Conductivity noise study of the insulator-metal transition and phase coexistence in epitaxial samarium nickelate thin films

Interaction between the lattice and the orbital degrees of freedom not only makes rare-earth nickelates unusually ``bad metal,'' but also introduces a temperature-driven insulator-metal phase transition. Here we investigate this insulator-metal phase transition in thin films of SmNiO3 using the slow time-dependent fluctuations (noise) in resistivity. The normalized magnitude of noise is found to be extremely large, being nearly eight orders of magnitude higher than thin films of common disordered metallic systems, and indicates electrical conduction via classical percolation in a spatially inhomogeneous medium. The higher-order statistics of the fluctuations indicate a strong non-Gaussian component of noise close to the transition, attributing the inhomogeneity to the coexistence of the metallic and insulating phases. Our experiment offers insight into the impact of lattice-orbital coupling on the microscopic mechanism of electron transport in the rare-earth nickelates.

Field Emission with Ultra low Turn On Voltage from Metal Decorated Carbon Nanotubes

A simple and scalable method of decorating 3D-carbon nanotube (CNT) forest with metal particles has been developed. The results observed in aluminum (AI) decorated CNTs and copper (Cu) decorated CNTs on silicon (Si) and Inconel are compared with undecorated samples. A significant improvement in the field emission characteristics of the cold cathode was observed with ultralow turn on voltage (E-to similar to 0.1 V/mu m) due to decoration of CNTs with metal nanoparticles. Contact resistance between the CNTs and the substrate has also been reduced to a large extent, allowing us to get stable emission for longer duration without any current degradation, thereby providing a possibility of their use in vacuum microelectronic devices.

Implications of multiple scattering on the assessment of black carbon aerosol radiative forcing

The effects of radiative coupling between scattering and absorbing aerosols, in an external mixture, on the aerosol radiative forcing (ARF) due to black carbon (BC), its sensitivity to the composite aerosol loading and composition, and surface reflectance are investigated using radiative transfer model simulations. The ARF due to BC is found to depend significantly on the optical properties of the `neighboring' (non-BC) aerosol species. The scattering due to these species significantly increases the top of the atmospheric warming due to black carbon aerosols, and significant changes in the radiative forcing efficiency of BC. This is especially significant over dark surfaces (such as oceans), despite the ARF due to BC being higher over snow and land-surfaces. The spatial heterogeneity of this effect (coupling or multiple scattering by neighboring aerosol species) imposes large uncertainty in the estimation ARF due to BC aerosols, especially over the oceans. (C) 2014 Elsevier Ltd. All rights reserved.

Pyridylenevinylene based Cu2+-specific, injectable metallo(hydro) gel: thixotropy and nanoscale metal-organic particles

A Cu2+-selective metallo(hydro) gelation of a p-pyridyl ended oligophenylenevinylene system is reported over its respective meta- and ortho-regioisomers. The metallogel formed via the self-assembly of the nanoscale-metal-organic particles is injectable and also shows multi-stimuli responsiveness, including thixotropy.

Multicomponent Assembly of Fluorescent-Tag Functionalized Ligands in Metal-Organic Frameworks for Sensing Explosives

Detection of trace amounts of explosive materials is significantly important for security concerns and pollution control. Four multicomponent metal organic frameworks (MOFs-12, 13, 23, and 123) have been synthesized by employing ligands embedded with fluorescent tags. The multicomponent assembly of the ligands was utilized to acquire a diverse electronic behavior of the MOFs and the fluorescent tags were strategically chosen to enhance the electron density in the MOFs. The phase purity of the MOFs was established by PXRD, NMR spectroscopy, and finally by singlecrystal XRD. Single-crystal structures of the MOFs-12 and 13 showed the formation of three-dimensional porous networks with the aromatic tags projecting inwardly into the pores. These electron-rich MOFs were utilized for detection of ex- plosive nitroaromatic compounds (NACs) through fluorescence quenching with high selectivity and sensitivity. The rate of fluorescence quenching for all the MOFs follows the order of electron deficiency of the NACs. We also showed the detection of picric acid (PA) by luminescent MOFs is not always reliable and can be misleading. This attracts our attention to explore these MOFs for sensing picryl chloride (PC), which is as explosive as picric acid and used widely to prepare more stable explosives like 2,4,6-trinitroaniline from PA. Moreover, the recyclability and sensitivity studies indicated that these MOFs can be reused several times with parts per billion (ppb) levels of sensitivity towards PC and 2,4,6-trinitrotoluene (TNT).

