Effect of hybridizing micron-sized Ti with nano-sized SiC on the microstructural evolution and mechanical response of Mg-5.6Ti composite

In this work, the effect of hybridizing micro-Ti with nano-SiC particulates on the microstructural and the mechanical behaviour of Mg-5.6Ti composite were investigated. Mg materials containing micron-sized Ti particulates hybridized with different amounts of nano-size SiC particulates were synthesized using the disintegrated melt deposition method followed by hot extrusion. The microstructural and mechanical behaviour of the developed Mg hybrid composites were studied in comparison with Mg-5.6Ti. Microstructural characterization revealed grain refinement attributed to the presence of uniformly distributed micro-Ti particles embedded with nano-SiC particulates. Electron back scattered diffraction (EBSD) analyses of Mg-(5.6Ti + 1.0SiC)(BM) hybrid composite showed relatively more localized recrystallized grains and lesser tensile twin fraction, when compared to Mg-5.6Ti. The evaluation of mechanical properties indicated that the best combination of strength and ductility was observed in the Mg-(5.6Ti + 1.0SiC)(BM) hybrid composites. The superior strength properties of the Mg-(5.6Ti + x-SiC)(BM) hybrid composites when compared to Mg-5.6Ti is attributed to the presence of nano-reinforcements, the uniform distribution of the hybridized particles and the better interfacial bonding between the matrix and the reinforcement particles, achieved by nano-SiC addition.

Tuning the photoluminescence of ZnO thin films by indium doping

Zinc Oxide (ZnO) and indium doped ZnO (IZO) thin films with different indium compositions were grown on p-type boron doped Si substrates by pulsed laser deposition (PLD). The effect of indium concentration on the structural, optical and electrical properties of the film was studied. XRD, XPS and Raman studies confirm the single phase formation and successful doping of In in to ZnO. We observed various photoluminescence emissions, ranging from UV to visible, with the incorporation of In into ZnO. Room temperature Current-Voltage (I-V) characteristics showed good p-n junction properties for n-type-undoped and In doped ZnO with p-type substrates. The turn on voltage was observed to be decreasing with increase in In composition.

A comparative study of room temperature ferromagnetism in MgO films deposited by rf/dc sputtering using high purity Mg and MgO targets

Thin films of nanocrystalline MgO were deposited on glass/Si substrates by rf/dc sputtering from metallic Mg, and ceramic MgO targets. The purpose of this study is to identify the differences in the properties, magnetic in particular, of MgO films obtained on sputter deposition from 99.99% pure metallic Mg target in a controlled Nitrogen + Oxygen partial pressure (O(2)pp)] atmosphere as against those deposited using an equally pure ceramic MgO target in argon + identical oxygen ambience conditions while maintaining the same total pressure in the chamber in both cases. Characterization of the films was carried out by X-ray diffraction, focussed ion beam cross sectioning, atomic force microscopy and SQUID-magnetometry. The `as-obtained' films from pure Mg target are found to be predominantly X-ray amorphous, while the ceramic MgO target gives crystalline films, (002) oriented with respect to the film plane. The films consisted of nano-crystalline grains of size in the range of about 0.4 to 4.15 nm with the films from metallic target being more homogeneous and consisting of mostly subnanometer grains. Both the types of films are found to be ferromagnetic to much above room temperature. We observe unusually high maximum saturation magnetization (MS) values of 13.75 emu/g and similar to 4.2 emu/g, respectively for the MgO films prepared from Mg, and MgO targets. The origin of magnetism in MgO films is attributed to Mg vacancy (V-Mg), and 2p holes localized on oxygen sites. The role of nitrogen in enhancing the magnetic moments is also discussed.

