Interfacial effects for shear waves in one dimensional periodic piezoelectric structure

Within the full system of Maxwell's equations this paper investigates the effects of three kinds of transmission conditions at the interfaces between the laminae of a periodic piezoelectric structure on band gaps of Bloch-Floquet waves propagating oblique to the interfaces. The results that are obtained show that under both electrically shorted and magnetically closed transmission conditions Bloch-Floquet waves exist only at acoustic frequencies. The effects of piezoelectricity on Bloch-Floquet wave band structures are studied at such frequencies. It is shown that for periodic crystal structures with laminae made of identical materials the propagation of Bloch-Floquet waves can occur under electrically shorted interface conditions but not under magnetically closed interface conditions.For electrically open interfaces with mechanically smooth contacts the dynamic setting of the problem provides solutions only for photonic crystals. In this case the piezoelectricity has no effect on band gaps.     

Interfaces in perovskite heterostructures

Recent advances in film synthesis have made it possible to investigate the properties of well-controlled interfaces in perovskite metal-oxides. A review of published experimental data and computational results indicate that so far most interfaces that have been analyzed in ferroelectric materials—while necessary to impose large lattice strain on the polar material—contribute little to the ferroelectricity and may instead be detrimental to the desired properties. In contrast, a very different situation arises at interfaces that show changes in the electronic configuration as a consequence of a compositional discontinuity. Data is shown for LaMnO₃/SrTiO₃ superlattices as an example of electronic effects that produce enhanced properties, further illustrating the richness of interfacial properties that can be obtained at interfaces (as shown in numerous published results for different but related interfaces).     

Low-frequency sound transmission through a gas-solid interface

Sound transmission through gas-solid interfaces is usually very weak because of the large contrast in wave impedances at the interface. Here, it is shown that diffraction effects can lead to a dramatic increase in the transparency of gas-solid interfaces at low frequencies, resulting in the bulk of energy emitted by compact sources within a solid being radiated into a gas. The anomalous transparency is made possible by power fluxes in evanescent body waves and by excitation of interface waves. Sound transmission into gas is found to be highly sensitive to absorption of elastic waves within a solid.     

Elliptic nanopores in deformed nanocrystalline and nanocomposite materials

A theoretical model is suggested which describes the nucleation of nanoscale pores (nanopores) of elliptic shape in deformed nanocrystalline and nanocomposite materials. In the framework of the model, elliptic nanopores in nanocrystalline and nanocomposite materials nucleate at interfaces in the stress fields of interfacial edge dislocations with large Burgers vectors. When elliptic nanopores nucleate, they remove the cores of interfacial dislocations. The stress field and energy of such dislocated elliptic nanopores are calculated, and their equilibrium sizes and shape parameters are revealed. It is theoretically shown that the elliptic shape of nanopores is due to the effects of interfaces (grain and interphase boundaries) on fracture processes at the nanoscale level.     

Simulation of Fission Product Release from Microfuel Particles Taking into Account the Effects of Trapped Fraction and Concentration Jumps at the Interfaces

A modification of the FP Kinetics code [1] has been performed to calculate the fission product release from HTGR microfuel particles, allowing for chemical binding, limited solubility effects, and component concentration jumps at the interfaces of the coating layers. A comparison is made of the release curves of Cs from microfuel particles calculated using the FP Kinetics and PARFUME codes [2]. It is shown that taking into account the concentration jumps at the interfaces of the silicon carbide layer makes it possible to give a noncontradictory explanation of the experimental data obtained for Cs release in post-reactor thermal testing. The need for performing experiments to determine the limits of solubility in coating materials is noted.

     

Organic photodetectors: Role of multiple donor–acceptor interfaces

We have fabricated photodetectors based on electron–accepting and electron-donating organic materials. Multiple heterojunctions between the donor and acceptor layers were introduced. The thickness of the donor and acceptor materials was controlled in the molecular scale. By keeping the total thickness of the devices the same, we have studied the performance of the photodetectors as a function of the number of such molecular-level interfaces. The results showed that the number of donor–acceptor interfaces enhanced exciton dissociation but, at the same time, hindered charge transport by introducing energy barriers. We have shown that a trade-off between the two effects existed at an optimum number of donor–acceptor interfaces, where the device showed better photodetector performance.     

