Abstract: A fluorescent organogel is obtained from the reaction of Zn(OAc)(2).2H(2)O, 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene (bpd), and tartaric acid (H(4)tar) in methanol. The gel is proposed to have formed by the cross-linking of linear 1D coordination polymers [Zn(bpd)](n) with tartarate coligand in a highly random fashion which entrapped the solvent molecules through hydrogen-bonding interactions between the tar coligand and solvent molecules. Higher dimensional coordination polymeric structure is proposed for this gel based on the corresponding complexes formed by oxalic and succinic acids. The presence of three components is essential for the gelation. Interestingly, organogelation of the coordination polymer has induced remarkable fluorescence properties in the weakly emissive bpd. Such fluorescence enhancement is attributed to the reduction in nonradiative decay in the aggregated state. The organogel exhibits viscoelastic behavior as evidenced from the rheological studies.
Abstract: Silver telluride nanowires incorporating silver were prepared by green chemical method in aqueous solution. First, Ag2TeO3 was prepared from aqueous solutions of sodium tellurite (Na2TeO3) and silver nitrate (AgNO3). At room temperature in basic solution, alpha-D-glucose reduces Ag2TeO3 to generate silver nanocrystals, whereas solvothermal reaction of Ag2TeO3 with (X-D-glucose at 165 degrees C generates Te, Ag, or Ag2Te-Ag axial hetrojunction nanowires depending upon the pH of the reaction mixture. These heterojunction nanowires, which exhibit electrical bistability at low voltage, can be used as data storage devices.
Abstract: A pH and mechano-responsive coordination polymeric gel was developed without the use of long chain hydrophobic groups. The hydrogel was synthesised by reacting the aqueous solution of Mg2+ with the basic aqueous solution of N-(7-hydroxyl-4-methyl-8coumarinyl)-alanine. The gelation is attributed to the self-aggregation of ID coordination polymers to form 3D nanostructures through non-covalent interactions to entrap water molecules. The freeze-dried hydrogel exhibits a fibrillar network structure with a uniform ribbon shape. UV/vis absorption studies illustrate that the hydrogel displays a typical pi-pi* transition. The fluorescence intensity of the hydrogel is enhanced drastically with a longer lifetime upon gel formation. Mechanical analysis including dynamic oscillation on shear, steady shear and creep (retardation-relaxation) testing have been performed to elucidate the supra-molecular nature of the 3D assembly. Together with the viscoelastic properties and biocompatibility, the Mg2+ hydrogel may find utility as a novel soft material in biomedical applications.
Abstract: Instant hydrogelation of coumarin-derivatized glycine has been demonstrated in the absence of long-chain hydrophobic groups upon formation of a zinc(II) coordination polymer, which exhibits fluorescence enhancement upon gelation.
Abstract: Fabrication of liquid crystalline (LC) nanomaterials in an aligned pattern along the multiwalled carbon nanotubes (CNT) has been reported here. The nanocomposite was prepared by sonicating esterified CNTs and the ferroelectric liquid crystal (FLC) in chloroform. The nanohybrid shish kebab (NHSK) like pattern was observed in SEM analysis. The nanocomposite materials were characterized by Fourier transform infrared spectroscopy (FTIR), polarizing optical microscopy and electron microscopy. The DC and AC electrical properties of the composite materials were investigated. The DC conductivity of the nanocomposite increased by 2 order from the FLC materials and AC relaxation has been observed, in the nanocomposite, which was totally absent in the FLC materials.
Abstract: A monolayer of inorganic nanoparticles and a monolayer of organic molecules have been electrostatically assembled in sequence. Such assemblies or organizations exhibit electrical rectification. When the sequence of the organization is reversed, the direction of rectification becomes opposite. In both n-type ZnO/organic and organic/n-ZnO assemblies, electron flow is favorable from the n-ZnO nanoparticle to the (electron-accepting) organic molecule. While the individual components do not show any rectification, substitutes of the organic molecule tune electrical rectification. Junctions between a p-type ZnO nanoparticle and an electron-donating metal phthalocyanine favor current flow in the nanoparticle-to-phthalocyanine direction. The rectification in a junction between a nanoparticle and an organic molecule is due to the parity between free carriers in the former component and the type of carrier-accepting nature in the latter one. By observing electrical rectification with the tip of a scanning tunneling microscope, organic/inorganic hybrid nanodiodes or rectifiers on the molecular/nanoscale have been established.
