A molecular view of TiOPc -- C$_{70 }$interface formation*

A key strategy for the improvement of organic electronic devices involves the optimization of chemical morphology for efficient charge separation. Fundamental studies of chemical morphology - electronic property relations, particularly along crucial domain boundaries, are needed to realize these goals. We present STM/STS studies of TiOPc: C$_{70}$ films, prepared by vapor deposition on Ag (111). Sequential deposition of C$_{70}$ onto the ordered honeycomb TiOPc phase generates extended domains of a co-crystalline C$_{70(1)}$TiOPc$_{(2) }$monolayer phase, characterized as a hexagonal network (2.1 nm nearest-neighbor C$_{70}$ packing). Subsequent deposition of C$_{70}$ onto this network proceeds in a layer-by-layer growth process, generated molecularly abrupt interfaces. The transport gap of each interface is measured by STS, and correlated to the C$_{70}$ packing density. The orderly structure evolution of the C$_{70}$-TiOPc is contrasted to that of the previously reported C$_{60}$-TiOPc and the implications for electronic transport are discussed.