Magnetic coupled electrochemistry: Exploring the use of superparamagnetic nanoparticles for capturing, transporting and concentrating trace amounts of analytes

We propose the use of functionalized superparamagnetic nanoparticles for capturing, and transporting analytes, in association with an external miniature magnet to deposit such nanocarrier species at the electrode surface. This approach can be employed for the electroanalytical determination of chemical species capable of interacting with the nanoparticles, or in the opposite case, to block their response at the electrode surface. The concept was successfully demonstrated by using aminofunctionalized nanoparticles to block the discharge of hexacyanoferrate(II) ions, and to enhance the signals of aquapentacyanoferrate(II) ions via coordination to the surface amino groups. Selective analysis was also performed for silver ions, surpassing the stripping methods in terms of versatility and usefulness. (C) 2010 Elsevier B.V. All rights reserved.

Solid-state NMR, ionic conductivity, and thermal studies of lithium-doped siloxane-poly(propylene glycol) organic-inorganic nanocomposites

Hybrid organic-inorganic ionic conductors, also called ormolytes (organically modified electrolytes), were obtained by dissolution of LiClO 4 in siloxane-poly(propylene glycol) matrixes. The dynamic features of these nanocomposites were studied and correlated to their electrical properties. Solid-state nuclear magnetic resonance (NMR) spectroscopy was used to probe the effects of the temperature and nanocomposite composition on the dynamic behaviors of both the ionic species ( 7Li) and the polymer chains ( 13C). NMR, dc ionic conductivity, and DSC results demonstrate that the Li + mobility is strongly assisted by the segmental motion of the polymer chain above its glass transition temperature. The ac ionic conductivity in such composites is explained by use of the random free energy barrier (RFEB) model, which is agreement with their disordered and heterogenous structures. These solid ormolytes are transparent and flexible, and they exhibit good ionic conductivity at room temperature (up to 10 -4 S/cm). Consequently, they are very promising candidates for use in several applications such as batteries, sensors, and electrochromic and photoelectro-chemical devices.

Magnetic fields and uniformity of radio frequency power deposition in low-frequency inductively coupled plasmas with crossed internal oscillating currents

Radial and axial distributions of magnetic fields in a low-frequency (∼460 kHz)inductively coupled plasmasource with two internal crossed planar rf current sheets are reported. The internal antenna configuration comprises two orthogonal sets of eight alternately reconnected parallel and equidistant copper litz wires in quartz enclosures and generates three magnetic (H z, H r, and H φ) and two electric (E φ and E r) field components at the fundamental frequency. The measurements have been performed in rarefied and dense plasmas generated in the electrostatic(E) and electromagnetic (H)discharge modes using two miniature magnetic probes. It is shown that the radial uniformity and depth of the rf power deposition can be improved as compared with conventional sources of inductively coupled plasmas with external flat spiral (“pancake”) antennas. Relatively deeper rf power deposition in the plasma source results in more uniform profiles of the optical emission intensity, which indicates on the improvement of the plasma uniformity over large chamber volumes. The results of the numerical modeling of the radial magnetic field profiles are found in a reasonable agreement with the experimental data.

Synthesis, Crystal Structure, and Magnetic Properties of a Ferromagnetically Coupled Angular Trinuclear Copper(11) Complex [Cu3(02CMe)4(bpy)s(HzO)](PF)62

