at the two nitrogen atoms, ready to be protonated. Reduction and de-excitation then yield the corresponding diazene complex; its generation represents the essential step in a nitrogen fixation and reduction protocol. The consecutive process of excitation, protonation, and reduction may be rearranged in any experimentally appropriate order. The protons needed for the reaction from dinitrogen to diazene can be provided by the ligand sphere of the complexes, which contains sulfur atoms acting as proton acceptors. These protonated thiolate functionalities bring protons close to the dinitrogen moiety. Because protonation does not change the pi*-antibonding character of the LUMO, the universal and well-directed character of the photochemical activation process makes it possible to protonate the dinitrogen complex before it is irradiated. The pi*-antibonding LUMO plays the central role in the activation process, since the diazenoid structure was obtained by excitation from various occupied orbitals as well as by a direct two-electron reduction (without photochemical activation) of the complex; that is, the important bending of N2 towards a diazenoid conformation can be achieved by populating the pi*-antibonding LUMO.     

Simultaneous quantification of total medium- and long-chain fatty acids in human milk by capillary gas chromatography with split injection

Four different quantification methods for the capillary gas chromatographic determination of medium-chain fatty acids (6:0-12:0) and myristic acid in human milk samples, using a split injector, were compared. Odd-carbon-numbered fatty acids (5:0-17:0) were added as internal standards. Each medium-chain fatty acid and myristic acid was calculated on the basis of: the peak area of the internal standard with one methylene group less; the peak area of the internal standard with one methylene group more; half the sum of the peak areas of the internal standards with one methylene group less and more (bracketting method); the peak area of 17:0. The peak-area ratio of each analyte and 17:0 in a standard was found to be subject to an unacceptably high coefficient of variation. From the methods using internal standards with one methylene group more and less, the bracketting method was found to be the best, resulting in recoveries close to 100%, with the lowest coefficients of variation. The method was applied for the determination of the fatty acid composition of mature milk samples of 47 Cura?aoan women.