Materials Literature
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Abstract The subtitutional doping of 120‐Å‐ sized TiO 2 Particles with Fe( III )ions has a profound effect on the charge carrier recombination time in this colloidal semiconductor. In undoped particles, the mean lifetime of an electronhole pair is ca. 30 ± 15 ns. Doping with 0.5% Fe( III ) drastically augments the cha…
Fr\"ohlich and Peierls showed that a one-dimensional system with a half-filled band can lower its ground-state energy by a dimerization from period 1 to period 2. It was an open question whether or not this dimerization was exact, i.e., whether additional symmetry breaking would further lower the energy. We prove that…
Calculations using nonlocal density-functional theory show that the total energies of atoms in states characterized by partially filled degenerate subshells are substantially lower when the charge density is not spherically averaged. This is in contrast to the case with local density theory in which spherical and nons…
By pseudopotential methods the electronic properties of quasicrystalline metal are examined from the nearly-free-electron viewpoint. The procedure results in the appearance of band gaps associated with each quasicrystal reciprocal-lattice vector, and these lead to singularities in both the density of states and the jo…
New results are presented on 1T-TaS 2 . They were obtained by combining convergent-beam electron diffraction with high-quality satellite dark-field imaging. In the nearly commensurate 1T 2 state linear defects were analysed as displacement faults and the fault planes and vectors were determined. The visibility of thes…
A reversible phase transition between the two polytypic phases 2H and 12R was found in PbI 2 near 367K which proves that these polytypes are thermodynamic equilibrium phases and not the result of growth processes. Disordered stackings were observed in samples which were annealed at temperatures above 420K. The phase t…
The modification to the structure and microstructure of chalcogenide films in contact with metals has been determined by electron microscopy and diffraction and the distribution of metal through these films has been determined by Auger electron spectroscopy. Chemical changes that occur when metal films are in contact…
The spectra of luminescence and photoexcitation as well as emission decay kinetics in various parts of spectra are investigated in ZnWO4 and CdWO4 crystals in a wide temperature range (4.2 to 300 K). The bands of red afterglow and of rapidly decaying violet luminescence are observed for the first time. The likeness of…
Thermoelectric power (TEP) measurements of ${\mathrm{TiSe}}_{2\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{S}}_{\mathrm{x}}$ solid solutions have been performed in the temperature range 10--315 K for 0\ensuremath{\lesssim}x<2. A phonon-drag effect is identified around 25 K. Its contribution to the TEP has been anal…
Effects of the 4d\ensuremath{\rightarrow}4f ``giant resonances'' of rare-earth constituents in phosphor host lattices were observed for the first time by means of luminescence excitation spectroscopy. Sintered powder samples of rare-earth (La,Gd) oxysulfides activated with terbium or europium were excited using monoch…
A simple explanation is offered for the magic numbers 11, 15, 19, and 23 for carbon clusters produced promptly by pulsed-laser ablation of carbon. The structure proposed for the eleven-member cluster has all C---C---C angles equal to 120\ifmmode^\circ\else\textdegree\fi{} with three five-member rigns about two atoms w…
The general solution of a Schr\"odinger equation with a quasiperiodic potential in $n$ dimensions is obtained. A boost technique is presented, which will transform the problem to the solution of a periodic pseudo-Schr\"odinger equation in $n+m$ dimensions, to which Floquet-Bloch theory is applicable. We show that the…
We present a continuum model for the growth of solid epitaxial films which takes account of both surface tension and lattice mismatch. Layer-by-layer film growth is found to be unstable for fixed particle number. We show that the conventional nucleation and growth scenario for film decay is in error above the rougheni…
Abstract show a nearly isotropic shrinkage of the structures of both rutile and anatase upon cooling from 295 to 15 K and no change in the sense of the coordination geometry about the Ti atom.
Raman spectra of the high-frequency (\ensuremath{\sim}1600 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) graphite interlayer modes have been studied in several Li-graphite intercalation compounds (GIC's) ${\mathrm{LiC}}_{\mathrm{p}}$=6,12,17,18. In stage-2 ${\mathrm{LiC}}_{17}$ we have also used these modes to study the…
We consider an infinite chain of atoms, where the bond lengths between neighbouring sites take two values, according to a quasi-periodic rule, associated to a circle map with an irrational rotation angle. In a particular case, this construction is related to the projection method used to describe quasi-crystals. The s…
Defect centers induced in GeO2 glass by either 100-KeV x rays at 77 K or γ rays at room temperature were studied by electron-spin resonance. The model of a singly charged oxygen vacancy defect center for the Ge E′ center (g∥ =2.0012, g⊥ =1.9945) was confirmed by the observation and computer simulation of the 73Ge hype…
We report on resonant and nonresonant Raman scattering by acoustic phonons in Fibonacci GaAs-AIAs superlattices. Spectra off resonance are dominated by doublets centered at frequencies that follow a power-law behavior, in good agreement with numerical calculations based on a continuum model. Resonant data show a weigh…
Replacement of B (B=S or Se) by Bi in Ge${B}_{4}$ produces semiconductive glasses with n-type thermoelectric power, in contrast to almost all other chalcogenide glasses, which are p type. I describe theoretically a structural model which explains why carrier-type reversal occurs for Bi replacement, but not for Sb repl…
We have studied the formation of amorphous silicon by rapid quenching of the melt using the Stillinger-Weber potential to model the interaction between silicon atoms. By quenching the melt at a rate of 3\ifmmode\times\else\texttimes\fi{}${10}^{14}$ K/s we form amorphous silicon. Excellent agreement with the experiment…