Dresden 2011 – scientific programme
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O: Fachverband Oberflächenphysik
O 85: Electron and spin dynamics I
O 85.6: Talk
Thursday, March 17, 2011, 17:45–18:00, WIL A317
Dynamics of the intramolecular charge transfer in alkanethiolate self-assembled monolayers — Ping Kao1, Stefan Neppl2, Peter Feulner2, David L. Allara1, and •Michael Zharnikov3 — 1Departments of Chemistry and Material Science, Pennsylvania State University, University Park, PA 16802, USA — 2Physik Department E20, Technische Universität München, D-85747 Garching, Germany — 3Angewandte Physikalische Chemie, Universität Heidelberg, D-69120 Heidelberg, Germany
Charge transport (CT) in individual molecules and their functional units is important for many frontier areas of modern science and technology. In particular, little is known about CT dynamics in self-assembled monolayers which are prototypes of future molecular electronics devices. By the example of alkanethiolate films on Au(111), we show that this phenomenon can be successfully addressed by resonant Auger spectroscopy, using the core hole clock method. The CT pathway was unambiguously defined by resonant excitation of the nitrile tailgroup attached to the alkyl backbone. The length of this backbone was varied to monitor the respective dependence of the CT time. Similar to the static conductance, this dependence was found to be coarsely described by an exponential function with an attenuation factor of 0.93 per a methylene unit. As a result, the CT time is quite long even for a short alkyl chain; e.g. ca. 100 fs for the chain of only four methylene units. In contrast, the CT time associated with the thiolate headgroup anchor was found to be less than 2.3 fs, suggesting an efficient interfacial coupling between the molecular backbone and substrate.