Electrical resistivity of monolayers and bilayers of alkanethiols in tunnel junction with gate electrode

The tunneling resistances of monolayers and bilayers of n-alkanethiols in macroscopic Hg-Hg junctions with an electrochemical gate are reported. The resistances near zero bias calculated per 1 hydrocarbon chain vary from (5 ± 4) × 1012 Ω for n-nonanethiol to (4 ± 2) × 1016 Ω for n-octadecanethiol. These values indicate that monolayers of hydrocarbons in Hg-Hg junctions are substantially more resistive as compared to measurements employing microscopic tunnel junctions. The tunneling resistances of monolayer junctions are approximately 1 order of magnitude larger than those of bilayer junctions containing the same number of atoms indicating inefficient electronic coupling across the non-bonded -CH3|Hg interface. The symmetric current-voltage curves observed for the asymmetric junctions of Hg-S-(CH2)n-CH3|Hg type suggest that these junctions do not behave as molecular diodes. Additional experimental evidence for the nature of the -CH3|Hg interface in the Hg-S-(CH2)n-CH3|Hg junction is also presented.