G. Plesch

A study of the dielectric characteristics of aluminum oxide thin films deposited by spray pyrolysis from Al(acac)3

Abstract The dielectric characteristics of aluminum oxide thin films deposited by the spray pyrolysis technique are reported. The films were deposited with different molarities from a spraying solution of aluminum acetylacetonate and N , N -dimethylformamide. The films were deposited on silicon substrates at temperatures ranging from 450 to 650°C. The addition of water mist during the deposition process led to a remarkable improvement of the overall characteristics of the films. Films with excellent dielectric characteristics and low surface roughness were obtained. The results of the characterization indicate that there is a significant presence of carbon in the films. This carbon in the films modifies the electrical conduction characteristics leading to behavior similar to that displayed by off-stoichiometric silicon oxide (SiO 2 ) films. It is observed that the overall resistivity of the film decreases when both the molarity of the solution and the deposition temperature increase. This behavior correlates with the increase in the amount of carbon remaining inside the film. The films as deposited have a surface state density in the range of 10 11 1/eV-cm 2 and are able to stand electric fields higher than 5 MV/cm without observing dielectric breakdown.

EPR, ligand field spectra and antimicrobial activity of some N-pyruvideneglycinatocopper(II) complexes

Abstract N-Pyruvideneglycinatocopper(II) complexes were synthesized of composition Cu(pyrgly)(L)(H 2 O) x with LH 2 O, x =2 ( I ); L=pyridine, x =2 ( II ); L=quinoline, x =2 ( III ); and L=aniline, x =1 ( IV ). The ligand field spectra provide evidence of a distorted octahedral Cu(II) coordination in ( I ) and ( III ), whereas in ( II ) and ( IV ) the coordination polyhedron around Cu(II) is square-pyramidal. According to the results of EPR spectra, the neutral ligand L strongly influences the weak exchange interactions between Cu(II) ions in the solid state. The effect of the ligand L on the local and cooperative symmetry is discussed. The complexes show antimicrobial activity, being most active against fungi.

In situ photoexcitation of silver-doped titania nanopowders for activity against bacteria and yeasts

Photocatalytic and in situ microbial activity of the amorphous and annealed states of Ag-doped and un-doped titania were examined. Studies on their structure, morphology, composition, and the photo-absorption characteristics of these materials were performed. These results were correlated with the photocatalytic and microbial activity against methicillin resistant Staphylococcus aureus K324 (MRSA), methicillin susceptible S. aureus ATCC 25923 (MSSA), Escherichia coli PA 170, and yeasts Candida albicans ATCC 90028. The annealed powders containing anatase form of titania exhibited relatively higher photocatalytic activity,corresponding to activity against MRSA,when exposed to UV-A radiation. In comparison, amorphous powders exhibited low photoactivity and showed poor antibacterial performance against MRSA under UV-A exposure. Doping of amorphous titania with Ag resulted in an anti-MRSA effect without exposure to UV radiation. In the Ag-doped crystalline anatase samples, the size of Ag primary nanocrystallites increased, which led to the decrease in the surface concentration of Ag and detriment anti-MRSA activity.

Coordination geometries and cooperative ordering effects in copper(II) complexes with tridentate Schiff base dianions 5 E.p.r. spectra of [N-salicylidene-(R,S)-alaninato]copper(II) complexes with derivatives of imidazole and pyrazole and structure of 1-methylimidazole[N-salicylidene-(R,S)-valinato]copper(II)

