Odd-Even Effects in Charge Transport across n-Alkanethiolate-Based SAMs

This paper compares rates of charge transport across self-assembled monolayers (SAMs) of n-alkanethiolates having odd and even numbers of carbon atoms (nodd and neven) using junctions with the structure M-TS/SAM//Ga2O3/EGaIn (M = Au or Ag). Measurements of current density, J(V), across SAMs of n-alkanethiolates on Au-TS and Ag-TS demonstrated a statistically significant odd-even effect on Au-TS, but not on Ag-TS, that could be detected using this technique. Statistical analysis showed the values of tunneling current density across SAMs of n-alkanethiolates on Au(TS) with nodd and neven belonging to two separate sets, and while there is a significant difference between the values of injection current density, J0, for these two series (log|J(0Au,odd)| = 4.0 +/- 0.3 and log|J(0Au),(even)| = 4.5 +/- 0.3), the values of tunneling decay constant, beta, for nodd and neven alkyl chains are indistinguishable (beta(Aueven) = 0.73 +/- 0.02 angstrom(-1), and beta A(u,odd)= 0.74 +/- 0.02 angstrom(-1). A comparison of electrical characteristics across junctions of n-alkanethiolate SAMs on gold and silver electrodes yields indistinguishable values of beta and J(0) and indicates that a change that substantially alters the tilt angle of the alkyl chain (and, therefore, the thickness of the SAM) has no influence on the injection current density across SAMs of n-alkanethiolates.