Structural Changes of Cu(110) and Cu(110)-(2 × 1)-O Surfaces under Carbon Monoxide in the Torr Pressure Range Studied with Scanning Tunneling Microscopy and Infrared Reflection Absorption Spectroscopy

The atomic structure of the clean Cu(110) and the oxygen covered Cu(110) surfaces in the presence of carbon monoxide (CO) gas in the Torr pressure range at 298 K is studied using scanning tunneling microscopy (STM) and infrared reflection adsorption spectroscopy (IRRAS). We found that the initially clean surface reconstructs to form short rows of Cu atoms along the [1-10] direction separated by missing rows. The adsorbed CO molecules show two different C-O stretch vibration modes originating from molecules bound to Cu atoms with different coordination numbers, in the middle and at the end of the atomic rows. On the oxygen covered p(2 × 1) surface, adsorbed CO is observed only after removal of surface O atoms by reaction with CO. In the presence of 1:5 and 1:1 mixtures of O₂ and CO at 298 K, the p(2 × 1)-O reconstructed surface transforms into Cu₂O, instead of reducing to metallic Cu.