On the Microstructure of Nanoporous Gold: An X-ray Diffraction Study

Abstract

The evolution of the grain structure, internal strain, and the lattice misorientations of nanoporous gold during dealloying of bulk (3D) Ag-Au alloy samples was studied by various in situ and ex situ X-ray diffraction techniques including powder and Laue diffraction. The experiments reveal that the dealloying process preserves the original crystallographic structure but leads to a small spread in orientations within individual grains. Initially, most grains develop in-plane tensile stresses, which are partly released during further dealloying. Simultaneously, the feature size of the developing nanoporous structure increases with increasing dealloying time. Finally, microdiffraction experiments on dealloyed micron-sized nanoporous pillars reveal significant surface damage introduced by focused ion beam milling.

Coarsening by network restructuring in model nanoporous gold

“…For the range of permissible values for τ and K 0 , the critical radius R * Au ranges between 1 nm and 10 nm. This range of predicted critical radii for np-Au lies below the average ligament radii reported in all experiments on np-Au of which we are aware [14,15,16,35,36,37,40], suggesting that coarsening by the mechanism described here may be operating very early in the dealloying and coarsening process.…”

“…Like some real np-Au [14,15,16,35,36,37]. A possible consequence of this difference is that our model may be more representative of np-Au in the initial stages of dealloying where ligament radii may be much smaller than those finally measured [14,15,16,35,36,37]. Despite this discrepancy, just as some experimentally synthesized np-Au structures [14], the ligament and pore radii of model np-Au scale with their relative densities in the same manner as conventional open cell foams do [38].…”

“…As most real np-Au, the model structures are crystalline and face-centered cubic with the lattice parameter corresponding to that of fcc gold [1,7,15,33] and the ligament surface normals of model np-Au are predominantly in the crystallographic 111 direction [34]. Like some real np-Au [14,15,16,35,36,37]. A possible consequence of this difference is that our model may be more representative of np-Au in the initial stages of dealloying where ligament radii may be much smaller than those finally measured [14,15,16,35,36,37].…”

“…Because several np-Au samples were found to contain lattice defects such as stacking faults, twins, and dislocations [1,13,15,16], it has been suggested that localized plastic deformation may cause volume reduction during dealloying.…”

Preparation of Nanoporous Ruthenium Catalyst and Its CO Oxidation Characteristics

“…This situation is different from that in the dealloying of AuAg to fabricate nanoporous Au, where the crystallite size is retained during nanoporosity formation and is typically much larger than ligament and pore sizes. 38) It is known and also confirmed by XRD analyses in this study (Figs. 4(a) and 6), that Ru 0.20 Mn 0.80 alloy has a face-centered-cubic (fcc) crystal structure, 28,39) while pure metallic Ru has a hcp structure.…”