  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 2D
herringbone structure previously unobserved for any linear acene, 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 bulk-like
electronic structure.
