Journal of Synchrotron Radiation

Volume 15, Part 5 (September 2008)

research papers

J. Synchrotron Rad. (2008). 15, 519-524 [ doi:10.1107/S0909049508020013 ]

Bond cutting in K-doped tris(8-hydroxyquinoline) aluminium

H.-H. Lee, J. Hwang and T.-W. Pi

Abstract: A series of Al 2p, K 2p, O 1s and N 1s core-level spectra have been used to characterize the interaction between potassium (K) and tris(8-hydroxyquinoline) aluminium (Alq₃) molecules in the K-doped Alq₃ layer. All core-level spectra were tuned to be very surface sensitive in selecting various photon energies provided by the wide-range beamline at the National Synchrotron Radiation Research Center, Taiwan. A critical K concentration (x = 2.4) exists in the K-doped Alq₃ layer, below which the K-doped atoms generate a strained environment near the O and N atoms within 8-quinolinoline ligands. This creates new O 1s and N 1s components on the lower binding-energy side. Above the critical K coverage, the K-doped atoms attach the O atoms in the Al-O-C bonds next to the phenoxide ring and replace Al-O-C bonds by forming K-O-C bonds. An Alq₃ molecule is disassembled into Alq₂ and Kq by bond cutting and bond formation. The Alq₂ molecule can be further dissociated into Alq, or even Al, through subsequent formations of Kq.

Keywords: tris(8-hydroxyquinoline) aluminium (Alq₃); K doping; bond cutting; interface; photoemission.