Vacuum-Level Shift at Al/LiF/Alq3 Interfaces: A First-Principles Study

Work function changes, or vacuum-level shifts (ΔVLS), in Al(001) surfaces by the adsorption of thin layers composed of tris(8-hydroxyquinolinato)aluminum (Alq3) and/or LiF are theoretically investigated. First-principles calculations reasonably reproduce experimentally obtained ΔVLS values, enabling us to discuss the underlying mechanism. Dipole moment of Alq3 and interfacial charge rearrangement (Pauli push-back effect) are the main reasons for ΔVLS at Al(001)-Alq3 and Al(001)-LiF interfaces, respectively. For a stacked Al(001)-LiF-Alq3 layer configuration, theory suggests a more complicated picture, which takes charge rearrangement between LiF and Alq3 layers into account, than a simple sum rule of dipole contributions from the two layers.