Growth mechanism of the Nb(X)Si-2 and [Nb(X)](5)Si-3 phases by reactive diffusion in Nb (X = Ti, Mo, or Zr)-Si systems

The effects of Mo, Ti, and Zr on the diffusion and growth of the Nb(X)Si-2 and Nb(X)(5)Si-3 phases in an Nb(X)-Si system are analyzed. The integrated diffusion coefficients are determined from diffusion couple experiments and compared with the data previously calculated in a binary Nb-Si system. The growth rates of both phases are affected by the addition of Mo and Zr, whereas the addition of Ti has no effect. The atomic mechanism of diffusion is also discussed based on the crystal structure and the possible changes in the defect concentrations due to alloying. Finally, the growth mechanism of the phases is discussed on the basis of a physico-chemical approach. (C) 2011 Elsevier Ltd. All rights reserved.

Thermoelectric properties of indium filled and germanium doped Co4Sb12 skutterudites

In-filled and Ge-doped Co4Sb12 skutterudites materials were synthesized by an induction melting process which was followed by annealing at 650 degrees C for 7 days. A structural, compositional, and morphological study was carried out by X-ray diffraction (XRD), electron probe micro analysis (EPMA), and scanning electron microscopy (SEM). The formation of a single skutterudite phase (delta-CoSb3) was confirmed by XRD and the composition of all the samples was verified by EPMA. The homogeneity and morphology of the samples was observed by potential Seebeck microprobe (PSM) and SEM, respectively. The PSM result confirmed the inhomogeneity of the samples. The temperature dependence of the Seebeck coefficient, electrical conductivity, and thermal conductivity were measured in the temperature range of 300-650 K. The samples of In0.16Co4Sb12-xGex (x = 0.05, 0.1, and 0.2) show a negative Seebeck coefficient confirming an n-type conductivity and the In0.16Co4Sb11.7Ge0.3 sample shows a positive Seebeck coefficient confirming a p-type conductivity. There was a change in the Seebeck coefficient from an n-type to a p-type at the doping concentration of x = 0.3 due to the excess Ge which increases in hole carrier concentration. Electrical conductivity decreases with an increase in Ge doping concentrations and with increases in temperature due to the bipolar effect. Thermal conductivity increases with an increase in carrier concentration and decreases when the temperature is increased. The highest ZT = 0.58 was achieved by In0.16Co4 Sb11.95Ge0.05 at 673K and In-filled and Ge-doped Co4Sb12 was not effective in improving the figure of merit. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3677982]

Photoluminescence study of mixed doped Ge-Se-In-Bi glasses

Photoluminescence studies, carried out using the Fourier Transform method rather than the conventional monochromator-dispersion method,are reported on glassy samples of indium-bismuth mixed doped Ge (10) Se(90-x-y) In (x) Bi (y) system (x,y = 5,10). The amorphous Bi2Se3 is found to be n-type like the crystalline counterpart. The possible contributions from microscopic cluster-level phase separation of Bi2Se3 and from the defects to the change in conductivity from p- to n- typein this system is discussed. The similar situation in related systems is also pointed out.

Gallium and indium co-doped ZnO thin films for white light emitting diodes

Ga and In co-doped ZnO (GIZO) thin films together with ZnO, In-doped ZnO (IZO), Ga-doped ZnO (GZO), and IZO/GZO multilayer for comparison, were grown on corning glass and boron doped Si substrates by PLD. The photoluminescence spectra of GIZO showed a strong white light emission and the current-voltage characteristics showed relatively lower turn-on voltage and larger forward current. The CIE coordinates for GIZO were observed to be (0.31, 0.33) with a correlated colour temperature of 6650 K, indicating a cool white light, and establishing a possibility of white light emitting diodes. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Temperature dependent photoemission spectroscopy on lightly-doped sodium tungsten bronze

Temperature dependent photoemission studies on lightly doped (x = 0.025) sodium tungsten bronzes, NaxWO3 have been investigated by high-resolution photoemission spectroscopy. The experimental results show evidence for polaron formation at the valence band edge and the photoemission spectra taken in different modes of the electron analyzer suggest that the density of states at the valence band edge gradually moves to other k-points in the Brillouin zone with increasing temperature and explain the dynamics of polarons in the insulating disordered sodium tungsten bronzes. (C) 2012 Elsevier Ltd. All rights reserved.

