Materials Literature
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A model of the low-frequency Raman scattering intensity in glasses is proposed, which describes the spectrum in the region of the boson peak, typical of glasses. The model considers the boson peak as a result of first-order light scattering by harmonic quasilocalized vibrations. The amplitude, frequency, and polarizat…
Local-density calculations on the ${\mathrm{CrO}}_{2}$ (001) surface are reported. The half-metallic character of the bulk is found to be maintained at the surface. Surface states of oxygen p character at the top of the valence band for the semiconducting spin direction are discussed.
We present a calculation of x-ray diffraction from a crystal with a surface oriented at an arbitrary angle relative to the axes of the bulk crystalline lattice, demonstrating that the scattering consists of rods in reciprocal space, each passing through a bulk peak and rotated away from the crystalline axes by an angl…
An energetic model of statistic domain behavior is applied on the magnetization process of grain oriented FeSi-steel sheets. The physical constants of the model are derived from anisotropic energy contributions, initial susceptibility, coercivity, and saturation magnetization. Calculated in the [100], [011], and [111]…
The elastic constants of face-centered-cubic and hexagonal-close-packed structures are calculated within an empirical tight-binding d-band model. The variation with band filling of the shear elastic constants is in contrast with the roughly parabolic behavior of the bulk modulus, cohesive energy, and atomic volume. Th…
At low temperatures and sufficient densities, free excitons in Si and Ge undergo simultaneous gas-liquid and insulator-metal transitions into droplets of electron-hole liquid. Some previous theoretical and experimental studies have suggested that, under certain values of density and temperature, there may be separate…
The electromechanical and dielectric responses of ferroelectric materials near paraelectric–ferroelectric (PF) phase transitions are examined both experimentally and theoretically. It is shown that the type of PF transition, i.e., first order and continuous transitions, and diffused phase transition found in relaxor f…
The evolution of nonequilibrium phase transitions during the decompression of high-pressure modifications of Si, Si/GaAs, Ge, and Ge/GaSb at different temperatures was studied. At temperatures below 120 K, the amorphization of Si and Ge high-pressure phases occurs upon the release of pressure. The positions of the tra…
Valency and 4f covalency of ${\mathrm{Cs}}_{2}$${\mathrm{RbTbF}}_{7}$ were studied by x-ray-absorption near-edge-structure (XANES) spectroscopy at the Tb-${\mathit{L}}_{\mathrm{I}\mathrm{\ensuremath{-}}\mathrm{III}}$, Tb-${\mathit{M}}_{\mathrm{I}\mathrm{V},\mathrm{V}}$, and F-K absorption thresholds as well as by 3d c…
Iron-rich intermetallic compounds Sm2Fe17−xSix and Sm2Fe17−xSixC (x=0, 1, 2, and 3) were studied. The as-prepared compounds are single phase with the rhombohedral Th2Zn17-type structure except for Sm2Fe17C and Sm2Fe16SiC which contain some amounts of α-Fe. The unit cell volumes and saturation magnetization at room tem…
As a result of the interaction between the spin and the magnetic field (B), special step structures are predicted to exist in the ballistic magnetoconductance of carbon nanotubes. The electronic structure of a carbon nanotube drastically changes from a metal (semiconductor) to a semiconductor (metal) during the variat…
The thermo-emf in bipolar semiconductors is calculated. It is shown that it is necessary to take into account the nonequilibrium distribution of electron and hole concentrations (Fermi quasilevels of the electrons and holes). We find that electron and hole electric conductivities of contacts of semiconductor samples w…
The influence of Sb, As, Ga, and In as surfactants on the Si/Si(111) homoepitaxy is studied using scanning tunneling microscopy. The nucleation of two-dimensional (2D) Si islands on the surfactant-terminated surface was studied as a function of temperature. The island densities and depleted zones show Arrhenius behavi…
The hydrodynamic model for the degenerate free-electron gas has been generalized for arbitrary frequencies. The result for the longitudinal dielectric function is \ensuremath{\epsilon}(\ensuremath{\omega},q)=1-${\mathrm{\ensuremath{\omega}}}_{\mathit{P}}^{2}$[\ensuremath{\omega}(\ensuremath{\omega}+i\ensuremath{\nu})-…
Using chemical-vapor deposition nanodispersed silicon has been prepared in carbon at temperatures between 850 and 1050 °C. Samples with up to 11% atomic silicon in carbon show the same pregraphitic x-ray-diffraction pattern as those without silicon. X-ray-absorption spectroscopy shows that the silicon is bonded mostly…
The stability of interfaces and the mechanisms of thin film growth on semiconductors are issues of central importance in electronic devices. These issues can only be understood through detailed study of the relevant microscopic processes. Experimental studies are able to provide detailed, atomic scale information for…
Ab initio molecular dynamics is used to study deformations of sodium clusters at temperatures $500\cdots 1100$ K. Open-shell Na$_{14}$ cluster has two shape isomers, prolate and oblate, in the liquid state. The deformation is stabilized by opening a gap at the Fermi level. The closed-shell Na$_8$ remains magic also at…
Using the non-empirical Variational Induced Breathing (VIB) model, the thermal properties of periclase (MgO) under high pressures and temperatures are investigated using molecular dynamics, which includes all anharmonic effects. Equations of state for temperatures up to 3000K and pressures up to 310 GPa were calculate…
Adaptive coordinates are shown to be effective in allowing the accurate calculation of structures and interatomic forces for solids containing first-row atoms using relatively small orthonormal sets of basis functions. Several polymorphs of ${\mathrm{SiO}}_{2}$ are studied as illustrative test cases.
Local-density-functional pseudopotential theory is used to investigate native defects in diamond, their structure, electronic, vibrational, and diffusive properties. We find the only truly stable structure for an interstitial atom to be the 〈100〉 split interstitial defect. This conclusion holds in the neutral, -1, +1,…