Chemical and microstructural modifications in LiPON thin films exposed to atmospheric humidity

Lithium phosphorus oxynitride (LiPON), the widely used solid electrolyte for thin film microbatteries, is not compatible with the ambient humid temperatures. The reasons for reduction in ionic conductivity of LiPON thin films from 2.8 x 10(-6) Scm(-1) to 9.9 x 10(-10) Scm(-1) when exposed to air are analyzed with the aid of AC impedance measurements, SEM, XPS and stylus profilometry. Initially, particulate-free film surfaces obtained soon after rf sputter deposition in N-2 ambient conditions becomes covered with microstructures, forming pores in the film when exposed to air. LiPON films are deposited on Ti coated silicon in addition to bare silicon, ruling out the possibility of stress-related rupturing from the LiPON/Si interface. The reduction of nitrogen, phosphorus, and increased presence of lithium, oxygen and carbon over the film surface lowers the ionic conductivity of LiPON films when exposed to air. (c) 2011 Elsevier B.V. All rights reserved.

Lanthanide Sulfate Frameworks: Synthesis, Structure, and Optical Properties

Layered lanthanide sulfate compounds with three different structures have been prepared and characterized. The compounds C10H10N2] La(SO4)(2)]center dot 2H(2)O (I), C10H10N2] La(SO4)(2)(H2O)(2)](2) (Ha), C10H10N2]Pr(SO4)(2)(H2O)(2)](2) (IIb), C10H10N2]Nd-2(SO4)(4)(H2O)(2)](2) (IIIa), C10H10N2]Sm-2(SO4)(4)(H2O)(2)](2) (IIIb), and C10H10N2]Eu-2(SO4)(4)(H2O)(2)] 2 (IIIC) have anionic lanthanide sulfate layers separated by protonated bipyridine molecules. The layers are formed by the connectivity between the lanthanide polyhedra and sulfate tetrahedra. The formation of a two-dimensional La-O-La layer (la), Pr-O-Pr chains (IIb), and a tetramer cluster (IIIa) is noteworthy. The compounds exhibit honeycomb (I), square (IIa, IIb), and honeycomb (IIIa-IIIc) net arrangements, when the connectivity between the lanthanide ions is considered. Optical studies indicate the observation of characteristic metal-centered emission at room temperature. The Nd compound (IIIa) exhibits a two-photon upconversion behavior.

Wet chemical syntheses of ultrafine multicomponent ceramic powders through gel to crystallite conversion

Coarse (BOn/2)-O-n+/xH(2)O (10

A characteristic based numerical method with tracking for nonlinear wave equations

Many physical problems can be modeled by scalar, first-order, nonlinear, hyperbolic, partial differential equations (PDEs). The solutions to these PDEs often contain shock and rarefaction waves, where the solution becomes discontinuous or has a discontinuous derivative. One can encounter difficulties using traditional finite difference methods to solve these equations. In this paper, we introduce a numerical method for solving first-order scalar wave equations. The method involves solving ordinary differential equations (ODEs) to advance the solution along the characteristics and to propagate the characteristics in time. Shocks are created when characteristics cross, and the shocks are then propagated by applying analytical jump conditions. New characteristics are inserted in spreading rarefaction fans. New characteristics are also inserted when values on adjacent characteristics lie on opposite sides of an inflection point of a nonconvex flux function, Solutions along characteristics are propagated using a standard fourth-order Runge-Kutta ODE solver. Shocks waves are kept perfectly sharp. In addition, shock locations and velocities are determined without analyzing smeared profiles or taking numerical derivatives. In order to test the numerical method, we study analytically a particular class of nonlinear hyperbolic PDEs, deriving closed form solutions for certain special initial data. We also find bounded, smooth, self-similar solutions using group theoretic methods. The numerical method is validated against these analytical results. In addition, we compare the errors in our method with those using the Lax-Wendroff method for both convex and nonconvex flux functions. Finally, we apply the method to solve a PDE with a convex flux function describing the development of a thin liquid film on a horizontally rotating disk and a PDE with a nonconvex flux function, arising in a problem concerning flow in an underground reservoir.

C-13 MAS NMR spectra of cis,cis-mucononitrile in liquid-crystalline media and in the solid state. Orientation of the carbon chemical-shift tensors

The spinning sidebands observed in the C-13 MAS NMR spectra of cis,cis-mucononitrile oriented in liquid-crystalline media and of the neat sample in the solid state are studied. There are differences in the sideband intensity patterns in the two cases. These differences arise because the order parameters which characterize the orientation of the solute in the liquid-crystalline media differ for different axes. It is shown that, in general, the relative intensities of the sidebands contain information on the sign and magnitude of an effective chemical-shift parameter which is a function of the sum of the products of the principal components of the chemical-shift tensor and the corresponding order parameters with respect to the director. A method for obtaining the orientation of the carbon chemical-shift tensor is proposed. The carbon chemical-shift tensors obtained from gauge-including atomic orbital calculations are also presented for comparison. (C) 1996 Academic Press, Inc.

