Fig. 3.

Adhesion strength of single-scale and multi-scale hairs against various substrates. (A) Measurement of shear force with an adhesive having nanohairs of 3 × 1 cm² in area against a flat Si surface. (B) Measurement of shear force with the same adhesive against a rough surface (backside of Si wafer). (C) Two- and 3-dimensional AFM micrographs and the corresponding surface profile of the backside of Si wafer used in the roughness adaptation tests of nanohairs. (D) Measurement and comparison of shear force with an adhesive patch having single-scale hairs and an adhesive patch having multiscale hierarchical hairs against flat Si and rough Si surfaces with 5 different roughness heights. For rough surfaces, microlattice structures with different heights (1.5, 2, 5, 10, and 20 μm) were used. (E and F) Three-dimensional micrographs and the corresponding surface profiles of the lattice structures with roughness height of 1.5 (E) and 10 (F) μm.