A combined photoelectron spectroscopy (PES), X-ray absorption spectroscopy (XAS)
and scanning tunneling microscopy (STM) study has been performed to follow the
change in adsorption geometry and to characterize the adsorbate interaction with the
substrate for dierent thicknesses of lutetium biphthalocyanine (LuPc2) adlayers on
pristine Si(100)-2x1 reconstructed stepped surface. A shift to lower binding energies
with increasing thickness has been shown. The STM results showed clustering of
LuPc2 starting from submonolayer coverages and two distinct adsorption types have
been identied. The STM and PES results have been linked together to propose two
dierent adsorption types involving a stronger and weaker interaction with the Si
dangling bonds. A change in average angle of molecules with respect to the normal
of the surface for increasing thicknesses has been seen from the XAS measurements,
leading to disordered layers for thicker films.