FIG. 1.
(a) Scanning electron micrograph of a PMMA split-disk consisting of opposing half-disks of radius r = 25 m and an intermediate coupling gap of d = 1200 nm patterned by electron-beam lithography on a silicon substrate. (b) Scanning electron image of a polymeric split-disk (r = 25 m, d = 4.5 m) fabricated by direct laser writing on a PDMS elastomer substrate. (c) Illustration of the coupling process: Mechanically stretching the substrate in x-direction (blue arrows) results in a lateral contraction in y-direction (green arrows) and consequently in a reduction of the gap width between the opposing half-disks. The dotted lines illustrate the pre-stretching state, whereas the red, filled half-disks represent the opposing half-disks with a reduced gap after applying substrate strain. (b) and (c) based on Ref. 40.