Dielectric anomaly in strontium borate-bismuth vanadate glass nanocomposite

Transparent glass nanocomposites in the pseudo binary system (100 - x) SrB4O7 (SBO)-x Bi2VO5.5 (BiV) (0 less than or equal to n less than or equal to 70) were prepared by the splat quenching technique. The nano-crystallization of bismuth vanadate (BiV) in 50 SBO-50 BiV (in mol%) glass composite has been demonstrated. These were characterized for their structural, thermal and dielectric properties. As-quenched composites under study have been confirmed to be amorphous by X-ray powder diffraction (XRD) studies. The glass transition temperature (T-g) and crystallization temperatures (T-er) were determined using differential thermal analyses (DTA), High resolution transmission electron microscopic (HRTEM) studies carried out on heat-treated samples reveal the presence of spherical nanosize crystallites of Bi2VO5.5 (BiV) dispersed in the glassy matrix of SrB4O7 (SSO). The dielectric constant (epsilon (r)) and the dielectric loss (D) measurements were carried out on the as-quenched and heat-treated glass nanocomposite samples in the frequency range 100 Hz-10 MHz. The as-quenched and the heat-treated at two different temperatures (720 and 820 K) samples exhibited broad dielectric anomalies in the vicinity of the ferroelectric-to-paraelectric transition temperature of the parent BiV ceramics. The Curie-Weiss law was found to be valid at a temperature above the transition temperature, establishing the diffused nature of the transition. (C) 2001 Elsevier Science Ltd. All rights reserved.

Constitutive Response of Passivated Copper Films: Experiments and Analyses

The constitutive behavior of passivated copper films is studied. Stresses in copper films of thickness ranging from 1000 nm to 40 nm, passivated with silicon oxide on a quartz or silicon substrate, were measured using the curvature method. The thermal cycling spans a temperature range from - 196 to 600°C. It is seen that the strong relaxation at high temperatures normally found in unpassivated films is nonexistent for passivated films. The copper film did not show any rate-dependent effect over a range of heating/cooling rate from 5 to 25°C/min. Further analyses showed that significant strain hardening exists during the course of thermal loading. In particular, the measured stress- temperature response can only be fitted with a kinematic hardening model, if a simple constitutive law within the continuum plasticity framework is to be used. The analytic procedures for extracting the film properties are presented. Implications to stress modeling of copper interconnects in actual devices are discussed.

Microscopic modelling of adsorption and the generalised surface layer hypothesis

Two- and three-state models for the adsorption of organic compounds at the electrode/electrolyte interface are proposed. Different size requirements, if any, for the neutral molecule and the adsorbing solvent are also considered. It is shown how the empirical, generalised surface layer (GSL) relationship (between the potential difference and the electrode charge) formulated by Damaskin et al. can be understood at the molecular level.

Current views on microscopic thermodynamics of liquid alloys

An attempt has been made to review current information on the microscopic thermodynamics of liquid alloys. For complex alloys, and for alloys of simple metals with strong "compound-forming" tendencies, the fluctuation approach developed by Bhatia and his co-workers provides a useful link between the fluctuation in concentration and number density of atoms in the mixture on the one hand, and macroscopic thermodynamic properties on the other. Some selected examples of the application of structural data of liquid alloys to estimating macroscopic thermodynamic properties such as the Gibbs free energy of mixing, coupled with the fluctuation approach are given. The relevant thermodynamic quantities such as vapor pressure and entropy are also discussed, to facilitate the understanding of the present status of the fundamental and powerful links between macroscopic and microscopic (atomic scale) structure of liquid alloys (Mg--Sn, Li--Pb, Hg--K). 63 ref.--AA

