Nadejda Popovska

In situ monitoring of the acetylene decomposition and gas temperature at reaction conditions for the deposition of carbon nanotubes using linear Raman scattering

To understand the reaction mechanisms taking place by growing carbon nanotubes via the catalytic chemical vapor deposition process, a strategy to monitor in situ the gas phase at reaction conditions was developed applying linear Raman spectroscopy. The simultaneous determination of the gas temperature and composition was possible by a new strategy of the evaluation of the Raman spectra. In agreement to the well-known exothermic decomposition of acetylene, a gas temperature increase was quantified when acetylene was added to the incident flow. Information about exhaust gas recirculation and location of the maximal acetylene conversion was derived from the composition measurements.

Methylated [(arene)(1,3-cyclohexadiene)Ru(0)] complexes as low-melting MOCVD precursor complexes with a controlled follow-up chemistry of the ligands

[(Benzene)(2-methyl-1,3-cyclohexadiene)Ru(0)] (1), [(1,3-cyclohexadiene)(toluene)Ru(0)] (2), and [(methyl-cyclohexadiene)(toluene)Ru(0)] (3, mixture of isomers) have been prepared and tested as new metal organic ruthenium precursor complexes for chemical vapor deposition (MOCVD) with favorable properties. 1 is a low-melting precursor complex (mp = 29 °C) and the isomeric mixture 3 forms a liquid at room temperature. X-ray diffraction studies of single crystals of complexes 1 and 2 are characteristic for true Ru(0) π-complexes without molecular structure peculiarities or significant intermolecular interactions in the solid state, which could hinder undecomposed evaporation. Differential thermal analysis (DTA), differential scanning calorimetry (DSC) and vapor pressure data qualify the compounds as almost ideal MOCVD precursors. Thin ruthenium films have been deposited successfully on silicon wafers and substrate temperatures between 200 and 450 °C in inert gas atmospheres. Film growth and properties were evaluated by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and four-point probe conductivity measurements. All films consist of polycrystalline metallic ruthenium with a low surface roughness.

Reinforcing Effect of Carbon Short Fibers Coated with Pyrolytic Carbon in Ceramic Matrix Composites

Carbon short fibers (6000 filaments) with a length of 6 mm were uniformly coated with pyrolytic carbon (pyC) in continuous CVD process using propane—hydrogen mixture as precursor. The process conditions for the fiber coating were optimized to meet a high deposition rate at minimum soot formation in parameter screening experiments using nonporous graphite substrates. The coated fibers were characterized by SEM and Raman spectroscopy. Their reinforcing effect was investigated in composites with C/SiC matrix. As a result of fiber coating the bending strength of the composites was increased about 30% and elongation at break increased by a factor of nine. The pyC coating modifies the fiber—matrix interface preventing too strong a bonding, resulting in damage tolerant behavior of the composites.

Thermal Conductivity of Biomorphic Porous SiC Based Ceramics

Biomorphic porous SiC composite ceramics were produced by chemical vapor infiltration and reaction (CVI-R) technique using paper preforms as template. The thermal conductivity of four samples with different composition and microstructure was investigated: a) C-template b) C-SiC, c) C-SiC-Si3 N4 and d) SiC coated with a thin layer of TiO2 . The SiC-Si3 N4 composite ceramic showed enhanced oxidation resistance compared to single phase SiC. However; a key property for the application of these materials at high temperatures is their thermal conductivity. The later was determined experimentally at defined temperatures in the range 298–373K with a laser flash apparatus. It was found that the thermal conductivity of the porous ceramic composites increases in the following order: C-template < C-SiC < C-SiC-Si3 N4 < SiC-TiO2 . The results were interpreted in regard to the porosity and the microstructure of the ceramics.Copyright

Temporally resolved characterization of iron nanoparticles using a time-resolved laser technique

For the first time, time-resolved laser-induced incandescence (TiRe-LII) has been used to investigate the metal-organic chemical vapor deposition (MOCVD) process of iron in a fluidized bed reactor characterizing nanoparticles deposited on a substrate surface.