Abstract: Soluble poly(3-hexylthiophene) (P3HT)-multiwalled carbon nanotube (MWNT) nanocomposites (PCNCs) are prepared by the in-situ oxidative polymerization of 3-hexylthiophene (3HT) in a dispersion of MWNT in CHCl3. The MWNT-P3HT nanocomposite produces blackish-brown solution in chloroform, making it an easily processable system. With increase in MWNT concentration the molecular weight of P3HT has increased, but at higher MWNT concentration (8% w/w) the molecular weight has decreased. The head-tail (H-T) regioregularity of the samples remains the same with that of pure P3HT. The TEM pictures of PCNC-1 and PCNC-8 [the number indicates percentage (w/w) of MWNT with respect to monomer in the composite] show uniform wrapping of MWNT with P3HT. The increase of outer diameter in wrapped MWNT decreases with increase in MWNT concentration, but the PCNC-2.5 exhibits phase segregation by the formation of separate spheroid-like species on the partially wrapped MWNT surface. The higher molecular weight P3HT produced in the PCNC-2.5 has been attributed to this difference in morphology. Type 1 P3HT crystal is formed in all the PCNCs, and melting temperature shows an increase with increasing MWNT concentration except for the PCNC-2.5 sample. The glass transition temperature (T-g) remains unchanged in the PCNCs, but the beta-transition temperature (T-beta) varies differently in the different PCNCs. The storage modulus of PCNCs has increased abruptly (maximum increase 158%) in the PCNCs than that of pure P3HT. The UV-vis spectra of PCNCs show a red shift in the pi-pi* transition band while the emission spectra show a small blue shift with increase in MWNT concentration. Fluorescence quenching occurs in the PCNCs, and it increases with increase in MWNT concentration except for the PCNC2.5 sample. The conductivity values of both undoped and doped PCNCs have increased significantly with increase in MWNT concentration. FT-IR spectra and NMR spectra indicate the presence of both CH-pi and pi-pi interaction between P3HT and MWNT. Thus, the increased conductivity and mechanical properties of P3HT in the easily processable MWNT-P3HT nanocomposite are interesting for its probable use in different optoelectronic appliances.
Abstract: Bismuth ammonium citrate complex (C24H20Bi4O28 . 6NH(3) . 10H(2)O) interacted with sodium sulphide (Na2S) in presence of beta-cyclodextrin (beta-CD) yielding Bi2S3 nanospheres. Solvothermal treatment of the bismuth complex and dimethyl sulphoxide (DMSO) produced Bi2S3 nanorods. Reaction conditions were optimized to investigate the morphology evolution of the product. Electrical properties of the nanorods were monitored in details.
Abstract: Electronically interacting composites of nanomaterials and aromatic molecules show high electrical bistability caused by the interaction between the two pi-electron rich systems. The nanomaterials introduce channels for carrier transport that switch the organic molecules to their high-conducting state. The systems exhibit read-only and random-access memory applications.
Abstract: The article reports observed electrical bistability in thin films of ZnO nanoparticles embedded in an insulating polymer matrix. From the current-voltage and impedance characteristics, they studied transport mechanisms involved in the two conducting-states. The electrical bistability in such films has been associated with a memory phenomenon. The bistability, which is reversible in nature, led to read-only and random-access memory applications in the devices, based on such nanoparticles.
Abstract: Nanowires and microfibers of silver have been synthesized by the interaction of silver nitrate (AgNO3) and starch employing hydrothermal route in an autoclave at 170 degrees C for 24 h. Different morphological modifications, e.g., microrods and spheres to microrods/wires and nanoparticles through microwire bundles to microfibers, are obtained by varying reactant concentrations.
