Suppression of Charge Carrier Tunneling through Organic Self-Assembled Monolayers

Self-assembled monolayers of long chain alkanes deposited on silicon wafers using an optimally designed procedure exhibit very large energy barriers ( $\ensuremath{\sim}4.5$ eV) to carrier tunneling. The dc conductivity is found to be $\ensuremath{\sim}4.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ S/cm, close to that of bulk polyethylene, and independent of monolayer thickness. This demonstrates that the tunneling contribution to the overall conductivity can be made negligible when the organic structure is densely packed and highly ordered. Distinctly higher conductivity values are observed with disordered monolayers.