bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of the isotrop‐nematic phase transition in liquid crystals. I. Nucleation theory of phase transition
Authors: Oranth Norbert , Strohbusch Frank 
Published: March 2014

AbstractThe kinetics of the isotropic‐nematic phase transition under adiabatic conditions is described by the nucleation theory with a rate law of droplet growth derived from the time dependent Landau‐Ginzburg equation. As an example the time evolution of the nematic phase in supercooled 8CB is calculated. The results reveal a strong dependence of the size distribution function of nematic droplets, on the temperature and also significant changes during the process. The completion times are much longer than under isothermal conditions.
Kinetische Untersuchungen zur Reversibilität der Makromoleküladsorption an der Grenzfläche Wasser/Luft
Authors: Nitsch Walter , Kremnitz Wilfried , Schweyer Georg 
Published: March 2014

AbstractWith measured changes of surface pressure of spreaded monolayers (Polyethylenglycol) on aqueous subphases in a Langmuir trough. the kinetics of desorption was studied for different states of compression. — Because of an observed strong influence of the forced convection and the verification of the second Pick's law for desorption into the quiescent bulkphase it is concluded, that the molecular diffusion controls the desorption. This result leads to the conclusion of an always established equilibrium between monolayer and subsurface corresponding to a reversible state. — With the diffusion law for the measured desorption it is possible to calculate the concentrations in the subsurface equilibrated with the monolayer. These subsurface concentrations are shown to be very strong dependent from the state of compression. With the equilibrium values it is possible to derive that the high stability of the layers are caused by the very low diffusion flux as a consequence of an very low equilibrium concentration in the subsurface.
Surface enhanced raman scattering at electrodes: A status report
Authors: Chang Richard K. 
Published: March 2014

AbstractProgress during the first decade of surface enhanced Raman scattering (SERS) is briefly reviewed. Examples of SERS of adsorbed H2O. OH−, and H3O+ on Ag electrodes which have undergone an oxidation‐reduction cycle (ORC) are discussed in some detail in order to bring out the unique and general features of SERS in an electrochemical system. Experimental techniques to further enhance the SERS signal, as well as to decrease the SERS signal after an ORC, are reviewed as such results can provide clues to possible surface enhancement mechanisms. The two enhancement mechanisms (electromagnetic and charge transfer) are presented in a unified but simplistic picture which involves the nearly free s,p‐electron band and the more localized d‐electron band for the noble metals (Ag, Cu, and Au). The role of the intraband transitions in the electromagnetic and charge transfer enhancement processes is discussed in terms of the wave‐vector uncertainty associated with the Raman dipole located on or near the surface and with the localized metal clusters which are often referred to as SERS‐active sites. Several examples are cited in which experiments initially designed to prove the presence of one enhancement mechanism end up proving the existence of both enhancement mechanisms. Progress expected in the SERS field during the next decade is also suggested.
Infrared reflection‐absorption spectroscopy of adsorbed species on electrode surfaces using a laser source
Authors: Sass J.‐K. , Roe D. K. , Bethune D. S. , Luntz A. C. 
Published: March 2014

AbstractA substantial increase in optical sensitivity of infrared reflection‐absorption Spectroscopy (IRRAS) was achieved by the combination of a pulsed, tunable infrared laser and a novel thin layer cell which was designed to provide uniformity and control of solution layer thickness. The importance of these cell parameters is illustrated by optical model calculations and experimentally verified by vibrational spectra of CO adsorbed on Pt electrodes. Peak values of relative reflectance changes exceeding 10% were obtained at near‐monolayer coverages without any modulation technique. In view of these results, the ramifications of the wide range of incidence angles and of the lack of precise control of solution layer thickness in previous IRRAS studies are examined with regard to spectral fidelity and response to potential transients.
Ellipsometric study of the growth of thin organic polymer films
Authors: Hamnett Andrew , Hillman A. Robert 
Published: March 2014

