Interfacial Situations Research Articles

Steplike anomalous Hall behaviors in mixed-phase BiFeO3-based heterostructure

The heterostructures based on multiferroic BiFeO3 (BFO) have received much attention for the great potential in magnetoelectric coupling and spintronic applications. Therefore, the BFO films combined with rhombohedral (R) phase and tetragonal (T) phase can bring in various functionalities. Here, we demonstrate that the Ta/Pt/Co/Pt multilayers grown on R-, T-, and mixed-phase BFO exhibit perpendicular magnetic anisotropy. We find that the magnetic switching behavior of the multilayer is sensitive to the phase of the BFO layer. The Ta/Pt/Co/Pt layers grown on top of the pure R- or T-phase BFO show one-step anomalous Hall effect (AHE) switching. However, the layers grown on the mixed-phase BFO show steplike AHE switching. We attribute that the steplike switching behavior originates from the two different interfacial situations between mixed-phase BFO and above layers. Our results bring a potential avenue for realizing spintronic devices based on mixed-phased BFO.

Analysis of interfacial adhesion properties of nano-silica modified asphalt mixtures using molecular dynamics simulation

The presence of nano-silica can reduce the sensitivity to moisture damage of asphalt mixtures and improve the anti-oxidation aging ability of asphalt binder. In the present work, the interface adhesion of nano-silica modified asphalt to aggregate surfaces at the different interfacial situations (aggregate surface irregularity and seawater erosion) were investigated using molecular dynamics (MD) simulations. The sodium chloride solution is used to simulate seawater erosion. The asphalt 12-component molecular model is used for the analysis of thermodynamic properties such as density, the ratio of free volume, and cohesive energy density. Molecular structure properties of asphalt on the aggregate surfaces were analyzed by radial distribution function (RDF), relative concentration (RC), and mean square displacement (MSD) of asphalt molecule. The interface adhesion properties were investigated by calculating the work of adhesion at the different interfacial situations. The results show that oxidation aging promotes the asphaltene aggregate on the surface of the silica aggregate, while the effect of nano-silica is reversed. Increasing the surface roughness of the aggregate enhanced its adhesion strength. The asphalt mixtures are less resistant to sodium chloride solution erosion than water damage. Compared with the original asphalt binder, oxidized asphalt is more susceptible to damage by water or sodium chloride solution. The presence of nano-silica reduces the susceptibility of asphalt mixture to water damage or sodium chloride solution erosion. The research findings provide insights to more fully understand the micromechanisms of interface adhesion failure between asphalt binder and aggregate.

Scattering of antiplane shear waves by a circular cylinder in a traction-free plate

Following a well-established formula used by many researchers, the scattering of an anti-plane shear wave by an infinite elastic cylinder of arbitrary relative radius centered in a traction-free two-dimensional isotropic plate has been examined. The plate is divided into three regions by introducing two imaginary planes located symmetrically away from the surface of the cylinder and perpendicular to surfaces of the plate. The wave field is expanded into cylinder wave modes in the central bounded region containing the cylinder, while the fields in the other two outer regions are expanded into plate wave modes. A system of equations determining the expansion coefficients is obtained according to the traction-free boundary conditions on the plate walls and the stress and displacement continuity conditions across the imaginary planes. By taking an appropriate finite number of terms of the infinite expansion series and a few selected points on the two properly chosen virtual planes and the surfaces of the plate through convergence and precision tests, a matrix equation to numerically evaluate the expansion coefficients is found. The method of how to choose the locations of the imaginary planes and the terms of the expansion series as well as the points on each respective boundary is given in Sec. III in detail. Curves of the reflection and transmission coefficients against the relative radius of the cylinder in welded and slip or cracked interfacial conditions are shown. Analysis on the contrast variations of the reflection and transmission coefficients for a cylinder in bonded and debonded interfacial situations is made. The relative errors estimated by the deviation of the numerical results from the principle of the conservation of energy are found to be less than 2%.

Derivation of a general kinetic equation for transfer-controlled adsorption at liquid interfaces using Statistical Rate Theory

Recently, Joos proposed a new kinetic model for transfer-controlled surfactant adsorption at liquid interfaces. His model is general, in the sense that the change in interfacial tension is incorporated into adsorption rate descriptions, and its governing kinetic equation can be reduced to various specific expressions for individual situations, such as the Langmuir kinetic equation. Joos developed his kinetic model by simply drawing analogies between adsorption and electrode kinetics, where the rate expression was obtained by using conventional chemical reaction theory. In this paper, we present a quantum statistical formulation for surfactant adsorption kinetics. With the assumption of excited states for molecular adsorption, we derive a rate equation by using Statistical Rate Theory (SRT), which gives the expression for transition probabilities from a first-order perturbation analysis of the Schrödinger equation. This new derivation avoids using the principle of mass action and the law of Arrhenius–Eyring, and hence many empirical assumptions in conventional chemical reaction theory are not needed for describing adsorption kinetics. The resulting rate expression can be reduced to Joos's kinetic equation and hence serves as a confirmation of it. Simplifications of the general rate expression are also presented for specific interfacial situations of near equilibrium and far from equilibrium. A combination of these rate expressions with a surface tension–adsorption relation, e.g. the Frumkin equation, can result in equations that are experimentally accessible. Future work will be concentrated on experimental investigations that may provide further validation of the theory and estimates for the parameters used in the rate expressions, especially the symmetry factor α.

