Measuring direct flexoelectricity at the nanoscale

TL;DR

This paper reports the first direct measurements of flexoelectric charges in nanoscale materials, confirming the effect's significance at small scales and demonstrating its potential for nano-electromechanical systems.

Contribution

It provides the first direct measurement of flexoelectricity in nanoscale-thickness materials and explores how geometry influences the flexoelectric response.

Findings

Flexoelectric charges measured in 50 nm hafnium oxide layers.

Flexoelectric coefficient aligns with inverse effect measurements.

Modifying cantilever width increases the effective flexoelectric coefficient by 40%.

Abstract

Flexoelectricity is a property of all dielectric materials, where inhomogeneous strain induces electrical polarization. This effect becomes particularly prominent at the nanoscale where larger strain gradients can be obtained. While flexoelectric charges have been measured in mm-scale systems, direct measurements in nanoscale-thickness materials have not yet been achieved. Given that one of the most prominent applications of flexoelectricity is in nano-electro-mechanical systems (NEMS), confirming the presence and magnitude of the effect at these scales is essential. This study presents the first-ever measurements of flexoelectric-generated charges (direct effect) in nanoscale-thickness materials, using cantilevers with a 50 nm hafnium oxide layer. We confirm that the estimated flexoelectric coefficient from said measurements aligns with the values obtained from complementary experiments using the flexoelectric inverse effect. Additionally, by changing the cantilever geometry (modifying the width of the cantilevers), we demonstrate a 40% increase in the effective flexoelectric coefficient, explained by the interplay of different flexoelectric tensor components. These findings not only validate the presence of flexoelectric effects at the nanoscale but also open the possibility for full flexoelectric transduction of the motion in NEMS/MEMS devices.