Effects of low-energy electron and ion irradiation on CO/Cu(100): In-situ production and coadsorbate-induced adsorption of CO above room temperature

Abstract

The surface reactions of CO with clean, oxygen-precovered and carbon-precovered surfaces of Cu(100) assisted by low-energy electron or ion irradiation were investigated using high-resolution electron energy loss spectroscopy and temperature programmed desorption mass spectrometry. We observed an anomalous adsorption of “stabilized” CO species on Cu(100) above room temperature that were produced in situ by low-energy electron irradiation of CO/Cu(100) at 120 K and by low-energy ion irradiation of Cu(100) in CO or with pre- or postexposure of O2 in C2H4 at room temperature. The corresponding C–O stretch vibration was found to be redshifted by 73 cm-1 from its nominal position (2084 cm-1) at 120 K. Furthermore, unlike the normal C–O stretch that could only be observed below 200 K, the redshifted peak could be found up to 420 K. From the different mechanisms that could cause the observed redshift and stabilization effects, we propose a direct-interaction bonding model involving a “tilted” CO molecule on an atop site semibridge bonded to an O atom in a four-fold hollow site. Other processes such as reaction activation and creation of defect sites as well as sputtering effects induced by low-energy electron or ion irradiation are discussed.