Atmosphere effects in the processing of silicon carbide and silicon oxycarbide thin films and coatings

Silicon carbide and silicon oxycarbide films were prepared from solutions of polycarbosilane and methyldimethoxysilane + tetraethoxysilane, respectively, and deposited on different substrates (Si wafers, stainless steel plates, sapphire and SiC fibers). The coatings were heated at different temperatures and in different atmospheres, such as regular grade argon, ultra high purity and argon vacuum. The films were characterized using different techniques (FT-IR, XRD, SIMS, Ellipsometry).The influence of the processing parameters (heat treatment temperature and atmosphere) on the final microstructure of the coatings is discussed in this article.     

Electrochemical and Structural Characterisation of Dip-Coated Fe/Ti Oxide Films Prepared by the Sol-Gel Route

Thin solid films of mixed Fe/Ti oxide composition (Fe/Ti molar ratios: 0.5∶1, 1∶1, 1.5∶1) have been made from Fe(NO₃)₃ alcoholic solution to which Ti(OiPr)₄ was added. Films have been deposited by the dip-coating technique and heat-treated at 300°C and 500°C. Powders of Fe/Ti oxide heat-treated at 300°C are amorphous, while powders annealed at 500°C for 40 hours transformed to mixed rutile, pseudobrookite and hematite phases. The structure of the XRD amorphous films was identified with the help of near-normal reflection absorption (6°) (IRRA) and near-grazing incidence angle (NGIA) spectroscopy. NGIA FT-IR spectra of films are characterised with a single phonon mode appearing in the spectral range 600–950 cm⁻¹ which shifts with increasing Ti concentration from 675 cm⁻¹ (Fe₂O₃) to 904 cm⁻¹ (TiO₂) thus exhibiting one-mode behavior. Electrochemical investigations made with the help of cyclic voltammetry (CV) and chronocoulometry (CPC) performed in 0.01M LiOH and in 1M LiClO₄/propylene carbonate electrolytes revealed that films are able to uptake reversibly Li⁺ ions with a charge capacity (Q) per film thickness (d) in the range 0.1–0.26 mC/cm²nm and 0.06 mC/cm²nm, respectively. The temperature at which the films were prepared alters the rate of Li⁺ insertion which is faster for less compact films obtained at 300°C. In situ UV-VIS spectroelectrochemical measurements revealed that Fe/Ti oxide films bleached in the UV spectral region (300 nm<λ<450 nm) and colored in the VIS spectral region (450 nm<λ<800 nm), thus exhibiting mixed anodic and cathodic electrochromism.     

Gas hydrate single-crystal structure analyses

The first single-crystal diffraction studies on methane, propane, methane/propane, and adamantane gas hydrates SI, SII, and SH have been performed. To circumvent the problem of very slow crystal growth, a novel technique of in situ cocrystallization of gases and liquids resulting in oligocrystalline material in a capillary has been developed. With special data treatment, termed oligo diffractometry, structural data of the gas hydrates of methane, acetylene, propane, a propane/ethanol/methane-mixture and an adamantane/methane-mixture were obtained. Cell parameters are in accord with reported values. Host network and guest are subject to extensive disorder, reducing the reliability of structural information. It was found that most cages are fully occupied by a guest molecule with the exception of the dodecahedral cage in the acetylene hydrate which is only filled to 60%. For adamantane in the icosahedral cage a disordered model is proposed.     

Identification of clusters from reactions of ruthenium arene anticancer complex with glutathione using nanoscale liquid chromatography fourier transform ion cyclotron mass spectrometry combined with <Superscript>18</Superscript>O-labeling

Reactions of the anticancer complex [(eta(6)-bip)Ru(en)Cl](+) (where bip is biphenyl and en is ethylenediamine) with the tripeptide glutathione (gamma-L-Glu-L-Cys-Gly; GSH), the abundant intracellular thiol, in aqueous solution give rise to two ruthenium cluster complexes, which could not be identified by electrospray mass spectrometry (ESI-MS) using a quadrupole mass analyzer. Here we use Fourier transform ion cyclotron mass spectrometry (nanoLC-FT-ICR MS) to identify the clusters separated by nanoscale liquid chromatography as the tetranuclear complex [{(eta(6)-bip)Ru(GSO(2))}(4)](2-) (2) and dinuclear complex [{(eta(6)-bip)Ru(GSO(2))(2)}(2)](8-) (3) containing glutathione sulfinate (GSO(2)) ligands. Use of (18)OH(2) showed that oxygen from water can readily be incorporated into the oxidized glutathione ligands. These data illustrate the power of high-resolution MS for identifying highly charged multinuclear complexes and elucidating novel reaction pathways for metallodrugs, including ligand-based redox reactions.     

Theoretical studies on the infrared spectrum of the tetrahedral molecules R<Subscript>2</Subscript>MH<Subscript>2</Subscript> (R = D(H), CH<Subscript>3</Subscript>, OH; M = Ti,Zr, Hf)

Using Stuttgart/Dresden effective core potentials MWB28, MWB60, and GTO valence basis sets (8s7p6d)/[6s5p3d], (8s7p6d)/[6s5p3d] for Zr and Hf atoms and 6-311++G(3df,3pd) basis set for C, H, O, and Ti atoms, tight convergence criteria geometry optimizations and harmonic frequency calculations are performed at B3LYP and B3LYP/IEF-PCM levels of theory so as to model the gas phase and argon matrix infrared spectra of the tetrahedral molecules R₂MH₂ (R = D(H), CH₃, OH; M = Ti, Zr, Hf). Influence of the transition metal and/or substituent group on the symmetric and asymmetric stretching frequencies of the MH₂ fragment of the R₂MH₂ molecules is investigated at both the levels of theory. The modelling of the argon matrix effect improves the agreement between the calculated frequencies and the experimental ones. The calculated argon matrix to gas phase frequency shifts is compared reasonably to the experimental argon to neon matrix shifts.     

