Emergent phenomena at oxide interfaces

Recent technical advances in the atomic-scale synthesis of oxide heterostructures have provided a fertile new ground for creating novel states at their interfaces. Different symmetry constraints can be used to design structures exhibiting phenomena not found in the bulk constituents. A characteristic feature is the reconstruction of the charge, spin and orbital states at interfaces on the nanometre scale. Examples such as interface superconductivity, magneto-electric coupling, and the quantum Hall effect in oxide heterostructures are representative of the scientific and technological opportunities in this rapidly emerging field.     

Order-disorder behavior at thin film oxide interfaces

Order-disorder processes fundamentally determine the structure and properties of many important oxide systems for energy and computing applications. While these processes have been intensively studied in bulk materials, they are less investigated and understood for nanostructured oxides in highly non-equilibrium conditions. These systems can now be realized through a range of deposition techniques and probed at exceptional spatial and chemical resolution, leading to a greater focus on interface dynamics. Here we survey a selection of recent studies of order-disorder behavior at thin film oxide interfaces, with a particular emphasis on the emergence of order during synthesis and disorder in extreme irradiation environments. We summarize key trends and identify directions for future study in this growing research area.     

Microstructural investigation of interfaces in CMCs

This paper is focused on the importance of pyrocarbon interfaces in two types of ceramic matrix composites (C_f–SiC and SiC_f–SiBC), during creep tests under argon. The development of micromechanisms which consume energy and then allow a damage tolerance, depends on the morphology of the fiber/matrix interphase, which has been investigated by TEM and HRTEM.     

Atomic scale characterization of complex oxide interfaces

Complex oxides exhibit the most disparate behaviors, from ferroelectricity to high T _c superconductivity, colossal magnetoresistance to insulating properties. For these reasons, oxide thin films are of interest for electronics and the emerging field of spintronics. But epitaxial complex oxide ultrathin films and heterostructures can be significantly affected or even dominated by the presence of interfaces and may exhibit intriguing new physical properties quite different from the bulk. A study of the relations between structure and chemistry at the atomic scale is needed to understand the macroscopic properties of such “interface-controlled” materials. For this purpose, the combination of aberration-corrected Z-contrast scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) represents a very powerful tool. The availability of sub-Ångström probes allows a level of unprecedented detail when analyzing not only the interface structure with sensitivity to single atoms, but also the interface chemistry. In this work state of the art STEM-EELS will be applied to the study of different oxide interfaces in heterostructures with titanates, manganites and cuprates based on the perovskite structure.     

Experimental evidence of Snoek-like relaxation in annealed metallic glass

The frequency dependence of the internal friction (IF) of annealed Co-based metallic glass (MG) has been measured at elevated temperatures in the frequency range of 10⁻³≤f≤10³ Hz. It has been found that the IF increases with frequency decrease at a constant temperature. To explain this observation, an analytical model of IF due to anelastic relaxation in a symmetrical two-well potential has been proposed. The model shows that the IF rise with decreasing frequency observed in the experiment can be interpreted as a high frequency tail of a Snoek-like relaxation with distributed activation energies in deep relaxation centers of annealed glassy structure.     

Crystallization and thermochromism in tungsten oxide films annealed in vacuum

The crystalline phases formed in tungsten oxide (WO_{3 ? x} ) films upon isothermal step annealing in vacuum and air at various temperatures within 500?C750°C have been studied. The films were deposited onto silica glass substrates by reactive dc magnetron sputtering. It is established that the observed thermochromism is related to the presence of an oxygen-deficient WO_{3 ? x} phase belonging to the hexagonal system, which is intensely formed as the annealing temperature increases from 650 to 750°C.     

Surface analysis of polysiloxane/metal oxide interfaces

The interfaces between various types of silane-based primers and abraded mild-steel surfaces have been investigated using two surface-specific techniques in an attempt to ascertain the bonding mechanism between primer and metal. The XPS technique gave semi-quantitative information about the relative concentrations of primer and exposed steel while the SSIMS technique enabled the chemical state of the first few monolayers of surface to be elucidated. From some primer/metal systems the presence of FeSiO⁺ radicals was detected by SSIMS and it was found that the environmental resistance of structural adhesive joints, employing the various silane-based primers, could be directly related to the presence or absence of this radical.     

