Zhihao Yuan

Fabrication of Densely Packed AlN Nanowires by a Chemical Conversion of Al(2)O(3) Nanowires Based on Porous Anodic Alumina Film.

Porous alumina film on aluminum with gel-like pore wall was prepared by a two-step anodization of aluminum, and the corresponding gel-like porous film was etched in diluted NaOH solution to produce alumina nanowires in the form of densely packed alignment. The resultant alumina nanowires were reacted with NH3and evaporated aluminum at an elevated temperature to be converted into densely packed aluminum nitride (AlN) nanowires. The AlN nanowires have a diameter of 15–20 nm larger than that of the alumina nanowires due to the supplement of the additional evaporated aluminum. The results suggest that it might be possible to prepare other aluminum compound nanowires through similar process.

A facile shape-selective growth of ZnO nanotips and graded nanowires from its oriented nanorods in a saturated ZnS solution

A facile solution-based route is developed for the preparation of distinctive ZnO nanostructures via a dissolution-growth of ZnO nanorods in a saturated ZnS solution at a water-bath temperature of 95 °C. In the dissolution-growth process, a series of novel morphologies including nanotips, tapered and graded nanowires can be conveniently achieved by simply changing the heating time. The pointed ends of the nanotips have a diameter of several nanometers, and the graded nanowires have a gradient change in diameter from a few to tens of nanometers along the longitudinal direction with the size of the thin end matching the Bohr exciton radius of ZnO. Furthermore, the formation mechanism from the ZnO nanorods to the nanotips, to the tapered and graded nanowires is discussed based on shape-evolution observations.

Enhanced thermoelectric performance of n-type Bi2S3 with added ZnO for power generation

Although Bi2S3 is one of the promising thermoelectric materials, its practical application is limited by a relatively low dimensionless figure of merit (ZT), and especially low electrical conductivity. In this work, ZnO was used to tune the thermal and electrical properties of Bi2S3. In the preparation processes of mechanical alloying (MA) and spark plasma sintering (SPS), small amounts of ZnO converted to ZnS in the sulfur rich environment, accompanied by the production of sulfur vacancies and micro/nanostructures. The sulfur vacancies increased the electrical conductivity of n-type Bi2S3 and micro/nanostructures scattered phonons without commonly deteriorating electronic transport. The maximum ZT value of 0.66 at 675 K for Bi2S3 doped with 1.0 mol% ZnO was obtained and the results of this work perhaps provide a new way for designing and fabricating thermoelectric materials.

Improved H2S gas sensing properties of ZnO nanorods via decoration of nano-porous SiO2 thin layers

Oriented ZnO nanorods are successfully decorated with a thin layer of nano-porous SiO2 film via solution method. The as-prepared ZnO@SiO2 composite nanostructure displays superior stability for the detection of a low concentration H2S. A molecule-isolation mechanism is suggested to interpret the improved H2S sensing properties of the ZnO@SiO2 composite nanostructure.

Effect of magnetic gamma-iron oxide nanoparticles on the efficiency of dye-sensitized solar cells

In this study, we report on an internal magnetic field effect, originating from magnetic γ-Fe2O3 nanoparticles (NPs) dispersed into nanocrystalline TiO2 film, which improves the performance of dye-sensitized solar cells (DSSCs). The DSSCs based on γ-Fe2O3/TiO2 composite photoelectrode at an optimal amount of ∼1.5 wt% γ-Fe2O3 NPs exhibit an energy conversion efficiency of 6.92%, which is increased by 18% compared to that of DSSCs based on pure TiO2 photoelectrode (5.84%). The role of the magnetic property of γ-Fe2O3 NPs on the PCE of DSSCs is investigated. It is found that the internal magnetic field, originating from the γ-Fe2O3 NPs in the TiO2 electrodes, is the key factor leading to the improved photogenerated electron transfer ability and reduced charge recombination.

Preparation and characterization of metal Fe nanowires with graded diameter

Based on the porous anodic aluminum oxide templates with a graded pore diameter, Fe nanowires were achieved using alternating current electrochemical deposition. SEM and TEM results show that Fe nanowires have obviously graded diameters along the nanowirepsilas direction with gradient ranging from about 12 to 31nm. High-resolution TEM analysis indicates that the gradient Fe nanowires have a preferential growth along <111> direction. Melting-behavior suggests that diameter-graded Fe nanowires have a graded melting point along one-dimensional direction, which will be of great fundamental and practical interests. It is expected that the ability to fabricate the gradient nanowires could open up new opportunities for fundamental studies and the application of nanostructures.