Ordered structures of pentacene on Cu(110)

The authors report an investigation on the adsorption of pentacene molecules on Cu(110) in the submonolayer and monolayer ranges using scanning tunneling microscopy and low-energy electron diffraction. They identify and characterize three different phases for increasing pentacene coverage. For very low coverages [$≲0.1ML$ (monolayer)] pentacene molecules are highly mobile and adsorbed uniaxially oriented along the $[11¯0]$ substrate direction. For higher coverages the ordering along the [001] direction improves, until a $p(7×2)$ structure with imperfect registry along the $[11¯0]$ direction is formed at 0.89 ML. In both phases pentacene molecules occupy the Cu(110) troughs along the $[11¯0]$ direction. For even higher coverage (1.0 ML), a slight rotation of the molecular adsorption site gives rise to a complex $(61−14)$ structure based in a $c(12×2)$ cell. The appearance of two domains generates a long-range wavelike ordering. Annealing of the adlayer results in the formation of supramolecular complexes.