0D And 1D Semiconductor Nanomaterials: Structural Transformation And Growth Mechanism

Recently, semiconductor oxide nanomaterials have received intense research interests due to their unique properties and potential applications for devices. In this thesis, two kinds of important semiconductor oxides, TiO2 and SnO2, have been selected and their morphology and structure evolution between O-dimensional nanoparticles and 1-dimensional nanorods was studied using the mesoporous silica spheres (MS) and self-sacrificing titanate nanowires as templates, respectively. meanwhile, the growth mechanism was also proposed.1. The mesoporous silica spheres with uniform size have been fabricated by using the neutral surfactant, hexadecylamine, as template agent and TEOS as silicon source. Controllable synthesis of SnO2 nanocrystals inside mesopores via hydrothermal method has been reported and the controlled self-assembly process from separated particles to nanochains is investigated. With various concentration of MS precursors, the quantity of SnO2 nuclei formed on the surface of mesopores changed, which plays an important role in the morphological diversification. It is useful to understand the self-assembly behavior of nanomaterial under confinement situation. Photoluminescence spectra are also recorded on the prepared nanocomposite structure and the emission spectrum possesses two sharp emissions at 395 and 414 nm. The UV-visible absorption and Raman spectrum were carried out in order to characterize the opticl properties.2. Ordered TiO2 nanosheets have been successfully synthesised via a hydrothermal method by employing one-dimensional titanate hydrate (H2TinO2n+1·xH2O) as the self-sacrificing precursor and NH4F as a morphology controlling agent. The prepared TiO2 nanosheets are well crystallized, and have structural integrity and uniform size. The morphology and phase transformation has been studied by controlling the experimental conditions and the titanate nanowires are transformed into anatase TiO2 nansheets on the basis of the in situ topochemical transformation mechanism (dehydration in situ and local recrystallization). At the same time, the titanate nanowires play a key role in the transformation process by providing both the structural unit (e.g., TiO6 octahedra) to realize anantase transformation and locations for the aggragation of nanosheets. The effect of the TiO2 nanosheets scattering layer on the dye-sensitized solar cell performance was investigated, and the results show that the cell efficiency was improved significantly.