Template Synthesis Of Ordered Arrays Of One-Dimensional Nanostructures And Their Properties

In this dissertation, we studied on the ordered array of the metal nanotubes, zirconium oxide nanotubes, carbon nanotubes, and their concentric composite nanostructures. These nanostructures were fabricated in the pores of the alumina membrane and characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), x-ray diffraction(XRD) and Raman spectroscopy. The magnetization hysteresis loops of the magnetic nanostructures of Ni and Co were measured with a vibration sample magnetometer(VSM). The main results are as follows:1. Highly ordered magnetic Ni nanotubes with up to 35μm in length and 160 nm in outer diameter have been successfully prepared by electrodeposition in the pores of alumina membrane modified with an organoamine as pore-wall-modifying agent. Furthermore, using the array of Ni nanotubes with an alumina membrane support as a "second-order-template", cobalt nanowires encapsulated within Ni nanotubes were prepared by electrodeposition method. To the best of our knowledge, it is the first example of preparation of a perfect ordered array of such metal nanotubules with tens micrometers long. Magnetization measurements on the array of the Ni nanotubes and Co/Ni reveal an different uniaxial magnetic anisotropy.2. Various shapes of nanostructured cobalt, such as nanotubes, solid nanowires and nanowires composed of nanowhiskers were easily prepared by using an alumina membrane modified with an organoamine as a pore-wall modifying agent and adjusting current density. Such way for controlling the morphologies of the electrodeposited nano-objects has not been reported. The magnetic property measurements have revealed that these 1D Co nanostructures exhibit enhanced coercivities by comparison with that of the bulk Co and different uniaxial magnetic anisotropy. The present results testify that the shape of the template are not the only factor in determining the shape of the nano-subject. It may offer a new way to prepare other novel shape-controlled 1D metal nanostructures by using other type of pore-wall-modifying agent and adjusting the electrodeposition parameters. It also provides a new insight toward the understanding of the electrochemical growth process.3. A novel nanostructure of Ni nanotubes encapsulated in carbon nanotubes has been obtained via the pyrolysis of C₂H₂ on the array of Ni nanotubes. It is important to note that the Ni remains tubular structure, but its diameter becomes smaller after the catalytic pyrolysis reaction. This phenomenon gives an insight into the formation mechanism of the carbon nanotubes. A possible mechanism was proposed. To the best of our knowledge, such novel nanostructure of tube-in-tube has not been reported yet and might have many potential applications in catalysis, field emission, electrochemical research, and high-density magnetic memories, etc.4. An ordered array of ZrO₂ nanotubules was prepared with sol-gel technique using PAA membrane as a template. Furthermore, using the array of ZrO₂ nanotubules with an alumina membrane support as a " second-order-template", cobalt or nickel or copper nanowires encapsulated within ZrO₂ nanotubules were prepared by electrodeposition method. These synthetic strategies are very simple and effective. Magnetization measurements on the array of ordered Co/ZrO₂ and Ni/ZrO₂ composite nanostructure reveal an enhanced coercivity by comparison with that of the bulk metal. To the best of our knowledge, it is the first example of metal nanowires encapsulated in metal oxide tubules. From a technological point of view, this new type of composite nanostructure is more suitable for application in microelectronic devices such as chemical sensor, nanoelectrode emsembles for battery and electrochemistry and ultra-high-density magnetic recording, etc.5. The ordered arrays of size monodispersed carbon nanotubes have been prepared by pyrolysis of azobisisobutyronitrile at 600℃or acetylene at 700～720℃using Co as catalyst and alumina membrane as template. It is interesting that, in the former case, the carbon nanotubes is of bamboo-like structure with closed ends, which is quite different from the later case. The formation mechanism of the bamboo-like carbon nanotubes is tentatively proposed. Using the carbon nanotubes with open ends as a "second-order-template", the Co- or Ni-filled carbon nanotubes composites with high metal filling ratio have been obtained by electrodeposition. Especially, the length, diameter, wall thickness and structure of the composites can be easily controlled by template used and synthesis conditions. To the best of our knowledge, this is the first report on filling ferromagnetic metal, as a continuous nanowire with tens microns long, inside the aligned carbon nanotubes and forming an ordered array of metal-filled carbon nanotubes. Furthermore, this method can be applied to other metals and alloys. Precise and reproducible control of the dimensions of the ordered composite nanostructures should allow the reliable application studies on nanoelectronic devices, high-density magnetic memories, electrochemical energy storages and sensors, etc.Also, hollow Ni submicrospheres with the diameter in the range of 300～450 nm was prepared by chemical reduction of NiSO₄ by NaH₂PO₂ in polyglycol/cyclohexane/water emulsion and the magnetic properties of the nanostructure were measured. It is the one of a very few examples of the hollow metal spheres being successfully fabricated.