Nanoscale electrical and structural characterization of gold/alkyl monolayer/silicon diode junctions

The effect of molecular modification on gold-silicon diode junctions has been investigated by electrical and structural measurements at both the macroscale and the nanoscale levels. Diode junctions prepared with Si-C bonded, organic monolayers on silicon and thermally evaporated gold contacts yield identical macroscale barrier heights and ideality factors, irrespective of the alkyl chain length and end group of the molecular layer. Electrical and structural measurements on the nanoscale level, using ballistic emission electron microscopy (BEEM) and cross-sectional transmission electron microscopy (TEM), indicate laterally uniform penetration of deposited gold atoms into n-alkyl monolayers (20 nm resolution), whereas inhibited penetration occurs for thiol-terminated monolayers on silicon. Average BEEM transmission is reduced via scattering associated with the presence of an organic monolayer, with the largest effects observed for the thiol-terminated system.