Effects of ion bombardment to interfaces on residual internal stress and crystallite structures on multilayered films

The multilayers with 30 periods of Ni 81Fe 19/Cu bilayers were deposited by dual ion beam sputtering method. Only two monolayers at interfaces in [Ni 81Fe 19/Cu] 30 multilayers deposited by Ar and/or Kr sputtering were exposed to ion bombardment to change the interfacial situations, such as sharp interface, the local mixing and the interfacial diffusion. In this study, the relationship between residual internal stress and interfacial structure was investigated. The reduction of residual stress was attained by effect of Ar ion bombardment to interfaces at the restricted acceleration voltage of 160 V for the films by Ar sputtering and 140 V for the films by Kr sputtering, where clear interfaces and the best crystallinity seems to be attained in the multilayers.

Optical investigation of high-field conduction and prebreakdown in a dielectric liquid

Light emission studies of the high-field conduction and prebreakdown phenomena in a mixture of mono and dibenzyl-toluene (M/DBT), used as polypropylene impregnant in the all-film capacitor technology, have been undertaken to gain insight into the underlying physical mechanisms responsible for these processes. The absorption spectrum of this fluid, in the UV region, shows the appearance of structured bands at 348, 366 and 386 nm indicating a luminescence process via anthracene and 9-methylanthracene impurities at a concentration of 3/spl times/10/sup -3/ mol/l. Optical and electrical measurements were performed simultaneously on the electrically stressed fluid. Electroluminescence of the impurities contained in M/DBT has been investigated using a new uniform field electrode arrangement. The light inception stress was determined to be /spl sim/ 20 /spl mu/m/sup -1/ for ac excitation (50 Hz). Configurations with different interfacial situations were studied and we have evidenced a correlation between charge injection and electroluminescence activity. Spectral analysis of the light radiated by streamers in M/DBT in a needle-plane electrode geometry, under step voltage (1 to 50 /spl mu/s, 30 kV) revealed, for both polarities, the presence of H/sub 2/ and C/sub 2/ characteristic bands emerging from a continuum corresponding to the dissociation and recombination of molecular fragments.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Breakdown of a thin dielectric liquid layer

Measurements of electrical breakdown on thin (10-100- mu m) liquid dielectric (capacitor impregnant) layers for different interfacial situations are discussed. For this purpose a new uniform field electrode arrangement that represents interfacial conditions close to those of industrial practice was developed. It was investigated experimentally how the dielectric strength depends on such factors as electrode area, gap spacing, nature of the interface in contact with the liquid, and temperature. The breakdown phenomena are shown to be either related to high-field conduction (i.e., boiling or electrohydrodynamic cavitation leading to the generation of a vapor bubble in the prebreakdown regime) or related to the presence of particles or to local field enhancements. >

Interface influence on the high-field conduction phenomena of a thin dielectric liquid layer

We report experimental work on the ac conduction phenomena of a thin dielectric liquid (capacitor impregnant) layer at high-electric field for several interfacial situations. The features revealed by these experiments show a strong dependence of the liquid electric losses (at frequency 50 Hz) and according to that, the liquid is in contact with a metallic or a polymer interface. An attempt is made to comment these measurements in terms of the existing theories of ionic conduction in nonpolar liquids: it turns out that charge-carrier injection in the neighborhood of the interface is the dominant contribution of the high-field liquid conductivity. A theoretical evaluation based on a unipolar injection model is given in agreement with the experimental results obtained in the different configurations.

Low-frequency dispersion in volume and interfacial situations

The ubiquitous and little-understood phenomenon of low-frequency dispersion (LFD) is described and the experimental evidence for it is summarized for a variety of dielectric and semiconducting systems. Both frequency- and time-domain behaviour are reviewed and it is pointed out that very high charge densities are being stored at low frequencies. The connection between LFD and electrochemical reactions is emphasized. The physical conditions under which LFD can be seen are discussed with particular emphasis on the distinction between interfacial and volume processes. Earlier interpretations of LFD-like phenomena in terms of Maxwell-Wagner processes and fractal geometry of contacts are briefly discussed and found to be insufficient to account for the observed facts. It is concluded that there is likely to be more than one physical or physico-chemical cause giving rise to the variety of LFD phenomena observed in nature but their common feature must be a frequency independent ratio of loss to polarization. We define an “energy criterion” which gives a physical basis for the interpretation of power-law responses and on this basis we propose a new electrochemical model of very general applicability giving the correct dynamic response and having the advantage of not requiring enormous electric fields to account for the very high charge storage observed. Further critical experimental studies are required to elucidate the remaining questions.

