Flexoelectricity at fractal rough surfaces

Abstract

This study quantifies the role of surface roughness on interfacial flexoelectricity under normal compression and oscillation by examining a series of 3D-printed surfaces with diverse roughness features. For incipient contact, the measured flexoelectric charge is found to follow a power-law dependence on normal compression load, with the exponent positively correlated with the fractal dimension. The value of this power-law exponent is similar to that for contact stiffness. The underlying mechanism for this coincidence is elucidated by contact analyses based on geometric truncations of surface structures. Contact micromechanics show that the interfacial flexoelectric charge will increasingly concentrate on large microcontacts as the compression continues. A rougher surface with higher fractal dimension tends to demonstrate less heterogeneity for flexoelectric polarizations over microcontacts. This study provides systematic experimental measurements and comprehensive explanations for interfacial flexoelectricity and establishes quantitative links to multi-scale surface structures, shedding light on novel approaches for contact evaluation and flexoelectricity enhancement.