Microscopic study of the 2/5 fractional quantum Hall edge

This paper reports on our study of the edge of the 2/5 fractional quantum Hall state, which is more complicated than the edge of the 1/3 state because of the presence of edge sectors corresponding to different partitions of composite fermions in the lowest two Lambda levels. The addition of an electron at the edge is a nonperturbative process and it is not a priori obvious in what manner the added electron distributes itself over these sectors. We show, from a microscopic calculation, that when an electron is added at the edge of the ground state in the [N(1), N(2)] sector, where N(1) and N(2) are the numbers of composite fermions in the lowest two Lambda levels, the resulting state lies in either [N(1) + 1, N(2)] or [N(1), N(2) + 1] sectors; adding an electron at the edge is thus equivalent to adding a composite fermion at the edge. The coupling to other sectors of the form [N(1) + 1 + k, N(2) - k], k integer, is negligible in the asymptotically low-energy limit. This study also allows a detailed comparison with the two-boson model of the 2/5 edge. We compute the spectral weights and find that while the individual spectral weights are complicated and nonuniversal, their sum is consistent with an effective two-boson description of the 2/5 edge.

Oneand twodimensional single quantumand multiplequantumNMR methodologies: tools for chiral analyses

It is well known that enantiomers cannot be distinguished by NMR spectroscopy unless diastereomorphic interactions are imposed. Several chiral aligning media have therefore been reported for their visualization, although extensive studies are carried out using the liquid crystal made of polypeptide poly-γ-benzyl-L-glutamate (PBLG) in organic solvent. In PBLG medium the spin systems are weakly coupled and the first order analyses of the spectra are generally possible. But due to large number of pair wise interactions of nuclear spins resulting in many degenerate transitions the 1H NMR spectra are not only complex but also broad and featureless, in addition to an indistinguishable overlap of the spectra of enantiomers. This enormous loss of resolution severely hinders the analyses of proton spectra, even for spin systems with 5–6 interacting protons, thereby restricting itsroutine application. In this review we discuss our recently developed several one and multidimensional NMR experiments to circumvent these difficulties taking specific examples of the molecules containing a single chiral centre.

Development of novel multiple quantummethodologies for the analyses of complex protonNMR spectra of scalar coupled spins

One of the significant advancements in Nuclear Magnetic Resonance spectroscopy (NMR) in combating the problem of spectral complexity for deriving the structure and conformational information is the incorporation of additional dimension and to spread the information content in a two dimensional space. This approach together with the manipulation of the dynamics of nuclear spins permitted the designing of appropriate pulse sequences leading to the evolution of diverse multidimensional NMR experiments. The desired spectral information can now be extracted in a simplified and an orchestrated manner. The indirect detection of multiple quantum (MQ) NMR frequencies is a step in this direction. The MQ technique has been extensively used in the study of molecules aligned in liquid crystalline media to reduce spectral complexity and to determine molecular geometries. Unlike in dipolar coupled systems, the size of the network of scalar coupled spins is not big in isotropic solutions and the MQ 1H detection is not routinely employed,although there are specific examples of spin topology filtering. In this brief review, we discuss our recent studies on the development and application of multiple quantum correlation and resolved techniques for the analyses of proton NMR spectra of scalar coupled spins.

Mechanical properties of ZnS nanowires and thin films: Microscopic origin of the dependence on size and growth direction

Mechanical properties of ZnS nanowires and thin films are studied as a function of size and growth direction using all-atom molecular dynamics simulations. Using the stress-strain relationship we extract Young's moduli of nanowires and thin films at room temperature. Our results show that Young's modulus of 0001] nanowires has strong size dependence. On the other hand, 01 (1) over bar0] nanowires do not exhibit a strong size dependence of Young's modulus in the size range we have investigated. We provide a microscopic understanding of this behavior on the basis of bond stretching and contraction due to the rearrangement of atoms in the surface layers. The ultimate tensile strengths of the nanowires do not show much size dependence. To investigate the mechanical behavior of ZnS in two dimensions, we calculate Young's modulus of thin films under tensile strain along the 0001] direction. Young's modulus of thin films converges to the bulk value more rapidly than that of the 0001] nanowire.

