STM study on the copper oxide surfaces on Cu(111)*

It is known that copper oxide has two stable phases which are copper(II) oxide (CuO) and copper(I) oxide (Cu₂O). Cu₂O has cubic structure with band gap of around 2.1 eV while CuO belongs to monoclinic system with band gap of around 1.2 eV. Due to their semiconducting properties, these copper oxides have been widely studied for potential applications on supercapacitor, solar cell, etc. Copper oxide surfaces formed on Cu(111) are investigated via home-built low temperature scanning tunneling microscope (STM). Epitaxial Cu(111) films are prepared on sapphire substrate. Then, copper oxide is naturally formed on top of Cu(111) under ambient conditions. STM images show well aligned stripe patterns on copper oxide surfaces. It is found that observed stripe structures are due to local strain. Detail analysis on atomic structures and electronic properties of copper oxide surfaces will be discussed.