Studies of divacancy in Si using positron lifetime measurement

The charge state dependence of positron lifetime and trapping at divacancy (V₂) in Si doped with phosphorus or boron has been studied after 15 McV electron irradiation up to a fluence of 8.0×10¹⁷ e/cm². The positron trapping cross sections for V ₂ ^2– , V ₂ ^– and V ₂ ⁰ at 300 K were about 6×10^–14, 3×10^–14 and 0.1–3×10^–14 cm², respectively. For V ₂ ⁺ , however, no positron trapping was observed. The marked difference in the cross sections comes from Coulomb interaction between the positron and the charged divacancy. The trapping rates for V ₂ ⁰ and V ₂ ^2– have been found to increase with decreasing temperature in the temperature range of 10–300 K. These results are well interpreted by a two-stage trapping model having shallow levels with energy of 9 meV (V ₂ ⁰ ) and 21 meV (V ₂ ^2– ). The appearance of a shallow level for V ₂ ⁰ can not be explained by a conventional Rydberg state model. The lifetime (290–300 ps) in V ₂ ⁰ is nearly constant in the temperature range from 10 to 300 K, while that in V ₂ ^2– increases from 260 ps at 10 K to 320 ps at 300 K. The lifetime (260 ps) in V ₂ ^2– is shorter than that in V ₂ ⁰ at low temperature, which is due to the excess electron density in V ₂ ^2– . At high temperature, however, the longer lifetime of V ₂ ^2– than that of V ₂ ⁰ is attributed to lattice relaxation around V ₂ ^2– .     

Parametric modelling of Poisson-Gaussian random matrix ensembles

We analyse a scheme of transition from the Poissonian statistics for quantum levels to the Gaussian one of random matrix ensembles in the framework of level dynamics discussed by Yukawa. We propose a means of connecting these two limiting statistics by showing a result that Yukawa's parameter / of the exponential family can be efficiently replaced by the ratio <E>/<Q> which reflects directly a degree of the eigenvalue correlations of each sample matrix in the ensemble. On this basis, we discuss a correspondence between the level statistics of a generic quantum system and its classical regular/chaotic dynamics in terms of the semiclassical power spectrum and its second moment formulated by Feingold-Peres and Prosen-Robnik. We also discuss some limiting proceduresN (infinite limit of the matrix dimension) pertinent to the Gaussian ensembles, and remark about the possibility offractional power law of Brody's type.     

Direct and stepwise intercalation of alkylalcohols intoα-zirconium phosphate

Intercalation of alkylalcohols into -zirconium phosphate was investigated at 25°C and/or under reflux.n-Alcohols having two to five carbons and 2-propanol were taken up at 25°C. These alcohols, andn-hexanol and heptanol, also intercalated under reflux.n-Alcohols having eight to eighteen carbon atoms intercalated when a stepwise method was employed. 2-Butanol and tertiary amylalcohols intercalated under reflux using a butanol intercalate as a starting material. Ethanol-to-butanol intercalates were unstable at room temperature, losing alcohols and changing to -zirconium phosphate. The particle size of the -zirconium phosphate did not affect the intercalation of alcohols.     

o-Phenylene halocarbenonitrenes and o-phenylene chlorocarbenocarbene: a combined experimental and computational approach

[reaction: see text] Computations find that o-phenylene(halo)carbenonitrenes 2-XN, X = F, Cl, Br, have quinoidal singlet biradical ground states such as the parent o-phenylenecarbenonitrene (2-HN). Compared to the parent 2-HN, halogen substitution stabilizes the A' states relative to the A' ones. Halogen substitution also affects the barrier and exothermicity of the ring-opening reaction (to form unsaturated nitriles 4-XN, X = F, Cl, Br), but it has a smaller effect on the ring-closing reaction (to form benzo(aza)cyclobutadiene 3-XN, X = F, Cl, Br). Attempts to generate and observe the o-phenylene(halo)carbenonitrenes 2-XN, X = F, Cl, Br, using matrix isolation spectroscopy under conditions similar to those of the successful observation of 2-HN failed. Instead, the observed photoproducts were a mixture of 3-XN and 4-XN. In each case, the major product of the mixture appears to be the thermodynamically more stable one. In the case of X = Br, the observed mixture contains an additional component that is postulated to be Z-6-BrN. o-Phenylenechlorocarbenocarbene is also computed to have a quinoidal singlet biradical ground state and relatively stabilized A' excited states. Attempts to generate the biscarbene under matrix isolation conditions led to the detection of benzochlorocyclobutadiene (3-ClC), small amounts of the ring-open product (dienediyne 4-ClC), and cycloalkyne 5-ClC. Computations suggest that the formation of 5-ClC implies the generation of Z-6-ClC, which is analogous to the formation of Z-6-BrN from 2-BrN.     

Photoinduced electron-transfer systems consisting of electron-donating pyrenes or anthracenes and benzimidazolines for reductive transformation of carbonyl compounds

Photoinduced electron-transfer reactions of several ketone substrates were studied to evaluate the utilities of 1,6-bis(dimethylamino)pyrene (BDMAP), 1,6-dimethoxypyrene (DMP), 9,10-bis(dimethylamino)anthracene (BDMAA), and 9,10-dimethoxyanthracene (DMA) as electron-donating sensitizers cooperating with 2-aryl-1,3-dimethylbenzimidazolines. BDMAP and DMP generally led higher conversion of ketones and better yield of reduction products compared to BDMAA and DMA.     

Studies on the syntheses of heterocyclie compounds. Part DXXVII.. the absolute configuration of 1,2,3,4-tetrahydro-1-phenylisoquinolines

The absolute configuraiton at the C₁-position of 1,2,3,4-tetrahydro-1-phenylisoquinolines can be deduced from the CD curves of either the free base or its methiodide. Furthermore, the absolute con figuration of (⁺)-2-amino-1-(3-hydroxyphenyl)ethanol (V) was revised and found to have R-configuration at the C₁ -position.     

Water-swellable polyelectrolyte microgels polymerized in an inverse microemulsion using a nonionic surfactant

A series of poly(dimethylacrylamide-co-2-acrylamido-2-methyl-1-propanesulfonic acid) microgels slightly crosslinked by methylene-bis-acrylamide (MBA) were polymerized in a novel inverse microemulsion polymerization (IMEP) system. To determine a suitable composition of the IMEP system, the phase diagram of a pseudoternary system was made. The pseudoternary polymerization system consisted of n-hexane, a nonionic surfactant (polyoxyethylene oleyl ether, C18En), and an aqueous monomer solution. Polymerization was performed in a single-phase reversed micelle solution. The reversed micelles were about 50 nm in diameter, as determined by FF-TEM. The viscometric characteristics of the polymers extracted from the IMEP system were studied in 3 mM sodium chloride aqueous solution. The intrinsic viscosity values for the noncrosslinked and crosslinked (0.1 mol% MBA was incorporated) samples were 25 and 7.4 dl/g, respectively. The overlap concentration (c*) of crosslinked polymer microgel occurred at c[eta] = 1 in the solvent. When the volume fraction (phi) of the microgel was 0.7, the value of the apparent yield stress of the microgel solution was observed. These results show that the microgel has a significant thickening effect above c* due to friction between the microgel particles. It is assumed that the microgels polymerized in a confined space retain the shape or size of the nanosized reactor with a diameter on the order of 50 nm.