Cooling a Band Insulator with a Metal: Fermionic Superfluid in a Dimerized Holographic Lattice

A cold atomic realization of a quantum correlated state of many fermions on a lattice, eg. superfluid, has eluded experimental realization due to the entropy problem. Here we propose a route to realize such a state using holographic lattice and confining potentials. The potentials are designed to produces aband insulating state (low heat capacity) at the trap center, and a metallic state (high heat capacity) at the periphery. The metal ``cools'' the central band insulator by extracting out the excess entropy. The central band insulator can be turned into a superfluid by tuning an attractive interaction between the fermions. Crucially, the holographic lattice allows the emergent superfluid to have a high transition temperature - even twice that of the effective trap temperature. The scheme provides a promising route to a laboratory realization of a fermionic lattice superfluid, even while being adaptable to simulate other many body states.

Logarithmic corrections to extremal black hole entropy in N=2, 4 and 8 supergravity

We compute the logarithmic correction to black hole entropy about exponentially suppressed saddle points of the Quantum Entropy Function corresponding to Z(N) orbifolds of the near horizon geometry of the extremal black hole under study. By carefully accounting for zero mode contributions we show that the logarithmic contributions for quarter-BPS black holes in N = 4 supergravity and one-eighth BPS black holes in N = 8 supergravity perfectly match with the prediction from the microstate counting. We also find that the logarithmic contribution for half-BPS black holes in N = 2 supergravity depends non-trivially on the Z(N) orbifold. Our analysis draws heavily on the results we had previously obtained for heat kernel coefficients on Z(N) orbifolds of spheres and hyperboloids in arXiv:1311.6286 and we also propose a generalization of the Plancherel formula to Z(N) orbifolds of hyperboloids to an expression involving the Harish-Chandra character of sl (2, R), a result which is of possible mathematical interest.

Hexamethylenetetramine mediated simultaneous nitrogen doping and reduction of graphene oxide for a metal-free SERS substrate

We report a one-pot hydrothermal synthesis of nitrogen doped reduced graphene oxide (N-rGO) and Ag nanoparticle decorated N-rGO hybrid nanostructures from graphene oxide (GO), metal ions and hexamethylenetetramine (HMT). HMT not only reduces GO and metal ions simultaneously but also acts as the source for the nitrogen (N) dopant. We show that the N-rGO can be used as a metal-free surface enhanced Raman spectroscopy (SERS) substrate, while the Ag nano-particles decorated N-rGO can be used as an effective SERS substrate as well as a template for decorating various other nanostructures on N-rGO.

Optical detection of submicromolar levels of nitro explosives by a submicron sized metal-organic phosphor material

Two isomorphous submicron sized metal-organic network compounds, Y-2(PDA)(3)(H2O)1]center dot 2H(2)O (PDA = 1,4-phenylenediacetate), 1 and Y1.8Tb0.2(PDA)(3)(H2O)1]center dot 2H(2)O, Tb@1 have been synthesized by employing solvent assisted liquid grinding followed by heating at 180 degrees C for 1' min and washing with water. Single crystal X-ray data of bulk 1 confirmed a three dimensional porous structure. The structure and morphology of 1 and Tb@1 were systematically characterized by PXRD, TGA, DSC, IR, SEM and EDX analysis. Dehydrated Tb@1 Tb@1'] shows a high intense visible green emission upon exposure to UV light. The green emission of Tb@1' was used for the detection of nitro explosives, such as 2,4,6-trinitrophenol (TNP), 1,3-dinitro benzene (DNB), 2,4-dinitro toluene (DNT), nitro benzene (NB), and 4-nitro toluene (NT) in acetonitrile. The results show that the emission intensity of dehydrated Tb@1' can be quenched by all the nitro analytes used in the present work. Remarkably, Tb@1' exhibited a high efficiency for TNP, DNB and DNT detection with K-SV K-SV = quenching constant based on linear Stern-Volmer plot] values of 70 920, 44 000 and 35 430 M-1, respectively, which are the highest values amongst known metal-organic materials. Using this material submicromolar level (equivalent to 0.18 ppm), a detection of nitro explosives has been achieved.

A metal-free and a solvent-free synthesis of thio-amides and amides: an efficient Friedel-Crafts arylation of isothiocyanates and isocyanates

A rapid, metal-free and solvent-free (very low loading of solvent in few cases) reaction conditions for synthesizing thioamides and amides using a Bronsted super acid such as triflic acid has been developed. This method shows a broad substrate scope with a variety of electron-rich arenes including thiophene derivatives. The reaction works well for both aromatic as well as aliphatic isothiocyanates. Most of the thioamides are obtained in excellent yields in short reaction times and in most of the examples, a simple work up procedure has been developed which does not require further purification.

