• Volume 37, Issue 1

February 2014,   pages  1-166

• Synthesis and characterization of TiO2 –SiO2 nanoparticles as catalyst for dehydrogenation of 1,4-dihydropyridines

Nanoparticles of binary TiO2–SiO2 mixed oxides was prepared via sol–gel method using tetraethylorthosilicate (TEOS) and titanium isopropoxide (TIPP) in different reaction conditions (solvent and pH) using ammonium hyhdroxide, acetic acid, sodium hydroxide, ethyleneglycol and polyethylene glycol followed by calcination at 850–970° C. The morphologies, structures and chemical compositions were determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Fourier transmission infrared spectroscopy (FTIR) techniques. The catalytic activity of the obtained nanomaterials was explored for the dehydrogenation of 1,4-dihydropyridines (1,4-DHPs). Observation of 86–100% conversion and 100% selectivity towards the formation of desired products with prepared nanoparticles will be discussed here.

• Investigation of electroluminescence properties of CdTe@CdS core-shell nanocrystals (NCs)

In this work, CdTe@CdS NCs were synthesized using a thermochemical approach and synthesized NCs were used as an emissive layer, a light emitting device, with ITO/MoO3/PVK/CdTe@CdS(core-shell)/Mg:Ag structure. Structural and optical properties of synthesized NCs were investigated by means of XRD, UV–Vis and photoluminescence (PL) analyses. Fabricated device was characterized by electroluminescence spectra. XRD analysis demonstrated cubic phase NCs. Photoluminescence spectra showed a narrow band emission with a peak centred at about 600 nm. Fabricated device showed an emission at 600 nm, which is related to CdTe@CdS NCs. Turn on voltage of fabricated device is about 8 V and brightness is 53.7 Cd/m2 at a working voltage of about 14.57 V.

• Green wet chemical route to synthesize capped CdSe quantum dots

In the present work, we report green synthesis of tartaric acid (TA) and triethanolamine (TEA) capped cadmium selenide quantum dots (CdSe QDs) employing chemical bath deposition (CBD) method. The mechanism of capping using non-toxic binary capping agents is also discussed. Stable QDs of various sizes were obtained by varying pH of the bath. The structural, morphological and spectroscopic characterization of the as-prepared samples by XRD, SEM, optical absorption and photoluminescence (PL) is also reported.

• Influence of preparation conditions on superconducting properties of Bi-2223 thin films

We report electrical transport properties of Bi2Sr2Ca2Cu3O10+𝑥 (Bi-2223) superconducting thin films fabricated by pulsed-laser deposition on SrTiO3 substrate. The aim of the study was to investigate the influence of preparation conditions such as deposition temperature (𝑇S), annealing time (𝑡A) and deposition rate (𝑟). A critical temperature (𝑇c) as high as 110 K and critical current density (𝐽c) of 6.2 × 106 A/cm2 at 20 K were obtained for 𝑇S = 760° C, 𝑡A = 4h and 𝑟 = 1.5 Å/s. We also investigated the effect of Li doping on Bi-2223 thin films. Li intercalation results in high resistive onset transition temperature and the resistivity shows broadening in magnetic field that increases with field. The large broadening of resistivity curve in magnetic field suggests that this phenomenon is directly related to the intrinsic superconducting properties of the copper oxide superconductors. The sudden drop in 𝐽c at relatively low magnetic field (𝐻 &lt; 0.5 tesla) is due to the effect of Josephson weak-links at the grain boundaries.

• Bath temperature impact on morphological evolution of Ni(OH)2 thin films and their supercapacitive behaviour

Nanostructured Ni(OH)2 thin films were deposited over stainless steel (SS) and glass substrate via simple chemical bath deposition (CBD) method. NiCl2 :6H2O were used as source of nickel and aqueous ammonia as a complexing agent. The coating process of Ni(OH)2 material over substrate is based on the decomposition of ammonia complexed nickel ions at two different bath temperatures. The changes in structural, morphological and electro-chemical properties are examined as an impact of bath temperature. XRD studies reveal formation of mixed phase of 𝛼 and 𝛽 at lower bath temperature (313 K) while, pure 𝛽 phase of Ni(OH)2 thin films deposited was observed at higher bath temperature (353 K). The morphological evolution from honeycomb structure to vertically aligned flakes over the substrate is observed as the influence of bath temperature. The supercapacitive performance based on the morphology examined by using cyclic voltammetric measurements in 1 M KOH. The maximum specific capacitances of 610 and 460 F/g were observed for the vertical flake and honeycomb structured Ni(OH)2 thin films, respectively.

