Surface and interface analysis of tris-(8-hydroxyquinoline) aluminum and indium–tin-oxide using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS)

An understanding of the surface and interface state of the organic material and the underlying anode material is meaningful for organic light-emitting devices (OLEDs). The morphology, surface and interface electron states of the tris-(8-hydroxyquinoline) aluminum (Alq3) and the underlying indium–tin-oxide (ITO) have been investigated using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) technology. AFM observations indicated that the Alq3 particles show a pin-like shape and are parallel to each other. XPS analysis of the Alq3/ITO surface suggests that the Al atoms have a valence of +3. The C atoms mainly bond to C, N and O atoms. The N and O atoms also interact with Al atoms through coordination bonds, in additional to bonding to C atoms. The O atoms basically originate from quinolate rings and the absorbed O2 and water. Argon ion beam sputtering and XPS were used to analyze the interface between Alq3 and ITO films. Results demonstrate that, as sputtering time increases, the core levels of Al 2p, C 1s, N 1s, O 1s and In 3d spectra all have chemical shifts to higher or lower binding energy, but the alteration of the peak shape, position and area of Al 2p, C 1s, N 1s, O 1s and In 3d spectra are different.