No abstract

It is found that the TiO2 ultrafine particles (UFP) coated with a layer of stearic acid radicals had a significant red shift of their absorption band edge and clear photoluminescence at room temperature (RT), which are in contrast with that of bulk TiO2 and naked TiO2 UFP. It was concluded that these results are related to the self-trapped exciton absorption due to the interfacial dipole layer of stearic acid radicals on the TiO2 UFP surface.

We have given a detailed investigation of the energy spectrum and the electrical properties of a two-dimensional electron gas modulated by a general form of one-dimensional periodic magnetic field along the x direction, by generalizing the theory of Peeters and Vasilopoulos and that of Xue and Xiao on the magnetic modulation in the lowest order of approximation of Fourier transformation. The presence of the magnetic modulation lifts the degeneracy of the Landau levels, which are broadened into bands, and leads to Weiss-like oscillations in the magnetoresistance. The oscillations in ρ xx (and the modulation correction ρ xx ) and ρ yy (and ρ yy ) are out of phase, while ρ xy oscillates in phase with ρ xx . The amplitude of oscillation of the modulation correction ρ xx is much larger than those of ρ yy and ρ xy . We also find the surprising result that, while the Hall resistance displays quantized plateaux, the transport across the magnetic barriers can be nearly dissipationless. The contribution of high-frequency components of Fourier transformation is obvious at high fields and is negligible at low fields.