• Analysis of Li-related defects in ZnO thin films influenced by annealing ambient

Li-doped ZnO thin films were grown on quartz substrates by radio frequency magnetron sputtering and in situ annealing under O2 or Ar ambient. Li-related defects in ZnO films strongly depend on the annealing ambient. AFM and XRD indicated that ZnO films possessed a good crystallinity with 𝑐-axis orientation, uniform thickness and dense surface. Electrical and optical properties demonstrated that, an amount of LiZn defect had existed in ZnO annealed under O2 ambient and an amount of Lii(o) defect had existed in ZnO annealed under Ar ambient. First-principle calculations were performed to calculate formation energies of Li-doped ZnO in order to explain the formation mechanism of Li-related defects in ZnO.

• Effects of thickness on electronic structure of titanium thin films

Effects of thickness on the electronic structure of e-beam evaporated thin titanium films were studied using near-edge X-ray absorption fine structure (NEXAFS) technique at titanium 𝐿2,3 edge in total electron yield (TEY) mode and transmission yield mode. Thickness dependence of 𝐿2,3 branching ratio (BR) of titanium was investigated and it was found that BR below 3.5 nm shows a strong dependence on film thickness. Mean electron escape depth (𝜆) in titanium, an important parameter for surface applications, was determined to be 𝜆 = 2.6 ± 0.1 nm using 𝐿2,3 resonance intensity variation as a function of film thickness. The average 𝐿3/𝐿2 white line intensity ratio of titanium was obtained as 0.89 from the ratio of amplitudes of each 𝐿3 and 𝐿2 peaks and 0.66 from the integrated area under each 𝐿3 and 𝐿2 peaks. In addition, a theoretical calculation for pure titanium was presented for comparison with experimental data.

• Electrical conduction and thermal properties of Bi-doped Pr0.7Sr0.3MnO3 manganite

Electrical and thermal properties of Bi-doped Pr0.7Sr0.3MnO3 (PSMO) compounds are reported here. It is observed that Bi-doped PSMO compounds follow variable range conduction mechanism. Specific heat, thermal conductivity and thermo-power measurements show that larger Bi-ion, in place of smaller Pr ion, enhances their transition temperatures (𝑇MI, 𝑇C, 𝑇CP). Thermo-power measurements further strengthen our conclusion for the presence of magnetic polaron, generated due to hybridization of Bi3+–6s2 and O2-–2𝑝 orbital and polaronic conduction mechanism.

• Effect of copper doping on structural, optical and electrical properties of Cd0.8Zn0.2S films prepared by chemical bath deposition

Cd0.8Zn0.2S:Cu films of 1.3–6.1 mole percentage of copper have been grown on mica substrate by using chemical bath deposition technique. The films have been characterized by using XRD, SEM and UV spectrophotometer. X-ray diffraction studies have shown that the films are polycrystalline. The average crystallite size as measured from XRD data is in the range of 125–130 nm. The activation energies of Cd0.8Zn0.2S:Cu films, as observed from d.c. conductivity studies in the temperature range (77–300 K) studied, decreased with the increase in Cu concentration. The optical absorption studies have revealed that the energy gap increases gradually with an increase in Cu concentration, whereas conductivity studies have shown an anomalous increase in conductivity in films of 3.8 mole percentage of Cu. SEM pictures have revealed the presence of defects with spherical structure having fibre network. The variation of electrical conductivity is explained based on the defects present and by adopting tunneling mechanism.

• Electrochemical behaviour of graphene–poly (3,4-ethylene- dioxythiophene) (PEDOT) composite electrodes for supercapacitor applications

In this paper, we report on the electrochemical characteristics of graphene–PEDOT composite electrodes. The electrodes were made of indium tin oxide (ITO) substrates by simple processes of electrophoretic deposition of graphene followed by electropolymerization of EDOT monomer. The composite electrode was obtained by electrochemical measurements, a median specific capacitance of 1410 F/g and a median area capacitance of 199 mF cm−2 at a scan rate of 40 mVs−1. The composite showed good stability characteristics after repeated scans in cyclic voltammmetry and fared much better than a thin film of PEDOT. The thermal stability of the composite is also much superior when compared to the polymer with a weight loss temperature of 350° C for the composite and 250° C for the polymer, respectively. The above electrochemical and thermal behaviours of the composite are correlated to the unique morphology of electrodeposited graphene that provides a conductive and high surface area template for electropolymerization.

