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(a) Atomic force microscopy (AFM) height image of the apex of the sharp tip with contour lines, height step 0.25 nm, obtained by scanning on TGT1. Inset shows the whole tip; (b) Area of the tip contours at 0–10 nm tip height determined from AFM image, compared with expected contour area from a spherical indentor with the effective tip radius calibrated on FS (40 nm).
