Nanostructures of cuprous oxide and cuprous chloride: Synthesis and characterization.

摘要

Bose-Einstein condensation (BEC) of excitons in semiconductor systems has attracted increasing research interests for many years. Cuprous oxide (Cu2O) and Cuprous Chloride (CuCl) are two model systems for the study of BEC of excitons and biexcitons. Their large exciton binding energies and small exciton Bohr radii provide stable excitonic structures for the BEC study. Nanostructures of these materials will increase the exciton binding energies due to spatial confinements. This dissertation is focused on the synthesis and characterization of nanostructures of Cu2O and CuCl.; Self-assembled Cu2O nanodots have been grown on LaAlO 3 (001) substrates using metalorganic chemical vapor deposition (MOCVD). Dot morphology has been extensively studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Epitaxial growth and excellent crystallinity of these nanodots are confirmed by structure characterization using X-ray diffraction (XRD). Evolution of the shape, size, and density of the nanodots during growth has been analyzed using SEM and AFM. Due to its large chemical mismatch and large lattice mismatch with LaAlO3 substrate, the Cu2O nanodots formation follows the Volmer-Weber model of island growth. Kinetic study shows that Ostwald ripening is restrained by an attachment/detachment barrier in the nanodot growth.; A non-catalyst lateral growth of Cu2O nanorods on silicon substrates has been realized using a two-step MOCVD process. One-dimensional Cu2O nanorods were found to grow only on the sidewalls of silicon substrates. The crystal structure of these rods is verified to be single crystal Cu2O by transmission electron microscopy (TEM) study. The effects of the substrate crystallographic orientation, substrate geometrical orientation, and oxygen plasma have been investigated. A flow assisted vapor-solid growth mechanism is proposed for the sidewall growth of Cu2O nanorods.; Recent results of CuCl thin film and nanodot growth are also presented. These structures are deposited using thermal evaporation. Optimal growth conditions have been investigated for CuCl grown on Si (111) and c-plane sapphire substrates respectively. Optical constants of CuCl films, such as the complex refractive indices and dielectric functions, are calculated by ellipsometry measurement. Room temperature optical transmission measurement reveals the distinct excitonic structures of CuCl.