Low temperature and self catalytic growth of ultrafine ITO nanowires by electron beam evaporation method and their optical and electrical properties

We report the self catalytic growth of Sn-doped indium oxide (ITO) nanowires (NWs) over a large area glass and silicon substrates by electron beam evaporation method at low substrate temperatures of 250-400 degrees C. The ITO NWs growth was carried out without using an additional reactive oxygen gas and a metal catalyst particle. Ultrafine diameter (similar to 10-15 nm) and micron long ITO NWs growth was observed in a temperature window of 300-400 degrees C. Transmission electron microscope studies confirmed single crystalline nature of the NWs and energy dispersive spectroscopy studies on the NWs confirmed that the NWs growth proceeds via self catalytic vapor-liquid-solid (VLS) growth mechanism. ITO nanowire films grown on glass substrates at a substrate temperature of 300-400 degrees C have shown similar to 2-6% reflection and similar to 70-85% transmission in the visible region. Effect of deposition parameters was systematically investigated. The large area growth of ITO nanowire films would find potential applications in the optoelectronic devices. (C) 2014 Elsevier Ltd. All rights reserved.

Room Temperature Growth of Ultrathin Au Nanowires with High Areal Density over Large Areas by in Situ Functionalization of Substrate

Although ultrathin Au nanowires (similar to 2 nm diameter) are expected to demonstrate several interesting properties, their extreme fragility has hampered their use in potential applications. One way to improve the stability is to grow them on substrates; however, there is no general method to grow these wires over large areas. The existing methods suffer from poor coverage and associated formation of larger nanoparticles on the substrate. Herein, we demonstrate a room temperature method for growth of these nanowires with high coverage over large areas by in situ functionalization of the substrate. Using control experiments, we demonstrate that an in situ functionalization of the substrate is the key step in controlling the areal density of the wires on the substrate. We show that this strategy works for a variety of substrates ranging like graphene, borosil glass, Kapton, and oxide supports. We present initial results on catalysis using the wires grown on alumina and silica beads and also extend the method to lithography-free device fabrication. This method is general and may be extended to grow ultrathin Au nanowires on a variety of substrates for other applications.

Ultrathin Au nanowires supported on rGO/TiO2 as an efficient photoelectrocatalyst

We report the synthesis of stable rGO/TiO2/Au nanowire hybrids showing excellent electrocatalytic activity for ethanol oxidation. Phase-pure anatase TiO2 nanoparticles (similar to 3 nm) were grown on GO sheets followed by the growth of ultrathin Au nanowires leading to the formation of a multidimensional ternary structure (0-D TiO2 and 1-D Au on 2-D graphene oxide). The oleylamine used for the synthesis of the Au nanowires not only leads to stable Au nanowires anchored on the GO sheets but also leads to the functionalization and room temperature reduction of GO. Using control experiments, we delineate the role of the three components in the hybrid and show that there is a significant synergy. We show that the catalytic activity for ethanol oxidation primarily stems from the Au nanowires. While TiO2 triggers the formation of oxygenated species on the Au nanowire surface at a lower potential and also imparts photoactivity, rGO provides a conducting support to minimize the charge transfer resistance in addition to stabilizing the Au nanowires. Compared with nanoparticle hybrids, the nanowire hybrids display a much better electrocatalytic performance. In addition to high efficiency, the nanowire hybrids also show a remarkable tolerance towards H2O2. While our study has a direct bearing on fuel cell technology, the insights gained are sufficiently general such that they provide guiding principles for the development of multifunctional ternary hybrids.

Giant Magnetoresistance and Related Properties of Rare Earth Manganates and Other Oxide Systems

Giant magnetoresistance (GMR), which was until recently confined to magnetic layered and granular materials, as well as doped magnetic semiconductors, occurs in manganate perovskites of the general formula Ln(1-x)A(x)MnO(3) (Ln = rare earth; A = divalent ion). These manganates are ferromagnetic at or above a certain value of x (or Mn4+ content) and become metallic at temperatures below the curie temperature, T-c. GMR is generally a maximum close to T-c or the insulator-metal (I-M) transition temperature, T-im. The T-c and %MR are markedly affected by the size of the A site cation, [r(A)], thereby affording a useful electronic phase diagram when T-c or T-im is plotted against [r(A)]. We discuss GMR and related properties of manganates in polycrystalline, thin-film, and single-crystal forms and point out certain commonalities and correlations. We also examine some unusual features in the electron-transport properties of manganates, in particular charge-ordering effects. Charge ordering is crucially dependent on [r(A)] or the e(g) band width, and the charge-ordered insulating state transforms to a metallic ferromagnetic state on the application of a magnetic field.

