bluuebunny/crossref_metadata_2025 huggingface dataset:
Bindungsstruktur in plasmapolymerisierten Schichten aus Vinyltrimethylsilan
Authors: Kruse A. , Hennecke M. , Baalmann A. , Schlett V. , Stuke H.
Published: July 2012

Plasma polymer films of vinyltrimethylsilane (VTMS) were deposited by radiofrequency (RF. 13.56 MHz) or Microwave (MW, 2.45 GHz) discharges in two reactors of the same volume and geometry.—The polymer films were characterized by electron spectroscopy for chemical analysis (ESCA) and infrared spectroscopy (FTIR). It turned out, that the RF—and the MW—polymers had almost the same Si/C‐composition ratio of 1/5 in the entire range of RF‐and MW‐power (60–150 W). Although the Si/C film‐composition remains almost constant, the binding states of Si‐and C‐atoms in the respective ESCA‐spectra are changing. While the CSi part of the C1s‐peak increases with the RF‐or MW‐power, the CH/CC part of the peak decreases, indicating a loss of hydrogen in the polymer films.—Obviously the fragmentation of the VTMS‐monomer is quite different for the two types of plasma discharges. While films of the RF‐plasma clearly show strong contributions of the methyl and vinyl groups, these groups are completely missing for the MW‐plasma polymers.—From these results structure models of the plasma polymers have been developed.
Membrane‐Properties of Polymer Films: The Acid‐Doping Reaction of Polyaniline
Authors: Asturias Gabriel E. , Jang Guang‐Way , Macdiarmid Alan G. , Doblhofer Karl , Zhong Chuanjian
Published: July 2012

The protonation/deprotonation reaction of polyaniline in the emeraldine oxidation state (PANI‐E) is discussed on the basis of membrane‐equilibrium considerations. The important role of the partitioning of H+ between the polymer and the bathing solution is pointed out. The concentration of (free) H+ in the polymer phase is used as a parameter in formulating the dissociation equilibrium of the Brønsted acid (PANI‐E)H+. It is shown that the pKa value determined for this dissociation equilibrium, pKa ≈ 5, is practically constant for all experimental conditions considered in this work. However, the pH of the bathing solution which leads to a defined protonation state of the PANI‐E may vary widely depending on the partitioning equilibrium for H+. This fact is demonstrated experimentally, and the experimental findings are shown to agree with theoretical predictions based on estimated and experimentally determined Donnan potentials.
Properties of Thin Palladium‐Films and Their Hydrogen‐Permeability
Authors: Züchner H. , Schlüter H.‐J. , Rauf T. , Hergemöller R.
Published: July 2012

Thin Pd films are used as protective layers against reoxidation of cleaned less noble metals in order to allow an easy hydrogen uptake. The hydrogen permeability through the Pd‐films into the substrate metal depends strongly on the film preparation conditions especially on the deposition rate and substrate temperature during deposition. Various measurements (including resistivity, electrochemical diffusion, SIMS and AES, gravimetrical and X‐ray diffraction measuring techniques) have been applied to characterize film samples prepared in different ways in order to find the optimal conditions to prepare protective but hydrogen permeable Pd‐films. It could be shown that the hydrogen uptake from the gas phase is mainly determined by adsorption layers on the film surface, additionally the hydrogen permeability is closely connected with the structure of the interface between film and substrate. Low deposition rates and increased substrate temperatures during preparation are the basis to obtain Pd‐films with best properties for an easy hydrogen uptake and permeability.
Layered Structures in Electrolessly Deposited Nickel/Phosphorus Films
Authors: Paletschek Axel , Ramiaramanana Patrick , Weil Konrad G.
Published: July 2012

Electrolessly deposited nickel/phosphorus films with average phosphorus contents above 20 at% consist of a glassy matrix which contains variable amounts of fcc nickel crystals, supersaturated with phosphorus. The relative amounts of these crystalline inclusions can be varied widely when additives are present during the plating process. In earlier studies we could demonstrate that the crystalline inclusions were of columnar shape and extend through the whole film. In this paper we will report on experiments aimed at the finding of additives which lead to the formation of layered structures with subsequent predominantly crystalline and predominantly glassy layers.
Investigation of Rhodamine 6G Adsorption at the Fused‐Silica/Ethanolic Solution Interface Using Optical Second Harmonic Generation
Authors: Hill W. , Werner L. , Marlow F.
Published: July 2012

Adsorption of rhodamine 6G molecules at the interface between fused‐silica and ethanolic solution is investigated by means of optical second harmonic generation (SHG). In internal reflection geometry, the SHG intensities as a function of angle of incidence exhibit characteristic points arising from beginning total reflection of both fundamental and harmonic waves. Curve shapes of SHG responses depend on dispersion and absorption of the solution. The fit of the angular dependences by an interface model taking into account complex refractive indices of the solution yields optical constants, which are necessary for the determination of surface concentration and orientation of the adsorbed molecules. A relation between tensor components of the nonlinear susceptibility of a layer of plate‐like molecules can be used for the calculation of a mean refractive index inside the layer, which leads to a more realistic determination of nutation angles of the molecules.
XPS and Electrochemical Studies of Thin TiN Layers
Authors: Siemensmeyer B. , Bade K. , Schultze J. W.
Published: July 2012

