Preparation of polycrystalline Ti-Al-O films by magnetron sputtering ion plating: constitution, structure and morphology

Ti-Al-O layers were deposited on Si-<100> wafers at 500 °C by means of reactive magnetron sputtering ion plating (R-MSIP). An Al-target was sputtered in rf-mode and a Ti-target in dc-mode simultaneously by an oxygen/argon plasma. The influence of the Al- and Ti-sputter powers on composition, structure, and morphology of the Ti-Al-O layers and the binding states of the components were investigated. The analysis with EPMA, XPS, AES and TEM yielded the following results: Ti-Al-O coatings with different Ti, Al, and O contents in the range of TiO₂ to Al₂O₃ were grown. TEM structure analysis revealed: the pure TiO₂ film consisted of the tetragonal phases rutile and anatase; the two structures were found in the titanium-rich Ti-Al-O film, too, but with significant smaller lattice constants. The aluminium-rich Ti-Al-O film displayed the same cubic structure of γ-Al₂O₃ as determined for the pure Al₂O₃ film, but the lattice constant is significant lower. Evaluation of the TEM pattern of the film with a Ti/Al ratio of 0.8 indicates a hexagonal structure with lattice constants similar to those of κ′-Al₂O₃. All films are nanocrystalline and not textured. Received: 24 June 1996 / Revised: 27 December 1996 / Accepted: 4 January 1997     

Microstructure and electrical properties of BaTiO<Subscript>3</Subscript> and (Ba,Sr)TiO<Subscript>3</Subscript> ferroelectric thin films on nickel electrodes

Nickel thin films have been sputtered on standard Si/SiO₂ substrates with TiO₂ as an adhesive layer. The thermal stability of these substrates was analyzed. SEM images show an increase in grain size with annealing temperature. They were found to be stable till 800°C, beyond which the nickel layer disintegrated. These substrates were used for deposition of BaTiO₃ and (Ba,Sr)TiO₃ dielectric thin films under a reducing atmosphere. The dielectric thin films were processed with various pyrolysis and annealing temperatures in order to optimize the dielectric properties. Increased pyrolysis temperatures showed an increase in the grain size. Results on these nickelised substrates were finally compared with dielectric films deposited on platinized silicon substrates under identical conditions but crystallized in an oxygen atmosphere.     

Thec logc contribution to the electrolyte conductance and Onsager's reciprocal relation

The differential equations and the boundary conditions for the nonequilibrium binary distribution function of an unsymmetrical binary electrolyte are derived from the Ebeling-Falkenhagen continuity equation. The connection between the Onsager reciprocal relation and the binary distribution functions is shown. Further, Feistel's result for thec logc contribution to the conductance is extended to unsymmetrical binary electrolytes. The reason for the difference between Feistel's and Chen'sc logc term is explained, and the significance of Onsager's reciprocal relation for the calculation ofc logc and higher-concentration contributions of the conductance is discussed.     

Synthesis and selective silylation of ω-hydroxy functionalized (η-alkenyl)carbene complexes of chromium(0) and tungsten(0) Part 11. The chemistry of metallacyclic alkenylcarbene complexes

Tungsten(0) carbene complexes of the type (OC)₅WC(NMeCH₂CHCHCH₂OH)R 2 (R=Me: 2a; R=Ph: 2b) were generated by aminolysis of (OC)₅WC(OMe)R with cis-NHMeCH₂CHCHCH₂OH. Like their Cr-congeners 1, complexes 2 exist at room temperature as mixtures of Z- and E-isomers with regard to the C-N bond. The metallacyclic complexes (OC)₄WC(η²-NMeCH₂CHCHCH₂OH)R (4) were obtained in good yields upon photo-decarbonylation of 2. Deprotonation/silylation of the complexes (OC)₄MC(η²-NMeCH₂CHCHCH₂OH)Me (M=Cr: 3a; M=W: 4a) with one equivalent of ⁿBuLi/Me₃SiCl gave (OC)₄MC(η²-NMeCH₂CHCHCH₂OSiMe₃)CH₃ (M=Cr: 5; M=W: 6), whereas with two equivalents of ⁿBuLi/Me₃SiCl complexes (OC)₄MC(η²-NMeCH₂CHCHCH₂OSiMe₃)CH₂SiMe₃ (M=Cr: 7; M=W: 8) were formed. Hydrolysis of the latter yielded selectively (OC)₄MC(η²-NMeCH₂CHCHCH₂OH)CH₂SiMe₃ (M=Cr: 9; M=W: 10). The complexes 1-10 were analyzed in solution by one- and two-dimensional NMR spectroscopy (¹H, ¹³C, ²⁹Si, ¹H/¹H COSY, ¹H/¹H NOESY, ¹³C/¹H HETCOR).     

