Ion-beam-induced surface damages on tris-(8-hydroxyquinoline) aluminum

Surface damage of tris-(8-hydroxyquinoline) aluminum (Alq3) film by 100 eV Ar+ irradiation has been studied by using both x-ray and ultraviolet photoelectron spectroscopies (XPS and UPS). XPS core level electron density curves revealed that some N–Al and C–O–Al bonds in Alq3 molecules were broken by the irradiation. Correspondingly, the valence band structure of the Alq3 molecule, as measured by UPS, was tremendously changed. The highest occupied state extended towards the Fermi level (EF), implying that a metal-like conducting surface was formed. This kind of damaged surface would cause nonradiative quenching in an electroluminescence device when electrons are injected from the cathode into the Alq3 layer, and possibly result in electrical shorts.