Investigations on microstructure, composition and properties of PECVD TiNx-coatings

Nearly stoichiometric TiN_x-coatings have been deposited on different substrates using a gaseous reaction mixture of TiCl₄, N₂, H₂ and Ar in a pulsed d.c. plasma discharge. The influence of substrate temperature, plasma power density, argon partial pressure and type of substrate on chlorine content, texture and microstructure of the coatings has been investigated keeping constant the other parameters of the plasma enhanced chemical vapor deposition (PECVD) process. Microstructure has been characterized by scanning electron microscopy (SEM) fractographs of the coatings and by determination of texture. The chlorine content quantitatively determined from energy-dispersive X-ray spectra (EDX) using a chlorine containing mineral as standard decreases on an increase of substrate temperature or plasma power density. Texture changes from 200 to 111 and random and microstructure changes from columnar growth to granular for decreasing substrate temperature as well as decreasing plasma power density. Argon partial pressure does not affect the microstructure but the texture. The properties of the coatings are independent of type of substrate for higher plasma power densities. Oxygen present at the surface of the substrate stimulates the development of a texture at low plasma power densities.     

Short circuit diffusion in CuSn6/Ni/Au planar tricouples

To investigate processes of short circuit and uphill diffusion, low-temperature diffusion experiments were carried out with sandwich samples of CuSn6/Ni/Au in the kinetic regimeB after Harrison. Two kinds of base material CuSn6 with different grain sizes were chosen. The first material was cold rolled CuSn6 with a mean grain size of 3–4 m. The second was annealed CuSn6 with a mean grain size of 40 m. The Ni and Au layers with thicknesses in the m range were deposited by galvanization. The sheets were prepared by ion beam slope cutting, characterized by scanning electron microscopy and transmission electron microscopy. After annealing at 576 K up to 120 d, the samples were investigated with glow discharge spectroscopy and scanning electron microscopy. Concentration penetration plots made with glow discharge spectroscopy showed a different diffusion behaviour dependent on the CuSn6 material. The diffusion processes in the samples of cold rolled CuSn6 are more extensive than in the annealed CuSn6 samples. To find out causes of this phenomenon, a model of short circuit diffusion was developed and concentration penetration curves were calculated numerically with the finite difference method. Images of an ion beam slope cut sample show grain growth in the Au layer.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Cu-N Films grown by reactive MSIP: Constitution, structure and morphology

Cu-N layers were deposited on Si-100 wafers and amorphous carbon coated platinum nets at low temperatures (< 100 °C) by means of Reactive Magnetron Sputtering Ion Plating (MSIP). For this, a Cu-target was sputtered in rf-mode in a nitrogen plasma, and the influence of the parameters sputtering power and nitrogen partial pressure on composition, structure, texture and morphology of the Cu-N layers was investigated. The analysis with EPMA, XPS, HEED, XRD, TEM and SEM yielded the following results: With appropriate settings of the process parameters the nitrogen content of the films could be controlled-in this investigation between 0 to 28 at-%. The HEED analysis shows, that at the near surface region films with a nitrogen content in the range of 16–28 at-% were grown with DO₉ structure of Cu₃N. The films were textured: [100] in the case of 16–26.3 at-% nitrogen, [210] + [110] at 28 at-%. XRD analysis of the crystal structure of the bulk of a nitrogen-rich film (26.3 at-% nitrogen) confirm the result of HEED analysis. In the bulk of the nitrogen-poor film (16.4 at-%) two phases were detected, metallic copper with Al structure and Cu₃N with DO₉ structure. XPS analysis revealed that all films were oxidized at the surface to Cu₂O.Dedicated to Professor Dr. rer. nat. Dr. h. c. Hubertus Nickel on the occasion of his 65th birthday     

Quenching of Flame Propagation Through Endothermic Reaction

The propagation of a premixed laminar flame supported by an exothermic chemical reaction under adiabatic conditions but subject to inhibition through a parallel endothermic chemical process is considered. The temperature dependence of the reaction rates is assumed to have a generalised Arrhenius type form with an ignition temperature, below which there is no reaction. The heat loss through the endothermic reaction, represented by the dimensionless parameter , has a strong quenching effect on wave initiation and propagation. The temperature profile can have a front or a pulse structure depending on the relative value of the ignition temperatures and on the value of the parameters and , the latter represents the rate at which inhibitor is consumed relative to the consumption of fuel. The wave speed-cooling parameter () curves are determined for various values of the other parameters. These curves can have three different shapes: monotone decreasing, -shaped or S-shaped, with the possibility of having one, two or three different flame velocities for the same value of the cooling parameter .     

