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

We studied the adsorption of tris(8-hydroxyquinoline)aluminum (Alq3) molecules on cobalt surfaces using density functional theory with the generalized gradient approximation. The van der Waals interaction between Alq3 molecules and cobalt surfaces was included by the dispersion correction. Magnetization of Alq3 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 Alq3 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/Alq3 surface. Our calculated energy-level alignment at interfaces is consistent with experimental observations.