Materials Literature
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Abstract The isothermal cure of a diglycidyl ether of bisphenol A with a tetrafunctional aromatic diamine has been studied in an attempt to achieve full cure (maximum glass transition temperature, T g ∞ , ca. 170°C). Since high temperatures of cure are necessary for high T g ∞ systems (because of low reaction rates af…
Abstract The effects of solvent size, temperature, and polymer molecular weight on the swelling of poly(methyl methacrylate) (PMMA) thin films in low molecular weight alcohols were investigated using an in situ ellipsometer. Apparent activation energies were indicative of non‐Fickian diffusion, although optical data s…
Neutron spectroscopy has been performed on a sample of PuO 2 , enriched to 94% with the non-absorbing isotope 242 Pu, to measure the crystal-field potential. The authors find levels consistent with the weak-field case crystal-field parameters recently derived for UO 2 and NpO 2 , but inconsistent with a weak-field int…
High-resolution neutron powder diffraction studies were performed on several compounds of the type YFe 12-x Al x (x=8, 7, 6). The authors observed a strong preferential site occupation of Fe on one of the three non-equivalent transition metal sites of the hMn 12 -type structure. In particular the 8f site is found to b…
Symmetry arguments are used to classify the various modes of instabilities of one-dimensional periodic patterns. An important feature of this theory is to point out the coupling between these modes and the phase of the cellular structure. A number of results presented allow to interpret recent observations in hydrodyn…
An optical study of the smectic-O films which float on the free surface of droplets of racemate MHTAC [1(methyl)-heptyl-terephtalidene-bis-amino cinnamate] in the isotropic phase, is presented. It allows us to elucidate the herringbone structure of the molecules in this original liquid-crystal phase, and to estimate t…
Third-order optical susceptibilities (χ(3)) of poly{(7-oxo-7, 10H-benz[de]imidazo[4′,5′:5,6]benzimidazo [2,1-a]isoquinoline-3,4:10,11-tetrayl)-carbonyl}, referred to as BBL, and poly(6,9-dihydro-6,9-dioxobisbenzimidazo[2,1b:1′,2′j] benzo[1mn]-[3,8]phenanthroline-3,12-diyl), known as BBB, have been determined using the…
Indium tin oxide films are prepared by in-situ evaporation in a partial vacuum with varying compositions of indium to tin and the ac conductivity of these films is investigated over a frequency range of 1 to 10 kHz. The results show distinct linear regimes in the log–log plots for all compositions, suggesting hopping-…
(I) C 8 H 6 S 6 + .I 3 − cristallise dans P2 1 /c avec a=15,307, b=9,622 et c=12,013 A, β=110,69°, Z=4; affinement jusqu'a R=0,0374. (II) C 7 H 4 S 6 + .I 3 − cristallise dans P2 1 /c avec a=14,583, b=9,350 et c=11,995 A, β=107,76, Z=4; affinement jusqu'a R=0,0301. Les deux sels sont isostructuraux l'empilement compre…
Amorphous C-Ge multilayers have been produced with periods varying from 2.6 to 12.5 nm. We have studied the multilayers using Raman spectroscopy and dc conductivity measurements and found that their properties change significantly when the carbon sublayer thickness is smaller than 2.5 nm. This value corresponds to the…
This work reports on the result of electrical conductivity measurements carried out on coconut-shell activated carbon. The results suggest that the charge carriers moved by variable-range hopping below 200 K, by hopping among localized energy states between 200 K and 385 K, and by percolation through energy states clo…
Tetragonal-to-orthorhombic phase transition at about 410 K is found by a X-ray powder diffraction study on the title oxide synthesized in a lamp-image floating zone furnace. The crystal structures of tetragonal and orthorhombic forms of the oxide are determined carefully by X-ray and neutron single crystal diffraction…
The ${F}_{A}$\ensuremath{\rightarrow}(${F}_{2}^{+}$${)}_{A}$ thermal conversion in additively colored and x-ray-irradiated Na-doped ${\mathrm{CaF}}_{2}$ crystals was studied using different methods: optical absorption and luminescence, thermal-stimulated polarization, ionic thermocurrent, and photoconductivity. The ex…
The surface core-level shift of the As 3d and the In 4d levels on the (110) cleavage surface of InAs has been measured. The presence of the surface is found to lower the As 3d binding energy by 300\ifmmode\pm\else\textpm\fi{}20 meV and to increase the In 4d binding energy by 270\ifmmode\pm\else\textpm\fi{}40 meV relat…
Ultrathin films of F-bridged Al-phthalocyanine polymer, (AlPcF)n, grown by the molecular-beam epitaxy technique show unusual spectroscopic properties which can be described by the possibility of pseudomorphic layer formation at the thin-film/substrate interface. A change in the electronic structure of the molecules of…
At present the collective motion algorithm is the only Monte Carlo technique which allows the simulation of monodisperse polymer melts on a lattice at a volume fraction of unity. Here we describe the algorithm in detail and show that it fulfils the condition of detailed balance. It yields chain dimensions which are sl…
Raman spectroscopy is used to investigate the structural changes in isochronally annealed a-Ge/SiOx superlattices. The Ge crystallization temperature is found to be higher in superlattices with thinner Ge layers, which can be interpreted in terms of the retardation of nucleation and growth of Ge microcrystallites near…
Molecular-dynamics methods are used to model diffusion in a \ensuremath{\Sigma}=5 [100] Al tilt boundary and in bulk. The diffusion coefficient D and activation energy Q for atoms in the boundary and in bulk are calculated for several different Al empirical interatomic pair potentials. These include a Morse potential,…
We have compared the step coverage of plasma enhanced chemical vapor deposition tetraethylorthosilicate films of microwave downstream, high frequency radio frequency (rf), and low frequency rf depositions. The microwave-downstream deposition, characterized by bimolecular surface reactions, produces a conformal step co…
The existing discrepancy between theoretical models and experimental results for hydrogen-donor complexes in crystalline silicon is resolved using first-principles pseudopotential-density-functional calculations for the hydrogen-phosphorus pair. In the configuration which is the global energy minimum, H is located on…