Electron transport through thin organic films in metal-insulator-metal junctions based on self-assembled monolayers

This paper describes an experimentally simple system for measuring rates of electron transport across organic thin films having a range of molecular structures. The system uses a metal-insulator-metal junction based on self-assembled monolayers (SAMs); it is particularly easy to assemble. The junction consists of a SAM supported on a silver film (Ag-SAM(1)) in contact with a second SAM supported on the surface of a drop of mercury (Hg-SAM(2))-that is, a Ag-SAM(1)SAM(2)-Hg junction. SAM(1) and SAM(2) can be derived from the same or different thiols. The current that flowed across junctions with SAMs of aliphatic thiols or aromatic thiols on Ag and a SAM of hexadecane thiol on Hg depended both on the molecular structure and on the thickness of the SAM on Ag: the current density at a bias of 0.5 V ranged from 2 × 10-10 A/cm2 for HS(CH2)15CH3 on Ag to 1 × 10-6 A/cm2 for HS(CH2)15H3 on Ag, and from 3 x 10-6 A/cm2 for HS(Ph)3H (Ph = 1,4-C6H4) on Ag to 7 × 10-4 A/cm2 for HSPhH on Ag. The curr...