Deposition Sequence Determines Morphology of C-60 and 3,4,9,10-Perylenetetracarboxylic Diimide Islands on CaF2(111)

Abstract

The coadsorption of C-60 and 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) molecules on atomically flat terraces of the CaF2(111) surface is studied under ultra-high vacuum conditions using non-contact atomic force microscopy (NC-AFM). Deposition of PTCDI molecules on CaF2(111) yields needle-shaped, molecularly well-ordered crystals. Upon following deposition of C-60 molecules, the PTCDI islands are completely covered by C-60. For the opposite deposition order, the initially grown C-60 islands are not covered by PTCDI molecules, instead, most of the PTCDI molecules condense in pure islands, while only few PTCDI molecules nucleate at the edges of previously grown C-60 islands. Simultaneous deposition of both molecules results in an intermixed phase with yet another island morphology. The observed fundamental differences in island morphology suggest that different dewetting barriers are involved in the formation process. (C) 2011 The Japan Society of Applied Physics