Structural transition of pentacene monolayer on Ga bilayer: From brick-wall structure to herringbone pattern of molecular dimers

摘要

Utilizing the substrate of Ga bilayer grown on Si(111)-root 3 x root 3-Ga, we have investigated the structural transition of pentacene monolayer induced by moderate annealing. Short-range ordering has been observed in the monolayer pentacene deposited at room temperature. Annealing the sample at similar to 350 K produced ordered pentacene monolayer with the "brick-wall" adsorption pattern. The STM images with sub-molecular resolution revealed that the orbital symmetry of the HOMO is reduced from D-2h to C-2t, due to the substrate-molecule interaction, while the deeper HOMO-1 orbital remains intact. Further annealing at similar to 400 K led to the formation of molecular dimers as well as the structural transition from "brick-wall" packing to "herringbone" pattern. (c) 2005 Elsevier B.V. All rights reserved.