Understanding the Growth of Copper Oxide Nanowires and Layers by Thermal Oxidation over a Broad Temperature Range at Atmospheric Pressure

In this paper, we explore the development of copper oxide layers and their evolution into nanowires on thermally oxidized copper and underlying chemical processes governing the growth of unidirectional, one-dimensional copper oxide (CuO), especially focusing on the role of underlying oxide layers. Extensive experimental data sets of grown nanowires in an ambient atmosphere at different oxidation temperatures and times were collected, analysed, and correlated with theoretical modeling of growth processes. Detailed microstructural analysis revealed that upon annealing in air, the Cu2O layer of randomly oriented columnar grains forms first, followed by preferentially oriented CuO grains, evolving into CuO nanowires. Our results highlight the importance of copper and oxygen diffusion and concentration in equilibrium between Cu2O and CuO phases in the oxide film and indicate that CuO nanowires originate in twinned CuO grains, which elongate due to the twin boundary's instability. With broad experimental data sets on growth conditions, we obtain the complete picture of experimental and modeled growth of copper oxide nanowires, which will enable the tailored design of nanowires and their implementation in catalysis, sensing, and other applications.