Interaction of naphthalocyanine with oxygen and with Si(111)7x7: an in situ X-Ray photoelectron spectroscopy study

We present a series of X-ray photoelectron spectroscopy experiments performed on the naphthalocyanine/Si(111)7 x 7 interface. The samples have been prepared in situ with two nominal thicknesses, one of these corresponding to submonolayer deposition. The organic thin films have been doped by varying the oxygen exposure during their growth. An integer ratio of the estimated oxygen atoms per naphthalocyanine (NPC) molecule in the quantitative XPS elemental analysis of the spectra provides evidence of preferential adsorption of oxygen in molecular form onto NPC. A careful analysis of the spectra indicates that oxygen mainly interacts with the inner porphyrin structure of the molecule. The substrate has been observed to influence the spectra only at the submonolayer stage of NPC deposition and at the lowest measured oxygen amount: the effect is a charge transfer from the Si(111)7 x 7 metallic substrate preferentially to the outer benzenic ring of the cross-shaped molecule. (C) 1999 Elsevier science B.V. All rights reserved.