Frequency dependence of the conductivity of amorphous germanium films between 20 Hz and 26 GHz

Conductivity measurements on amorphous Ge films in the frequency range 20 Hz–26 GHz are described. Above 100 MHz the frequency dependence of the conductivity at room temperature satisfied the power law σ∝ω^s with s=0.45-0.7. No saturation of the conductivity was observed. When the Ge films were doped with 0.1–1 at. % Sb the conductivity was frequency independent up to 26 GHz. A.c. hopping conduction seems to be compatible with the experimental results.     

Cermet compact made from semiconducting InSb with constant electrical resistance in the 4–400 K range

A study of the electrophysical properties of samples prepared by phase transformation of stoichiometric InSb into lnSb-Sb-In₂O₃ cermet compact has been performed (InSb, In₂O₃-semiconductors, antimony-metallic conductivity). Samples were prepared by isothermal partial oxidation at 200–500°C for 1–50 h. Bulk and thin-film samples annealed at 400°C for 1–50 h possess relatively constant electrical resistance over the wide temperature interval measured: 4–400 K. The conversion degree, β, and molar ratio, f = In₂O₃/2Sb were calculated from the isothermal thermogravimetry data according to the reaction equation 2InSb+3/2O₂ = In₂O₃+2Sb at temperatures T < 400°C, when no ascertainable amount of antimony is escaping from the system. The β-value increases with temperature, T, and time of oxidation annealing, t. However, instead of being constant, i.e. f = 0.5, f increases for T > 400°C and t > 1 h. The X-ray powder diffraction, thermogravimetry, differential thermogravimetry and differential thermal analysis measurements and studies revealed that metallic antimony escapes partially from the InSb-Sb-In₂O₃ system obtained at T ≥ 400°C. As a result, the mutual volume ratio of individual InSb, Sb and In₂O₃ components is changed, and so also is the overall character of the electrical resistivity of the samples. Due to the partial escape of Sb↑ from the system at T ≥ 400°C, the following reaction is appropriate: 2InSb + 3/2O₂ = In₂O₃ + (2 − z) Sb↑ = In₂O₃+Sb/f+ zSb, where z is the volatilized portion of Sb and f is the molar ratio of the reaction products, i.e. f = In₂O₃/(2 − z)Sb = 1/(2 − z). The SEM observations revealed a growing grain size with temperature and time of annealing, lowering the grain-boundary density and thus also the resistivity of the samples. The properties of the obtained ternary compact may be influenced significantly, if instead of stoichiometric InSb, the initial In-Sb with a variable In/Sb ratio is used.     

Hydrogenation of phenylacetylene and 3-phenylpropyne using Rh(diene) complexes under homogeneous and heterogeneous conditions

Hydrogenation of phenylacetylene (PA) and 3-phenylpropyne (PP) was carried out using [Rh(diene)Cl]₂ complexes (diene is hexadiene (HD), cycloocta-1,5-diene (COD), norborna-2,5-diene (NBD)) in their immobilized forms and compared with hydrogenation in homogeneous arrangement. Immobilization brings significant increase of the catalytic activity and product selectivity in the step-wise hydrogenation to corresponding vinyl-resp. allyl-benzenes. Diene-ligand effect was apparent in PA hydrogenation; the product selectivity decreased in order Rh(HD) > Rh(NBD) > Rh(COD) and catalytic activity decreased in order Rh(HD) > Rh(COD) > Rh(NBD).     

The study of vapour phase hydrogen peroxide decontamination process as a potential method for degradation of organic pollutants

BACKGROUND: The work is focused on the application of vapour phase hydrogen peroxide (VPHP) as a highly promising and effective decontamination technique. The aim of this work was to assess the use of this validated technique for the removal of chemicals from contaminated surfaces and examine the impact of key parameters on the course of the decontamination process. RESULTS: Unique sophisticated laboratory equipment was developed to test the effect of VPHP on chemical substances. It was used for the evaluation of the role of crucial parameters such as the relative humidity, condensation and synergistic effect of UV radiation on the VPHP agent efficiency on a model compound (vanillin) degradation. The degradation rate of the model substance was notably affected by all these factors. CONCLUSION: VPHP could be used for an efficient decomposition of vanillin. The course of the decontamination process was strongly influenced by condensation (showing a substantial difference between ‘wet’ and ‘dry’ processes) and the synergistic effect of UV radiation influencing the reaction rate and degree of decomposition. Copyright © 2010 Society of Chemical Industry     

Two-Step Preparation of Benzylacetone

Two-step preparation of benzylacetone has been investigated using layered double hydroxides (LDHs) as catalysts for aldol condensation of benzaldehyde and acetone and Ni supported catalysts for consecutive hydrogenation of benzylideneacetone. Activity and selectivity of LDHs of various Mg/Al ratios to desired product, benzylideneacetone, have been compared in the liquid phase at 333 K. An aldol condensation yield at 100 % conversion of benzaldehyde was 78 % using catalyst HT-2.0. In the following, optimal hydrogenation conditions—temperature of 353 K, hydrogen pressure of 5 MPa and 5 wt% of catalyst NiSAT^® 320 were found. At 95 % conversion of benzylideneacetone the selectivity to desired product was 99 %.     

Competitive Catalytic Hydrogenation in the Liquid Phase on Solid Catalysts

Abstract

Problems of heterogeneously catalyzed hydrogenation have received increased attention recently. Although the process ranks among those most widely used in the industrial practice, knowledge of it is still inadequate. One of the interesting problems, still also unexplored from the theoretical point of view, concerns competitive catalytic hydrogenations, i.e., reaction systems in which more than one compound react simultaneously. Basically, these systems can be divided into two classes: (1) various functional groups enter the reaction and (2) the reacting functional groups are the same. Competing groups capable of hydrogenation may be contained in one or several molecules.     

Silicon nitride films prepared by reactive plasma sputtering

Silicon nitride films were prepared by reactive plasma sputtering in nitrogen at a pressure of 2×10^-4 Torr. The residual gas in the reactor during film sputtering was analysed. The chemical composition of the films was determined from infrared absorption spectra in the wavelength region 2.0–15.0 μm and by the elastic scattering of ³He particles.The best quality silicon nitride films were obtained in pure nitrogen at the minimum residual gas pressures. An absorption minimum at 11.0 μm in the infrared spectra, corresponding to the Si-N chemical bond in the Si₃N₄ molecule, was observed in our films, indicating that their composition was close to stoichiometric.With a residual hydrogen pressure above 10% or a residual oxygen pressure above 2% the generation of new chemical bonds Si-H, N-H and Si-O respectively was observed in the silicon nitride films.