Fig. 4: Piezoelectric force microscopy (PFM) investigation of thin NbOX2.
From: Data-driven discovery of high performance layered van der Waals piezoelectric NbOI2
a Topography, b In-plane (IP) phase, c IP amplitude, and d phase profile across antiparallel polarization states of 82-nm-thick NbOI2 flake. e–g Vector PFM IP amplitude images of 10-nm-thick NbOI2 showing spontaneous polarization at 90° e, 45° f, and 0° g angles relative to the cantilever long axis. h PFM amplitude profiles along the polar and nonpolar axes of the 10-nm-thick NbOI2 flake. Scale bars: 4 μm. Drive voltage: b, c 5 V, e–h 3 V. Drive frequency: b, c 65 kHz, e 827 kHz, f 974 kHz, g 890 kHz.
