We present optical measurements of random arrays of aligned carbon nanotubes, and show that the response is consistent with conventional radio antenna theory. We first demonstrate the polarization effect, the suppression of the reflected signal when the electric field of the incoming radiation is polarized perpendicular to the nanotube axis. Next, we observe the interference colors of the reflected light from an array, and show that they result from the length matching antenna effect. This antenna effect could be used in a variety of optoelectronic devices, including THz and IR detectors.

Zirconium oxide (ZrO 2 or zirconia) nanostructures were synthesized by a hydrothermal route. Surface morphology analysis depicts the formation of various zirconia nanostructures at different synthesis conditions. X-ray diffraction examination demonstrates that the as-synthesized zirconia is of pure monoclinic phase (m-ZrO 2 ). High resolution transmission electron microscopy (HRTEM) further confirms the high crystalline feature of the m-ZrO 2 nanostructures. X-ray photoelectron spectroscopy (XPS) core-level spectra of Zr 3d and O 1s for the ZrO 2 nanostructures have been studied to understand further the electronic states and chemical environment of the Zr and O atoms in ZrO 2 for different synthesis conditions. XPS results also indicate the existence of oxygen defects and zirconia suboxides which affect the structural and optical properties of zirconia nanostructures. The nanostructures show UV-vis absorption band around 290 nm at room temperature. The band gap energy is determined, in the range of 2.5-3.8 eV for zirconia nanostructures synthesized at various conditions. A broad emission band with maximum intensity at around 400 nm is observed in the photoluminescence (PL) spectra of zirconia nanostructures at room temperature depicting the violet emission, which can be attributed to the ionized oxygen vacancy in the material.

Intensive studies have been carried out on controlling the periodicity and alignment of large-scale periodic arrays of carbon nanotubes (CNTs) using plasma-enhanced chemical vapor deposition. Catalytic dots are first prepared by self-assembly of polystyrene spheres on chromium-coated silicon substrates. Preparation parameters for CNTs growth including temperature, thickness of catalytic dots, plasma current intensity, and pregrowth plasma etching time are fine tuned and analyzed to achieve optimal combinations. High-quality aligned CNTs arrays with long-range periodicity and controlled diameters have been achieved. The good periodicity and alignment are critical for their applications such as photonic crystals, negative index of refraction, etc.

Current efforts of guided growth of carbon nanotubes alone cannot make large-scale and directed assembly of them. The nanopelleting concept overcomes this limitation by embedding carbon nanotubes in microscale pellets that can be transplanted readily. This technique includes vertical growth of carbon nanotubes, pellet casting, planarization, pellet separation, and transplantation. A specific manufacturing process is developed and tested with favorable results. This technology will enable directed assembly of carbon nanotubes in a long-range order.

No abstract