bluuebunny/crossref_metadata_2025 huggingface dataset:
Proton Delocalization and Thermally Activated Quantum Correlations in Water: Complex Scaling and New Experimental Results
Authors: Chatzidimitriou‐Dreismann C. A. , Brändas E. J.
Published: July 2012

Recently we applied, for the first time, the general theory of dilation analyticity (or: Complex Scaling Method, CSM) to quantum statistics of nonequilibrium. A novel kind of (universal) coherence was revealed from first quantum theoretical principles. The corresponding irreducible structures we called coherent‐dissipative structures, since they represent a short‐lived and spatially restricted cooperative phenomenon. The crucial points of the theory are stressed. Similarities as well as differences with (i) the BCS‐states of superconductivity, (ii) the dissipative structures of the Brussels school, and (iii) Yang's concept of ODLRO are mentioned. Very recently the general theory was applied to different dynamical processes in amorphous condensed matter, and specific and quantitative predictions were made. In connection with current work, we discuss here in some detail two new predicted effects concerning protonic delocalization in water (and other materials) and proper experiments to test them. These effects are: (1) a novel relation between proton transfer rates and proton mobility in water; (2) an anomalous decrease of proton mobility in H2O/D2O mixtures. Both effects are shown to contradict the predictions of all thus far existing theories or models. Current experimental results verify undoubtedly our theoretical predictions.
Mean First Passage Times and Nonlinear Relaxation Time for Nonlinear Models Driven by Dichotomous Noise
Authors: Behn Ulrich , Schiele Konrad , Müller Reinhard
Published: July 2012

The mean first passage time to reach a noise induced state starting from a local minimum of the stationary probability density is calculated analytically for the Stratonovich model exploiting a natural reflecting boundary condition. Furthermore, the nonlinear relaxation time is calculated and compared with the mean first passage time. The results are checked by digital simulation for typical values of the parameters.
Pair Nucleation Rate in a Driven Sine‐Gordon Chain
Authors: Marchesoni F.
Published: July 2012

Thermal production of soliton‐antisoliton pairs in an overdamped driven sine‐Gordon chain occurs through the activation of a critical nucleus. The relevant pair nucleation rate is calculated explicitly by extending Kramers' theory to the case of an infinite dimensional, multistable system with one neutral equilibrium mode.
Anomalous Diffusion in Disordered Systems: An Effective Medium Description
Authors: Schirmacher Walter
Published: July 2012

The effective medium theory of diffusion in topologically disordered systems is reviewed with emphasis on the description of disorder induced anomalous diffusion. The effective medium approximation (EMA), for which a new derivation is given, is shown to provide a reliable and simple scheme to discuss the diffusive motion of particles in disordered systems such as electrons in the localized energy region of disordered semiconductors or ions in amorphous solids. Explicit calculations for some pertinent models are presented and the consequences of anomalous diffusion to a.c. conductivity, transient photoconductivity, neutron scattering and NMR data are discussed.
Influence of Non‐Linear Dissipation on Quantum Tunneling
Authors: Riseborough Peter S.
Published: July 2012

The influence of a non‐linear dissipation mechanism on the dynamics of a particle, which performs tunneling through a potential barrier, is investigated. The particular dissipation mechanism considered contains terms quadratic in the normal modes of the heat bath, in addition to linear couplings. The nonlinear terms are shown to affect the incoherent tunneling rate.
Some New Approaches to Semiclassical and Quantum Transition State Theory
Authors: Miller William H.
Published: July 2012

Semiclassical and quantum mechanical transition state theory is reviewed and two new approaches described. One is a general implementation of a semiclassical rate expression [Miller, Faraday Discuss. Chem. Soc. 62, 40 (1977)] that involves the “good” action‐angle variables associated with the saddle point (i.e., transition state) of a potential energy surface. The other is an evaluation of a formally exact quantum expression for the rate [Miller, Schwartz, and Tromp, J. Chem. Phys. 79, 4889 (1983)] in terms of Siegert eigenvalues associated with the transition state. Siegert eigenvalues are usually associated with scattering resonances, so their identification with the saddle point of a potential surface, and the expression for the reaction rate in terms of them, is quite an unexpected and novel development.
A Feynman Path Integral Approach for Calculating Quantum Rate Constants in Complex Systems
Authors: Voth Gregory A.
Published: July 2012

A theoretical framework is discussed in which imaginary time Feynman path integration is adapted to define a quantum mechanical free energy for activated rate processes. Recently developed variational theories for the estimation of this factor, as well as the quantum dynamical corrections to the rate constant, are also discussed.
The Role of Barrier Fluctuations in the Tunneling Problem
Authors: Kagan Yu.
Published: July 2012

Interaction of a tunneling particle with fluctuations of the barrier induced by phonon or electron excitations is analyzed. Special role of nonadiabatic excitations with the energy smaller than the reciprocal time a particle spends under the barrier is discussed. In an insulator the interaction with barrier fluctuations can play a dominant role leading to qualitatively alteration of the pattern of the quantum diffusion. At that, the increase of the tunneling transition amplitude (coherent bandwidth) instead of the polaronic narrowing and significant change of the temperature dependence of incoherent tunneling motion take place. Analysis of recent experimental results on the quantum diffusion of muonium in KCl crystal revealing the decisive role of the barrier fluctuations is given. – The infrared divergence accompanying the rescattering of the electron‐hole excitations near the Fermi‐surface causes the increase of the interaction with the barrier fluctuations in a metal. Rigorous analysis for a two‐well system with a completely arbitrary interaction of the electrons with a tunneling particle is carried out. It shows that there are no parameter values for which the interaction with barrier fluctuations overweight the intrawell interaction though the inelastic transition rate sharply enhances. The general problem of the validity of substitution of a phonon heat bath for an electron one is discussed.
Tunneling in Metals as a Dissipative Quantum Process
Authors: Kondo J.
Published: July 2012

