Fabrication, Characterization of Ultra-low-density Bulk Nanoporous Gold with Uniform Structure and Volume Shrinkage Control During Drying

Ultra-low-density bulk nanoporous gold (NPG) is required in inertial confined fusion (ICF) experiments. Existing bulk NPG has some limitations in ICF application due to non-uniformity structure or residues of C originated from organic template. Here, combined with dealloying, NPG with submicron cavities and nanopores was prepared by nano-SiO₂ templates. However, the smaller templates bring greater challenges for the volume shrinkage control during drying as gold content on each shell is extremely low for ultra-low density. Therefore, the influence of drying methods on volume shrinkage was investigated. The results show that volume shrinkage is up to 86.41% during conventional drying, but it is controlled below 4% by supercritical CO₂ drying. Finally, NPG with ultra-low-density of 0.35 g/cm³ was fabricated. Compared to NPG prepared by micro templates, the NPG with 500 nm spherical cavities and 2∼70 nm nanopores reduces the size difference between large cavities and nanopores and significantly improves the uniformity of its structure.