Influence of minor addition of boron on tensile and fatigue properties of wrought Ti-6Al-4V alloy

Addition of boron to cast Ti-6Al-4V alloy leads to significant refinement in grain size, which in turn improves processibilty as well as the mechanical properties of the as-cast alloy. Room temperature tensile and fatigue properties of Wrought Ti-6Al-4V-B alloys with B up to 0.09 wt.% are investigated. Thermo-mechanical processing at 950 degrees C caused kinking of alpha lamellae and alignment of TiB particles in the flow direction with a negligible change in prior beta grain and colony sizes, indicating the absence of dynamic recrystallisation during forging. Characterisation with the aid of X-ray and electron back scattered diffraction reveal a strong basal texture in B free alloy which gets randomised with the 0.09B addition in the forged condition. Marginal enhancement in tensile and fatigue properties upon forging is noted. B free wrought Ti-6Al-4V alloy exhibits better tensile strength as compared to B containing alloy, due to the operation of < c+a > slip on pyramidal planes with high value of CRSS as compared to < a > slip on basal and prismatic planes. Decrease in fatigue strength of Ti-6Al-4V-0.04B in as-cast and the wrought state is observed due to increase in the volume fraction of grain boundary a phase with B addition, which acts as a crack nucleation site. No significant effect of TiB particles on tensile and fatigue properties is observed. (C) 2012 Elsevier B.V. All rights reserved.

Microstructure and texture evolution during beta extrusion of boron modified Ti-6A1-4V alloy

Boron addition to conventional titanium alloys below the eutectic limit refines the cast microstructure and improves mechanical properties. The present work explores the influence of hypoeutectic boron addition on the microstructure and texture evolution in Ti-6Al-4V alloy under beta extrusion. The beta extruded microstructure of Ti-6Al-4V is characterized by shear bands parallel to the extrusion direction. In contrast, the extruded Ti-6Al-4V-0.1B alloy shows a regular beta worked microstructure consisting of fine prior beta grains and acicular alpha-lamellae with no signs of the microstructural instability. Crystallographic texture after extrusion was almost identical for the two alloys indicating the similarity in their transformation behavior, which is attributed to complete dynamic recrystallization during beta processing. Microstructural features as well as crystallographic texture indicate dominant grain boundary related deformation processes for the boron modified alloy that leads to homogeneous deformation without instability formation. The absence of shear bands has significant technological importance as far as the secondary processing of boron added alloys in (alpha + beta)-phase field are concerned. (C) 2012 Elsevier B.V. All rights reserved.

Size-mediated cytotoxicity of nanocrystalline titanium dioxide, pure and zinc-doped hydroxyapatite nanoparticles in human hepatoma cells

Nanoparticles are highly used in biological applications including nanomedicine. In this present study, the interaction of HepG2 hepatocellular carcinoma cells (HCC) with hydroxyapatite (HAp), zinc-doped hydroxyapatite, and titanium dioxide (TiO2) nanoparticles were investigated. Hydroxyapatite, zinc-doped hydroxyapatite and titanium dioxide nanoparticles were prepared by wet precipitation method. They were subjected to isochronal annealing at different temperatures. Particle morphology and size distribution were characterized by X-ray diffraction and transmission electron microscope. The nanoparticles were co-cultured with HepG2 cells. MTT assay was employed to evaluate the proliferation of tumor cells. The DNA damaging effect of HAp, Zn-doped HAp, and TiO2 nanoparticles in human hepatoma cells (HepG2) were evaluated using DNA fragmentation studies. The results showed that in HepG2 cells, the anti-tumor activity strongly depend on the size of nanoparticles in HCC cells. Cell cycle arrest analysis for HAp, zinc-doped HAp, and TiO2 nanoparticles revealed the influence of HAp, zinc-doped HAp, and titanium dioxide nanoparticles on the apoptosis of HepG2 cells. The results imply that the novel nano nature effect plays an important role in the biomedicinal application of nanoparticles.

Cobalt-doped ZnO nanowires on quartz: Synthesis by simple chemical method and characterization

The synthesis of cobalt-doped ZnO nanowires is achieved using a simple, metal salt decomposition growth technique. A sequence of drop casting on a quartz substrate held at 100 degrees C and annealing results in the growth of nanowires of average (modal) length similar to 200 nm and diameter of 15 +/- 4 nm and consequently an aspect ratio of similar to 13. A variation in the synthesis process, where the solution of mixed salts is deposited on the substrate at 25 degrees C, yields a grainy film structure which constitutes a useful comparator case. X-ray diffraction shows a preferred 0001] growth direction for the nanowires while a small unit cell volume contraction for Co-doped samples and data from Raman spectroscopy indicate incorporation of the Co dopant into the lattice; neither technique shows explicit evidence of cobalt oxides. Also the nanowire samples display excellent optical transmission across the entire visible range, as well as strong photoluminescence (exciton emission) in the near UV, centered at 3.25 eV. (C) 2012 Elsevier B.V. All rights reserved.

Excitation energy transfer from dye molecules to doped graphene

Recently, we have reported theoretical studies on the rate of energy transfer from an electronically excited molecule to graphene. It was found that graphene is a very efficient quencher of the electronically excited states and that the rate infinity z(-4). The process was found to be effective up to 30 nm which is well beyond the traditional FRET limit. In this report, we study the transfer of an amount of energy (h) over bar Omega from a dye molecule to doped graphene. We find a crossover of the distance dependence of the rate from z(-4) to exponential as the Fermi level is increasingly shifted into the conduction band, with the crossover occurring at a shift of the Fermi level by an amount (h) over bar Omega/2.