Abstract: Steady-state, FT-IR and time-resolved spectroscopic measurements were carried out on the two novel synthesized pi-conjugated rigid naphthothiophene compounds, 7-methoxynaphtho[1,2-b]thiophene (7MNT) and 7-methoxynaphtho[1,2-b]thiophene-2-carboxylic acid (7MTCA) in chloroform (CHCl3) medium as well as in presence of TiO2 nanoparticles. 7MTCA multichromophoric system contains both electron donor (-OCH3) and acceptor functionalities, (-COOH) at the two different ends of the rigid naphthothiophene moiety whereas in 7MNT only the electron donor functional group, -OCH3, is present. Thus 7MNT looks like the donor part of 7MTCA where -COOH group overlaps, due to its free rotation, with the electron rich site 7MNT part. The experimental findings observed from steady-state absorption, fluorescence and time-resolved spectroscopic (fluorescence lifetime and transient absorption) measurements demonstrate that the survival duration of charge-separated species formed within 7MTCA due to intramolecular photoinduced electron-transfer (PET) reactions between the donor -OCH3 and acceptor -COOH functional groups, attached at the two different ends of this compound, could be enhanced by inhibiting the energy wasting charge recombination process through complexation of the carboxylate group (-COOH) with TiO2 nanoparticles. Thus, in the present investigation TiO2 appears not to act as an acceptor but its presence helps to survive or protect the charge-separated species formed within 7MTCA. The possibility of designing of low-cost artificial (model) solar energy conversion devices by linking the organic donor-acceptor (DA) systems like 7MTCA with TiO2 core is hinted. (c) 2007 Elsevier B.V. All rights reserved.
Abstract: We form pn-junctions by electrostatic binding of a p-type and an n-type ZnO nanoparticle. Current-voltage characteristics of pn-junctions are rectifying in nature. Individual components of the junction do not show any rectification. An np-junction, formed by reversing the binding sequence of the two types of nanoparticles, shows rectification in the reverse bias direction. By controlling the type of dopants in the ZnO nanoparticles, pn(+) (and n(+)p) and nn(+) (and n(+)n) junctions are formed that exhibit rectification. Current rectification in a junction between two nanoparticles shows that a depletion layer may have formed even in the quantum dot regime.
Abstract: We fabricate dye-sensitized solar cells (DSSC) using vertically oriented, high density, and crystalline array of ZnO nanowires, which can be a suitable alternative to titanium dioxide nanoparticle films. The vertical nanowires provide fast routes or channels for electron transport to the substrate electrode. As an alternative to conventional ruthenium complex, we introduce Rose Bengal dye, which acts as a photosensitizer in the dye-sensitized solar cells. The dye energetically matches the ZnO with usual KI-I-2 redox couple for dye-sensitized solar cell applications. (C) 2007 Elsevier B.V. All rights reserved.
Abstract: The authors provide two routes to increase the photocurrent of organic photodetectors that are based on electron-donor and electron-acceptor materials. During device fabrication, they introduce carbon nanotubes, which act as channels for electron transport. The channels in effect provide an approach to address the problem of low carrier mobility in the conjugated organics. The authors also make use of the (electrically) bistable nature of the acceptor material, namely, rose bengal in a favorable way. During device characterization, they switch its conductivity to decrease device resistance and yield higher photocurrent. Both the routes enhance photocurrent in these donor-acceptor-type photodetectors. (c) 2007 American Institute of Physics.
Abstract: We have introduced functionalized multiwalled carbon nanotubes (CNTs) in donor/acceptor-type photovoltaic devices. We fabricated the devices based on heterostructure between polymer-CNT composite and buckminsterfullerene (C-60) layers. Due to the functional groups of the CNTs, a homogeneous blend of CNT-polymer composite could be obtained. In the composite, the nanotubes acted as exciton dissociation sites and also hopping centers for hole transport. The CNTs in the polymer-CNT/C-60 device provided higher exciton dissociation volume and increased mobility for carrier transport. We have observed an increase in open-circuit voltage and short-circuit current in the polymer-CNT/C-60 devices as compared to the polymer/C-60 ones.
Abstract: We have observed electrical bistability and large conductance switching in functionalized carbon nanotube (CNT)-conjugated polymer composites at room temperature. The concentration of the CNTs in the polymer matrix controlled the degree of bistability. Conduction mechanism applicable in each of the conducting states has been identified. The switching had an associated memory phenomenon and was reversible in nature. In the bistable devices, the active layer retained its high-conducting state until a reverse voltage erased it. We could "write" or "erase" a state and "read" it for many cycles for random-access memory applications.
Abstract: A simple solution phase approach is described to prepare tellurium nanorods which undergo morphological modifications to yield different microstructures under varied experimental conditions. The morphology of the prepared products is drastically altered in presence of a few oxidizing agents such as sodium oxychloride (NaOCl), hydrogen peroxide (H2O2) etc. The effects of poly (sodium 4-styrene sulphonate) (PSS) and Isooctyl phenoxy poly oxyethanol (TritonX-100) on the size and shape of the products in presence of air/NaOCl have also been monitored.