TiN layers were prepared by implantation of 3 keV N2+ into Ti. The resulting layer thickness was 8 nm. Implantation, XPS and electrochemical studies were carried out in a closed system. Therefore no air oxidation took place between preparation and analysis. The electrochemical investigations (current, capacity, electron transfer and photoelectrochemical measurements) revealed the stability of TiN up to 1.3 V. At higher potentials oxidation to TiO2 and N2 dissolved in TiO2 took place. The reaction products could be detected with XPS. Sputter depth profiles revealed a layer structure Ti/TiN/TiO2. The layer thicknesses of TiO2 were smaller than on Ti at the same potentials. Photoelectrochemical experiments indicated similar electronic properties for the oxide layers on Ti and TiN. During oxidation no photocurrent was observed for TiN below 1.5 V. The stability of TiN against oxidation is explained by a N3‐ layer at the surface with a large electron density screening the underlying Ti ions and inhibiting oxidation.
Thin Pyrite Films Prepared by Sulphurization of Electrodeposited Iron Films
Authors: Pimenta G. , Schröder V. , Kautek W.
Published: July 2012

A simple procedure for the production of pyrite (FeS2) thin films starting from the pure elements is presented. A pure, highly (110) oriented polycrystalline iron precursor layer could be successfully electrodeposited. Direct sulphurization of those films on Mo foils resulted in pyrite with (200) oriented grains embedded in a randomly oriented matrix. No other iron sulphide phase like e.g. marcasite was observed. XPS shows the presence of at least 97% FeS2. Depth profiles demonstrate the stoichiometric homogeneity across the films.
Surface Analysis Investigations on the Reaction of FeS2 with Alkali Metals
Authors: Bronold M. , Pettenkofer C. , Jaegermann W.
Published: July 2012

The reactions of cleaved (100) single crystal surfaces of FeS2 with in‐situ deposited lithium and potassium have been studied with X‐ray and ultraviolet photoelectron spectroscopy. Room temperature deposition of K leads to the formation of KFeS2 as has been verified by comparism with core level and valence band spectra of polycrystalline KFeS2. The reaction products formed by deposition of Li are thought to be Li2S and FeS. The results of the UHV experiments are compared to electrochemical measurements.
Metal‐Support Interaction in a Pt  TiO2 Thin Film System: Observation of the Pt3Ti Phase at 823 K
Authors: Lamber R. , Schulz‐Ekloff G.
Published: July 2012

It is shown by means of analytical electron microscopy that platinum dispersions on TiO2 (anatase) films form a Pt3Ti alloy under thermal treatment at 823 K in hydrogen. The formation of the Pt3Ti intermetallic compound is accompanied by the local reduction of the TiO2 support to titanium suboxides (Ti4O7).
Adsorption and Polymerization of Thiophene on a Ag(111) Surface
Authors: Baumgärtner K. M. , Volmer‐Uebing M. , Taborski J. , Bäuerle P. , Umbach E.
Published: July 2012

The adsorption and in‐situ polymerization of monothiophene on Ag(111) has been studied by X‐ray photoemission (XPS), programmed thermal desorption (TDP) and mass spectrometry. Thiophene is physisorbed on Ag(111) and desorbs entirely below 250 K. Three different desorption peaks representing multilayers and two different monolayer states can be distinguished by TPD. X‐ray irradiation leads to polymerization in multilayers which is accelerated by enhanced substrate temperatures, whereas the polymerization process is quenched at the Ag surface.
Etching Pretreatment and Galvanic Cu Enhancement of Laser‐Deposited Ultrathin Ni Structures on p‐Si
Authors: Sorg N. , Kautek W. , Paatsch W.
Published: July 2012

Detailed investigations about the influence of pretreatment on the surface composition are presented. XPS data show that in 2 M NH4F radically etched Si is widely inert in respect to oxide formation at air: even after 1.5 h air contact, the oxidized Si is still less than 4 surface atom%. The same amount of oxide can be built up, however, by a 3 min contact with aqueous solution. This indicates the important role of water and humidity in the oxide formation at air.—A galvanic procedure to enhance photodeposited metal structures with a high lateral resolution is demonstrated. Cu can be electrodeposited in the dark restricted to this primary Ni structure. The thickness of the stripes could be enhanced by more than one order of magnitude while their width remained unchanged. This dark current process can only take place because the band bending has been reduced to such an extent that thermionic emission of electrons from the valence band to the metal is possible. This occurs exclusively under the metal (Ni) covered areas.
Isotope Effect in the Time Resolved Fluorescence of Anthracene in Small Unilamellar Vesicles
Authors: Brand K. , Hof M. , Schneider F. W.
Published: July 2012

The fluorescence decay of anthracene in small unilamellar vesicles (SUV) was determined employing a precise single photon counting technique. The fluorescence data were fitted best by a biexponential decay law. The longer component τ2 (4.75 ns at 26.0 °C) represents the decay time of anthracene being quenched by the lipid molecules. The shorter (red shifted) component τ1 (1.47 ns at 26.0 °C) displays a strong solvent (H2O/D2O) isotope effect. Therefore it is suggested that a number of H2O molecules may be present in the interior of the lipid bilayer. Both τ1 and τ2 processes display an apparent negative activation energy below the main phase transition which may be explained by a pre‐equilibrium whose ΔH0 is more negative than the positive activation energy of the subsequent emission step.
Investigations on Conducting Polymer Films with a Fast Electrochemical Quartz Crystal Microbalance
Authors: Dusemund C. , Schwitzgebel G.
Published: July 2012

A fast electrochemical quartz crystal microbalance (EQCM) is presented, by means of which it is possible to obtain a resolution of a few nanograms within a measuring time of one millisecond. So, mass changes accompanying cyclic voltammetry (CV) of high scan rates as well as step experiments can be recorded.—The EQCM was used for the investigation of ion‐exchange properties of conducting polymers, especially polypyrrole, which was electropolymerised potentiodynamically onto gold in aqueous solution. The insertion and expulsion of counterions (anions and/or cations) during the electrochemical change of the oxidation state of the film was studied. From the mass change and the accompanying current the different contributions of the ions to the exchange could be determined.
Contraction of Small Features in Hardened Thin Films of Novolak
Authors: Köhler J. M. , Ritzel O. , Brodkorb W. , Dittrich P.
Published: July 2012

