Department of Physics

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IIT Jodhpur

We report a detailed numerical investigation on transverse localization of light in a 1D disordered lattice consisting of a large array of coupled waveguides in the presence of nonlinearity in the medium. Our study reveals that the presence of a focusing type of nonlinearity favors faster localization of light while a defocusing type of nonlinearity degrades the quality of localization. It is shown that presence of either of these could over-shadow localization of light unless the strength of disorder is sufficiently strong. Influence of the input beam width on propagation of light in such a disordered nonlinear medium has also been discussed. The present study should be useful in potential applications, in which one could exploit dominance of focusing nonlinearity on transverse localization of light in a disordered medium. © 2012 Elsevier B.V. All rights reserved.

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Optics Communications

Role of optical nonlinearity on transverse localization of light in a disordered one-dimensional optical waveguide lattice

Reduced graphene oxide (RGO) with a layered and porous structure was synthesized by thermal exfoliation of graphite oxide. Synthesized RGO is very light weight and flaky. The formation of RGO was studied using Fourier transform infrared and Raman spectroscopies, X-ray diffraction and scanning electron microscopy. Composites were prepared by dispersing 2%, 4% and 10% by weight of the synthesized RGO into nitrile butadiene rubber (NBR) matrix. Microwave absorption properties of RGO/NBR composites were investigated by measuring their complex permittivity and permeability by using waveguide method. Simulation studies show that 10 wt.% of graphene oxide in NBR matrix exhibits high values of reflection loss (>10 dB) over a wide frequency range 7.5-12 GHz and maximum loss is 57 dB at 9.6 GHz at a thickness of 3 mm. © 2011 Elsevier Ltd. All rights reserved.

Carbon

Microwave absorbing properties of a thermally reduced graphene oxide/nitrile butadiene rubber composite

A novel "one-pot" synthetic method has been reported for the preparation of (NiFe 2O 4) x-(BaFe 12O 19) 1-x composites. The synthesized composites were characterized using thermogravimetric analysis, differential scanning calorimetric analysis, X-ray diffraction, dynamic light scattering technique, scanning electron microscopy, and vibrating sample magnetometer. The (NiFe 2O 4) x-(BaFe 12O 19) 1-x composites prepared by this method showed crystallographically two phase behavior, but magnetically a good single phase exchange spring-coupled behavior with high saturation magnetization as well as high coercivity. © 2011 The American Ceramic Society.

Journal of the American Ceramic Society

A novel but simple "one-Pot" synthetic route for preparation of (NiFe 2O 4) x-(BaFe 12O 19) 1-x composites

In this investigation, rapidly quenched ribbons prepared by a melt spinning technique have been used as a magnetostrictive sensor (MsS) element for the generation and detection of guided waves traversing through a pipe. The materials we have used in the present study are the rapidly quenched Fe 80Si 8B 12 and Fe 40Ni 40B 20 which have a high magnetostriction constant. The experiments were conducted on a bare Al tube after generating proper dispersion curves. The experiments were carried out using as-spun and annealed ribbons. After optimizing the AC magnetizing field, DC bias field and frequency (from software), longitudinal guided waves were generated in the tubes using MsS ribbons. Measurements were carried out to test the sensitivity of this sensor to both circumferential discontinuity (saw cut) and defect free bare aluminum tubes at a frequency of 76kHz. The effect of defect size on the sensor signal was also investigated. Using the present technique, the defects were not only identified but their location in the pipe was also estimated. © 2012 IOP Publishing Ltd.

