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DS: Fachverband Dünne Schichten
DS 25: Symposium: Real Time Growth Studies III
DS 25.7: Invited Talk
Thursday, March 29, 2007, 17:30–18:15, H32
Charge Injection across Self-Assembly Monolayers in Organic Field Effect Transistors: Odd-Even Effects — •Fabio Biscarini1, Pablo Stoliar1, Rajendra Kshirsagar1, Massimiliano Massi1, Paolo Annibale1, Cristiano Albonetti1, and Dago de Leeuw2 — 1CNR-Istituto per lo Studio dei Materiali Nanostrutturati, Bologna, Italy — 2Philips Research Labs, Eindhoven, The Netherlands
We investigate the role of self-assembly monolayers of chain length n, with n ranging between 3 and 18, in modulating the charge injection in pentacene field effect transistors.
The charge carrier mobility exhibits large fluctuations correlated with odd-even n. For n < 8, increases by one order of magnitude. For n > 8, charge mobility decays exponentially with an inverse decay length β=0.6 Å−1.
Charge injection across the interface occurs by tunneling of holes mediated by the alkanethiol layer. At short chain length, decreasing of both interfacial morphological disorder and pentacene-surface interactions dominates over the increasing thickness of the alkanethiol monolayer. At long chain length, the charge injection across the alkanethiol monolayer governs the transistor response.
The odd-even effect is ascribed to the anisotropic coupling between the alkanethiol terminal sigma bond and the HOMO level of ordered pentacene molecules. Our results show that the pentacene transistor is a sensitive gauge for probing charge transport across single monolayers.