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Double Layer Structure (double + layer_structure)

Distribution by Scientific Domains

Physics and Astronomy	50%

Selected Abstracts

Syntheses, Crystal Structures, and Characterizations of a Series of New Layered Lanthanide Carboxylate-Phosphonates

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2006
Si-Fu Tang
Abstract Hydrothermal reactions of different lanthanide(III) salts with (H2O3PCH2)2NCH2COOH (H5L1) led to two new layeredlanthanide(III) carboxylate-diphosphonates, namely La(H2L1)(H2O)2·H2O (1) and La(H2L1)(H2O) (2). The structure of compound 1 features a layered architecture in which the nine-coordinate La3+ ions are bridged by phosphonate groups of the ligands. The carboxylate group of the phosphonate ligand remains protonated and is involved in the interlayer hydrogen bonding. Compound 2 features a double layer structure in which the La3+ ion is eight-coordinated and the carboxylate group of the ligand is chelated to a La3+ ion in a bidentate fashion. Hydrothermal reactions of lanthanide(III) salts with 4-HOOC,C6H4,CH2N(CH2PO3H2)2 (H5L2) afforded three new compounds, namely, La(H4L2)(H3L2)(H2O)·2H2O (3), Er(H3L2)(H4L2) (4), and Er(HL3)(H2L3)(H2O) (5) [H2L3 = H2O3PCH2N(CHO)(CH2,C6H4,COOH)]. H2L3 was formed by the in situ oxidation of one P,C bond of the H5L2 ligand. Compound 3 features a (002) lanthanum(III) phosphonate layer in which the seven-coordinate La3+ ions are bridged by diphosphonate moieties of the ligands. The carboxylate group remains protonated and is involved in the interlayer hydrogen bonding. The structure of compound 4 contains a 1D chain along the a axis in which each pair of ErO6 octahedra is bridged by a pair of phosphonate groups. These 1D chains are further interconnected by hydrogen bonds between noncoordinated phosphonate oxygen atoms into a (002) layer with the phenyl carboxylate groups hanging on the interlayer space. The structure of compound 5 is also layered. The interconnection of Er3+ ions by bidentate and tetradentate bridging phosphonate groups resulted in a (002) inorganic layer with the organic groups orientated to the interlayer space. Luminescence properties of compounds 4 and 5 have also been studied.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Chitosan Hydrogel-Capped Porous SiO2 as a pH Responsive Nano-Valve for Triggered Release of Insulin

ADVANCED FUNCTIONAL MATERIALS, Issue 5 2009
Jianmin Wu
Abstract A pH responsive, chitosan-based hydrogel film is used to cap the pores of a porous SiO2 layer. The porous SiO2 layer is prepared by thermal oxidation of an electrochemically etched Si wafer, and the hydrogel film is prepared by reaction of chitosan with glycidoxypropyltrimethoxysilane (GPTMS). Optical reflectivity spectroscopy and scanning electron microscopy (SEM) confirm that the bio-polymer only partially infiltrates the porous SiO2 film, generating a double layer structure. The optical reflectivity spectrum displays Fabry,Pérot interference fringes characteristic of a double layer, which is characterized using reflective interferometric Fourier transform spectroscopy (RIFTS). Monitoring the position of the RIFTS peak corresponding to the hydrogel layer allows direct, real-time observation of the reversible volume phase transition of the hydrogel upon cycling of pH in the range 6.0,7.4. The swelling ratio and response time are controlled by the relative amount of GPTMS in the hydrogel. The pH-dependent volume phase transition can be used to release insulin trapped in the porous SiO2 layer underneath the hydrogel film. At pH 7.4, the gel in the top layer effectively blocks insulin release, while at pH 6.0 insulin penetrates the swollen hydrogel layer, resulting in a steady release into solution. [source]

PIII nitriding of fcc-alloys containing Ni and Cr

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2008
Johanna Lutz
Abstract Face-centred cubic (fcc) alloys such as austenitic stainless steel, Ni base alloys and Co base alloys are important materials with a high corrosion resistance. Nitrogen insertion by PIII into all these alloys at moderate temperatures leads to the formation of an expanded austenite structure. A similar activation energy for the thermally assisted diffusion of about 0.75 eV was found for steel and CoCr alloys with CrN precipitates beyond 400 °C in both systems. However, a double layer structure was observed for CoCr, similar to Ni alloys, in contrast to a single layer for austenitic steel. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Diamagnetic and nonlinear Zeeman shifts in spatially separated electron and hole layers of semiconductor heterostructures with disorder

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003
J. Desforges
Abstract The effect of the diamagnetic shift on the formation of excitons is investigated for double layer semiconductor systems in which electrons and holes are spatially separated. The effect of disorder due to interface roughness of the double layer structures is included in the calculation of exciton density. Numerical calculations are performed based on an effective lattice-gas model where the electron,hole system is divided into unit cells. The exciton density is calculated by using the partition function method. The effect of the nonlinear Zeeman splitting is also included in the numerical calculations. It is found that the density of the optically allowed exciton states (excitons with Sz = 0) increases under the influence of either or both the diamagnetic and the nonlinear Zeeman shifts. [source]