Structural, optical, and electrical properties of bulk single crystals of InAsxSb(1-x) grown by rotatory Bridgman method

Radially-homogeneous and single-phase InAsxSb(1−x) crystals, up to 5.0 at. % As concentration, have been grown using the rotatory Bridgman method. Single crystallinity has been confirmed by x-ray and electron diffraction studies. Infrared transmission spectra show a continuous decrease in optical energy gap with the increase of arsenic content in InSb. The measured values of mobility and carrier density at room temperature (for x = .05) are 5.6×104 cm2/V s and 2.04×1016 cm−3, respectively.

Three-system and single-system static distance relays

Static distance relays employing semiconductor devices as their active elements offer many advantages over the conventional electromagnetic and rectifier relays. The paper describes single-system and three-system static distance relays, which depend for their operation on the instantaneous-comparison or `block-spike¿ scheme. Design principles and typical discriminating and logic circuits are described for the new relaying equipment. The relaying circuitry has been devised for obtaining uniform performance on all kinds of faults, by the use of two phase detectors¿one for multiphase faults and one for earth faults. The phase detector for multiphase faults provides an improved polar characteristic in the complex-impedance plane, which fits only around the fault area of a transmission line. The other features of the relay are: reliable pickup for close-in faults, least susceptibility to maloperation under power-swing conditions, and reduction in cost and panel space required. The operating characteristics of the relays, as expressed by accuracy/range charts, are also presented.

Growth of silicon nanowires by electron beam evaporation using indium catalyst

For the first time silicon nanowires have been grown on indium (In) coated Si (100) substrates using e-beam evaporation at a low substrate temperature of 300 degrees C. Standard spectroscopic and microscopic techniques have been employed for the structural, morphological and compositional properties of as grown Si nanowires. The as grown Si nanowires have randomly oriented with an average length of 600 nm for a deposition time of 15 min. As grown Si nanowires have shown indium nanoparticle (capped) on top of it confirming the Vapor Liquid Solid (VLS) growth mechanism. Transmission Electron Microscope (TEM) measurements have revealed pure and single crystalline nature of Si nanowires. The obtained results have indicated good progress towards finding alternative catalyst to gold for the synthesis of Si nanowires. (C) 2011 Elsevier B.V. All rights reserved.

Molecular charge-transfer interaction with single-layer graphene

While the effect of electrochemical doping on single-layer graphene (SG) with holes and electrons has been investigated, the effect of charge-transfer doping on SG has not been examined hitherto. Effects of varying the concentration of electron donor and acceptor molecules such as tetrathiafulvalene (TTF) and tetracyanoethylene (TCNE) on SG produced by mechanical exfoliation as well as by the reduction of single-layer graphene oxide have been investigated. TTF softens the G-band in the Raman spectrum, whereas TCNE stiffens the G-band. The full-width-at-half-maximum of the G-band increases on interaction with both TTF and TCNE. These effects are similar to those found with few-layer graphene, but in contrast to those found with electrochemical doping. A common feature between the two types of doping is found in the case of the 2-D band, which shows softening and stiffening on electron and hole doping, respectively. The experimental results are explained on the basis of the frequency shifts, electron-phonon coupling and structural inhomogeneities that are relevant to molecule-graphene interaction.

Longitudinal Magnetic Field Effect on Nonlocal Ultrasonic Vibration Analysis of Single-Walled Carbon Nanotubes Based on Wave Propagation Approach

This paper studies the effect of longitudinal magnetic field on ultrasonic vibration in single walled carbon nanotubes (CNTs) based on nonlocal continuum medium theory. Governing partial differential equations of CNTs are derived by considering the Lorentz magnetic forces applied on CNTs induced by a longitudinal magnetic field through Maxwell equations. The vibration characteristics of CNTs under a longitudinal magnetic field are obtained by solving the governing equations via wave propagation approach. The effects of longitudinal magnetic field on vibration of CNTs are discussed through numerical experiments. The present analysis show that vibration frequencies of CNTs drops dramatically in the presence of the magnetic field for various circumferential wavenumbers. Such effect is also observed for various boundary conditions of the CNT. New features for the effect of longitudinal magnetic field on ultrasonic vibration of CNTs, presented in this paper are useful in the design of nano-drive device, nano-oscillator and actuators and nano-electron technology, where carbon nanotubes act as basic elements.