Smart Materials and Structures

Generation and detection of guided waves in a defective pipe using rapidly quenched magnetostrictive ribbons

Reactions of acyclic and cyclic organotellurium (IV) compounds [R 2TeI 2 {R 2 = (C 2H 5) 2, (n-C 3H 7) 2, C 5H 10}] with the silver salt of carboxylic acids and sodium diethyldithiocarbamate form the organotellurium (IV) complexes (C 2H 5) 2Te(4-NO 2C 6H 4OCO) 2 (1), (C 2H 5) 2Te(C 6H 5CHCHOCO) 2 (2), (n-C 3H 7) 2Te(C 6H 5OCO) 2 (3), (n-C 3H 7) 2Te(4-NO 2C 6H 4OCO) 2 (4), (n-C 3H 7) 2Te(3,5-NO 2C 6H 3OCO) 2 (5), (n-C 3H 7) 2Te(4-OCH 3C 6H 4OCO) 2 (6), (n-C 3H 7) 2Te(C 6H 5CHCHOCO) 2 (7), C 5H 10Te(C 6H 5CHCHOCO) 2 (8) and C 5H 10TeCl[SCSN- (C 2H 5) 2] (9). The X-ray structures of some of these organotellurium (IV) derivatives indicate that they possess ψTBP geometry and dimeric and tetrameric supramolecular associations are achieved through cooperative participation of inter- and/or intramolecular Te⋯O secondary bonds and/or C-H⋯O hydrogen bonds. The intramolecular Te⋯O secondary bond lengths seem to be dependent on the cis- and trans-position placements of free oxygens of the carboxylate groups. It is found that the third-order non-linear optical susceptibilities (χ (3)) of these complexes are in the range 7.21-8.20 × 10 -14 esu and the second order hyperpolarizabilities (γ) are in the range 4.89-5.56 × 10 -32 esu. The presence of the telluracyclopentane (C 5H 10Te) cyclic organic group and cinnamate (C 6H 5CHCHOCO)/diethyldithiocarbamate (SCSN(C 2H 5) 2) ligands having conjugation in the organotellurium (IV) derivatives (8 and 9), appears to be responsible for the higher χ (3) and γ values. © 2012 Elsevier Ltd. All rights reserved.

Polyhedron

Synthesis, crystal structure, supramolecular associations and third-order non-linear optical (NLO) properties of some organotellurium (IV) derivatives

In this paper we present the structure and spectroscopic, photophysical and nonlinear optical studies of covalently functionalized novel graphene oxide-[Cu, Zn, Sn, H 2 (metal free), VO] porphyrin composites. The composites were characterized by Field Enhanced Scanning Electron Microscopy (FE-SEM), micro-Raman, optical absorption, Fourier transform infrared (FT-IR), steady state and time resolved fluorescence spectroscopic techniques. The composites exhibit strong fluorescence quenching, suggesting strong electronic interactions between the porphyrin and graphene oxide molecules. Nonlinear optical absorption (NLA) studies of graphene oxide-porphyrin composites were investigated using the Z-scan technique at 532 and 800 nm with nanosecond (ns) and femtosecond (fs) laser pulses. Composites show strong two-photon absorption (TPA) as well as excited state absorption (ESA) leading to reverse saturable absorption (RSA) behaviour in the ns regime and saturable absorption (SA) behaviour was observed in fs regime. The metal free porphyrin-graphene oxide (GO) composite shows significant nonlinear absorption behaviour as well as highest fluorescence quenching behaviour compared to other GO-porphyrin composites. We further observed the enhanced figure of merit (FOM) values for composites in comparison with individual molecules. © 2012 The Royal Society of Chemistry.

Journal of Materials Chemistry

Synthesis and structural, spectroscopic and nonlinear optical measurements of graphene oxide and its composites with metal and metal free porphyrins

We have investigated the structure and magnetism of self-assembled, 20nm diameter iron oxide nanoparticles covered by an oleic acid shell for scrutinizing their structural and magnetic correlations. The nanoparticles were spin-coated on an Si substrate as a single monolayer and as a stack of 5ML forming a multilayer. X-ray scattering (reflectivity and grazing incidence small-angle scattering) confirms high in-plane hexagonal correlation and a good layering property of the nanoparticles. Using polarized neutron reflectivity we have also determined the long range magnetic correlations parallel and perpendicular to the layers in addition to the structural ones. In a field of 5kOe we determine a magnetization value of about 80% of the saturation value. At remanence the global magnetization is close to zero. However, polarized neutron reflectivity reveals the existence of regions in which magnetic moments of nanoparticles are well aligned, while losing order over longer distances. These findings confirm that in the nanoparticle assembly the magnetic dipoledipole interaction is rather strong, dominating the collective magnetic properties at room temperature. © 2012 IOP Publishing Ltd.

