Morphological and topological analysis of coarsened nanoporous gold by x-ray nanotomography

Nanoporous gold has numerous potential applications 1 in optical-active materials, catalysts, sensors, mechanical actuators, fuel cell and microbalance electrodes, and as a coating for medical devices. Nanoporous gold is fabricated by dealloying silver-gold solid solutions. This results in fully openporosity bicontinuous nanoporous structures, following the rearrangement of the gold atoms into interconnected ligaments as the silver atoms are selectively removed. 2 Optimization of the optical, chemical, and mechanical properties of nanoporous gold depends on its pore size, which is tunable by structural coarsening during annealing. 3 Various electronbased techniques have been employed to determine the morphology of nanoporous gold films after dealloying, but none are suited to three-dimensional 3D study of thick specimens of coarsened nanoporous gold. Tomographic transmission electron microscopy provides very high spatial resolution but is limited to examining thin films, and cannot image coarsened structures once the gold ligament size is close to the electron penetration depth. 4,5 Focused ion beam FIB-scanning electron microscopy serial sectioning 6 combines high resolution with depth penetration, however, being a destructive method, it cannot be used to observe dynamic processes and structural evolution in 3D. X-ray microcomputed tomography is a powerful nondestructive tomographic tool whose resolution is however typically limited to the micron scale. 7 Transmission x-ray microscopy TXM using synchrotron x-ray sources offers 30 nm resolution, fast image acquisition, and the ability to nondestructively image samples tens of microns thick. Combining TXM with tomographic methods allows complex nanostructures to be imaged in 3D. 8 Here, we perform x-ray nanotomography on a dealloyed and coarsened nanoporous gold wire. We quantitatively analyze the morphological and topological properties of nanoporous gold from the reconstructed images using methods developed in earlier work. 9