Electrostatic Origin of Meandering C60 Chain Formation at ZnPc Interfaces*

We present STM investigations of interface-formation and nanophase separation in binary films of zinc phthalocyanine (ZnPc) and C$_{60}$ on Ag(111) and Au(111) supports. We report ZnPc:C$_{60}$ 1-D and 2-D interfaces with distinctive molecular orientations and unusually low C$_{60}$ packing densities. Meandering C$_{60}$ chains of single-molecular width arise without registration to the underlying ZnPc template, islanding into a disordered chain phase. These structures are reminiscent of dipole fluids (albeit of single molecular widths!) We present detailed measurements and analysis of C$_{60}$ wandering chain formation on ZnPc/Ag (111) and ZnPc/Au (111) substrates. We explore the physical origin of these structures through simulations with a model potential that incorporates short-range C$_{60}$ -- C$_{60}$ attraction and a long-range dipolar repulsion. From simulations of realized structures, we~ estimate the effective dipole needed for chain formation. DFT calculations on the C60/ZnPc/Ag(111) structure support these conclusions and provide more detailed insight on the electrostatic interactions that drive chain formation.