Unravelling and quantifying the fundamental diffusion pathways of atoms on metal surfaces in electrolyte solutions with EC-STM

Surface diffusion is one of the key mechanisms behind the kinetics of electrochemical reactions at electrode surfaces at the atomic scale. It impacts crystal growth during electrodeposition, drives surface restructuring during electrochemical cycling and influences, if not determines, even the adsorption/desorption of molecular intermediates and reaction products at catalytic surface sites such as kinks and terraces. Atomic scale diffusion does not only determine the final morphology of deposited thin films but can be also responsible for the deterioration of nanosized catalysts affecting the lifetime of electrocatalytic reactions. Electrochemists are “blind” to actual surface phenomena, as they typically only measure the average current and overpotential responses coming from the entire exposed surface. In addition, surface diffusion effects are often washed out by mass transport and (pseudo)capacitive effects as well. Hence, there is a clear need to break down all diffusion pathways and effects of atoms on metallic surfaces, including additives and chemical composition. These questions can only be tackled with microscopic techniques that reach both space and time resolution at the atomic level. The complexity of this problem requires a multidisciplinary approach with expertise in electrochemistry, surface science, physics, and advanced instrumentation/characterization. 

In this PhD topic, we will use nanotechnology and concepts from fundamental surface science established in vacuum to disentangle all involved diffusion pathways and effects. We will create nano-labs of adatom and vacancy islands, which allows us to study the mass transport between them that is governed on Gibbs-Thomson (curvature effects); the most fundamental driving force for diffusion. It is possible to disentangle different pathways by time and distance scaling-laws: diffusion limited vs. attachment/detachment limited diffusion has been discovered this way in vacuum. These basic insights are crucial also in electrochemistry and have not been addressed before. This PhD topic will be a collaboration between IMEC/KULeuven in Leuven, Belgium with prof. Philippe Vereecken and the University of Leiden, Leiden, The Netherlands with Dr. Marcel Rost. Most of the experimental work will be executed at the university of Leiden with extended visits at the IMEC labs also in Leuven. 

The experiments will be performed on a specialized, home-built Electrochemical Scanning Tunneling Microscope (ECSTM) that holds several world records. The complicated machine requires an ambitious person, preferably an experimental physicist, with an eye for details, who also is willing to learn the basics of electrochemistry. Also physical chemists with background in electrochemistry, who are hands on with electronics and love technical details, and who are interested in fundamental, physical surface science are welcome to apply

For examples please see: https://www.youtube.com/user/DrMRost