Dimer ordering of CuTtertBuPc molecules on the Ag/Si(111)-( 3 × 3)R30∘ surface: a scanning tunnelling microscopy/spectroscopy study

The room temperature growth and ordering of copper(II) 2,9,16,23-tetra-tert-butyl-phthalocyanine (CuTtertBuPc) molecules on the Ag/Si(111)- surface have been investigated using scanning tunnelling microscopy/spectroscopy (STM/STS). Results indicate a well-ordered molecular layer in which the phthalocyanine molecules have a flat orientation with the molecular plane lying parallel to the substrate and forming a dimer structure on the surface. STS data obtained from one monolayer (ML) of the CuTtertBuPc on the Ag/Si(111)- surface show excellent agreement with valence-band x-ray photoemission and x-ray absorption spectra taken from thin films of CuTtertBuPc (10–20 ML) prepared in situ on the clean Si(111) substrate. Combining the spectroscopy results it was found that the highest occupied molecular orbital (HOMO) of the CuTtertBuPc is the half-occupied MO of b1g symmetry with mixed Cu 3d(x2–y2) and ligand 2p character which was confirmed by density functional theory calculations and x-ray emission spectroscopy data.