Investigation of additional responses caused by sample surface topography in piezoresponse force microscopy measurement

The purpose of this study is to elucidate the origin of the additional response signals arising from the surface topography of samples during piezoresponse force microscopy (PFM) measurements. Periodic mountain-shaped protrusions with triangular cross-sections were fabricated on the surface of a silicon single crystal, a material with no inherent piezoelectricity, and PFM measurements were performed. The results indicated that when the measurement sensitivity direction of the PFM and the ridge direction of the protrusions formed specific angles, piezoelectric response images influenced by the surface topography were generated. Two-dimensional electrostatic field analysis confirmed that the contribution of converse flexoelectricity to this phenomenon was very small and negligible. Conversely, PFM measurements conducted both in-plane and out-of-plane on the sample, as well as measurements on a conductive material, revealed that the additional piezoelectric response - which was dependent on the surface topography - was induced by electrostatic forces due to the charging of the sample surface. The signal intensity was found to increase as the angle between the direction of the inclined plane and the in-plane sensitivity direction became smaller, as the tip diameter increased. These findings highlight the importance of accounting for the dominant influence of electrostatic forces in the interpretation of piezoelectric response data. Furthermore, they provide valuable insights into the effect of sample topography on PFM measurements.