The synthesis, X-ray crystal structure, and magnetic properties of an angular trinuclear copper(II) complex [Cu3(O2CMC)4(bpy)3(H2O)](PF6)2 (1), obtained from a reaction of Cu2(O2CMe)4(H2O)2 With 2,2'-bipyridine (bpy) and NH4PF6 in ethanol, are reported. Complex 1 crystallizes in triclinic space group P1BAR with a = 11.529(1) angstrom, b = 12.121(2) angstrom, c = 17.153(2) angstrom, alpha = 82.01(1)-degrees, beta = 79.42(1)-degrees, gamma = 89.62(1)-degrees, and Z = 2. A total of 6928 data with I > 2.5sigma(I) were refined to R = 0.0441 and R(w) = 0.0557. The structure consists of a trinuclear core bridged by four acetate ligands showing different bonding modes. The coordination geometry at each copper is distorted square-pyramidal with a CuN2O2...O chromophore. The Cu...Cu distances are 3.198(1) angstrom, 4.568(1) angstrom, and 6.277(1) angstrom. There are two monoatomic acetate bridges showing Cu-O-Cu angles of 93.1(1) and 97.5(1)-degrees. Magnetic studies in the temperature range 39-297 K show the presence of a strong ferromagnetically coupled dicopper(II) unit (2J = +158 cm-1) and an essentially isolated copper(II) center (2J' = -0.4 cm-1) in 1. The EPR spectra display an axial spectrum giving g(parallel-to) = 2.28 (A(parallel-to) = 160 X 10(-4) cm-1) and g(perpendicular-to) = 2.06 (A(perpendicular-to) = 12 X 10(-4) cm-1) for the normal copper and two intense isotropic signals with g values 2.70 and 1.74 for the strongly coupled copper pair. The structural features of 1 compare well with the first generation models for ascorbate oxidase.

Coupled phonons, magnetic excitations, and ferroelectricity in AlFeO3: Raman and first-principles studies

We determine the nature of coupled phonons and magnetic excitations in AlFeO3 using inelastic light scattering from 5 to 315 K covering a spectral range from 100 to 2200 cm(-1) and complementary first-principles density functional theory-based calculations. A strong spin-phonon coupling and magnetic ordering-induced phonon renormalization are evident in (1) anomalous temperature dependence of many modes with frequencies below 850 cm(-1), particularly near the magnetic transition temperature T-c approximate to 250 K, and (2) distinct changes in band positions of high-frequency Raman bands between 1100 and 1800 cm(-1); in particular, a broad mode near 1250 cm(-1) appears only below T-c, attributed to the two-magnon Raman scattering. We also observe weak anomalies in the mode frequencies similar to 100 K due to a magnetically driven ferroelectric phase transition. Understanding of these experimental observations has been possible on the basis of first-principles calculations of the phonons' spectrum and their coupling with spins.

Structural and magnetic properties of SmCo5/Co exchange coupled nanocomposite thin films

We investigated the structural and magnetic properties of SmCo5/Co exchange coupled nanocomposite thin films grown by magnetron sputtering from Sm and Co multitargets successively. The growth of the films was carried out at elevated substrate temperature followed by in situ annealing. On Si (100) substrate, X-ray diffraction confirms the formation of textured (110) SmCo5 hard phase, whereas on MgO (110) substrate, the diffraction pattern shows the epitaxial growth of SmCo5 phase with crystalline orientation along 100] direction. Secondary Ion Mass Spectroscopy reveals the structural transformation from multilayered (Sm/Co) to SmCo5/Co nano-composite films due to high reactivity of Sm at elevated temperature. Transmission electron microscopy indicates the existence of nanocrystalline phase of SmCo5 along with unreacted Co. Observed single phase behavior in magnetic hysteresis measurements indicates well exchange coupling between the soft and the hard phases in these nano-composite films. For samples with samarium layer thickness, t(sm)=3.2 nm and cobalt layer thickness, t(Co)= 11.4 nm, the values of (BH)(max) were obtained as 20.1 MGOe and 12.38 MGOe with H-c value similar to 3.0 kOe grown on MgO and Si substrates, respectively.

Giant actuation in bulk carbon nanotubes under coupled electric and magnetic fields

We report an enhanced actuation in bulk carbon nanotubes (CNTs) under coupled electric and magnetic fields, which is much higher than that evaluated in the presence of individual fields. Coupled electric and magnetic fields induce a directional actuation demonstrating a transformation from polarity independent to dependent actuation behavior of CNTs. Both qualitative and quantitative analyses are performed to understand this transformation in the bulk CNTs. Moreover, actuations along radial and axial directions of CNTs have also demonstrated a similar directional behavior.

