THE INVESTIGATION OF REDOX REACTIONS WITH A SCANNING TUNNELING MICROSCOPE - EXPERIMENTAL AND THEORETICAL ASPECTS

The tunneling current between the tip and a sample in a scanning tunneling microscope (STM) can be enhanced by the presence of an electroactive adsorbate on the sample. We have used the transfer Hamiltonian mechanism to determine the dependence of this current on various system parameters like the bias voltage, the energy of reorganization, and the electronic coupling of the redox centre to the tip and the substrate. We estimate that a fast redox couple would rise give to currents in the pA to nA range; furthermore, the adsorbate density of states will be reflected in dj/dV. We also discuss experimental considerations in examining electron transfer via a redox adsorbate using an STM.