Spin-dependent electronic structure of the Co/Al(OP)3 interface

We have studied the spin-dependent electronic properties of the interface formed between epitaxial Co thin films deposited on Cu(001) and the experimental molecule tris-(9-oxidophenalenone)-aluminum(III) (Al(OP)(3)), created as a variation of the prototypical organic semiconductor Alq(3) to tailor the spin filtering properties by modifying chemisorption with cobalt. The interfaces have been grown under ultra-high vacuum conditions by progressive deposition of 0.5-5 nm Al(OP)(3) on the freshly prepared cobalt substrate. For every growth step we have monitored the energy level alignment at the interface as well as the spin polarization of the occupied manifold by spin-resolved photoemission spectroscopy. We identify two hybrid interface states in the energy window of 2 eV below the Fermi energy. The first is at 0.9 eV below EF and shows an 8% higher spin polarization than Co, while the second is at 1.6 eV below EF and shows a spin polarization reduced by 4%.