Determination of two-dimensional structures of ultrathin films of H-2- and Cu-phthalocyanine on MoS2 by angle-resolved ultraviolet photoemission and low energy electron diffraction

The angle-resolved ultraviolet photoelectron spectra of ultrathin films of metal-free phthalocyanine (H(2)Pc) and copper phthalocyanine (CuPc) on MoS2 single crystal surfaces were measured using synchrotron radiation. The take-off and azimuthal angle dependencies of the photoelectron intensity were analyzed using independent-atomic-center approximation combined with molecular orbital calculation. Further, the low energy electron diffraction was observed for the same ultrathin films. The results indicate that H(2)Pc and CuPc molecules form a square lattice with respect to the three equivalent crystal axes of the MoS2 surface, and at the lattice point lie flat on the substrate with a molecular azimuthal rotation of about 7 degrees.