Structural evolution of pentacene on a Ag(110) surface

Structural evolution of pentacene thin films on Ag(110) crystal, during molecular deposition and during a subsequent change of substrate temperature, was investigated in situ by a molecular beam epitaxy low-energy electron diffraction technique. The pentacene molecules exhibit high mobility on the Ag(110) surface at room temperature and the adsorbate shows a structural evolution from disorder in the submonolayer to an ordered structure when it reaches one monolayer. Heating the substrate to 145 degreesC results in no further structural transition. The ordered monolayer structure on Ag(110) has two domains mirrored at the crystal axis of the silver substrate. Molecular mechanics calculations indicate that the pentacene molecules lie flat on the Ag(110) surface, which is in good agreement with the experimental results. The calculation also gives the favorable position; i.e., the orientation of pentacene on the Ag(110).