STRUCTURE AND REACTION PROPERTIES OF THIN AL FILMS DEPOSITED ON NI(110)

A variety of experimental techniques, including scanning tunneling mic roscopy (STM) and thermal desorption spectroscopy (TDS) have been used to investigate the structure and reaction properties of thin Al films on Ni(110) as a model for technical Raney nickel catalysts. The measu rements show that ill grows by the Volmer-Weber growth mode, with Al i slands reaching a height of 30 Angstrom before the first Al layer is c ompleted. On exposure to deuterium the TDS spectra indicate that the a ddition of Al produces a new deuterium chemisorption state with a deso rption energy which decreases from 27 to 14 kJ/mol with increasing deu terium coverage. This new bound stare is attributed to deuterium atoms bound to adsorption sites in the vicinity of Al islands. Thermal deso rption measurements also reveal that the deuterium initial sticking co efficient S-o decreases with Al coverage. The results can be explained by a simple model which shows that for low Al coverages each Al islan d inhibits deuterium dissociation in a region which is about three tim es larger than the island area. (C) 1998 Published by Elsevier Science B.V. All rights reserved.