High-Performance Stacked TiO2-ZrO2 and Si-doped ZrO2 Metal-Insulator-Metal Capacitors

Metal-insulator-metal (MIM) capacitors for DRAM applications have been realised using stacked TiO2-ZrO2 (TiO2/ZrO2 and ZrO2/TiO2) and Si-doped ZrO2 (TiO2/Si-doped ZrO2) dielectrics. High capacitance densities (> 42 fF/mu m(2)), low leakage current densities (< 5 x 10(-7) A/cm(2) at -1 V), and sub-nm EOT (< 0.8 nm) have been achieved. The effects of constant voltage stress on the device characteristics is studied. The structural analysis of the samples is performed by X-ray diffraction measurements, and this is correlated to the electrical characteristics of the devices. The surface chemical states of the films are analyzed through X-ray photoelectron spectroscopy measurements. The doped-dielectric stack (TiO2/Si-doped ZrO2) helps to reduce leakage current density and improve reliability, with a marginal reduction in capacitance density; compared to their undoped counterparts (TiO2/ZrO2 and ZrO2/TiO2). We compare the device performance of the fabricated capacitors with other stacked high-k MIM capacitors reported in recent literature.

Effect of Size Reduction on Magnetic Ordering in Sm1-x Ca (x) MnO3 (x=0.35, 0.65 and 0.92) Manganites: Magnetic and EMR Studies

We have employed the highly sensitive electron magnetic resonance technique complimented by magnetization measurements to study the impact of size reduction on the magnetic ordering in nanosized Sm1-x Ca (x) MnO3 (x = 0.35, 0.65 and 0.92). In the bulk form, x = 0.35 sample shows a charge ordering transition at 235 K followed by a mixed magnetic phase, the sample with x = 0.65 exhibits charge order below 275 K and shows an antiferromagnetic insulator phase below 135 K while that with x = 0.92 has a ferromagnetic-cluster glass ground state. Thus, a comparative study of magnetic ground states of bulk and nanoparticles (diameter similar to 25 nm) enables us to investigate size-induced effects on different types of magnetic ordering. It is seen that in the bulk samples the temperature dependences of the EPR parameters are quite different from each other. This difference diminishes for the nanosamples where all the three samples show qualitatively similar behavior. The magnetization measurements corroborate this conclusion.

Na2.44Mn1.79(SO4)(3): a new member of the alluaudite family of insertion compounds for sodium ion batteries

Sodium-ion batteries have been extensively pursued as economic alternatives to lithium-ion batteries. Investigating the polyanion chemistry, alluaudite structured Na2Fe2II(SO4)(3) has been recently discovered as a 3.8 V positive electrode material (Barpanda et al., Nature Commun., 5: 4358, 2014). Registering the highest ever Fe-III/Fe-II redox potential (vs. Na/Na+) and formidable energy density, it has opened up a new polyanion family for sodium batteries. Exploring the alluaudite family, here we report isotypical Na2+2xMn2-xII(SO4)(3) (x = 0.22) as a novel high-voltage cathode material for the first time. Following low-temperature (ca. 350 degrees C) solid-state synthesis, the structure of this new alluaudite compound has been solved adopting a monoclinic framework (s.g. C2/c) showing antiferromagnetic ordering at 3.4 K. Synergising experimental and ab initio DFT investigation, Na2+2xMn2-xII(SO4)(3) has been found to be a potential high-voltage (ca. 4.4 V) cathode material for sodium batteries.

Energy-savvy solid-state and sonochemical synthesis of lithium sodium titanate as an anode active material for Li-ion batteries

Lithium sodium titanate insertion-type anode has been synthesized by classical solid-state (dry) and an alternate solution-assisted (wet) sonochemical synthesis routes. Successful synthesis of the target compound has been realized using simple Na- and Li-hydroxide salts along with titania. In contrast to the previous reports, these energy-savvy synthesis routes can yield the final product by calcination at 650 -750 degrees C for limited duration of 1-10 h. Owing to the restricted calcination duration (dry route for 1-2 h and wet route for 1-5 h), they yield homogeneous nanoscale lithium sodium titanate particles. Sono-chemical synthesis reduces the lithium sodium titanate particle size down to 80-100 nm vis-a-vis solid-state method delivering larger (200-500 nm) particles. Independent of the synthetic methods, the end products deliver reversible electrochemical performance with reversible capacity exceeding 80 mAh.g(-1) acting as a 1.3 V anode for Li-ion batteries. (C) 2015 Elsevier B.V. All rights reserved.

