Epitaxial electrodeposition of copper(I) oxide on single-crystal copper

Epitaxial thin films of copper(I) oxide (Pn3m, a = 0.427 nm) were electrodeposited onto [110]-, [111]-, and [100]-oriented single-crystal copper (Fm3m, a = 0.3615 nm) by reduction of copper(II) lactate in solution. Cu2O films grown on Cu(110) and Cu(III) exhibited both an out-of- and in-plane orientation following that of the substrate as measured by 2 theta and azimuthal X-ray scans, up to a thickness of 0.8 mum. X-ray diffraction studies showed that Cu2O films deposited onto Cu(100) grow initially with a near-[III] orientation up to a critical thickness, beyond which film growth is primarily in the [100] direction. The films were found to be both in- and out-of-plane oriented throughout, as measured by azimuthal X-ray scans. In situ 2 theta X-ray measurements showed a critical thickness for growth in the [100] direction of about 360 nm. As determined from scanning electron microscopy images, the Cu2O films deposited onto Cu(100) grew with triangular facets consistent with the [III] orientation prior to the critical thickness, and then as pyramidal islands over the initial triangular layers above this thickness. A proposed interface model of Cu2O(III) over Cu(100) yields a low mismatch and a high number of atomic contact points per unit area, offering a possible explanation for the initial [III]-oriented deposition.