Abstract: A simple solution phase approach is described to prepare tellurium nanorods which undergo morphological modifications to yield different microstructures under varied experimental conditions. The morphology of the prepared products is drastically altered in presence of a few oxidizing agents such as sodium oxychloride (NaOCl), hydrogen peroxide (H2O2) etc. The effects of poly (sodium 4-styrene sulphonate) (PSS) and Isooctyl phenoxy poly oxyethanol (TritonX-100) on the size and shape of the products in presence of air/NaOCl have also been monitored.
Abstract: Recrystallization of elemental selenium (Se) from aqueous solution in presence of sodium sulphite (Na2SO3) and sodium sulphide (Na2S) acting as complexing agents has resulted in the formation of nano and microstructures of Se having five different morphological modifications. (1) An aqueous solution of sodium selenosulphate (Na2SO3Se) obtained by dissolving Se in Na2SO3 under refluxing condition yields hemispherical microcrystals. (2) The filtrate of the above reaction mixture on aging produces hexagonal prismatic microrods of Se. Addition of Na2SO3Se solution to formalin (HCHO) at room temperature and refluxing conditions generates (3) Se nanorods, and (4) spherical microcrystals, respectively. (5) Recrystallization of Se from aqueous solution of Na2S develops flower shaped microcrystals.
Abstract: Nano-crystal embedded PbO-P2O5 glass has been prepared and characterized by XRD and TEM measurements. The ultrasonic velocity and attenuation measured within the temperature range 80-300 K show significant structure and interesting feature with the presence of nano-crystalline region. The glass samples were prepared by melt-quench method and nano-crystals of different sizes were produced by heat treatment of the glasses for different durations of heating. All the processes were carried out at or above glass transition temperature. A theoretical model that takes account of the effects of thermally activated relaxation, anharmonicity as well as microscopic elastic inhomogeneities arising out of fluctuations has been successfully applied to interpret the variation of ultrasonic velocity and attenuation data. An interesting outcome of this application has been to propose a method for the determination of the size of nano-crystals from the ultrasonic attenuation data.
Abstract: Silver selenide nanocrystals were synthesized using a chemical route by the interaction of ammoniacal silver nitrate and sodium selenosulfate in aqueous medium. The prepared samples were characterized by XRD, EDXA, and TEM. UV-VIS absorption spectrum of the nanocrystals shows that the optical band gap of the material is 1.72 eV, which is quite larger than the bulk phase of the materials. Thermal analysis exhibits that the phase changes from beta to alpha at the transition temperature 406 K. Electrical conduction and thermoelectric power measurements also show the presence of two distinct phases of the materials and characteristic changes in transport properties due to the nanosize of the materials.
Abstract: We report electrical bistability in electrostatic assembly of CdSe nanoparticles. We obtained thin films of the nanoparticles via layer-by-layer electrostatic assembly technique, which provided a nanoscale control to tune the thickness. Devices based on such thin films exhibit electrical bistability along with memory phenomenon. The bistability is due to charge confinement in the nanoparticles. Conduction mechanism changes from an injection-dominated to a bulk one during switching from a low-to a high-conducting state. Additionally, results from impedance spectroscopy show that the dielectric constant of the material increases during the transition. Both random-access and read-only memory applications are observed in these systems.
Abstract: The authors introduce dopants in vertically grown single crystalline ZnO nanowires in a controlled manner. A section of the nanowires is doped with aluminum as donor during crystal nucleation, resulting in n-n(+) junction. Current-voltage characteristics of these single nanowire junctions via scanning tunneling microscopy and mercury-probe methods are asymmetric, displaying rectifying behavior. By inversing the junction during the growth or by introducing lithium as acceptor to form a n-p junction, the directionality of current flow in the nanowires becomes reversed. The single nanowire diode junctions are very stable in ambient condition and hence open up a new dimension in nanoelectronics. (c) 2006 American Institute of Physics.
Abstract: We have observed electrical bistability and large conductance switching in functionalized carbon nanotube (CNT)-conjugated polymer composites at room temperature. The concentration of the CNTs in the polymer matrix controlled the degree of bistability. Conduction mechanism applicable in each of the conducting states has been identified. The switching had an associated memory phenomenon and was reversible in nature. In the bistable devices, the active layer retained its high-conducting state until a reverse voltage erased it. We could “write” or “erase” a state and “read” it for many cycles for random-access memory applications.
