We report on the theoretical investigation of how geometrically uniform highly doped silicon nanowires can break up into a series of islands that exhibit Coulomb blockade. By using a newly developed numerical simulation in which random ionized dopants are introduced explicitly and the electron distribution is calculated self-consistently under the Thomas-Fermi approximation, we demonstrate natural formation of electron islands in the nanowires owing to the random dopant potential. We study the quasi-one-dimensional nature of the electron islands formed in the nanowires. The offset charge effects on the current threshold of the nanowire transistors are then investigated by feeding the derived structural parameters such as inter-island capacitance and tunnel resistance into a Monte Carlo single electron transport simulator. We show that the overall threshold voltage distribution can roughly be described as a two-'macro'-island system despite a complex series of multiple electron islands.

The magnon spectrum and thermodynamic properties of GdCI,, a ferromagnet in which the dipolar interactions are comparable in magnitude with the exchange interactions. are investigated both analytically and numerically. The calculations make use of formal results derived previously by Cottam for a general ferromagnetic insulator with dipole-dipole interactions. The magnon energies at low temperatures are calculated, including the leading order effects of spin wave interactions. The dispersion relation is found to be very anisotropic, and in particular it has a minimum energy gap of approximately 0,36 K at k = (0, 0,0,28)A By numerical integration over the whole Brillouin zone, results are obtained for the spontaneous magnetization over a wide range of temperatures, and the Curie temperature is estimated. A comparison is made with experimental data. Calculations are also carried out for the static susceptibility and the magnetic specific heat.

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