Understanding Nano-Impact Current Spikes: Electrochemical Doping of Impacting Nanoparticles

We demonstrate the generic value of a rigorous analysis of spike shapes observed in nanoimpact experiments. To this end, we investigate the electrochemical doping of insoluble nanoparticles impacting on a biased electrode surface and develop an analytical model of the doping process is developed that accounts for the diffusion of ions inside nanoparticles as well as a numerical model for the response characteristics of the analogue measurement circuitry. By this means, spike shapes that are experimentally observed in the electrode current are predicted and directly compared with experimental data, while appropriate fitting procedures allow detailed physical insights into the ionic mass transport within the particle. Using the oxidative doping of ferrocene nanoparticles with tetrafluoroborate anions as a paradigm case, we demonstrate that size distributions of particle populations showing excellent agreement with scanning electron microscopy measurements can be extracted from experimental data and ionic diffusion inside the particle can be quantified.