Femtosecond optical pulse propagation in a quantum well ͑QW͒ waveguide and a quantum wire ͑QWR͒ waveguide was investigated by cross-correlation frequency resolved optical gating ͑XFROG͒ spectroscopy. An optical pulse transmitted through the GaAs QW waveguide was found to stretch greatly from 140 fs to almost 1 ps due to nonlinear dispersion around the heavy hole exciton resonance at transverse electric polarization in a near resonant experiment. In contrast, only slight chirping of the pulse transmitted was observed either at transverse magnetic polarization or off resonance for both polarizations. In the GaAs QWR waveguide, the polarization anisotropy of a crescent shaped QWR could also be observed in terms of dispersion by XFROG spectroscopy in spite of the small absorption compared with that in the QW.
Single crystalline ZnO disk-like structure with good luminescent properties was obtained by a low temperature solution based method. Micro-emulsion was employed to assist the shape control. The product has a perfect hexagonal shape with flat bottom and up surfaces, and has a wide size distribution, the size ranges from nano to micro-scale. Electron diffraction (ED) pattern coupled with transmission electron microscopy (TEM) indicate that the single disk was single-crystalline. In cathodoluminescence (CL) studies at room temperature for wavelengths between 350 and 675 nm, we have observed a single exciton peak around 390 nm without any deep-level emission. The monochromatic CL mapping in the ultra-violet (UV) region has such properties as: the intensity is concentrated along the boundary of the cavity; the emission is predominantly at the corner.
We have developed nanometer-scale vertical ferromagnetic tunnel junctions using a Si-based inorganic electron beam resist process, including barrier layer fabrication using metal evaporation in ozone atmosphere. The current–voltage (I–V) characteristics of Ni/NiO/Co multiple junctions with diameters of 20 nm have been measured in a magnetic field to investigate spin-polarized tunneling in the Coulomb blockade regime. The temperature dependence of the I–V curve indicates that Coulomb blockade phenomena occur at temperatures below 40 K, agreeing with the estimation of the single-electron charging energy from the device geometries. The magnetoresistance is strongly enhanced by magnetization reversal of Ni and Co, and the obtained MR ratio is greater than 100% in the Coulomb blockade regime at 15 K.
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