Cyclization of enediyne radical cations through chemical, photochemical, and electrochemical oxidation: The role of state symmetry

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a �Full Text� option. The original article is trackable via the �References� option.

Chain folding and A:T pairing in human telomeric DNA: a model-building and molecular dynamics study

The various types of chain folding and possible intraloop as well as interloop base pairing in human telomeric DNA containing d(TTAG(3)) repeats have been investigated by model-building, molecular mechanics, and molecular dynamics techniques. Model-building and molecular mechanics studies indicate that it is possible to build a variety of energetically favorable folded-back structures with the two TTA loops on same side and the 5' end thymines in the two loops forming TATA tetrads involving a number of different intraloop as well as interloop A:T pairing schemes. In these folded-back structures, although both intraloop and interloop Watson-Crick pairing is feasible, no structure is possible with interloop Hoogsteen pairing. MD studies of representative structures indicate that the guanine-tetraplex stem is very rigid and, while the loop regions are relatively much more flexible, most of the hydrogen bonds remain intact throughout the 350-ps in vacuo simulation. The various possible TTA loop structures, although they are energetically similar, have characteristic inter proton distances, which could give rise to unique cross-peaks in two-dimensional nuclear Overhauser effect spectroscopy (NOESY) experiments. These folded-back structures with A:T pairings in the loop region help in rationalizing the data from chemical probing and other biochemical studies on human telomeric DNA.

Chemical Degradation of Poly(styrene disulfide) and Poly(styrene tetrasulfide) by Triphenylphosphine

The chemical degradation of polysulfide polymers, viz., poly(styrene disulfide), PSD, and poly(styrene tetrasulfide), PST, has been achieved using triphenylphosphine, TPP. The reaction was monitored using P-31 NMR spectroscopy. The solubility analysis of the reaction residues reveals that while PSD degrades completely, PST on the other hand, undergoes complete degradation only when the concentration of TPP is increased. Moreover, the reaction of PST with TPP occurs at room temperature whereas PSD requires a higher temperature. The reaction products were analyzed using the direct pyrolysis mass spectrometric (DP-MS) technique, and their formation has been explained through an ionic mechanism.

Photodimerization of coumarins in solid cyclodextrin inclusion complexes

The photodimerizations of coumarin and eight of its derivatives are found to proceed selectively in solid inclusion complexes with beta- and gamma-cyclodextrins (beta- and gamma-CD). The distribution of photodimers from these complexes is compared with those from the neat coumarin solids and their solutions in a variety of solvents. By assuming that the stereochemistry of the dimers reflects the packing arrangements of their precursors in the CD complexes, several hypotheses concering the locations and arrangements of the coumarins in the host toruses have been made. The stoichiometries of the complexes have been assigned on the basis of the presence or absence of photodimers and from NMR integration ratios of characteristic coumarin and saccharide protons. The relative orientations of substituted coumarins within a complex are inferred from the stereochemistry of the photodimers. Depending upon the substitution pattern of the coumarin molecules and the type of CD employed, complexes whose guest-host stoichiometries are 1:1, 2:1, and 2:2 have been identified. In several instances, dimers not available from irradiation of neat solid coumarins or their solutions have been obtained from the CD complexes.

Structural, optical and EPR studies on ZnO:Cu nanopowders prepared via low temperature solution combustion synthesis

Cu (0.1 mol%) doped ZnO nanopowders have been successfully synthesized by a wet chemical method at a relatively low temperature (300 degrees C). Powder X-ray diffraction (PXRD) analysis, scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Fourier transformed infrared (FTIR) spectroscopy, UV-Visible spectroscopy, Photoluminescence (PL) and Electron Paramagnetic Resonance (EPR) measurements were used for characterization. PXRD results confirm that the nanopowders exhibit hexagonal wurtzite structure of ZnO without any secondary phase. The particle size of as-formed product has been calculated by Williamson-Hall (W-H) plots and Scherrer's formula is found to be in the range of similar to 40 nm. TEM image confirms the nano size crystalline nature of Cu doped ZnO. SEM micrographs of undoped and Cu doped ZnO show highly porous with large voids. UV-Vis spectrum showed a red shift in the absorption edge in Cu doped ZnO. PL spectra show prominent peaks corresponding to near band edge UV emission and defect related green emission in the visible region at room temperature and their possible mechanisms have been discussed. The EPR spectrum exhibits a broad resonance signal at g similar to 2.049, and two narrow resonances one at g similar to 1.990 and other at g similar to 1.950. The broad resonance signal at g similar to 2.049 is a characteristic of Cu2+ ion whereas the signal at g similar to 1.990 and g similar to 1.950 can be attributed to ionized oxygen vacancies and shallow donors respectively. The spin concentration (N) and paramagnetic susceptibility (X) have been evaluated and discussed. (C) 2011 Elsevier B. V. All rights reserved.