Investigation of Harmattan particulates from Kano and Ife, Nigeria

The size distribution, elemental composition, shape and surface texture of harmattan particulates of distinctly located points have been examined. The characterized particle size ranges are 0.7–16.4 m and 0.6–19.7 m for Kano and Ife, respectively. A total of 12 elements (Al, Si, P, S, Cl, K, Ca, Mn, Ti, Fe, Cu, and Zn) were detected with varying degrees of concentration. The plotted element concentration curves favored micron and submicron particle diameters. The particle shapes exhibit high/low sphericity. The plotted size distribution curves exhibited a marked downward shift in particle diameter from Kano to Ife.     

BAND-LIKE TEXTURE OF ETHYLCYANOETHYL CELLULOSE MESOPHASE

In the ethyl-cyanoethylcellulose ((E-CE)C)/dichloroacetic acid (DCA) cholesteric liquid crystalline solution, the hand-like texture is formed when the mesophase aggregates with the disk-like texture grow to big enough and merge with each other with increasing concentration. The band-like texture is composed of parallel equidistant bright and dark alternative strips which are about 0.2-2.0 μm in width. In the band-like texture, the layers of ordered polymer chains are perpendicular to the solution film and the axes of helicoids are parallel to it. The width of the strips is different in different zones. Under the effect of an external magnetic field, the strips in the band-like texture first become wider and then narrower gradually.Moreover, the axes of helicoids in the (E-CE) C/DCA mesomorphic solution change from the direction normal to the magnetic field to the agreement with the magnetic field direction.     

Simulation of titration curves indicated with two indicator electrodes (biamperometry)

A rigorous method to simulate titration curves with indication using two indicator electrodes (biamperometry) is presented. Computer simulations can be carried out for reversible as well as for irreversible systems. The different parameters like the area of the individual electrodes, applied potential difference, heterogeneous rate constant, and the kinetic parameter were varied and investigated as to their influence upon the shape of the titration curves. The theoretically derived effects match with the effects obtained by experiment. Considering the effects described here, it is possible to tailor the shape of the titration curve by the experimental conditions for specific applications in order to get an optimum shape at the end point of the titration.     

Incremental Gravimetry: A Method for Two-Parameter Model Building of Binary Gas Co-Adsorption Equilibria

This paper presents and develops a novel methodology to determine thermodynamic parameters of binary gas co-adsorption equilibria at given total pressure, based exclusively on binary gravimetric measurements at this same total pressure, together with single component isotherms. By Incremental Gravimetry, we designate a procedure in which the adsorbent sample is submitted to increments of composition of a flowing binary gas, and the corresponding increments of weight of the sample at equilibrium are measured. The experimental example is the co-adsorption of methane and carbon dioxide on Norit activated carbon near ambient temperature and pressure. The approach relies on the thermodynamics of non-ideal adsorbed solutions. The experimental methodology is described, the underlying theory is then presented. Compact analytical expressions are established that relate the measured limiting slopes of the incremental gravimetric curves (at infinite dilution of one component in the other) to quantities that derive only from the pure component isotherms, and to the infinite dilution activity coefficients. The latter are then uniquely determined. Classical two-parameter models for the composition dependence of activity coefficients are then implemented to reconstruct the complete binary isotherms and the incremental gravimetric curves. The comparison of the latter with the measured curves permits to test the different models.     

Intensity distribution in the vibronic side bands of the Γ7(2 T 2g ) → Γ8(4 A 2g ) origin of ReX 6 2- doped K2PtCl6-type crystals

Intensities of vibronic transitions are calculated using an electronic vibrational coupling scheme of symmetrized and localized interactions. The model consists of an active central ion subject to a valence force field originating from nearest-neighbor displacements. The intensities of vibronic fundamentals are obtained from a generalized Lorentzian line shape function which is applied to the ₇(² T _2g ) ₈(⁴ A _2g ) transition of ReCl ₆ ^2- and ReBr ₆ ^2- in various cubic host crystals A₂MX₆ (A = Rb, Cs; M = Te, Sn, Pb; X = Cl, Br). Relative intensities of the odd vibronic side bands are calculated without knowing actual values for ligand field and spin-orbit coupling parameters, and considering only octahedral vibrational frequencies. The sidebands acquire intensity by a coupling which is cubic in the electron coordinates and linear in the nuclear normal coordinates. With some necessary approximations the present model is able to reproduce the experimental intensity distribution satisfactorily.Dedicated to Professor Dr. H. Hartmann on the occasion of his 65th birthday     