Cis‐trans Isomerism in Copper(II) Complexes with N‐acyl Thiourea Ligands

The N‐acyl thiourea complexes bis[N,N‐diethyl‐N′‐(p‐nitrobenzoyl)‐thioureato]copper(II) ( 1a,1b ) and bis(N,N‐diphenyl‐N′‐benzoylthioureato)copper(II) ( 2a,2b ) crystallize in each case in two modifications. X‐ray structural analysis shows that 1a and 1b are cis‐trans isomers. This is very unusual for N‐acyl thioureato complexes because with exception of one platinum(II) complex up to now only cis complexes have been found. In contrast X‐ray structural analysis of both forms 2a and 2b of the other complex shows no cis‐trans pair. Both modifications are cis complexes. In solution both isomers of the copper(II) complexes are observable by EPR spectroscopy.     

Chemical reaction studies in CH4/Ar and CH4/N2 gas mixtures of a dielectric barrier discharge

Chemical reactions in a dielectric barrier discharge at medium pressure of 250-300 mbar have been studied in CH(4)/Ar and CH(4)/N(2) gas mixtures by means of mass spectrometry. The main reaction scheme is production of H(2) by fragmentation of CH(4), but also production of higher order hydrocarbon molecules such as C(n)H(m) with n up to 9 including formation of different functional CN groups is observed. Formation of C(2)H(2), C(2)H(4), and C(2)H(6) molecules has been investigated in some detail. Significant differences are noted in comparison to a theoretical estimate.     

Mechanisms for the solvolytic decompositions of nucleoside analogues—I: Acidic hydrolysis of 2-substituted 1-(1-ethoxyethyl)benzimidazoles

A few 2-substituted 1-(1-ethoxyethyl)benzimidazoles have been prepared and the rate constants for their hydrolysis measured at various temperatures and oxonium ion concentrations. The formal kinetics followed and the effect of varying the 2-substitution on the hydrolysis rate suggest that the acid-catalyzed cleavage of these compounds involves a rapid initial protonation of the benzimidazole ring and a subsequent rate-limiting heterolysis of the protonated substrate to form a free nitrogen base and an ocarbenium ion derived from the ethoxyethyl group. The values obtained for the entropy of activation are consistent with the assumed unimolecular nature of the rate-limiting step. The effects of 2-substituents on the acidities of the protonated substrates and their heterolysis rates have been compared. The latter partial reaction has been suggested to be the subject of steric acceleration.     

Objective comparison of concentration profiles in solids by means of mathematical statistics

To compare concentration profiles in solids in an objective manner, a multi-dimensional generalization of the comparison of two means by Student'st-test is proposed. The approach is based on piecewise modelling the profiles using rougha priori information, estimating the model parameters and their covariance matrix and comparing the estimated parameters by use of multidimensional test variables. The piecewise modelling is treated in the most important cases in such a way that the partial functions are straight lines or cubic polynoms (splines) with continuity at all knots in each case. It enables us to compare whole profiles as well as the most relevant parts of them. Two ways of estimating the covariance matrix as a generalization of the variance estimation are discussed. The approach is useful for any kind of line profiles if rough information on the profile type is available. As an example SIMS depth-profiles of aluminum obtained from thin-layer systems after different technological heat treatments are considered. These profiles are modeled by three straight lines.     

Chiroptical detection during liquid chromatography,part 5: On-line measurement of circular dichroism spectra Δε(λ) during stops of chromatographic flow

Summary A procedure is described which serves to measure circular dichrograms () on line during stops of flow in liquid chromatography. Since the concentration of substrate in the spectrometer cell during the stop is not known, the differential absorption coefficients are calculated from the experimental differential absorbances A by means of UV absorption (i. e. photomultiplier voltage) data. Verifications of the procedure are obtained by its application to three substrates (Table 1), the () spectra of which were known. The present on-line technique is compared with a corresponding off-line method.The N,N-dimethylthiobenzamides1 and2 as well as the 9,10-phenanthrenequinone7 consist of interconvertible enantiomers because their planar states are destabilized by steric overcrowding of groups. The unknown dichrograms () of1, 2 and7 are obtained (Figs. 2 and 4) and discussed with reference to the helicities of these molecules.In memory of the late Professor Dr. Dr. h. c. Günther Snatzke.