• Study of electroless copper plating on ABS resin surface modified by heterocyclic organosilane self-assembled film

6-(3-triethoxysilylpropyl)amino-1, 3, 5-triazine-2, 4-dithiol monosodium (TES) was used to fabricate self-assembled film on corona pretreated acrylonitrile–butadiene–styrene (ABS) resin surface. The self-assembled film modified ABS resin was treated by electroless copper plating. Orthogonal test was carried out to study optimal condition of the process. The surface appearance, plating rate and thickness of electroless copper films were investigated to determine the optimal time of corona-discharge, self-assembly and electroless copper plating. SEM results indicated that porous morphology appeared on ABS resin surface modified by TES self-assembled film and the surface roughness also increased. The adhesion test showed that the adhesion property between ABS resin and copper was excellent. The surface of electroless copper film had high brightness under the optimal condition of 1 min corona-discharge, 30 min self-assembly and 10 min electroless copper plating. The electroless-copper plating temperature was 55 ∼ 60°C and pH was 13 ∼ 13.5.

• NbCl5 and CrCl3 catalysts effect on synthesis and hydrogen storage performance of Mg–Ni–NiO composites

Two kinds of novel materials, Mg–1.6 mol% Ni–0.4 mol% NiO–2 mol% MCl (MCl = NbCl5, CrCl3), along with Mg–1.6 mol% Ni–0.4 mol% NiO for comparison, were examined for their potential use in hydrogen storage applications, having been fabricated via cryomilling. The effects of NbCl5 and CrCl3 on hydrogen storage performance were investigated. A microstructure analysis showed that besides the main Mg and Ni phases, NiO and Mg2Ni phases were present in all samples. MgCl2 was only found in halide-doped samples and NbO was only found in NbCl5-doped samples after ball milling. The particle size decreased significantly after 7 h of cryomilling. MgH2, Mg2NiH4 and Mg2NiH0.3 were present in all the samples, while NbH2 was only observed in the NbCl5 -doped sample after absorption. The NbCl5-containing composite exhibited a low onset absorption temperature of 323 K, which was 10 K lower than that of the no-halide doped catalyst. It absorbed 5.32 wt% of hydrogen in 370 s at 623 K under 4 MPa hydrogen pressure and can absorb 90% of its full hydrogen capacity in 50 s. Having an onset desorption temperature of 483 K in vacuum, the NbCl5 -containing composite desorbed hydrogen faster than the no-halide doped sample. The hydriding–dehydriding kinetics performance of the CrCl3-doped sample did not improve, but it did exhibit a lower onset desorption temperature of 543 K under 0.1 MPa, which was 20 K lower than that of the no-halide doped sample. NbO, NiO and NbH2 played important roles in improving absorption and desorption performances.

• Relook on fitting of viscosity with undercooling of glassy liquids

The present approach is on the modification of viscosity fitting of undercooled liquid as a function of undercooling. The method consists of finding analytical solution of three arbitrary constants of the Vogel–Fulcher–Tamman (VFT) equation by choosing three viscosity data at three critical temperatures for an undercooled liquid. Three critical temperatures are liquidus temperature (𝑇l), crystallization onset temperature (𝑇x) and glass transition temperature (𝑇g). The experimental viscosity data at or very near to these three critical temperatures (depending on the availability in literature) have been utilized to achieve the analytical solution. The analytical solution of VFT equation is further examined by selecting the experimental data points away from the critical temperatures in order to check their (𝑇l, 𝑇x and 𝑇g) significance towards the solution. Total absolute error (TAE) and total squared error (TSE) values obtained from the present method with respect to the experimental viscosity data in the temperature range between 𝑇l and 𝑇g are very much comparable and in most of the cases lower than that of existing best-fit' cited in the literature for a number of glassy alloys. Moreover, this method interestingly enables us to find the fragility parameters for a number of glassy alloys and convincingly explain their true glass forming abilities (GFA).

• High mobility polymer gated organic field effect transistor using zinc phthalocyanine

Organic thin film transistors were fabricated using evaporated zinc phthalocyanine as the active layer. Parylene film prepared by chemical vapour deposition was used as the organic gate insulator. The annealing of the samples was performed at 120°C for 3 h. At room temperature, these transistors exhibit 𝑝-type conductivity with field-effect mobilities ranging from 0.025–0.037 cm2/Vs and a (𝐼on/𝐼off) ratio of ∼ 103. The effect of annealing on transistor characteristics is discussed.

