NiPC/Si(111)(7 × 7) STUDIED WITH XPS, STM AND TAPPING MODE AIR AFM

Abstract

We evaporated a few angstroms of nickel phthalocyanine (NiPC) in ultrahigh vacuum (UHV) on clean single crystal substrates of Si (111)(7×7) and studied in situ the structural and electronic properties of the interface with X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). The mesoscopic morphology of the samples has also been studied in air with a tapping mode atomic force microscope (TM-AFM). XPS measurements with variation of the NiPC thickness suggest planar adsorption of the first layer of admolecules; in particular, we found evidences for stronger chemisorption at the outer benzene rings of the PC molecule. UHV STM measurements confirm the XPS results; despite the lack of intermolecular resolution we show an image suggesting chemisorption commensurate with the substrate lattice and planar stacking consistent with the intermolecular stacking in the known crystalline phases of metal phthalocyanines. TM-AFM shows a growth mode in terms of flat islands of 20–35 Å typical height and a few hundreds of nm width. The potential of imaging with TM-AFM elastic sample properties of soft materials deposited on hard substrates is addressed.