 Solution

A conventional tapping tip tapers toward its apex, so its shank contacts an overhanging feature before its apex can probe underneath it. Critical-dimension atomic force microscopy instead uses a calibrated flared or laterally extended tip, with a relatively narrow neck and side-sensitive control. The lateral extension can contact a reentrant sidewall while the neck clears the upper edge. The measured profile still includes the tip's finite shape and must be interpreted with a tip calibration; changing the tip does not automatically eliminate all convolution errors.^[ref]