Electrical switching behavior of amorphous Ge15Te85 Si--x(x) thin films with phase change memory applications

Amorphous Ge15Te85-xSix thin film switching devices (1 <= x <= 6) have been deposited in sandwich geometry, on glass substrates with aluminum electrodes, by flash evaporation technique. These devices exhibit memory type electrical switching, like bulk Ge15Te85-xSix glasses. However, unlike the bulk glasses, a-Ge15Te85-xSix films exhibit a smooth electrical switching behavior. The electrical switching fields of a-Ge15Te85-xSix thin film samples are also comparable with other chalcogenide samples used in memory applications. The switching fields of a-Ge15Te85-xSix films have been found to increase with increasing Si concentration. Also, the optical band gap of a-Ge15Te85-xSix films is found to increase with Si content. The observed results have been understood on the basis of increase in network connectivity and rigidity with Si addition. (C) 2013 Elsevier Ltd. All rights reserved.

Temperature dependent magnetic ordering and electrical transport behavior of nano zinc ferrite from 20 to 800 K

The nano ZnFe2O4 compound was prepared by eco-friendly hydrothermal method. The characterization of the sample for its structure, morphology and composition were done by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), dynamic light scattering, Fourier transform infrared spectroscopy, zeta surface profiler and UV-Visible spectroscopy studies. The PXRD measurement reveals that the compound shows spinel cubic phase belong Fd (3) over barm (227) space group. Morphology of the compound from SEM and surface profile shows nearly spherical agglomerated particles with well defined grains and grain boundaries. The material shows the semiconducting behavior with E-g of 2.3 eV at room temperature (RT). The variation in the magnetic ordering was observed for wide range of temperature. The compound behaves like a soft magnetic material with ferrimagnetic at various temperatures except at RT. Both magnetic and EPR studies supports the superparamagnetic behavior of the the sample. The DC conductivity, dielectric and AC conductivity behavior of the 1000 degrees C pellets sintered for 2 h shows good frequency dependent transport properties. The present study facilitate in selecting the suitable materials for the nanoelectronics and spintronic applications. (C) 2013 Elsevier B.V. All rights reserved.

Tuning solubility and stability of hydrochlorothiazide co-crystals

Hydrochlorothiazide (HCT), C7H8ClN3O4S2, is a diuretic BCS (Biopharmaceutics Classification System) class IV drug which has primary and secondary sulfonamide groups. To modify the aqueous solubility of the drug, co-crystals with biologically safe co-formers were screened. Multi-component molecular crystals of HCT were prepared with nicotinic acid, nicotinamide, succinamide, p-aminobenzoic acid, resorcinol and pyrogallol using liquid-assisted grinding. The co-crystals were characterized by FT-IR spectroscopy, powder X-ray diffraction (PXRD) and differential scanning calorimetry. Single crystal structures were obtained for four of them. The N-H center dot center dot center dot O sulfonamide catemer synthons found in the stable polymorph of pure HCT are replaced in the co-crystals by drug-co-former heterosynthons. Isostructural co-crystals with nicotinic acid and nicotinamide are devoid of the common sulfonamide dimer/catemer synthons. Solubility and stability experiments were carried out for the co-crystals in water (neutral pH) under ambient conditions. Among the six binary systems, the co-crystal with p-aminobenzoic acid showed a sixfold increase in solubility compared with pure HCT, and stability up to 24 h in an aqueous medium. The co-crystals with nicotinamide, resorcinol and pyrogallol showed only a 1.5-2-fold increase in solubility and transformed to HCT within 1 h of the dissolution experiment. An inverse correlation is observed between the melting points of the co-crystals and their solubilities.

Projection Error Propagation-based Regularization (PEPR) method for resistivity reconstruction in Electrical Impedance Tomography (EIT)

A novel Projection Error Propagation-based Regularization (PEPR) method is proposed to improve the image quality in Electrical Impedance Tomography (EIT). PEPR method defines the regularization parameter as a function of the projection error developed by difference between experimental measurements and calculated data. The regularization parameter in the reconstruction algorithm gets modified automatically according to the noise level in measured data and ill-posedness of the Hessian matrix. Resistivity imaging of practical phantoms in a Model Based Iterative Image Reconstruction (MoBIIR) algorithm as well as with Electrical Impedance Diffuse Optical Reconstruction Software (EIDORS) with PEPR. The effect of PEPR method is also studied with phantoms with different configurations and with different current injection methods. All the resistivity images reconstructed with PEPR method are compared with the single step regularization (STR) and Modified Levenberg Regularization (LMR) techniques. The results show that, the PEPR technique reduces the projection error and solution error in each iterations both for simulated and experimental data in both the algorithms and improves the reconstructed images with better contrast to noise ratio (CNR), percentage of contrast recovery (PCR), coefficient of contrast (COC) and diametric resistivity profile (DRP). (C) 2013 Elsevier Ltd. All rights reserved.

