Materials Literature
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An ideal superparaelectric is treated as an ensemble of independent, coherently polarizing regions, of linear dimension lambda , each of which behaves as a 'Devonshire ferroelectric', with transition temperature T 0 , and local polarization, P s approximately (T-T 0 ) 1 2/. For sufficiently small lambda , the directio…
Photoionization thresholds for silicon clusters in the size range Si2 to Si200 have been examined by laser photoionization with detection by reflectron time-of-flight mass spectrometry. Stimulated Raman scattering light of narrow bandwidth 193 nm radiation was used as the ionization light source down to 146 nm. A char…
Twin related domain formation is examined as a strain relaxation mechanism for a heteroepitaxial tetragonal film on a cubic substrate. Elastic relaxations are calculated for a single twin band in which the c axis of the tetragonal domains is either related by a 90° rotation about an axis in the plane of the film or by…
Cathodoluminescence (CL) spectroscopy was used to study exciton recombination at temperatures from 80 to 280 K in undoped and boron-doped diamond particles grown by hot-filament chemical vapor deposition. Spectral lines due to free and bound excitons were observed in the near-band-gap region, 4.6--5.5 eV. (The band ga…
We study both analytically and numerically phonon transmission fluctuations and localization in partially ordered superlattices with correlations among neighboring layers. In order to generate a sequence of layers with a varying degree of order we employ a model proposed by Hendricks and Teller as well as partially or…
Absolute cross sections for electron-impact dissociation of SiF 4 from threshold to 300 eV are presented for formation of the neutral radicals SiF 3 , SiF 2 , SiF and Si. This measurement was accomplished with threshold-ionization mass spectrometry in a dual electron-beam device. The threshold energy for dissociation…
The effect of electrode surface roughness on the breakdown potential in SF 6 , SF 6 -N 2 , and SF 6 -CO 2 has been measured and calculated using two surface-roughness models (a multi-ridge model and a single-needle-tip-protrusion model). The calculations are in reasonable agreement with the experimental results, indic…
Abstract Blends of polyimide isomers containing hexafluoroisopropylidene in the central moiety of the diamine residue have been studied. The isomers differed by having either a meta or a para linkage between the diamine and dianhydride residues. The miscibility of these materials was investigated by studying the glass…
Abstract Porous polydimethylsiloxane (PDMS) membranes were prepared by catalytic hydrosilyiation cure of a silicone compound containing a vinyl group and a SiH group in the presence of additives such as water, ethanol, ethylene glycol, and 2‐methoxyethanol. The pores were formed in the membrane as a result of hydrogen…
Abstract Unreacted PC/PBT blends have been obtained by melt blending in all the composition ranges. The followed processing method produced partially miscibilized and crystalline blends. The plot of the density of the amorphous part of the blends against its composition indicates that this parameter is more important…
Abstract Injectable collagen is a concentrated dispersion of collagen fibers in aqueous solution that is used to correct dermal contour defects through intradermal injection. The effect of hydrophobic forces on the rheology of concentrated dispersions of collagen fibers was studied by dynamic rheological measurements…
Abstract To determine the structure‐transport properties relations, we synthetized segmented polyether polyurethane with increasing rigidity. The formulation is based on poly(tetramethylene oxide diol) (PTMO) of different molecular weights, diphenylmethane aiisocyanate (MDI), and butanediol (BD). The synthesis is effe…
Abstract A thin membrane of bacterial cellulose (BC) obtained from Acetobacter culture was tested for its performance as a dialysis membrane in aqueous systems. The BC membrane showed superior mechanical strength to that of a dialysis‐grade regenerated cellulose membrane, allowing the use of a thinner membrane than th…
Experiments were performed on amorphous silica at temperatures of 1000°–2850°C and pressures of 9–14 GPa using a 2000‐t uniaxial split‐sphere multianvil apparatus (USSA‐2000). The melting curve of coesite was extended from 8 to 13.7 GPa, and the melting temperatures indicate a slope that is almost independent of press…
We investigate statistical-mechanical models on aperiodic structures ( e.g. quasi-periodic, random, self-similar). We derive a condition for the relevance of any kind of aperiodicity near a continuous phase transition, in the spirit of the Harris criterion. This explains why crystals and quasi-crystals exhibit the sam…
A variety of magnetic phase transitions have been observed for all the RFe 10 Mo 2 compounds from AC and DC magnetic measurements in the temperature range between 4.2 and 300 K. The alloys with R = Nd, Tb and Dy exhibit spin reorientation transitions and with R = Ho, Er and Tm some unidentified magnetic phase transiti…
We report visible light emission from porous structures formed in bulk and thin-film polycrystalline silicon materials by anodic etching in an HF:ethanol solution. Our results indicate photoluminescence (PL) peaks at wavelengths between 650 and 655 nm and with intensities comparable to those typically obtained from po…
An electrochemical technique is proposed to form a solid-state electrical contact of porous Si (PS) electroluminescence (EL) diodes. The PS layers were created by anodizing nondegenerate p-type single-crystal Si wafers in an HF solution, and then electrochemically polymerizing semitransparent conducting polypyrrole fi…
Pressure-induced structural transformation in ${\mathrm{SiO}}_{2}$ glass is investigated with molecular dynamics. At high densities, the height of the first sharp diffraction peak is considerably diminished, its position changes from 1.6 to 2.2 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$, and a new peak appears at 2…
Here we demonstrate the first evidence that phase separation in polymer solutions could be essentially different from that in binary liquid systems. This difference is likely to originate from the strong asymmetry in molecular dynamics between the two separated phases. When the rheological time of the polymer-rich pha…