Dry Synthesis of Triple Cumulative Double Bonds (CCCN) on Si(111)-7 × 7 Surfaces

The interactions of cyanoacetylene and diacetylene with a Si(111)-7 × 7 surface have been studied as model systems to mechanistically understand the chemical binding of unsaturated organic molecules to diradical-like silicon dangling bonds. Vibrational studies show that cyanoacetylene mainly binds to the surface through a diradical reaction involving both cyano and C⋮C groups with an adjacent adatom−rest atom pair at 110 K, resulting in an intermediate containing triple cumulative double bonds (CCCN). On the other hand, diacetylene was shown to the covalently attached to Si(111)-7 × 7 only through one of its C⋮C groups, forming an enynic-like structure with a CC−C⋮C skeleton. These chemisorbed species containing triple cumulative double bonds (CCCN) and CC−C⋮C may be employed as precursors (or templates) for further construction of bilayer organic films on the semiconductor surfaces.