Adsorption of tris(8-hydroxyquinoline)aluminum molecules on cobalt surfaces

We studied the adsorption of tris(8-hydroxyquinoline)aluminum (Alq ₃) molecules on cobalt surfaces using density functional theory with the generalized gradient approximation. The van der Waals interaction between Alq ₃ molecules and cobalt surfaces was included by the dispersion correction. Magnetization of Alq ₃ molecules, adsorption energies, and bonding energies were obtained for smooth and defective surfaces and for various molecule-surface configurations. Electronic structures were analyzed for states that are relatively stable. We found that both the permanent electric dipole of Alq ₃ molecules and the charge redistribution near the interface contribute to the interface dipole, and the interface dipole due to charge redistribution is important to determine the work function of a Co/Alq ₃ surface. Our calculated energy-level alignment at interfaces is consistent with experimental observations.