Growth and characterization of self-assembled Cd1−xMgxO (0 ≤ x ≤ 1) nanoparticles on r-sapphire substrates

Abstract

In this work, the growth of isolated Cd_1−xMg_xO nanoparticles on r-sapphire substrates is extended to the entire range of Mg content (0 ≤ x ≤ 1) using the spray pyrolysis method. The sizes of the Cd_1−xMg_xO nanoparticles were in the ranges 4–6 nm and 15–30 nm (with a nanoparticle density of 10¹⁰ cm⁻²). The composition of the nanoparticles was determined using transmission electron microscopy energy dispersive X-ray analysis (TEM-EDAX), while the compound formation was confirmed using X-ray photoelectron spectroscopy. A systematic decrease in the a lattice parameter of Cd_1−xMg_xO on increasing the Mg content substantiated the successful incorporation of Mg²⁺ ions into the cubic CdO lattice. Single-phase cubic Cd_1−xMg_xO nanoparticles were obtained in the range of nominal Mg content 0% to 30% (0 ≤ x ≤ 0.26), whereas a Mg content of about 40% (nominal) forced a phase separation where Cd_1−xMg_xO and Mg_1−xCd_xO co-exist (the Mg nominal content was 40% to 90%), providing experimental evidence of the phase separation that exists in the MgO–CdO system. This phase separation was detected using selected area electron diffraction and X-ray diffraction measurements. Cross-sectional transmission electron microscopy analysis shows the growth of a single layer of isolated and crystalline Cd_1−xMg_xO nanoparticles over the r-sapphire substrate.