Behaviour of a two-layered beam under impact loading

A dynamic model for multilayered beams under impact loading is proposed. The model is based on Timoshenko beam theory but accommodates interlayer slip. Different impact loads as well as different interfacial situations are investigated. The transient behaviour of a two-layered beam is determined by the characteristic method solution of the dynamic governing equations. The results are found to be in close agreement with the finite element analysis code ABAQUS.

Reduced Hamiltonian method for solving the tight-binding model of interfaces

A new method is presented for solving the tight-binding equations for interfaces and surfaces. The method can be applied to a variety of interfacial situations including heterojunctions and superlattices in which disruptions occur over many atomic layers away from the interfaces. The method features an expansion of the total wave function in terms of bulk states with complex wave vectors in regions where there is no interfacial disruption, and transfer matrices in regions where there is interfacial disruption. It is simple to implement and computationally more efficient than any previous method of solving the interface tight-binding equations.

Electrochemical behaviour of natural and biosynthetic polynucleotides at the mercury electrode VII. Studies on the adsorption and reduction of DNA and biosynthetic polynucleotides with a new potentiostatic double step-sweep method,

By a new potentiostatic double step-sweep method conveniently applicable with common commercial polarographic equipment the adsorption and interfacial behaviour of DNA of different origin and of related biosynthetic polynucleotides has been studied in moderately acid solution (pH 5.6) of different ionic strengths over the whole extended potential range of adsorption up to −1.6 V (SCE) at the HMDE. Furthermore the new method has proved to be an efficient tool to follow the kinetics of the reduction of strongly adsorbed substances to as well strongly adsorbed reduction products. Three potential ranges corresponding to different interfacial situations can be distinguished for the investigated polynucleotides. In the first range between −0.4 and − 1.2 V (SCE) the biopolymer is adsorbed. If the biopolymer has initially a double stranded form progressive irreversible deconformation occurs as well in this potential range furnishing further evidence for the previously developed concept of the sequence of interfacial events. In the second range between −1.2 and −1.6 V biopolymers are adsorbed and (in the double stranded case after prior deconformation) the adenine and cytosine moieties undergo a totally irreversible reduction forming according to the nature of the polynucleotide a more or less completely blocking film of strongly adsorbed reduced biopolymer. In the third range beyond −1.6 V no adsorption and thus reduction occurs. The kinetic parameters kct and αcna of the rate determining step of the charge transfer reaction in which the adsorbed biopolymer is reduced have been studied as function of the nature and structure of the polynucleotide, of its base composition and of ionic strength In general the measurements improve significantly the understanding of the complicated behaviour of DNA and related biosynthetic polynucleotides at charged interfaces and confirm in various ways our previous resulis and conclusions.

Electrochemical behaviour of natural and biosynthetic polynucleotides at the mercury electrode: VII. Studies on the adsorption and reduction of DNA and biosynthetic polynucleotides with a new potentiostatic double step-sweep method

By a new potentiostatic double step-sweep method conveniently applicable with common commercial polarographic equipment the adsorption and interfacial behaviour of DNA of different origin and of related biosynthetic polynucleotides has been studied in moderately acid solution (pH 5.6) of different ionic strengths over the whole extended potential range of adsorption up to −1.6 V (SCE) at the HMDE. Furthermore the new method has proved to be an efficient tool to follow the kinetics of the reduction of strongly adsorbed substances to as well strongly adsorbed reduction products. Three potential ranges corresponding to different interfacial situations can be distinguished for the investigated polynucleotides. In the first range between −0.4 and − 1.2 V (SCE) the biopolymer is adsorbed. If the biopolymer has initially a double stranded form progressive irreversible deconformation occurs as well in this potential range furnishing further evidence for the previously developed concept of the sequence of interfacial events. In the second range between −1.2 and −1.6 V biopolymers are adsorbed and (in the double stranded case after prior deconformation) the adenine and cytosine moieties undergo a totally irreversible reduction forming according to the nature of the polynucleotide a more or less completely blocking film of strongly adsorbed reduced biopolymer. In the third range beyond −1.6 V no adsorption and thus reduction occurs. The kinetic parameters k ct and α cn a of the rate determining step of the charge transfer reaction in which the adsorbed biopolymer is reduced have been studied as function of the nature and structure of the polynucleotide, of its base composition and of ionic strength In general the measurements improve significantly the understanding of the complicated behaviour of DNA and related biosynthetic polynucleotides at charged interfaces and confirm in various ways our previous resulis and conclusions.