Impact of particle size on conductivity and storage capacity as derived from the core–space charge model

The impact of interfaces on variety of materials properties scales with the density of interfaces within a material. This statement holds true independent of the specific interfacial mechanism, as long as the density of interfaces is rather low. If the spacing between interfaces is being further reduced, interesting non-trivial effects are expected and have also been observed. In this paper, the ionic conductivity in ionic conductors and the storage capacity (non-stoichiometry) of mixed conductors as a function of size are considered. The discussion is based on the core–space charge model in which we assume that only the core of an interface exhibits its own defect energetics, while the energetics of the space charge layers remain unaltered (compared to the bulk). It is shown that in the case of Schottky profiles anomalous conductivity effects are predicted. As regards the non-stoichiometry effects, it is demonstrated that at sizes small compared to the Debye length the difference between a composite consisting of an ionic and an electronic conductor and a «true» mixed conductor becomes blurred. The latter effect has recently been detected in the field of Li-batteries and is here commented on.     

The effects of restricted diffusion in nuclear magnetic resonance microscopy

A stochastic computer simulation is used to investigate the effects of restricted diffusion in NMR microscopy. It is shown that diffusion contributes to a loss of interfacial resolution through two main mechanisms. The first applies to spatial regions bound by impermeable interfaces and involves diffusive averaging of the frequency differences set up by the applied field gradients. This effect can be made arbitrarily small by increasing the magnitude of the field gradient. The second mechanism involves diffusion through permeable membranes or interfaces defining the sample morphology. This effect can, in principle, be reduced by multiple echo imaging with short pulse spacings. The possibility of imaging diffusive flow through a permeable interface is discussed.     

Does roughening of rock-fluid-rock interfaces emerge from a stress-induced instability?

Non-planar solid-fluid-solid interfaces under stress are very common in many industrial and natural materials. For example, in the Earth’s crust, many rough and wavy interfaces can be observed in rocks in a wide range of spatial scales, from undulate grain boundaries at the micrometer scale, to stylolite dissolution planes at the meter scale. It is proposed here that these initially flat solid-fluid-solid interfaces become rough by a morphological instability triggered by elastic stress. A model for the formation of these unstable patterns at all scales is thus presented. It is shown that such instability is inherently present due to the uniaxial stress that promotes them, owing to the gain in the total elastic energy: the intrinsic elastic energy plus the work of the external forces. This is shown explicitly by solving the elastic problem in a linear stability analysis, and proved more generally without having resort to the computation of the elastic field.     

Interference effects in low coherence interferometry and optical coherence tomography

Optical coherence tomography (OCT) relies on the construction of two-dimensional images from a series of depth scans. These depth scans are made up of a series of interferograms relating to reflections from individual interfaces within a sample. The theoretical resolution of an OCT system is given as half the coherence length of the light source used and therefore interfaces between layers with different refractive indices, which are separated by less than this distance, cannot be resolved. We consider the occurrence of interference between adjacent interferograms and its consequence in signal, and image interpretation. Computational simulations were created to model two or three interfaces in close proximity such that interference would occur between component interferograms. Further to this, images were acquired of an air wedge between two glass slides that corresponded to the simulations. The results of both the simulated OCT signals and those from the air wedge showed the presence of interference effects that could influence the interpretation of the final (OCT) image.     

