Epitaxial growth and microstructure of CU_2O nanoparticle/thin films on SrTiO_3(100)

摘要

Cuprous oxide (Cu_2O) was grown on SrTiO_3 (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 Cu_2O phase, posseting an epitaxial orientation of Cu_2O(001) || STO(001) and Cu(100) || STO(100) with respect to the substrate. The morphology of the Cu_2O 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 Cu_2O pyramids. The pyramids are invariantly defined by the Cu_2O {111} planes. Given the fact that the {111} planes correspond to the lowest surface energy of Cu_2O, 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.