The geometry of sub‐half‐micron features of thin films of cross linked novolak, which are formed by a three‐layer‐resist process, is found to be dependant not only on the conditions of preparation, but on the feature size, too. Small features show a reduction of the expected height up to more than 30 per cent of the thickness of the original thin film. Smaller features are stronger contracted than larger. The contraction effect increases with decreasing curing time and curing temperature during the thermal cross linking process. It decreases with decreasing thermal stress during the reactive ion etching of the novolak film. There is assumed, that the effect depends on surface forces of small novolak features and the local mobility of polymer net work. The effect will become important in the further development of microlithographic technologies.
Plasma‐Etching of Nafion® and Deposition of Electrocatalysts by MOPECVD
Authors: Zylka D. , Schmeußer M. , Ledjeff K.
Published: July 2012

Cation exchange membranes are used as solid polymer electrolytes (SPE) for proton transport in special types of electrolysers and fuel cells. A good contact with the electrodes is necessary to achieve high efficiency. Therefore, surface treatment of the solid polymer electrolyte using a plasma etching process is investigated to create favourable conditions for the preparation of sufficient membrane electrocatalyst composites. Nafion® membranes are etched in a pulsed 27 MHz oxygen/argon plasma under different conditions. The adjustment of the plasma parameters determine the surface structure and properties of the membrane after the etching process.—With a view to coat membranes in future, a new coating technique for temperature sensitive substrates by means of an MOPECVD process is beeing developed. Platinum, ruthenium and tin organyls are decomposed in argon/hydrogen plasma to create metallic thin films. The plasma parameters RF‐power, pressure, electrode temperature and plasma gas mixture significantly affect the quality of metal films deposited using this technique. After the optimization of these parameters the production of films with conductivities corresponding to their bulk metals is now possible.
Growth of Thin Films of Lanthanide Oxides and Lanthanide Copper Oxides by MOCVD
Authors: Gerfin Tobias , Becht Michael , Dahmen Klaus‐Hermann
Published: July 2012

Thin films of CeO2, Nd2O3 and Nd2CuO4 were prepared by MOCVD on quartz, sapphire, MgO[100] and Si[100]. The usual β‐diketonato complexes were used as precursors. Preliminary information about the thermal stability and possible fragmentation of the precursors was obtained by thermal analysis and mass spectrometry. The good cristallinity of the films was demonstrated by XRD. In all three compounds a preferential orientation was found. The morphology and elemental distribution on the films was investigated by profilometry and EMPA. For the deposition of CeO2 films from the precursor Ce(dpm)4 a variety of carrier and reaction gases were investigated.
Raman Spectra of Water to 400°C and 3000 bar
Authors: Kohl W. , Lindner H. A. , Franck E. U.
Published: July 2012

A small‐size high‐temperature, high‐pressure Raman cell of about 1.6 cm3 internal volume with four sapphire windows is described. It can be used to 400°C and 3000 bar. The OD‐stretching bands around 2600 cm−1 of HDO diluted in H2O have been measured from 25°C to 400°C and in a density range between 0.04 g·cm−3 to 1.0 g·Cm−3. The critical temperature of water Tc is 374°C, the critical density ϱC = 0.32 g°cm−3. At the supercritical temperature of 400°C the OD‐band was determined at densities from 0.04 to 0.8 g·cm−3. At nearly constant densities between 1.0 and 0.8 g·cm−3 the band was recorded from 25 to 400°C. Thus the OD‐band, which depends on hydrogen bonding, could be studied in a wide range of temperatures and pressures, avoiding the immediate critical region.—At 400°C and low density the sharp narrow OD‐band has a maximum frequency of 2727 cm−1. It becomes broader and shifts to 2668 cm−1 at 0.8 g·cm−3. A very broad band occurs at 25°C and 1 g·cm−3 at 2530 cm−1. Depolarization ratios were measured, local field corrections were applied and permitted the determination of isotropic and anisotropic spectra. The transition of band shape in the wide range of temperature and density is always smooth with no prominent features. As compared with a two‐component hydrogen‐bonded and non‐bonded “mixture” model a description with a “continuum”‐model as proposed by Efimov et al. appears to be preferable. Specific interaction energies have been derived from this description.
Imidazole‐Catalyzed Hydrolysis of Substituted Benzoate Esters. A Detailed Kinetic and Mechanistic Study
Authors: Menegheli Paulo , Farah João P. S. , Seoud Omar A. El
Published: July 2012

Kinetic and mechanistic details of the imidazole‐catalyzed hydrolysis of substituted phenyl benzoates in 10% acetonitrile in water (V/V) were examined. The following 4 ester series were studied: p‐nitrophenyl p‐X‐benzoates (X = CH3, H, Cl, CN, NO2, series I), p‐Y‐phenyl p‐nitrobenzoates (Y = CH3, H, Cl, CN, NO2, series II), 2, 4‐dinitrophenyl p‐X‐benzoates (X = CH3O, H, Cl, CN, NO2, series III) and p‐Y‐phenyl 2,4‐dinitrobenzoates (Y = CH3, H, Cl, CN, NO2, series IV). Based on: catalytic rate constants, activation parameters, kinetic solvent isotope effects, Hammett (δ) values and the spectroscopic detection of the reaction intermediates, the following conclusions were reached: a) imidazole acts as a nucleophilic catalyst, i.e., the hydrolysis occurs via the intermediate formation of acylimidazole; b) the leaving group is the phenoxide ion; c) the rate limiting step is the decomposition of the tetrahedral intermediate that precedes the acylimidazole (series I, II and IV) or the attack of imidazole on the acyl group of the ester (series III).
The Dimerization Energies of the Ge2S2, Ge2Se2, and Ge2Te2 Molecules
Authors: Balducci G. , Sacconi L. Vitalini , Gigli G.
Published: July 2012

