Naphthalocyanine molecules onto Si(111)7x7 and Si(100)2x1: modes of adsorption investigated with XPS

We have deposited various thicknesses of metal free naphthalocyanine (H2NPc ) in ultra-high vacuum onto Si(111)7 x 7 and Si(100)2 x 1 and studied the i nterfaces in situ by means of standard monochromatized X-ray photoelectron spectroscopy. By comparing the core level N 1s and C 1s spectra obtained fo r the pure molecule with those typical of the interface at the submonolayer and intermediate level of deposition, we derived information on the ways o f adsorption of the isolated molecules onto the substrates used. In particu lar, NPc adsorbs planarly to the Si(111)7 x 7 substrate showing strong chem isorption effects involving all the atoms of the molecule. However, the che misorption involves only two C atoms when using the Si(100)2 x 1 substrate. In this case, the NPc molecules are likely to be adsorbed in an out-of-pla nar mode. We also show in this paper some experimental evidence on the NPc/ Si(100)2 x 1 system at the lowest coverages in the presence of oxygen that confirm, even for the Si(100)2 x 1 case, our recent findings onto Si(111)7 x 7, i.e, the preferential adsorption of molecular oxygen onto the NPc mole cules. (C) 1999 Elsevier Science B.V, All rights reserved.