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

Surface damage of tris-(8-hydroxyquinoline) aluminum $({\mathrm{Alq}}_{\mathrm{3}})$ film by 100 eV ${\mathrm{Ar}}^{+}$ 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 ${\mathrm{Alq}}_{\mathrm{3}}$ molecules were broken by the irradiation. Correspondingly, the valence band structure of the ${\mathrm{Alq}}_{\mathrm{3}}$ molecule, as measured by UPS, was tremendously changed. The highest occupied state extended towards the Fermi level ${\mathrm{(E}}_F\mathrm{),}$ 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 ${\mathrm{Alq}}_{\mathrm{3}}$ layer, and possibly result in electrical shorts.