The germanium monochalcogenide molecules Ge2S2, Ge2Se2, and Ge2Te2 were identified in a Knudsen cell mass spectrometric study of the vapors in equilibrium over solid GeS, GeSe, and GeTe. From a second and third law evaluation of the equilibrium data the following dimerization energies ΔH0,dimo were determined: 106.5 ± 2.1, 102.1 ± 4.6, 102 ± 8 kJ mol−1 for Ge2S2, Ge2Se2, Ge2Te2, respectively. These data and literature data allow to look into trends of the bonding energetics of group IVB‐VIB gaseous compounds.
Two‐Dimensional Phase Transitions and Correlation Field Splitting in Unimolecular Layers of CO Physisorbed on NaCI(100) as Detected by Polarization Fourier‐Transform IR Spectroscopy
Authors: Heidberg J. , Suhren M. , Weiss H.
Published: July 2012

A phase transition in the monolayer CO physisorbed on NaCI(100) was observed by means of polarization Fourier‐transform infrared spectroscopy. Above 35 K the spectra are in concert with molecules oriented perpendicularly to the surface, the unit cell being of p(1 × 1) symmetry. Below 35 K the molecules tilt, and a correlation field splitting appears. In this temperature range the spectra are in accordance with a p(2 × 1) structure with two equivalent molecules per unit cell, which are connected by a glide plane. Submonolayer spectra indicate random distribution of perpendicularly oriented CO molecules above 35 K, while at temperatures below 35 K ordered islands are formed.
Adsorption and Reaction of Butenes on Polycrystalline Nickel Films
Authors: Klingenberg B. , Haseneder R. , Borgmann D. , Wedler G.
Published: July 2012

Supplementary to literature on spectroscopic investigations of butenes adsorbed on transition metal surfaces at 273 K, the gas phase which is in equilibrium with the adsorbed layer has been analysed. Isothermic reaction mass spectrometry (IRMS) and thermal desorption spectroscopy (TDS) were applied. It is shown that for cis‐2‐butene, trans‐2‐butene, 1‐butene and 2‐methyl‐propene (iso‐butene) considerable hydrogen abstraction and partly C–C‐bond cleavage takes place. In the monolayer range methane appears in the gas phase. At coverages exceeding a monolayer hydrogen, butane and butene become the main components. Thermal desorption spectroscopy after adsorption at 77 K shows only hydrogen and methane at rather high temperatures. Starting with a multilayer adsorption of butenes at 77 K leads to desorption of butene, butane, hydrogen and methane.
Adsorption and Reaction on Oxide Surfaces: CO and CO2 on Cr2O3(111)
Authors: Kuhlenbeck H. , Xu C. , Dillmann B. , Haßel M. , Adam B. , Ehrlich D. , Wohlrab S. , Freund H.‐J. , Ditzinger U. A. , Neddermeyer H. , Neumann M. , Neuber M.
Published: July 2012

We have investigated the adsorption of CO and CO2 on epitaxially grown Cr2O3(111) by means of EELS. LEED, ARUPS, NEXAFS and XPS. CO is found to adsorb on the oxide surface in an ordered (√3 × √3)R30° structure with the molecular axis oriented approximately parallel to the surface. CO2 on the other hand reacts with the chromium oxide to form a surface carbonate. Adsorption of CO, respectively reaction of CO2 only takes place on a clean, freshly flashed oxide surface. Preadsorption of oxygen leads to a surface which is rather inert to adsorption, likely due to electronic or steric reasons.
Volume‐Gravimetric Measurements of Binary Gas Adsorption Equilibria
Authors: Keller J. U. , Staudt R. , Tomalla M.
Published: July 2012

Adsorption equilibria of binary gas mixtures on rigid solid adsorbents like activated carbons (AC) and molecular sieves (MS) can be measured “on line” by combining the (well known) gravimetric and the volumetric method. The resulting volume‐gravimetric method is described. Also the basic equations necessary to calculate the masses of each of the two adsorbed components are formulated. Explicit solutions for binary ideal gas adsorptives are given. The experimental device used for measurement is outlined. Data for coadsorption equilibria of a N2/CH4 mixture on activated carbon AK WS IV‐G 20575 at T = 298 K in the pressure range 1–20 bar are reported and discussed to a certain extend.
35Cl Nuclear Quadrupole Resonance and X‐Ray Studies on Mono‐, Di‐, and Trichloroacetates of Dimethylanilines
Authors: Basaran Reha , Dou Shi‐Qi , Weiss Alarich
Published: July 2012

The 35Cl NQR spectra of 15 mono‐, di‐, and trichloroacetates of dimethylanilines [2,3‐, 2,4‐, 2,5‐, 2,6‐, 3,5‐(CH3)2C6H3NH3⊕] [Cl3‐nHn CCOO⊖],n = 0,1,2, have been studied in the range 77 ≤ T/K ≤ Tb (Tbleaching out). – 35Cl NQR signals are observable for trichloroacetates of dimethylanilines in the range 77 ≤ T/K ≤ 200, dichloroacetates of dimethylanilines in the range 77 ≤ T/K ≤ Tdecomposition, and for monochloroacetates of dimethylanilines in the range 77 ≤ T/K ≤ room temperature. – The crystal structures of [2,3‐(CH3)2C6H3NH3⊕] [Cl2HCCOO⊖] and of [2,4‐(CH3)2C6H3NH3⊕] [Cl3‐nHnCCOO⊖], n = 1,2, were determined at room temperature. Crystal structures and 35Cl NQR spectra are compared and discussed.
Photoelectrochemical Investigations on Al and In Co‐doped ZnS Thin Film Electrodes in an Aqueous Electrolyte
Authors: Döring H. , Hashimoto K. , Fujishima A.
Published: July 2012