Debye-Hückel theory for interfacial geometries

The Debye-Hückel theory for bulk electrolyte solutions is generalized to planar interfacial geometries, including screening effects due to mobile salt ions which are confined to the interface and solutions with in general different salt concentrations and dielectric constants on the two sides of the interface. We calculate the general Debye-Hückel interaction between fixed test charges, and analyze a number of relevant special cases as applicable to charged colloids and charged polymers. Salty interfaces, which are experimentally realized by monolayers or bilayers made of cationic and anionic surfactants or lipids, exert a strong attraction on charged particles of either sign at large separations from the interface; at short distances image-charge repulsion sets in. Likewise, the effective interactions between charged particles are strongly modified in the neighborhood of such a salty interface. On the other hand, charged particles which are immersed in a salt solution are repelled from the air (or a substrate) interface, and the interaction between two charges decays algebraically close to such an interface. These general results have experimentally measurable consequences for the adsorption of charged colloids or charged polymers at monolayers, solid substrates, and interfaces.     

The reflection of ultrasound from partially contacting rough surfaces

Ultrasound is commonly used to detect and size cracks in a range of engineering components. Modeling techniques are well established for smooth and open cracks. However, real cracks are often rough (relative to the ultrasonic wavelength) and closed due to compressive stress. This paper describes an investigation into the combined effects of crack face roughness and closure on ultrasonic detectability. A contact model has been used to estimate the size and shape of scatterers (voids) at the interface of these rough surfaces when loaded. The response of such interfaces to excitation with a longitudinal ultrasonic pulse over a wide range of frequencies has been investigated. The interaction of ultrasound with this scattering interface is predicted using a finite-element model and good agreement with experiments on rough surfaces is shown. Results are shown for arrays of equi-sized scatterers and a distribution of scatterer sizes. It is shown that the response at high frequencies is dependent on the size, shape, and distribution of the scatterers. It is also shown that the finite-element results depart from the mass-spring model predictions when the product of wave number and scatterer half-width is greater than 0.4.     

Fundamentals of surface thermodynamics

The nonequilibrium behavior for mixtures of fluids in interfaces is discussed. In particular, a thermodynamic field theory is given for media in thin, curved regions (interfaces with finite thickness), which separates two media with different physical properties. The moving interface is considered as semipermeable and a generalized transport equation and specific balance equations are derived. A systematic investigation of constitutive equations is made and in the limit as the thickness of the interface goes to zero it is shown that all relevant interfacial relations can be found.     

光学薄膜界面互相关特性的确定

本文实验测量了光学薄膜的散射波场分布,根据多层光学薄膜的矢量散射理论,确定了膜层界面的互相关特性.当空间频率较低时,对于膜层层数较少的膜系,膜堆内的各界面是完全相关的;若空间频率较高,则逐渐趋于部分相关模型.实验指出,膜层界面的互相关特性亦与所采用的蒸发技术有关.     

Quasiperiodicity in irrational interfaces

Recent work on quasiperiodicity in irrational grain boundaries is reviewed and generalized to heterophase interfaces. The concept of local isomorphism is shown to be very important at irrational interfaces, replacing translational invariance at periodic interfaces. Symmetry related variants of irrational interfaces are enumerated and line defects separating energetically degenerate domains of irrational interfaces are characterised by products of space group operations, one from each crystal. The symmetry operations relating the variants belong to a six dimensional crystal and the variants are locally isomorphic. A framework is described for discussing the symmetries and long range order at interfaces regardless of whether they are rational or irrational.     

Confinement effects in electrical resistivity and spin-valve magnetoresistance in metallic layered structures

Quantum size effects in electronic transport properties of metallic trilayers are analysed theoretically. It is shown that electron confinement leads to oscillations in electrical resistivity with two different periodicities. The short oscillation period is determined by the appropriate Fermi wavelength, whereas the long period depends on the potential step at interfaces. When the outer films in the trilayer are ferromagnetic, then the oscillations in the resistivity give rise to similar oscillations in the spin-valve magnetoresistance.     

Dislocation substructures and internal stress fields in bulk- and differentially quenched rails

A layer-by-layer analysis of rails bulk-hardened in oil and differentially hardened in a variety of regimes is performed by means of transmission electron microscopy. Quantitative parameters of dislocation substructures and internal stress fields, and their dependences on the distance from the tread contact surface are established. It is shown that the most dangerous stress concentrators are interfaces between globular cementite matrix particles; such interfaces form predominantly in rails subjected to bulk quenching.     

