Abstract: Starting from a model of rigid interacting C-60 polymer chains on an orthorhombic lattice, we study the mutual orientation of the chains and the stability of the crystalline structures Pmnn and I2/m. We take into account (i) van der Waals interactions and electric quadrupole interactions between C-60 monomers on different chains as well as (ii) interactions of the monomers with the surrounding alkali atoms. The direct interactions (i) always lead to an antiferrorotational structure Pmnn with alternate orientation of the C-60 chains in planes (001). The interactions (ii) with the alkalis consist of two parts: translation-rotation (TR) coupling where the orientations of the chains interact with displacements of the alkalis, and quadrupolar electronic polarizability (ep) coupling, where the electric quadrupoles on the C-60 monomers interact with induced quadrupoles due to excited electronic d-states of the alkalis. Both interactions (ii) lead to an effective orientation-orientation interaction between the C-60 chains and always favor the ferrorotational structure I2/m, where C-60 chains have a same orientation. The structures Pmnn for KC60 and I2/m for Rb- and CsC60 are the result of a competition between the direct interaction (i) and the alkali-mediated interactions (ii). In Rb- and CsC60 the latter are found to be dominant, the preponderant role being played by the quadrupolar electronic polarizability of the alkali ions. (C) 2002 American Institute of Physics.

Abstract: Explicit analytic expressions are obtained for the density of states D(E) and Fermi energy E-F of a two-dimensional electron gas in the presence of a weak and periodic unidirectional electric or magnetic modulation and of a uniform perpendicular magnetic field B. The Landau levels broaden into bands and their width, proportional to the modulation strength, oscillates with B and gives rise to Weiss oscillations in D(E), E-F and the transport coefficients. When both electric and magnetic modulations are present the position of the resulting oscillations depends on the ratio delta between the two modulation strengths. When the modulations are out of phase there is no shift in the position of the oscillations when delta varies and for a particular value of delta the oscillations are suppressed.

Abstract: Results are presented on the photoluminescence (PL) characterization of heavily doped p(+) Czochralski silicon, which has been subjected to a two-step, oxygen precipitation heat treatment. It will be shown that the presence of oxygen precipitates gives rise to the D1, D2 and D5 lines, where the energy of the D1 line shifts to lower values for a stronger degree of precipitation. The occurrence of these PL features is also a function of the boron concentration in the p(+) material. The PL results are compared with Fourier transform infrared absorption data and with transmission electron microscope, results. From this, it is concluded that PL has a good potential for use in the assessment of oxygen precipitation in heavily doped silicon.

Abstract: The purpose of this Brief Report is to point out the mistake in a formula for anisotropic electron scattering, previously published in Phys. Rev. A 41, 1112 (1990), which is widely used in Monte Carlo models of gas discharges. Anisotropic electron scattering is investigated based on the screened Coulomb potential between electrons and neutral atoms. The approach is also applied for electron scattering by nonpolar neutral molecules. Differential cross sections for electron scattering by Ar, N2, and CH4 are constructed on the basis of momentum and integrated cross sections. The formula derived in this paper is useful for Monte Carlo simulations of gas discharges.

Abstract: The multiband effective-mass model of cylindrical self-assembled quantum dots in a magnetic field normal to the layer of the quantum dots is presented. The strain distribution is computed by the valence force field method. The strain-dependent multiband Hamiltonian is modified into an axially symmetric form, which commutes with the total angular momentum F-2 = fh. where f denotes the total magnetic quantum number. The heavy hole and the light hole parts in the mixed hole state are resolved. It is found that the heavy hole component dominates in the ground states for both f = 1/2 and 3/2. The electronic structure exhibits numerous anticrossings between the hole levels. The Zeeman splitting between the +\f\ and -\f\ states is also computed. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: We report the suppression of the Hall effect in a mesoscopic Hall cross with a strong magnetic field only in the centre and vanishingly small outside, The local magnetic field is produced by placing Dy pillar on top of a structure with a high-mobility two-dimensional electron gas. The effect is found to be due to a sharp increase of the number of back-scattered and quasi-localised electron orbits. The possibility of localising electrons inside the magnetic inhomogeneity region is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: We investigate the energy levels of the negatively and positively charged excitons (also called trions) in a 200 Angstrom wide GaAs quantum well in the presence of a perpendicular magnetic field. A comparison is made with the experimental results of Glasberg et al. (Phys. Rev. B. 59 (1999) R10 425) and of Yusa et al. (cond-mat/0103505). (C) 2002 Elsevier Science B.V. All rights reserved.