Materials Literature
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Microcrystallites of the layered semiconductor ${\mathrm{PbI}}_{2}$ were prepared in colloidal form and examined by transmission electron microscopy and optical absorption. The crystallites have lateral dimensions grouped around 12, 18, and 29 A\r{} corresponding to close-packed clusters with bulk ${\mathrm{PbI}}_{2}$…
The static properties of spin density waves (SDW) in (TMTSF) 2 PF 6 were determined by a precise analysis of 1 H-NMR lineshape in the low temperature SDW state. The observed angular dependence of lineshape was well reproduced by a picture of incommensurate sinusoidal SDW's. The wave number was found to be (0.5, 0.24±0…
Calculation of the lattice dynamical properties of black phosphorus, which is a narrow-gap covalent semiconductor with a layered structure, based on the valence force field model is presented. The results obtained are in good agreement with the experiments, except for infrared active optical modes. The results are dis…
A fundamental aspect in the study of the charge–transfer (CT) organic crystals with ionic or partially ionic ground states is the investigation of the spectroscopic effect of the electron–molecular vibration coupling. 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (TCNQF4), an electron acceptor much stronger tha…
A new model is presented that makes it possible to determine the degree of electron transfer in alloys from measurements of the Auger parameter. This approach is superior to the use of core-ionization-energy shifts in conjunction with a potential model. The Auger parameter does not depend on any reference level, where…
In this paper we examine the following problem: Given a band of localized states randomly distributed in space and obeying a distribution function for energies, how does an excitation diffuse as a function of time and initial energy? This question is encountered in luminescence, photoconductivity, and transport work i…
The macroscopic polarizability of silicon is calculated from first principles as a function of the lattice distortion induced by a zone-center optical phonon. The electronic response to the electric field is dealt with by dielectric matrices, and the lattice distortion is treated by frozen-phonon techniques. Our resul…
A comprehensive development of the charge-transfer theory of surface enhanced Raman scattering (SERS) is presented. We incorporate the Herzberg–Teller mixing of zero-order Born–Oppenheimer electronic states by means of vibronic interaction terms in the Hamiltonian. This is similar to the theory of Tang and Albrecht12…
The dispersion relations are solved for waves guided by a thin, lossy metal film surrounded by media of dielectric constant ${\ensuremath{\epsilon}}_{1}$ and ${\ensuremath{\epsilon}}_{3}$. For symmetric structures (${\ensuremath{\epsilon}}_{1}$=${\ensuremath{\epsilon}}_{3}$), there are the usual two Fano modes whose v…
The recombination kinetics of charged carriers in GaAs have been investigated on a picosecond time scale. A pump-probe technique was used to measure reflectivity changes as a function of time up to 900 ps. Initially, (1.2±0.2)×1020 carriers/cm3 were excited into the conduction band. The decay curve indicated dominance…
The authors prove a theorem that relates the energies of unit transmission through a finite, repeated one-dimensional structure to the band structure of the associated infinite lattice formed by periodic repetition of the one-dimensional structure.
We have experimentally discovered that in a nematic liquid crystal subjected to an ac electric field, the first convective structure at low frequencies is in fact a set of oblique rolls, contrary to the accepted picture. We show that it is a new structure with a helical flow motion, and thus lower in symmetry than the…
The origins and development of the concept of carbonaceous mesophase, as derived from discotic aromatic nematic liquid crystals, enable applications to be made to industrial processes. The world availability of pitch materials is such that there is an abundance of pitch which produces cokes of little commercial value.…
A new approach to Preisach's hysteresis model, which emphasizes its phenomenological nature and mathematical generality, is briefly described. Then the theorem which gives the necessary and sufficient conditions for the representation of actual hysteresis nonlinearities by Preisach's model is proven. The significance…
A pulsed plane-wave technique was used to measure the thermophysical properties of the sodium halides under pressure. The thermal conductivity lambda was found to increase with pressure in the 0-4 GPa. The experimental results are compared with the values estimated from the Leibfried-Schlomann model.
A new method for the investigation of methyl group rotation dynamics in free radicals in solids is described, based on the temperature dependence of the methyl protons ENDOR enhancement. The method is shown to work for hindering barriers of any height, and for both radicals trapped in single crystals and in powdered s…
Temperature dependence (4.2-300K) of the static dielectric constant epsilon is reported for two antiferromagnets namely MnF 2 (T N approximately=67.3K) and MnO (T n approximately=118K) for the electric field E parallel and perpendicular to the spin easy axis. Comparison with the temperature variation of epsilon in the…
Two compounds have been synthesized that feature a photosensitive o-nitrobenzyl moiety attached directly to the carbamate nitrogen of carbamoylcholine. The well-characterized acetylcholine analogue, carbamoylcholine, was released from these derivatives in response to laser light pulses at wavelengths between 300 and 3…
Received 15 November 1985DOI:https://doi.org/10.1103/PhysRevLett.56.1509©1986 American Physical Society
The technique of polarization-dependent near-edge x-ray absorption is applid to an interface by taking advantage of core-level and Auger energy shifts for interface atoms. For epitaxial Ca${\mathrm{F}}_{2}$/Si(111) several unoccupied Ca- and F-derived interface states are found. The orientation of the corresponding or…