There are two characteristic energies for the proton in metals: the orbiting frequency within a site (hω0) and the tunneling integral between neighbouring sites (Δ). Since typically hω0 is 1000 K and Δ less than 10 K, the temperature range defined by hω0 >> kT >> Δ is experimentally accessible. This is peculiar to the proton and proton isotopes. – Low‐energy excitations of the metal electrons cannot follow instantaneously the orbiting motion of the proton in a single well. They are equal to those when the proton potential is averaged over the proton wave function representing the orbiting motion. When the proton tunnels to another site, the low‐energy excitations must be rearranged to correspond to the new proton position. Then the tunneling integral of the proton acquires a factor of the overlap integral between two electronic wave functions corresponding to two proton positions. This integral turns out to be much smaller than unity and depends on a power of the temperature when hω0 >> kT >> Δ. This power law is a result of the non‐adiabatic response of the metal electrons to proton motion. Such a power law will manifest itself in diffusion constant of the proton or proton isotopes.
Low‐Temperature Tunneling of Hydrogen in Nb(OH)x and Nb(NH)x.
Authors: Wipf H.
Published: July 2012

Hydrogen interstitials in Nb are trapped by O or N impurity atoms below ∼ 160 K. The trapped hydrogen occupies two nearest‐neighbor tetrahedral sites. It represents, therefore, a model system for experimental studies of the tunneling dynamics of a particle in a double‐well potential. The tunneling dynamics of the trapped hydrogen was investigated by neutron spectroscopy in the temperature range between 0.05 and 160 K. The experiments demonstrate the transition from a low‐temperature coherent tunneling (T ≦ 10 K) to an incoherent jump diffusion at elevated temperatures (T ≧ 10 K). Up to ∼ 60 K, both coherent tunneling and jump diffusion is controlled by a nonadiabatic coupling of the hydrogen to conduction electrons (Kondo's coupling constant K = 0.0055 ± 0.005). Above ∼ 60 K, the jump diffusion of the hydrogen is increasingly dominated by an interaction with phonons.
Coherence in Disordered Condensed Matter. V: Thermally Activated Quantum Correlations in High‐Tc Superconductivity
Authors: Brändas E. J. , Chatzidimitriou‐Dreismann C. A.
Published: July 2012

The fermionic second order reduced density matrix with complex dilation and thermalization describes generally quantum correlation effects in condensed matter. Connection with recent experiments on high‐Tc copper‐oxide superconductors is made. The following experimental results are explained from first theoretical principles: (1) Quantum correlation contributions to the energy gap in agreement with e.g. precise infrared experiments. (2) The universal relation between Tc and ns/m* (carrier density over effective mass) [Uemura et al., Phys. Rev. Lett. 62, 2317 (1989)]. (3) The saturation of Tc with increasing carrier density. (4) The considerable absorption “in” the energy gap. A prediction concerning the sudden breakdown of superconductivity at a specific (high) carrier density follows from the general theory. All the above results are independent of the specific (and still unknown) Cooper pair formation mechanism.
Electric Field Induced Structure Changes in Nonionic Water‐in‐Oil Microemulsions: Field Dependence of the Electric Conductivity
Authors: Runge F. , Röhl W. , Ilgenfritz G.
Published: July 2012

Water‐in‐oil microemulsions, stabilized by the nonionic surfactant Igepal CO‐520, show a temperature dependent structure change which can be monitored by electric conductivity. We show that the transition which involves the percolation of the aqueous phase can also be induced by high electric fields. A system is investigated which contains only a few volume percent of the aqueous phase (0.1 M KCl) in a mixture of n‐ and c‐hexane but still exhibits a highly cooperative transition from the conducting state at lower temperature to the almost nonconducting state at higher temperature. Electric fields, applied up to ca. 10 kV cm−1, shift the transition curves to the high temperature side, i.e. restore a structure with continuous water channels. The percolation point exhibits a quadratic field strength dependence. The dynamics of the transition in the micro‐ to millisecond range shows characteristic differences below and above the percolation point. The transient behavior and the electric field strength dependence of the conductivity change are discussed with respect to a theory [9] developed for ionic microemulsions. – A special field pulse method is described which allows measurement of current relaxation and electric birefringence.
The Asymmetrical Diacetylene Derivatives FBS/TFMBS and DNP/MNP: Synthesis and Solid State Properties
Authors: Strohriegl P. , Gmeiner J. , Müller I. , Gruner‐Bauer P. , Dormann E. , Enkelmann V.
Published: July 2012

The synthesis of two new asymmetrical diacetylene (DA) derivatives is described: 1‐(4‐fluorobenzenesulfonyloxy)‐6‐(4‐trifluoromethylbenzenesulfonyloxy)‐2,4‐hexadiyne (FBS/TFMBS) and 1‐(2,4‐dinitrophenoxy)‐6‐(4‐methyl‐2‐nitrophenoxy)‐2,4‐hexadiyne (DNP/MNP). Results are presented on crystal growth, crystal structure analysis and dielectric properties. Both DAs polymerize thermally in the solid state and have polar (“ferroelectric”) individual chains. The different chains in the unit cell are arranged centrosymmetrically in FBS/TFMBS, but non‐centrosymmetrically in DNP/MNP.
Structural, Optical, and Electronic Properties of Silicon/Boron Phosphide Heterojunction Photoelectrodes
Authors: Goossens A. , Kelder E. M. , Beeren R. J. M. , Bartels C. J. G. , Schoonman J.
Published: July 2012

