The position of adsorbed oxygen on Cu(i 10) surfaces was determined with Low Energy Ion Scattering (LEIS). The experiments were performed by bombarding the copper surface at small angles of incidence with low energy Ne* ions (3-5 keV). lMeasurements of the Ne+ ions scattered by adsorbed oxygen showed regular peaks in the azimuthal distribution of the scattered ions due to a shadowing effect. From the symmetry of the azimuthal distributions it follows that the centre of an adsorbed oxygen atom on the Cu(i 10) surface lies about 0.6 A below the midpoint between two neighbouring Cu atoms in a (001) row. A comparison of the azimuthal distributions of Ne+ ions scattered from clean Cu surfaces and oxygen-covered Cu surfaces showed that hardly any surface reconstruction had occurred in the oxygen-covered surfaces. The applied method seems to be an appropriate one for locating adsorbed atoms because it uses only simple qualitative considerations about azimuthal distributions of scattered ions.

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A preliminary report is given on experiments concerning the ion-induced adsorption of oxygen on copper. A strong enhancement of the sticking probability of oxygen is found during bombardment of the surface with neon ions in the keV region. The increase in the sticking probability is proportional to the primary ion intensities, used in this work (0.25-10/~A/ cm2).

The interaction of molecular oxygen with a Cu( 110) surface is investigated by means of low energy ion scattering (LEES) and secondary ion emission. The position of chemi~rbed oxygen relative to the matrix atoms of the Cu(l IO) surface could be determined using a shadow cone model, from measurements of Ne+ ions scattered by adsorbed oxygen atoms. The adsorbed oxygen atoms are situated 0.6 + 0.1 A below the midpoint between two adjacent atoms in a (100) surface row. The results of the measurements of the ion impact desorption of adsorbed oxygen suggest a dominating contribution of sputtering processes. Ion focussing effects also contributes to the oxygen desorption. The ion induced and the spontaneous oxygen adsorption processes are studied using different expe~ental methods. Sticking probab~ty values obtained during ion bombardment show a strong increase due to the ion bombardment.

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