Photoemission study of aluminum/tris-(8-hydroxyquinoline) aluminum and aluminum/LiF/tris-(8-hydroxyquinoline) aluminum interfaces

We have investigated the interfaces of aluminum on tris-(8-hydroxyquinoline) aluminum (Alq(3)) and aluminum on LiF/Alq(3), using x-ray and ultraviolet photoemission spectroscopy (UPS). Aluminum appears to react destructively with Alq(3) causing significant modification of the oxygen, nitrogen, and aluminum spectra. The well-defined UPS spectrum of Alq(3) is quickly destroyed by very low coverages of aluminum. With only a 5 Angstrom layer of LiF on the Alq(3), the reaction with aluminum is significantly suppressed. The Alq(3) molecular orbital features in the UPS shift to higher binding energy but remain easily recognizable. In addition, a well-defined gap-state forms which is significantly different from that produced without LiF. Both the core-level spectra and the gap-state suggest that the Alq(3) anion is formed in the presence of aluminum and LiF. (C) 2000 American Institute of Physics. [S0021-8979(00)02101-0].