INDIUM ADSORPTION SITES AT PD(100) SURFACES STUDIED BY PAC SPECTROSCOPY

Perturbed gammagamma-angular correlation (PAC) experiments have been p erformed to study the occupation of different surface sites by In-111 probe atoms at vicinal Pd surfaces with (100) terrace orientation. Wit hin an isochronal annealing sequence In probes are observed to dwell i n adatomic and substitutional step and terrace sites, in agreement wit h earlier experiments on Cu, Ag and Ni surfaces. The temperature depen dence of the electric field gradient for In-111 atoms occupying substi tutional terrace sites deviates from the behaviour detected on Cu(100) , Ag(100) and Ni(100) surfaces. The observed deviation in the low-temp erature regime is attributed to the adsorption of hydrogen.