Local enrichment of the finite cell method for problems with material interfaces

This paper proposes an efficient, hierarchical high-order enrichment approach for the finite cell method applied to problems of solid mechanics involving discontinuities and singularities. In contrast to the standard extended finite element method, where new degrees of freedom are introduced for all finite elements located in the enrichment zone, we define the enrichment on a so-called overlay mesh which is superimposed over the base mesh. The approximation on the base mesh is obtained by means of the finite cell method where the hp-d method is employed to introduce the hierarchical extension on the overlay mesh. We present two different strategies for defining the enrichment on the superimposed overlay mesh. In the first approach, the enrichment is based on a local h-, p- or hp-refinement utilizing the finite element method on the overlay mesh. Alternatively, the enrichment is constructed by means of the partition of unity method introducing carefully selected enrichment functions suitable for the problem at hand. Our results reveal that the proposed method improves the accuracy of the finite cell method significantly with only a minimum number of additional degrees of freedom. In this paper we will focus on examples with material interfaces although the method can also be applied to problems involving strong discontinuities and singularities. Accurate stress distribution and an exponential rate of convergence are the two striking characteristics of the proposed method. Due to the hierarchical approach it paves the way to using different approaches for the approximation on the base and the overlay mesh and accordingly allows multiscale problems to be addressed as well.     

Temperature-jump investigation of alkyl chain length effects on sorption/desorption kinetics at reversed-phase chromatographic interfaces

The influence of the alkyl chain length on the kinetics of solute retention at reversed-phase chromatographic surfaces is examined. A Joule-discharge temperature-jump relaxation experiment was used to monitor reversible sorption/desorption kinetics at C4- and C8-modified silica/solution interfaces. Biexponential sorption/desorption relaxation kinetics were observed for a charged fluorescent probe, 1-anilino-8-naphthalenesulfonate (ANS), on both C4- and C8-silica surfaces. Both relaxation rates on C4 surfaces were sufficiently slow to be measured and increased linearly with solute concentration. One of the relaxations on a C8 surface is too fast to be resolved from the heating rate, similar to behavior of the solute on a longer chain C18-silica. These observations suggest that sorption kinetics on the intermediate chain length surfaace, C4-silica, are different from kinetics on longer chain length surfaces, C8- and C18-silica. From a fit of the data to a two-step kinetic model, the rates of both adsorption and partition of the ionic probe on the C4 chain are estimated; both rates exhibit significant influence over the equilibrium constant. The relaxation rate of a neutral probe, N-phenyl-1-naphthylamine, is also measured; the results indicate a fast (diffusion-controlled) adsorption step, followed by a detectable barrier to partition that is similar to the partition barrier for ANS on the C4-silica surface. These results show that the alkyl chain length of modified silica strongly influences retention kinetics.     

退火对反应磁控溅射制备ITO薄膜性能影响

采用铟锡合金靶 (铟 锡 ,90 - 10 ) ,通过直流反应磁控溅射在玻璃基片上制备出ITO薄膜 ,并在大气环境下高温退火处理。研究了退火温度对薄膜结构、光学和电学性能的影响。研究表明 ,随着退火温度升高薄膜的电学特性得到很大提高     

Intergranular films at Au-sapphire interfaces

The existence of nanometer-thick amorphous equilibrium films at metal-ceramic interfaces has been experimentally verified for the Au–Al₂O₃ system. The films were formed using a novel experimental approach, in which thin sputtered films of Au were dewetted on a sapphire substrate which was previously partially wetted with drops of anorthite glass (CaO–2SiO₂–Al₂O₃). High-resolution transmission electron microscopy and qualitative analytical transmission electron microscopy were used to confirm the existence of the amorphous films. In addition, positive and relatively large Hamaker constants were calculated for the Au-film-Al₂O₃ interface, which indicates the existence of an attractive van der Waals force which stabilizes the film, similar to equilibrium films at grain boundaries in ceramics. A ∼ 1 nm thick surface film was also detected on the (0001) surface of sapphire substrates partially wetted by anorthite glass. The refractive index required to stabilize the surface films, via a positive Hamaker constant, is explored.     