Charge-transfer interaction mediated organogels from bile acid appended anthracenes: rheological and microscopic studies

In this article we present dual-component charge-transfer interaction (CT) induced organogel formation with bile acid anthracene conjugates as donors and 2,4,7-trinitrofluorenone (TNF) as the acceptor. The use of TNF (1) as a versatile electron acceptor in the formation of gels is demonstrated through the formation of gels with different steroidal groups on the anthracene moiety in a variety of solvents ranging from aromatic hydrocarbons to long chain alcohols. Thermal stability and variable temperature fluorescence experiments were performed on these CT gels. Dynamic rheological experiments conducted on these gels suggest that these are viscoelastic soft materials and with the gel strength can be modulated by varying the donor/acceptor ratios.

Microscopic dynamics of nanoparticle monolayers at air-water interface

We present results of surface mechanical and particle tracking measurements of nanoparticles trapped at the air-water interface as a function of their areal density. We monitor both the surface pressure (II) and isothermal compression modulus (epsilon) as well as the dynamics of nanoparticle clusters, using fluorescence confocal microscopy while they are compressed to very high density near the two dimensional close packing density Phi similar to 0.82. We observe non-monotonic variation in both epsilon and the dynamic heterogeneity, characterized by the dynamical susceptibility chi(4) with Phi, in such high density monolayers. We provide insight into the underlying nature of such transitions in close packed high density nanoparticle monolayers in terms of the morphology and flexibility of these soft colloidal particles.. We discuss the significance our results in the context of related studies on two dimensional granular or colloidal systems. (C) 2013 Elsevier Inc. All rights reserved.

Microscopic and dielectric studies of ZnO nanoparticles loaded in ortho-chloropolyaniline nanocomposites

We have studied the preparation of zinc oxide nanoparticles loaded in various weight percentages in ortho-chloropolyaniline by in situ polymerization method. The length of the O-chloropolyaniline tube is found to be 200 nm and diameter is about 150 nm wherein the embedded ZnO nanoparticles is of 13 nm as confirmed from scanning electron microscopy as well as transmission electron microscopy characterizations. The presence of the vibration band of the metal oxide and other characteristic bands confirms that the polymer nanocomposites are characterized by their Fourier transmission infrared spectroscopy. The X-ray diffraction pattern of nanocomposites reveals their polycrystalline nature. Electrical property of nanocomposites is a function of the filler as well as the matrix. Cole-Cole plots reveal the presence of well-defined semicircular arcs at high frequencies which are attributed to the bulk resistance of the material. Among all nanocomposites, 30 wt% shows the low relaxation time of 151 s, and hence it has high conductivity.

Solvation dynamics of tryptophan in water-dimethyl sulfoxide binary mixture: In search of molecular origin of composition dependent multiple anomalies

Experimental and simulation studies have uncovered at least two anomalous concentration regimes in water-dimethyl sulfoxide (DMSO) binary mixture whose precise origin has remained a subject of debate. In order to facilitate time domain experimental investigation of the dynamics of such binary mixtures, we explore strength or extent of influence of these anomalies in dipolar solvation dynamics by carrying out long molecular dynamics simulations over a wide range of DMSO concentration. The solvation time correlation function so calculated indeed displays strong composition dependent anomalies, reflected in pronounced non-exponential kinetics and non-monotonous composition dependence of the average solvation time constant. In particular, we find remarkable slow-down in the solvation dynamics around 10%-20% and 35%-50% mole percentage. We investigate microscopic origin of these two anomalies. The population distribution analyses of different structural morphology elucidate that these two slowing down are reflections of intriguing structural transformations in water-DMSO mixture. The structural transformations themselves can be explained in terms of a change in the relative coordination number of DMSO and water molecules, from 1DMSO:2H(2)O to 1H(2)O:1DMSO and 1H(2)O:2DMSO complex formation. Thus, while the emergence of first slow down (at 15% DMSO mole percentage) is due to the percolation among DMSO molecules supported by the water molecules (whose percolating network remains largely unaffected), the 2nd anomaly (centered on 40%-50%) is due to the formation of the network structure where the unit of 1DMSO:1H(2)O and 2DMSO:1H(2)O dominates to give rise to rich dynamical features. Through an analysis of partial solvation dynamics an interesting negative cross-correlation between water and DMSO is observed that makes an important contribution to relaxation at intermediate to longer times.