• Modelling anisotropic water transport in polymer composite reinforced with aligned triangular bars

This work reports anisotropic water transport in a polymer composite consisting of an epoxy matrix reinforced with aligned triangular bars made of vinyl ester. By gravimetric experiments, water diffusion in resin and polymer composites were characterized. Parameters for Fickian diffusion and polymer relaxation models were determined by least-square curve fitting to the experimental data. Diffusion parameters of epoxy and vinyl ester resin were used as input during development of finite element (FE) model of polymer composite. Through transient FE diffusion analysis, anisotropic water transport in thickness direction of the polymer composite was numerically predicted and validated against experimental results. The case of using impermeable triangular bars was also numerically simulated. The diffusivity of reinforced aligned triangular bars was confirmed to affect anisotropic water transport in the composite. The results of this work suggest possible use of polymer composite for barrier and fluid removal applications.

• Influence of hydrophobic characteristic of organo-modified precursor on wettability of silica film

The objective of this study is to design new hybrid silica materials as templates with hydrophobic properties, prepared at room temperature by a base catalyzed sol–gel process. As silica sources, organoalkoxysilanes functionalized with short hydrophobic chains were used: tetraethylorthosilicate (TEOS), methyltriethoxysilane (MTES), vinyltriethoxysilane (VTES), octyltriethoxysilane (OTES) and isobutyltriethoxysilane (iTES). It was shown that hydrophobicity of the functionalized silica nanoparticles increased as a function of length of the aliphatic chains (MTES &lt; iTES &lt; OTES) or when, instead of a hydrophobic alkyl chains (substituting group of silica precursors), a monounsaturated group was used (VTES). It was observed that the samples responded in a specific way to each type (hydrophilic or hydrophobic) of the dropped liquid. Even though the experiments were limited to short hydrocarbon chains, they showed that there is a threshold to reach high hydrophobicity of the hybrid surface.

• Sintering, camber development of layer composites and a new method to eliminate or decrease camber

Zinc–magnesium titanate dielectrics/nickel–zinc–copper ferrite layer composites were prepared by tape-casting technique combined with a uniaxial pressure shaping technique. The sintering and camber development of the composites were investigated. The results show that the difference of shrinkage in the later stages of sintering is the main cause of camber distortion. To eliminate or decrease the camber, a new method semi-fixed uniaxial pressure technique (SUP) was proposed. This method uses uniaxial pressures by which different radial densities can be introduced when one layer's edge is clamped and the other is free while laminating two different layers. The results obviously show that the SUP technique can decrease the camber and the camber curvature shows an inverse quadratic dependence on the applied pressure.

• Photoluminescence, thermally stimulated luminescence and electron paramagnetic resonance studies of U6+ doped BaSO4

U6+ doped BaSO4 samples were synthesized by precipitation route. PL, TL and EPR investigations of 𝛾 and self 𝛼 irradiated samples were carried out. PL spectra of these samples give structured broad band peaking around 518 nm with five vibronic bands centred around 498.4, 516.0, 533.7, 554.0 and 575.1 nm, respectively and the average frequency of symmetric stretching of O=U=O in the ground electronic state was found to be 674 cm−1. Trap level spectroscopic studies of U doped BaSO4 give glow peaks at 411, 488 and 512 K, respectively and their spectral characteristics are typical of UO$_{2}^{2+}$ emission. EPR studies of 𝛾-irradiated U6+:BaSO4 sample have shown the presence of sulphoxy centred radicals like SO$_{4}^{−}$ and SO$_{3}^{−}$ in addition to OH$^{\bullet}$, O$_{3}^{−}$ and SH2−. TSL peaks at 411 and 488 K were correlated with thermal destruction of SO$_{4}^{−}$ and SO$_{3}^{−}$ radicals.

• Investigation of thermoelectric SiC ceramics for energy harvesting applications on supersonic vehicles leading–edges

Utilizing thermoelectric technology to aerodynamic heat harvesting on the leading-edge is worth noticing in the thermal protection systems. In this paper, a nose-tip model in a supersonic flow field is developed to predict the thermoelectric performance of SiC ceramics structures. The generation performance is numerically investigated in terms of the computational fluid dynamics and the thermal conduction theory. The output power and energy efficiency of the nose-tip model are obtained with Mach number varying from 2.5–4.5. The generated power reaches 1.708 W/m2 at a temperature difference of 757 K at 𝑀 = 4.5. With respect to the Thomson effect, the output power decreases rapidly. However, larger output power and energy efficiency would be obtained with the increase of Mach number, with or without considering the Thomson heat. Moreover, under the higher Mach numbers, larger range of output current value is available.

