Effects of Metal−Molecule Contact and Molecular Structure on Molecular Electronic Conduction in Nonresonant Tunneling Regime: Alkyl versus Conjugated Molecules

The effect of metal-molecule contacts and molecular structures on the electronic conduction of alkyl and conjugated molecular junctions in nonresonant tunneling regime was investigated based on a proposed multibarrier tunneling (MBT) model, where the molecular junction was decomposed into three individual barriers through the molecular body and metal-molecule contacts on either side of the molecule. The resistance-area product (RA), specific contact resistance (RC), and decay coefficients (
C,
P,
Body, and
o) were estimated for alkyl and two selected conjugated molecules (oligoacene and oligophenylene) between Au contacts, and the result of RA (alkyl) > RA (oligoacene) g RA (oligophenylene) for a given molecular length was obtained from different decay coefficients for different molecules. By assuming the tunneling around the highest occupied molecular orbital of alkyl molecules (like a hole type tunneling), RC for alkanemonothiol and alkanedithiol junctions with various metallic (Ag, Cu, and Au) contacts was observed to decrease when metal work function was increased.