Iron contamination in ion implanted silicon,as revealed by x-ray and electron diffraction

A surface contamination effect was detected by double-crystal x-ray diffraction analysis of silicon wafers implanted with silicon ions at different doses and energies after annealing at 700 °C.The hypothesis of recoiled oxygen from the native oxide, as the impurity responsible for surface strain, was excluded by x-ray characterization of a series of samples implanted through thermally grown silicon oxides. The surface positions of the strain, resulting from x-ray analysis after 700 °C annealing and the analysis of the electron diffraction patterns, taken on particles originated from precipitation of the impurity by 1000 °C heating, allowed to conclude that the contamination phenomenon is due to iron atoms coming from the ion implanter.     

Liapunov direct method in approaching bifurcation problems

Summary A concept of total stability for continuous or discrete dynamical systems and a generalized definition of bifurcation are given: it is possible to show the link between an abrupt change of the asymptotic behaviour of a family of flows and the arising of new invariant sets, with determined asymptotic properties. The theoretical results are a contribution to the study of the behaviour of flows near an invariant compact set. They are obtained by means of an extension of Liapunov's direct method. A Dario Graffi nel suo 70° compleanno Entrata in Redazione il 9 febbraio 1975. Work performed under the auspices of the Italian Council of Research (C.N.R.).     

Highly Sensitive Fluorescent pH Microsensors Based on the Ratiometric Dye Pyranine Immobilized on Silica Microparticles

Pyranine (HPTS) is a remarkably interesting pH-sensitive dye that has been used for plenty of applications. Its high quantum yield and extremely sensitive ratiometric fluorescence against pH change makes it a very favorable for pH-sensing applications and the development of pH nano-/microsensors. However, its strong negative charge and lack of easily modifiable functional groups makes it difficult to use with charged substrates such as silica. This study reports a methodology for noncovalent HPTS immobilization on silica microparticles that considers the retention of pH sensitivity as well as the long-term stability of the pH microsensors. The study emphasizes the importance of surface charge for governing the sensitivity of the immobilized HPTS dye molecules on silica microparticles. The importance of the immobilization methodology, which preserves the sensitivity and stability of the microsensors, is also assessed.     

Synthesis of Asymmetric Monomethine Cyanine Dyes with Red‐Shifted Optical Properties

Six novel asymmetrical monomethine cyanine dyes were synthesized via the condensation reaction of 1‐butyl‐2‐(methylthio)benzo[c,d]indol‐1‐ium iodide and various 1,5‐substituted indolenine salts under basic conditions. The dyes were characterized using UV–vis spectroscopy, fluorescence, ¹H NMR, ¹³C NMR, and mass spectrometry; furthermore, the purity of these compounds was observed using LC/ELSD/MS.     

Ring strain effects: VI—benzocyclobutadienoquinone radical anion

Electron paramagnetic resonance studies were carried out on the radical anion of 4-deuterobenzocyclobutadienoquinone. The hyperfine coupling constants which had been assigned previously were found to be in error. The effects of the strained 4-membered ring on the spin density distribution are discussed.     

Photoexcited triplets of dyes in zeolitic nanostructured channels. A time resolved EPR study

Two dyes (4-nitrostilbene, NST and 4-N,N-dimethylamino-4'-nitrostilbene, DANS) included in zeolites with nanometric channels and different Si : Al ratios have been photoexcited and their triplet state studied by time resolved EPR (TR-EPR). This is the first time that a TR-EPR spectrum of photoexcited triplet states of dyes in zeolites has been observed. The zeolites used were ZSM-5 and mordenite, with either protons or lithium as charge compensating ions, and the aluminium-free porosil. The ZFS parameters and the polarized spin populations have been obtained, and compared with those obtained in glassy solutions and in the organic nanostructured matrix perhydrotriphenylene (PHTP). For (3)DANS in neutral solvents and in PHTP the dimethylamino group is pi conjugated, whereas only its acid form is detected in all the zeolites. In the latter the spectra of the radical cations formed by spontaneous oxidation have also been observed both by cw-EPR and TR-EPR, the last spectra being spin polarized in emission. The mobility of the triplets is discussed, taking into account the spin polarization of the radical cations indicating a strong radical-triplet interaction.     

Immunohistological detection of <Emphasis Type="Italic">Chlamydia pneumoniae</Emphasis> in the Alzheimer's disease brain

Background  

Sporadic late-onset Alzheimer's disease (AD) appears to evolve from an interplay between genetic and environmental factors. One environmental factor that continues to be of great interest is that of Chlamydia pneumoniae infection and its association with late-onset disease. Detection of this organism in clinical and autopsy samples has proved challenging using a variety of molecular and histological techniques. Our current investigation utilized immunohistochemistry with a battery of commercially available anti-C. pneumoniae antibodies to determine whether C. pneumoniae was present in areas typically associated with AD neuropathology from 5 AD and 5 non-AD control brains.     

Acknowledgement

Acknowledgement

Acknowledgement     

Interference study of the chi c0(13P0) in the reaction -pp-->pi0pi0

Fermilab experiment E835 has observed (-)pp annihilation production of the charmonium state chi(c0) and its subsequent decay into pi(0)pi(0). Although the resonant amplitude is an order of magnitude smaller than that of the nonresonant continuum production of pi(0)pi(0), an enhanced interference signal is evident. A partial wave expansion is used to extract physics parameters. The amplitudes J=0 and 2, of comparable strength, dominate the expansion. Both are accessed by L=1 in the entrance (-)pp channel. The product of the input and output branching fractions is determined to be B((-)pp-->chi(c0))xB(chi(c0)-->pi(0)pi(0))=(5.09+/-0.81+/-0.25)x10(-7).