Figure 1: Schematic representations of the preparation window and growth mechanism of the FDs.

(a) (left) Schematic representations of the FDs grown at various molar ratios and pumping rates (other form factors were the same). (right) The corresponding SEM images of the FDs with six typical morphologies: (I) FD I, size 1.5–2.5 μm; (II) FD II, size 1.8–3 μm; (III) FD III, size 3–5.5 μm; (IV) FD IV, size 3.5–6.5 μm; (V) FD V, size 5–7 μm; and (VI) FD VI, size 5.5–7.5 μm. (Insets I–IV scale bars are 200, 300, 400 and 600 nm, respectively. Insets V and VI scale bars are 1μm. (b) A schematic representation showing the adsorption of NH₂OH on silver surfaces and the plausible formation process of FDs. (c) A table listing the adsorption energy (E_ad) and N-Ag distance (d_N-Ag) of NH₂OH adsorption on (4 × 4) silver surfaces. The N-Ag distance is defined as the distance between the N atom in NH₂OH and its underlying Ag atom. (d) The detailed morphology of a virtual branch of various FDs (I, III and VI) as shown in (a).