Sivers effect and transverse single spin asymmetry in e+p(up arrow) -> e+J/psi+X

We discuss the possibility of using electroproduction of J/psi as a probe of gluon Sivers function by measuring single spin asymmetry (SSA) in experiments with transversely polarized protons and electron beams. We estimate SSA for JLab, HERMES, COMPASS, and eRHIC energies using the color evaporation model of charmonium production and find asymmetry up to 25% for certain choices of model parameters which have been used earlier for estimating SSA in the SIDIS and Drell-Yan processes.

Bismuth catalyzed growth of silicon nanowires by electron beam evaporation

Silicon nanowires (NWs) have been grown in the vapor phase for the first time with bismuth (Bi) as a catalyst using the electron beam evaporation method at a low substrate temperature of 280 degrees C. The grown Si nanowires were randomly oriented on the substrate with an average length of 900 nm for a deposition time of 15 min. Bi faceted nanoparticles (crowned) at the end of the grown Si nanowires have been observed and attributed to the Vapor-Liquid-Solid (VLS) growth mechanism. Transmission Electron Microscopy analysis on the nanowires revealed their single crystalline nature and interestingly bismuth particles were observed in Si nanowires. The obtained results have shown a new window for Si nanowires growth with bismuth as a catalyst. (C) 2012 Elsevier B.V. All rights reserved.

Electron rich supramolecular polymers as fluorescent sensors for nitroaromatics

Three pi-electron rich fluorescent supramolecular polymers (1-3) have been synthesized incorporating 2-methyl-3-butyn-2-ol groups in reasonable yield by employing Sonagashira coupling. They were characterized by multinuclear NMR (H-1, C-13), ESI-MS and single crystal X-ray diffraction analyses 1 = 1( 2-methyl-3-butyn-2-ol) pyrene; 2 = 9,10-bis(2-methyl-3-butyn-2-ol) anthracene; 3 = 1,3,6,8-tetrakis(2methyl- 3-butyn-2-ol) pyrene]. Single crystal structures of 1-3 indicated that the incorporation of hydroxy (-OH) groups on the peripheral of the fluorophores helps them to self-associate into an infinite supramolecular polymeric network via intermolecular hydrogen bonding interactions between the adjacent discrete fluorophore units. All these compounds showed fluorescence characteristics in chloroform solution due to the extended pi-conjugation and were used as selective fluorescent sensors for the detection of electron deficient nitroaromatics. The changes in photophysical properties of fluorophores (1-3) upon complex formation with electron deficient nitroaromatic explosives were studied in chloroform solution by using fluorescence spectroscopy. All these fluorophores showed the largest quenching response with moderate selectivity for nitroaromatics over various other electron deficient/ rich aromatic compounds tested (Chart 1). Analysis of the fluorescence titration profile of 9,10-bis(2-methyl-3butyn- 2-ol) anthracene fluorophore (2) with 1,3,5-trinitrotoluene/ 2,4-dinitrotoluene provided evidence that this particular fluorophore detects nitroaromatics in the nanomolar range 2.0 ppb for TNT, 13.7 ppb for DNT]. Moreover, sharp visual color change was observed upon mixing nitroaromatic (DNT) with fluorophores (1-3) both in solution as well as in solid phase. Furthermore, the vapor-phase sensing study of thin film of fluorophores (1-3) showed efficient quenching responses for DNT and this sensing process is reproducible. Selective fluorescence quenching response including a sharp visual color change for nitroaromatics make these tested fluorophores (1-3) as potential sensors for nitroaromatic compounds with a detection limit of ppb level.

