Epitaxial growth and microstructure of Cu2O nanoparticle/thin films on SrTiO3(100)

Cuprous oxide (Cu2O) was grown on SrTiO3 (STO)(100) by oxygen plasma-assisted molecular-beam epitaxy. The microstructure of the grown layer and the Cu valence state were analysed using x-ray diffraction (XRD), x-ray photo-electron spectroscopy (XPS), atomic force microscopy (AFM) and cross-sectional transmission electron microscopy (TEM) as well as electron diffraction. The grown layer was dominated by the Cu2O phase, possessing an epitaxial orientation of and with respect to the substrate. The morphology of the Cu2O film shows a dependence on the growth rate. Typically, fast growth will lead to the formation of a thin film with a relatively smooth surface. Slow growth will lead to the development of nanoparticles, featuring the formation of Cu2O pyramids. The pyramids are invariantly defined by the Cu2O{111} planes. Given the fact that the {111} planes correspond to the lowest surface energy of Cu2O, slow growth will give the system enough time to allow it to adopt the pyramid configuration by which the overall energy of the system is minimized.