Energy level alignment symmetry at Co/pentacene/Co interfaces

We have employed x-ray and ultraviolet photoemission spectroscopies (XPS and UPS) to study the energy level alignment and electronic structure at the Co/pentacene/Co interfaces. In the case of pentacene deposition on Co we found an interfacial dipole of about 1.05 eV and a hole injection barrier of 0.96 eV, whereas for the case of Co deposition on pentacene we found a similar value for the hole injection barrier and vacuum level alignment (similar to 0 eV interfacial dipole), respectively. By combining XPS and UPS we were able to identify that chemical reaction occurs between pentacene and Co. The results of the deposition of the reactive Co on pentacene indicates only a small penetration depth of the metal atoms into the pentacene layer. A complete band diagram for the layered Co/pentacene/Co structure is presented in the frame of a model with interfacial dipoles. Finally, our findings are linked to spin injection experiments.