AbstractEllipsometry has been used to study the contrasting electrochemical growth mechanisms and properties of two organic redox polymer films on Pt. The first part of the work is a study of the anodic polymerisation of thionine from aqueous solution. Initially, a monolayer of PtO is formed on the electrode. Thereafter uniform growth of polythionine proceeds under diffusional control, as evidenced by the square root dependence of film thickness on time. Quantitation of this relationship shows that the film contains ∼50% (by volume) organic polymer, ∼25% counterions and ∼25% H2O. Reduction requires additional counterion ingress, but the absence of significant expansion implies some solvent loss. Optical properties of the film are rather similar to those of the monomeric redox system and show a Nernstian potential dependence, in agreement with coulometric data. The second part of the work is an analogous study on the polymerisation of thiophene from CH3CN solutions. This process is kinetically controlled. At short times there is evidence for nucleation. At longer times, nuclei overlap and uniform growth is indicated by a linear increase of film thickness with time. The evolution of polymer optical properties during this process was monitored. Optical properties of both redox states were determined at several wavelengths and contrast markedly with parameters for the monomer. Switching between redox states is rapid and involves swelling via solvent ingress on reduction. Ellipsometric data acquired during voltammetric scans reveal, however, that the sequence of events in this process is complex.
Photoetching of polycrystalline n‐CdS film electrodes in a photoelectrochemical cell: An electrolyte electroreflectance study
Authors: Ferrer I. J. , Salvador P. 
Published: March 2014

AbstractPhotoelectrochemical etching (photoetching) of polycrystalline CdS electrodes has been investigated, by the first time, by electrolyte electroreflectance (EER) technique. EER is shown to be a very powerful tool for the “in situ” study of the potential distribution changes occurring at the semiconductor‐electrolyte interface, even in the case of polycrystalline electrodes with scarce specular reflection. The EER study of the effect of photoetching on the photoelectrochemical behaviour of polycrystalline CdS electrodes allows a further insight into the origin and mechanisms involved in this interesting etching technique.
Intensity modulated photocurrent spectroscopy of n‐GaAs
Authors: Peat R. , Peter L. M. 
Published: March 2014

AbstractSurface recombination at n‐GaAs photoelectrodes in alkaline selenide solutions has been investigated by intensity modulated photocurrent spectroscopy (IMPS). The technique involves sinusoidal modulation of the incident photon flux and frequency response analysis of the photocurrent. Recombination processes give rise to characteristic changes in the phase and amplitude of the periodic photocurrent, and the time constants for the relaxation of carriers in surface states can be obtained conveniently from analysis in the complex plane. The method can detect shifts in the band edge energies that result from changes in the surface dipole at the semiconductor solution interface, and the results indicate that the band edge energies of GaAs vary with electrode potential and illumination intensity. The effect of ruthenium treatment on surface recombination has also been explored by the technique.
Remarkably high photovoltages generated at n‐type silicon semiconductor electrodes coated with extremely small platinum islands
Authors: Nakato Yoshihiro , Tsubomura Hiroshi 
Published: March 2014

AbstractA photoelectrochemical solar cell, equipped with an n‐type silicon semiconductor electrode coated with sparsely scattered, extremely small platinum islands, generates a remarkably high open‐circuit photovoltage of 0.68 V compared with that of a normal p‐n junction silicon solid solar cell (0.59 V). This result is explained by our theory recently proposed on the mechanism of the generation of photovoltages at semiconductor electrodes covered with discontinuous metal layers. The present result is encouraging as a novel approach to highly efficient solar cells.
Growth and morphology of electrodeposited semiconducting films
Authors: Decker F. , Moro J. R. , Ferreira J. L. S. , Vanzi M. 
Published: March 2014

AbstractSemiconducting CdSe films have been electrodeposited on a variety of substrates by means of two techniques. The processes of nucleation, coalescence and growth have been accompanied ex‐situ by scanning electron microscopy, and in‐situ by optical reflectance. We analyze the growth mode for different film thicknesses and we discuss the applications in solar cells and other devices.
Simulation of electrochemical interface properties: UHV‐investigation on CuInSe2 and CuInS2
Authors: Sander M. , Lewerenz H.‐J. , Jaegermann W. , Schmeißer D. 
Published: March 2014

AbstractThe interaction of water and chlorine with cleaved CuInSe2 and CuInS2 surfaces is studied by XPS and UPS. Whereas water appears to adsorb undissociatively, chlorine interacts chemically with the surfaces. Photoinduced changes of valence band spectra are investigated and their relevance with respect to surface states and band bending is discussed.
Photocurrent spectroscopy of anodic films on metal electrodes
Authors: Peter L. M. 
Published: March 2014

