Chemical conversion synthesis of ZnS shell on ZnO nanowire arrays: morphology evolution and its effect on dye-sensitized solar cell.

Heterostructured ZnO/ZnS core/shell nanowire arrays have been successfully fabricated to serve as photoanode for the dye-sensitized solar cells (DSSCs) by a facile two-step approach, combining hydrothermal deposition and liquid-phase chemical conversion process. The morphology evolution of the ZnS coated on the ZnO nanowires and its effect on the performance of the DSSCs were systematically investigated by varying the reaction time during the chemical conversion process. The results show that the compact ZnS shell can effectively promote the photogenerated electrons transfer from the excited dye molecules to the conduction band of the ZnO, simultaneously suppress the recombination for the injected elelctrons from the dye and the redox electrolyte. As reaction time goes by, the surface of the nanowires becomes coarse because of the newly formed ZnS nanoparticles, which will enhance the dye loading, resulting in increment of the short-circuit current density (J(SC)) . Open-circuit photovoltage decay measurements also show that the electron lifetime (τ(n)) in the ZnO/ZnS core/shell nanostructures can be significantly prolonged because of the lower surface trap density in the ZnO after ZnS coating. For the ZnO/ZnS core/shell nanostructures, the J(SC) and η can reach a maximum of 8.38 mA/cm(2) and 1.92% after 6 h conversion time, corresponding to 12- and 16-fold increments of as-synthesized ZnO, respectively.

Heavily doped ZnO nanobelts and their violet emission.

In-doped ZnO nanobelts have been synthesized by a thermal evaporation method with absence of catalysts. The morphology and microstructure of the doped ZnO nanobelts have been extensively investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). The results show that the belts grow along the (1010) direction with the typical lengths in the range of several tens to several hundreds of micrometers, and the typical widths of the belts are several hundreds of nanometers. According to the XRD pattern of the sample, the most of belts are ZnO with heavy doping content and ternary Zinc Indium Oxide (such as Zn5In2O8, Zn4In2O7). The X-ray energy dispersive spectrometer (EDS) analysis demonstrates that the In content in the as-examined belt is as high as 27 at%. Notably, the photoluminescence spectrum reveals a novel violet emission peak (425 nm) in the as-synthesized product.

Bud-like silica nanowires with self-assembled long segmented stems: a novel nanostructure and its growth mechanism.

A large quantity of bud-like silica nanowires with self-assembled long segmented stems were synthesized through thermal evaporation via using a piece of Si wafer and the mixture of Ga2O3 and carbon powder as source materials. The segmented stems were assembled from the bottom part of the bud-like silica nanowires with diameter of approximately 0.5 microm and length up to more than 20 microm. The bud-like silica nanowires could have one, two or three segmented stems. Some bud-like silica nanostrutures have a bowl-shaped cavity at their tips, others have a tail growing from their tips. The aligned silica nanowires were found extending from the thin silica shell coating the Ga ball, instead of nucleating and growing from the surface of the Ga ball directly. These interesting results could help us understand the diversity and versatility of the silica nanostructures which can be fabricated, and the knowledge of their growth mechanisms.