Sonoluminescence and acoustically driven optical phenomena in solids and solid–gas interfaces

During the last decade, significant progress has been achieved in our understanding of the generation of light in acoustic fields, a research area which is known as sonoluminescence (SL). Some of the data obtained, including SL effects in water, have previously been reviewed in the literature. This article takes a broader view and reports on experimental evidence of SL phenomena in solids and solid–gas interfaces as well as on interpretations and potential applications. It is shown that the understanding of SL is facilitated when couched in the language of moving dislocations which produce vacancy–interstitial pairs of host atoms. Radiative transitions in defect pairs would then constitute the SL effect in solids. It is further shown that the occurrence of electric fields due to the generated point defects and charged dislocations produces a number of interesting phenomena. These fields are particularly important for the occurrence of SL at solid–gas interfaces which has been suggested to be initiated by gas discharges due to strong electric fields of charged dislocations. The appearance of acoustically driven internal electric fields is shown to lead to remarkable effects with regard to exciton lifetimes. The storage of photogenerated electron–hole pairs in the moving piezoelectric potential of acoustic waves allows prolonged exciton recombination times of μs in InGaAs/GaAs quantum well structures. The intertwining of acoustically driven long-range electric fields and microfields occurring at the exciton sites turns out to be a prerequisite for attaining the lifetime tuning of the bound excitons in CdS crystals. The review is concluded by discussing sonoluminescence effects in granular systems. Implications for the relevance of this effect to the dynamical behavior of granular media are outlined.     

Influence of the Morphology of Lysozyme‐Shelled Microparticles on the Cellular Association,Uptake, and Degradation in Human Breast Adenocarcinoma Cells

The ultrasound‐assisted self‐assembly and cross‐linking of lysozyme at the water–air and water–perfluorohexane interfaces are shown to produce lysozyme‐shelled hollow microbubbles (LSMBs) and microcapsules (LSMC), respectively. The arrangement of lysozyme at the air–liquid or oil–liquid interfaces is accompanied by changes in the bioactivity and conformational state of the protein. The interaction of LSMB and LSMC with human breast adenocarcinoma cells (SKBR3) is studied. LSMB and LSMC are phagocyted by cells within 2 h without exerting a cytotoxic activity. The cellular internalization kinetics of LSMB and LSMC and the effects on cell cycle are evaluated using flow cytometry. Evidence for the internalization of microparticles and degradation within the cell are also monitored by confocal and scanning electron microscopic analyses. The integrity of cell membrane and cell cycle is not affected by LSMBs and LSMCs uptake. These studies show that the positively charged LSMB and LSMC are not cytotoxic and can be readily internalized and degraded by the SKBR3 cells. LSMBs and LSMCs show a different uptake kinetics and intracellular degradation pattern due to differences in the arrangement of the protein at the air–liquid or oil–liquid interfaces.     

From monoscale to multiscale modeling of fatigue crack growth: Stress and energy density factor

The formalism of the earlier fatigue crack growth models is retained to account for multiscaling of the fatigue process that involves the creation of macrocracks from the accumulation of micro damage.The effects of at least two scales,say micro to macro,must be accounted for.The same data can thus be reinterpreted by the invariancy of the transitional stress intensity factors such that the microcracking and macrocracking data would lie on a straight line.The threshold associated with the sigmoid curve disappears.Scale segmentation is shown to be a necessity for addressing multiscale energy dissipative processes such as fatigue and creep.Path independency and energy release rate are monoscale criteria that can lead to unphysical results,violating the first principles.Application of monoscale failure or fracture criteria to nanomaterials is taking toll at the expense of manufacturing super strength and light materials and structural components.This brief view is offered in the spirit of much needed additional research for the reinforcement of materials by creating nanoscale interfaces with sustainable time in service.The step by step consideraton at the different scales may offer a better understanding of the test data and their limitations with reference to space and time.