AbstractThe mechanisms of photocurrent generation in thin anodic films on metals are reviewed. It is shown that photocurrent spectra can be analysed to give absorption spectra or film thickness data, and several experimental examples of the quantitative application of photo‐current Spectroscopy are discussed in order to illustrate the main features of the analysis.
Amorphous semiconductor‐electrolyte junctions. Photoelectrochemical behaviour of thin Nb2O5 anodic films
Authors: Quarto Francesco Di , Piazza Salvatore , Sunseri Carmelo 
Published: March 2014

AbstractAn approach to the study of the photocharacteristics of amorphous semiconductor/electrolyte junctions is proposed which takes into account the main differences in the electronic structure and the transport properties of the amorphous semiconductors (a‐SC) with respect to the crystalline counterparts. The influence of the wavelength of the incident light on the photocurrent vs electrode potential curves is explained on the basis of the geminate recombination theory in a‐SC. The implications of the model are shortly discussed.
Mechanisms of charge transfer at the semiconductor‐electrolyte interface: Oxygen electroreduction at naked and platinized n‐TiO2 electrodes
Authors: Tafalla D. , Salvador P. 
Published: March 2014

AbstractThe electroreduction of oxygen at a n‐TiO2 single crystal was studied by the rotating ring‐disc electrode technique. The overpotential of the reaction was found to be higher at acidic than at basic pH, this pH effect being more important at low bandbending than at high bandbending. At potentials positive of flat band the cathodic current was not found to be proportional to the O2 concentration of the electrolyte, both at acidic and basic pH. The amount of H2O2 generated as final product of the reaction was found to be higher in the low current region (high bandbending) than in the high current region (small bandbending). — All these experimental features was explained on the basis of a two‐step kinetic model involving bandgap surface states probably associated with chemisorbed OH− groups. The first, limiting step of the reaction was considered to be the formation of the superoxide ion. The generation of H2O2 as final product was determined by the facility of these species to be chemisorbed on the TiO2 surface. — The main effect of Pt deposition is to reduce the overpotential for O2 electroreduction, the same mechanism as for the naked electrode being apparently valid.
Physical and electrochemical aspects of charge transfer reaction inverse photoemission spectroscopy (CTRIPS): Photon energy enhancement for high injection currents
Authors: McLntyre R. , Roe D. K. , Sass J. K. , Gerischer H. 
Published: March 2014

AbstractTransient measurements of the faradaic current due to hole injection into Au(111) electrodes and of the light emission caused by radiative decay of the excited holes are reported. By compensating for the ohmic solution resistance the time constant for charging the double layer was greatly reduced, such that much higher injection currents were achieved at the desired potential. With this provision, the spectral distribution of the emitted radiation was characterized by photon energies well above the difference between the Gibbs free energies for electrons at the Fermi‐level of the metal and in the injecting thianthrene cationic species. Regularly spaced structural features were also observed in the CTRIPS spectra. As an explanation of the photon energy enhancement a 2‐quantum process, involving the interaction of a primary hole and a secondary electron, is proposed.
Monte Carlo Simulation of Model Three‐Component Liquid Systems
Authors: Yurtsever Ersin , Karaaslan Hasan 
Published: March 2014

AbstractA two‐dimensional model for studying the miscibility of binary liquid mixtures is proposed. The parameters are optimized so that the phase separation can be observed. The degree of mixing is investigated by the distribution functions and the structural drawings of the system at equilibrium. It is shown that immiscible liquid mixtures can be “remixed” by the addition of small chains with polar ends.
Vapour‐Liquid Equilibrium of n‐Tetradecane and of n‐Hexadecane with Hexafluorobenzene and with Hexafluorobenzene + Benzene at 323.15 K
Authors: Aracil J. , Rubio R. G. , Renuncio J. A. R. , Peña M. Diaz 
Published: March 2014

AbstractThe vapour pressures of the binary systems formed by n‐hexadecane and by n‐tetradecane with hexafluorobenzene and of the corresponding ternary systems with benzene have been measured at 323.15 K using a static technique. Thermodynamic consistency of the data has been checked using a Padé approximant for the binary systems, and several empirical equations for describing the GEm of the ternary systems. The predictions of several GEm and group contribution models have been compared with the experimentals results.
Deuterium Isotope Effects in Binary Critical Mixtures Study of the Systems Methanol/Isooctane and Acetonitril/Water
Authors: Hürth M. , Woermann D. 
Published: March 2014

