Tetragonal CuO: End member of the 3d transition metal monoxides

Monoclinic CuO is anomalous both structurally as well as electronically in the 3d transition metal oxide series. All the others have the cubic rocksalt structure. Here we report the synthesis and electronic property determination of a tetragonal (elongated rocksalt) form of CuO created using an epitaxial thin-film deposition approach. In situ photoelectron spectroscopy suggests an enhanced charge-transfer gap Delta with the overall bonding more ionic. As an end member of the 3d transition monoxides, its magnetic properties should be that of a high T-N antiferromagnet.