Metallic Top Contacts to Self-Assembled Monolayers of Aliphatic Phosphonic Acids on Titanium Nitride

We report on the successful fabrication of large-area molecular junctions comprised of a self-assembled monolayer (SAM) of molecules with an alkyl backbone sandwiched between two solid state contacts. Alkyl phosphonic acid monolayers were deposited on sputter-deposited titanium nitride from solution. Top contacts were formed through electron beam evaporation of titanium through a shadow mask and subsequent evaporation of gold as a capping layer. A measured tunneling current attenuation constant of ß = 0.52/C atom obtained from DC current-voltage characteristics of molecules with varying length indicates successful and reproducible junction formation. We rationalize our findings by the lack of interaction between top contact and substrate.