Elucidating the effect of precursor decomposition time on the structural and optical properties of copper(i) nitride nanocubes

Abstract

To study the effect of time on the colloidal synthesis of Cu₃N nanoparticles, copper(II) nitrate was thermally decomposed at 260 °C for up to 60 min in octadecylamine as a stabilizing ligand. Thermolysis of the nitrate followed four steps which included; nucleation, growth, ripening and decomposition. At 5 min, partially developed nanocubes were found in a dense population of Cu₃N nuclei. Well-defined Cu₃N nanocubes were obtained at 15 min with no presence of the nuclei. TEM images showed disintegration of the cubes at 20 min and as time progressed, all the Cu₃N decomposed to Cu by 60 min. The formation of the Cu₃N nanocubes was confirmed by XRD and XPS. FTIR suggested the formation of a nitrile (RCN) as a result of the thermal decomposition in octadecylamine (ODA) and this was confirmed using NMR and hence, a reaction mechanism was then proposed. The optical properties of the as-synthesized Cu₃N were studied using UV-vis and photoluminescence spectroscopies. The absorption spectra for particles synthesized from 5 min to 15 min showed a singular exciton peak while from 20 min to 60 min two peaks were observed. The two peaks may both be associated with the two direct transitions observed in Cu₃N or the more red-shifted peak could be a result of localized surface plasmon resonance due to the Cu nanoparticles. Nevertheless, similar to other studies, it is clear that the optical properties of Cu₃N are complex.