Using atomically resolved electron energy-loss spectroscopy, the atomic-plane-by-atomic-plane, unit-cellby-unit-cell stoichiometry, and charge characteristics of the oxide interface (Nd 0.35 Sr 0.65)MnO 3 /SrTiO 3 , with a primitive polar discontinuity of (Nd 0.35 Sr 0.65 O) 0.35+-(TiO 2) 0 , were thoroughly investigated. (Nd 0.35 Sr 0.65)MnO 3 is a strongly correlated insulator and the interface was characterized to be insulating. The cell-specific stoichiometric evaluation unveiled an extensive interdiffusion across the interface. The plane-specific charge characterization revealed that the interdiffusion grades the primitive polar discontinuity. Despite the graded polar discontinuity, a charge transfer inversely into (Nd 0.35 Sr 0.65)MnO 3 was firmly resolved with a length scale of ∼2 nm and a charge density on the order of ∼10 13 /cm 2 and is effectively mediated by an asymmetric Ti interdiffusion. The intricate electronic correlations of the interfacial (Nd 0.35 Sr 0.65)MnO 3 unit cells and the interdiffusion-induced chemical disorder tend to render the charges localized, resulting in a localized two-dimensional electron density and thus the insulating interface, in distinct contrast to the conventional understanding of a vanishing charge density for an insulating interface and the metallic two-dimensional electron gas found at other classical polar-discontinuous interface systems. A potential strain manipulation on the electronic localization of the electron density was also proposed.

No abstract

A numerical scheme based on the method of fundamental solutions is proposed for the solution of two-dimensional boundary inverse Stokes problems, which involve over-specified or under-specified boundary conditions. The coefficients of the fundamental solutions for the inverse problems are determined by properly selecting the number of collocation points using all the known boundary values of the field variables. The boundary points of the inverse problems are collocated using the Stokeslet as the source points. Validation results obtained for two test cases of inverse Stokes flow in a circular cavity, without involving any iterative procedure, indicate the proposed method is able to predict results close to the analytical solutions. The effects of the number and the radius of the source points on the accuracy of numerical predictions have also been investigated. The capability of the method is demonstrated by solving different types of inverse problems obtained by assuming mixed combinations of field variables on varying number of under-and over-specified boundary segments.

The present work describes the application of the method of fundamental solutions (MFS) for the solution of cutoff wavelengths of elliptical waveguides. Since the MFS employs a formulation using boundary values only, the cutoff wavelengths are determined by applying the singular value decomposition (SVD) technique. The use of the MFS to solve the governing (Helmholtz) equation guarantees a solution without singularities, since it does not use discretized points to determine the solution at the interior of the computational domain. The combination of the MFS and SVD techniques has resulted in a simpler and efficient numerical solution procedure, as compared to other schemes. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 552–558, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20695

Field emission of electrons from narrow-band-gap and wide-band-gap one-dimensional nanostructures were studied. N-type silicon substrates enhanced the emission from the low-band-gap silicon nanowires and carbon nanotubes, whereas p-type substrates were a better choice for field emission from wide-band-gap silicon carbon nitride nanocrystalline thin films and nanorods. The role of the substrate-nanostructure interface was modeled based on different junction mechanisms to explain, qualitatively, the fundamentally different emission behavior of these nanostructures when n-and p-type silicon substrates were used. The results could be explained on the basis of simple carrier transport across the silicon-silicon nanowire interface and subsequent tunneling of electrons for the silicon nanowires. Schottky barrier theory can explain the better field emission of electrons from the n-type silicon supported carbon nanotubes. The decreased barrier height at the interface of the silicon-silicon carbon nitride heterojunction, when p-type silicon substrate was used, could explain the superior field emission in comparison to when n-type silicon substrates were used.