Charge injection across self-assembly monolayers in organic field-effect transistors: odd-even effects.
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.
Stoliar
Pablo
P
Nanotechnology of Multifunctional Materials (NMM) Research Division, CNR-ISMN, Via Gobetti 101, I-40129 Bologna, Italy.
Kshirsagar
Rajendra
R
Massi
Massimiliano
M
Annibale
Paolo
P
Albonetti
Cristiano
C
de Leeuw
Dago M
DM
Biscarini
Fabio
F