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

Abstract

We have investigated the interfaces of aluminum on tris-(8-hydroxyquinoline) aluminum (Alq3) and aluminum on LiF/Alq3, using x-ray and ultraviolet photoemission spectroscopy (UPS). Aluminum appears to react destructively with Alq3 causing significant modification of the oxygen, nitrogen, and aluminum spectra. The well-defined UPS spectrum of Alq3 is quickly destroyed by very low coverages of aluminum. With only a 5 Å layer of LiF on the Alq3, the reaction with aluminum is significantly suppressed. The Alq3 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 Alq3 anion is formed in the presence of aluminum and LiF.

Charge injection spectroscopy of Alq3 thin films deposited on bare and LiF-modified metal substrates

“…Experimentally, a lower binding energy state was observed for very thin (0.5-1 nm) Alq 3 on Ag [21] and Al [22]. The chemical reaction of Alq 3 with an Al electrode was reported [23], but on the Ag electrode, the lowering of the binding energy of the HOMO by about 0.5 eV was attributed to the formation of a polarized molecular layer, or interface dipole [21]. A reaction of Alq 3 with Au also seems unlikely.…”

Organic Electronic Devices and Their Functional Interfaces

“…A detailed analysis has suggested that alkali halides undergo dissociation when Al is deposited on top, thus releasing the alkali-metal atom to react with the organic semiconductor in immediate proximity. [104][105][106][107][108] 2.1.6. Doped Charge-Transport Layers…”

Electronic structure of interfaces with conjugated organic materials

“…In this context, the use of alkali halides (e.g., LiF, CsF) has turned out to be very helpful in confining the organic/metal reacted region. A detailed analysis has suggested that alkali halides undergo dissociation when Al is deposited on top, thus releasing the alkali atom to react with the organic semiconductor in immediate proximity [47][48][49][50]. A particularly interesting low work function metal is Sm (φ ≈ 2.8 eV).…”