Charge distribution in monolayers of charge transfer complexes probes by scanning tunneling spectroscopy
Prof. Dr. Katharina Franke (Freie Universität Berlin)

The charge state crucially influences the chemical reactivity, electronic conductivity and magnetic properties of a molecule. We present strategies to control the charge state of organic molecules by atomic and molecular doping and show how magnetic properties of single molecules are controlled by their atomic scale surrounding.

In particular, we demonstrate the transfer of a single electron into the electron acceptor molecule TCNQ (tetracyanoquinodimethane) from co-adsorbed alkali metals and organic electron donor molecules in self-assembled monolayers on a metal surface. The presence of an unpaired electron spin is demonstrated by a Kondo resonance in tunnelling spectra, which arises from the screening of the magnetic moment by the substrate electrons. When we use tetramethyl-tetrathiafulvalene as electron donor, we can further manipulate the charge state of TCNQ by the electric field of the tip of the scanning tunnelling microscope. This reversible control of the charge state is comparable to gating three-terminal quantum dots.