The effect of Se doping on spectroscopic and electrical properties of GeTe

Selenium doped thin films of GeTe alloys were investigated for their structural modifications by X-ray Diffraction, Fourier Transform Infrared Spectroscopy, X-ray photoelectron Spectroscopy (XPS) and Raman Spectroscopy. The band gap increase from 0.69 to 1.10 eV with increasing Se addition signifies the possibility of band gap tuning in the material. Disorder decreases, band widens and conductivity saturates about 0.20 at.% of Se addition. Structural changes are explained by the bond theory of solids. The as-deposited films are amorphous and 0.50 at.% Se alloy forms a homogeneous amorphous phase with a mixture of Ge-Se and Te-Se bonds. The XPS core level spectra and Raman spectra investigation clearly indicate the formation of Ge-Se, GeTe2 and Te-Se bonds with Se addition. Crystallization temperature is found to be increasing with Se and the 0.10 at.% Se alloy is found to have a higher resistance contrast compared to other Se concentration alloys. Up to 0.10 at.% of Se addition can enhance GeTe phase change memory properties. (C) 2013 Elsevier B.V. All rights reserved.

Anthracene-Containing Conjugated Polymer Showing Four Optical Transitions Upon Doping: A Spectroscopic Study

An anthracene-containing poly(arylene-ethynylene)-alt-poly(arylene-vinylene) (PAE-PAV) of general constitutional unit (PhCCAnthrCCPhCHCHAnthrCHCH)(n) bearing two 2-ethylhexyloxy solubilizing side chains on each phenylene (Ph) unit has been synthesized and characterized. The basic electrochemical characterization was done, showing the existence of two non-reversible oxidation and one reversible reduction peaks. The optical properties, the real and imaginary part of the dielectric function, were probed using spectroscopic ellipsometry (SE). The vibrational structure of the undoped/doped polymer was investigated using Fourier transformed infrared spectroscopy. A strong change in the polaronic absorption was observed during the doping, which after modeling revealed the existence of two separated transitions. The optical changes upon doping were additionally recorded using the SE technique. Similar to the results from FT-IR spectroscopy, two new in-the-gap absorptions were found. Moreover, the electrical conductivity as well as the mobility of positive carriers were measured. In the undoped state, the conductivity of the polymer was found to be below the detection limit (doping the conductivity increased to 0.69 S cm(-1). (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 338-346

Nanostructured CexZn1-xO thin films: Influence of Ce doping on the structural, optical and electrical properties

Thin films of CexZn1-xO thin films were deposited on glass substrates at 400 degrees C by nebulizer spray pyrolysis technique. Ce doping concentration (x) was varied from 0 to 10%, in steps of 2.5%. X-ray diffraction reveals that all the films have polycrystalline nature with hexagonal crystal structure and high preferential orientation along (002) plane. Optical parameters such as; transmittance, band gap energy, refractive index (n), extinction coefficient (k), complex dielectric constants (epsilon(r), epsilon(i)) and optical conductivity (sigma(r), sigma(i)) have been determined and discussed with respect to Ce concentration. All the films exhibit transmittance above 80% in the wavelength range from 330 to 2500 nm. Optical transmission measurements indicate the decrease of direct band gap energy from 3.26 to 3.12 eV with the increase of Ce concentration. Photoluminescence spectra show strong near band edge emission centered similar to 398 nm and green emission centered similar to 528 nm with excitation wavelength similar to 350 nm. High resolution scanning electron micrographs indicate the formation of vertical nano-rod like structures on the film surface with average diameter similar to 41 nm. Electrical properties of the Ce doped ZnO film have been studied using ac impedance spectroscopy in the frequency range from 100 Hz-1 MHz at different temperatures. (C) 2013 Elsevier B.V. All rights reserved.