Second‐order convected particle domain interpolation (CPDI2) with enrichment for weak discontinuities at material interfaces

Convected particle domain interpolation (CPDI) is a recently developed extension of the material point method, in which the shape functions on the overlay grid are replaced with alternative shape functions, which (by coupling with the underlying particle topology) facilitate efficient and algorithmically straightforward evaluation of grid node integrals in the weak formulation of the governing equations. In the original CPDI algorithm, herein called CPDI1, particle domains are tracked as parallelograms in 2‐D (or parallelepipeds in 3‐D). In this paper, the CPDI method is enhanced to more accurately track particle domains as quadrilaterals in 2‐D (hexahedra in 3‐D). This enhancement will be referred to as CPDI2. Not only does this minor revision remove overlaps or gaps between particle domains, it also provides flexibility in choosing particle domain shape in the initial configuration and sets a convenient conceptual framework for enrichment of the fields to accurately solve weak discontinuities in the displacement field across a material interface that passes through the interior of a grid cell. The new CPDI2 method is demonstrated, with and without enrichment, using one‐dimensional and two‐dimensional examples. Copyright © 2013 John Wiley & Sons, Ltd.     

氦气/液氧喷射泵水调试验

在水调试验台上对自行设计的氦气/液氧喷射泵进行了试验研究.研究结果表明,在其它条件相同的情况下,随着氦气耗量增加,液氧流量呈先增加后减小趋势,其最大值对应的氦气压力比为1.62-2.95,引射效率约100-160.实践表明,水调试验结果与预冷循环系统调试结果基本一致,为预冷循环系统喷射泵设计提供了高可靠的模拟环境.     

A thermodynamic analysis of ceramic oxide/liquid metal interfaces

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Atomistic simulation of misfit dislocation in metal/oxide interfaces

In this work, we use a Chen–Möbius inversion method to get the interatomic potentials for metal/oxide interfaces, and then study the misfit dislocation in a series of interfaces, including Au/MgO, Rh/MgO and Ni/MgO. The calculation shows that dislocation line always prefers at the first monolayer of metal side, with metal on top of Mg at the dislocation core, and metal on top of O at the interface coherent area. Also, the Burgers vector for these interfaces is determined at two cases. For Rh/MgO and Ni/MgO, it keeps the value of . But for Au/MgO, it changes from to a[1 0 0] as the number of monolayers in metal side increases. This work shows a theoretical understanding of misfit dislocations in metal/oxide interfaces, from dislocation structure, density to Burgers vector orderly, and gives some hints to experiments.     

Ionic conductivity in oxide heterostructures: the role of interfaces

Abstract

Rapidly growing attention is being directed to the investigation of ionic conductivity in oxide film heterostructures. The main reason for this interest arises from interfacial phenomena in these heterostructures and their applications. Recent results revealed that heterophase interfaces have faster ionic conduction pathways than the bulk or homophase interfaces. This finding can open attractive opportunities in the field of micro-ionic devices. The influence of the interfaces on the conduction properties of heterostructures is becoming increasingly important with the miniaturization of solid-state devices, which leads to an enhanced interface density at the expense of the bulk. This review aims to describe the main evidence of interfacial phenomena in ion-conducting film heterostructures, highlighting the fundamental and technological relevance and offering guidelines to understanding the interface conduction mechanisms in these structures.     

Ionic conductivity in oxide heterostructures: the role of interfaces

Rapidly growing attention is being directed to the investigation of ionic conductivity in oxide film heterostructures. The main reason for this interest arises from interfacial phenomena in these heterostructures and their applications. Recent results revealed that heterophase interfaces have faster ionic conduction pathways than the bulk or homophase interfaces. This finding can open attractive opportunities in the field of micro-ionic devices. The influence of the interfaces on the conduction properties of heterostructures is becoming increasingly important with the miniaturization of solid-state devices, which leads to an enhanced interface density at the expense of the bulk. This review aims to describe the main evidence of interfacial phenomena in ion-conducting film heterostructures, highlighting the fundamental and technological relevance and offering guidelines to understanding the interface conduction mechanisms in these structures.