Low temperature growth of SnO2 nanowires by electron beam evaporation and their application in UV light detection

For the first time, high quality tin oxide (SnO2) nanowires have been synthesized at a low substrate temperature of 450 degrees C via vapor-liquid-solid mechanism using an electron beam evaporation technique. The grown nanowires have shown length of 2-4 mu m and diameter of 20-60 nm. High resolution transmission electron microscope studies on the grown nanowires have shown the single crystalline nature of the SnO2 nanowires. We investigated the effect of growth temperature and oxygen partial pressure on SnO2 nanowires growth. Variation of substrate temperature at a constant oxygen partial pressure of 4 x 10(-4) mbar suggested that a temperature equal to or greater than 450 degrees C was the best condition for phase pure SnO2 nanowires growth. The SnO2 nanowires grown on a SiO2 substrate were subjected to UV photo detection. The responsivity and quantum efficiency of SnO2 NWs photo detector (at 10V applied bias) was 12 A/W and 45, respectively, for 12 mu W/cm(2) UV lamp (330 nm) intensity on the photo detector.

Electron paramagnetic resonance, magnetic and electrical properties of CoFe2O4 nanoparticles

CoFe2O4 nanoparticles were prepared by solution combustion method. The nanoparticle are characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy and scanning electron microscopy (SEM). PXRD reveals single phase, cubic spinel structure with Fd (3) over barm (227) space group. SEM micrograph shows the particles are agglomerated and porous in nature. Electron paramagnetic resonance spectrum exhibits a broad resonance signal g=2.150 and is attributed to super exchange between Fe3+ and Co2+. Magnetization values of CoFe2O4 nanoparticle are lower when compared to the literature values of bulk samples. This can be attributed to the surface spin canting due to large surface-to-volume ratio for a nanoscale system. The variation of dielectric constant, dielectric loss, loss tangent and AC conductivity of as-synthesized nano CoFe2O4 particles at room temperature as a function of frequency has been studied. The magnetic and dielectric properties of the samples show that they are suitable for electronic and biomedical applications.

Thermoelectric performance of a single-layer graphene sheet for energy harvesting

We investigate the thermoelectric (TE) figure-of-merit of a single-layer graphene (SLG) sheet by a physics-based analytical technique. We first develop analytical models of electrical and thermal resistances and the Seebeck coefficient of SLG by considering electron interactions with the in-plane and flexural phonons. Using those models, we show that both the figure-of-merit and the TE efficiency can be substantially increased with the addition of isotope doping as it significantly reduces the phonon-dominated thermal conductivity. In addition, we report that the TE open circuit output voltage and output power depends weakly on the SLG sheet dimensions and sheet concentration in the strongly diffusive regime. Proposed models agree well with the available experimental data and demonstrate the immense potential of graphene for waste-heat recovery application.

Single-step synthesis of internally functionalizable hyperbranched polyethers

Radical catalyzed thiol-ene reaction has become a useful alternative to the Huisgen-type azide-yne click reaction as it helps expand the variability in reaction conditions as well as the range of clickable entities. In this study, the direct generation of a hyperbranched polyether (HBPE) having decyl units at the periphery and a pendant allyl group on every repeat unit of the polymer backbone is described; the allyl groups serve as a reactive handle for postpolymerization modifications and permits the generation of a variety of internally functionalized HBPEs. In this design, the AB(2) monomer carries two decylbenzyl ether units (B-functionality), an aliphatic OH (A-functionality) and a pendant allyl group within the spacer segment; polymerization of the monomer readily occurs at 150 degrees C via melt transetherification process by continuous removal of 1-decanol under reduced pressure. The resulting HBPE has a hydrophobic periphery due to the presence of numerous decyl chains, while the allyl groups that remain unaffected during the melt polymerization provides an opportunity to install a variety of functional groups within the interior; thiol-ene click reaction with two different thiols, namely 3-mercaptopropionic acid and mercaptosuccinic acid, generated interesting amphiphilic structures. Preliminary field emission scanning electron microscope (FESEM) and Atomic Force Microscopy (AFM) imaging studies reveal the formation of fairly uniform spherical aggregates in water with sizes ranging from 200 to 400 nm; this suggests that these amphiphilic HBPs is able to reconfigure to generate jellyfish-like conformations that subsequently aggregate in an alkaline medium. The internal allyl functional groups were also used to generate intramolecularly core-crosslinked HBPEs, by the use of dithiol crosslinkers; gel permeation chromatography traces provided clear evidence for reduction in the size after crosslinking. In summary, we have developed a simple route to prepare core-clickable HBPEs and have demonstrated the quantitative reaction of the allyl groups present within the interior of the polymers; such HB polymeric systems that carry numerous functional groups within the core could have interesting applications in analyte sequestration and possibly sensing, especially from organic media. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4125-4135