Microstructural evolution and mechanical properties of Mg composites containing nano-B4C hybridized micro-Ti particulates

In this work, the microstructural evolution and mechanical properties of extruded Mg composites containing micro-Ti particulates hybridized with varying contents of nano-B4C are investigated, and compared with Mg-5.6Ti. Microstructural characterization showed the presence of uniformly distributed micro-Ti particles embedded with nano-B4C particulates that resulted in significant grain refinement. Electron back scattered diffraction (EBSD) analyses of Mg-(5.6Ti + x-B4C)(BM) hybrid composites showed that the addition of hybridized particle resulted in relatively more recrystallized grains, realignment of basal planes and extension of weak basal fibre texture when compared to Mg-5.6Ti. The evaluation of mechanical properties indicated improved strength with ductility retention in Mg-(5.6Ti + x-B4C)(BM) hybrid composites. When compared to Mg-5.6Ti, the superior strength properties of the Mg-(5.6Ti + xB(4)C)(BM) hybrid composites are attributed to the presence of nano-reinforcements, the uniform distribution of the hybridized particles, better interfacial bonding between the matrix and the reinforcement particles and the matrix grain refinement achieved by nano-B4C addition. The ductility enhancement obtained in hybrid composites can be attributed to the fibre texture spread and favourable basal plane orientation achieved due to nano B4C addition. (C) 2013 Elsevier B.V. All rights reserved.

Doping a Correlated Band Insulator: A New Route to Half-Metallic Behavior

We demonstrate in a simple model the surprising result that turning on an on-site Coulomb interaction U in a doped band insulator leads to the formation of a half-metallic state. In the undoped system, we show that increasing U leads to a first order transition at a finite value U-AF between a paramagnetic band insulator and an antiferomagnetic Mott insulator. Upon doping, the system exhibits half-metallic ferrimagnetism over a wide range of doping and interaction strengths on either side of U-AF. Our results, based on dynamical mean field theory, suggest a new route to half metallicity, and will hopefully motivate searches for new materials for spintronics.

Effect Of Mo Doping On The Electrical Properties Of VO2 Phase

Solution combustion synthesis technique was adopted to synthesize V2O5, and Mo doped phases, The as-synthesized V2O5, has been reduced by a novel reduction technique to form VO2 typephase. The monophasic nature of the samples as revealed by XRD data and systematic shift in peak position indicated solid solubility up to 2 at % of Mo in VO2 lattice. The crystallite size was found to similar to 40 nm. Particle size measurement carried out using Transmission electron microscope ( TEM) agreed with XRD experiments. Scanning electron microscope revealed the morphology of the particles to be plate like and bimodal. Variation in the metal- insulator transition temperature as a function of doping was investigated by 4-probe electrical resistivity measurement on sintered ceramics.

Biodegradable Mg and Mg based alloys for biomedical implants

Mg and its alloys become natural biomaterials as the elemental Mg is found in the human body in abundance and their mechanical properties being akin to the natural bone as well as due to their inherent bioabsorbable/bioresorbable property. This paper discusses the development of new Mg alloys and their corrosion characteristics in detail. The latest advancements in coating of Mg alloys to control their degradation rate are also reviewed along with the future challenges that need to be addressed.

Tailoring the Microstructural, Optical, and Electrical Properties of Nanocrystalline WO3 Thin Films Using Al Doping

We have studied the influence of Al doping on the microstructural, optical, and electrical properties of spray-deposited WO3 thin films. XRD analyses confirm that all the films are of polycrystalline WO3 in nature, possessing monoclinic structure. EDX profiles of the Al-doped films show aluminum peaks implying incorporation of Al ions into WO3 lattice. On Al doping, the average crystallite size decreases due to increase in the density of nucleation centers at the time of film growth. The observed variation in the lattice parameter values on Al doping is attributed to the incorporation of Al ions into WO3 lattice. Enhancement in the direct optical band gap compared to the undoped film has been observed on Al doping due to decrease in the width of allowed energy states near the conduction band edge. The refractive indices of the films follow the Cauchy relation of normal dispersion. Electrical resistivity compared to the undoped film has been found to increase on Al doping.

