Reorganization energy upon charging a single molecule on an insulator measured by atomic force microscopy

Realizing single-electron transport between adsorbates on a non-conductive lm is a key goal of molecular electronics [1{3]. Importantly, electron-transfer rates in molecular systems depend on a few fundamental parameters, such as distance between adsorbates, temperature [4{6] and in particular the Marcus reorganization energy [7]. This crucial parameter is the energy gain resulting from the distortion of the equilibrium nuclear geometry in the molecule and its environment upon charging. Here, we investigate redox reactions of naphthalocyanine molecules on a multilayered insulating NaCl lm at 5 K. By employing the atomic force microscope as an ultra-low current meter based on single-electron detection we show that the differential conductance related to charge-state transitions can be measured. The hole reorganization energy of naphthalocyanine on NaCl is then quantified as (0.8 0.2) eV. Density functional theory calculations corroborate the measured energy values and provide a detailed picture of the ionic and atomic relaxations upon individual charging. Our approach presents a versatile route to perform tunneling spectroscopy of single adsorbates on insulating substrates and provides fundamental insight into single-electron transport between molecules.

For further information please contact lgr@zurich.ibm.com