Effect of equal channel angular extrusion on wear and corrosion behavior of the orthopedic Ti-13Nb-13Zr alloy in simulated body fluid

We report investigations on the texture, corrosion and wear behavior of ultra-fine grained (UFG) Ti-13Nb-Zr alloy, processed by equal channel angular extrusion (ECAE) technique, for biomedical applications. The microstructure obtained was characterized by X-ray line profile analysis, scanning electron microscope (SEM) and electron back scattered diffraction (EBSD). We focus on the corrosion resistance and the fretting behavior, the main considerations for such biomaterials, in simulated body fluid. To this end. potentiodynamic polarization tests were carried out to evaluate the corrosion behavior of the UFG alloy in Hanks solution at 37 degrees C. The fretting wear behavior was carried out against bearing steel in the same conditions. The roughness of the samples was also measured to examine the effect of topography on the wear behavior of the samples. Our results showed that the ECAE process increases noticeably the performance of the alloy as orthopedic implant. Although no significant difference was observed in the fretting wear behavior, the corrosion resistance of the UFG alloy was found to be higher than the non-treated material. (c) 2012 Elsevier B.V. All rights reserved.

Hardness and Nitrogen Bonding Structure of A(x)Ti(1-x)N/CrN Multilayer Hard Coating

AlxTi1-xN/CrN multilayer coatings were fabricated by magnetron sputtering and those hardness variations were studied by observing the crack propagation and measuring the chemical bonding state of nitrides by Ti addition. While AlN/CrN multilayer shown stair-like crack propagation, AlxTi1-xN/CrN multilayer illustrated straight crack propagation. Most interestingly, Ti addition induced more broken nitrogen bonds in the nitride multilayers, leading to the reduction of hardness. However, the hardness of Al0.25Ti0.75N/CrN multilayer, having high Ti contents, increased by the formation of many Ti-N bond again instead of Al-N bond. From these results, we found that linear crack propagation behavior was dominated by broken nitrogen bonds in the AlxT1-xN/CrN multilayer coatings.

Unusual photoresponse of indium doped ZnO/organic thin film heterojunction

Photoresponse of n-type indium-doped ZnO and a p-type polymer (PEDOT:PSS) heterojunction devices are studied, juxtaposed with the photoluminescence of the In-ZnO samples. In addition to the expected photoresponse in the ultraviolet, the heterojunctions exhibit significant photoresponse to the visible (532 nm). However, neither the doped ZnO nor PEDOT: PSS individually show any photoresponse to visible light. The sub-bandgap photoresponse of the heterojunction originates from visible photon mediated e-h generation between the In-ZnO valence band and localized states lying within the band gap. Though increased doping of In-ZnO has limited effect on the photoluminescence, it significantly diminishes the photoresponse. The study indicates that optimally doped devices are promising for the detection of wavelengths in selected windows in the visible. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4704655]

Role of electrolyte additives on in-vitro electrochemical behavior of micro arc oxidized titania films on Cp Ti

The present work is aimed at studying the influence of electrolyte chemistry on the voltage-time (V-T) response characteristics, phase structure, surface morphology, film growth rate and corrosion properties of titania films fabricated by micro arc oxidation (MAO) on Cp Ti. The titania films were developed with a sodium phosphate based reference electrolyte comprising the additives such as sodium carbonate (Na2CO3), sodium nitrite (NaNO2) and urea (CO(NH2)(2)). The phase composition, surface morphology, elemental composition and thickness of the films were assessed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques. The corrosion characteristics of the fabricated films were studied under Kokubo simulated body fluid (SBF) condition by potentiodynamic polarization, long term potential and linear polarization resistance (LPR) measurements and electrochemical impedance spectroscopy (EIS) methods. In addition, the corrosion characteristics of the grown films were analyzed by EIS curve fitting and equivalent circuit modeling. Salt spray test (SST) as per ASTM B 117 standard was also conducted to verify the corrosion resistance of the grown films. The XRD results showed that the titania films were composed of both anatase and rutile phases at different proportions. Besides, the films grown in carbonate and nitrite containing electrolyte systems showed an enhanced growth of their rutile phase in the 1 0 1] direction which could be attributed to the modifications introduced in the growth process by the abundant oxygen available during the process. The SEM-EDX and elemental mapping results showed that the respective electrolyte borne elements were incorporated and distributed uniformly in all the films. Among all the grown films under study, the film developed in carbonate containing electrolyte system exhibited considerably improved corrosion resistance due to suitable modifications in its structural and morphological characteristics. The rate of anatase to rutile phase transformation and the rutile growth direction were strongly influenced by the abundant oxidizing species available during the film growth process. (C) 2012 Elsevier B. V. All rights reserved.