Synthesis and photoluminescence properties of a novel Sr2CeO4:Dy3+ nanophosphor with enhanced brightness by Li+ co-doping

A series of Dy3+ (0.5-9 mol%) and Li+ (0.5-3 mol%) co-doped strontium cerate (Sr2CeO4) nanopowders are synthesized by low temperature solution combustion synthesis. The effects of Li+ doping on the crystal structure, chemical composition, surface morphology and photoluminescence properties are investigated. The X-ray diffraction results confirm that all the samples calcined at 900 degrees C show the pure orthorhombic (Pbam) phase. Scanning electron microscopy analysis reveals that the particles adopt irregular morphology and the porous nature of the product. Room temperature photoluminescence results indicate that the phosphor can be effectively excited by near UV radiation (290 to 390 nm) which results in the blue (484 nm) and yellow (575 nm) emission. Furthermore, PL emission intensity and wavelength are highly dependent on the concentration of Li+ doping. The emission intensity is enhanced by similar to 3 fold with Li+ doping. White light is achieved by merely varying dopant concentration. The colour purity of the phosphor is confirmed by CIE co-ordinates (x = 0.298, y = 0.360). The study demonstrates a simple and efficient method for the synthesis of novel nanophosphors with enhanced white emission.

Using heat treatment effects and EBSD analysis to tailor microstructure of hybrid Mg nanocomposite for enhanced overall mechanical response

In this study, a detailed investigation on the effect of heat treatment on the microstructural characteristics, texture evolution and mechanical properties of Mg-(5.6Ti+2.5B(4)C)(BM) hybrid nanocomposite is presented. Optimised heat treatment parameters, namely, heat treatment temperature and heat treatment time, were first identified through grain size and microhardness measurements. Initially, heat treatment of composites was conducted at temperature range between 100 and 300 degrees C for 1 h. Based on optical microscopic analysis and microhardness measurements, it was evident that significant grain growth and reduction in microhardness occurred for temperatures > 200 degrees C. The cutoff temperature that caused significant grain growth/matrix softening was thus identified. Second, at constant temperature (200 degrees C), the effect of variation of heat treatment time was carried out (ranging between 1 and 5 h) so as to identify the range wherein increase in average grain size and reduction in microhardness occurred. Furthering the study, the effect of optimised heat treatment parameters (200 degrees C, 5 h) on the microstructural texture evolution and hence, on the tensile and compressive properties of the Mg-(5.6Ti+2.5B(4)C)(BM) hybrid nanocomposite was carried out. From electron backscattered diffraction (EBSD) analysis, it was identified that the optimised heat treatment resulted in recrystallisation and residual stress relaxation, as evident from the presence of similar to 87% strain free grains, when compared to that observed in the non-heat treated/as extruded condition (i.e. 2.2 times greater than in the as extruded condition). For the heat treated composite, under both tensile and compressive loads, a significant improvement in fracture strain values (similar to 60% increase) was observed when compared to that of the non-heat treated counterpart, with similar to 20% reduction in yield strength. Based on structure-property correlation, the change in mechanical characteristics is identified to be due to: (1) the presence of less stressed matrix/reinforcement interface due to the relief of residual stresses and (2) texture weakening due to matrix recrystallisation effects, both arising due to heat treatment.

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.

Enhancing the photocatalytic efficiency of sprayed ZnO thin films through double doping (Sn plus F) and annealing under different ambiences

Doubly (Sn + F) doped zinc oxide (ZnO:Sn:F) thin films were deposited onto glass substrates using a simplified spray pyrolysis technique. The deposited films were annealed at 400 degrees C under two different ambiences (air and vacuum) for 2 h. The photocatalytic activity of these films was assessed through photocatalytic decolorization kinetics of Methylene Blue (MB) dye and the decolorization efficiency of the annealed films was compared with that of their as-deposited counterpart. The photocatalytic studies reveal that the ZnO:Sn:F films annealed under vacuum environment exhibits better photocatalytic efficiency when compared with both air annealed and as-deposited films. The SEM and TEM images depict that the surface of each of the films has an overlayer comprising of nanobars formed on a bottom layer, having spherical grains. The studies show that the diameter of the nanobars plays crucial role in enhancing the photocatalytic activity of the ZnO:Sn:F films. The structural, optical and electrical studies substantiate the discussions on the photocatalytic ability of the deposited films. (C) 2014 Elsevier B.V. All rights reserved.