Fig. 2. Topography-guided nano-kirigami.

(A) Schematic illustration of residual stress distribution of gold nanofilm under global ion beam irradiation. In this bilayer model (section S1), the constant tensile stress (σ_t) is dominant within the top amorphous layer, and the elastic stress (σ_b) is linearly distributed across the bottom polycrystalline layer. In such a case, when one edge is fixed (as noted by the red squares), the cantilever will bend upward. While both boundaries of the cantilever are fixed, the film could bend downward under the topography-guided stress equilibrium. (B and C) SEM images of (B) a tongue-like structure and (C) a flower-like structure before and after global ion beam irradiation. The calculated (Cal) structures well represent the upward bending process. (D and E) SEM images of (D) a spider web–like and (E) a concentric arc structure before and after global ion beam irradiation, showing distinctive downward buckling amplitudes under the same irradiation. (F to H) SEM images of (F) a twisted triple Fibonacci spiral, (G) window decoration–type nanobarriers, and (H) a deformable spiral. Calculated results in (B) to (E) are displayed with the same color bar as in (B). Scale bars, 1 μm.