Fig. 4.
SEM images showing the evolution of laser-induced surface structures with varying the laser fluence. (a) SEM images of random roughness at F = 0.1 J/cm2, (b) fs-LIPSSs at F = 0.30 J/cm2, (c) fs-LIPSSs covered with nano/microstructures at F = 0.5 J/cm2, a combination of 1D rods, conical and spherical structures at (d) F = 1.2 J/cm2, F = 1.5 J/cm2, and F = 2.0 J/cm2. The measured values of θM for different surface structures are shown. The insets of Fig. 4(d-f) are the rods, cones and spherical structures, respectively. The scale-bar in the insets is 500 nm. The scale-bar of 1 µm shown in Fig. 4(a) is same for Fig. 4(a-f).