Abstract1-Methylimidazole[N-salicylidene-(R,S)-valinato]copper(II) shows square-planar coordination around the Cu2+ ion, coordinated in the basal plane by O,N,O atoms from the tridentate Schiff base dianion and by N from the coordinated 1-methylimidazole. In the crystal structure, enantiomers related by an inversion centre are bound by H bonds to units with a CuċCu distance of 8.039Å. Intermolecular H bonds stabilize stacking of such units, which are propagated along the [010] axis. Two such chain systems in the unit cell are related by a glide plane parallel to (010). The basal planes of two magnetically non-equivalent complexes are canted by an angle of 74.64∘. The shortest CuċCu distance between non-parallel-aligned coordination polyhedra is 10.518Å. On the other hand, the closest CuċCu spacing of parallel-orientated coordination polyhedra is 5.628Å. Hence, in the e.p.r. powder spectrum only the coupling between ferrodistortively ordered coordination polyhedra is manifested.E.p.r. and ligand field spectra of a series of [N-salicylidene-(R,S)-alaninato]copper(II) complexes with imidazole, pyrazole and some of their derivatives provide evidence for coordination geometries ranging from square-pyramidal, with various strengths of axial interaction, to square-planar. The cooperative ordering phenomena in the structure are discussed on the basis of the e.p.r. powder spectra. When the e.p.r. spectra yield crystal g values from two coupled molecular g tensors of orthorhombic symmetry, a simple model based on consistency of G parameters was developed for evaluation of the canting angle 2γ between aligned coordination polyhedra and molecular g values, respectively. The data obtained from the e.p.r. powder measurements are in excellent agreement with the results of single X-ray structural studies.

EPR, ligand field spectra and antimicrobial activity of dimeric aryloxyacetatocopper(II) complexes with antipyrine

Abstract Copper(lI) complexes with aryloxyacetato ligands and antipyrine (Apy) of the general formula [Cu2- (RCOO)4(Apy)2] were prepared with RCOO− as phenoxyacetato, 3-methylphenoxyacetato, 4-methylphenoxyacetato, 4-chlorophenoxyacetato, 2-methyl- 4-chlorophenoxyacetato, 3-methyl-4-chlorophenoxyacetato and 2-naphthoxyacetato anions. The parameters of the triplet spin state EPR spectra at X and Q band frequencies (D|hc = 0.37 cm−1, g⊥ = 2.07, g‖ = 2.38, A‖|c = 0.007 cm−1) provide evidence of a dimeric carboxylato-bridged structure with apically bound antipyrine. The almost constant EPR data as well as the energies of the ligand field transitions at 77 K [dx2−y2 ← dxz, dyz (14000 cm−1), dx2−y2 ← dxy (11200 cm−1) and dx2−y2 ← dz2 (9500 cm−1)] indicate that the square-pyramidal geometry of the CuO5 polyhedra is nearly unaffected by the substituents on the aryloxyacetato group. The complexes show antimicrobial activity, being most efficient against Candida albicans and Bacillus subtilis.

Thick films of ceramic, superconducting, and electro-ceramic materials

The use of thick films becomes more and more important in particular for electronic and microelectronic applications. The term “thick film ” does not relate so much to the thickness of the film but more to the kind of deposition. Thick films are made by low-priced processes such as doctor (dr) blading, screen-printing, or spraying methods, etc. The preparation of thick films of ceramic material by these methods generally implies a processing sequence of the following steps: preparation of the oxide powders; preparation of pastes and slurries; painting/printing, etc.of the pastes onto a suitable substrate; drying at low temperature; and sintering at high temperature to get a consolidated layer. These technologies and the fabricated thick films of thermoresistive and superconducting materials will be discussed.

Thin YBCO films prepared by low-temperature spray pyrolysis

Thin YBCO films were prepared from aerosol by a low-temperature deposition process consisting of two steps-the deposition at atmospheric pressure and firing in vacuum degraded by partial pressure of oxygen-both at temperatures not exceeding 600 degrees C. A stoichiometric 1-2-3 aqueous nitrate solution of Y, Ba and Cu constituents was used as a source of aerosol. MgO and Al2O3 substrates were heated to 140 to 160 degrees C during deposition. The obtained films were 1 to 10 mu m thick with Tc>80 K and Jc=103 to 104 A cm-2. However, detailed TG, DTG and DTA studies performed by the authors and others showed that thermal decomposition of the nitrates used only starts at temperatures higher than 200 degrees C. The use of low substrate temperatures during deposition (140 to 160 degrees C in this case) is apparently the reason for rather low Jc values. Optimization of the preparation process is suggested, which could lead to higher Jc values at processing temperatures not exceeding 600 to 700 degrees C. Such temperatures are still interesting for substrates with elevated diffusivity into prepared films.

