Initial growth of pentacene on a Si(111)--In surface

We have investigated the initial pentacene growth on the Si(111)--In surface using scanning tunneling microscopy. At a low coverage, the molecules lie down flat and form locally ordered molecular layers that are nucleated at the Si step edges. At a higher coverage, two kinds of pentacene crystals with the so-called herring-bone arrangement are grown directly on the surface with the longer molecular axis ('c' axis) being directed parallel to the surface. The pentacene growth on the surface is considered to be a 3D island growth mode. Two minor crystal structures that are poly-crystal and striped layer are also observed. All experimental results suggest that the surface is rather moderate compared with a reactive surface, which allows for molecular diffusion and rearrangement.