Morphology, Composition and Sensor Performance of Nanoporous Au(Pt)

Abstract

Recent atom-probe tomography (APT) and ATEM studies of dealloyed layers in binary AgAu and ternary AgAuPt alloys showed the various ways in which more-noble elements enrich during dealloying, at the atomic scale (1). We have since extended this research in several directions – towards less expensive alloys, lean in more-noble elements, and towards the potential applications of such materials in gas sensing. In this presentation, we will start with a review of published and unpublished data from the APT study, which was done using alloys with 23 at% (Au + Pt). New information will then be shown for alloys with less than 6 at.% (Au + Pt). The dealloyed layers are very Ag-rich, and very interesting conflicts arise between enrichment of the more-noble element(s) on the ligament surfaces and the ultimate supply of those elements. For gas sensing applications, we take advantage of the effect of adsorption on ligament surfaces on electron scattering during conduction in the confined metal phase. Delicate impedance measurements at the milli-ohm level show that two kinds of environmental effect can be distinguished. Adsorption of water or other gases up to several molecular layers induce changes in the measured resistance of the metal phase, while thicker layers induce a double-layer charge separation leading to capacitive changes.