Single crystalline magnetite, maghemite, and hematite nanoparticles with rich coercivity

One-pot synthesis of amorphous iron oxide nanoparticles with two different dimensions (<5 nm and 60 nm) has been achieved using the reverse micelle method, with <5 nm nanoparticles separated from the stable colloid by exploiting their magnetic behaviour. The transformation of the as-prepared amorphous powders into Fe3O4 and Fe2O3 phases (gamma and alpha) is achieved by carrying out controlled annealing at elevated temperatures under different optimized conditions. The as-prepared samples resulting from micellar synthesis and the corresponding annealed ones are thoroughly characterized by powder X-ray diffraction, transmission electron microscopy (TEM), and by Raman and X-ray photoelectron spectroscopies. Expectedly, the magnetic characteristics of Fe3O4 and Fe2O3 phase (gamma and alpha) nanoparticles are found to have strong dependence on their phase, dimension, and morphology. The coercivity of Fe3O4 and Fe2O3 (gamma and alpha) nanoparticles is reasonably high, even though high resolution TEM studies bring out that these nanoparticles are single crystalline. This is in contrast with previous reports wherein poly-crystallinity of iron oxides nanoparticles has been regarded as a prerequisite for high coercivity.

Experimental study of fracture behavior of magnesium single crystals

In this work, the fracture behavior of magnesium single crystals is studied by conducting experiments with notched three point bend specimens of three crystallographic orientations. In the first and second orientations, the c-axis is along the normal to the flat surface of the notch, while in the third it is aligned with the notch front. For all the orientations, in situ electron back scattered diffraction observations made around the notch root show profuse tensile twinning of {10 (1) over bar2} type. Further, in the first two orientations basal and prismatic slip traces are identified from optical metallography. The width of the most prominent twin saturates at around 120-150 mu m, while twins continue to nucleate farther away to accommodate plastic deformation. In all the orientations, crack initiation occurs before the attainment of peak load and the crack grows stably along twin-matrix interface before deflecting at twin-twin intersections. Results show that profuse tensile twinning is an important energy dissipating mechanism that enhances the fracture toughness. (C) 2013 Elsevier B.V. All rights reserved.

Synthesis, Characterization and Properties of Single-Walled Carbon Nanohorns

Single-walled nanohorns (SWNHs) have been prepared by sub-merged arc discharge of graphite electrodes in liquid nitrogen. The samples were examined by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. Nitrogen and boron doped SWNHs have been prepared by the sub-merged arc discharge method using melamine and elemental boron as precursors. Intensification of Raman D-band and stiffening of G-band has been observed in the doped samples. The electrical resistance of the SWNHs varies in opposite directions with nitrogen and boron doping. Functionalization of SWNHs through amidation has been carried out for solubilizing them in non-polar solvents. Water-soluble SWNHs have been produced by acid treatment and non-covalent functionalization with a coronene salt. SWNHs have been decorated with nanoparticles of Au, Ag and Pt. Interaction of electron donor (tetrathiafulvalene, TTF) and acceptor molecules (tetracyanoethylene, TCNE) with SWNHs has been investigated by Raman spectroscopy. Progressive softening and stiffening of Raman G-band has been observed respectively with increase in the concentration of TTF and TCNE.