This paper presents structural, optical, and electronic properties of Si coated with a thin epitaxial layer of n‐type BP, which serves as protective optical window. n‐Si/n‐BP, as well as p‐Si/n‐BP heterostructures have been grown by CVD and investigated. p‐Si/n‐BP heterojunction photo‐electrodes produce large and stable photocurrents up to 15 mA/cm2 when applied in liquid junction solar cells. The origin of this photocurrent is discussed. Impedance spectroscopy is used to obtain Mott‐Schottky plots from which the flatband potential of crystalline boron phosphide is determined. The band structure of the heterojunction is shown to agree with the optical features. Finally, the distribution of the potential drop in the hetero‐structure is elucidated.
Solvent Self Diffusion Coefficients and 109Ag NMR Chemical Shifts in Silver Nitrate/Acetonitrile/Water Mixtures – Correlation with Macroscopic Transport Properties –
Authors: Wittekopf Burghard , Weiden Norbert , Weil Konrad G.
Published: July 2012

We used the 1H NMR spin echo technique to determine the self diffusion coefficients of acetonitrile and of water in acetonitrile/water/silver nitrate mixtures. Both diffusion coefficients decrease strongly with increasing salt concentration. By comparison with earlier determined electric conductivity and viscosity data we find, that the ratio of molar conductivity and water self diffusion coefficient is constant, as well as the product of the viscosity and the acetonitrile self diffusion coefficient. The 109Ag NMR chemical shifts in these mixtures show, that silver ions are only solvated by acetonitrile.
Photo‐Enhancement of Electrochromism in MoO3 Thin Films
Authors: Yao J. N. , Loo B. H. , Hashimoto K. , Fujishima A.
Published: July 2012

MoO3 thin films after irradiated with a UV light showed enhancement in electrochromism when compared to the non‐irradiated ones. It was found that the change in absorbance for the irradiated portion was as large as six times that of the non‐irradiated portion of a sample. This enhancement in electrochromism may be due to the differences in the electrical conductivity and film crystallinity between the irradiated and non‐irradiated samples.
Determination of the Structure of Fluid Deuterium Chloride by Neutron Diffraction at High Pressure
Authors: Bausenwein T. , Bertagnolli H. , Tödheide K. , Chieux P.
Published: July 2012

High‐pressure neutron diffraction measurements on liquid and fluid deuterium chloride are reported. Temperature and density were varied over a broad range involving pressures up to nearly 2000 bars. The employed high‐pressure equipment and the pressure cell are presented. Data evaluation up to the corrected structure factor is described. Several correction procedures for multiple scattering and self‐absorption and for inelastic scattering effects are discussed with regard to their applicability in the present case. The intramolecular structure is determined by fitting to the total differential cross section as well as to the separated intramolecular cross section. A separation of the intra‐ and the intermolecular contribution is done by means of Fourier transformation. The dependence of the intermolecular radial distribution function on temperature and density is shown.
The Absorption Spectrum of the Nitrate (NO3) Radical in Aqueous Solution
Authors: Herrmann H. , Exner M. , Zellner R.
Published: July 2012

Absorption coefficients for the nitrate (NO3) radical in aqueous solution have been determined using multichannel optical absorption in the range λ = 540 – 760 nm. NO3 radicals were generated by excimer laser photolysis of (NH4)2[Ce(NO3)6] at 351 nm. For the quantum yield of NO3 formation from this process a value of ϕ(NO3) = (0.85 ± 0.09) has been determined using a Br− scavenging technique. With this value the absolute absorption coefficient of NO3 at the maximum of its absorption at 635 nm was found as ϵ = (527 ± 105) l/mol · cm (base 10). Absorption coefficient data for the range 540–760 nm are presented in 2 nm intervals. The oscillator strength of the (0‐0) band transition near 665 nm has been calculated to be (1.6 ± 0.5) · 10−3 in reasonable agreement with the gas phase value.
The Influence of Unimolecular Fall‐off Behaviour on Pyrolysis Systems. A Case Study
Authors: Olzmann M. , Scherzer K. , Schwede M.
Published: July 2012

The influence of unimolecular fall‐off effects on the kinetic modelling of larger pyrolysis systems is estimated theoretically for the case of propane decomposition at nearly industrial conditions (1100 K, 0.1 MPa). The ordinary differential equation system based on a mechanism of 34 elementary reactions and 20 chemical species is integrated by means of a Gear algorithm two times, on the one hand with the thermal high‐pressure rate constants and on the other hand with constants corrected for the fall‐off effects in the case of unimolecular as well as in the case of bimolecular association reactions. RRKM theory, combined with an empirical treatment of weak‐collision effects, provides ratios of k/k∞ between 0.2 and 0.9. It turns out that corrections in this order of magnitude have only little influence on the concentrations of stable products, whereas radical species show, at least partly, a higher sensitivity. This results in larger deviations of the concentrations of compounds formed by radical recombination that, nevertheless, contribute to the overall products only to a small extent.
Fluoride Ion Diffusion in MSn2F5 (M+  NH4+, Rb+, Cs+) Studied by 1H and 19F Nuclear Magnetic Relaxation and Electrical Conductivity
Authors: Hirokawa Kiyofumi , Kitahara Hiroshi , Furukawa Yoshihiro , Nakamura Daiyu
Published: July 2012