Ag-doped hydroxyapatite as efficient adsorbent for removal of Congo red dye from aqueous solution: Synthesis, kinetic and equilibrium adsorption isotherm analysis

In the present study a versatile and efficient adsorbent with high adsorption capacity for adsorption of Congo red dye in aqueous solution at ambient temperature without adjusting any pH is presented over the Ag modified calcium hydroxyapatite (CaHAp). CaHAp and Ag-doped CaHAp materials were synthesized using facile aqueous precipitation method. The physico-chemical properties of the materials were determined by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Transmission electron microscopy (TEM), UV-Visible spectroscopy, N-2 physisorption and acidity was determined by n-butylamine titration and pyridine adsorption methods. XRD analysis confirmed all adsorbents exhibit hexagonal CaHAp structure with P6(3)/m space group. TEM analysis confirms the rod like morphology of the adsorbents and the average length of the rods were in the range of 40-45 nm. Pyridine adsorption results indicate increase in number of Lewis acid sites with Ag doping in CaHAp. Adsorption capacity of CaHAp was found increased with Ag content in the adsorbents. Ag (10): CaHAp adsorbent showed superior adsorption performance among all the adsorbents for various concentrations of Congo red (CR) dye in aqueous solutions. The amount of CR dye adsorbed on Ag (10): CaHAp was found to be 49.89-267.81 mg g(-1) for 50-300 ppm in aqueous solution. A good correlation between adsorption capacity and acidity of the adsorbents was observed. The adsorption kinetic data of adsorbents fitted well with pseudo second-order kinetic model with correlation coefficients ranged from 0.998 to 0.999. The equilibrium adsorption data was found to best fit to the Langmuir adsorption isotherm model. (C) 2015 Elsevier Inc. All rights reserved.

Dispersible crystalline nanobundles of YPO4 and Ln (Eu, Tb)-doped YPO4: rapid synthesis, optical properties and bio-probe applications

Undoped and Ln(3+) (Eu and Tb)-doped crystalline nanobundles of YPO4 were prepared by a facile microwave-assisted route with water as a solvent and without using any surfactant. TEM investigations reveal that the as-prepared powder consists of lenticular-shaped nanobundles (similar to 100 nm in diameter) made of very small nanorods with diameter less than 10 nm and length varying from 20 to 50 nm. Each nanorod in turn is single crystalline, as revealed by HRTEM imaging. The as-prepared nanobundles are easily dispersible in various solvents, especially water, without any surface functionalization, which is critical for various bio-probe applications like cell and tissue imaging. The Eu- and Tb-doped YPO4 nanobundles show good photoluminescence properties and were further evaluated for their use as fluorescent biolabels. Our results show that HeLa cells labelled with Eu- and Tb-doped YPO4 nanobundles show bright red (Eu) and green (Tb) intracellular luminescence under a confocal microscope. Concentration-and time-dependent MTT cell viability assays show that the nanobundles show low toxicity towards cells which makes them promising in bioimaging field.

Injection barrier induced deviations in space charge limited conduction in doped poly(3-methylthiophene) based devices

The carrier density dependent current-voltage (J V) characteristics of electrochemically prepared poly(3-methylthiophene) (P3MeT) have been investigated in Pt/P3MeT/Al devices, as a function of temperature from 280 to 84 K. In these devices, the charge transport is found to be mainly governed by different transport regimes of space charge limited conduction (SCLC). In a lightly doped device, SCLC controlled by exponentially distributed traps (Vl+1 law, l > 1) is observed in the intermediate voltage range (0.5-2 V) at all temperatures. However, at higher bias (> 2 V), the current deviates from the usual Vl+1 law where the slope is found to be less than 2 of the logJ-logV plot, which is attributed to the presence of the injection barrier. These deviations gradually disappear at higher doping level due to reduction in the injection barrier. Numerical simulations of the Vl+1 law by introducing the injection barrier show good agreement with experimental data. The results show that carrier density can tune the charge transport mechanism in Pt/P3MeT/Al devices to understand the non-Ohmic behavior. The plausible reasons for the origin of injection barrier and the transitions in the transport mechanism with carrier density are discussed. (C) 2015 AIP Publishing LLC.

