Unconventional carrier-mediated ferromagnetism above room temperature in ion-implanted (Ga,Mn)P:C

Ion implantation of Mn ions into hole-doped GaP has been used to induce ferromagnetic behavior above room temperature for optimized Mn concentrations near 3 at. %. The magnetism is suppressed when the Mn dose is increased or decreased away from the 3 at. % value, or when n-type GaP substrates are used. At low temperatures the saturated moment is on the order of 1 Bohr magneton, and the spin wave stiffness inferred from the Bloch-law T(3/2) dependence of the magnetization provides an estimate T(c)=385 K of the Curie temperature that exceeds the experimental value, T(c)=270 K. The presence of ferromagnetic clusters and hysteresis to temperatures of at least 330 K is attributed to disorder and proximity to a metal-insulating transition.     

Synthesis of 2H-labeled alkoxyethyl phosphodiester (AZT) derivatives for solid-state 2H-NMR studies

Two specifically ²H-labeled alkoxyethyl phosphodiester AZT derivatives 9 and 14 were synthesized. Pilot [²H]-solid-state nmr experiments on conjugate 14 demonstrated their usefulness in studying interactions with model or biological membranes.     

N.M.R. study of segmental molecular interactions in liquid crystals

Abstract

A simple statistical model of interacting non-rigid molecules, based on a perturbation expansion of the pair correlation function and the additivity of segmental interactions, is applied to the study of orientational order as measured by N.M.R. in the nematic and S_A phases of 4-n-alkyl-4′-cyanobiphenyls (N-CB, N = 5 to 8), the nematic and S_C phases of 4-n-alkyloxybenzoic acids (N-OBA, N = 7, 8) and the D _h0 columnar discotic phase of hexa-alkyloxytriphenylenes (N-THE, N = 5 to 8). The order parameters of each homologous series are correctly described in terms of two isotropic and two anisotropic segmental coupling constants. The model predicts certain relations among coupling constants pertaining to different homogous series. These predictions are supported by the results obtained for the three types of compounds studied.     

Ultra-performance liquid chromatography/tandem mass spectrometry method for the determination of lercanidipine in human plasma

A simple, sensitive and rapid ultra-performance liquid chromatography/positive electrospray ionization tandem mass spectrometry (UPLC/ESI-MS/MS) method has been developed and validated for the determination of lercanidipine in human plasma. Lercanidipine and the internal standard, nicardipine, were extracted from plasma by liquid-liquid extraction using tert-butyl methyl ether as the extraction solvent. UPLC analysis was performed isocratically on an AcQuity UPLC BEH C18 analytical column (2.1 x 50.0 mm i.d., particle size 1.7 microm). The mobile phase consisted of 70% acetonitrile in water containing 0.2% v/v formic acid and pumped at a flow rate of 0.30 mL/min. ESI in positive ion mode, with multiple reaction monitoring (MRM), was chosen for the detection of the analytes. The assay was linear over a concentration range of 0.05-30 ng/mL for lercanidipine with a limit of quantitation of 0.05 ng/mL. Quality control samples (0.05, 0.15, 15 and 25 ng/mL) in five replicates from five of analytical runs demonstrated intra-assay precision (% CV < or =7.3%), inter-assay precision (% CV < or =6.1%) and an overall accuracy (% relative error) of less than 6.2%. A run time of less than 1.0 min for each sample made it possible to analyze a large number of human plasma samples per day. The method can be used to quantify lercanidipine in human plasma covering a variety of pharmacokinetic or bioequivalence studies.     

N.M.R. study of segmental molecular interactions in liquid crystals

A simple statistical model of interacting non-rigid molecules, based on a perturbation expansion of the pair correlation function and the additivity of segmental interactions, is applied to the study of orientational order as measured by N.M.R. in the nematic and S_A phases of 4-n-alkyl-4'-cyanobiphenyls (N-CB, N = 5 to 8), the nematic and S_C phases of 4-n-alkyloxybenzoic acids (N-OBA, N = 7, 8) and the D_h0 columnar discotic phase of hexa-alkyloxytriphenylenes (N-THE, N = 5 to 8). The order parameters of each homologous series are correctly described in terms of two isotropic and two anisotropic segmental coupling constants. The model predicts certain relations among coupling constants pertaining to different homogous series. These predictions are supported by the results obtained for the three types of compounds studied.     

Thin porous anodic alumina films: Interface trap density determination

The electrical properties of thin porous alumina films in the form of MOS structures were studied with dielectric spectroscopy at room temperature. The thickness of the samples was found to be approximately 95 nm with a cross section area of 1.6×10⁻³ cm².C-V andG-V measurements were performed by applying a loop sweep voltage 2.0 V to −5.0 V. Correction to the measurements were performed by considering a series resistanceR _S and leakage currentI _DC. TheC-V results show hysteresis effects due to the presence of positive charges in porous alumina. These charges may be are attributed to the residual electrolyte during the anodization process in the sample preparation. Three distinct regions in theC-V results are observed, namely the inversion, the depletion and the accumulation regions. In the voltage region, where depletion of carriers is observed,C-f andG-f measurements were recorded in the frequency range 1 Hz to 10⁶ Hz. The conductance method was applied for the calculation of the density D_it of carriers, trapped in the interface between insulator and semiconductor, and of the response time τ_it as a function of the applied bias voltage were performed. The values obtained for D_it and τ_it are of the order of 3×10¹² eV⁻¹ cm⁻² and 10⁻³ s, respectively, and they are voltage dependent. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.