Studies on aluminum-isopropoxide doped poly(ethylene oxide), poly(vinyl alcohol), and poly(ethylene oxide)-poly(vinyl alcohol) blends

Poly( ethylene oxide), poly(vinyl alcohol): and their blend in a 40 : 60 mole ratio were doped with aluminum isopropoxide. Their structural, thermal, and electrical properties were studied. Aluminum isopropoxide acts as a Lewis acid and thus significantly influences the electrical properties of the polymers and the blend. It also acts as a scavanger for the trace quantities of water p-resent in them, thereby reducing the magnitude of proton transport. It also affects the structure of polymers that manifests in the thermal transformation and decomposition characteristics.

Mesostructured lamellar chromium oxide

Mesostructured lamellar chromium oxide with an interlayer separation of 29 Angstrom has been prepared by employing a cationic surfactant. The introduction of phosphate groups in the oxide increases the interlayer separation to 32 Angstrom.

Synthesis of platestacks and microtowers of zinc by thermal evaporation

Zinc microtower and platestacks were synthesized by thermal evaporation of zinc. This synthesis was carried out under high vacuum conditions in the absence of catalyst and carrier gas. The morphology, composition and microstructural properties of the Zn nanostructures were studied by XRD, SEM and TEM. The synthesized microtowers and platestacks were single crystalline in nature. These microtowers and platestacks showed a layered structures consisting of several hexagonal nanoplates. Based on the morphological and composition analysis, we have proposed a vapor-solid mechanism to explain the growth of these nanostructures.

N-acetyl cysteine enhances imatinib-induced apoptosis of Bcr-Abl(+) cells by endothelial nitric oxide synthase-mediated production of nitric oxide

Imatinib, a small-molecule inhibitor of the Bcr-Abl kinase, is a successful drug for treating chronic myeloid leukemia (CML). Bcr-Abl kinase stimulates the production of H2O2, which in turn activates Abl kinase. We therefore evaluated whether N-acetyl cysteine (NAC), a ROS scavenger improves imatinib efficacy. Effects of imatinib and NAC either alone or in combination were assessed on Bcr-Abl(+) cells to measure apoptosis. Role of nitric oxide (NO) in NAC-induced enhanced cytotoxicity was assessed using pharmacological inhibitors and siRNAs of nitric oxide synthase isoforms. We report that imatinib-induced apoptosis of imatinib-resistant and imatinib-sensitive Bcr-Abl(+) CML cell lines and primary cells from CML patients is significantly enhanced by co-treatment with NAC compared to imatinib treatment alone. In contrast, another ROS scavenger glutathione reversed imatinib-mediated killing. NAC-mediated enhanced killing correlated with cleavage of caspases, PARP and up-regulation and down regulation of pro- and anti-apoptotic family of proteins, respectively. Co-treatment with NAC leads to enhanced production of nitric oxide (NO) by endothelial nitric oxide synthase (eNOS). Involvement of eNOS dependent NO in NAC-mediated enhancement of imatinib-induced cell death was confirmed by nitric oxide synthase (NOS) specific pharmacological inhibitors and siRNAs. Indeed, NO donor sodium nitroprusside (SNP) also enhanced imatinib-mediated apoptosis of Bcr-Abl(+) cells. NAC enhances imatinib-induced apoptosis of Bcr-Abl(+) cells by endothelial nitric oxide synthase-mediated production of nitric oxide.

Macroporous metal oxide foams through self-sustained combustion reactions

A number of macroporous metal oxide foams were prepared through self-sustained combustion reactions starting from dough made of the corresponding metal nitrate, urea and starch. The nitrate ion acts as an oxidizing agent, urea as fuel and starch as an organic binder. The metal oxide foams are characterized by scanning electron microscopy and powder X-ray diffraction.

Activities in the $FeTiO_{3}-NiTiO_{3}$ Solid Solution from Alloy-Oxide Equilibria at 1273 K

Nine tie-lines between Fe-Ni alloys and FeTiO3-NiTiO3 solid solutions were determined at 1273 K. Samples were equilibrated in evacuated quartz ampoules for periods up to 10 days. Compositions of the alloy and oxide phases at equilibrium were determined by energy-dispersive x-ray spectroscopy. X-ray powder diffraction was used to confirm the results. Attainment of equilibrium was verified by the conventional tie-line rotation technique and by thermodynamic analysis of the results. The tie-lines are skewed toward the FeTiO3 corner. From the tie-line data and activities in the Fe-Ni alloy phase available in the literature, activities of FeTiO3 and NiTiO3 in the ilmenite solid solution were derived using the modified Gibbs-Duhem technique of Jacob and Jeffes [K.T. Jacob and J.H.E. Jeffes, An Improved Method for Calculating Activities from Distribution Equilibria, High Temp. High Press., 1972, 4, p 177-182]. The components of the oxide solid solution exhibit moderate positive deviations from Raoult's law. Within experimental error, excess Gibbs energy of mixing for the FeTiO3-NiTiO3 solid solution at 1273 K is a symmetric function of composition and can be represented as: Delta G(E) = 8590 (+/- 200) X-FeTiO3 X-NiTiO3 J/mol Full spectrum of tie-lines and oxygen potentials for the three-phase equilibrium involving Fe-Ni alloys, FeTiO3-NiTiO3 solid solutions, and TiO2 at 1273 K were computed using results obtained in this study and data available in the literature.

