Materials Literature
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We have made a comparative theoretical study of the most common forms of unhydrogenated amorphous carbon (\ensuremath{\alpha}-C), namely, of the dense, diamondlike phase and the low-density evaporated \ensuremath{\alpha}-C (e-C). Emphasis is given to the connection among the structure, energetics, and stability of the…
Diamond was deposited on synthetic graphite, highly oriented pyrolytic graphite and on substrates covered with graphite powder. Scanning electron microscopy and transmission electron microscopy were used to examine the samples. A strong preference for nucleation of diamond on the edges of the graphite sheets was obser…
The \ensuremath{\pi}-electronic excitations and excited-state geometries of trans-stilbene (tS) are found by combining exact solutions of the Pariser-Parr-Pople (PPP) model and semiempirical Parametric Method 3 (PM3) calculations. Comprehensive comparisons with tS spectra are obtained and related to the fluorescence a…
The structures of the complexes [FeCl 2 (CH 3 CN) 4 ][FeCl 4 ], tetrakis(acetonitrile)dichloroiron(III) tetrachloroferrate(1-), and [AlCl(CH 3 CN) 5 ][FeCl 4 ] 2 .CH 3 CN, pentakis(acetonitrile)chloroaluminium(III) bis[tetrachloroferrate(1-)] acetonitrile solvate, have been determined from single-crystal X-ray diffrac…
We present here a granular-rod model for the metallic state of the conducting polymer, polyaniline. In this model the metallic islands correspond to single strands of the polymer. The macroscopic conductivity results from anisotropic three-dimensional variable-range hopping in the network of metallic rods. We incorpor…
We present momentum-resolved inverse-photoemission data from Ge(100)2\ifmmode\times\else\texttimes\fi{}1, Si(100)2\ifmmode\times\else\texttimes\fi{}1, and GaAs(100)4\ifmmode\times\else\texttimes\fi{}2 surfaces. The bulk conduction bands of these three semiconductors are mapped along the \ensuremath{\Gamma}X direction.…
We have carried out a local-density-functional calculation of the three-dimensional (3D) band structure of the conducting polymer poly(phenylene vinylene) (PPV). The motivation was to investigate the effects of interchain coupling. The major effects are due to coupling of carbons in the rings to their closest neighbor…
We present valence and core-level photoemission measurements from vacuum-fractured, single-crystal barium titanate. These results resolve contradictory measurements in the literature which have employed other methods of sample surface preparation. The valence-shell electronic structure is compared with previously publ…
The atomic and electronic structures of microtubules of graphitic carbon have been investigated by ab initio molecular dynamics. Fully optimized atomic structures of two microtubules, a reflection symmetric and a chiral, are found to differ little from their ideal, graphite-derived geometries. Both are semiconductors…
We report here results from experiments on low-frequency Raman scattering from CdS microcrystals of various sizes embedded in a germanium dioxide glass matrix. We observed peaks in the low-frequency region in the tail parts of the Rayleigh lines and we found that the frequencies of these peaks were proportional to the…
Abstract The cure of a liquid dicyanate ester monomer, which reacts to form a high‐ T g (≈200°C) polycyanurate network, has been investigated using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and a dynamic mechanical technique, torsional braid analysis (TBA). The monomer is…
The administration of drugs directly into the central nervous system using polymers as drug carriers may improve the treatment of malignant brain tumors. In this study, the effect of the interstitial, localized delivery of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) incorporated into controlled release polymers implan…
Polyaniline (PANI) films of superior homogeneity can be prepared by using functionalized protonic acids to protonate the polymer and simultaneously induce solubility, in the conducting form, in common organic solvents. The results of measurements of the temperature dependence and magnetic-field dependence of the condu…
Nanometer-size semiconductor particles coated with another semiconductor can exhibit unusual and interesting phenomena associated with the redistribution of the electron and hole wave functions. Using the band offsets and effective masses, the overlap of the electron and hole wave functions can be altered by changing…
The electronic structure of coaxial, graphene double-layer tubules is predicted for various combinations of metallic and insulating constituent inner and outer monolayers, depending on the diameter and chirality of the tubule. For the examples chosen, some of the energy bands of the inner and outer tubules are coupled…
The electronic structure of nanocrystalline Si which shows visible photoluminescence is calculated using the density-functional approach for finite structures. Except for geometry this is the same theory as for first-principles band structures of semiconductors and other solids. Our results for clusters ranging up to…
A homogeneous system for the selective, catalytic oxidation of methane to methanol via methyl bisulfate is reported. The net reaction catalyzed by mercuric ions, Hg(II), is the oxidation of methane by concentrated sulfuric acid to produce methyl bisulfate, water, and sulfur dioxide. The reaction is efficient. At a met…
Single-domain microcrystals of LaC(2) encapsulated within nanoscale polyhedral carbon particles have been synthesized in a carbon arc. Typical particle sizes are on the order of 20 to 40 nanometers. The stoichiometry and phase of the La-containing crystals have been assigned from characteristic lattice spacings observ…
The reaction between methane and oxygen over platinum and rhodium surfaces in metalcoated ceramic monoliths can be made to produce mostly hydrogen and carbon monoxide (greater than 90% selectivity for both) with almost complete conversion of methane and oxygen at reaction times as short as 10(-3) seconds. This process…
The dielectric constants of a series of hydrothermally grown berlinite crystals containing increasing amounts of H 2 O were determined using a two-terminal method and empirically determined edge corrections with kappa 11 T ranging from 4.67 to 4.86 and kappa 33 T from 4.54 to 4.76. The extrapolated values for 'dry' be…