bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigations on the Reactant Gas Pressure Dependence of Sputtering Yields of Several Transition Metals
Authors: Brudny M. M. , Seidel W. 
Published: July 2012

AbstractSputtering yields of polycrystalline samples of V, Co, Ni, Cu, Zn, Pd, Pt and Ag were investigated as a function of oxygen pressure from residual gas conditions (po2 ≦ 0.002 mPa) to 6 mPa. Ar+ ions (2 keV; 35μA/cm2; incidence angle θ = 45°) were used for bombardment. Also sputtering yields of Fe, Nb and Ta were observed at residual gas conditions and for 2 mPa of O2 and for Ti, Cr and Cd under 2 mPa of O2. The sputtering yields were found to decrease with increasing oxygen pressure. This decrease is most pronounced for metals which are easily oxidized. Sputtering yields of V, Ni, Zn, Pd and Ag were also found to decrease under N2, N2O and NO. Using linear cascade theory the sputtering yields under oxygen were estimated and compared with experimental data. Satisfying correspondence was achieved, if different surface binding energies were assumed for clean and oxidized surfaces respectively.
Electrochemical Study of the Intercalation Reactions of Perchloric and Nitric Acid
Authors: Scharff P. , Stumpp E. 
Published: July 2012

AbstractHNO3 and HClO4 were intercalated into the graphite lattice by means of chemical oxidants and by electrochemical oxidation. In both cases the potential variation versus time was recorded in order to trace the intercalation process. Compared with H2SO4, the intercalation reactions of nitric and perchloric acid proved to be fast. Impedance measurements indicated that the penetration of the phase boundary by acid anions, acid molecules and water as well as intercalate nucleation determine the reaction rate of the chemical insertion reactions. Biintercalation and cointercalation compounds with HNO3 and HClO4 were prepared for the first time.
Passivation of Zinc in Acid Electrolytes Under Galvanostatic Conditions
Authors: Krohn Holger , Rashwan Salah , Beck Fritz 
Published: July 2012

AbstractPassivation behaviour of zinc electrodes in 4–10 M H2SO4 and some hydrogensulphates and alkylammonium salts with anions containing S–VI in the concentration range 0.5–5 M were studied under galvanostatic conditions. After a transition time τ, voltage increased steeply, indicating the onset of passivation. The product j · √τ is found to be roughly constant. This is explained in terms of an accumulation of zinc ions in front of the electrode up to the point, where the concentration reaches saturation. From the Sand constant, a diffusion coefficient was calculated in the right order, depending on the electrolyte composition. The passive layer is assumed to be the corresponding zinc salt. Only at 30–100 V, dielectric break down occurs under potentiostatic conditions. Open circuit potential in the passive region attains in short times (ms) the active potential again. From this it is concluded that the thickness of the zinc salt layer must be extremely small.
Photochemistry of Semiconductor Colloids. 36. Fluorescence Investigations on the Nature of Electron and Hole Traps in Q‐Sized Colloidal CdS Particles
Authors: Eychmüller A. , Hässelbarth A. , Katsikas L. , Weller H. 
Published: July 2012

AbstractThe fluorescence properties of surface modified quantum‐sized CdS colloids were investigated by means of static and time‐resolved low temperature fluorescence spectroscopy. All samples investigated had high fluorescence quantum yields already at room temperature and exhibited either exclusively excitonic or a mixture of excitonic and trapped fluorescence. Mechanisms are presented which explain both the static and time‐resolved behaviour of both the excitonic and trapped fluorescence. The excitonic fluorescence is described as delayed fluorescence occuring by detrapping of electrons. Extremely shallow traps having trap depths of a few meV are discussed.
On the Promoting Effect of Alkali Metals on the Adsorption of Nitriles on the Gold (100) Surface
Authors: Solomun T. , Neumann A. , Christmann K. 
Published: July 2012

AbstractSubmolayer concentrations of (strongly electropositively polarized) Na and K on the Au(100) surface create three new acctonitrile (CH3CN) and benzonitrile (C6H5CN) binding states (the γ‐states) on the high‐temperature side of the corresponding molecular thermal desorption spectra (β‐state) observed for the clean, unpromoted Au surface. The additional states appear with both alkali metals and nitriles, whereby they are energetically about equally spaced (ΔT ≈ 30 K with K, and ΔT ≈ 50 K with Na) and sequentially populated, indicating a more general electrostatic modification of the nitrile's adsorptive bonding in the vicinity of an adsorbed alkali atom. The triplet of TD states is tentatively interpreted as being caused by a subsequent filling of a coordination shell formed by the nitriles around each individual alkali metal atom. Similar energetics involved in the formation of gas‐phase and surface cluster complexes of the kind Meδ+ {N  C–CH3}δ− is noted and discussed.
Hole Injection into Dislocations in p‐Silicon Electrodes
Authors: Morrison S. R. , Kerchove F. Vanden , Gomes W. P. 
Published: July 2012

