Interaction of Silver, Cesium, and Zinc with Alumina Surfaces: Thermal Desorption and Photoemission Studies

Abstract

Cs, Ag, and Zn behave in a different way when deposited on surfaces of ultrathin (15−20 A) films of alumina. In the case of Cs/Al2O3, the alkali atoms wet the oxide, forming strong chemisorption bonds. At small coverages of Cs, desorption of the alkali occurred between 600 and 1000 K. As the amount of Cs deposited increased, there was a reduction in the Cs desorption temperature to ∼350 K. This broad range of desorption temperatures reflects a continuous decrease in the Cs adsorption energy from 63 to 18 kcal/mol with increasing Cs coverage. The deposition of small amounts of Cs induced large (0.9−1.1 eV) positive shifts in the binding energies of the O KVV, O 1s, and Al 2p features of the alumina films. This is consistent with a transfer of electrons from Cs into surface states of alumina that produces a transformation similar to a change from p-type to n-type semiconductors. Ag and Zn do not wet the surface of alumina well and form three-dimensional clusters or particles. In these systems, the activatio...