Coordination geometries and cooperative ordering effects in copper(II) complexes with tridentate Schiff base dianions—III. EPR study on N-salicylideneglycinatocopper(II) complexes with thiourea derivatives

Abstract N-Salicylideneglycinatocopper(II) complexes of the composition Cu(salgly) (Ls)(H2O)x were synthesized with Ls = thiourea, N-methylthiourea, N,N,N′,N′-tetramethylthiourea, N-ethylthiourea, N,N′-diethylthiourea, N-(2-chlorophenyl)thiourea, N,N′-diphenylthiourea, N,N′-ethylenethiourea, N,N′-phenylenethiourea [≡ 1,3-dihydrobenzimidazole-2-thione]; and x = 0 or 1. The EPR spectra gave evidence for square-pyramidal coordination around CuII, however, with a different strength of axial interaction originating from an oxygen atom from the adjacent complex molecule. In the case of monohydrates bonding of a water molecule is also possible. In two examples, even square-planar geometry, without any significant axial interaction can be assumed. The great variety of cooperative ordering phenomena in the structure, which is caused mainly by the extraordinary flexibility of the Schiff base ligand, results in coupling patterns ranging from ferrodistortive to antiferrodistortive. These patterns are remarkably influenced by the substitutions on thiourea. Both the global and local symmetry effects are analysed with the aid of EPR spectroscopy.

EPR study of local and cooperative symmetry effects in N-salicylideneglycinatocopper(II) complexes

Abstract N-Salicylideneglycinatocopper(II) complexes of the composition Cu(salgly)(L)(H2O)x with L = imidazole, x = O (I); L = 2-propylimidazole, x = 1, (II); L = pyridine, x = O (III); L = pyrazole x = 1 (IV) and L = 3,5-dimethylpyrazole, x = 1 (V) were synthesized, The EPR and ligand field specra of these compounds as well as of N-salicylideneglycinatothioureacopper(II) (IV) give evidence for a square-pyramidal Cu(II) coordination. The EPR spectra of I, II, and III can be reasonably interpreted using axial molecular g tensors, whereas the molecular g tensors of IV, V and VI exhibit orthorthombic symmetry. The experimental EPR spectrum of VI shows molecular g values in accordance with the ferrodistortive order found previously by X-ray structure analysis. In V no exchange interactions between crystallographically nonequivalent Cu(II) ions were found. The complexes I–IV show exchange coupled g parameters, corresponding to an antiferrodistortive (I, III) or disturbed antiferrodistortive ordering (II, IV). The alkyl-substitution on the neutral ligand and the presence of water in the crystal structure strongly influence the exchange interactions between Cu(II) ions.

Study of copper-chromium oxide catalyst: I. Thermal decomposition of copper(III) chromate, CuCrO4

Abstract The kinetics, mechanism, and activation energy of the isothermal decomposition of CuCrO4 was studied using an isothermal TG method and an X-ray high-temperature diffraction technique in either air or a flowing atmosphere of N2. The enthalpy change ΔH of the decomposition reaction 2 CuCrO 4 → CuO + CuO + CuCr 2 O 4 + 3 2 O 2 was determined by DSC analysis. The mechanism of the thermal decomposition of CuCrO4 is well represented by the standard Avrami-Erofeev kinetic equation [− ln (1 − α)] 1 2 = kt . According to this mechanism, the reaction rate is controlled by the formation and growth of nuclei on the surface of the reactant. The activation energy EA of the process in air is EA = (248 ± 8) kJ mole−1, in flowing atmosphere of nitrogen EA = (229 ± 8) kJ mole−1. ΔH in air is 110 kJ mole−1, in flowing nitrogen 67 kJ mole−1. The lower values of ΔH and EA in the flowing atmosphere of nitrogen are due to the fast elimination of O2 from the reaction interface. However, the decay of the crystalline portion of CuCrO4 during its thermal decomposition, studied by the X-ray diffraction, is controlled by a different reaction mechanism (first-order kinetics). The reaction mechanism is discussed in the relation to the crystal structure of the reactants.