Materials Literature
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Abstract Polyimide fibers have been produced from both polyamic acid and polyimide resins, derived from 2, 2‐bis (3,4‐dicarboxyphenyl) hexafluoropropane dianhydride and 2, 2‐bis (4‐4‐aminophenoxy) phenyl) hexafluoropropane, by extrusion into various aqueous organic media. Polyimide fibers obtained from polyamic acid f…
We present a formalism to compute the optical-activity tensor in the long-wavelength limit neglecting local-field corrections with a nearly first-principles approach. The calculation of optical activity requires perturbation theory in the vector potential in order to describe the rotation of the plane of polarization…
Highly efficient infrared-to-visible upconversion has been observed in Er3+-doped BaCl2 phosphors. The composition optimized for maximum green emission was around 25ErCl3 (mol %), which contains 5–15 mol % more active Er3+ ions than those in the conventional Er3+-doped fluoride phosphors. Pumped by a 0.8 μm laser diod…
The electronic structure of \ensuremath{\beta}-phase NiTi has been calculated using a first-principles linear-combination-of-atomic-orbitals method. The resulting band structure was fitted with a nonorthogonal tight-binding Hamiltonian from which electron-phonon matrix elements were evaluated. The soft phonon near ${\…
The results of measurements of the optical band gap of ${\mathrm{Zn}}_{3}$${\mathrm{N}}_{2}$ films, which crystallize in cubic antibixbyite structure (space group: Ia3), are presented. The polycrystalline films are prepared by direct reaction between ${\mathrm{NH}}_{3}$ and zinc films on quartz substrates kept at 410…
A first-principles band calculation and theoretical simulation of scanning tunneling microscopy and spectroscopy (STM and STS) are performed on a stepped surface of graphite. The calculated band structure and the density of states are similar to those of fullerene tubules. Unlike in fullerene tubules, however, a local…
An elastic-plastic finite element method numerical model previously developed (see Part I of this article) for predicting thermal residual stresses at graded ceramic-metal interfaces has been applied to determine interface conditions favorable for achieving residual stress reductions. Using Al2O3-Ni as a model system,…
Magnetic properties of carbon nanotubes (CN's) are calculated in the effective-mass theory. The magnetic moment in a magnetic flux parallel to the tube axis oscillates as a function of the flux with period determined by the flux quantum and phase depending on whether CN is metallic or semiconducting. For a magnetic fi…
Electron and x-ray-diffraction studies of nanotubes have revealed that the distances between the graphitic sheets are larger by a few percent than those in bulk graphite. The mean value of the interlayer spacings is 0.344\ifmmode\pm\else\textpm\fi{}0.001 nm.
We have studied the microstructure and optical properties of free-standing porous Si thin films fabricated by electrochemical anodization. Raman-spectroscopy and transmission-electron-microscopy examinations show that Si crystallite spheres with diameters of several nanometers are dispersed in the amorphous phase. The…
We analytically study phonon transmission and localization in random superlattices by using a Green's-function approach. We derive expressions for the average transmission rate and localization length, or Lyapunov exponent, in terms of the superlattice-structure factor. This is done by considering the backscattering o…
The oxygen 1s x-ray-absorption spectra of ${\mathrm{SrTiO}}_{3}$ and ${\mathrm{TiO}}_{2}$, in both the rutile and anatase crystal structure, are analyzed using the oxygen p-projected density of states of ground-state band-structure calculations. Good agreement is found and it is concluded that multielectron effects, t…
An elastic-plastic finite element method numerical model has been formulated to study residual stresses developed at graded ceramic-metal interfaces during cooling. The results were compared with those obtained for sharp (nongraded) interfaces to assess the potential for achieving residual stress reductions. Analyses…
We have used femtosecond optical spectroscopy to study the dynamics of excitons strongly confined in microcrystallites of the narrow-band-gap semiconductor PbS. The transient absorption of the lowest exciton level exhibits terahertz-frequency vibronic quantum beats. Far-infrared measurements show that the vibrations a…
Raman spectroscopy is used to study residual stress in diamond grown on Ti--6Al--4V by chemical vapor deposition. A general model is developed to use Raman spectroscopy to measure biaxial stress in polycrystalline, diamond-structure films. The as-grown film has 7.1 GPa of residual compressive stress, consistent with t…
High-resolution ${\mathit{p}}_{\mathit{z}}$- and ${\mathit{p}}_{\mathit{x},}$y-projected fine structure for the 1s carbon core level in graphite are compared with symmetry-projected calculations. A very sharp transition occurs about 7.6 eV above the Fermi energy in the ${\mathit{p}}_{\mathit{x},}$y results, agreeing c…
Lithium borosilicate and lithium chloroborosilicate were prepared. These are considered basic systems to study the effect of chloride ions on structure and ionic conductivity. It was found that the replacement of Li 2 O by LiCl enhanced the conductivity. It was also found that the molar volume increases on increasing…
Abstract Sorption and diffusion of dichloromethane vapor were measured in amorphous syndiotactic polystyrene films, obtained with different cooling conditions and after controlled aging times at different temperatures. The diffusional behavior, at the temperature of 25°C, was characterized by three stages, depending o…
Uphill diffusion, the diffusion of a component up its own concentration gradient, has often been observed in experimental studies of diffusion in synthetic multicomponent systems and natural silicate melts. To apply experimental data to natural processes, it is necessary to quantify this effect. A modified effective b…
The solvent dependence of the second hyperpolarizability, gamma, of a variety of unsaturated organic compounds has been measured by third harmonic generation at 1907 nanometers. It is seen that the measured gamma is a function of solvent polarity. These solvent-dependent hyperpolarizabilities are associated with chang…