Effect of metal oxidation state on FRET: a Cu(I) silent but selectively Cu(II) responsive fluorescent reporter and its bioimaging applications

Copper(II) and copper(I) complexes of a newly designed and crystallographically characterized Schiff base (HL) derived from rhodamine hydrazide and cinnamaldehyde were isolated in pure form formulated as Cu(L)(NO3)] (L-Cu) (1) and Cu(HL)(CH3CN)(H2O)]ClO4 (HL-Cu) (2), and characterized by physicochemical and spectroscopic tools. Interestingly, complex 1 but not 2 offers red fluorescence in solution state, and eventually HL behaves as a Cu(II) ions selective FRET based fluorosensor in HEPES buffer (1 mM, acetonitrile-water: 1/5, v/v) at 25 degrees C at biological pH with almost no interference of other competitive ions. The dependency of the FRET process on the +2 oxidation state of copper has been nicely supported by exhaustive experimental studies comprising electronic, fluorimetric, NMR titration, and theoretical calculations. The sensing ability of HL has been evaluated by the LOD value towards Cu(II) ions (83.7 nM) and short responsive time (5-10 s). Even the discrimination of copper(I) and copper(II) has also been done using only UV-Vis spectroscopic study. The efficacy of this bio-friendly probe has been determined by employing HL to detect the intercellular distribution of Cu(II) ions in HeLa cells by developing image under fluorescence microscope.

Synthesis and crystal structure of copper (II) uracil ternary polymeric complex with 1,10-phenanthroline along with the Hirshfeld surface analysis of the metal binding sites for the uracil ligand

The study of models for ``metal-enzyme-substrate'' interaction has been a proactive area of research owing to its biological and pharmacological importance. In this regard the ternary copper uracil complex with 1,10-phenanthroline represents metal-enzyme-substrate system for DNA binding enzymes. The synthesis of the complex, followed by slow evaporation of the reaction mixture forms two concomitant solvatomorph crystals viz., {Cu(phen)(mu-ura)(H2O)](n)center dot H2O (1a)} and {Cu(phen)(mu-ura)(H2O)](n)center dot CH3OH (1b)}. Both complexes are structurally characterized, while elemental analysis, IR and EPR spectra were recorded for 1b (major product). In both complexes, uracil coordinates uniquely via N1 and N3 nitrogen atom acting as a bidentate bridging ligand forming a 1-D polymer. The two solvatomorphs were quantitatively analyzed for the differences with the aid of Hirshfeld surface analysis. (C) 2014 Elsevier B.V. All rights reserved.

On the Two-Step Mechanism for Synthesis of Transition-Metal Nanoparticles

The two-step particle synthesis mechanism, also known as the Finke-Watzky (1997) mechanism, has emerged as a significant development in the field of nanoparticle synthesis. It explains a characteristic feature of the synthesis of transition metal nanoparticles, an induction period in precursor concentration followed by its rapid sigmoidal decrease. The classical LaMer theory (1950) of particle formation fails to capture this behavior. The two-step mechanism considers slow continuous nucleation and autocatalytic growth of particles directly from precursor as its two kinetic steps. In the present work, we test the two-step mechanism rigorously using population balance models. We find that it explains precursor consumption very well, but fails to explain particle synthesis. The effect of continued nucleation on particle synthesis is not suppressed sufficiently by the rapid autocatalytic growth of particles. The nucleation continues to increase breadth of size distributions to unexpectedly large values as compared to those observed experimentally. A number of variations of the original mechanism with additional reaction steps are investigated next. The simulations show that continued nucleation from the beginning of the synthesis leads to formation of highly polydisperse particles in all of the tested cases. A short nucleation window, realized with delayed onset of nucleation and its suppression soon after in one of the variations, appears as one way to explain all of the known experimental observations. The present investigations clearly establish the need to revisit the two-step particle synthesis mechanism.

Heat kernels on the AdS(2) cone and logarithmic corrections to extremal black hole entropy

We develop new techniques to efficiently evaluate heat kernel coefficients for the Laplacian in the short-time expansion on spheres and hyperboloids with conical singularities. We then apply these techniques to explicitly compute the logarithmic contribution to black hole entropy from an N = 4 vector multiplet about a Z(N) orbifold of the near-horizon geometry of quarter-BPS black holes in N = 4 supergravity. We find that this vanishes, matching perfectly with the prediction from the microstate counting. We also discuss possible generalisations of our heat kernel results to higher-spin fields over ZN orbifolds of higher-dimensional spheres and hyperboloids.