trast is completely reversed when the sample was physically rotated at 180° (cf. Figure 3a,b). Both fea- tures have contrast reversal and a predicted d 15 (␣) de- pendence point to the piezoelectric origin of the signal. This also rules out possible contribution of spurious electrostatic signal as it suggests only OOP compo- nent. 19 In addition, piezoresponse signal was indepen - dent of the vertical force (Supporting Information, Fig- ure S1), and force⫺distance curves for PNTs were identical to those taken on a rigid substrate (Support- ing Information, Figure S2) without any sign of mechan- ical indentation of the former. This excludes possible artifacts related to electric-field-controlled stiffness and slip motion of the tip