X-ray photoelectron spectroscopy has been applied to interface studies of Ag/tris-(8-hydroxyquinoline) aluminum (Alq(3)) and Ag/LiF/Alq(3). For Ag/Alq(3), diffusion of Ag atoms into the Alq(3) layer occurs immediately after the adhesion of the metal onto the organic layer and the process lasts several hours. Insertion of a monolayer-thick LiF buffer at the interface can effectively block the diffusion process. This is quite different from what is observed from Al/LiF/Alq(3), where Al penetrates into the LiF layer as deep as several nanometers. It is thus concluded that the LiF buffer may play different roles in Ag/LiF/Alq(3) and Al/LiF/Alq(3) and hence different mechanisms may dominate in the two cases for the enhanced carrier injection observed. (c) 2006 Elsevier B.V. All rights reserved.