Generation of “stabilized” surface species by low-energy interactions of ethylene ions with O- or N-precovered Cu(100) at room temperature

Abstract

The dissociative adsorption and surface reactions induced by low-energy (≤200 eV) irradiation of unmass-selected ethylene ions on clean, O-precovered and N-precovered Cu(100) surfaces at room temperature (RT) were investigated by high-resolution electron energy loss spectroscopy (EELS) and temperature-programmed desorption mass spectrometry. Ion irradiation of a clean Cu(100) surface in ethylene at 200 eV impact energy was found to produce hydrocarbon fragments that adsorbed readily on the surface at RT and decomposed completely after annealing to above 600 K. For an O-precovered Cu(100) surface at RT, the hydrocarbon species so produced appeared to react with the pre-deposited O atoms to form “stabilized” CO. In addition to the red-shifted CO stretch observed at a low ethylene ion dose, a blue-shifted CO stretch was also found at a higher ethylene ion dosage. The observed red and blue shifts were attributed to adsorption of CO stabilized by a proposed direct interaction mechanism involving neighboring surface O atoms and C-containing species, respectively. In the case of low-energy ion irradiation of a N-precovered Cu(100) surface in ethylene, EELS features attributable to CN and N–H stretching vibrations were observed, giving support to the formation of CN and NH radicals as a result of surface reactions between the hydrocarbon species and the pre-deposited N atoms. The present work provides further evidence for in-situ formation and stabilized adsorption of unique surface species generated by the low-energy ion irradiation process.