Synthesis of freestanding cupric oxide nanotubes with close ends from copper nanowires by the Kirkendall effect

Abstract

Vertically grown cupric oxide semiconductors have a number of applications such as chemical sensors, nanogas sensors, and catalysts. Typically, a template based synthesis technique is used followed by an additional wet etching process for the synthesis of vertically oriented cupric oxide nanotubes. However, such a synthesis technique has some inherent disadvantages, notably, the obvious complexities involved in the process and the possibility of contamination and deformation of the structure. Here, the authors report the growth of freestanding copper nanostructures via metal organic chemical vapor deposition, followed by thermal oxidation. To the best of our knowledge, this is the first report of a successful synthesis of vertically aligned cupric oxide nanotubes with closed ends from copper nanowires. The synthesis was performed at 300 degrees C in air via the Kirkendall effect without the use of any template. Subsequently, the 5 mu m long copper nanowires having diameters of 70 nm were thermally oxidized to yield cupric oxide nanotubes with closed ends. The nanotubes were 5 mu m in length, and had wall thicknesses and diameters of 18 nm and 70-100nm, respectively. Transmission electron microscopy images clearly show that the nanotubes are comprised of crystalline cupric oxide. Furthermore, I-V characteristics of the nanotubes exhibit p-type semiconducting behavior. Our work suggests that the cupric oxide nanotubes may find applications in one-dimensional devices such as in the field of optics, as nanobiosensors and gas sensors. (C) 2016 American Vacuum Society.