Controlled ligament coarsening in nanoporous gold by annealing in vacuum versus nitrogen

Influence of gas atmospheres and ceria on the stability of nanoporous gold studied by environmental electron microscopy and in situ ptychography

“…Nevertheless, systematic investigations of the inuence of the X-ray dose should be performed in future. In contrast to previous studies, 18,24 it could be shown that np-Au samples did not start to change in vacuum at temperatures below 700 C. At those high temperatures, a simultaneous material loss and sintering were observed. Interestingly, the loss observed during in situ ptychography in 20% O 2 /He at ambient pressure started at much lower temperature than under vacuum conditions, but at a comparable temperature to the onset of coarsening during ETEM analysis in oxygen atmosphere.…”

“…Lattice diffusion of gold was suggested as an alternative mechanism in this case. Furthermore, both Kuwano-Nakatani et al 24 and Sun et al 18 did not observe any strong coarsening in vacuum. Kuwano-Nakatani et al 24 did not detect any coarsening behavior at 400 C in argon either, whereas Chen et al 10 reported a pronounced coarsening at 600 C. Moreover, a stabilization of the structures could be reached by the latter in CO atmosphere and Biener et al 16 reported a stabilization by treatment with ozone compared to annealing in helium.…”

“…11,13 Up to now, the coarsening effects of np-Au have mostly been studied by electron microscopy, following ex situ treatment in various atmospheres. 10,11,14,17,18 According to these studies, the observed coarsening is almost exclusively explained by surface diffusion of gold, 10,14,18,19 which is driven by minimization of surface energy. Besides these processes, Kolluri and Demkowicz 20 discussed the effect of volume diffusion, which plays a role during the collapse of neighboring ligaments, especially in the early state of coarsening during corrosion.…”

Pore and ligament size control, thermal stability and mechanical properties of nanoporous single crystals of gold

“…c) Average ligament size was calculated by measuring the narrowest point of each ligament. 29 In order to understand the influence of different Ge concentration on the ligament size, additional samples were evaporated with other Au-Ge ratios. Evaluation of these samples showed general tendency of higher ligament size for higher Ge concentration ( Figure S1).…”

Metallic muscles and beyond: nanofoams at work

“…In the majority of cases, metal nanofoams are produced through dealloying. In the literature, several processing conditions and results are highlighted and reference can be made to [48][49][50][51][52][53][54][55][56][57][58][59][60]. For this process to work, an alloy must be produced between the required metal and another that can be etched away in some manner.…”