Surfactant solubility and micellization in ternary eutectic melt (acetamide plus urea plus ammonium nitrate)

Cationic surfactants such as dodecyltrimethylammonium bromide (DTAB), tetradecyltrimehtylammonium bromide (TTAB) and hexadecyltrimethylammonium bromide (HTAB); and anionic surfactants such as sodium decyl sulphate (SDeS), sodium dodecyl sulphate (SDS) and sodium tetradecyl sulphate (STDS) have been used to determine their solubility and micellization in ternary eutectic melt (acetamide + urea + ammonium nitrate) at 50 degrees C. We employed the electrical conductivity and the surface tension measurement techniques to determine the critical micelle concentration (CMC). The deviation in the slope of the specific conductance/surface tension against surfactant concentration plots indicated the aggregations of surfactants and hence, their CMC. CMC decreases with increase of alkyl chain length due to the increased van der Waals forces. The calculated increment in Gibb's energy per methylene group for cationic and anionic surfactants is about -6 kJ mol(-1) and -4 kJ mol(-1) respectively. It is found that, the CMCs of the surfactants in the ternary melt are higher than the CMCs of same surfactants in water (similar to 25 degrees C). (C) 2012 Elsevier B.V. All rights reserved.

Electrical breakdown of carbon nanotube devices and the predictability of breakdown position

We have investigated electrical transport properties of long (>10 mu m) multiwalled carbon nanotubes (NTs) by dividing individuals into several segments of identical length. Each segment has different resistance because of the random distribution of defect density in an NT and is corroborated by Raman studies. Higher is the resistance, lower is the current required to break the segments indicating that breakdown occurs at the highly resistive segment/site and not necessarily at the middle. This is consistent with the one-dimensional thermal transport model. We have demonstrated the healing of defects by annealing at moderate temperatures or by current annealing. To strengthen our mechanism, we have carried out electrical breakdown of nitrogen doped NTs (NNTs) with diameter variation from one end to the other. It reveals that the electrical breakdown occurs selectively at the narrower diameter region. Overall, we believe that our results will help to predict the breakdown position of both semiconducting and metallic NTs. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. http://dx.doi.org/10.1063/1.4720426]

Electrical characteristics of multiwalled carbon nanotube arrays and influence of pressure

We have investigated the current-voltage characteristics of carbon nanotube arrays and shown that the current through the arrays increases rapidly with applied voltage before the breakdown occurs. Simultaneous measurements of current and temperature at one end of the arrays suggest that the rapid increase of current is due to Joule heating. The current through the array and the threshold voltage are found to increase with decreasing pressure. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. http://dx.doi.org/10.1063/1.3702777]

Influence of Sn doping on structural, optical and electrical properties of ZnO thin films prepared by cost effective sol-gel process

Tin (Sn) doped zinc oxide (ZnO) thin films were synthesized by sol-gel spin coating method using zinc acetate di-hydrate and tin chloride di-hydrate as the precursor materials. The films were deposited on glass and silicon substrates and annealed at different temperatures in air ambient. The agglomeration of grains was observed by the addition of Sn in ZnO film with an average grain size of 60 nm. The optical properties of the films were studied using UV-VIS-NIR spectrophotometer. The optical band gap energies were estimated at different concentrations of Sn. The MOS capacitors were fabricated using Sn doped ZnO films. The capacitance-voltage (C-V), dissipation vs. voltage (D-V) and current-voltage (I-V) characteristics were studied and the electrical resistivity and dielectric constant were estimated. The porosity and surface area of the films were increased with the doping of Sn which makes these films suitable for opto-electronic applications. (C) 2012 Elsevier B.V. All rights reserved.

Electrical Transport Properties of Buckled Carbon Nanotube Arrays

We report on the electrical transport properties of buckled carbon nanotube arrays synthesized by pyrolysis. Analyzing the experimental data based on the general theory of semiconductors, the arrays are predicted to be semiconducting and the band gap can be evaluated. The band gap of different arrays is in 25-50 meV range.