Al doped and Al‐In co‐doped ZnS thin film electrodes were grown by electron‐beam evaporation on ITO (indium‐tin oxide) glass substrate, and their photoelectrochemical properties were investigated. These thin films were also characterized by optical absorption, X‐ray diffraction (XRD) and X‐ray photoelectron spectrum (XPS) measurements. The doping of the ZnS film with Al alone did not result in a satisfactory n‐type semiconductor. For Al‐In co‐doped ZnS thin films prepared by the thermal diffusion of a thin In layer which was deposited previously on the ITO‐glass substrate, however, the barrier resistance between ITO and ZnS was lowered, and a clear n‐type semiconductor characteristic was observed. The efficiencies of both the photocurrent and photocorrosion of ZnS in an aqueous electrolyte were increased with higher Al concentration.
The Photochemistry of α‐Phenoxyacetophenones Investigated by Flash‐CIDNP‐spectroscopy
Authors: Palm W.‐U. , Dreeskamp H. , Bouas‐Laurent H. , Castellan A.
Published: July 2012

The photochemistry of 14 different substituted α‐phenoxyacetophenones (1) was studied by CIDNP‐spectroscopy using an XeCl excimer laser (308 nm) and a 250 MHz 1H‐NMR spectrometer. To characterize the excited states the electronic absorption and emission spectra as well as disappearance quantum yields were investigated also. – Two reaction channels were established: 1) β‐cleavage from the singlet state; and 2) the formation of acetophenones via the respective enol forms where the origin of the polarization remains unclear. It is concluded that these are the main reaction channels, since all products formed show polarizations in the CIDNP‐spectra. – In contrast to the current assumptions for the typical acetophenone reaction of (1) leading to the β‐cleavage, we are led to interprete the CIDNP‐spectra of (1) as a result of a reaction due to the phenoxy part with all characteristics of a photo‐Claisen reaction.
Structural Properties of Mixed Langmuir‐Blodgett Films of 11‐(9‐Carbazolyl)undecanoic Acid and Palmitic Acid Deposited from Compressed Monolayers
Authors: Nagamura Toshihiko , Kamata Shigenobu , Ogawa Teiichiro
Published: July 2012

The surface pressure‐molecular area isotherms for various mixtures of 11‐(9‐carbazolyl)undecanoic acid (CUA) and palmitic acid (PA) showed plateau at about 13 mN · m−1 at 15°C. The width of plateau increased with the molar fraction of CUA. A bilayer structure due to the squeezing‐out of CUA from mixed monolayers at the air/water interface was suggested from π‐A isotherms and the limiting area. The structure of Langmuir‐Blodgett (LB) films of a 1:2.7 mixture of CUA and PA deposited at 15°C and 20 mN · m−1 by a vertical dipping method was studied by the small‐angle X‐ray scattering, absorption, and capacitance measurements These results showed that LB films deposited at 20 mN · m−1 were usual Y‐type composed of a monolayer unit. It was strongly suggested that CUA partially squeezed‐out at the air/water interface was reorganized to mixed monolayers during a transfer process.
Electroreduction of Substituted Naphthylhydrazones in DMSO
Authors: Vasudevan D. , Venkatachalam C. S. , Kalidas C.
Published: July 2012

Studies on the electroreduction of 4‐chloro‐1‐naphthylhydrazonodimedone (4‐Cl‐1‐NHD), 4‐sulpho‐1‐naphthylhydrazonodimedone (1‐NHD‐4‐SO3H) and 2‐hydroxy‐4‐sulpho‐1‐naphthylhydrazonodimedone (2‐OH‐1‐NHD‐4‐SO3H) have been carried out in 0.1 M TEAI‐DMSO using various electrochemical techniques. Each depolariser exhibits three polarographic dc waves, ac peaks or CV peaks, respectively, the nature of which have been discussed. Further, from the results of microcoulometry and macroscale cpe. a complex mechanism has been suggested for the electroreduction of these hydrazones. The mechanism has been supported by in‐situ EPR measurements, evaluations of the charge‐transfer rate constants and chromatographic analysis (by TLC and HPLC) on the products of macroscale cpe.
Heat of Dilution in Aqueous and Methanolic Formaldehyde Solutions
Authors: Hasse Hans , Maurer Gerd
Published: July 2012

As part of an ongoing project dealing with thermodynamic properties of formaldehyde containing fluid mixtures, heats of dilution of formaldehyde, water, methanol and trioxane containing mixtures have been measured in a heat flow calorimeter at temperatures between 298 and 363 K. New mixing cells, allowing pressurization and avoiding vapor‐space, were used to take over 300 data points covering binary, ternary and quarternary mixtures. The observed heats of dilution are generally small (less than 250 J/mol). They are correlated using a physico‐chemical model. Physical effects are considered by the UNIFAC‐group contribution method, reaction enthalpies are used for the description of the chemical contributions. The model allows a good representation of most of the binary data, extrapolations to multicomponent systems using binary data alone are, however, only qualitatively correct.
Power‐Law Behavior in the Frequency dependence of the Electrical Conductivity of Poly(L‐Glutamic Acid) Aqueous Solutions
Authors: Bordi F. , Cametti C. , Paradossi G.
Published: July 2012

The electrical conductivity of poly(L‐glutamic acid) in aqueous solutions was measured in the frequency range from 0.5 MHz to 100 MHz, following the entire helix‐coil transition induced by change of pH. The frequency behavior of the conductivity can be described by a power law whose exponent varies from 2 at low degree of ionization (full‐helix conformation) to about 1 at higher degrees of ionization (full‐coil conformation). A possible mechanism involving the motion of polar side chains is proposed.
A Molecular Dynamics and X‐ray Diffraction Study of MgCl2 in Methanol
Authors: Tamura Y. , Spohr E. , Heinziger K. , Pálinkás G. , Bakó I.
Published: July 2012