Synthesis, and crystal and electronic structure of sodium metal phosphate for use as a hybrid capacitor in non-aqueous electrolyte

Energy storage devices based on sodium have been considered as an alternative to traditional lithium based systems because of the natural abundance, cost effectiveness and low environmental impact of sodium. Their synthesis, and crystal and electronic properties have been discussed, because of the importance of electronic conductivity in supercapacitors for high rate applications. The density of states of a mixed sodium transition metal phosphate (maricite, NaMn1/3Co1/3Ni1/3PO4) has been determined with the ab initio generalized gradient approximation (GGA)+Hubbard term (U) method. The computed results for the mixed maricite are compared with the band gap of the parent NaFePO4 and the electrochemical experimental results are in good agreement. A mixed sodium transition metal phosphate served as an active electrode material for a hybrid supercapacitor. The hybrid device (maricite versus carbon) in a nonaqueous electrolyte shows redox peaks in the cyclic voltammograms and asymmetric profiles in the charge-discharge curves while exhibiting a specific capacitance of 40 F g(-1) and these processes are found to be quasi-reversible. After long term cycling, the device exhibits excellent capacity retention (95%) and coulombic efficiency (92%). The presence of carbon and the nanocomposite morphology, identified through X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) studies, ensures the high rate capability while offering possibilities to develop new cathode materials for sodium hybrid devices.

Boron-doped carbon nanoparticles: Size-independent color tunability from red to blue and bioimaging applications

Here, we report the hydrothermal synthesis of boron-doped CNPs (B-CNPs) with different size/atomic percentage of doping and size-independent color tunability from red to blue. The variation of size/atomic percentage of B is achieved by simply varying the reaction time, while the color tunability is obtained by diluting the solution. With dilution, the luminescence spectra are not only blue-shifted, the intensity increases as well. The huge blue-shift in the emission energy (similar to 1 eV) is believed to be due to the increase in the interparticle distance. The quantum yield with optimum dilution is found to increase with boron doping though it is very low as compared to CNPs and nitrogen-doped CNPs. Finally, we show that B-CNPs with a quantum yield of 0.5% can be used for bioimaging applications. (C) 2015 Elsevier Ltd. All rights reserved.

Electronic and Magnetic Properties of Yttrium-doped Silicon Carbide Nanotubes: Density Functional Theory Investigations

The electronic structure of yttrium-doped Silicon Carbide Nanotubes has been theoretically investigated using first principles density functional theory (DFT). Yttrium atom is bonded strongly on the surface of the nanotube with a binding energy of 2.37 eV and prefers to stay on the hollow site at a distance of around 2.25 angstrom from the tube. The semi-conducting nanotube with chirality (4, 4) becomes half mettalic with a magnetic moment of 1.0 mu(B) due to influence of Y atom on the surface. There is strong hybridization between d orbital of Y with p orbital of Si and C causing a charge transfer from d orbital of the Y atom to the tube. The Fermi level is shifted towards higher energy with finite Density of States for only upspin channel making the system half metallic and magnetic which may have application in spintronic devices.

Structural and Optical Modification in Bi doped As40S60 Thin Films.

The influence of substitution of Bi atom instead of S atoms on the structural and optical properties of thin films of As40S60 are reported. The density is found to be increased with the addition Bi heavy metal into As2S3. The amorphous to polycrystalline structure of the bulk sample is observed for Bi more than 7%. The glass transition temperature is found to be decreased with addition of Bi. The absorption edge shifts to shorter wavelength, thereby decreasing optical band gap of BixAs(40)S(60-x) (x= 0,2 and 4% here) film. The optical parameter change is discussed from the stand point of chemical bonds formed in the films and related to the defect states produced due to incorporation of Bi atoms in place of chalcogenide S atoms.

