High resonant reflection of a confined free space beam by a high contrast segmented waveguide

High resonant reflection of a free space wave from a deeply corrugated slab waveguide is shown to take place in the case of a focused free space beam under normal incidence. It is described as a result of a strong intra-guide coupling coefficient allowing the coupled wave to be closely localized under the incident beam, therefore to interfere with it with high contrast effects. The coupled mode inspired analysis gives the possibility of optimizing the resonant structure; it is related and compared with the photonic crystal vision of the same functional structure to which it confers more intelligibility.     

Misfit dislocations in limited inhomogeneous media: A review

Elastic fields of translation and misfit dislocations (resp. TD's and MD's) are investigated for two types of inhomogeneous materials.First, a multilayer formed by parallel heterointerfaces or free surfaces and containing one periodic array of interfacial MD's. In the more simple case of a thin layer on a substrate, analytic solutions can be found for the displacement field u relative to a single or a hexagonal periodic array of MD's. In the less simple case of a thin bicrystal and a layer sandwiched between two semi-infinite media, explicit solutions can still be extracted. For the general case of a multilayer material which involves a number N>2 heterointerfaces, analytic expressions become intractable. Solutions can nevertheless be obtained from the numerical inversion of linear equations which express the limiting boundary conditions along the heterointerfaces.Second, a thin bicrystal containing an heterointerface perpendicular to the two free surfaces of a foil. Starting from the elastic field of an edge TD parallel to the free surfaces, it is shown how to derive that of (i) a coherent heterointerface, (ii) a semicoherent heterointerface containing a single MD, and (iii) two close and parallel coherent heterointerfaces. Numerical calculations and graphs illustrate the solutions for metals (Al, Al₂Cu), semiconductor materials (CoSi₂, Si, GaAs), thin foils of the GaAs/Si type and a / superalloy.     

Organometallic early lanthanide clusters: syntheses and X-ray structures of new monocyclopentadienyl complexes

The reaction of Ln(BH(4))(3)(THF)(3) or LnCl(3)(THF)(3) with 1 equiv of KCp*' ligand (Cp' = C(5)Me(4)n-Pr) afforded the new monocyclopentadienyl complexes Cp*'LnX(2)(THF)(n) (X = BH(4), Ln = Sm, n = 1, 1a, Ln = Nd, n = 2, 1b; X = Cl, Ln = Sm, n = 1, 3a) and [Cp*'LnX(2)](n') (X = BH(4), n' = 6, Ln = Sm, 2a, Ln = Nd, 2b; X = Cl, Ln = Nd, 4b). All these compounds were characterized by elemental analysis and (1)H NMR. Crystals of mixed borohydrido/chloro-bridged [Cp*'(6)Ln(6)(BH(4))(12-x))Cl(x)(THF)(n')] (x = 10, n' = 4, Ln = Sm, 2a', Ln = Nd, 2b'; x = 5, n = 2, Ln = Sm, 2a' ') were also isolated. Compounds 2a, 2b, 2a', 2b', and 2a' were structurally characterized; they all exhibit a hexameric structure in the solid state containing the [Cp*(3)Ln(3)X(5)(THF)] building block. The easy clustering of THF adducts first isolated is illustrative of the well-known bridging ability of the BH(4) group. Hexameric 2a was found to be unstable in the presence of THF vapors; this may be correlated to the opening of unsymmetrical borohydride bridges observed in the molecular structure.     

Redetermination de la structure cristalline du tetrafluoroantimonate III de sodium NaSbF4 - interaction liaison fluor-paire electronique libre

The crystal structure of NaSbF₄ has been redetermined by X-ray diffraction. The coordination about antimony is AX₆E with a 2.2.2.1 geometry. The units are linked by fluorine bridges and form a double layer perpendicular to the a axis. Infrared and Raman spectra were recorded and are discussed in terms of the distorted octahedral arrangement of fluorines about each antimony.