THE ADSORPTION OF CO ON NI(100) STUDIED BY LOW-ENERGY ION-SCATTERING

The adsorption of CO on Ni(100) at room temperature was studied by He+ ion scattering and simultaneous measurement of the work function change. The scattered ion intensities arise from O and Ni only, and confirm the orientation of the molecule with oxygen pointing away from the surface. The variation of the ion scattering signals with exposure is in proportion to the work function change, i.e. coverage. Despite a work function change up to 0.9 eV, no correspondingly large change in ion neutralization is observed. The ion escape probability for scattering from O is found to be about 8% for coverages up to 0.5 monolayers. For the first time also ICISS measurements from adsorbed molecules are shown, the results being compatible with the c (2 × 2) structure formed at an exposure of about 5 Langmuirs. © 1990 Pergamon Press plc.