Self-Limiting C$_{60}$-Pentacene Network on Ag(111)*

During Scanning Tunneling Microscopy investigations of C$_{60}$:Pentacene (Pc) interfaces on Ag(111), we identified a new network structure. This binary arrangement forms readily by sequential deposition: Pc, of $\sim $0.3 mL coverage, is first evaporated onto the Ag(111), forming a 2-D gas. Subsequent C$_{60}$ deposition produces a network, consisting of chains of close-packed C$_{60}$ molecules, spaced by C$_{60}$ molecules. The characteristic 1 x 2.5 nm$^{2}$ pores are sized to accommodate Pc molecules. Spontaneous formation of this structure from an iniital Pc coverage ranging from 0.3 to 0.6 mL, indicates a self-limiting assembly process. Drawing upon topographic and Z(V) measurements, we propose a structural model and describe molecular mechanisms that could cause this self-limiting behavior.