Materials Literature
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The spatial and temporal evolution of photodarkening in chalcogenide glasses is simulated by a simple kinetic model and tested against experiments. In the model, photodarkening, a gradual decrease of the energy of the absorption edge caused by above-band-gap illumination, is the additional absorption at defects create…
The anions of (TMTSF) 2 ClO 4 order below about 24 K. The speed at which this transition is passed has a drastic influence on the low temperature electronic properties of this salt. We determined as a function of the cooling rate the number of ordered ClO 4 as well as the average size of the ordered domains. A high re…
The phase transition sequence of a K 2 ZnBr 4 crystal was investigated by DTA and dielectric measurements. It was found that the crystal undergoes at least two phase transitions, at -118°C and around 200°C, on heating. Ferroelectricity was observed below the lower transition point.
We report a first-principles, local-density-functional (LDA) calculation of the electronic structure of crystalline, three-dimensional (3D) trans-(CH${)}_{\mathit{x}}$. For the perfect crystal, we find a broken-symmetry ground state having P${2}_{1}$/a space-group symmetry, corresponding to in-phase dimerization on ne…
In the present work we make M\"ossbauer and magnetization studies of the ${\mathrm{Ti}}^{4+}$-substitution effect in the ${\mathrm{Ni}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Zn}}_{\mathit{y}}$${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$ ferrite (y=0.3 and 0.4). In this range the M\"ossbauer spectra are not relaxed a…
Hydration phase transitions in Na vermiculite, a specific example of expandable 2:1 layered silicates, were examined as a function of temperature at a constant water-vapor pressure by x-ray diffraction. The samples exhibited well-defined 0-, 1-, and 2-water-layer hydration states (WLHS's) with the basal spacings of 9.…
We report on the molecular-beam-epitaxy growth of CdS films on CdTe(110), studied with reflection high-energy electron diffraction (RHEED) and angle-resolved photoemission spectroscopy. The exponential attenuation of the Te 4d core-level emission as a function of the CdS film thickness and the persistency of the subst…
The influence of surface roughness on the electrical conductivity of polycrystalline metal films has to be considered at two different length scales. The large-scale surface roughness due to the granular arrangement of these films gives rise to a fluctuating film cross section. One-dimensional models of these fluctuat…
A simple but tractable model of the density of exciton states associated with potential fluctuations in semiconductor alloys is proposed. It consists of minimizing the fluctuation entropy related to the composition fluctuation \ensuremath{\Delta}x averaged over a volume V, for a given localization energy \ensuremath{\…
Photoelectron diffraction has been measured from a (001) single-crystal surface of aluminum. Anisotropies of the photocurrent of 73% and 65% have been observed in azimuthal scans of 2s and 1s core-level intensities comprising the [011] direction. Azimuthal intensity scans have also been measured for the plasmon-loss p…
Polarized, depolarized, isotropic, difference, and reduced Raman spectra were obtained from vitreous silica, irreversibly compacted at 600 °C and 50 kbar, to ambient densities as high as 2.73 g cm−3. The 60 cm−1 ‘‘Boson’’ peak; and, the intense optic, Si–O–Si bending peak at 440 cm−1 including its low-frequency should…
The weak-localization phenomenon for two-dimensional (2D) electronic systems is invoked to explain the negative magnetoresistance as well as the low-temperature dependence of the resistivity of pyrocarbon samples heat treated between 2000 and 2600 \ifmmode^\circ\else\textdegree\fi{}C. The 2D character is found to orig…
Optical absorption over a large dynamic range obtained by two different experimental techniques is reported for an undoped α-Al2 O3 single crystal. Absorption data are presented in two energy ranges: 0.94–3.5 eV and 4.5–8.6 eV. Vacuum ultraviolet (vuv) absorption measurements were performed on three boules of Czochral…
This work studies the pressure-induced semiconductor-to-metal transition (SMT) in the TmSe-TmTe alloy system. This SMT is accompanied by a valence instability of the Tm ions. Single-crystalline semiconducting ${\mathrm{TmSe}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Te}}_{\mathit{x}}$ alloys are investigated und…
We have used a new, approximate method for computing total energies and forces in covalent systems and investigated the electronic and vibrational spectra and equilibrium structures of small Si clusters (${\mathrm{Si}}_{\mathit{n}}$ with n=2--7). The method uses an electronic-structure tight-binding formalism based on…
Using a phenomenological lattice-dynamical theory in the quasiharmonic approximation, we present a comprehensive study to understand the effects of pressure on the vibrational properties of Ga-In pnictides that exhibit a sphalerite crystal structure. The existing pressure-induced Raman scattering data for phonon frequ…
First-order Raman scattering from graphite irradiated by an electron beam has been studied by using the laser microprobe technique. An approximately linear relation is exhibited between the linewidth of the ${\mathit{E}}_{2\mathit{g}}$ mode and the reciprocal of the crystallite size. The observed linewidths are larger…
Self-consistent ab initio band-structure calculations using the augmented-spherical-wave method were performed for the hypothetical compounds ${\mathrm{YFe}}_{12}$ and ${\mathrm{YFe}}_{8}$${\mathit{M}}_{4}$ (M=Ti, V, Cr, Mn, Mo, and W) with the ${\mathrm{ThMn}}_{12}$ structure, in which the M atoms occupy the 8(i) cry…
An interaction potential consisting of two-body and three-body covalent interactions is proposed for ${\mathrm{SiO}}_{2}$. The interaction potential is used in molecular-dynamics studies of structural and dynamical correlations of crystalline, molten, and vitreous states under various conditions of densities and tempe…
Molecular modeling of alcohol dehydrogenase suggests that His-47 in the yeast enzyme (His-44 in the protein sequence, corresponding to Arg-47 in the horse liver enzyme) binds the pyrophosphate of the NAD coenzyme. His-47 in the Saccharomyces cerevisiae isoenzyme I was substituted with an arginine by a directed mutatio…