Functional methods in the theory of magnetoimpurity states of electrons in quantum wires

Functional methods are used to study magnetoimpurity states of electrons in nanostructures. The Keldysh formalism is applied to these states. The theory is illustrated using a quantum wire sample with impurity atoms capable of localizing electrons in a magnetic field. The characteristics of magnetoimpurity states of electrons in the wire are calculated using the model of a Gaussian separable potential.Comment: 15 pages, 1 figur

Propagation of wave packets in randomly stratified media

The propagation of a narrow-band signal radiated by a point source in a randomly layered absorbing medium is studied asymptotically in the weak-scattering limit. It is shown that in a disordered stratified medium that is homogeneous on average a pulse is channelled along the layers in a narrow strip in the vicinity of the source. The space-time distribution of the pulse energy is calculated. Far from the source, the shape of wave packets is universal and independent of the frequency spectrum of the radiated signal. Strong localization effects manifest themselves also as a low-decaying tail of the pulse and a strong time delay in the direction of stratification. The frequency-momentum correlation function in a one-dimensional random medium is calculated.Comment: 11 pages, 3 figures, Revtex-4. Submitted to Phys. Rev.

Solid-state metathesis reactions under pressure: A rapid route to crystalline gallium nitride

High pressure chemistry has traditionally involved applying pressure and increasing temperature until conditions become thermodynamically favorable for phase transitions or reactions to occur. Here, high pressure alone is used as a starting point for carrying out rapid, self-propagating metathesis reactions. By initiating chemical reactions under pressure, crystalline phases, such as gallium nitride, can be synthesized which are inaccessible when initiated from ambient conditions. The single-phase gallium nitride made by metathesis reactions under pressure displays significant photoluminescence intensity in the blue/ultraviolet region. The absence of size or surface-state effects in the photoluminescence spectra show that the crystallites are of micron dimensions. The narrow lines of the x-ray diffraction patterns and scanning electron microscopy confirm this conclusion. Brightly luminescent thin films can be readily grown using pulsed laser deposition

Acoustic Cyclotron Resonance and Giant High Frequency Magnetoacoustic Oscillations in Metals with Locally Flattened Fermi Surface

We consider the effect of local flattening on the Fermi surface (FS) of a metal upon geometric oscillations of the velocity and attenuation of ultrasonic waves in the neighborhood of the acoustic cyclotron resonance. It is shown that such peculiarities of the local geometry of the FS can lead to a significant enhancement of both cyclotron resonance and geometric oscillations. Characteristic features of the coupling of ultrasound to shortwave cyclotron waves arising due to the local flattening of the FS are analyzed. PACS numbers 71.18.+y; 72.15.Gd; 72.15.-vComment: 8 pages, 3 figures, text revise

Optically pure heterobimetallic helicates from self-assembly and click strategies

Single diastereomer, diamagnetic, octahedral Fe(II) tris chelate complexes are synthesised that contain three pendant pyridine proligands pre-organised for coordination to a second metal. They bind Cu(I) and Ag(I) with coordination geometry depending on the identity of the metal and the detail of the ligand structure, but for example homohelical (ΔFe,ΔCu) configured systems with unusual trigonal planar Cu cations are formed exclusively in solution as shown by VT-NMR and supported by DFT calculations. Similar heterobimetallic tris(triazole) complexes are synthesised via clean CuAAC reactions at a tris(alkynyl) complex, although here the configurations of the two metals differ (ΔFe,ΛCu), leading to the first optically pure heterohelicates. A second series of Fe complexes perform less well in either strategy as a result of lack of preorganisation

A layered surface acoustic wave gas sensor based on a polyaniline/In2O3 nanofibre composite

A polyaniline/In2O3 nanofibre composite based layered surface acoustic wave ( SAW) sensor has been developed and investigated for different gases. Chemical oxidative polymerization of aniline in the presence of finely divided In2O3 was employed to synthesize a polyaniline nanofibre/In2O3 nanoparticle composite. The nanocomposite was deposited onto a layered ZnO/64 degrees YX LiNbO3 SAW transducer. The novel sensor was exposed to H-2, NO2 and CO gases. Fast response and recovery times with good repeatability were observed at room temperature

PSSA doped polyaniline nanofiber based ZnO/64° YX LiNbO3 SAW H2 gas sensor

A polyaniline (PANI) nanofiber based surface acoustic wave (SAW) gas sensor, has been developed and investigated towards hydrogen (H<sub>2</sub>) gas. A template-free, rapidly-mixed reaction approach was employed to synthesize polyaniline nanofibers, which utilized chemical oxidative polymerization of aniline. Hydrochloric acid (HCl) was used as the dopant acid in the synthesis of the polyaniline nanofibers. Polystyrene sulfonic acid (PSSA) was used to re-dope PANI nanofibers after dialyzing with ammonium hydroxide. Then PSSA doped nanofibers were deposited onto a ZnO/64 YX LiNbO<sub>3</sub> SAW transducer. The sensor was exposed to various concentrations of H<sub>2</sub> gas in an ambient of synthetic air, and operated at room temperature

Probing Spin-Charge Relation by Magnetoconductance in One-Dimensional Polymer Nanofibers

Polymer nanofibers are one-dimensional organic hydrocarbon systems containing conducting polymers where the non-linear local excitations such as solitons, polarons and bipolarons formed by the electron-phonon interaction were predicted. Magnetoconductance (MC) can simultaneously probe both the spin and charge of these mobile species and identify the effects of electron-electron interactions on these nonlinear excitations. Here we report our observations of a qualitatively different MC in polyacetylene (PA) and in polyaniline (PANI) and polythiophene (PT) nanofibers. In PA the MC is essentially zero, but it is present in PANI and PT. The universal scaling behavior and the zero (finite) MC in PA (PANI and PT) nanofibers provide evidence of Coulomb interactions between spinless charged solitons (interacting polarons which carry both spin and charge)

Doped and dedoped polyaniline nanofiber based conductometric hydrogen gas sensors

Template-free, rapid polymerisation was employed to synthesize polyaniline nanofibers using chemical oxidative polymerisation of aniline, with HCl as a dopant. The doped and dedoped nanofibers were deposited onto conductometric sapphire transducers for gas sensing applications. The sensors were exposed to various concentrations of hydrogen (H2) gas at room temperature. The sensitivity was measured to be 1.11 for doped and 1.07 for dedoped polyaniline nanofiber sensors upon exposure to 1% H2. Fast response times of 28 seconds and 32 seconds were observed for dedoped and doped sensors respectively. The dedoped nanofiber sensor outperforms the doped sensor in terms of baseline stability and repeatability. Due to its room temperature operation, the gas sensor is promising for environmental applications

Nanomaterial based room temperature Hydrogen gas sensors

Polyaniline (PANI) nanofiber and PANI/semi-conducting metal oxide nanofiber composites based layered surface acoustic wave (SAW) and conductometric sensors have been developed and investigated towards hydrogen (H<sub>2</sub>) gas. Chemical oxidative polymerization of aniline was employed to synthesize pure PANI nanofibers as well as PANI/semi-conducting metal oxide composites. The nano-materials were deposited onto layered ZnO/64deg YX LiNbO<sub>3</sub> SAW and conductometric transducers. The novel sensors were exposed to H<sub>2</sub> gas. Fast response and recovery with good repeatability were observed at room temperature