Role of stress on charge transfer through self-assembled alkanethiol monolayers on Au

We have studied charge transfer through alkanethiol molecules self-assemble d on Au(lll) substrates using interfacial force microscopy. Simultaneous me asurement of the tip-substrate current and the normal interfacial force rev eals the critical role of tip-film contact. Measurable currents are seen on ly for tip-applied stresses above about 20 MPa, after which the current ris es exponential with stress. We suggest that charge transfer results from st ress-induced band-gap states near the Fermi level in these normally highly insulating molecular films.