Charge transfer and polarization screening at organic/metal interfaces:: Distinguishing between the first layer and thin films

We studied the core hole screening at organic/metal interfaces using combined photoemission spectroscopy (PES) and X-ray excited Auger electron spectroscopy (XAES) as a function of the organic layer thickness. As a model system for organic semiconductor/metal interfaces, magnesium phthalocyanine was evaporated onto gold foil. It was found that the screening of double hole final states is remarkably increased for molecules directly at the interface, whereas further layers are effected very weakly. The screening mechanism is discussed in terms of both charge transfer and electronic polarization.