Low-temperature scanning tunneling microscopy and near-edge X-ray absorption fine structure investigation of epitaxial growth of F16CuPc thin films on graphite

Low-temperature scanning tunneling microscopy (LT-STM) and near-edge X-ray absorption fine structure (NEXAFS) measurements are used to study the epitaxial growth and molecular orientation of organic thin films of copper hexadecafluorophthalocyanine (F16CuPc) on highly oriented pyrolytic graphite (HOPG). Our results show that F16CuPc molecules lie flat on HOPG up to 5 nm thickness, stabilized by interfacial and interlayer pi-pi interactions. LT-STM experiments reveal the coexistence of two different in-plane orientations of the F16CuPc monolayer on HOPG. On the second layer of F16CuPc on HOPG, however, all F16CuPc molecules possess the same in-plane orientation.