Selective molecular adsorption in sub-nanometer cages of a Cu2O surface oxide

In this study the identity of diverse adsorption sites on a 5-7 Cu2O/Cu(111) surface oxide structure has been identified. The 5-7 membered rings formed by a topological defect on stoichiometric Cu2O present different electronic structures from the originating hexagonal rings, as shown by combined bias dependent scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The adsorption of CO as a probe molecule on the 5-7 structure, studied using infrared reflection-absorption spectroscopy (IRRAS), shows the existence of special adsorption sites. By combining experimental and theoretical results, it is determined that CO molecules can be selectively confined inside the 7-membered oxide rings with internal dimensions of ∼0.85 nm, leading to a marked different adsorbate-substrate interaction than in either clean Cu(111) or Cu2O. The implication of these newly discovered sites on the chemistry of copper for catalytic reactions is discussed.