Schematic diagram of f-d curves conducted using sTNP tip. (a) f-d Curves obtained from a grounded metal surface using charged/uncharged sTNP tip. (b) Electrostatic force acting on charged sTNP tip when Vapp = +25, 0, and −25 V in the Z direction at X = 11 μm.
Chang et al. Nanoscale Research Letters 2013 8:519 doi:10.1186/1556-276X-8-519