Molecular Orientation and Aggregation of Titanyl Phthalocyanine Molecules on Graphite Substrates: Effects of Surface Topography of the Substrate

Abstract

Penning ionization electron spectroscopy (PIES) was used to investigate the effects of crystallographic inperfection of the substrate surface on organic ultrathin-film growth. For titanyl phthalocyanine (OTiPc) evaporated on graphite, it was found that the molecular orientation and aggregation in the film depend significantly on the type of graphite substrate. On a highly oriented pyrolytic graphite (HOPG), OTiPc film prepared by 1-monolayer-equivalence (MLE) deposition consists of islands of double layers, while on Grafoil, the molecules do not aggregate as on the HOPG, and form a monolayer. This large difference originated from the surface topography of the two graphite substrates.

Optical transition energies of isolated molecular monomers and weakly interacting two-dimensional aggregates

“…[77]. We could not determine a significant tendency of the individual PTCDA molecules in the pores to migrate and to form domains when the substrate was kept at 300 K. Consequently, although molecular migration is a known effect described in the literature [78][79][80], it cannot be traced in the room-temperature optical measurements of as-deposited PTCDA films on h-BN/Rh(111). At elevated temperatures (above roughly 400 K) the latter do indeed rearrange and form extended domains.…”

Control of the dipole layer of polar organic molecules adsorbed on metal surfaces via different charge-transfer channels

“…12 Dependence of the ELA on the polar-molecule orientation and packing density has also been reported [13][14][15][16][17][18][19][20][21][22] , and connection to device applications has been demonstrated. [23][24][25] Hosokai et al, who compared the as-grown (AG) and annealed (AN) chlorogallium-phthalocyanine (ClGaPc) films grown on highly oriented pyrolytic graphite (HOPG), reported large band bending of the HOMO state for the AG films with a stacked bilayer structure, but this band bending could be suppressed in the AN films because of the formation of a uniform Cl-up configuration after the thermal treatment; 13 the substrate, HOPG, was however fairly inert in this case, and charge transfer at the organic/metal interface was expected to be minimal.…”

Impact of an interface dipole layer on molecular level alignment at an organic-conductor interface studied by ultraviolet photoemission spectroscopy

“…These measurements demonstrate the effect of the dipole layer on the interface energy level alignment. We use graphite to obtain a well-defined dipole layer in an oriented OTiPc monolayer [38][39][40] and to minimize substrate-molecule interactions and the resulting changes in the molecular electronic states. We confirm that the change in substrate vacuum level is negligibly small when CuPc is deposited directly onto the graphite surface, indicating that the molecule-substrate interaction is weak, and that the formation of a dipole layer due to molecule-substrate interaction can be neglected in the present system.…”

“…The latter technique is recognized as the most sensitive spectroscopy to the outermost surface layer. [38][39][40][41][42] We discuss the true effect of the interface dipole layer on E F matching and energy level alignment between the organic layer and the substrate in the presence of an interface (OTiPc) dipole layer. We demonstrate that a shift in E B (referenced to E F ) equal to the potential difference introduced by the dipole layer is observed for the valence levels of CuPc when a dipole layer is intentionally inserted between CuPc and the substrate.…”