Materials Literature
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Poly(vinyl acetate) (PVAc)/poly(ethylene oxide) (PEO) blends were prepared by casting from either benzene or chloroform. The solvent effects on the crystallization behavior and thermodynamic properties of the blends were studied by the differential scanning calorimeter (DSC). Two grades of PEO with different molecular…
Polypyrrole films doped with p-toluenesulfonate and poly(4-styrenesulfonate) anions were synthesized electrochemically. These films were treated with water and dilute NaOH solution for varying periods of time. The films do not lose the anions readily when treated with water. In NaOH, dedoping occurs rapidly, either vi…
The lack of suitable crystals has meant that it has not been possible to carry out a conventional single-crystal X-ray structure analysis to determine the structure of red fluorescein. Instead, the application of a Monte Carlo method has allowed the crystal structure to be determined directly from powder X-ray diffrac…
Macrocyclization of 2,3-dicyano-1,4-diox-2-ene with magnesium propoxide in propanol provided the enantiomerically pure C4-symmetric (porphyrazinato)magnesium(II) complex 1. The structure of the macrocycle was confirmed by an X-ray crystallographic study on the demetalated porphyrazine.
The use of adhesives is widespread and growing, and there are few modern artefacts, from the simple cereal packet, to the jumbo jet, that are without this means of joining. Adhesion Science provides an illuminating account of the science underlying the use of adhesives, a branch of chemical technology which is fundame…
The three-dimensional structure of the enzyme 3-oxo-delta5-steroid isomerase (E.C. 5.3.3.1), a 28-kilodalton symmetrical dimer, was solved by multidimensional heteronuclear magnetic resonance spectroscopy. The two independently folded monomers pack together by means of extensive hydrophobic and electrostatic interacti…
The crystal structure of the arabinose-binding and dimerization domain of the Escherchia coli gene regulatory protein AraC was determined in the presence and absence of L-arabinose. The 1.5 angstrom structure of the arabinose-bound molecule shows that the protein adopts an unusual fold, binding sugar within a beta bar…
The problem of Fermi-level pinning at semiconductor-metal contacts is readdressed starting from first-principles calculations for Al/GaAs. We give quantitative evidence that the Schottky barrier height is very little affected by any structural distortions on the metal side---including elongations of the metal-semicond…
The kinetics of a first-order, solid-solid phase transition were investigated in the prototypical nanocrystal system CdSe as a function of crystallite size. In contrast to extended solids, nanocrystals convert from one structure to another by single nucleation events, and the transformations obey simple unimolecular k…
Miniaturized triblock copolymers have been found to self-assemble into nanostructures that are highly regular in size and shape. Mushroom-shaped supramolecular structures of about 200 kilodaltons form by crystallization of the chemically identical blocks and self-organize into films containing 100 or more layers stack…
We use recent theoretical advances to develop a new functional form for interatomic forces in bulk silicon. The theoretical results underlying the model include a novel analysis of elastic properties for the diamond and graphitic structures and inversions of ab initio cohesive energy curves. The interaction model incl…
The shape of metallic constrictions of nanoscopic dimensions (necks) formed using a scanning tunneling microscope (STM) is shown to depend on the fabrication procedure. Submitting the neck to repeated plastic deformation cycles makes possible to obtain long necks or nanowires. Point-contact spectroscopy results show t…
Pd and Pt have been shown to be highly polarizable when mixed with ferromagnets like Ni, Fe, and Co. In these alloys the total moment, or magnetization cloud, is produced by the magnetic moment plus the induced moment on the surrounding atoms. With diffuse magnetic scattering of neutrons, it is possible to measure the…
We have developed an artificial preparation scheme to produce ferrite films in which magnetic and nonmagnetic layers were alternated at the atomic scale. Laser ablation deposition (LAD) was used to deposit layers of lithium ferrite and aluminum oxide to a thickness ranging between 2–3 Å each. In contrast to previous e…
Phosphorus doped polycrystalline diamond films were grown by hot-filament chemical vapor deposition using trimethyl phosphite as the doping source. Phosphorus incorporation into the diamond films was established using secondary ion mass spectroscopy. Current–voltage characteristics were measured and the resistivities…
The use of additives of corundum structure M{sub 2}O{sub 3} (M=Cr, Al) is an effective way of promoting grain growth of uranium dioxide. The high-temperature compressive deformation of large-grained UO{sub 2} doped with these oxides has been investigated and compared with that of pure UO{sub 2} with a standard microst…
Ferrimagnetic Nd6Fe14−xAlx compounds with x=3, 3.5, and 4 have been studied by magnetization measurements in fields up to 9 T. Néel temperatures were determined from Mössbauer spectra to be 308, 286, and 239 K, respectively. The net magnetization at T=4.2 K is 3.6 μB/f.u.(x=3), 2.2 μB/f.u.(x=3.5), and zero for x=4. Me…
In this work we have studied in detail the effect of MgO on magnetic properties and intergranular microstructure. We have found that both coercivity and thermal stability can be remarkably enhanced by the intergranular addition of MgO. For Nd22Fe71B7 magnets with 2 wt % MgO addition, the coercivity at room temperature…
Mossbauer effect studies (ME) for members of the alkylene-diammonium series, (CH2)n(NH3)2Fe(II)Cl4, where n=3, 4, 5, and 6 are presented. At 78 K the ME spectra reveal similar general features showing an 8 line well split hyperfine spectra; the effective magnetic field is in the range 18.5–20 T. Fitting the magnetizat…
Ceramic samples of composition (La1−xGdx)2/3Ca1/3MnO3 were prepared and used as targets to grow films onto LaAlO3 substrates by pulsed laser deposition. Comparison of the electrical resistance and thermopower, measured vs temperature and applied magnetic fields, indicates transport dominated by positively charged smal…