Structural evolution of the self-assembled layers of funtionalized fullerenes on metal surfaces.

Self-assembled organic thin films have a great number of practical applications, ranging from sensors and biological interfaces in medical implants to organic electronics and photovoltaics. Self-assembled monolayers (SAMs) form as a result of a delicate balance between competing molecule-substrate and intermolecular interactions. To control such self-assembly processes, it is mandatory to understand how this balance reflects onto the SAM's final structure. Here, we present a STM study of the self-assembly of C60 functionalized with alkane chains of various lengths (F-C60) on Ag(111). We find that F-C60 molecules lay down on the Ag surface and form a zigzag like pattern with an oblique unit cell of size dependent on the alkyl chain lengths and two molecules per basis. The C60s are placed at a larger than van der Waals distance. The symmetry of the F-C60 SAM is dictated by the alkane-surface interaction while the size of the unit cell is a consequence of the intermolecular interactions. These results show that C60s can be assembled in 2D and non-compact molecular arrays with a surface density controllable via appropriate chemical functionalization. Funded by the NSF Center for High-rate Nanomanufacturing (NSF NSEC-425826).