(Keynote) Imaging Electrochemical Growth Using Liquid Cell Transmission Electron Microscopy

Transmission electron microscopy is very helpful in measuring structure and composition after electrochemical growth has finished. However, it is also possible to image structures while they are still growing, by carrying out electrodeposition inside the electron microscope. The trick is to confine the electrolyte in a layer that is thin enough to be transparent to the imaging electrons – of the order of a few hundred nanometers – and to include electrodes with a geometry that allows the reaction to be controlled and visualized. To do this, we use microfabrication techniques to build liquid cells with thin windows of silicon nitride. Once filled with electrolyte, a liquid cell is placed in the microscope and controlled by a potentiostat during imaging. We can then relate changes in morphology to electrochemical parameters, providing a detailed probe of growth mechanisms with good temporal and spatial resolution.

In this presentation, we first describe practical aspects of liquid cell electron microscopy, particularly the competing requirements of resolution and diffusion – in other words, the extent to which a liquid layer that is thin enough to provide high resolution images can also replicate a process of interest. We then describe measurements of nucleation and growth during the deposition of metal films, and quantify the onset of growth instabilities. We show movies of the interface evolution of galvanostatically deposited Cu from an acidic electrolyte: initially, the kinetics are consistent with kinetic roughening theory, and later, with diffusion limited growth models. Macroscale models appear to predict the behavior over long length and time scales, but short scale behavior differs from spatially averaged measures, affecting the onset of the instability. We demonstrate some control of interface evolution through pulse plating and inorganic additives. We finally discuss liquid cell microscopy of electroless deposition and of corrosion processes in metal films, and combine metal dissolution with reduction by the electron beam to produce nanostructures. Developments in equipment and modelling are making liquid cell microscopy increasingly quantitative, suggesting exciting possibilities for detailed interrogation of a wider range of electrochemical growth physics.