Cu-phthalocyanine long-range ordered bulk growth due to the weak interaction with highly oriented pyrolytic graphite substrate

Abstract

We investigate the relationship between the ordered growth of copper-phthalocyanine (CuPc) on highly oriented pyrolytic graphite (HOPG) and the electronic interaction at the interface. Via spot profiles analysis of electron diffraction patterns we determine an ordered growth for all measured CuPc films ranging from sub-monolayer to 3.3 nm. In particular we found that for CuPc thick films the ordered domains have a dimension of 50 nm. Electronic structure of CuPc/HOPG interface was studied by means of photoelectron and electron energy loss spectroscopies (EELS). From photoelectron spectroscopy we observe that molecules at the interface are weakly physisorbed. This weak interaction contributes to the formation of ordered 2-D islands. Since the geometry of the surface unit cell does not change with film thickness, the second CuPc layer grows stacked flat on the first one, forming ordered 3-D islands. It follows that the ordered bulk phase derives from the weak interaction between Pcs and HOPG. The Q band of CuPc/HOPG, measured via EELS, is different from the ones of the most common Pc phases. Therefore, electron diffraction and EELS measurements indicate the formation of a novel Pc long-range ordered structure observed only at this interface.