EDX depths analysis of MIS-structures

Based on experimental energy transfer distributionsdE/dx including the X-ray depth distribution function (x,E ₀,Z) an effective-layer method has been developed in order to homogenize a multilayer target. Effective layer thicknesses are related to real layer thicknesses by means of equal transmission-energy rates. This method has been proved by EDX measurements of Au-SiO₂-Si structures showing good agreement with the real structures.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Investigation of sample decomposition for the trace determination of arsenic, antimony and selenium in organic and inorganic materials using the Wickbold combustion method

Summary The suitability and efficiency of the Wickbold combustion unit in combination with the new pre-combustion unit VE (manufactured by Fa. Heraeus Quarzglas GmbH) is investigated with respect to its use for the decomposition of samples for the determination of the trace elements arsenic, antimony and selenium. Certified solid reference samples were analyzed for their contents of these elements by decomposition in this apparatus and detection by hydride-AAS. Several additional experimental parameters were investigated in detail. Different absorption solutions were tested as well as the influence of the temperature of the new oven and the influence of the sample size. The new pyrolysis unit is compared with the traditional Wickbold pyrolysis method. Furthermore, the Wickbold method and an aqua regia extraction were compared. The advantages of the Wickbold unit combined with the new combustion unit are shown (especially) for routine analysis of several volatile elements. The versatility of the unit for this group of elements is demonstrated for inorganic as well as organic samples. As there is little need for additional chemicals, this method works with almost no blank value, resulting in very low limits of detection. These are mainly influenced by the method of detection. It is possible to detect 2 g/L arsenic, 3 g/L selenium and 5 g/L antimony without enrichment.Dedicated to Professor Dr. Krivan on the occasion of his 60th birthday.     

Enrichment of nitrophenols from water by means of solid-phase microextraction

The fundamental suitability of solid-phase microextraction (SPME) has been investigated for the enrichment of partially well water-soluble and differently substituted polar nitrophenols. Two commercially available fibers coated with 100 m polydimethylsiloxane or 85 m polyacrylate, respectively, were compared with regard to the efficiency of the enrichment of these compounds. For all the compounds investigated, polyacrylate fiber showed a better affinity when the exposure time was longer in comparison with polydimethylsiloxane fiber. The salting-out and the enrichment at low pH-values increased the sensitivity of the process significantly.Dedicated to Professor Dr. H. Kriegsmann on the occasion of his 70th birthday     

Falling sphere viscometry in gravitational and magnetic fields

The classical falling sphere method based onStokes' law is well known. Using gravitational forces, however, restricts the range of measurements considerably. This advantage can be overcome by applying iron spheres in a magnetic field, which allows to measure polymer melts with viscosities up to ₀=10⁹ Pa s (with very strong magnets available even more). A special measuring cell designed for application in the magnetic field is tested with several silicon oils in the gravitational field too. In both cases wall and end corrections toStokes' law have to be considered and are of main concern. Another important point is a reliable temperature measurement. Results especially for the high viscosity region of polymer melts are given.Herrn Prof. Dr.K. Komarek zum 60. Geburtstag gewidmet.     

Effect of polymer additives on magnetic modulation of the yield of products of recombination of triplet radical ion pairs in electron phototransfer between N,N-Dimethylaniline and pyrene. 2. Poly-N-tert-butylacrylamide in methanol

The effect of a magnetic field on the intensity of delayed fluorescence of pyrene excimers formed during evolution of pyrene — N,N-dimethylaniline radical ion pairs (RIP) in methanol containing glycerol or poly-N-tert-butylacrylamide was comparatively investigated by laser strobe fluorometry. Different methods of restricting the molecular mobility of the reagents cause different values of the magnetic effect with the same microviscosity measured with the spin probe orientational correlation time. This result contradicts the data obtained previously for mixtures with polyacrylamide and can be explained with the data on cross-linking of the polymer-containing solution. The viscosity of the microenvironment of the RIP partners is 10 times higher than the viscosity of the solvent. The presence of a maximum on the curve of the change in the magnetic effect in restriction of the molecular mobility was attributed to an increase in the lifetime of the radical pair and a change in the ratio of the relaxation rates and yield of radicals in bulk.N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117334 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 2059–2065, September, 1992.     

