Spherical Particles of Zirconia-Titania of Hexagonal Structure from a Neutral Amine Route

Through the sol–gel process, using the so-called neutral amine route, spherical particles of 1:1 zirconia–titania were synthesized from zirconium(IV) and titanium(IV) butoxides as well as 1,12-diaminododecane as precursor species. The obtained product exhibited a hexagonal structure, as determinated by X-ray diffraction data. The obtained material was also characterized by thermogravimetry, differential scanning calorimetry, infrared spectroscopy, scanning electron microscopy, and surface area measurements. Despite the release of template molecules on heating, the spherical morphology was retained up to about 1200°C, at which the disruption of the spheres took place.     

Effects of Adsorbed Polyaniline on Redox Process on MoO3 Surface

The effects exhibited by adsorbed conducting polyaniline on the redox process on a molybdenum oxide surface were studied. Thermogravimetric results indicate a 4% polyaniline deposition. Cyclic voltammograms of the adsorbed polymer on MoO3 show that polyaniline exerts remarkable effects on the molybdenum blue oxidation-reduction process, with oxidation and reduction potentials of 0.33 and 0.18 V, respectively. This effect strongly enhances the electrode response, and can be used as an important tool in qualitative and/or quantitative determinations of molybdenum in solution as well as in any substrate. Copyright 1999 Academic Press.     

Recombination and transport in microcrystalline pin solar cells studied with pulsed electrically detected magnetic resonance

An analysis of spin-dependent processes in microcrystalline silicon (μc-Si:H) pin solar cells is presented using pulsed electrically detected magnetic resonance (pEDMR). In this first study it is shown that by modulating the morphology of the n-type contact layer from amorphous to microcrystalline, pronounced changes in the pEDMR spectra may be observed. Due to the fact that pEDMR allows a deconvolution of the spin-dependent signals in time as well as in magnetic field domain, we were able to significantly reduce the complexity of the spectra compared to conventional EDMR. In the samples containing amorphous n-type contact layers we found signals from shallow localized conduction band tail states and phosphorous donor states. Upon replacement of this layer by its microcrystalline counterpart both signals disappeared. Possible spin-dependent transport mechanisms involving paramagnetic states in the various layers are discussed in view of sign and time evolution of the associated pEDMR signals.     

Perdeuterated Conjugated Polymers for Ultralow‐Frequency Magnetic Resonance of OLEDs

The formation of excitons in OLEDs is spin dependent and can be controlled by electron‐paramagnetic resonance, affecting device resistance and electroluminescence yield. We explore electrically detected magnetic resonance in the regime of very low magnetic fields (<1 mT). A pronounced feature emerges at zero field in addition to the conventional spin‐ Zeeman resonance for which the Larmor frequency matches that of the incident radiation. By comparing a conventional π‐conjugated polymer as the active material to a perdeuterated analogue, we demonstrate the interplay between the zero‐field feature and local hyperfine fields. The zero‐field peak results from a quasistatic magnetic‐field effect of the RF radiation for periods comparable to the carrier‐pair lifetime. Zeeman resonances are resolved down to 3.2 MHz, approximately twice the Larmor frequency of an electron in Earth's field. However, since reducing hyperfine fields sharpens the Zeeman peak at the cost of an increased zero‐field peak, we suggest that this result may constitute a fundamental low‐field limit of magnetic resonance in carrier‐pair‐based systems. OLEDs offer an alternative solid‐state platform to investigate the radical‐pair mechanism of magnetic‐field effects in photochemical reactions, allowing models of biological magnetoreception to be tested by measuring spin decoherence directly in the time domain by pulsed experiments.     

Investigation of third-order nonlinear optical susceptibility in polymer complexes of diarylidenealkanones

The third-order nonlinear optical susceptibility in polymer complexes of diarylidenealkanones has been investigated by the third harmonic generation technique at a wavelength of 1.06 μm. The macroscopic nonlinear susceptibility χ ⁽³⁾ measured is compared with the calculated γ values of the second-rank molar hyperpolarizability tensor. It is demonstrated that low-molecular chromophores can be used in syntheses of the stable polymer composite systems with a high nonlinear optical susceptibility. A further improvement in the nonlinear optical properties of complexes between deprotonated chromophores and high-basicity polymers can be achieved using the proposed methods. __________ Translated from Fizika Tverdogo Tela, Vol. 42, No. 11, 2000, pp. 2099–2102. Original Russian Text Copyright ? 2000 by Ten’kovtsev, Yakimanski, Lukoshkin, Dudkina, Boehme.     

The energetic and structural effects of steric crowding in phosphate and dithiophosphinate complexes of lanthanide cations M3+: a computational study

Metal-ligand binding strength and selectivity result from antagonistic metal-ligand M-L attractions and ligand-ligand L-L repulsions. On the basis of quantum-mechanical (QM) calculations on lanthanide complexes, we show that this interplay determines the binding affinities in the gas phase. In the series of [ML3] complexes (M = La, Eu, and Yb) with negatively charged phosphoryl ligands L- = (MeO)2PO2- and Me2PS2-, the binding energies follow the order Yb3+ > Eu3+ > La3- for a given ligand, and (MeO)2PO2- > Me2PS2- for a given cation. However, adding a neutral LH ligand to [ML3] changes the order to Eu3+ > Yb3+ > La3+ for the oxygen ligand and La3+ > Eu3- > Yb3+ for the sulfur ligand, indicating that steric strain in the first coordination sphere is largest for the smallest cation and for sulfur binding sites. We investigated the question of additional hydration of the [ML3LH] complexes in aqueous solution by molecular dynamics (MD) simulations, using two sets of atomic charges. It was found that pairwise additive potentials overestimate the coordination and hydration numbers of the cations, while adding polarization energy terms for the ligands yields better agreement between QM and MD results and supports the concept of steric strain in the first coordination sphere.     

The Tetracyanopyridinide Dimer Dianion, σ‐[TCNPy]22−

The reaction of 2,3,5,6‐tetracyanopyridine (TCNPy) and Cr(C₆H₆)₂ forms diamagnetic σ‐[TCNPy]₂^2? possessing a 1.572(3) Å intrafragment sp³–sp³ bond. This is in contrast to the structurally related 1,2,4,5‐tetracyanobenzene and 1,2,4,5‐tetracyanopyrazine that form π‐dimer dianions possessing long, multicenter bonds.