A recently developed flexible three‐site model for methanol was employed to perform a Molecular Dynamics simulation of a 0.6 molal MgCl2 solution. The ion‐methanol and ion‐ion potential functions were derived from ab initio calculations. The structural properties of the solution are discussed on the basis of radial and angular distribution functions, the orientation of the methanol molecules, and their geometrical arrangement in the solvation shells of the ions. The dynamical properties of the solution are calculated from various autocorrelation functions. Results are presented for the influence of the individual ions on self‐diffusion coefficients, hindered translations, and internal vibrations of the methanol molecules. The comparison of calculated X‐ray structure and pair correlation functions with those got from a newly performed X‐ray measurement on the same solution shows good agreement.
Calculation of High Pressure Phase Equilibria of Mixtures of Ethylene, Vinylacetate and an (Ethylene‐Vinylacetate) Copolymer
Authors: Finck Udo , Wohlfarth Christian , Heuer Tilo
Published: July 2012

Some new measurements of the high pressure demixing behaviour have been done in the system ethylene, vinyl acetate and an (ethylene‐vinylacetate) copolymer. Calculations of phase equilibria using the chain‐of‐rotators equation of state are compared with these new experimental data The miscibility gap of the ternary mixture can be predicted on the basis of a group contribution approach using interaction parameters from low molecular weight binary mixtures only. The model describe the phase separation (besides of polydispersity effects) sufficiently accurate up to high pressures. The derivation of the spinodal equation for ternary mixtures facilitates the calculation procedures applied. The model calculations detect a closed miscibility gap at higher pressures than in the binary subsystem composed of ethylene and the (ethylenevinylacetate) copolymer. Experimental evidence for this behaviour is open, however.
Solvent Induced Broadening of Fluorescent Electronic Transitions of Paraterphenyl
Authors: Sander R. , Menzel R. , Naumann K.‐H.
Published: July 2012

We investigate the solvent influence to the inhomogeneous broadening of the fluorescent electronic transitions of paraterphenyl. The broadening is described in a phenomenological way by modeling the measured spectra with a sum of Gaussian functions. Lorentzian functions are also tested. Although the solvent properties are varied considerably the halfwidth of these subbands only changes about ± 12%. Molecular dynamic calculations predicted an influence of geometric solvent parameters like packing density and solvent diameter to the inhomogenous broadening. A method for the calculation of these parameters from thermodynamic properties of the solvents is presented. The halfwidths of the fitted subbands are discussed as functions of several solvent parameters (e.g. dielectric constant, geometric solvent parameters). By normalizing the halfwidths to a constant packing density of solvent molecules the correlations can be improved. It becomes evident, that geometric solvent properties do have at least a similar effect to inhomogeneous broadening of the measured electronic transitions than other solvent parameters.
A STM Investigation of Pt‐Single Crystal Surfaces in Air and Electrolyte Solutions
Authors: Vogel R. , Kamphausen I. , Baltruschat H.
Published: July 2012

We describe the construction of a beetle‐type scanning tunneling microscope optimized for in situ measurements. The influence of the crystal preparation technique on the surface structure is reported. Whereas annealing of platinum single crystals in iodine vapour yields smooth surfaces for the low index faces, which are protected from contamination in air by the adsorbed iodine, facetting occurs in the case of stepped surfaces. — The iodine adlattices are resolved both in air and electrolyte: Pt(111) (3 × 3)‐I and Pt(100) (√2 × 5√2)R45°I, thus confirming previous LEED results.
Electric Double Layer at the Membrane/Solution Interface: Distribution of Electric Potential and Estimation of the Charge Stored
Authors: Manzanares J. A. , Mafé S. , Bisquert J.
Published: July 2012

The classical equations for the equilibrium electric double layer (EDL) at the charged membrane/solution interface have been solved and distributions of the electric potential and estimations of the charge stored are presented for some typical situations. The theoretical treatment is based on the full, non‐linearized Poisson‐Boltzmann equation, and includes partition coefficients and an adsorption isotherm for the concentration‐dependent fixed charge in a membrane immersed in a ternary electrolyte system. The physical trends observed for the Donnan and surface potentials and for the charge stored when the characteristics parameters of the EDL are varied have been discussed. Finally, the results obtained with the depleted layer model with concentration‐dependent fixed charge are compared to those resulting from the diffuse double layer model.
Kinetics of the Dehydration of the β‐Cages of Sodium Faujasites as Studied by H‐NMR Spectroscopy
Authors: Basler W. D. , Lechert H. T. , Carboo D. , Knöchel A.
Published: July 2012

The kinetics of the dehydration of the β‐cages of sodium faujasites have been studied by NMR methods. For Na — Y type (Si/Al > 2) the rate of passing from the β‐cages into the supercages is slow and only weakly dependent on temperature (activation energy EA = 4.1 kJ/mol). This is in contrast to the strongly temperature dependent (Ea = 100 kJ/mol) rate of penetration from the supercages into the β‐cages. A model is proposed assuming the formation of a water‐ion complex. The slow rate is explained by a negative complex formation entropy (−40R) due to spatial constraints in the β‐cages. The activation energy is small because the enthalpy of the penetration is nearly canceled by the negative complex formation enthalpy.
Thermodynamic Activation Parameters for Viscous Flow in Acetonitrile‐Water‐Electrolyte Systems
Authors: Kumar Gopu
Published: July 2012