Monte Carlo simulation of network formation based on structural fragments in epoxy-anhydride systems

A method combining the Monte Carlo technique and the simple fragment approach has been developed for simulating network formation in amine-catalysed epoxy-anhydride systems. The method affords a detailed insight into the nature and composition of the network, showing the distribution of various fragments. It has been used to characterize the network formation in the reaction of the diglycidyl ester of isophthalic acid with hexahydrophthalic anhydride, catalysed by benzyldimethylamine. Pre-gel properties like number and weight distributions and average molecular weights have been calculated as a function of epoxy conversion, leading to a prediction of the gel-point conversion. Analysis of the simulated network further yields other characteristic properties such as concentration of crosslink points, distribution and concentration of elastically active chains, average molecular weight between crosslinks, sol content and mass fraction of pendent chains. A comparison has been made of the properties obtained through simulation with those predicted by the fragment approach alone, which, however, gives only average properties. The Monte Carlo simulation results clearly show that loops and other cyclic structures occur in the gel. This may account for the differences observed between the results of the simulation and the fragment model in the post-gel phase. Copyright (C) 1996 Elsevier Science Ltd.

Structure-potential relationship and nature of disorder in liquids and glassy solids

A method based on the minimal-spanning tree is extended to a collection of points in three dimensions. Two parameters, the average edge length and its standard deviation characterize the disorder. The structural phase diagram for a monatomic system of particles and the characteristic values for the uniform random distribution of points have been obtained. The method is applied to hard spheres and Lennard-Jones systems. These systems occupy distinct regions in the structural phase diagram. The structure of the Lennard-Jones system approaches that of the defective close-packed arrangements at low temperatures whereas in the liquid regime, it deviates from the close-packed configuration.

Wet chemical formation of nanoparticles of binary perovskites through isothermal gel to crystallite conversion

Coarse BO2·xH2O (2 < x < 80) gels, free of anion contaminants react with A(OH)2 under refluxing conditions at 70�100°C giving rise to crystallites of single phased, nanometer size powders of ABO3 perovskites (A = Ba, Sr, Ca, Mg, Pb; B = Zr, Ti, Sn). Solid solutions of perovskites could be prepared from compositionally modified gels or mixtures of A(OH)2. Donor doped perovskites could also be prepared from the same method so that the products after processing are often semiconducting. Faster interfacial diffusion of A2+ ions into the gel generates the crystalline regions whose composition is controllable by the A/B ratio as well as the A(OH)2 concentration.

Intraloop and Interloop Interactions in the Folded-G Quartet Structure of Oxytricha Telomeric Sesquence

The antiparallel intramolecular G quartet structure for the 3.5 copy Oxytricha telomeric sequence d(G(4)T(4))(3)G4 has been established using a combination of spectroscopic and chemical probing methods. In the presence of Naf ions, this sequence exhibits a circular dichroism spectrum with a positive band at 295 nm and a negative band around 265 nm, characteristic of an antiparallel G quartet structure. Further, we show that d(G(4)T(4))(3)G(4) adopts an antiparallel intramolecular G quartet structure even in K+ unlike d(G(4)T(4)G(4)). KMnO4 probing experiments indicated the existence of intra and interloop interactions in the Na+ induced structure. We have found that K+ not only increases the thermal stability of,G quartet structure but also binds to the loop region and disrupts stacking and interloop interactions. Biological consequences of such cation-dependent conformational micro-heterogeneity in the loop region of G quartet structures is also discussed.

Characteristic water contents of a fine-grained soil-water system

This paper critically appraises the limitations of the liquid-limit water content of clayey soils determined conventionally either by percussion cup or by the cone penetration method. It is shown that the conventional liquid limit and plastic limit are arbitrary, strength-based water contents and that they cannot represent the plasticity limits, and that the state of the soil-water system at the conventional liquid limit does not correspond to a stress-free reference state. The present investigation identifies three characteristic limiting water contents for a soil-water system which have well-defined, unique mechanisms controlling them, namely the free swell limit, settling limit and shrinkage limit. Simple procedures for the determination of the free swell limit and settling limit of natural soils are presented. The settling limit is shown to be the 'real liquid limit' of any clayey soil. With a number of experimental illustrations, it is clearly shown that the settling limit represents the maximum water-holding capacity of clayey soils and that it corresponds to the stress-free reference state.