Monolayer and bilayer pentacene on Cu(111)

The morphology and electronic structure of pentacene (Pn) deposited on Cu(111) was studied using scanning tunneling microscopy (STM) and spectroscopy (STS). Deposition of a multilayer followed by annealing to reduce coverage to a monolayer results in the formation of either of two unique phases: a two-dimensional herringbone structure previously unobserved for any linear acene to our knowledge, or a "random-tiling" structure. Coverage greater than a monolayer promotes the formation of a bilayer phase similar to that observed for Pn/Ag(111). STS shows that the electronic structure of the first layer is strongly modified due to its proximity to the substrate, while the second layer exhibits nearly bulklike electronic structure.