Thermal stability and flame resistance of polypyrrole-coated PET fibres

Electro-conducting doped polypyrrole was deposited by in situ oxidative polymerisation on PET non-wovens. Thermal properties were evaluated by means of DSC and TG in nitrogen and air. Flame resistance tests reveal that coated PET fibres resist to direct contact with fire. By thermal analysis, it was found that PPy reduces the temperature at which thermo-oxidative degradation of PET occurs. Polypyrrole-coated PET non-wovens were heated above the melting point of PET for 30 min. After the heating the fibres become brittle and frail, but SEM observations revealed that they maintained their fibrous shape. A loss of chlorine was found because of intense heating.     

3,5-Bis(2-hydroxyphenyl)-1<Emphasis Type="Italic">H</Emphasis>-1,2,4-triazole based ligands — protonation and metal complex formation

3,5-Bis(2-hydroxyphenyl)-1H-1,2,4-triazole (H₂L^a) and 4-[3,5-bis(2-hydroxyphenyl)-1H-1,2,4-triazol-1-yl]benzoic acid (H₃L^b) have been prepared, and crystal structure of the intermediate 2-(2-hydroxyphenyl)-4H-1,3-benzoxazin-4-one has been determined. Temperature dependent ¹H NMR spectroscopic measurements of H₂L^a indicated dynamic behavior with the equilibrium between the two asymmetric tautomers. For H₃L^b, pD-dependent ¹H NMR spectroscopic measurements showed small but characteristic shifts in the range of 0 ≤ pD ≤ 1, indicative of a triazole nitrogen atom protonation; the corresponding pK _a of 0.98 ± 0.04 was determined by spectrophotometric titrations. (H₂O, 26°C, 1 M KCl/HCl). Formation of [Fe^III(L^a)]⁺ (pH 2.5) and [Fe^III(L^a)₂]⁻ (pH > 6) was verified by UV-Vis spectroscopy. Complex formation of H₃L^b with Al³⁺ and VO²⁺ was investigated by ¹H NMR spectroscopic titration and cyclic voltammetry, respectively. Single crystals of the phenoxo bridged [V^VO(HL^b)(EtO)]₂·2EtOH were characterized by X-ray structural analysis. Dedicated to Professor Milan Melník on the occasion of his 70th birthday     

Optimization of the Production of Thermostable endo-β-1,4 Mannanases from a Newly Isolated <Emphasis Type="Italic">Aspergillus niger gr</Emphasis> and <Emphasis Type="Italic">Aspergillus flavus gr</Emphasis>

The aim of this work was to establish optimal conditions for the maximum production of endo-β-1,4 mannanases using cheaper sources. Eight thermotolerant fungal strains were isolated from garden soil and compost samples collected in and around the Gulbarga University campus, India. Two strains were selected based on their ability to produce considerable endo-β-1,4 mannanases activity while growing in liquid medium at 37 °C with locust bean gum (LBG) as the only carbon source. They were identified as Aspergillus niger gr and Aspergillus flavus gr. The experiment to evaluate the effect of different carbon sources, nitrogen sources, temperatures and initial pH of the medium on maximal enzyme production was studied. Enzyme productivity was influenced by the type of polysaccharide used as the carbon source. Copra meal defatted with n-hexane showed to be a better substrate than LBG and guar gum for endo-β-1,4 mannanases production by A. niger gr (40.011 U/ml), but for A. flavus gr (33.532 U/ml), the difference was not significant. Endo-β-1,4 mannanases produced from A. niger gr and A. flavus gr have high optimum temperature (65 and 60 °C) and good thermostability in the absence of any stabilizers (maintaining 50% of residual activity for 8 and 6 h, respectively, at 60 °C) and are stable over in a wide pH range. These new strains offer an attractive alternative source of enzymes for the food and feed processing industries.     

Surface chemistry and electronics of semiconductor–nanosystem junctions I: metal-nanoemitter-based solar cells

Photoelectrochemically prepared nanotopographies on semiconductors are used for realization of nanoemitter solar devices that are active in the photovoltaic and the photoelectrocatalytic mode. The development of solar devices by a nonlinear electrochemical process and combined chemical/electrochemical metal deposition is described. Based on this low-temperature scalable approach, first efficiencies of 7.3% in the photovoltaic mode are reported for the photoelectrochemical solar cell n-Si/SiO₂/Pt/I₃ ⁻–I⁻. With p-Si/Pt nanocomposite structures, light-induced H₂ evolution is achieved. The surface chemistry and morphology is analyzed by photoelectron spectroscopy (PES), Fourier transform infrared spectroscopy, and high-resolution scanning electron microscopy. The operational principle of Pt-based nanoemitter solar devices that use silicon single crystal absorbers is analyzed by Mott–Schottky plots, chronoamperometric profiles, and PES. Related to simultaneous oxide formation during Pt deposition, evidence for the formation of a metal–oxide–semiconductor junction is obtained that explains the observed electronic behavior. Contribution to the Fall Meeting of the European Materials Research Society, Symposium D: 9th International Symposium on Electrochemical/Chemical Reactivity of Metastable Materials, Warsaw, 17th–21st September 2007.