Microfabrication of Nanoporous Gold
Fabrication of microstructures comprising NPG requires precise control over selective corrosion of the precursor alloy. In many designs, the precursor alloy is constrained to a substrate, and complex surface reconstruction during dealloying potentially leads to a high overall stress in the newly formed NPG. Hence, constrained NPG thin films or suspended NPG structures often develop cracks in fabrication. Similarly, nanovoids in thin-film precursor alloys or low Au content in the precursor alloys may lead to fractures in the NPG thin films, which compromise the integrity and functionality of the resulting architecture. Recently developed scalable electrochemical methods for which the rate of removal of the less noble elements in the precursor alloy can be precisely controlled produce crack-free blanket films constrained to a substrate. In this chapter, conventional as well as newly developed NPG fabrication techniques are assessed from a microscale fabrication perspective, with regard to the NPG product quality, means of tailoring the final porous structure, and their compatibility with the standard microdevice fabrication techniques.