Roger Newman1 Ayman El Zoka1 Brian Langelier2 Gianluigi Botton2

1, University of Toronto, Toronto, Ontario, Canada
2, McMaster University, Hamilton, Ontario, Canada

I was shown recently that thin nanoporous dealloyed layers on a binary AgAu alloy could be efficiently filled by electrodeposition of Cu, giving mechanical stabilization prior to the use of atom-probe tomography for atomic-scale analysis [1]. In those analyses, it was shown for the first time that it is possible to capture the early-stage dealloying of AgAu in aqueous perchloric acid, with ligaments of only a few nm width and ligament cores at or near the bulk alloy composition. More recently, similar analyses have been done on very thin (sub-micron) dealloyed layers on ternary AgAuPt alloys with [Pt] from 1 to 3 at%. A great deal of effort has gone into the optimization of the electrodeposition method and the inclusion of the diffuse layer-substrate interface in the APT sample. Beyond that, it has been necessary to quantify and correct for the ion trajectory aberrations that may exist in the data, in order to gain new information on the concentration and distribution of Pt on ligament surfaces. These analyses of the raw data are ongoing, and are giving new insights into the mechanism of Pt redistribution. The electrodeposition process is of fundamental interest in its own right, and our studies have now been extended to other metals, and to electrodeposited oxides. Generally speaking, the success of the electrodeposition method is ascribed to a combination of small dealloyed layer thickness (and thus short characteristic diffusion time to the dealloying front), simple deposition mechanism, and favourable kinetics. Various templating methods based on these procedures are being studied. Similar studies on dealloyed layers subjected to post-treatments, such as heating in oxidizing or reducing environments, are also under way, supported by in situ environmental TEM.

[1] A.A. El-Zoka, B. Langelier, G.A. Botton, and R.C. Newman (2017), Enhanced analysis of nanoporous gold by atom probe tomography. Materials Characterization 128: 269-277.