Changes in the electronic structure of DiMePTCDI films on S-GaAs(1 0 0) upon exposure to oxygen

The electronic properties of N,N0-dimethyl-3,4,9,10-perylene tetracarboxylic diimide (DiMePTCDI) films deposited on S-GaAs(1 0 0) surfaces are studied by ultraviolet photoelectron spectroscopy (UPS). The energy position of the highest occupied molecular orbital (HOMO) of clean DiMePTCDI films is found to be at 2.04 0.10 eV with respect to Fermi level. Exposure to oxygen results in a shift of the HOMO from its original position by 0.25 0.10 eV towards the middle of the band gap. The shift explains the dramatic decrease of the current in the current–voltage (I–V) characteristics upon oxygen exposure of Ag/DiMePTCDI/S-GaAs(1 0 0) Schottky diodes. # 2004 Elsevier B.V. All rights reserved.