HYDROGEN ADSORPTION ON ERSI1.7(0001)

The adsorption of hydrogen atoms on ErSi1.7(0001) thin films, epitaxia lly grown on Si(111), has been studied in situ by low-energy electron- diffraction, photoemission, temperature programmed desorption (TPD), a nd work-function measurements. The results obtained with these techniq ues indicate that, at low hydrogen exposures, the adsorption sites on the silicide surface are very similar to those on Si(111), confirming the structural model of a silicide terminated by a buckled silicon pla ne without Si vacancies. At larger exposures, a second state is observ ed by TPD at higher desorption temperature. This state is not observed by TPD on Si(111) and is attributed to hydrogen chemisorbed in the su bsurface region of the silicide.