Zone-cast Films of Hexabenzocoronene-C12H25

Organic electronics have the promising prospects of cheap plastic sensors and circuits. A requirement for fully exploiting the potential of electronically and optically anisotropic organic molecules is to have excellent control with the molecular orientation and ordering [1,2]. Disk-shaped (“discotic”) hexabenzocoronenes (HBC) substituted with alkyl side chains, cf. Fig. 1, tend to micro-segregate into columns of stacked aromatic cores. These stacks can be considered molecular “coax-cables ” of π-electron rich wires yielding a good (hole) mobility kept separated by electronically inactive alkyl side chains. Epitaxial growth on polytetrafluoroethylene alignment layers has been reported for HBC-C8,2 cast from solution [3]. The films were processed using zone casting, with glass microscopy slides as substrates [4]. This technique yields a high degree of in-plane alignment without using a pre-aligned substrate. The processing is highly reproducible, yielding homogeneous films of thickness ~150Å. Figure 1: a) The chemical structure of HBC-C12H25. b) A GID diffraction image showing the reflections in a plane perpendicular to the stacking direction. The image has been synthesized from many line scans. Note the many orders of reflections. The blank region close to the Qz axis cannot be reached using GID. Grazing Incidence Diffraction (GID) studies were performed at the z-axis diffractometer at the wiggle