Photoemission of Al q 3 and C 60 films on Al and Li F ∕ Al substrates

Photoemission studies of thin films of Al q 3 and C 60 deposited on Al and Li F ∕ Al substrates have been performed in order to deduce the interactions of the organic films with the substrates. For all cases there is evidence of strong interaction resulting in the formation of interfacial dipoles. Attempts to explain the origin of these interfacial dipoles and the type of interface formed in each case have been done through analysis of the valence electronic structure and core levels of the materials. The origin of the interfacial dipoles is mainly covalent interaction when the organic films are deposited on Al substrates, and charge transfer between the organic molecules and the metal through the LiF sandwich layer when the organic films are deposited on Li F ∕ Al substrates. For thick-enough LiF films, however, there is no interaction between the organic films and the substrates. In no case does the LiF dissociate, unlike what is found for the reverse order of deposition. Two charge-transfer-induced gap states are found for (sub)monolayer films of Al q 3 deposited on Li F ∕ Al . We propose that the formation of two gap states corresponds to negatively charged fac- Al q 3 .