Nanotechnology

Self-assembled iron oxide nanoparticle multilayer: X-ray and polarized neutron reflectivity

Cellular Automata (CA) have long attracted interest as abstract computation models, but only in the last few years have serious attempts started to implement them in terms of molecules. Such nano-technological innovations promise very cost-effective fabrication because of the regular structure of CA, which allows assembly through molecular self-organization. The small sizes of molecules combined with their availability in Avogadro-scale numbers promises a huge computational power, in which the massive parallelism inherent in CA can be effectively exploited. This paper discusses the molecular CA in (Bandyopadhyay et al., Nature Physics 2010) and shows novel features that have never been proposed in conventional CA models. The interaction rules in the molecular CA are found to be of a mixed variety, ranging from conventional direct-neighborhood type of rules to rules with long-distance interactions between cells. The probabilities according to which rules are applied in the molecular CA are dynamically influenced by the patterns on the cellular space. This results in extremely rich behavior, as compared to conventional models, which has the potential to be utilized for efficient configuration of patterns on the cellular space. © Springer Science+Business Media B.V. 2012.

Natural Computing

On Cellular Automata rules of molecular arrays

Nucleic acid interaction with nanoscale objects like carbon nanotubes (CNTs) and dendrimers is of fundamental interest because of their potential application in CNT separation, gene therapy and antisense therapy. Combining nucleic acids with CNTs and dendrimers also opens the door towards controllable self-assembly to generate various supra-molecular and nano-structures with desired morphologies. The interaction between these nanoscale objects also serve as a model system for studying DNA compaction, which is a fundamental process in chromatin organization. By using fully atomistic simulations, here we report various aspects of the interactions and binding modes of DNA and small interfering RNA (siRNA) with CNTs, graphene and dendrimers. Our results give a microscopic picture and mechanism of the adsorption of single- and double-strand DNA (ssDNA and dsDNA) on CNT and graphene. The nucleic acid-CNT interaction is dominated by the dispersive van der Waals (vdW) interaction. In contrast, the complexation of DNA (both ssDNA and dsDNA) and siRNA with various generations of poly-amido-amine (PAMAM) dendrimers is governed by electrostatic interactions. Our results reveal that both the DNA and siRNA form stable complex with the PAMAM dendrimer at a physiological pH when the dendrimer is positively charged due to the protonation of the primary amines. The size and binding energy of the complex increase with increase in dendrimer generation. We also give a summary of the current status in these fields and discuss future prospects. © Indian Academy of Sciences.

Fulltext

Journal of Biosciences

Interaction of nucleic acids with carbon nanotubes and dendrimers

Novel red emitting KCaBO3:Eu phosphors have been synthesized by solid-state reaction at various temperatures. Systematic studies on annealing effects and consequent structural evolution and optical properties were investigated by various structural and photoluminescence studies. With an increase in annealing temperature (from 700 °C to 950 °C), these phosphors show a gradual change from a mixed low crystalline phase to a highly crystalline single phase, with minimized volatile impurities. Photoluminescence studies revealed that the low-temperature annealed phosphors showed distinct mixed emission composed of blue and red emissions upon UV excitation. Such dual emission is due to the coexistence of Eu3+ and Eu2+ ions, wherein the reduction of Eu3+ into Eu2+ was attributed to the presence of volatile impurities. Relatively high-temperature annealed phosphors exhibit strong red color photoluminescence due to homogeneously occupied Eu3+ ions in the host crystal charge-compensated (with K+ ions) sites of Ca2+ ions. The dominant red-to-orange emission intensity ratios and Judd-Ofelt parameters of Eu3+ ions support the strong covalent nature and site-occupation of higher asymmetry sites of K+ and Ca2+ ions. High emission life times and efficient and stable photoluminescence at different excitation wavelengths make these phosphors suitable for white LEDs and other display applications. © The Royal Society of Chemistry 2012.