Dealloying Kinetics of AgAu Nanoparticles by In-situ Liquid Cell Scanning Transmission Electron Microscopy.

Understanding the formation and evolution of bi-continuous nanoporous structure during dealloying has been one of the most challenging subjects of the dealloying research. However, previous in-situ investigations either suffer from insufficient spatial resolution (e.g. X-ray tomography) or lack morphology visualization and mass information (e.g. scanning tunneling microscopy). In this work, we report the kinetics of the whole course of dealloying by utilizing the liquid cell aberration-corrected scanning transmission electron microscopy. With Z-contrast imaging analysis, the in-situ sub-nano-scale characterization reveals two new phenomena, an initial period of dealloying indicative of an initial length scale for bulk dealloying, and a large volume shrinkage in a nanoscale alloy precursor. We explain the particle size-dependent volume shrinkage with the formation of a dense shell, and quantify the dependence with a simple geometric model. These insights into the mechanisms of dealloying will enable deliberate designs of nanoporous structures.