Papers by Author: Fei Xu

Abstract: In this paper, aluminum–doped nano-crystalline zinc oxide (ZnO:Al or AZO) thin films were deposited on fused quartz substrate by pulsed laser ablation at various temperatures. The physical phase and surface morphology were characterized by using X-ray diffraction (XRD) and atomic force microscope (AFM), respectively. The variation of the optical band gap (E^g_opt) of the films with the temperature was measured through transmittance in UV-VIS wavelength. The results showed that there was a blue shift of E^g_opt from 3.44 eV to 3.62 eV as the growing temperature decreased from 500°C to 200°C. The value of E^g_opt immediately recurred from 3.30 to 3.35 eV after a thermal annealing of the samples at 700 °C, inclining to a normal value of bulk zinc oxide. The analyses of XRD and AFM testified that the presence of amorphous phase in the AZO films was the main reason for the blue shift of the optical band gap E^g_opt.

Abstract: Highly Oriented TiO₂ Nanotube (NT) Arrays Were Fabricated by Anodizing Ti Foils. the Morphology of the NT Arrays Was Characterized by Scanning Electron Microscope. by Adjusting the Anodization Time, the Lengths and Diameters of TiO₂ NT Arrays Changed from 6.7 to 19.5 μm, and 90 to 110 Nm, Respectively. as Confirmed by X-Ray Diffraction and Raman Spectra, the as-Anodized TiO₂ NTs Were Amorphous but Transformed into Anatase Phase after Annealing at 450°C for 3 H. Reflectance Spectrum of TiO₂ NT Arrays Showed that NT Layer of Longer Length Lowered the Reflectance in the Visible Spectrum because of Light Trapping Effects of NTs, Thus Enhancing Light Harvesting of NTs. Dye-Sensitized Solar Cells Were Fabricated Using TiO₂ NT Arrays with Different Tube-Lengths. Analysis of Photocurrent Density-Voltage (J-V) Characteristics Showed that Higher Photoconversion Efficiencies Were Achieved with Longer NT Lengths.

Abstract: Dry and wet oxidation silica films doped with silicon ions were prepared using metal vapor vacuum arc (MEVVA) ion source implanter. The does of Si ion beams were kept constant at 3×1016 /cm2 and the energy varied from 42KeV to 70KeV. Five photoluminescence (PL) bands at the wavelength of 560nm, 580nm, 620nm, 650nm and 730nm have been observed at room temperature in all samples. The results of XRD showed none of Si nanocrystals were formed in the as-implanted silica films and originations of the PL bands were defects introduced by implantation. The 560nm PL band originated from oxygen surplus defect small peroxy radical (SPR), whereas the PL bands which ranges from the wavelength of 620nm to 730nm were attributed to non bridge oxygen hole center (NBOHC). Elevating implantation energy resulted in intensity increasing of 560nm PL band of dry oxidation samples but had inverse effects on wet oxidation samples. Influence mechanism of implantation energy on the defect photoluminescence was discussed in this article.