UV enhanced synthesis of high density Au coated ZnO nanocomposite.

We report the synthesis of high density Au coated ZnO nanocomposites by UV irradiation using a mixed solution of ZnO nanowires, HAuCl4 and Na2CO3. This synthesis process is easier and faster than a hydrothermal process in synthesizing Au/ZnO nanocomposites. The morphology, size distribution and density of the Au nanoparticles on the ZnO nanowires, which affect the photocatalytic efficiency of the synthesized Au/ZnO nanocomposite, were affected by the pH of the mixed solution. In order to obtain damage-free ZnO nanowires and small Au nanoparticles, the pH of the mixed solution should be adjusted to 7-8. UV irradiation promoted the formation of metallic Au nuclei, regardless of the presence of a ZnO photocatalyst. Au/ZnO nanocomposites were fabricated by Au reduction due to UV irradiation, followed by attachment of metallic Au nuclei to the ZnO nanowires, rather than by the photocatalytic reaction of ZnO. We propose this process as the dominent mechanism of the UV enhanced synthesis of Au/ZnO nanocomposites.

Density control and wettability enhancement by functionalizing carbon nanotubes with nickel oxide in aluminum-carbon nanotube system.

Excellent mechanical properties of carbon nanotubes (CNTs) make them ideal reinforcements for synthesizing light weight, high strength metal matrix composite. Aluminum is attractive matrix due to its light weight and Al/CNT composites are promising materials for various industrial applications. Powder metallurgy and casting techniques are normally used for bulk fabrications of composites. Casting process which can mass-produce delicate product is more suitable than existing powder metallurgy in view point of application in industries. In CNT-metal matrix composites, however, composite bulk fabrication has been limited because of the large density gap and poor wettability between the metal and CNTs. This study suggests a method for alleviating such problems. It was found that the wettability between aluminum and CNT could be enhanced by functionalizing the CNTs with nickel oxide. This functionalization of CNTs with heavier element also reduces the density gap between the matrix and reinforcements. It is suggested that this method could possibly be used in a casting process to enable mass fabrication of CNT-metal matrix composites.

Graphene growth at the interface between Ni catalyst layer and SiO2/Si substrate.

Graphene was synthesized deliberately at the interface between Ni film and SiO2/Si substrate as well as on top surface of Ni film using chemical vapor deposition (CVD) which is suitable for large-scale and low-cost synthesis of graphene. The carbon atom injected at the top surface of Ni film can penetrate and reach to the Ni/SiO2 interface for the formation of graphene. Once we have the graphene in between Ni film and SiO2/Si substrate, the substrate spontaneously provides insulating SiO2 layer and we may easily get graphene/SiO2/Si structure simply by discarding Ni film. This growth of graphene at the interface can exclude graphene transfer step for electronic application. Raman spectroscopy and optical microscopy show that graphene was successfully synthesized at the back of Ni film and the coverage of graphene varies with temperature and time of synthesis. The coverage of graphene at the interface depends on the amount of carbon atoms diffused into the back of Ni film.

Fabrication of CdTe/Te hetero-nanostructures by vapor-solid process.

CdTe/Te core-shell heterostructures were fabricated by the vapor phase synthesis at low temperatures using a quartz tube furnace. Two step vapor-solid processes were employed. First, various tellurium structures such as nanowires, nanorods, nanoneedles, microtubes and microrods were synthesized under different deposition conditions. These tellurium nanostructures were then used as substrates in the second step to synthesize the CdTe/Te core-shell heterostructures. Using this method, various sizes, shapes and types of CdTe/Te core-shell structures were fabricated under a range of conditions. The temperature, pressure and gas flow rate were very important parameters for synthesizing these nanostructures in the vapor phase process. The morphology, crystal structure and orientation were characterized by field-emission scanning microscopy, field-emission transmission electron microscopy and X-ray diffraction. The vapor phase process at low temperatures appears to be an efficient method for producing a variety of Cd/Te hetero-nanostructures. In addition, the hetero-nanostructures can be tailored to the needs of specific applications by deliberately controlling the synthetic parameters.