Feakins‐Lawrence extension of Eyring's transition state theory for viscosity of electrolyte solutions has been applied to aqueous acetonitrile solutions of potassium halides and tetraalkylammonium bromides at 5, 15, 25 and 35°C. The molar contributions of the electrolytes namely free energy (Δμ3o*), enthalpy (ΔH3o*) and entropy (ΔS3o*) to the activation parameters for viscous flow of the ternary system were evaluated using viscosity data. The results are discussed in terms of ion solvent bond‐making, bond‐breaking and in the light of the recently proposed new theory of Feakins.
Contact‐Complex Formation Reaction between Solvent Molecules in Square‐Well Fluids 1. One‐Dimensional Fluid
Authors: Yoshimura Y.
Published: July 2012

Contact‐complex formation reaction between solvent molecules in square‐well fluids has been studied for the one‐dimensional system. The packing effect due to the hard repulsive interaction stabilizes the contact complex, while the effect of the attractive interaction always restrains the contact‐complex formation in one‐dimensional fluids. The density dependence of the equilibrium constant shows an interesting behavior due to the trade‐off between these two factors. When the attractive interaction is sufficiently large, the equilibrium constant may decrease with increasing density. On the other hand, the equilibrium constant of the contact‐complex formation converges to that in the hard rod fluid at the high density limit. The results qualitatively agree with the findings for the solvent effects on the electron‐donor‐acceptor‐complex formation reaction.
Photoisomerization Dynamics of 3,3′‐Diethyl Oxacarbocyanine. Intramolecular and Solvent Viscosity Effects
Authors: Ponterini Glauco , Caselli Monica
Published: July 2012

The dynamics of photoisomerization and of ground‐state back isomerization of 3,3′‐diethyl oxacarbocyanine (DOC) in linear alcohols are analyzed. “Intramolecular” activation energies are obtained and compared with those of the corresponding dicarbocyanine (DODCI) in an attempt at establishing the consequence of the polymethine chain lengthening on the isomerization dynamics. The activation energy for the photoisomerization of DOC is slightly lower than that of DODCl, whereas the reverse is found for the ground‐state back isomerization. The coupling of the internal twisting coordinate with solvent drag is analyzed within the framework of the hydrodynamic Kramers model. Although this approach does not provide a fully satisfactory description of the experimental points, it has been taken as a reference model: the parameters obtained from the data fitting have been assigned a semi‐quantitative significance and a number of possible reasons of breakdown of the hydrodynamic Kramers description have been considered and qualitatively discussed.
CARS Measurements and Numerical Simulation Results for Methane/Air Counterflow Flames
Authors: Dießel E. , Dreier T. , Lange B. , Wolfrum J. , Behrendt F. , Warnatz J.
Published: July 2012

In extension of previous work a comparison has been made between experiments and numerical simulation results across the flame front of an atmospheric pressure methane/air counterflow diffusion stabilized in the forward stagnation region of a cylindrical porous burner plate. Temperature profiles have been measured by CARS spectroscopy on molecular nitrogen. The experimental data are compared with results of numerical calculations using a computer code based on a one‐dimensional boundary layer approximation. This work covers pure diffusion flames at different strain rates as well as partially premixed flames at two stoichiometries and strain rates. The results indicate good agreement between measured and calculated temperature profiles with regard to peak temperature location of the flame front, temperature gradients and overall shape of the non‐premixed and partially premixed flames, respectively.
Isomerization of Meta‐Xylene Over Pentasil‐Type Microporous Gallosilicates
Authors: Richter M. , Kosslick H. , Tuan Vu Anh , Richter‐Mendau J. , Parlitz B. , Ehrhardt K. , Vorbeck G. , Szulzewsky K.
Published: July 2012

The isomerization of meta‐xylene under normal pressure was studied in the temperature range 570–770 K on three catalyst series, viz. (i) gallosilicates with a constant Si/Ga ratio of 50, but different synthesis times ranging from 5 to 96 h, (ii) gallosilicates with a higher (100) and lower (25) Si/Ga ratio after 48 h and 96 h crystallization time, and (iii) a series that included a ZSM‐5 zeolite, a gallosilicate, and a ferrisilicate, all with comparable concentrations of Brønsted acid sites. The characterization of the catalysts is based on XRD, electron microscopy (TEM, SEM), ammonia thermodesorption, thermoanalysis and n‐hexane adsorption. Synthesis products that were characterized by X‐ray diffraction to have 100% crystallinity, acquire further acidity when the synthesis time is prolonged. This effect is due to an additional insertion of gallium in framework positions from a reservoir of nonframework gallium species. — The isomerization on gallosilicates proceeds with negligible disproportionation to toluene. The activity is intermediate, compared to the ZSM‐5 zeolite and to the ferrisilicate. The shape selectivity of the gallosilicates is inversely related to the crystallinity. — The kinetics of the isomerization can be described by a parallel two step model, in good agreement with experimental results. The significance of internal mass transport effects is discussed.
Electronic Spectra of 1,4‐Diketo‐3,6‐Diphenyl‐Pyrrolo‐[3,4‐c]‐Pyrrole in the Solid State
Authors: Mizuguchi Jin , Rihs Grety
Published: July 2012

The title compound (DPP) is a new red pigment based on the diketopyrrolopyrrole chromophore. The evaporated film of DPP has a vivid red whose absorption spectrum is very similar to the molecular spectrum in solution. When exposed to acetone vapor, the film turns orange, and changes in photoelectrical properties take place. Electronic spectra of DPP have therefore been investigated mainly in evaporated films from the standpoint of π‐π interactions along the stacking axis. Special attention has been paid to the temperature dependence of the absorption spectra in connection with lattice contractions. The effective overlap of π‐electrons between molecular planes strongly influences the electronic system and perturbs the molecular‐like spectrum in the solid state. Several solid state spectra can arise from DPP, depending on the extent of the π‐π interactions.
Electronic Properties of 1,4‐Dithioketo‐3,6‐Diphenyl‐Pyrrolo‐[3,4‐c]‐Pyrrole in Solution and in the Solid State
Authors: Mizuguchi Jin , Rochat Alain Claude , Rihs Grety
Published: July 2012

