Interfaces between 8-hydroxyquinoline aluminum and cesium as affected by their deposition sequences

Abstract

The electronic structures of tris(8-hydroxyquinoline) aluminum (Alq 3) deposited on clean or Cs pre-covered Ag substrates have been studied by ultraviolet photoelectron spectroscopy. Interface of Cs deposited on Alq 3 has also been prepared for comparison. For a low coverage of Cs on Ag, deposition of Alq 3 on top of the Cs cannot induce any new electronic features. The low work function of the Cs reduces the barrier height of electron injection at the Alq 3/Cs/Ag contact to 0.3 eV, as compared to 1.6 eV for the Alq 3/Ag contact. For high Cs coverage, the Cs may diffuse as neutral atoms and undergo oxidation into the Alq 3 layer and form a new gap state at 0.9 eV above the Alq 3 highest occupied state, which is the same as that of Cs deposited on the Alq 3.