Figure 7. Wear characteristics of hydrogel nano-probes and regeneration via oxygen plasma ashing.

(a) Scanning electron microscopy (SEM) images of hydrogel probe tips taken before and after wear tests. Imaging mode, condition and surrounding media are indicated on the left side of each micrograph. A hard silicon calibration grating sample was used for test cases 1–4, and a PDMS calibration grating sample replicated from the silicon grating was used for test case 5. All scale bars are 500 nm. (b) Increased tip radius and total wear volume after scanning a 0.246-m length (12 frame imagings with a scan size of 40 × 40 μm²) for each operating condition. (c) SEM images of worn hydrogel nano-probe tips before (i, ii) and after (iii, iv) oxygen plasma ashing. Hydrogel nano-probes with tip radii of 130 and 340 nm were re-sharpened to have sub 30 nm tip radii after plasma ashing. All scale bars are 5 μm.