We have studied growth of carbon nanotubes by chemical vapor deposition and zinc oxide nanowires by physical vapor deposition on carbon cloth with iron sulfate or stainless steel as a catalyst, and various combinations of carbon source and carrier gases. The field emission of these nanostructures shows a combined result of field enhancement from carbon nanotubes or Zinc oxide nanowires and carbon cloth. An emission current density of 1 mA/cm2 was obtained at 0.4 V/μm and 0.7 V/μm for nanotubes and nanowires, respectively. Field enhancement factor of ~4x104 has been observed. Moreover, electron transport characteristics and structural studies of carbon nanotubes have been investigated. Microscopic observations of electric wall-by-wall breakdown imply that transport in the nanotubes is not ballistic and that a significant scattering occurs as carriers traverse nanotubes length.
Large-scale, two-dimensional arrays of periodic particles were prepared by nanosphere lithography. We modified the fabrication technique based on a self-assembly of latex particles on water surface in order to improve mask quality and size. Modifications of particles arrangement in an array were also practicable by using double-layered masks and mask transfer method. Such particle arrays were used for catalytic growth of aligned carbon nanotubes and ZnO nanorods with various configurations, length, and diameter. These exhibit interesting phenomena - antenna effects, photonic bandgap behavior, subwavelength lensing, and enhanced field emission. Therefore, they can be used in variety of future optoelectronic devices, such as THz and IR detectors.
A variety of novel ZnO nanostructures such as nanowires, nanowalls, hierarchical nanostructures with 6-, 4-, and 2-fold symmetries, nanobridges, nanonails have been successfully grown by a vapor transport and condensation technique. Doping both In and Sn into ZnO hierarchical nanostructures can be created. The 2-fold eutectic ZnO structures can also be created without any doping in the source. It was found that the hierarchical nanostructures can be divided into two
categories: homoepitaxial and heteroepitaxial where heteroepitaxy creates the multifold nanostructures. The novel ZnO nanowalls and aligned nanowires on a-plane of sapphire substrate have also been synthesized and the photoluminescence is studied. The ZnO nanowires also demonstrated very good field emission properties, comparable to carbon nanotubes. These nanostructures may find applications in a variety of fields such as field emission, photovoltaics, transparent EMI shielding, supercapacitors, fuel cells, high strength and multifunctional nanocomposites, etc. that require not only high
surface area but also structural integrity.