Imaging the charge distribution within a single molecule

Knowing the charge distribution within individual nanostructures or molecules on surfaces is important for applications in which charge is to be moved on the nanometre scale, such as nanoelectronics and organic photovoltaics. Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) are established tools for studying electronic and structural properties of surfaces and adsorbates with atomic precision. However, the charge distribution is not directly accessible with these techniques. Kelvin probe force microscopy (KPFM), on the other hand, can be used to measure the local contact potential difference (LCPD), a quantity closely related to the distribution of charge on a surface. Here we use a combination of STM, AFM, and KPFM to investigate naphthalocyanine, a single-molecule hydrogen-tautomerisation switch. In particular, we show for the first time LCPD maps with submolecular resolution, and demonstrate that they reflect the intramolecular distribution of charge, as verified by comparison with density functional theory (DFT) calculations. We anticipate that our findings will lead to fundamental insights into single-molecule switching and bond formation—processes that are usually accompanied by an intra- or intermolecular redistribution of charge.

By: Fabian Mohn, Leo Gross, Nikolaj Moll, and Gerhard Meyer

Published in: RZ3873 in 2011


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