Detection of sugar-lectin interactions by multivalent dendritic sugar functionalized single-walled carbon nanotubes

We show that single walled carbon nanotubes (SWNTs) decorated with sugar functionalized poly (propyl ether imine) (PETIM) dendrimer is a very sensitive platform to quantitatively detect carbohydrate recognizing proteins, namely, lectins. The changes in electrical conductivity of SWNT in field effect transistor device due to carbohydrate-protein interactions form the basis of present study. The mannose sugar attached PETIM dendrimers undergo charge-transfer interactions with the SWNTs. The changes in the conductance of the dendritic sugar functionalized SWNT after addition of lectins in varying concentrations were found to follow the Langmuir type isotherm, giving the concanavalin A (Con A)-mannose affinity constant to be 8.5 x 10(6) M-1. The increase in the device conductance observed after adding 10 nM of Con A is same as after adding 20 mu M of a non-specific lectin peanut agglutinin, showing the high specificity of the Con A-mannose interactions. The specificity of sugar-lectin interactions was characterized further by observing significant shifts in Raman modes of the SWNTs. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4739793]

Electrical transport studies of MBE grown InGaN/Si isotype heterojunctions

The temperature dependent electrical transport behavior of n-n InGaN/Si heterostructures grown by plasma-assisted MBE was studied. Structural characteristics of the as-grown InGaN epilayers were evaluated high resolution X-ray diffraction and composition of InGaN was estimated from photoluminescence spectra using standard Vegard's law. Current density-voltage plots (J-V-T) revealed that the ideality factor (eta) and Schottky barrier height (SBH) (Phi(b)) are temperature dependent and the incorrect values of the Richardson's constant (A**) produced, suggests an inhomogeneous barrier at the heterostructure interface. The higher value of the ideality factor compared to the ideal value and its temperature dependence suggest that the current transport is mainly dominated by thermionic field emission. (C) 2012 Elsevier B.V. All rights reserved.

Electrical properties of buckled multiwalled carbon nanotube arrays in the diffusive regime

We report the geometrical effect of graded buckled multiwalled carbon nanotube arrays on the electrical transport properties in the diffusive regime, via successive breakdown caused by the Joule heating. This breakdown occurs in the straighter region. Empirical relations involving the current-carrying ability, resistance, breakdown power, threshold voltage, diameter and length of carbon nanotube arrays are discussed on the basis of an extensive set of experimental data along with justification. The experimental results are corroborated by the density functional tight-binding calculations of electronic band structure. The band gap decreases as buckleness increases leading to the enhancement in the current-carrying ability and elucidating the role of buckleness in carbon nanotubes. Copyright (c) EPLA, 2012

High field carrier transport in graphene: Insights from fast current transient

In this work, we observe gate tunable negative differential conductance (NDC) and current saturation in single layer and bilayer graphene transistor at high source-drain field, which arise due to the interplay among (1) self-heating, (2) hot carrier injection, and (3) drain induced minority carrier injection. The magnitude of the NDC is found to be reduced for a bilayer, in agreement with its weaker carrier-optical phonon coupling and less efficient hot carrier injection. The contributions of different mechanisms to the observed results are decoupled through fast transient measurements with nanosecond resolution. The findings provide insights into high field transport in graphene. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4754103]

Influence of GaN underlayer thickness on structural, electrical and optical properties of InN films grown by PAMBE

We present an extensive study on the structural, electrical and optical properties of InN thin films grown on c-Al2O3, GaN(130 nm)/Al2O3, GaN(200 nm)/Al2O3 and GaN(4 mu m)/Al2O3 by using plasma-assisted molecular beam epitaxy. The high resolution X-ray diffraction study reveals better crystalline quality for the film grown on GaN(4 mu m)/Al2O3 as compared to others. The electronic and optical properties seem to be greatly influenced by the structural quality of the films, as can be evidenced from Hall measurement and optical absorption spectroscopy. Kane's k.p model was used to describe the dependence of optical absorption edge of InN films on carrier concentration by considering the non-parabolic dispersion relation for carrier in the conduction band. Room temperature Raman spectra for the InN films grown on GaN show the signature of residual tensile stress in contrast to the compressive stress observed for the films grown directly on c-Al2O3. (C) 2012 Elsevier B.V. All rights reserved.