Effect of an external magnetic field on photolysis of aqueous solutions of cyclohexanone

The effect of an external magnetic field on the ratio of the yields of the basic products of photolysis of aqueous solutions of cyclohexanone was investigated by high-resolution NMR spectroscopy. It was shown that the magnetic field does not significantly affect the yield of the products of the reaction with a 0.2 M concentration of the starting ketone, the yield of 5-hexenal decreases, and the yield of caproic acid and the rate of photolysis increase below 0.02 M. The observed effects are explained by association of cyclohexan-one with involvement of the HFI mechanism from the theory of radical pairs.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1196–1197, May, 1991.     

Features of nuclear magnetic relaxation of water and benzene molecules during absorption on activated carbons and estimation of pore size distribution in adsorbents

Nuclear magnetic relaxation in activated carbon—water and activated carbon—benzene adsorption systems was studied by pulse NMR methods. Activated carbons characterized by different porous structures and chemical state of the surface were used. The application of the three-pulse Goldman—Shen sequence to the adsorption system generates a dipole echo caused by the dipole-dipole coupling of structural protons, which is not averaged due to their mobility during experiment. The non-exponential character of relaxation attenuations of the transverse and longitudinal nuclear magnetizations of physically adsorbed molecules in activated carbon pores is a result of differencies in pore sizes. The pore sizes in activated carbon and the size distribution were determined from the data of nuclear magnetic relaxation with allowance for the contribution from the structural protons.     

Synthesis of magnetic DDAB vesicles

The synthesis of magnetic vesicles is described. The vesicles are constituted by didodecyldimethylammonium bromide and have a diameter of about 1 m. An aqueous magnetic fluid, constituted by charged magnetic nanoparticles dispersed in water without surfactant, is encapsulated in the vesicle with a volume fraction in particles that may range up to 10%. The first step of the encapsulation is the synthesis of a multiple emulsion the intermediate oily phase being evaporated to obtain the DDAB bilayer. The magnetic vesicles thus synthesized align and change shape when a magnetic field is applied.     

Effective magnetization of rotating free ferromagnetic metal clusters

The deflection of free magnetic metal clusters in a Stern-Gerlach magnetic field is studied. In particular we investigate magnetic resonance effects resulting from lattice anisotropy and cluster rotation. In analogy to small suspended particles in an oscillating magnetic field the anisotropy field fixed to the rotating atomic lattice of the cluster acts on the cluster magnetization like an rf field in NMR experiments. In our calculation we have used the Bloch equations and assumed different anisotropy field symmetries (uniaxial, cubic). A minimum in the magnetization as a function of the Stern-Gerlach field and also of the cluster size, as observed recently, is obtained under certain conditions. However, such a resonance behavior occurs only if the distribution of the rotation frequency _rot is relatively narrow, while a broad distribution of _rot yields an almost superparamagnetic behavior. In addition, the strength of the anisotropy field and the relaxation time are important variables which determine the magnetic behavior of the clusters.     

Magnetic properties of chromium sulfide selenides and sulfides

Summary The structural parameters of chromium sulfide selenides are intermediate between those of the sulfides and the selenides. The nature of the dependence of the magnetic properties of the sulfide selenides on temperature and composition has much in common with that for the sulfides. The presence of selenium atoms in the sulfide lattice leads merely to some distortion of the anomalies which are observed for the pure sulfides. In the mixed chalcogenides of chromium, gradual oxidation of the monosulfide by selenium takes place, with the conversion of Cr(II) into Cr(III). The principal contribution to the magnetic moments is made by the spin values, equal to 4.9 _B for Cr(II) and 3.87 _B for Cr(III). The slight increase in the lattice parameters of the sulfide selenides (increase in the Cr–Cr distances) compared with the sulfides leads to a decrease in the exchange interactions in the sulfide selenides compared with the sulfides. This is indicated by the change in the paramagnetic Curie temperature with change in composition.Institute of Catalysis, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 14, No. 1, pp. 163–166, January–February, 1973.     

Magnetic phase transitions and specific heat of single crystalline cupric oxide

The antiferromagnetic phase transitions in a CuO single crystal are studied by specific heat in magnetic fields up to 6T. The magnetic field dependence of the incommensurate-to-commensurate-antiferromagnetic transition atT _L is found to be highly anisotropic.T _L is observed to increase nonlinearly for B_a c-axis, whereas, a linear reduction is observed forB _a b-axis. The magnetic field dependence ofT _L and the jumps in magnetic susceptibility atT _L are explained thermodynamically using the Clausius-Clapeyron equation.We thank Dr. T. Chattopadhyay for providing the CuO crystal. We thank K. Ripka and the Röntgen service of the institute for technical assistance.