Materials Literature
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In kilogram quantities ; pure poly(propylene imine) dendrimers can be prepared in an extremely simple reaction sequence comprising Michael addition (primary amines to acrylonitrile) and heterogeneous hydrogenation with a Raney cobalt catalyst. Both steps proceed quantitatively and selectively and can be employed with…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTExpanding roles for templates in synthesisSally Anderson, Harry L. Anderson, and Jeremy K. M. SandersCite this: Acc. Chem. Res. 1993, 26, 9, 469–475Publication Date (Print):September 1, 1993Publication History Published online1 May 2002Published inissue 1 September 1993https…
Abstract A polyimide hybrid with montmorillonite clay mineral has been synthesized from a dimethylacetamide (DMAC) solution of poly(amic acid) and a DMAC dispersion of montmorillonite intercalated with an ammonium salt of dodecylamine. Montmorillonite consists of stacked silicate sheets about 2000 Å in length, 10 Å in…
Deviations from thermally activated and from exponential response are typical features of the vitrification phenomenon and previously have been studied using viscoelastic, dielectric, calorimetric, optical, and other techniques. Linear response data from literature on about 70 covalent glass formers, ionic melts, supe…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis and characterization of nearly monodisperse CdE (E = sulfur, selenium, tellurium) semiconductor nanocrystallitesC. B. Murray, D. J. Norris, and M. G. BawendiCite this: J. Am. Chem. Soc. 1993, 115, 19, 8706–8715Publication Date (Print):September 1, 1993Publication H…
Anodic oxidation in hydrochloric (HCl) acid and chemical dissolution in hydrofluoric (HF) acid solutions of porous silicon (PS) layers obtained from lightly doped p-type substrates have been investigated. It is shown that the wettability of PS, which is a highly hydrophobic and organophilic material, strongly affects…
The age and season of death of mammals, as well as other aspects of their life history, can be estimated from seasonal bands in dental cementum that result from variations in microstructure. Scanning electron micrographs of goats fed controlled diets demonstrate that cementum bands preserve variations in the relative…
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” opt…
The recently determined phonon dispersion curves of alpha -quartz have been analysed with various polarizable-ion, bond-charge and shell models, the shell models giving a very satisfactory account of the dispersion curves as well as of the scattering intensities. Due to the use of interatomic potentials the number of…
Anharmonic effects in crystals typically result in the symmetric broadening of the single-phonon Lorentzian line shape. However, a simple model, based on consideration of a highly anharmonic potential, shows that anharmonicity can lead not only to asymmetric line shapes but also to line shapes composed of multiple sub…
Surface modification of a P2 beam-exposed InGaAs surface and an As2 beam-exposed InP surface was studied in situ using reflection high energy electron diffraction during gas source molecular beam epitaxy. It is revealed that the InP surface remained stable under As2 beam exposure after forming an InAs surface layer a…
We report the fabrication of high aspect ratio, sub-10 nm size, structures in silicon without involving any wet chemical etching. A 50 nm thick double layer of low and high molecular weight polymethylmethacrylate resist was exposed with an 80 kV electron beam of diameter smaller than 5 nm. After exposure the resist wa…
This letter is aimed at understanding the intergranular conduction in zinc oxide varistors. In particular, we have studied current-voltage and Arrhenius plots of the resistive current for the prebreakdown conduction. A current-temperature (I-T) relation has been found to present two breaks at ∼370 and ∼240 K. Although…
Optical second-harmonic and sum-frequency spectra of clean and oxidized Si(100) and Si(111) samples reveal a strong resonance band at 3.3 eV photon energy. It is concluded that the resonance arises from direct transitions between valence and conduction band states in a few monolayers of strained silicon at the Si-${\m…
The electromagnetic levitation technique is applied to undercool melts of quasicrystal-forming alloys of Al-Cu-Co and Al-Cu-Fe. Undercooling with respect to the solidification of the decagonal phase (quasiperiodic in two dimensions) is measured in situ by contactless temperature measurements. The undercoolings are ana…
An amorphous carbon network generated by quenching high-density high-temperature liquid carbon using tight-binding molecular-dynamics simulation is found to contain a large fraction of tetrahedral bonding sites. Investigations of the structural, vibrational, and electronic properties of the theoretical model provide f…
The structure of molten lithium nitrate at 573 K has been investigated by applying the technique of neutron diffraction to five isotopically enriched samples: NLiNNO3, 0LiNNO3, 7LiNNO3, 7Li15NO3 and 0Li15NO3. The ion-ion and ion-counterion partial structure factors relating to g Li-Li(r), g Li-N(r), g Li-O(r) partial…
As determined by quantitative differential thermal analysis, the enthalpies of fusion of forsterite and spinel, are ΔH f = 142 ± 14 and 107 ± 11 kJ/mol at 2174 and 2408 K, respectively. Significant premelting has been observed for forsterite, beginning about 100 K below the congruent melting point. When heated in grap…
Abstract A survey by X‐ray diffractometry was carried out to confirm the two crystalline phase Iα/Iβ(triclinic/monoclinic) system of native celluloses. We have investigated cellulose samples from 12 different origins and measured the d ‐spacings with reasonable precision. The samples were then subjected to the hydroth…
Among the mechanisms suggested to account for degradation of varistor materials, ion migration has strong support. Mobile, positively charged ions in the depletion layer would be the key element in degradation. In this context, the authors discuss the consequences of an electrical stressing on the current-temperature…