Structural, thermal and electrical properties of poly(methyl methacrylate)/CaCu3Ti4O12 composite sheets fabricated via melt mixing

Poly(methyl methacrylate) (PMMA) and CaCu3Ti4O12 (CCTO) composites were fabricated via melt mixing followed by hot pressing technique. These were characterized using X-ray diffraction, thermo gravimetric, thermo mechanical, differential scanning calorimetry, fourier transform infrared (FTIR) and Impedance analyser for their structural, thermal and dielectric properties. Composites were found to have better thermal stability than that of pure PMMA. However, there was no significant difference in the glass transition (T (g) ) temperature between the polymer and the composite. The appearance of additional vibrational frequencies in the range 400-600 cm(-1) in FTIR spectra indicated a possible interaction between PMMA and CCTO. The composite, with 38 vol% of CCTO (in PMMA), exhibited remarkably low dielectric loss at high frequencies and the low-frequency relaxation is attributed to the interfacial polarization/MWS effect. The origin of AC conductivity particularly in the high-frequency region was attributed to the electronic polarization.

Pulsed Electrical Stimulation and Surface Charge Induced Cell Growth on Multistage Spark Plasma Sintered Hydroxyapatite-Barium Titanate Piezobiocomposite

The primary purpose of the present work was to illustrate whether cell proliferation can be enhanced on electroactive bioceramic composite, when the cells are cultured in the presence of external electrical stimulation. The two different aspects of the influence of electric field (E-field) application toward stimulating the growth/proliferation of bone/connective tissue cells in vitro, (a) intermittent delivery of extremely low strength pulsed electrical stimulation (0.5-4V/cm, 400s DC pulse) and (b) surface charge generated by electrical poling (10kV/cm) of hydroxyapatite (HA)-BaTiO3 piezobiocomposite have been demonstrated. The experimental results establish that the cell growth can be enhanced using the new culture protocol of the intermittent delivery of electrical pulses within a narrow range of stimulation parameters. The optimal E-field strength for enhanced cellular response for mouse fibroblast L929 and osteogenic cells is in the range of 0.5-1V/cm. The MTT 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide] assay results suggested the increased viability of E-field treated cells over 7d in culture, implicating the positive impact of electrical pulses on proliferation behavior. The alizarin red assay results showed noticeable increase in Ca-deposition on the E-field treated samples in comparison to their untreated counterparts. The negatively charged surfaces of developed piezocomposite stimulated the cell growth in a statistically noticeable manner as compared with the uncharged or positively charged surfaces of similar composition.

Alumina and Silica based Epoxy Nano-composites for Electrical Insulation

Plain epoxy resins or resin impregnated cellulose have found application as electrical insulation in power equipment. In the past, their performance was improved by the use of inorganic oxide fillers of microscopic dimensions. In the recent past nano-particle doped epoxy insulation came into use with a view to further enhance the dielectric properties. This paper reports dielectric investigations into epoxy nano-composites based on a class of metal oxides, Al2O3 and SiO2. In particular, consideration has been given to the partial discharge performance and electrical breakdown under different voltage profiles as a function of the volumetric composition of the nano-particles in epoxy resin.

Dielectric and electrical studies of Pr3+ doped nano CaSiO3 perovskite ceramics

CaSiO3 nano-ceramic powder doped with Pr3+ has been prepared by solution combustion method. The powder Ca0.5Pr0.05SiO3 is investigated for its dielectric and electrical properties at room temperature to study the effect of doping. The sample is characterized by X-ray diffraction and infrared spectroscopy. The size of either of volume elements of CaSiO3:Pr3+ estimated from transmission electron microscopy is about 180-200 nm. The sample shows colossal dielectric response at room temperature. This colossal dielectric behaviour follows Debye-type relaxation and can be explained by Maxwell-Wagner (MW) polarization. However, analysis of impedance and electric modulus data using Cole-Cole plot shows that it deviates from ideal Debye behaviour resulting from the distribution of relaxation times. The distribution in the relaxation times may be attributed to existence of electrically heterogeneous grains, insulating grain boundary, and electrode contact regions. Doping, thus, results in substantial modifications in the dielectric and electrical properties of the nano-ceramic CaSiO3. (C) 2013 Elsevier Ltd. All rights reserved.

