Shape-tailored porous gold nanowires: from nano barbells to nano step-cones

Step-like porous gold nanowires of different shapes and diameters have been prepared by sequentially depositing alloy segments composed of different gold/silver ratios and de-alloying the silver component. For example, step-cone and nano-barbell porous gold nanowires were generated by a membrane-templated sequential deposition of gold-silver alloy segments from plating solutions of respectively decreasing or alternating gold/silver composition ratios. Alloy segments of different gold/silver ratios, prepared by using different plating potentials, also lead to multistep nanowires. In addition to step-like nanowires, we describe the preparation of cone- and bone-shaped porous nanowires from alloy nanowires of longitudinally changing compositions, generated via deposition from a flowing plating solution of a continuously changing composition. Such customization of the porous gold nanostructure is attributed to the chemical removal of silver and the different extents of gold reordering from alloy segments of different compositions. The latter leads to porous gold segments of smaller diameters from silver-rich alloy segments. The new "nanomachining" concept is versatile and could be extended to nanowires of diverse shapes with a variety of properties, generating an attractive assortment of nano-hardware.