AbstractCathodic hole injection by Fe(CN)63‐ ions was observed at mechanically damaged, i.e. dislocation containing, p‐Si electrodes in contact with aqueous electrolytes. The injection current was observed to start at a potential corresponding to a substantial band bending and to reach a saturation region. In that saturation region the current density was somewhat less than linearly dependent on the Fe(CN)63‐ concentration and increased with increasing depth of damage, i.e. average depth of dislocations. The observations could be explained by a model in which it was assumed that the dislocations behave as micro‐electrodes with hole injection limited by Fe(CN)63‐ diffusion to the electrodes. The holes are then conducted along the dislocation lines to where tunneling to the valence band becomes possible.
Characterization of Surface Layers on GaAs Single Crystals in Contact with Acid Aqueous Solutions
Authors: Lingier S. , Gomes W. P. 
Published: July 2012

AbstractFrom ellipsometric measurements, combined with surface analysis by SEM, Auger spectroscopy and X‐ray diffraction, it appears that a porous arsenic layer develops upon the p‐type gallium arsenide electrode surface in acid, aqueous indifferent electrolyte solution during anodic current flow. Due to its porosity, this layer does not affect the forward current‐potential characteristics of the electrode. Also under open‐circuit circumstances in the same electrolyte, the arsenic layer appears to grow. The probable reactions corresponding to both arsenic deposition processes are discussed.
Electronic Structure and Spectra of Some Carbamates INDO/S‐CI Treatment
Authors: Hamed Maher M. , Moustafa H. , Hilal Rifaat , El‐Kourashy A. G. 
Published: July 2012

AbstractThe electronic absorption spectra of some aryl‐ and diaryl‐carbamates have been measured and the observed complex spectral profiles have been computer deconvoluted. MO computation of the spectra using INDO/S‐CI method, allowed the assignment of the observed bands and identifying their origin.
Photoisomerization in Dense Gases and Liquids
Authors: Schroeder Jörg 
Published: July 2012

AbstractThe pressure and temperature dependence of the rate coefficient for the singlet state photoisomerization of trans‐stilbene and all‐trans‐diphenylbutadiene in supercritical and liquid alkane solvents reveal the importance of specific solvent effects modifying the reaction path on the potential energy surface. In the gas‐liquid transition range the barrier height for the reaction seems to be lowered due to increasing solvation of the reactants in solute‐solvent clusters. At higher pressures, the transition to the Smoluchowski‐limit within each solvent is well described by Kramers' model. Differences between solvents can be attributed to a solvent‐dependent barrier shape. Deviations from this description only appear for stilbene at higher viscosities. In part, they seem also be due to a specific influence of the compressed solvent on the reaction path and to a frequency dependence of the friction. Solvent‐size dependent micro‐friction effects do not seem to be responsible for the observed solvent dependence of the reaction rates. Manifestations of multidimensional barrier crossing show up in the strong temperature dependence of the rate coefficient at constant solvent self‐diffusion coefficient. Apparently, the reaction path on the energy surface changes with temperature leading to an effectively temperature dependent height and shape of the barrier for the reaction with increasing excitation of “perpendicular” modes. Possible reasons for the striking difference of the friction dependence of the rate coefficient between stilbene and diphenylbutadiene at intermediate to high friction are also discussed.
Femtosecond Studies of the Photoisomerization of cis‐Stilbene in Solution
Authors: Repinec S. T. , Sension R. J. , Hochstrasser R. M. 
Published: July 2012

AbstractFemtosecond laser studies on cis‐stilbene photoisomerization in alkane solvents show a weak friction dependence on the excited state lifetime. A possible barrier crossing process is indicated when these results are compared with various potential models. The anisotropy values of the transient absorptions allow the assignment of the various excited states to A type in C2 symmetry. Anisotropy measurements in the regions of product ground state absorptions demonstrate a high alignment between reactant cis and product trans and a low alignment between cis and product dihydrophenanthrene (DHP) transition dipoles. These results indicate a significant angular displacement of the ethylene bond during isomerization. In addition, time resolved absorption studies detecting product trans fluorescence estimate an initial internal temperature of 725 ± 100 K which decays with ca. 14 ps time constant.
Classical and Quantum Models of Activationless Reaction Dynamics
Authors: Jean John M. , Fleming Graham R. , Friesner Richard A. 
Published: July 2012

AbstractTwo aspects of barrierless processes are discussed. Adiabatic processes are discussed briefly in the context of diffusion to a sink. Second, a multi‐level Redfield theory is developed as a model for rate processes where vibrational relaxation and dephasing occur on the time scale of the electronic process. The results of numerical calculations are presented and deviations from the Golden Rule predictions discussed.
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

AbstractRecently 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

AbstractThe 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

AbstractThermal 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

AbstractThe 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

AbstractThe 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

AbstractSemiclassical 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.
The Role of Barrier Fluctuations in the Tunneling Problem
Authors: Kagan Yu. 
Published: July 2012

AbstractInteraction 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

AbstractThere 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

AbstractHydrogen 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

AbstractThe 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

AbstractWater‐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

AbstractThe 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

AbstractThis 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.