The near IR optical absorption of the title compound (DTPP) is of practical importance for laser printers and information storage applications based on GaAs laser diodes. Electronic properties of DTPP have been investigated in solution and in the solid state from the standpoint of deprotonation and intermolecular hydrogen bonding. The electronic state of the dithioketopyrrolopyrrole chromophore is found to be most sensitively affected by an environment of proton acceptors which interact with the NH group. The deprotonation (= N−) in solution leads to increased electron density on the nitrogen atom. As a consequence, there is more overall electron density in the chromophore which contributes to a large bathochromic displacement. A similar increase in electron density is also operative in the solid state through the inter‐molecular hydrogen bonds between the NH group of one DTPP and the sulfur of the neighboring molecule. This is responsible for the large bathochromic shift of DTPP from the solution to the solid state. The visible absorption in the solid state is attributed to transitions along the molecular plane. On the other hand, the strong near IR absorption is interpreted as being due to interplanar π — π interactions along the stacking axis perpendicular to the molecular plane.
TiO2 Thin Films Prepared by Pulsed Beam Chemical Vapor Deposition from Titanium Tetraisopropoxide and Water
Authors: Döring H. , Hashimoto K. , Fujishima A.
Published: July 2012

TiO2 thin films were deposited by pulsed beam chemical vapor deposition from titanium tetraisopropoxide and H2O vapors. Each reactant gas was introduced to a chamber alternately using commercial automobile electric fuel injectors as beam sources. These thin films, deposited at various substrate temperatures, were characterized by measuring optical absorption spectra, X‐ray diffractions and X‐ray photoelectron spectra. Their properties were compared with those of TiO2 films deposited by electron beam evaporation.
Electrochemical and Thermodynamic Aspects Controlling the Iron‐Hexacyanoferrate Redox System in Ethylene Glycol‐Water Mixed Solvent
Authors: Hilal N. H. , El‐Shazly Sh. A. , Bekheet A. M. , Badawy W. A.
Published: July 2012

The effect of ethylene glycol on the electrochemical behaviour of the Au‐rde in the iron‐hexacyanoferrate redox system was studied. A standard potentiostatic technique was used to trace the kinetic parameters controlling the anodic and cathodic processes occurring at the electrode/electrolyte interface. The thermodynamic parameters of the ethylene glycol‐water mixed solvent were evaluated. The results revealed that the presence of ethylene glycol in the solvent mixture retards the diffusion processes and enhances the charge transfer kinetics. The rate of the anodic process was found to be entropy controlled and the isokinetic temperature of the cathodic process was fairly close to the experimental temperature indicating the presence of compensation effects between the entropy and enthalpy changes.
Melt‐Spinning of AB5.5‐Type Hydride‐Forming Compounds and the Influence of Annealing on Electrochemical and Crystallographic Properties
Authors: Notten P. H. L. , Daams J. L. C. , Einerhand R. E. F.
Published: July 2012

Non‐stoichiometric almost single‐phase AB5.5 materials were prepared using the melt‐spinning technique. Characteristic of these materials is the anisotropically deformed crystal lattices (decreased a‐axis and increased c‐xis), resulting from the excess of B‐elements incorporated in the hP6‐CaCu5 structure. These materials show (i) an excellent long‐term stability during electrochemical cycling in alkaline solution, indicating that the oxidation resistivity strongly depends on the extent of the crystal lattice deformation and (ii) a relatively poor electrocatalytic activity which can be attributed to the absence of highly catalytic second‐phase alloys. Annealing of the as‐prepared samples induces the deformed crystal lattice to relax by secreting the excess of B‐elements. As a consequence, double‐phase materials are formed, consisting of hydride‐forming compounds with compositions close to the AB5 stoichiometry and second‐phase alloys. These double‐phase materials combine a relatively poor long‐term cycling stability with a high electrocatalytic activity.
Studies of Polymer Solvation by Dielectric Relaxation Spectroscopy V: Polyvinylpyrrolidone in Pyrrolidone
Authors: Rohmann M. , Stockhausen M.
Published: July 2012

The dielectric spectrum of PVP 1200 in pyrrolidone solution is measured between 2 MHz and 72 GHz at temperatures of 20, 40, and 60°C. Polymer concentrations are up to a monomole fraction of 0.5. The results are described in terms of Debye type components. For pure pyrrolidone two components are required which are probably caused by associated and monomeric solvent. Additional low frequency components ascribable to the polymer appear with PVP solutions. Here the solvent contributions can be distinguished into unaffected, loosely affected and tightly bound solvent. As a peculiar feature there is direct evidence of the interchange of solvent‐solvent to solvent‐polymer interaction.
The Vaporization of Cesium/Antimony Alloys under Equilibrium and Nonequilibrium Conditions
Authors: Hartmann Andreas , Weil Konrad G.
Published: July 2012

We evaporate cesium/antimony alloys either from a Knudson cell or from a Langmuir source. The compositions of the resulting molecular beams are determined mass spectrometrically. Using a quartz microbalance, we can determine total evaporation rates of the alloys. In all cases the alloys evaporate incongruently, antimony is enriched in the vapor. Comparison of Knudsen data with those obtained from Langmuir evaporation enables us to calculate evaporation coefficients for the individual evaporating species. The intermetallic molecules have evaporation coefficients in the order of magnitude of 0.1–0.5, while atomic cesium has an evaporation coefficient of about 0.01. From this we conclude that adsorbed neutral cesium is not a precursor for the formation of the intermetallic molecules.