Strong interface p-doping and band bending in C60 on MoOx

The electronic energy level evolution of fullerene (C-60) on molybdenum oxide (MoOx)/conducting indium tin oxide (ITO) interfaces has been investigated with ultra-violet photoemission spectroscopy (UPS), inverse photoemission spectroscopy (IPES) and atomic force microscopy (AFM). It was found that the thermally evaporated MoOx inter-layer substantially increased the surface workfunction. This increased surface workfunction strongly attract electrons towards the MoOx layer at the C-60/MoOx interface, resulting in strong inversion of C-60. Energy levels of C-60 relax gradually as the thickness of C-60 increases. An exceptionally long (>400 angstrom) band bending is observed during this relaxation in C-60. Such a long band bending has not been reported so far, for the organic/insulator (MoOx) interface. The effect of air exposed MoOx inter-layer between ITO and C-60 has also been investigated. After air exposure of MoOx almost no band bending was observed and the electronic energy levels of C-60 remained more or less flat. (C) 2011 Elsevier B.V. All rights reserved.