Fluoride ion diffusion in NH4Sn2F5, RbSn2F5, and CsSn2F5 was investigated by measuring the electrical conductivity (σ) and nuclear magnetic relaxation times (T1, T1ϱ, and T2) of 1H and 19F nuclei. The frequency dependence of T1 (1H) shows a logarithmic divergence in the high‐temperature phase of NH4Sn2F5, indicating that the fluoride ion diffusion in this phase is two‐dimensional. In the room‐temperature phases of NH4Sn2F5 and RbSn2F5, this two‐dimensionality of the diffusion is weakened. An asymmetric T1ϱ minimum observed for NH4Sn2F5 and RbSn2F5 was analyzed using an analytical expression, τ ln {1 + (ωτ)−1‐β}, for the spectral density of the 2D fluoride ion diffusion, and the β parameter introduced explain the asymmetry of the T1ϱ minimum and a large difference between apparent activation energies deduced from T1 and T2 data. The activation energies determined from the relaxation times in the high‐temperature limit agree well with those from the σ measurements.
The Effect of Temperature on the Double Layer Dielectric Relaxation in Polystyrene Latices
Authors: Bordi F. , Cametti C.
Published: July 2012

Dielectric properties of polystyrene latices suspended in aqueous electrolyte solution (10−4 M NaCl) are investigated at different temperatures in the interval 0 to 50°C in the frequency range 1 kHz–10 MHz. where these charged colloidal systems generally display two distinct dielectric dispersions. The temperature dependence of the dielectric parameters describing the low‐frequency process is compared with predictions of some well‐established theoretical treatments based on counterion polarization models. The observed behavior is consistent with the counterion polarization at the interface with the dispersed particle when the contribution of the diffuse part of the double layer is included.
Evaluation of the Thermophysical Properties of Toluene and n‐Heptane from 180 to 320 K and up to 260 MPa from Speed‐of‐Sound Data
Authors: Sun T. F. , Bominaar S. A. R. C. , Ten Seldam C. A. , Biswas S. N.
Published: July 2012

A number of important thermophysical properties of liquid toluene and n‐heptane have been evaluated in the temperature range form 180 to 320 K and at pressures up to 260 MPa using the previously reported speed‐of‐sound data and following a modified computational method originally developed by Davis and Gordon. The derived properties include the density, the isobaric thermal expansivity, the isothermal compressibility, the specific heat, the entropy and the enthalpy. The derived density data for the two liquids have been used to examine the validity of several empirical equations of state for liquids.
EXAFS Studies of Aqueous Solutions of Rubidium Bromide
Authors: Bertagnolli H. , Ertel T. S. , Hoffmann M. , Frahm R.
Published: July 2012

We report the results of extended X‐ray absorption fine structure (EXAFS) measurements performed on aqueous solutions of rubidium bromide (RbBr) at room temperature. The measurements were made at the Br and Rb K‐edges. Average Rb+–OH2, Br− – OH2 and Rb–Br distances were determined from the quantitative analysis of the EXAFS data.
The Influence of an Oxidation Step in the Adsorbed Layer on the ip vs. Sweep Rate Relationship. — A Diagnostic Criterium Based on the Linear Sweep Voltammetric Method
Authors: González J.
Published: July 2012

A new diagnostic criterium has been deduced for an electrochemical system adsorbed which oxidizes, giving rise to a new adsorbed intermediate. The rate equations, combined with linear sweep conditions lead to ip vs. ν (sweep rate) plots, which are linear for low scan rates and tend to a limiting value at higher sweep rates. Two examples of this very frequent behaviour are given.
Crystallization of Cold Condensed Lead Chloride (PbCl2)
Authors: Zuber Ralf , Weil Konrad G.
Published: July 2012

By comparison of the UV spectra of freshly prepared cold condensed lead chloride films with those of tempered ones, it can be seen that initially non crystalline material is formed. The excitonic transitions give rise to broad structureless bands. Upon annealing, these bands shift and become more sharply. From the excitonic absorption at about 270 nm the non crystalline to crystalline transition can be monitored quantitatively. We can demonstrate that this is a first order phase transition. Nucleation is a necessary step. The initial non crystalline state therefore is metastable and not a frozen‐in state.
Thermodynamics of the Ternary Mixture Propan‐1‐ol + Triethylamine + n‐Heptane. Experimental Results and ERAS‐Model Calculations of HE and VE
Authors: Bender M. , Hauser J. , Heintz A.
Published: July 2012

Molar excess enthalpies (HE) and molar excess volumes (VE) of the liquid mixture Propan‐1‐ol (PrOH) + Triethylamine (TEA) + n‐Heptane have been measured by flow calorimetry and the vibrating tube technique respectively. Data of the three binary systems have also been obtained. The excess properties are dominated by strong hydrogen bondings due to the self‐association of PrOH and the association of PrOH with TEA. The third component, heptane, serves mainly as an inert diluting solvent. HE and VE are positive for PrOH + heptane and also for TEA + heptane to a much smaller extent. Strongly negative values of both HE and VE have been obtained for PrOH + TEA. The values obtained for the ternary system lie in between these extreme cases showing certain compositions where HE and VE vanish.—An extended version of the so‐called ERAS model has been used for describing HE and VE of the complete ternary system. The parameters adjusted to the binary data reveal that the hydrogen bonding enthalpies and volumes between PrOH and TEA are distinctly stronger than between self‐associating PrOH molecules. In addition the widely applied NRTL‐model has also been used for describing HE of the ternary systems. VE, however, can not be calculated with the NRTL model.
The Influence of the Local Anaesthetic Tetracaine on the Temperature and Pressure Dependent Phase Behaviour of Model Biomembranes
Authors: Winter R. , Christmann M.‐H. , Böttner M. , Thiyagarajan P. , Heenan R. K.
Published: July 2012

