Tuning the alignment of pentacene on copper substrate by annealing-assistant surface functionalization

Controlling the alignment and packing structure of organic molecules on solid substrate surfaces at molecule level is essential to develop high-performance organic thin film (OTF) devices. Pentacene, which is a typical p-type semiconductor material usually adopts lying-down geometry on metal substrates owning to π-d coupling between pentacene and metal substrates. However, in this study, we found that pentacene molecules can be adsorbed on an anneal-treated Cu (111) surface with their long axis perpendicular to substrate surface. Highly ordered single-layer pentacene film with stand-up molecular geometry was achieved on this substrate. It was found that the functionalization of Cu surface with C=O groups due to annealing treatment should be accounted for standing-up geometry of pentacene on Cu substrate. This observation shed light on the tuning of the alignment and packing structure of organic molecules.