THE INTERACTION OF CO WITH THE CU3PT(111) SURFACE

Cu3Pt undergoes a bulk order-disorder phase transition at around 850 K. The interaction of CO with the ordered as well as a "disordered" (with a somewhat higher Pt concentration) surface of the Cu3Pt(111) alloy in the temperature range 50-400 K was studied with AES, LEED, TDS, UPS and work function (WF) measurements. On both Cu3Pt(111) surfaces a chemisorbed CO state is observed. The two photoemission peaks characteristic for chemisorbed CO are found at 9.2 eV (5-sigma/1-pi) and 11.7 eV (4-sigma), similar as for CO/Pt(111). In contrast to the CO/Cu systems no satellite was observed. Above 1 ML at 50 K, on both surfaces three new states in the UPS spectra are present at 7.6 eV (5-sigma), 10.8 eV (1-pi) and 13.2 eV (4-sigma) for the ordered surface and at 7.2 eV (5-sigma), 10.7 eV (1-pi) and 13.0 eV (4-sigma) for the "disordered" surface indicating a physisorbed CO state. The chemisorbed CO desorbs at 330 K from ordered and at 300 K from "disordered" Cu3Pt(111) which raises the WF by no more than 0.05 eV. The stronger interaction of CO with the ordered Cu3Pt(111) surface than with the "disordered" surface, suggests a possible ligand effect from Cu on Pt.