Blocking of interfacial diffusion at Ag/Alq3 by LiF

X-ray photoelectron spectroscopy has been applied to interface studies of Ag/tris-(8-hydroxyquinoline) aluminum (Alq3) and Ag/LiF/Alq3. For Ag/Alq3, diffusion of Ag atoms into the Alq3 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/Alq3, 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/Alq3 and Al/LiF/Alq3 and hence different mechanisms may dominate in the two cases for the enhanced carrier injection observed.