Materials Literature
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A semiempirical tight-binding method was used to calculate the band structures of ${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ alloys coherently grown on (001)-, (111)-, and (110)-oriented ${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Ge}}_{\mathit{y}}$ substrates. T…
Photoelectron spectra resulting from sequential or simultaneous absorption of two photons have been studied at four different silicon surfaces. To study energy-relaxation lifetimes, one laser pulse populates conduction states and normally unoccupied surface states, from which photoelectrons are excited by the second p…
We present a self-consistent-field structure for the thermodynamic description of concentrated solutions of liquid-crystal polymers. The polymers are assumed to be locally stiff but capable of curvature over large distances. The formulation of the chain geometry is that of a wormlike polymer, but the final analysis is…
We report optical-absorption, photoluminescence (PL), and picosecond photoinduced absorption (PA) decay in films of poly-3-hexyl-thiophene at pressures up to 80 kbar. The spectral bands redshift nonlinearly with pressure and the PL intensity decreases markedly. Thermochromic transitions are completely inhibited at pre…
The electronic structures of 15 models of periodic graphitelike carbon surfaces (PGCS) with negative Gaussian curvatures are studied by a first-principles method. These models, which consist of P, D, and G surfaces of PGCS and range from 24 to 216 atoms in the unit cell, have different structural characteristics. Resu…
We report ab initio molecular-dynamics simulations of small aluminum clusters, ${\mathrm{Al}}_{\mathit{n}}$ of n=2--6 and 12, 13, 55, and 147, using the density-functional, local-orbital method of Sankey. Equilibrium structures and total energies were calculated and compared with experiment and the predictions of othe…
A DNA polymer with hundreds or thousands of base pairs is modeled as a thin elastic rod. To find the equilibrium configurations and associated elastic energies as a function of linking number difference (ΔLk), a finite element scheme based on Kirchhoff’s rod theory is newly formulated so as to be able to treat self-co…
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…