By using differential scanning calorimetry and neutron small‐angle scattering, the effect of the local anaesthetic tetracaine on the temperature and pressure dependent phase behaviour of model biomembrane systems, such as pure and cholesterol—containing 1, 2‐dimyristoyl‐phosphatidylcholine bilayers, has been investigated. The results provide insight into the thermodynamic and structural consequences of the incorporation of the anaesthetic into the membranes and might thus help in understanding the molecular mechanisms underlying the pharmacological action of local anaesthetics and the antagonistic effect of pressure against anaesthesia, which has been observed in vivo. Furthermore, as tetracaine can be viewed as a model system for amphiphilic molecules, knowledge of its concentration, temperature and pressure dependent phase behaviour helps in understanding the general physico‐chemical action of amphiphilic molecules on membranes.
A Computer‐controlled System of Transmission Lines for the Determination of the Complex Permittivity of Lossy Liquids between 8.5 and 90 GHz
Authors: Barthel J. , Bachhuber K. , Buchner R. , Hetzenauer H. , Kleebauer M.
Published: July 2012

A system of computer controlled transmission lines based on the method of travelling waves is presented, permitting the precise determination of complex permittivities of medium to high loss liquids at 8.5 to 90 GHz. It consists of a newly developed apparatus for the E‐band region (60 ≤ v/GHz ≤ 90), which is described in detail, together with existing X‐ (8.5 ≤ v/GHz ≤ 12.4), Ku‐ (12.4 ≤ v/GHz ≤ 18), and A‐band (26.4 ≤ v/GHz ≤ 40) set‐ups now appropriately adapted for computer control. Consistency and accuracy of the equipment are evidenced with the help of permittivity data for water, methanol, N‐methylformamide (NMF), and N,N‐dimethylformamide (DMF).
1H NMR Studies on Molecular Motions of tert‐Butylammonium Ions in [(CH3)3CNH3]2TeX6 (X = Cl, Br) and Their Partially Deuterated Analogs, [(CD3)3CNH3]2TeX6 and [(CH3)3CND3]2TeX6 (X = Cl, Br)
Authors: Ishida Hiroyuki , Inada Syuichi , Hayama Naomi , Nakamura Daiyu , Ikeda Ryuichi
Published: July 2012

Temperature dependences of the 1H spin‐lattice relaxation time, T1, and the second moment of 1H NMR absorptions were studied in tert‐butylammonium hexachlorotellurate(IV), hexabromotellurate(IV), and their partially deuterated analogs. From X‐ray powder patterns taken at room temperature, both complexes were found to be isomorphous with each other. For [(CH3)3CNH3]2TeBr6, a phase transition was located at 136 K by differential thermal analysis. Three kinds of motions: the reorientations of the CH3 groups about their CC bonds, the NH3+ group about its CN bond, and the tert‐butyl group about the CN bond, were observed by 1H NMR, and their motional parameters were determined. Among the three motions, the NH3+ motion was found to occur at the lowest temperature with quite small activation energies (7.9–10.1 kJ mol−1) compared with those in the simple halides.
Chlorine Perchlorate Formation in the Gas Phase Photolysis of Chlorine Dioxide
Authors: Zabel F.
Published: July 2012

OClO/O2/N2 mixtures were photolyzed in a temperature controlled 4201 reaction chamber at temperatures between 249 and 300 K and total pressures between 0.5 and 1000 mbar. Initial OClO concentrations were in the range (1.7–5.7) · 1015 molecule/cm3. Reaction mixtures were analyzed in situ via long‐path IR absorption using a Fourier‐transform spectrometer. In some experiments product spectra were simultaneously monitored in the IR and the UV. Depending on reaction conditions, the product IR spectra were dominated by absorption bands of Cl2O3 or Cl2O4 or a mixture of both. Evidence is presented for the crucial role of O atoms in the Cl2O4 formation, suggesting either of the two mechanisms: (I) OClO + O + M → ClO3 + M → ClO3 + ClO + M → Cl2O4 + M, or (II) OClO + ClO + M → Cl2O3 + M, Cl2O3 + O + M → Cl2O4 + M. Both the weak temperature dependence and the strong pressure dependence of the Cl2O4 yield support mechanism (I). In addition, Cl2O6 was detected as a minor product of OClO photolysis under certain reaction conditions, both by its IR and UV absorption.
Is there a “Universal” Explanation for the “Universal” Dynamic Response?
Authors: Funke K.
Published: July 2012

Structurally disordered solid electrolytes, both crystalline and glassy, as well as ionic melts, exhibit a set of spectroscopic peculiarities that are at variance with the predictions of simple random‐hopping models. Typically, stretched exponential functions are encountered where ordinary exponential functions are expected. The effect has come to be called “universal dynamic response.” In this paper, it is traced back to a mean square displacement which, in a broad time regime, varies as time to the power of β, with 0 < β < 1. Computer simulations as well as model considerations show that this particular shape of the mean square displacement is caused by the frequent occurrence of correlated forward‐backward hopping sequences. The latter processes result from the mutual repulsive Coulomb interaction of the mobile ions.
A Molecular Dynamics Study of the Dependence of the Conductivity of Sodium Beta″‐Alumina on Temperature and Frequency
Authors: Smith W. , Gillan M. J.
Published: July 2012

The first results of an extensive simulation study of diffusion in sodium beta”‐alumina are presented. The simulations are performed by the molecular dynamics technique on a large periodic system of 3213 ions, including all the ions in the spinel blocks, with a realistic model for the interactions between the ions. From simulations performed at a series of temperatures between 200 and 1200 K, we obtain the ionic conductivity, which, in accord with experiments, shows non‐Arrhenius behaviour. The frequency‐dependent conductivity shows marked dispersion at low temperatures, which agrees qualitatively with recent measurements. The reasons for this dispersion are discussed.
Diffusion Limited Percolation: A Model for Transport in Ionic Glasses
Authors: Bunde Armin , Maass Philipp , Ingram Malcolm D.
Published: July 2012

