IBA APPLIED TO ADSORPTION AND COADSORPTION STUDIES OF H-2 AND C6H6 ON NI(111)

15N-induced nuclear reactions on H and D have been used to study hydrogen and benzene adsorption on Ni(111) in a UHV system connected to a Van de Graaff accelerator and equipped with surface cleaning facilities. Analysis can be performed in vacuum or in a gas atmosphere which is of particular interest for molecules with a low sticking probability like H2. The coverage of hydrogen on the Ni surface has been measured in the 10-8-10-2 mbar pressure range taking into account the contribution of the nuclear reactions induced on hydrogen atoms in the gas phase for pressures higher than 10-5 mbar. When the analysis is performed after gas evacuation (H2 or C6H6) an ion-induced desorption effect can be observed and a low irradiation fluence is required (integrated charge of 1 μC) setting a detection limit of 7.5 × 1013 at/cm2. Working with or without gas pressure points out for C6H6 a second phase reversibly adsorbed on the surface. In the coadsorption study with labelled molecules (C6D6H2 or C6H6D2) the nonresonant nuclear reactions on deuterium allow to analyse deuterium without interference from hydrogen and a detection limit of 2.2 × 1014 at/cm2 is obtained at a 8 MeV incident energy. The variation of the D concentration on the surface precovered with benzene as a function of hydrogen exposure, points out an exchange reaction between adsorbed molecules. © 1990.