• Soft mode and acoustic mode ferroelectric properties of deuterated triglycine sulphate crystal

A mathematical study about deuterated triglycine sulphate (CD2CD2COOD)3D2SO4 crystal by a theoretical model which is extended with two sublattice pseudospin lattice coupled mode model by adding third, fourth and fifth order phonon anharmonic interaction terms as well as external electric field term in the crystal Hamiltonian. Double-time temperature dependent Green's function is used to derive soft mode frequency, dielectric permittivity, microwave absorption, quality factor, acoustic attenuation, electric conductivity, smooth function, relaxation time, ratio of figure of merits and respective applications in modern technologies. All theoretical results have a good agreement with experimental data.

• Porous graphitic materials obtained from carbonization of organic xerogels doped with transition metal salts

Porous carbons with a well developed graphitic phase were obtained via the pyrolysis of FeCl3-, NiCl2-, and CoCl2-doped organic xerogels. Doping was realized through salt solubilization in a water/methanol solution of resorcinol and furfural. Carbon xerogels with tailored particles, porous morphology and various degrees of graphitization were obtained depending of the water/methanol ratio and the salt content and type in the starting solution of substrates. When obtained via pyrolysis, carbon xerogels retain the overall open-celled structure exhibiting depleted microporosity and a well-developed mesoporic region that expands into macropores. The removal of metal leads to carbon xerogels with specific surface areas between 170 and 585 m2/g and pore volume up to 0.76 cm3/g. The possibility of enhancing the porosity of xerogels via templating with colloidal silica was also investigated. It was assumed that from the three investigated salts, FeCl3 makes the best choice for graphitization catalyst precursor to obtain uniformly graphitized mesoporous carbon xerogels. The obtained carbon samples were characterized by means of SEM, TEM, X-ray diffraction, Raman spectroscopy, N2 physisorption and thermogravimetric analysis.

• Studies on bulk growth, structural and microstructural characterization of 4-aminobenzophenone single crystal grown from vertical Bridgman technique

Bulk single crystal of 4-aminobenzophenone with a size of 25 mm dia. and 35 mm length has been grown by vertical Bridgman technique. The crystal system of the grown crystal was confirmed by X-ray diffraction analysis. Crystalline perfection was analysed by high resolution X-ray diffraction studies. Chemical etching was carried out for the first time in 4-aminobenzophenone single crystal to study the defects presented in the grown crystal and the growth mechanism involved. Several organic etchants were employed with different etching time to select suitable etchant for studying dislocation pattern and other structural defects existing in the grown crystal. Etch patterns such as spirals and striations observed for the selective etchants provide considerable information on growth mechanism of the crystal.

• Characterization of neutrophil adhesion to different titanium surfaces

Although titanium (Ti) is known to elicit a foreign body response when implanted into humans, Ti implant healing resembles normal wound healing in terms of inflammatory cell recruitment and inflammation persistence. Rough implant surfaces may present better conditions for protein adsorption and for the adhesion of platelets and inflammatory cells such as neutrophils. Implanted biomedical devices initially interact with coagulating blood; however, direct contact between the oxide layer of the implant and neutrophils has not been completely described. The aim of the present study is to compare the behaviours of neutrophils in direct contact with different Ti surfaces. Isolated human neutrophils were placed into contact with Ti discs, which had been rendered as smooth' or rough', following different surface treatments. Scanning electron microscopy and flow cytometry were used to measure cell adhesion to the surfaces and exposure of membrane proteins such as CD62L and CD11b. Topographic roughness was demonstrated as higher for SLA treated surfaces, measured by atomic force microscopy and elemental analysis was performed by energy dispersive X-ray, showing a similar composition for both surfaces. The adhesion of neutrophils to the rough' Ti surface was initially stronger than adhesion to the `smooth' surface. The cell morphology and adhesion marker results revealed clear signs of neutrophil activation by either surface, with different neutrophil morphological characteristics being observed between the two surface types. Understanding the cellular mechanisms regulating cell–implant interactions should help researchers to improve the surface topography of biomedical implant devices.

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