Experimental determination of the attenuation length of electrons in organic molecular solids: The example of PTCDA

If electron spectroscopic techniques are applied in surface and interface science, quantification of surface sensitivity is of crucial interest. In this article, we present a systematic experimental investigation of the effective electron attenuation length (EAL) in organic materials, on the example of PTCDA. The effective attenuation length was determined in a comprehensive experiment over a wide range of energies especially in the range of interest for surface analysis. The overlayer method was used and proven to be adequate for the utilized model system PTCDA on Ag(111) since the preparation parameters could be controlled extremely well. Compared to calculations which we performed applying the TPP2M formula the results show the expected offset which is due to the additional elastic contribution in the measured values. Furthermore, a comparison with the widely used universal curve [1] shows that this description does not match the data on PTCDA very well. However, the curvature of the theoretical curve derived from the TPP2M approach [2] matches or our experimental EAL data reasonably good. (C) 2011 Elsevier B.V. All rights reserved.