On the dielectric dispersion and absorption in nanosized manganese zinc mixed ferrites

The temperature and frequency dependence of dielectric permittivity and dielectric loss of nanosized Mn1-xZnxFe2O4 (for x = 0, 0.2, 0.4, 0.6, 0.8, 1) were investigated. The impact of zinc substitution on the dielectric properties of the mixed ferrite is elucidated. Strong dielectric dispersion and broad relaxation were exhibited by Mn1-xZnxFe2O4. The variation of dielectric relaxation time with temperature suggests the involvement of multiple relaxation processes. Cole-Cole plots were employed as an effective tool for studying the observed phenomenon. The activation energies were calculated from relaxation peaks and Cole-Cole plots and found to be consistent with each other and indicative of a polaron conduction.

Magnetization, magnetotransport and electron magnetic resonance studies of nanoparticles and nanowires of Pr0.5Sr0.5MnO3

In this paper, we present the preparation and characterization of nanoparticles and nanowires of Pr0.5Sr0.5MnO3 (PSMO). The main results of this investigation are as follows: (a) a comparison with the properties of the bulk material shows that the ferromagnetic (FM) transition at 270 K remains unaffected but the anti-ferromagnetic (AFM) transition at TN = 150 K disappears in the nanoparticles, (b) the size induced ground state magnetic phase (below 150 K) is predominantly FM, coexisting with a residual AFM phase, and (c) the temperature dependence of magnetic anisotropy shows complex behaviour, being higher in the nanoparticles at high temperatures and lower at moderately lower temperatures in comparison with the bulk. The results obtained from the extensive magnetization, magnetotransport and electron magnetic resonance studies made on various samples are presented and discussed in detail.

Remarkable Capacity Retention of Nanostructured Manganese Oxide upon Cycling as an Electrode Material for Supercapacitor

Electrochemical capacity retention of nearly X-ray amorphous nanostructured manganese oxide (nanoMnO2) synthesized by mixing directly KMnO4 with ethylene glycol under ambient conditions for supercapacitor studies is enhanced significantly. Although X-ray diffraction (XRD) pattern of nanoMnO2 shows poor crystallinity, it is found that by Mn K-edge X-ray absorption near edge structure (XANES) measurement that the nanoMnO2 obtained is locally arranged in a δ-MnO2-type layered structure composed of edge-shared network of MnO6 octahedra. Field emission scanning electron microscopy and XANES measurements show that nanoMnO2 contains nearly spherical shaped morphology with δ-MnO2 structure, and 1D nanorods of α-MnO2 type structure (powder XRD) in the annealed (600 °C) sample. Volumetric nitrogen adsorption−desorption isotherms, inductively coupled plasma analysis, and thermal analysis are carried out to obtain physicochemical properties such as surface area (230 m2 g−1), porosity of nanoMnO2 (secondary mesopores of diameter 14.5 nm), water content, composition, etc., which lead to the promising electrochemical properties as an electrode for supercapacitor. The nanoMnO2 shows a very high stability even after 1200 cycles with capacity retention of about 250 F g−1.

Using lead sulphate instead of lead oxide in flux growth of yttrium iron garnet(YIG) crystals

Crystal growth of YIG from fluxes containing lead sulphate in place of lead oxide in the usual lead oxide-lead fluoride-boron oxide flux system has been tried. Lead sulphate decomposes during crystal growth giving lead oxide and sulphur trioxide. Due to the influence of sulphur trioxide in the system the yield of crystals almost doubles. There is no change either in the morphology of the crystals or their lattice parameter. It is possible that solubility of YIG is different in the new flux and the changed solubility causes the increase in yield of crystals.

A Method for the Deposition of Transparent Conducting Thin-Films of Tin Oxide

A modified method has been developed for the deposition of transparent semiconducting thin films of tin oxide, involving the chemical vapour phase oxidation of tin iodide. These films show sheet resistances greater than 100 Ω/□ and an average optical transmission in the visible range exceeding 80%. The method avoids uncontrolled contamination, resulting in better reproducibility of the films. The films showed direct and indirect transitions and the possibility of an indirect forbidden transition. X-ray diffraction studies reveal that the films are polycrystalline. The low mobility values of the films have been attributed to the grain boundary scattering effect.