A MatLAB Based Virtual Phantom for 2D Electrical Impedance Tomography (MatVP2DEIT): Studying the Medical Electrical Impedance Tomography Reconstruction in Computer

Electrical Impedance Tomography (EIT) is a computerized medical imaging technique which reconstructs the electrical impedance images of a domain under test from the boundary voltage-current data measured by an EIT electronic instrumentation using an image reconstruction algorithm. Being a computed tomography technique, EIT injects a constant current to the patient's body through the surface electrodes surrounding the domain to be imaged (Omega) and tries to calculate the spatial distribution of electrical conductivity or resistivity of the closed conducting domain using the potentials developed at the domain boundary (partial derivative Omega). Practical phantoms are essentially required to study, test and calibrate a medical EIT system for certifying the system before applying it on patients for diagnostic imaging. Therefore, the EIT phantoms are essentially required to generate boundary data for studying and assessing the instrumentation and inverse solvers a in EIT. For proper assessment of an inverse solver of a 2D EIT system, a perfect 2D practical phantom is required. As the practical phantoms are the assemblies of the objects with 3D geometries, the developing of a practical 2D-phantom is a great challenge and therefore, the boundary data generated from the practical phantoms with 3D geometry are found inappropriate for assessing a 2D inverse solver. Furthermore, the boundary data errors contributed by the instrumentation are also difficult to separate from the errors developed by the 3D phantoms. Hence, the errorless boundary data are found essential to assess the inverse solver in 2D EIT. In this direction, a MatLAB-based Virtual Phantom for 2D EIT (MatVP2DEIT) is developed to generate accurate boundary data for assessing the 2D-EIT inverse solvers and the image reconstruction accuracy. MatVP2DEIT is a MatLAB-based computer program which simulates a phantom in computer and generates the boundary potential data as the outputs by using the combinations of different phantom parameters as the inputs to the program. Phantom diameter, inhomogeneity geometry (shape, size and position), number of inhomogeneities, applied current magnitude, background resistivity, inhomogeneity resistivity all are set as the phantom variables which are provided as the input parameters to the MatVP2DEIT for simulating different phantom configurations. A constant current injection is simulated at the phantom boundary with different current injection protocols and boundary potential data are calculated. Boundary data sets are generated with different phantom configurations obtained with the different combinations of the phantom variables and the resistivity images are reconstructed using EIDORS. Boundary data of the virtual phantoms, containing inhomogeneities with complex geometries, are also generated for different current injection patterns using MatVP2DEIT and the resistivity imaging is studied. The effect of regularization method on the image reconstruction is also studied with the data generated by MatVP2DEIT. Resistivity images are evaluated by studying the resistivity parameters and contrast parameters estimated from the elemental resistivity profiles of the reconstructed phantom domain. Results show that the MatVP2DEIT generates accurate boundary data for different types of single or multiple objects which are efficient and accurate enough to reconstruct the resistivity images in EIDORS. The spatial resolution studies show that, the resistivity imaging conducted with the boundary data generated by MatVP2DEIT with 2048 elements, can reconstruct two circular inhomogeneities placed with a minimum distance (boundary to boundary) of 2 mm. It is also observed that, in MatVP2DEIT with 2048 elements, the boundary data generated for a phantom with a circular inhomogeneity of a diameter less than 7% of that of the phantom domain can produce resistivity images in EIDORS with a 1968 element mesh. Results also show that the MatVP2DEIT accurately generates the boundary data for neighbouring, opposite reference and trigonometric current patterns which are very suitable for resistivity reconstruction studies. MatVP2DEIT generated data are also found suitable for studying the effect of the different regularization methods on reconstruction process. Comparing the reconstructed image with an original geometry made in MatVP2DEIT, it would be easier to study the resistivity imaging procedures as well as the inverse solver performance. Using the proposed MatVP2DEIT software with modified domains, the cross sectional anatomy of a number of body parts can be simulated in PC and the impedance image reconstruction of human anatomy can be studied.

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.

Structural, Electrical and Magnetic Behaviour of FeTe0.5Se0.5 Superconductor

We report the synthesis as well as structural and physical properties of the bulk polycrystalline FeTe and FeTe0.5Se0.5 compounds. These samples are synthesised by the solid state-reaction method via vacuum encapsulation. Both studied compounds are crystallized in a tetragonal phase with space group P4/nmm. The parent FeTe compound shows an anomaly in resistivity measurement at around 78 K, which is due to the structural change along with a magnetic phase transition. The superconductivity in the FeTe0.5Se0.5 sample at 13 K is confirmed by the resistivity measurements. DC magnetisation along with an isothermal (M-H) loop shows that FeTe0.5Se0.5 possesses bulk superconductivity. The upper critical field is estimated through resistivity rho (T,H) measurements using Gingzburg-Landau (GL) theory and is above 50 T with 50 % resistivity drop criterion. The origin of the resistive transition broadening under magnetic field is investigated by thermally activated flux flow. The magnetic field dependence of the activation energy of the flux motion is discussed.

