Figure 3.
(a) SEM images of a pilum-shaped tip with details shown in (b), (c) and (d) on the apical part, showing a radius of curvature rtip ≈ 12 nm and an apical angle of ≈24° (t1 = 20 s, V1 = 5 VDC, t2 = 90 s, V2 = 2.1 VDC).
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