Gap state formation by interfacial interaction between Al and 8-hydroxyquinolatolithium.

The interfacial interaction between hydroxyquinolatolithium (Liq) and Al was studied with in situ synchrotron radiation photoemission (SRP) and density functional theory (DFT) calculation. The metal Al was deposited on pristine Liq molecular layer in a stepwise manner and the SRP measurements were conducted before and after each deposition step. The SRP results were analyzed by DFT calculation using a simple model and the key interaction between them was explained: Liq is not broken to generate free Li(+) ions upon Al interaction, unlike the reaction of its inorganic counterpart Al-LiF-Alq(3), but rather makes a Liq-Al complex with charge donation from Al to Liq. Electrons from Al fill the LUMO level of Liq and generate a new gap state. The charge control properties of the Liq layer could be explained with this gap state in terms of the intermediate-state assisted carrier transport.