Comprehensive Characterization of Hybrid Junctions Comprised of a Porphyrin Monolayer Sandwiched Between a Coinage Metal Overlayer and a Si(100) Substrate

The promise of molecular electronics has stimulated a variety of approaches for making hybrid junctions wherein molecules are sandwiched between two metal contacts or a metal and a semiconductor contact. However, the fate of molecules subsequent to deposition of a top metal contact has generally not been well characterized. Toward this goal, the interaction of evaporated Cu, Ag, and Au films deposited in varying thicknesses (3, 5, and 8 nm) on a series of monolayer-coverage porphyrins covalently attached to Si(100) substrates was investigated. Each porphyrin contains a triallyl tripod attached to the porphyrin via a p-phenylene unit, which anchors the porphyrin to the Si(100) substrate via hydrosilylation of the allyl groups. All of the porphyrins are Zn chelates bearing meso p-tolyl substituents orthogonal (lateral) to the tripodal surface anchor, but contain different substituents in the meso position opposite (distal) to the surface anchor, p-tolyl, α,α,α-trifluoro-p-tolyl, pentafluorophenyl, or p-cyan...