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

Abstract 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 (Alq 3 ) 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 Alq 3 particles show a pin-like shape and are parallel to each other. XPS analysis of the Alq 3 /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 O 2 and water. Argon ion beam sputtering and XPS were used to analyze the interface between Alq 3 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.