We present a novel model for ionic transport in glasses which we call diffusion limited percolation. The model focuses on the fact that each mobile ion prefers and maintains its own distinct characteristic environment in the glassy network. This leads to mismatch effects and to the existence of a memory effect which strongly influences the process of ion migration. We show that by our simple model a variety of so far imperfectly understood phenomena can be explained, among them the drastic increase of the dc conductivity of oxide glasses with the modifier content and the mixed alkali effect.
Frequency‐Dependent Conductivity. Ionic Conductivity and Memory Effects in Glassy Electrolytes
Authors: Ingram Malcolm D. , Maass Philipp , Bunde Armin
Published: July 2012

Ionic conductivities in glass depend very strongly on temperature, frequency and glass composition. In the absence of well‐defined structure, the behaviour of vitreous electrolytes may be strongly influenced by various “memory effects”. These include the classical ion‐atmosphere effect which tends to return ions to their starting positions – and hence causes a reduction in ion mobilities – and a newly formulated site memory effect, which effectively creates “cation vacancies”, and leads to conductivity enhancement. The site memory effect gives a straightforward explanation for compositional variations in conductivity (including the mixed alkali effect) and points up a connection with “strength” and “fragility” concepts of glass/melt structure.
Dynamics of Supercooled Molten Salts
Authors: Bosse J. , Henel M.
Published: July 2012

For the density modes of a supercooled multi‐component liquid a closed set of non‐linear integro‐differential equations is derived within the mode‐coupling approximation. Its solution requires all partial static structure factors as input information. The scope of the theory is demonstrated by studying the solutions of strongly simplified equations‐of‐motion representing a schematic model of both a molten salt near the glass transition and a glassy ionic conductor.
Hopping Conductivity in Hydrogen‐Bonded Antiferroelectric Compounds
Authors: Hutton S. L. , Fehst I. , Loidl A.
Published: July 2012

Antiferroelectric betaine phosphate (BP: (CH3)3NCH2COO · H3PO4) and ferroelectric betaine phosphite (BPI: (CH3)3NCH2COO · H3PO3) are molecular crystals of the amino acid betaine and the phosphoric or phosphorous acids, respectively. In both compounds the inorganic components are linked by hydrogen bonds to one‐dimensional chains. The two isostructural compounds form solid solutions BPxBPI1‐x at any concentration. Here we report measurements of the dielectric permittivity for concentrations 0.85 ≤ × ≤ 1 at frequencies 10−2 ≤ v ≤ 109 Hz and temperatures 2 K ≤ T ≤ 300 K. The dielectric response in BP:BPI (x = 0.95) is dominated by contributions from pure hopping conductivity which we ascribe to the motion of the protons along the one‐dimensional chains. The onset of electric order supresses the a.c. conductivity. It will also be seen that BP:BPI (x = 0.95) shows dc conductivity in addition to the observed ac conductivity. These results are contrasted to BP and BP:BPI (x = 0.85) which reveal pure relaxational behavior.
Dielectric Studies under Pressure of the Plastic Phases of Some Alcohols
Authors: Würflinger Albert
Published: July 2012

The phase behaviours and dielectric properties of the plastic phases of several cyclic and branched alcohols have been studied up to pressures of 300 MPa and frequencies to 13 MHz. High values for the static permittivity are found for the liquid and the solid phases below the melting curve. For these compounds the dielectric relaxation occurs at relatively low frequencies. The loss curves have been fitted to modified Debye equations and expressions of Jonscher and Dissado & Hill. The temperature and pressure dependence of the dielectric relaxation time enables us to determine the activation enthalpy and volume, respectively. The activation quantities and parameters for the spectral shape functions of the cyclic and branched alcohols are compared and discussed.
Molecular Motions in Liquid Crystal Side‐Chain Polymers
Authors: Haase W. , Bormuth F. J. , Pfciffer M. , Jakob E.
Published: July 2012

Dielectric relaxation spectroscopy is used to investigate the molecular dynamics of liquid crystalline side chain polymers. The purpose of this comparative study is to show the influence of chemical and structural variations on the molecular dynamics and thus to contribute on the general understanding of the relaxation behaviour. On the basis of our recent measurements and by comparison to the data in literature we are able to give a detailed interpretation of the different processes in terms of basic molecular movements.
Considerations and Examples for a Uniform Behaviour of Spin‐Lattice Relaxation in Glasses
Authors: Grüne M. , Müller‐Warmuth W.
Published: July 2012

The NMR spin‐lattice relaxation of cation conducting glasses with an extended accessible relaxation range has been discussed in terms of current models on jump diffusion. Glassy systems with different mechanisms of motion and crystalline solids with a disordered sublattice have been found to show a similar relaxation behaviour. Spin‐lattice relaxation of all glasses appears to be quite similar, even if a quantitative description is still lacking.
Depolarized Light Scattering at the Liquid to Glass Transition
Authors: Fuchs M. , Latz A.
Published: July 2012

Depolarized light scattering spectra in supercooled liquids are studied. Starting from a microscopic dielectric model an exact projection operator formalism is used. The change from liquid (e.g. Rytov Dip) to solid like (e.g. transverse phonon peaks) spectra upon supercooling is explained with the frequency dependence of the elasto optic constants.
DD‐Fusionsreaktionen an einem PdAg(D)‐Target in einem Minireaktor
Authors: Gentsch H.
Published: July 2012

