Patterns of Ensemble Variation of the Optical Properties of ZnO Nanowires Grown with Copper and Gold Catalysts

Understanding the source of variation of the optical properties within an ensemble of nanowires (NWs) is an important step toward fabrication of NWs with more uniform and better-controlled properties. This in turn will facilitate the development of complex architectures for device applications. Analysis of gold- and copper-catalyzed zinc oxide (ZnO) NWs grown in a high temperature tube furnace on a sapphire substrate shows that the structural and optical properties vary with NW growth sites on the substrate. Results show that there are systematic changes in the optical properties of the ZnO NWs from the center to the edge of the substrate, and also from “upstream” to “downstream” along the gas flow direction, implying changes in the availability of the source material and catalyst over the substrate surface during the growth. Photoluminescence microscopy has been used to map out these changes and unravel the growth patterns. We observe two distinct trends that are labeled the “edge” trend and the “gas flo...