One-step growth of isolated CdO nanoparticles on r-sapphire substrates by using the spray pyrolysis methodology

Abstract

In spite of the remarkable properties of CdO, there are only a few reports on CdO nanostructures, especially on isolated NPs. In this paper, we analyze the growth of isolated CdO nanoparticles (NPs) on 0.5° miscut r-sapphire substrates by using the spray pyrolysis methodology in its classical configuration. A systematic study has been performed to optimize the growth parameters such as precursor concentration, growth time, spray rate and growth temperature to obtain CdO NPs (size: 6–10 nm to 35–100 nm depending on the growth conditions). The study shows the control over the size and density of the CdO nanoparticles that can be achieved by adjusting the growth parameters. The CdO nanoparticles were assembled in a parallel chain on the steps of the substrate surface (density: 2.1 ± 0.1 × 10¹⁰ NPs per cm²), which provided nucleation sites for the CdO adatoms, in addition to the free surface bonds on the substrate. A surface treatment of the r-sapphire substrate prior to the growth process provided additional nucleation sites for CdO nanoparticles resulting in an increase of the density (3.3 ± 0.2 × 10¹⁰ NPs per cm²). High-resolution transmission electron microscopy, X-ray diffraction and selected area electron diffraction analysis display the polycrystalline nature of the CdO samples, whereas X-ray photoelectron spectroscopy study confirmed the compound formation. The study shows the versatility of the spray pyrolysis technique to grow isolated nanoparticles of CdO on substrates in a single step, without any template assistance and/or post annealing treatment.