Fig. 2. Ferroelectric hysteresis and domain switching.
a Piezoresponse vs frequency under different VAC for the Te nanowire on an Au-coated silicon substrate, measured at a representative location on the inclination edge, showing a resonance peak around 365 kHz. Inset shows the linear dependence of piezoresponse amplitude on VAC with an effective piezoelectric coefficient d33 of ~3.1 pm/V. Phase–voltage hysteresis loops and amplitude–voltage butterfly loops measured by vertical ON-field (b) and OFF-field (c) PFM, where DC bias voltage (VDC) is applied to the tip before (“OFF-field”) or during (“ON-field”) the AC drive. Phase mapping (OFF-field) measured by vertical PFM before electric poling (d), after poling at +2.5 V (e), and after poling at −2.5 V (f), overlaid on the 3D topography image of the nanowire (width ~300 nm, thickness ~18.9 nm). The area of Te nanowire is marked by the cyan dashed line. VDC = 0 V for (a) and (b–f) were measured with VAC = 1.5 V driving on the resonance frequency.