Penning ionization electron spectroscopy of titanyl phthalocyanine ultrathin films: electronic state and molecular orientation

Penning ionization electron spectroscopy (PIES) was used to investigate the molecular orientation, aggregation of molecules, and electronic structure of ultrathin films of titanyl phthalocyanine (OTiPc) vapor deposited on graphite and MoS2 substrates. For the monolayer film, the molecular orientation was remarkably different between the two substrates. At room temperature, molecules spread over and almost cover the substrate on graphite, whereas they aggregate and form islands on MoS2. The PIES band due to the nonbonding orbital of the oxygen atom extending perpendicular to the molecular plane is extraordinary strong for the He*(2(3)S) metastable atom but not for the He*(2(1)S), indicating that the potential for the entrance channel is quite different between the two species. (C) 1998 Elsevier Science B.V.