Metal-oxide film and photonic structures for integrated device applications

The application of photonic crystal technology on metal-oxide film is a very promising field for future optical telecommunication systems. Band gap and polarization effects in lithium niobate (LiNbO3) photonic crystals and bismuth-substituted iron garnets (BiYIG) photonic crystals are investigated in this work reported here. The design and fabrication process are similar for these two materials while the applications are different, involving Bragg filtering in lithium niobate and polarization rotation in nonreciprocal iron garnets. The research of photonic structures in LiNbO3 is of high interest for integrated device application due to its remarkable electro-optical characteristics. This work investigated the photonic band gap in high quality LiNbO3 single crystalline thin film by ion implantation to realize high efficiency narrow bandwidth filters. LiNbO3 thin film detachment by bonding is also demonstrated for optical device integration. One-dimensional Bragg BiYIG waveguides in gyrotropic system are found to have multiple stopbands and evince enhancement of polarization rotation efficiency. Previous photon trapping theory cannot explain the phenomena because of the presence of linear birefringence. This work is aimed at investigating the mechanism with the support of experiments. The results we obtained show that selective suppression of Bloch states in gyrotropic bandgaps is the key mechanism for the observed phenomena. Finally, the research of ferroelectric single crystal PMN-PT with ultra high piezoelectric coefficient as a biosensor is also reported. This work presents an investigation and results on higher sensitivity effects than conventional materials such as quartz and lithium niobate.

Preparation of highly-ordered TiO₂ nanotube arrays and their applications in Dye-sensitized solar cells

Titanium oxide is an important semiconductor, which is widely applied for solar cells. In this research, titanium oxide nanotube arrays were synthesized by anodization of Ti foil in the electrolyte composed of ethylene glycol containing 2 vol % H2O and 0.3 wt % NH4F. The voltages of 40V-50V were employed for the anodizing process. Pore diameters and lengths of the TiO2 nanotubes were evaluated by field emission scanning electron microscope (FESEM). The obtained highly-ordered titanium nanotube arrays were exploited to fabricate photoelectrode for the Dye-sensitized solar cells (DSSCS). The TiO2 nanotubes based DSSCS exhibited an excellent performance with a high short circuit current and open circuit voltage as well as a good power conversion efficiency. Those can be attributed to the high surface area and one dimensional structure of TiO2 nanotubes, which could hold a large amount of dyes to absorb light and help electron percolation process to hinder the recombination during the electrons diffusion in the electrolyte.