SEM images showing six different stages of the galvanic replacement reaction that involves the use of Ag nanospheres as a sacrificial template. (A–F) Ag nanospheres titrated with 0, 0.5, 0.75, 1.25, 1.75, and 3.0 mL of 0.03 mM aqueous HAuCl4, respectively. The insets show TEM images of each respective sample. Scale bar = 30 nm for all TEM images.