Site-specific physisorption and chemical reaction of subphthalocyanine molecules on silicon(111)-(7×7)

Scanning tunneling microscopy of functional subphthalocyanine (SubPc) molecules on Si(111)-$(7\mathrm{}\times 7)$ demonstrates site-dependent molecular physisorption and dissociative chemical reaction. The threefold symmetry of both, the molecule and the substrate lead to unique interactions. At room temperature, single molecules are discriminated to physisorb only in one specific site on the triangular subunit cell of the Si surface: the inactive chlorine (Cl) head of SubPc is anchored onto one Si restatom, and its threefold aza-nitrogens sit closer to the surrounding Si adatoms. A lateral displacement from this position results in a breakup of the molecules into low-molecular components due to electrophilic attack at the Si adatom dangling bonds on the active molecular sites of SubPc.