Abstract: Bismuth selenide (Bi2Se3) nanotubes have been synthesized for the first time using dimethyl formamide (DMF) by solvothermal method. Ammonium bismuth citrate (C24H20B14O28,6NH(3),10H(2)O), elemental selenium (Se) and DMF when treated solvothermally in an autoclave at 165 degrees C formed Bi2Se3 nanocrystals of different morphologies. The morphological modifications are found to depend on the duration of heat treatment and the relative proportions of the reactants. Heat treatment for 24 h yields Bi2Se3 nanotubes whereas large needle shaped structures. are produced on altering the relative proportions of the reactants during the same period. The as synthesized products were characterized by XRD, EDXA and TEM. (c) 2006 Elsevier B.V. All rights reserved.
Abstract: In situ Ag nanoparticles are produced on reduction of Ag+ with N,N-dimethylformamide in the presence of poly(vinylidene fluoride) (PVF2). The plasmon band transition is monitored with time in the reaction mixture for three sets of experiments by UV-vis spectroscopy. The plasmon band absorbance increases sigmoidally with log(time). Analysis of the data with the Avrami equation yields an exponent n value between 1.5 and 2.0, indicating two-dimensional nucleation with linear or diffusion controlled growth. The TEM study of the polymer nanocomposites (PNC) indicates both spherical and rodlike morphology for PNC0.5 and PNC2.5 samples, whereas the PNC11 sample has spherical and agglomerated structures (the numerical number associated with PNC indicates percentage (w/w) of Ag in the nanocomposite). The WAXS and FTIR studies indicate the formation of piezoelectric beta-polymorphic PVF2 in the nanocomposites. The DSC study indicates some increase of the melting point and enthalpy of fusion of PVF2 in the nanocomposite, although with increase in Ag nanoparticle concentration the increase is smaller. The crystallization temperatures of PNCs also increased, indicating nucleating effect of Ag nanoparticles in the composite. In the TGA curves, the PNCs exhibit a three-step degradation process. The degradation temperatures of PNCs are lower than that of PVF2. The storage modulus data indicate a significant reinforcement of the mechanical property in the PNCs where also the reinforcement effect decreases with increasing nanoparticle concentration. Both the loss modulus and tan delta plots indicate two peaks; the lower temperature peak has been attributed for glass transition temperature, whereas the higher one has been attributed to a similar type relaxation process for the crystalline-amorphous interface. The increase in the glass transition is marginal for the PNCs, but the increase of later transition temperature is somewhat higher. The FTIR study shows that the dipolar interaction of the >CF2 dipole with the surface charges of Ag nanoparticle stabilizes the nanoparticle in the nanocomposite.
Abstract: A simple solution phase approach using dimethyl formamide (DMF) as solvent is utilized to obtain selenium (Se) microcrystals. Different morphological modifications of the products result from varied reaction environments. Solvothermal treatment of Se with DMF in an autoclave at 170 degrees C yields rod-like, and feather-shaped microcrystalline structures while reduction of selenium dioxaide (SeO2) by DMF generates microspheres at 30 degrees C and 80 degrees C, rods admixed with spherical particles at 120 degrees C and predominantly micro rods at 150 degrees C. (C) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Abstract: The mechanical and electrical properties of three lead-vanadate glass samples, namely the conventional (regular) lead-vanadate glass, the silver oxide doped variety and the doped glass containing nanocrystalline structures developed on heating have been studied. It is found that the nanostructured ceramic has its mechanical properties enhanced in comparison with those of the conventional or doped glasses. The I-V profiles of the lead-vanadate and the doped glasses manifest ohmic behavior, while a pronounced hysteresis loop is conspicuous in the case of the nanostructured glass sample. The mechanism of conduction in the lead-vanadate glass and the effect of doping with silver oxide as well as the nanocrystalline structure generation have been investigated in detail. (c) 2006 Elsevier B.V. All rights reserved.
Abstract: This Letter reports a new method (refluxed) along with the conventional sonication method for preparation of nanoparticles of well-known electron acceptor 9-cyanoanthracene (9CNA). The photophysical properties of the nanostructured 9CNA, prepared from both the methods were investigated by steady-state and time resolved spectroscopic techniques. Nanoclusters, made from the refluxed method, are mostly one-dimensional wire-like structure whereas in the sonication method formations of both one and three-dimensional nanocluster of 9CNA were confirmed from TEM investigation. Irradiation of both the 9CNA nano dispersions results in formations of both the delocalized pi-electronic (polaron–exciton) and the locally excited states. (c) 2005 Elsevier B.V. All rights reserved.