Controlling magnetic ordering in coupled nanomagnet arrays

We have fabricated using high-resolution electron beam lithography circular magnetic particles (nanomagnets) of diameter 60 nm and thickness 7 nm out of the common magnetic alloy supermalloy. The nanomagnets were arranged on rectangular lattices of different periods. A high-sensitivity magneto-optical method was used to measure the magnetic properties of each lattice. We show experimentally how the magnetic properties of a lattice of nanomagnets can be profoundly changed by the magnetostatic interactions between nanomagnets within the lattice. We find that simply reducing the lattice spacing in one direction from 180 nm down to 80 nm (leaving a gap of only 20 nm between edges) causes the lattice to change from a magnetically disordered state to an ordered state. The change in state is accompanied by a peak in the magnetic susceptibility. We show that this is analogous to the paramagnetic-ferromagnetic phase transition which occurs in conventional magnetic materials, although low-dimensionality and kinetic effects must also be considered.

Carrier concentration profiling in magnetic GaMnSb/GaSb investigated by electrochemistry capacitance-voltage profiler

Depth profiles of carrier concentrations in GaMnSb/GaSb are investigated by electrochemistry capacitance-voltage profiler and electrolyte of Tiron. The carrier concentration in GaMnSb/GaSb measured by this method is coincident with the results of Hall and X-ray diffraction measurements. It is indicated that most of the Mn atoms in GaMnSb take the site of Ga, play a role of acceptors, and provide shallow acceptor level(s).

Coupled thermal-magnetic analysis on thermally actuated superconducting flux pump

This paper presents numerical analysis of the thermally actuated superconducting flux pump. Visualization of the behavior of the magnetic flux helps our understanding of flux injection mechanism. In addition, in order to confirm validity of the result, we conducted a preliminary flux pump experiment. This result qualitatively agrees well with the experimental one. The flux pump system utilizes a particular behavior that permeability of some materials such as Gadolinium is sensitive to the temperature. In this paper a simple heater is used to control the flux pump system. © 2010 IEEE.

Suppression of exciton recombination in symmetric GaAs0.7Sb0.3/GaAs/GaAs0.7P0.3 coupled quantum wells induced by an in-plane magnetic field

Suppression of the exciton recombination in GaAs0.7Sb0.3/GaAs/GaAs0.7P0.3 coupled quantum well (CQW) induced by an external magnetic field is investigated theoretically. Unlike the usual electro-Stark effect, the exciton energy dispersion of an exciton is modified by an external in-plane magnetic field, the ground state of the magnetoexciton shifts from a zero in-plane center of mass (CM) momentum to a finite CM momentum, and the Lorentz force induces the spatial separation of electron and hole. Consequently, this effect renders the ground state of magnetoexciton stable against radiative recombination due to momentum conservation. This effect depends sensitively on the thickness and height of GaAs0.7Sb0.3 layer, therefore it could provide us useful infometion about the band alignment of CQW. (C) 2004 American Institute of Physics.

Coherent tunnelling in coupled quantum wells under a uniform magnetic fields

Coherent tunnelling is studied in framework of the effective mass approximation for an asymmetric coupled quantum well. The Hartree potential due to the electron-electron interaction is considered in our calculation. The effects of the longitudinal and transverse magnetic field on coherent tunnelling characteristics are discussed. It has been found that the external field plays an important role in modulating the electron states.

Carrier concentration profiling in magnetic GaMnSb/GaSb investigated by electrochemistry capacitance-voltage profiler

Depth profiles of carrier concentrations in GaMnSb/GaSb are investigated by electrochemistry capacitance-voltage profiler and electrolyte of Tiron. The carrier concentration in GaMnSb/GaSb measured by this method is coincident with the results of Hall and X-ray diffraction measurements. It is indicated that most of the Mn atoms in GaMnSb take the site of Ga, play a role of acceptors, and provide shallow acceptor level(s).