AbstractThe shift of the critical temperature of binary mixtures with an upper critical point caused by a replacement of hydrogen atoms by deuterium in different parts of the molecules is studied. The systems are methanol (methanol, methanol‐d1, methanol‐d4)/isooctane and acetonitrile (acetonitrile, acetonitrile‐d3)/water (H2O, D2O). It is found that replacement of hydrogen atoms involved in hydrogen bonding (OH‐group of methanol, OH‐group of water) by deuterium leads to an increase of the miscibility gap.
Photospannung in monomolekularen Schichtsystemen mit Farbstoffaggregaten
Authors: Schreiber H. , Försterling H. D. , Kuhn H. 
Published: March 2014

AbstractA glass slide evaporated with a metal film is covered by Cd‐arachidate and dye monolayers of various architecture. The assembly is inserted in water. In case of aggregate‐forming dyes we observe a photovoltage (up to 60 mV) between metal and water. The results are interpreted by assuming the formation of electron‐hole pairs in the aggregate after excitation of the dye; the electrons are tunneling through the monolayer of the fatty acid to acceptors in the water; the holes are filled by electrons from the metal.
Structures in Mixtures of p‐tert‐Octylphenol Polyoxyethylene and Water. 1. Triton X‐114
Authors: Heusch Rudolf , Kopp Friedrich 
Published: March 2014

AbstractOn the basis of the phase diagram of water and the nonionic detergent Triton X‐114R (p‐tert‐octylphenol polyoxyethylene with 7 to 8 moles oxyethylene units), results of polarization microscopy and rheological studies are compared with results obtained by freeze‐fracture electron microscopy. The ultrastructure of the mesomorphic phase, the optically isotropic solution, and the phases separated in the miscibility gap are shown in detail.
Enthalpy of Demixing of a Binary Liquid Mixture of Critical Composition: Study of the System Isobutyric Acid/Water
Authors: Harnisch F. P. , Woermann D. 
Published: March 2014

AbstractA fast pressure jump technique is used to measure calorimetrically the temperature dependence of the enthalpy of demixing of an isobutyric acid/water mixture of critical composition in the vicinity of its upper critical point at temperatures below the critical temperature.
The Nature of the Reduced Defect and the Diffusion of GeO2 in Germaniadoped Vitreous Silica
Authors: Rau Hans , Hermann Wilhelm 
Published: March 2014

AbstractDiffusion constants of GeO2 in vitreous silica and absorbances at 242 nm were determined as a function of temperature, time and oxygen content of the gas surrounding the samples during annealing. The samples were prepared by the PCVD method (Plasma‐activated Chemical Vapour Deposition). Computer modelling showed that the reduced germanium centre absorbing at 242 nm is an antistructure defect (germanium on an oxygen site) and not GeO, as suggested by other publications. The diffusion constant of O2 molecules, relevant in the computer model, is given by magnified image The GeO2 diffusion constant decreases at a given temperature with increasing oxygen content of the sample and increases with the GeO2 content. An average value is given by magnified image.
Conducting Polymers from 3,4‐Disubstituted Polypyrroles
Authors: Rühe J. , Kröhnke C. , Ezquerra T. A. , Kremer F. , Wegner G. 
Published: March 2014

AbstractPyrrole derivatives, which were substituted in the 3,4‐position by a fused alkyl ring have been synthesized and their electrochemical and electrical properties have been investigated. — Compounds with a five, six, seven and twelve membered ring fused to the pyrrole moity were obtained by means of a 3 + 2 cycloaddition of tosylmethylisocyanide to an α,β‐unsaturated ketone. Electrooxidation in acetonitrile/ tetrabutylammonium perchlorate led to the deposition of brittle, black, conducting polymer films on the anode, which could be reversibly reduced and reoxidized in the range of +1 to −1 [V] vs. Ag/Ag+. The electrodeposited films swell in polar aprotic media. — The conductivity decreased with increasing ring size of the substituent from 0.4 S cm−1 (five membered ring) to 2 ± 10−4 S cm−1 (twelve membered ring), while the temperature dependence increased. — The polypyrrole derivative containing the twelve membered ring showed a strong frequency dependence of the conductivity at 100 K. By changing the frequency from 0.01 to 1000 KHz the conductivity increased by two orders of magnitude.
Variable Temperature15N CPMAS NMR Studies of Dye Tautomerism in Crystalline and Amorphous Environments
Authors: Wehrie Bernd , Limbach Hans‐Heinrich , Zimmermann Herbert 
Published: March 2014

