Epitaxial orientations of para-sexiphenyl platelets grown on alkali halide (001) surfaces

Thin film growth of simple aromatic molecules has been researched intensely in recent years in the burgeoning field of organic electronics. Film growth for simple rodlike molecules on the atomically well-defined and nonreactive alkali halide (001) surfaces also constitutes an archetypical model system for the study of molecular epitaxy. We have observed a surprising variety of preferential orientations of para-sexiphenyl platelets on a series of alkali halide surfaces with lattice constants ranging from 4.6 to 6.6 angstrom. We present a metric that helps to classify the dominant epitaxial orientations and allows us to predict epitaxial orientations on other rocksalt-type substrates, and we identified surface corrugation as the driving force for these preferred relative orientations.