Direct Observation of Valley Hybridization and Universal Symmetry of Graphene with Mesoscopic Conductance Fluctuations

In graphene, the valleys represent spinlike quantities and can act as a physical resource in valley-based electronics to produce novel quantum computation schemes. Here we demonstrate a direct route to tune and read the valley quantum states of disordered graphene by measuring the mesoscopic conductance fluctuations. We show that the conductance fluctuations in graphene at low temperatures are reduced by a factor of 4 when valley triplet states are gapped in the presence of short-range potential scatterers at high carrier densities. We also show that this implies a gate tunable universal symmetry class that outlines a fundamental feature arising from graphene's unique crystal structure.

Electrical transport characteristics of ZnO-Bi2O3-B2O3 glasses

Optically clear glasses in the ZnO-Bi2O3-B2O3 (ZBBO) system were fabricated via the conventional melt-quenching technique. Dielectric constant and loss measurements carried out on ZBBO glasses unraveled nearly frequency (1 kHz-10 MHz)-independent dielectric characteristics associated with significantly low loss (D = 0.004). However, weak temperature response was found with temperature coefficient of dielectric constant 18 +/- 4 ppm A degrees C-1 in the 35-250 A degrees C temperature range. The conduction and relaxation phenomena were rationalized using universal AC conductivity power law and modulus formalism respectively. The activation energy for relaxation determined using imaginary parts of modulus peaks was 2.54 eV which was close to that of the DC conduction implying the involvement of similar energy barriers in both the processes. Stretched and power exponents were temperature dependent. The relaxation and conduction in these glasses were attributed to the hoping and migration of Bi3+ cations in their own and different local environment.

Common Ground Method of Current Injection in Electrical Impedance Tomography

Surface electrodes are essentially required to be switched for boundary data collection in electrical impedance tomography (Ell). Parallel digital data bits are required to operate the multiplexers used, generally, for electrode switching in ELT. More the electrodes in an EIT system more the digital data bits are needed. For a sixteen electrode system. 16 parallel digital data bits are required to operate the multiplexers in opposite or neighbouring current injection method. In this paper a common ground current injection is proposed for EIT and the resistivity imaging is studied. Common ground method needs only two analog multiplexers each of which need only 4 digital data bits and hence only 8 digital bits are required to switch the 16 surface electrodes. Results show that the USB based data acquisition system sequentially generate digital data required for multiplexers operating in common ground current injection method. The profile of the boundary data collected from practical phantom show that the multiplexers are operating in the required sequence in common ground current injection protocol. The voltage peaks obtained for all the inhomogeneity configurations are found at the accurate positions in the boundary data matrix which proved the sequential operation of multiplexers. Resistivity images reconstructed from the boundary data collected from the practical phantom with different configurations also show that the entire digital data generation module is functioning properly. Reconstructed images and their image parameters proved that the boundary data are successfully acquired by the DAQ system which in turn indicates a sequential and proper operation of multiplexers.

Impact of chemical treatment on the surface, structure, optical and electrical properties of SnS thin films

The impact of chemical treatment on the surface morphology and other physical properties of tin monosulphide (SnS) thin films have been investigated. The SnS films treated with selected organic solvents exhibited strong improvement in their crystalline-quality and considerable decrease in electrical resistivity. Particularly, the films treated with chloroform showed very low electrical resistivity of similar to 5 Omega cm and a low optical band gap of 1.81 eV as compared to untreated and treated SnS films with other chemicals. From these studies we realized that the chemical treatment of SnS films has strong impact on their surface morphology and also on other physical properties. (C) 2012 Elsevier B.V. All rights reserved.

Electrical switching studies on amorphous Ge‐Te‐Sn thin films

Electrical switching studies on amorphous Ge17Te83−xSnx thin films (1 ≤ x ≤ 4) has been done to find their suitability for Phase Change Memory application; Bulk ingots in glassy form are prepared using conventional melt quenching technique and the thin films are coated using flash evaporation technique. Samples are found to exhibit memory type of electrical switching behavior. The switching voltages of Ge17Te83−xSnx thin films have been found to decrease with increase in Sn concentration. The comparatively lower switching voltages of Ge17Te83−xSnx samples, make them suitable candidates for phase change memory applications.