AbstractThis paper deals with the question of how symmetric double minimum potentials of isolated bistable molecules are affected in the ordered or disordered solid state, in a timescale of slow molecular motion. It is shown that high resolution solid state NMR under conditions of magic angle spinning (MAS) and cross‐polarization (CP) can contribute to answering this question. In particular, variable temperature high resolution solid state15N CPMAS NMR spectra (CP = cross polarization, MAS = magic angle spinning) of15N enriched tetraaza[14]annulene dyes in the crystalline state and imbedded in disordered glassy polystyrene are presented. These dyes interconvert fast between different tautomeric states whose gasphase degeneracy is lifted in the solid. By contrast to the crystalline state where all dye molecules experience the same solid state perturbation i.e. the same equilibrium constants of tautomerism, molecules dissolved in the glass exist in a multitude of different inequivalent sites with different solid state perturbations. This effect leads to a broad distribution of equilibrium constants of dye tautomerism. This interpretation is confirmed by NMR lineshape simulations and two‐dimensional15N CPMAS NMR experiments by which the temperature dependent distribution can be characterized. High temperature experiments in the region of the glass transition give insights into the process leading to motionally averaged symmetric double minimum potential of tautomerism within the NMR timescale. Thus, solid solution NMR studies provide information about elementary steps of molecular rearrangements in a timescale of slow solvent reorientation. In addition, dyes such as tetraaza[14]annulenes can be used as novel NMR probes for microscopic order and motion in glasses.
Structure and Phase Transitions of Aromatic Radical Cation Salts — a New Class of Organic Metals
Authors: Enkelmann V. , Göckelmann K. 
Published: March 2014

AbstractStable radical cation salts of a variety of simple arenes can be prepared by anodic oxidation. These highly conducting crystals of the composition (Ar2‐y)+X− (0 < y < 1, X = BF−4, ClO−4, PF−6, AsF−6, SbF−6) are deposited on the anode during the electrocrystallization. They can be considered as new family of organic conductors built up from simple, easily obtainable building blocks. — The packing found between the aromatic rings can be regarded as a model for the interchain interactions in conducting polymers, e.g. doped poly‐p‐phenylene. — The crystal structures of most radical cation salts can be characterized as columnar structures. The molecular overlap plays an important role in the electrical and magnetic properties. The geometry of this overlap is changed in metal‐insulator transitions which occur near 200 K. The phase transition in FA2PF6 has been investigated in detail and recent results are discussed. — In contrast to most radical cation salts which owing to their columnar structures are one‐dimensional conductors the salt of 2,6‐dimethylnaphthalene can be characterized as two‐ or three‐dimensional organic metal. The crystal structure of DMN3(SbF6)2(CH2Cl2) has been solved and is discussed in this paper.
Optical Absorption and Symmetries in Conducting Polymers
Authors: Sum U. , Fesser K. , Büttner H. 
Published: March 2014

AbstractVarious extensions of the original Su‐Schrieffer‐Heeger model for conducting polymers are discussed. The main emphasis lies on mechanisms which break fundamental symmetries of the one‐dimensional electron‐phonon system, esp. charge conjugation symmetry and supersymmetry are considered. It is shown that the optical spectra are characteristically changed by breaking these symmetries.
On the Removal of Metallic Mirrors by Free Radicals
Authors: Rice Francis Owen , Tweedell Joan 
Published: March 2014

AbstractLarge Radicals can be formed by passing chlorinated organic compounds at pressures of a few ram., through a furnace containing a pellet of sodium and heated to 350–400°C. It seems to us that the only radicals that will remove metallic mirrors (of tellurium or antimony, etc., previously deposited beyond the furnace) are those that can decompose into methyl or ethyl radicals plus an unsaturated molecule, without undergoing any transmigration of atoms.