CO adsorption on a PtCo(111) surface has been studied by scanning tunneling microscopy (STM). Comparison of images with chemical contrast of Pt and Co and images showing the CO molecules indicates that CO resides exclusively on top of Pt sites and never on Co. CO bonding is highly sensitive to the chemical environment. The probability to find CO on a Pt atom increases drastically with the number of its Co nearest-neighbors. Ab-initio calculations show that this ligand effect is due to different positions of the center of the Pt d-band.
Corresponding author: M. Schmid (schmid).
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