Deuteriumionen mit hoher Energie bis 30 ke V stoßen auf mit Deuterium gesättigtes PdAg23 als Target. 1st die Ionenenergie > 25 ke V, beginnt ein meßbarer Neutronenstrom. Der Neutronenstrom ist proportional zum Ionenstrom. Mitgeteilt werden Ergebnisse bei einem Ionenstrom von 2 μA und 27 ke V. Das PdAg ausgeführt als einseitig geschlossenes Rohr ist Kathode in einer Elektrolysezelle. Die offene Seite ist mit einer Vakuumapparatur verbunden. Von dieser Seite ragt eine koaxial angeordnete, hochspannungsisolierte Elektronenstoß‐Ionenkanone in das Rohr. Sie erzeugt Ionen aus dem eindiffundierenden Gas, die in dem starken elektrischen Feld im Vakuumspalt zwischen Ionenkanone und Metallrohr beschleunigt, mit hoher Energie gegen den Diffusionsstrom ins Metall eindringen. Die Fusionsrate ist um Faktor 100 größer als an einem reinen Gastarget.
High Resolution Spectroscopy of N3 by Laser Induced Fluorescence
Authors: Haas Tobias , Gericke Karl‐Heinz
Published: July 2012

The azide radical was generated in the gas‐phase photolysis of HN3 and detected by the high resolution laser induced fluorescence (LIF) technique. Rotationally resolved spectra of the Ã2Σu000 ← X̃2Πg000 and Ã2Σu010 → X̃2Πg010 transitions were obtained. Analysing single rotational lines, the spin splitting constant of the Ã2Σu000 state was derived to be γ = (1.35 ± 0.05) · 10−3 cm−1. Evidence was obtained for a lifetime τ of the Ã2Σu000 state of 0.37 ≤ τ ≤ 20 ns. The observed narrow linewidths are important in other experiments where the determination of scalar and vector properties allows an elucidation of reaction and photodissociation dynamics.
Fluorescent Dyes as Probes of Voltage Transients in Neuron Membranes Progress Report
Authors: Fromherz P. , Dambacher K. H. , Ephardt H. , Lambacher A. , Müller C. O. , Neigl R. , Schaden H. , Schenk O. , Vetter T.
Published: July 2012

Fluorescent dyes derived from anilino‐pyridinium are studied with respect to their application as probes of voltage‐transients in neuron membranes. Their photophysical properties are characterized in bulk solvents. The spectral features of their voltage‐sensitivity in membranes are determined. A mechanistic scheme of voltage‐sensitivity is proposed. The dyes are applied for optical recording in neurites of cultivated neurons of the leech. The relative sensitivity is evaluated from the fluorescence transients induced by hyperpolarization on the basis of the cable equation. The pervasion of a neuritic tree by action potentials is observed.
Laser Induced Reactions in and at Thin Semiconductor Films Progress Report
Authors: Schultze J. W. , Bade K. , Michaelis A.
Published: July 2012

Focussed laser light can be used to induce chemical or electrochemical reactions in the μm scale. The attainable high power densities allow to achieve fast reaction rates. At metals and insulators thermal heating dominates. On semiconductors short pulses or low energy densities cause mainly electronic processes under isothermal conditions. These will be emphasized in this paper for thin semiconductor films in electrolyte solutions. The induced reactions measured under potentiostatic or potentiodynamic conditions include electron (ETR) and ion transfer (ITR) as well.—Examples are discussed for n‐type semiconducting passive films on some base metals with thicknesses in the range from nm to μm. The ETR depend mainly on the potential showing the tendency to saturation while the ITR depend on the field strength. Doping by ion implantation reduces ETR and ITR as well. Amorphous films show a smaller tendency to inner reactions like breakdown. Bubble formation can be detected in a microscopic scale. Substrate effects are due to epitaxy on various grains, changes of the structure and crystallinity (suboxide and TiN) and electronic processes at the substrate surface (Al/Al2O3).
Plasma Polymerization
Authors: Kay E.
Published: July 2012

Plasma polymerization leads to polymer film formation at low temperatures, e.g. at room temperature, on any substrate. It is one of relatively few processes which permits the formation of very thin uniform polymer films which conform to a substrate of any shape. In general, such films are amorphous throughout, using electron diffraction as a criterion. By appropriate control of the rate limiting plasma processes the structure of the polymer can be modified at will. So, for example, the degree of cross‐linking and resultant chemical and physical properties can be manipulated over a wide range. Work in this laboratory has specialized in a unique process which permits uniform matrix isolation of a variety of materials, such as for example zero valent metal clusters, throughout the polymer matrix. The volume fraction and size of such clusters within the matrix can be readily controlled. Clearly, a variety of properties of such a composite system can be changed in a systematic way. Emission spectroscopy as well as mass spectrometry provide convenient means of monitoring some of the key processes occurring in the plasma. Solid state N.M.R., E.S.C.A., I.R., T.G.A., and D.T.A. and electron microscopy and diffraction serve to characterize the structure of the films.
The Adsorption of Ordered Polyimide Monolayers
Authors: Schedel‐Niedrig Th. , Keil M. , Sotobayashi H. , Schilling T. , Tesche B. , Bradshaw A. M.
Published: July 2012

Ordered polyimide monolayers can be prepared on solid surfaces using the Langmuir‐Blodgett technique of Kakimoto and co‐workers. In the present study we have investigated the adsorption of two different monolayers (PMDA‐ODA and PMDA‐PDA) on both graphite and oxidised silicon surfaces. Scanning tunneling microscopy indicates that on graphite both the rod‐like PMDA‐PDA and the zig‐zag PMDA‐ODA are characterized by a high degree of two‐dimensional order. X‐ray absorption near edge spectroscopy (XANES) at the carbon, nitrogen and oxygen K‐edges has been used to obtain information on the orientation of the different moieties in the polymer chain. These XANES data are compared to the corresponding spectra of pyromellitic diimide and diphenyl ether, which may be regarded as the building blocks of PMDA‐ODA polyimide, in order to obtain more insight into the origin of the resonances.
Diamond Thin Films: Preparation, Characterization and Selected Applications Progress Report
Authors: Bachmann Peter K. , Leers Dieter , Wiechert Detlef U.
Published: July 2012

