Interfacial Electronic Structure of Tris(8hydroxyquinoline)aluminum (III) on Cu(111)

Tris(8-hydroxyquinoline)aluminum (III) (Alq3), widely used in organic light-emitting diodes, has been examined on Cu(111) using two-photon photoemission (2PPE) spectroscopy supplemented by temperatureprogrammed desorption. Relative to Cu(111), clean and covered with typical aromatic molecules, the 2PPE intensities of Alq3 on Cu(111) are very strong. As a function of coverage, the interfacial energy level alignment of Alq3 with Cu(111) has been mapped and accords with an interface dipole model. In the electron time-of-flight spectrum of 2PPE, significant intensity extends to relatively long times and is ascribed to Alq3 photoluminescence rather than electron emission.