Distinguishing between interface dipoles and band bending at metal/tris-(8-hydroxyquinoline) aluminum interfaces

Using a combination of photoelectron spectroscopies and ellipsometry to stu dy the thin-film growth of Alq(3) (tris-(8-hydroxyquinoline) aluminum) on A g, we have been able to distinguish between molecular orbital energy shifts due to "band bending" and interface dipole formation. We have observed lar ge binding energy shifts (approximate to 0.5 eV) of the organic molecular l evels at low coverages. We conclude that these shifts are consistent with t he formation of a polarized molecular layer, or interface dipole, and are i nconsistent with an electrostatic band-bending model. (C) 2000 American Ins titute of Physics. [S0003-6951(00)01538-2].