Alignment of energy levels at the Al q3/La0.7 Sr0.3 Mn O3 interface for organic spintronic devices

The electronic structure of the interface between tris(8-hydroxyquinolino)- aluminum (Al q3) and La0.7 Sr0.3 Mn O3 (LSMO) manganite was investigated by means of photoelectron spectroscopy. As demonstrated recently, this interface is characterized by efficient spin injection in organic spintronic devices. We detected a strong interface dipole of about 0.9 eV that shifts down the whole energy diagram of the Al q3 with respect to the vacuum level. This modifies the height of the barrier for the injection into highest occupied molecular orbital level to 1.7 eV, indicating more difficult hole injection at this interface than expected for the undistorted energy level diagram. We believe that the interface dipole is due to the intrinsic dipole moment of the Al q3 layer. The presented data lead to significant progress in understanding the electronic structure of LSMO/Al q3 interface and represent a step toward the description of spin transport in organic spin valves.