Strain-Correlated Piezoelectricity in Quasi-Two-Dimensional Zinc-Oxide

Flexible, wearable, and human-compatible electronics are helping shape a future of integrated nanotechnologies. As such, piezoelectric and semiconducting materials have drawn intense interest by many research groups for the excellent potential to advance the field of wearable devices. Moreover, two-dimensional (2D) nanomaterials, valued for their enhanced mechanical, electronic, and structural properties, have moved to the forefront of compliant electronic devices. Therefore, a thorough understanding of the interfacial charge distribution is required when utilizing flexible piezoelectric semiconductors, such as zinc-oxide (ZnO). We present a method for monitoring the piezoelectric response of nanometer-thick 2D ZNO nanosheets (NS) grown via Ionic Layer Epitaxy (ILE). The direct piezoelectric effect, and the coupling of electronic dipole polarization to lattice strain within ZnO-NSs, is monitored <i>in situ</i> via piezo force microscopy (PFM). Using PFM we illustrate the effects of modulating strain in piezoelectric nanomaterials and its role in the polarization charge distribution across the surface of the 2D ZnO-NS. Subsequently, we show that the strain configuration (either tensile or compressive) can dramatically influence the measured piezoelectric coefficient (d₃₃) of the 2D ZnO-NS. Our results illustrate the critical need for understanding the interdependent roles of static piezoelectric charges, semiconducting properties, and strain, for future flexible devices.