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In the effort to develop atomistic models capable of accurately describing nanoscale systems with complex interfaces, it has become clear that simple treatments with rigid charge distributions and dispersion coefficients selected to generate bulk properties are insufficient to predict important physical properties. The quantum Drude oscillator model, a system of one-electron pseudoatoms whose “pseudoelectrons” are harmonically bound to their respective “pseudonuclei,” is capable of treating many-body polarization and dispersion interactions in molecular systems on an equal footing due to the ability of the pseudoatoms to mimic the long-range interactions that characterize real materials. Using imaginary time path integration, the Drude oscillator model can, in principle, be solved in computer operation counts that scale linearly with the number of atoms in the system. In practice, however, standard expressions for the energy and pressure, including the commonly used virial estimator, have extremely large variances that require untenably long simulation times to generate converged averages. In this paper, low-variance estimators for the internal energy are derived, in which the large zero-point energy of the oscillators does not contribute to the variance. The new estimators are applicable to any system of harmonic oscillators coupled to one another (or to the environment) via an arbitrary set of anharmonic interactions. The variance of the new estimators is found to be much smaller than standard estimators in three example problems, a one-dimensional anharmonic oscillator and quantum Drude models of the xenon dimer and solid (fcc) xenon, respectively, yielding 2–3 orders of magnitude improvement in computational efficiency. [ABSTRACT FROM AUTHOR]

We propose a ray optics model to calculate the trapping force on a dielectric particle located on the interface between two media and illuminated by a focused evanescent field beam. Such a focused evanescent beam is produced by a high numerical aperture objective with a central obstruction whose size satisfies the total internal reflection condition on the interface. The dependence of the lifting force on the obstruction size, the particle size, and the distance of the particle from the interface is revealed. [ABSTRACT FROM AUTHOR]

This article provides a concise discussion of thermodynamic and kinetic contributions to microstructure stabilization by dopant atoms located at interfaces in metallic nanocrystalline materials and an overview of recent molecular dynamics simulations used to study the behavior of dopant-modified interfaces in nanocrystalline copper. Molecular dynamics simulations show that antimony dopant atoms randomly positioned at copper grain boundaries can retard grain growth, in agreement with proposed thermodynamic and kinetic predictions. Simulations of uniaxial tensile deformation show a maximum in the flow strength at a grain size of 15 nm and that antimony dopants at the grain boundaries do not appreciably impact the nucleation of partial or full dislocations during uniaxial tensile deformation in nanocrystalline copper. [ABSTRACT FROM AUTHOR]

Mechanical properties of Ti/Al–7Si assemblies produced by insert moulding were studied with a classical push-out test and a variant that is the circular-bending test. Special care has been taken for controlling both the reactivity at the Ti/Al–7Si interface and the metallurgical health of the Al–7Si matrix. Mechanical tests until complete debonding have been completed with interrupted tests, metallographic characterizations and FEM analysis of elastic stress state. A mean shear strength of the interface of about 120 MPa was obtained. When the Ti insert is solely fretted in the matrix, without chemical interaction between Ti and the Al–7Si alloy, the mean shear strength is significantly lower (48 MPa). This result clearly shows that chemical interaction at the interface (formation of a thin TiSi layer at the Ti side and a thick Al3Ti(Si) layer at the Al–7Si alloy side) improves the mechanical properties of the assembly. It is also shown that the failure sequence is characterized both by crack propagation from bottom to top and matrix yielding from top to bottom. Actually, interface damaging begins by crack initiation at the specimen bottom face (not at the top face and under the indenter) in a nearly pure mode I solicitation at a radial tensile stress of about 100 MPa. [ABSTRACT FROM AUTHOR]

The article focuses on a study involving liquid crystal interfaces. The author revealed that the Bristol project focused on molecular orientation at the free surface of molecular fluids. He also stressed that the theoretical investigation on surface structure of liquid crystals used molecular cylindrical symmetry as its starting point.

The formation of the interface between the GaAs(100) single-crystal surface and PTCDA and NTCDA organic semiconductors is investigated. The method of total current spectroscopy makes it possible to trace the formation of the interfacial electronic structure. The two organic materials and the GaAs substrate are bonded together when the π electron cloud of an aromatic ring spreads toward the substrate. This modifies the electronic states of interfacial organic molecules and generates a dipole at the interface. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

The most widely used memory materials for rewritable phase-change optical disks are the GeTe—Sb2Te3 pseudobinary compounds. Among these compounds, Ge2Sb2Te5 crystallizes into a cubic close-packed structure with a six-layer period (metastable phase) in the non-thermal equilibrium state, and a trigonal structure with a nine-layer period (stable phase) in the thermal equilibrium state. The structure of the stable phase has Ge/Sb layers in which Ge and Sb are randomly occupied, as does the structure of the metastable phase, while the conventionally estimated structure had separate layers of Ge and Te. The metastable and stable phases are very similar in that Te and Ge/Sb layers stack alternately to form the crystal. The major differences between these phases are: (i) the stable phase has pairs of adjacent Te layers that are not seen in the metastable phase and (ii) only the metastable phase contains vacancies of ca 20 at. % in the Ge/Sb layers. [ABSTRACT FROM AUTHOR]

Shapes of the interface between the L1 and cubic Pn3m phases in the mixture C12EO2/water are studied. The concave and convex variants of the interface are realised using Pn3m crystals surrounded by the L1 phase and L1 inclusions on surfaces and in the bulk of the Pn3m phase. It is shown that both variants of the Pn3m/L1 interface contain the (111)-type facets in coexistence with everywhere else rough surfaces. The matching between facets and curved parts of the interface is angular. In the vicinity of the upper limit of the L1 + Pn3m coexistence domain, additional (200)-type facets appear on the interface. The influence of the contact angle at glass walls on shapes of crystals and of inclusions is discussed. [ABSTRACT FROM AUTHOR]

The general formulation of double refraction or internal double reflection with different directions of propagation vector and wave vector in a uniaxial crystal is analysed in terms of Huygens' principle. Then double refraction and double reflection along the sequential interfaces in a crystal are discussed. On this basis, a configuration of electro-optic 1× N optical switch with modulators and birefringent crystal slabs integrated in a single block of crystal is suggested, which is simple and compact in construction, low in loss and insensitive to environment. Finally, calculations are given which lead to a proposed design of a 1×4 switch. [ABSTRACT FROM AUTHOR]

The article focuses on the effects of adding and reducing atoms in copper-niobium multilayer nanocomposites forming two flaw-free interfaces between copper (Cu) and niobium (Nb). Study shows that radiation striking crystalline materials may damage their structure and other properties through the generation of vacancies or interstitials. It reveals that the first interface exists from the combination of the face-centered cubic Cu (111) plane and body-centered cubic Nb (110) plane. Other interface needs a straining and rotating of the Cu (111) to make it a 0.5% less dense in the interfacial area.