title: Charge injection across self-assembly monolayers in organic field-effect transistors: odd-even effects.
abstract: We investigate the role of self-assembly monolayers in modulating the response of organic field-effect transistors. Alkanethiol monolayers of chain length n are self-assembled on the source and drain electrodes of pentacene field-effect transistors. The charge carrier mobility mu exhibits large fluctuations correlated with odd-even n. For n < 8, mu increases by 1 order of magnitude owing to the decrease of the hole injection barrier and the improved molecular order at the organic-metallic interface. For n > or = 8, mu decays exponentially with an inverse decay length beta = 0.6 A(-1). Our results show that (i) charge injection across the interface occurs by through-bond tunneling of holes mediated by the alkanethiol layer; (ii) in the long-chain regime, the charge injection across the alkanethiol monolayer completely governs the transistor response; (iii) the transistor is a sensitive gauge for probing charge transport across single monolayers. The odd-even effect is ascribed to the anisotropic coupling between the alkanethiol terminal sigma bond and the HOMO level of ordered pentacene molecules.
authors.affiliation: Nanotechnology of Multifunctional Materials (NMM) Research Division, CNR-ISMN, Via Gobetti 101, I-40129 Bologna, Italy.
authors.forename: Pablo
authors.initials: P
authors.lastname: Stoliar
authors.forename: Rajendra
authors.initials: R
authors.lastname: Kshirsagar
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Massi
authors.forename: Paolo
authors.initials: P
authors.lastname: Annibale
authors.forename: Cristiano
authors.initials: C
authors.lastname: Albonetti
authors.forename: Dago M
authors.initials: DM
authors.lastname: de Leeuw
authors.forename: Fabio
authors.initials: F
authors.lastname: Biscarini