Preparation and characterization of vapor‐deposited diamond coatings and free‐standing diamond membranes are reviewed. General trends and implications of a C/H/O‐phase diagram, which provides a common basis for all diamond chemical vapor deposition methods are discussed. The status of selected mechanical, optical and electronical applications is summarized.
Grain Growth and Reaction in Nickel‐Silicon Thin‐Films
Authors: Knauth P. , Charaï A. , Bergman C. , Gas P.
Published: July 2012

Thin‐film reactions in nickel‐silicon bilayers were studied by differential scanning calorimetry and transmission electron microscopy. Interesting particularities of thin‐film reactions were observed: a small exothermic effect before the main peak of reaction is due to grain growth of polycrystalline nickel. The activation energy of the process ((220 ± 50) kJ/mol) is in the same order of magnitude as the activation energy of grain boundary self diffusion of nickel. A mean grain boundary enthalpy of nickel ((0.7 ± 0.3) J/m2) is calculated. The main exothermic peak is due to the formation of di‐nickel silicide; its molar enthalpy of formation (‐(155 ± 20) kJ/mol)) and the energy of activation of the reaction ((150 ± 30) kJ/mol) are in good agreement with literature values. The activation energy is comparable to the activation energy of grain boundary diffusion of nickel in δ‐Ni2Si.
LaF3 Thin Films as Chemically Sensitive Material for Semiconductor Sensors
Authors: Szeponik Jan , Moritz Werner , Sellam Farid
Published: July 2012

A new kind of semiconductor based fluoride sensor was prepared by growing thin polycrystalline LaF3 films directly on silicon substrates using vacuum vapour deposition technique. The EICS (Electrolyte Ion Conductor Semiconductor) structure was investigated by means of impedance spectroscopy, CV measurements and exchange measurements with labeled ions (18F). Whereas charge and potential conditions at the LaF3/ electrolyte interface are governed by the fast fluoride exchange the LaF3 bulk and the blocked Si/LaF3 interface determine the electrical behavior. Although the Si/LaF3 contact is not reversible the potential stability of the EICS structure is surprisingly high. Additional results at epitaxial LaF3 layers, prepared by MBE, were taken into account for comparision with those at polycrystalline layers.
Electrochemical Observation of Phase Transitions in Thin Films of Nickel/Phosphorus Alloys
Authors: Hofmann Udo , Weil Konrad G.
Published: July 2012

Thin films of Ni100‐xPx alloys with x = 26, 20, and 16 were prepared by electrodeposition onto one face of a gold plated quartz crystal which at the same time was part of a microbalance. Initially the films consisted of a mixture of an amorphous alloy and fcc nickel crystals, supersaturated with phosphorus. The compositions of the two phases as well as their relative amounts are determined by simultaneous measurement of charge and mass change during anodic oxidation of the film. Films that were annealed at different temperatures prior to their oxidation consist of other phases, known from the nickel phosphorus phase diagram. Hence, electrochemical measurements on annealed samples provide a simple access to the reaction pattern leading from a mixture of metastable phases to the final equilibrium state.
Resistance Changes of Thin Film Electrodes of Silver
Authors: Körwer D. , Schumacher D. , Otto A.
Published: July 2012

Resistance measurements of thin film electrodes allow to monitor different kinds of surface processes. We examined the resistance change of silver electrodes in KCl and KClO4 electrolytes due to anion adsorption and desorption, corrosion from Cl−, and surface roughness from oxidation reduction cycles or silver deposition from solution. Surface roughness is known to be important for surface enhanced Raman scattering (SERS). The influence of pyridine was investigated in some cases and in‐situ SER‐spectra were recorded during silver deposition.
Schichtsynthese von Übergangsmetallnitriden mit ionenstrahlunterstütztem Aufdampfen
Authors: Ensinger W.
Published: July 2012

Nitrides of titanium, chromium, molybdenum and tantalum were prepared by evaporation of the metal in an atmosphere of reduced nitrogen pressure under simultaneous irradiation with highly energetic nitrogen ions.—Chemical analysis showed that the elemental composition of the nitrides is strongly correlated with ion irradiation intensity and with chemical reactivity of the metal. Under identical process conditions titanium formed TiN, but chromium Cr2N. In case of molybdenum and tantalum X‐ray diffractometry revealed that by deposition under ion irradiation with high energy and beam intensity metastable nitrides with cubic structure could be formed.
Structural Relationships between Floating and Deposited Monolayers of Docosanoic Acid
Authors: Engel M. , Merle H. J. , Peterson I. R. , Riegler H. , Steitz R.
Published: July 2012

Floating docosanoic acid (behenic acid) monolayers in the SmI and SmH phase were deposited with the Langmuir‐Blodgett technique onto thin polymethylmethacrylate (PMMA) and Formvar substrates and investigated by electron diffraction. The molecular packing of the monolayers on the substrates vary from those on the water surface and are different for different substrates. On PMMA four phases (H, SmB, SmI, SmL) have been identified, depending on the deposition conditions. While SmB and SmI are known for docosanoic acid on the water surface, H and SmL have only been unequivocally observed in other substances or on other subphases. The monolayer structure on Formvar was identical under all deposition conditions and identified as the H‐phase. The monolayer/substrate interaction was directly addressed by measurements of the work of adhesion. The work of adhesion between the monolayer and PMMA depends strongly on the surface pressure, indicative of interactions that vary with the molecular arrangement in the monolayer.