Hetero-atom Doped Carbon Nanotubes for Dye Degradation and Oxygen Reduction Reaction

We report the synthesis of nitrogen doped vertically aligned multi-walled (MWNCNTs) carbon nanotubes by pyrolysis and its catalytic performance for degradation of methylene blue (MB) dye & oxygen reduction reaction (ORR). The degradation of MB was monitored spectrophotometrically with time. Kinetic studies show the degradation of MB follows a first order kinetic with rate constant k=0.0178 min(-1). The present rate constant is better than that reported for various supported/non-supported semiconducting nanomaterials. Further ORR performance in alkaline media makes MWNCNTs a promising cost-effective, fuel crossover tolerance, metal-free, eco-friendly cathode catalyst for direct alcohol fuel cell.

Fluoranthene derivatives as blue fluorescent materials for non-doped organic light-emitting diodes

In this study, we report synthesis of symmetrically and non-symmetrically functionalized fluoranthene-based blue fluorescent molecular materials for non-doped electroluminescent devices. The solid state structure of these fluorophores has been established by single crystal X-ray diffraction analysis. Furthermore, a detailed experimental and theoretical study has been performed to understand the effect of substitution of symmetric and non-symmetric functional groups on optical, thermal and electrochemical properties of fluoranthene. These materials exhibit a deep blue emission and high PLQY in solution and solid state. The vacuum deposited, non-doped electroluminescent devices with the device structure ITO/NPD (15 nm)/CBP (15 nm)/EML (40 nm)/TPBI (30 nm)/LiF (1 nm)/Al were fabricated and characterized. A systematic shift in the peak position of EL emission was observed from sky blue to bluish-green with EL maxima from 477 nm to 490 nm due to different functional groups on the periphery of fluoranthene. In addition, a high luminance of >= 2000 cd m(-2) and encouraging external quantum efficiency (EQE) of 1.1-1.4% were achieved. A correlation of the molecular structure with device performance has been established.

Study of coexisting phases in Bi doped La0.67Sr0.33MnO3

We report the remarkable phase separation behavior in La0.67Sr0.33MnO3 doped with Bi3+ ion at La site. The temperature dependent resistivity and magnetization of La0.67-xBixSr0.33MnO3 (x>0) show the presence of phase separation of ferromagnetic metallic and charge ordered antiferromagnetic insulating phases. Markedly, the field dependant magnetization studies of La0.67-xBixSr0.33MnO3 (x=0.3) show the metamagnetic nature of ferromagnetic metallic state implying the competition of coexisting ferromagnetic metallic and charge ordered antiferromagnetic phases. The electron spin resonance and exchange bias studies of La0.67-xBixSr0.33MnO3 (x=0.4 and 0.5) substantiate the coexistence of ferromagnetic clusters in antiferromagnetic matrix. (C) 2016 Elsevier B.V. All rights reserved.

White luminescence in Dy3+ doped BiOCl phosphors and their Judd-Ofelt analysis

White-light emitting Dy3+ doped layered BiOCl phosphors were synthesized by the solid state route and their structure was confirmed by the Rietveld refinement method. On substitution of Dy3+ ion to Bi3+-site in BiOCl, the photoluminescence spectra exhibit blue (F-4(9/2) -> H-6(15/2)), yellow (F-4(9/2) -> H-6(13/2)) and red (F-4(9/2) -> H-6(11/2)) emissions which function together to generate white light. It was found that the emission intensity increases up to 9 mol% of Dy3+ and then quenched due to dipole-dipole interaction. Judd-Ofelt theory and radiative properties suggest that the present phosphors have a long lifetime, high quantum efficiency, excellent color purity and better stimulated emission cross-section compared to reported Dy3+ doped compounds. The obtained color chromaticity results are close to the National Television System Committee standard and clearly establish the bright prospects of these phosphors in white luminescence. (C) 2015 Elsevier Ltd. All rights reserved.