THE USE OF LOW-ENERGY ION-SCATTERING SPECTROSCOPY FOR THE QUANTITATIVE-DETERMINATION OF ADSORPTION SITES IN SURFACE-CHEMISTRY STUDIES

Ion scattering spectroscopy (ISS) was used in conjunction with tempera ture-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) for the study of the adsorption of hydrogen, oxygen, ethyl iodid e, and 2-propyl iodide on Ni(100). In all those systems the decrease i n Ni ISS signal intensity seen during the uptake could be explained by shielding of the Ni surface atoms by the adsorbate. In addition, sinc e the ISS data could be correlated nicely with results from other tech niques, the conclusion was reached that matrix effects and changes in neutralization probabilities(due to variations in work function) were negligible for the systems studied here. Additional ISS studies for th e adsorption of 2-propyl iodide on oxygen-precovered Ni(100) indicated that those molecules bond preferentially to Ni (not O) sites. This co nfirms previous results which showed that the products of that system associated with chemistry on the Ni sites - propane, propene, and hydr ogen - dominated the TPD spectra for low coverages of either 2-propyl iodide or oxygen. In a broader sense, this work also shows that ISS ca n be used to determine adsorption sites in complex systems where other techniques are not applicable. (C) 1997 Elsevier Science B.V.