Temperature dependent electrical behaviour of Cu2SnS3 films

The temperature dependent electrical properties of the dropcasted Cu2SnS3 films have been measured in the temperature range 140 K to 317 K. The log I versus root V plot shows two regions. The region at lower bias is due to electrode limited Schottky emission and the higher bias region is due to bulk limited Poole Frenkel emission. The ideality factor is calculated from the ln I versus V plot for different temperatures fitted with the thermionic emission model and is found to vary from 6.05 eV to 12.23 eV. This large value is attributed to the presence of defects or amorphous layer at the Ag / Cu2SnS3 interface. From the Richardson's plot the Richardson's constant and the barrier height were calculated. Owing to the inhomogeneity in the barrier heights, the Richardson's constant and the barrier height were also calculated from the modified Richardson's plot. The I-V-T curves were also fitted using the thermionic field emission model. The barrier heights were found to be higher than those calculated using thermionic emission model. From the fit of the I-V-T curves to the field emission model, field emission was seen to dominate in the low temperature range of 140 K to 177 K. The temperature dependent current graphs show two regions of different mechanisms. The log I versus 1000/T plot gives activation energies E-a1 = 0.367095 - 0.257682 eV and E-a2 = 0.038416 - 0.042452 eV. The log ( I/T-2) versus 1000/T graph gives trap depths Phi(o1) = 0.314159 - 0.204752 eV and Phi(o2) = 0.007425- 0.011163 eV. With increasing voltage the activation energy E-a1 and the trap depth Phi(o1) decrease. From the ln (IT1/ 2) versus 1/T-1/ 4 graph, the low temperature region is due to variable range hopping mechanism and the high temperature region is due to thermionic emission. (C) 2014 Author(s).

Electrical switching, SET-RESET, and Raman scattering studies on Ge15Te80-xIn5Agx glasses

Bulk Ge15Te85-xIn5Agx glasses are shown to exhibit electrical switching with switching/threshold voltages in the range of 70-120V for a sample thickness of 0.3 mm. Further, the samples exhibit threshold or memory behavior depending on the ON state current. The compositional studies confirm the presence of an intermediate phase in the range 8 <= x <= 16, revealed earlier by thermal studies. Further, SET-RESET studies have been performed by these glasses using a triangular pulse of 6 mA amplitude (for SET) and 21 mA amplitude (for RESET). Raman studies of the samples after the SET and RESET operations reveal that the SET state is a crystalline phase which is obtained by thermal annealing and the RESET state is the glassy state, similar to the as-quenched samples. It is interesting to note that the samples in the intermediate phase, especially compositions at x = 10, 12, and 14 withstand more set-reset cycles. This indicates compositions in the intermediate phase are better suited for phase change memory applications. (C) 2014 AIP Publishing LLC.

Effect of morphology on electrical treeing in low density polyethylene nanocomposites

Influence of polymer morphology on the inception and the growth of electrical trees in unfilled low density polyethylene (LDPE) as well as LDPE filled with 1, 3 and 5% by weight nanoalumina samples stressed with 50 Hz ac voltage has been studied. It is seen that there is a significant improvement in tree inception voltage with filler loading in LDPE filled with nanoparticles. Tree inception voltage increased with the filler loading up to 3% by weight nanoalumina loading and showed a reduction at 5% by weight loading. Change in tree growth patterns from branch to bush as well as a slower tree growth with increase in filler loading in LDPE alumina nanocomposites were observed. The degree of crystallinity and change in crystalline morphology induced by the presence of alumina nanoparticles in LDPE was studied using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). DSC results show a similar melting behaviour for both unfilled LDPE and LDPE nanocomposites. However, there is a reduction in the degree of crystallinity for LDPE filled with 5% by weight nanoalumina. An increase in lamellae packing with increase in filler loadings and a highly disordered spherulitic structure for LDPE filled with 5% by weight nanoalumina was observed from the SEM images. The slow propagation of tree growth as well as reduction in tree inception voltage with increase in filler loadings were attributed to the morphological changes observed in the LDPE nanocomposites.